From 72c254eac3feb8fcb9664693a9b28ef7559efb93 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Fri, 20 Jan 2023 16:56:36 +0000
Subject: [PATCH 01/28] feat(peers): add script and modules

- parse package.json
- fetch peer dependencies online
- check if there are mismatches in peers
- keep things testable via functional
---
 README.md                        |  8 ++++
 colours.ts                       | 13 ++++++
 deps.ts                          |  7 ++++
 fetch_peer_dependencies.test.ts  | 70 ++++++++++++++++++++++++++++++++
 fetch_peer_dependencies.ts       | 35 ++++++++++++++++
 find_mismatches.test.ts          | 69 +++++++++++++++++++++++++++++++
 find_mismatches.ts               | 46 +++++++++++++++++++++
 fixtures/package.json            | 10 +++++
 fixtures/package_duplicate.json  |  9 ++++
 fixtures/package_typescript.json | 10 +++++
 fixtures/package_valid.json      | 15 +++++++
 main.test.ts                     |  3 ++
 main.ts                          | 43 ++++++++++++++++++++
 parse_dependencies.test.ts       | 56 +++++++++++++++++++++++++
 parse_dependencies.ts            | 52 ++++++++++++++++++++++++
 types.ts                         | 13 ++++++
 16 files changed, 459 insertions(+)
 create mode 100644 colours.ts
 create mode 100644 deps.ts
 create mode 100644 fetch_peer_dependencies.test.ts
 create mode 100644 fetch_peer_dependencies.ts
 create mode 100644 find_mismatches.test.ts
 create mode 100644 find_mismatches.ts
 create mode 100644 fixtures/package.json
 create mode 100644 fixtures/package_duplicate.json
 create mode 100644 fixtures/package_typescript.json
 create mode 100644 fixtures/package_valid.json
 create mode 100644 main.test.ts
 create mode 100644 main.ts
 create mode 100644 parse_dependencies.test.ts
 create mode 100644 parse_dependencies.ts
 create mode 100644 types.ts

diff --git a/README.md b/README.md
index ee0cd4d..0255bb7 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,10 @@
 # actions-npm-dependencies
+
 Validate your NPM dependencies without installing Node (WIP)
+
+## Todo
+
+- [X] Make it functional and composable
+- [X] Handle peer dependencies
+- [ ] Handle lock files? (probably not)
+- [ ] Great error messaging
diff --git a/colours.ts b/colours.ts
new file mode 100644
index 0000000..a8af971
--- /dev/null
+++ b/colours.ts
@@ -0,0 +1,13 @@
+import {
+  blue,
+  cyan,
+  gray,
+  yellow,
+} from "https://deno.land/std@0.171.0/fmt/colors.ts";
+
+export const colour = {
+  dependency: blue,
+  file: cyan,
+  subdued: gray,
+  version: yellow,
+};
diff --git a/deps.ts b/deps.ts
new file mode 100644
index 0000000..437c955
--- /dev/null
+++ b/deps.ts
@@ -0,0 +1,7 @@
+export { literal, object, record, string } from "https://esm.sh/zod@3.20.2";
+export { coerce, satisfies, SemVer, Range } from "https://esm.sh/semver@7.3.8";
+
+export {
+  assertEquals,
+  assertThrows,
+} from "https://deno.land/std@0.156.0/testing/asserts.ts";
diff --git a/fetch_peer_dependencies.test.ts b/fetch_peer_dependencies.test.ts
new file mode 100644
index 0000000..5785de8
--- /dev/null
+++ b/fetch_peer_dependencies.test.ts
@@ -0,0 +1,70 @@
+import { assertEquals } from "./deps.ts";
+import { Range, SemVer } from "./deps.ts";
+import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
+
+Deno.test("Can get peer dependencies", async () => {
+  const with_peer_deps = await fetch_peer_dependencies([
+    // { name: "@guardian/source-foundations", version: new SemVer("8.0.0") },
+    {
+      name: "@guardian/core-web-vitals",
+      version: new SemVer("2.0.2"),
+      peers: [],
+    },
+    // { name: "@guardian/libs", version: new SemVer("12.0.0") },
+    // { name: "@guardian/ab-react", version: new SemVer("2.0.1") },
+  ]);
+
+  assertEquals(with_peer_deps, [
+    {
+      name: "@guardian/core-web-vitals",
+      version: new SemVer("2.0.2"),
+      peers: [
+        {
+          name: "@guardian/libs",
+          range: new Range("^12.0.0"),
+          optional: false,
+        },
+        {
+          name: "tslib",
+          range: new Range("^2.4.1"),
+          optional: false,
+        },
+        {
+          name: "typescript",
+          range: new Range("^4.3.2"),
+          optional: true,
+        },
+        {
+          name: "web-vitals",
+          range: new Range("^2.0.0"),
+          optional: false,
+        },
+      ],
+    },
+  ]);
+});
+
+Deno.test("Can get optional peer dependencies", async () => {
+  const peer_deps = await fetch_peer_dependencies([
+    { name: "@guardian/libs", version: new SemVer("12.0.0"), peers: [] },
+  ]);
+
+  assertEquals(peer_deps, [
+    {
+      name: "@guardian/libs",
+      version: new SemVer("12.0.0"),
+      peers: [
+        {
+          name: "tslib",
+          range: new Range("^2.4.1"),
+          optional: false,
+        },
+        {
+          name: "typescript",
+          range: new Range("^4.3.2"),
+          optional: true,
+        },
+      ],
+    },
+  ]);
+});
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
new file mode 100644
index 0000000..b9bbb53
--- /dev/null
+++ b/fetch_peer_dependencies.ts
@@ -0,0 +1,35 @@
+import { literal, object, Range, record, string } from "./deps.ts";
+import { Dependency, PeerDependency } from "./types.ts";
+
+const { parseAsync: parse_peers } = object({
+  peerDependencies: record(string()).optional(),
+  peerDependenciesMeta: record(object({ optional: literal(true) })).optional(),
+});
+
+export const fetch_peer_dependencies = (
+  dependencies: Dependency[],
+): Promise<Dependency[]> =>
+  Promise.all(
+    dependencies.map((dependency) =>
+      fetch(
+        new URL(
+          `${dependency.name}@${dependency.version.version}/package.json`,
+          "https://esm.sh/",
+        ),
+      )
+        .then((res) => res.json())
+        .then(parse_peers)
+        .then(({ peerDependencies = {}, peerDependenciesMeta }) => ({
+          ...dependency,
+          peers: Object.entries(peerDependencies).map(([name, range]) => ({
+            name,
+            range: new Range(range),
+            optional: !!peerDependenciesMeta?.[name]?.optional,
+          })),
+        }))
+        .catch((error) => {
+          console.error("🚨 Failed to parse package.json for", dependency.name);
+          throw error;
+        })
+    ),
+  );
diff --git a/find_mismatches.test.ts b/find_mismatches.test.ts
new file mode 100644
index 0000000..2c4f013
--- /dev/null
+++ b/find_mismatches.test.ts
@@ -0,0 +1,69 @@
+import { assertEquals } from "./deps.ts";
+import { SemVer, Range } from "./deps.ts";
+import { find_mismatched_peer_dependencies } from "./find_mismatches.ts";
+
+Deno.test("Works when all depencies are matches", () => {
+  assertEquals(
+    find_mismatched_peer_dependencies([
+      {
+        name: "one",
+        version: new SemVer("1.0.0"),
+        peers: [
+          {
+            name: "two",
+            optional: false,
+            range: new Range("^2.0.0"),
+          },
+        ],
+      },
+      { name: "two", version: new SemVer("2.0.2"), peers: [] },
+    ]),
+    []
+  );
+});
+
+Deno.test("Fails on invalid range", () => {
+  assertEquals(
+    find_mismatched_peer_dependencies([
+      {
+        name: "one",
+        version: new SemVer("1.0.0"),
+        peers: [
+          {
+            name: "two",
+            optional: false,
+            range: new Range("^2.0.3"),
+          },
+        ],
+      },
+      { name: "two", version: new SemVer("2.0.2"), peers: [] },
+    ]),
+    [
+      {
+        name: "two",
+        optional: false,
+        range: new Range("^2.0.3"),
+        required_by: "one",
+      },
+    ]
+  );
+});
+
+Deno.test("Allows optional deps to fail if absent", () => {
+  assertEquals(
+    find_mismatched_peer_dependencies([
+      {
+        name: "one",
+        version: new SemVer("1.0.0"),
+        peers: [
+          {
+            name: "two",
+            optional: true,
+            range: new Range("^2.0.3"),
+          },
+        ],
+      },
+    ]),
+    []
+  );
+});
diff --git a/find_mismatches.ts b/find_mismatches.ts
new file mode 100644
index 0000000..323ea60
--- /dev/null
+++ b/find_mismatches.ts
@@ -0,0 +1,46 @@
+import { colour } from "./colours.ts";
+import { satisfies } from "./deps.ts";
+import { Dependency } from "./types.ts";
+
+export const find_mismatched_peer_dependencies = (
+  dependencies: Dependency[],
+) => {
+  const peers = dependencies.flatMap(({ name, peers }) =>
+    peers.map((peer) => ({ ...peer, required_by: name }))
+  );
+
+  const mismatched = peers.filter((peer_dependency) => {
+    const local_version = dependencies.find(
+      ({ name }) => name === peer_dependency.name,
+    );
+    if (!local_version) {
+      return !peer_dependency.optional;
+    }
+    return !satisfies(local_version.version, peer_dependency.range);
+  });
+
+  if (mismatched.length === 0) {
+    console.info(`✅ All ${colour.file("peerDependencies")} satisfied}`);
+  } else {
+    console.error(
+      `🚨 The following ${colour.file("peerDependencies")} are unsatisfied:`,
+    );
+
+    for (const { name, range, required_by } of mismatched) {
+      console.error(
+        `   - ${
+          [
+            colour.dependency(name),
+            colour.subdued("@"),
+            colour.version(range.raw),
+            " (from ",
+            colour.dependency(required_by),
+            " )",
+          ].join("")
+        }`,
+      );
+    }
+  }
+
+  return mismatched;
+};
diff --git a/fixtures/package.json b/fixtures/package.json
new file mode 100644
index 0000000..2850bb8
--- /dev/null
+++ b/fixtures/package.json
@@ -0,0 +1,10 @@
+{
+  "dependencies": {
+    "@guardian/source-foundations": "8.0.0",
+    "@guardian/core-web-vitals": "2.0.2"
+  },
+  "devDependencies": {
+    "@guardian/libs": "^12",
+    "@guardian/ab-react": "^2.0.1"
+  }
+}
diff --git a/fixtures/package_duplicate.json b/fixtures/package_duplicate.json
new file mode 100644
index 0000000..9eded57
--- /dev/null
+++ b/fixtures/package_duplicate.json
@@ -0,0 +1,9 @@
+{
+  "dependencies": {
+    "@guardian/source-foundations": "8.0.0",
+    "@guardian/libs": "^12"
+  },
+  "devDependencies": {
+    "@guardian/libs": "^12"
+  }
+}
diff --git a/fixtures/package_typescript.json b/fixtures/package_typescript.json
new file mode 100644
index 0000000..306a2d6
--- /dev/null
+++ b/fixtures/package_typescript.json
@@ -0,0 +1,10 @@
+{
+  "dependencies": {
+    "@guardian/source-foundations": "8.0.0"
+  },
+  "devDependencies": {
+    "typescript": "^4.2.4",
+    "@guardian/libs": "^12",
+    "@guardian/ab-react": "^2.0.1"
+  }
+}
diff --git a/fixtures/package_valid.json b/fixtures/package_valid.json
new file mode 100644
index 0000000..4a194d9
--- /dev/null
+++ b/fixtures/package_valid.json
@@ -0,0 +1,15 @@
+{
+  "dependencies": {
+    "@guardian/ab-core": "2.0.0",
+    "@guardian/core-web-vitals": "2.0.2",
+    "@guardian/source-foundations": "8.0.0",
+    "react": "^16.13.1",
+    "react-dom": "^16.13.1",
+    "tslib": "^2.4.1",
+    "web-vitals": "^2.0.1"
+  },
+  "devDependencies": {
+    "@guardian/libs": "^12",
+    "@guardian/ab-react": "^2.0.1"
+  }
+}
diff --git a/main.test.ts b/main.test.ts
new file mode 100644
index 0000000..10da7df
--- /dev/null
+++ b/main.test.ts
@@ -0,0 +1,3 @@
+Deno.test("Parses package.json", () => {
+  return;
+});
diff --git a/main.ts b/main.ts
new file mode 100644
index 0000000..f0b57e6
--- /dev/null
+++ b/main.ts
@@ -0,0 +1,43 @@
+import { parse_declared_dependencies } from "./parse_dependencies.ts";
+import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
+import { colour } from "./colours.ts";
+import { find_mismatched_peer_dependencies } from "./find_mismatches.ts";
+
+const [package_file] = Deno.args;
+
+if (!package_file) {
+  console.error("🚨 No package.json passed as argument");
+  Deno.exit(1);
+}
+
+const filename = Deno.cwd() + "/" + package_file;
+
+const package_content = await Deno.readTextFile(filename).catch(() => "");
+
+if (package_content) {
+  console.info(`✅ Found package.json file`);
+} else {
+  console.error("🚨 No package.json found at", colour.file(filename));
+  Deno.exit(1);
+}
+
+const dependencies = parse_declared_dependencies(package_content);
+
+if (dependencies.length === 0) {
+  console.info("✅ You have no dependencies and therefore no issues!");
+  Deno.exit();
+}
+
+const dependencies_with_peers = await fetch_peer_dependencies(dependencies);
+
+const { length: number_of_mismatched_deps } = find_mismatched_peer_dependencies(
+  dependencies_with_peers,
+);
+
+if (number_of_mismatched_deps === 0) {
+  console.info("✅ Everything is fine with your dependencies");
+} else {
+  console.info("🚨 This shal");
+}
+
+Deno.exit(number_of_mismatched_deps);
diff --git a/parse_dependencies.test.ts b/parse_dependencies.test.ts
new file mode 100644
index 0000000..a3b9d38
--- /dev/null
+++ b/parse_dependencies.test.ts
@@ -0,0 +1,56 @@
+import { assertEquals, assertThrows, SemVer } from "./deps.ts";
+import { parse_declared_dependencies } from "./parse_dependencies.ts";
+
+Deno.test("Handles valid package.json", () => {
+  const json = `
+  {
+    "dependencies": {
+      "one": "1.0.0",
+      "two": "~1.1.0"
+    },
+    "devDependencies": {
+      "three": "^1.1.1",
+      "four": "0.0.1"
+    }
+  }
+  `;
+
+  assertEquals(parse_declared_dependencies(json), [
+    {
+      name: "one",
+      version: new SemVer("1.0.0"),
+      peers: [],
+    },
+    {
+      name: "two",
+      version: new SemVer("1.1.0"),
+      peers: [],
+    },
+    {
+      name: "three",
+      version: new SemVer("1.1.1"),
+      peers: [],
+    },
+    {
+      name: "four",
+      version: new SemVer("0.0.1"),
+      peers: [],
+    },
+  ]);
+});
+
+Deno.test("Warns on duplicate dependencies", () => {
+  const json = `
+  {
+    "dependencies": {
+      "one": "1.0.1",
+      "two": "2.0.1"
+    },
+    "devDependencies": {
+      "two": "2.0.2"
+    }
+  }
+  `;
+
+  assertThrows(() => parse_declared_dependencies(json));
+});
diff --git a/parse_dependencies.ts b/parse_dependencies.ts
new file mode 100644
index 0000000..be6fc9a
--- /dev/null
+++ b/parse_dependencies.ts
@@ -0,0 +1,52 @@
+import { object, record, string, coerce } from "./deps.ts";
+import { colour } from "./colours.ts";
+import { Dependency } from "./types.ts";
+
+const { parse } = object({
+  dependencies: record(string()).optional(),
+  devDependencies: record(string()).optional(),
+});
+
+const parse_dependencies = (o: Record<string, string>): Dependency[] =>
+  Object.entries(o).map(([name, version]) => {
+    const semver = coerce(version);
+    if (!semver) throw new Error(`Could not parse semver: ${version}`);
+    return {
+      name,
+      version: semver,
+      peers: [],
+    };
+  });
+
+const find_duplicates = (deps: Dependency[]): string[] => {
+  const seen = new Set<string>();
+  const duplicates = new Set<string>();
+
+  for (const { name } of deps) {
+    if (seen.has(name)) duplicates.add(name);
+    seen.add(name);
+  }
+
+  return [...duplicates];
+};
+
+export const parse_declared_dependencies = (contents: string): Dependency[] => {
+  const { dependencies = {}, devDependencies = {} } = parse(
+    JSON.parse(contents)
+  );
+
+  const deps = [dependencies, devDependencies].map(parse_dependencies).flat();
+
+  const duplicates = find_duplicates(deps);
+
+  if (duplicates.length > 0) {
+    console.warn("🚨 Duplicate dependencies found:");
+    for (const duplicate of duplicates) {
+      console.warn(`   - ${colour.dependency(duplicate)}`);
+    }
+
+    throw new Error("Duplicates found");
+  }
+
+  return deps;
+};
diff --git a/types.ts b/types.ts
new file mode 100644
index 0000000..e5bb9a5
--- /dev/null
+++ b/types.ts
@@ -0,0 +1,13 @@
+import { SemVer, Range } from "./deps.ts";
+
+export interface Dependency {
+  name: string;
+  version: SemVer;
+  peers: PeerDependency[];
+}
+
+export interface PeerDependency {
+  name: string;
+  range: Range;
+  optional: boolean;
+}

From 36641e70038898da8f63e13747fa218658d078bc Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Mon, 23 Jan 2023 15:39:18 +0000
Subject: [PATCH 02/28] refactor: single pass analysis of satisfied

Instead of looping twice over the dependencies,
check whether they are satisfied via the registry
call directly based on minimum range version or optional.
---
 deps.ts                         |  2 +-
 fetch_peer_dependencies.test.ts | 70 ++++++++++++++++++------
 fetch_peer_dependencies.ts      | 94 +++++++++++++++++++++++++++------
 find_mismatches.test.ts         | 67 +++++++++++------------
 find_mismatches.ts              | 63 +++++++++++-----------
 main.ts                         | 10 ++--
 parse_dependencies.test.ts      | 14 ++---
 parse_dependencies.ts           | 11 ++--
 types.ts                        | 14 ++---
 9 files changed, 221 insertions(+), 124 deletions(-)

diff --git a/deps.ts b/deps.ts
index 437c955..245a4d1 100644
--- a/deps.ts
+++ b/deps.ts
@@ -1,5 +1,5 @@
 export { literal, object, record, string } from "https://esm.sh/zod@3.20.2";
-export { coerce, satisfies, SemVer, Range } from "https://esm.sh/semver@7.3.8";
+export * from "https://esm.sh/semver@7.3.8";
 
 export {
   assertEquals,
diff --git a/fetch_peer_dependencies.test.ts b/fetch_peer_dependencies.test.ts
index 5785de8..fa9aab9 100644
--- a/fetch_peer_dependencies.test.ts
+++ b/fetch_peer_dependencies.test.ts
@@ -1,43 +1,40 @@
-import { assertEquals } from "./deps.ts";
-import { Range, SemVer } from "./deps.ts";
+import { assertEquals, SemVer } from "./deps.ts";
+import { Range } from "./deps.ts";
 import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
 
 Deno.test("Can get peer dependencies", async () => {
   const with_peer_deps = await fetch_peer_dependencies([
-    // { name: "@guardian/source-foundations", version: new SemVer("8.0.0") },
     {
       name: "@guardian/core-web-vitals",
-      version: new SemVer("2.0.2"),
-      peers: [],
+      range: new Range("2.0.2"),
     },
-    // { name: "@guardian/libs", version: new SemVer("12.0.0") },
-    // { name: "@guardian/ab-react", version: new SemVer("2.0.1") },
   ]);
 
   assertEquals(with_peer_deps, [
     {
       name: "@guardian/core-web-vitals",
-      version: new SemVer("2.0.2"),
+      range: new Range("2.0.2"),
+      versions: [new SemVer("2.0.2")],
       peers: [
         {
           name: "@guardian/libs",
           range: new Range("^12.0.0"),
-          optional: false,
+          satisfied: false,
         },
         {
           name: "tslib",
           range: new Range("^2.4.1"),
-          optional: false,
+          satisfied: false,
         },
         {
           name: "typescript",
           range: new Range("^4.3.2"),
-          optional: true,
+          satisfied: true,
         },
         {
           name: "web-vitals",
           range: new Range("^2.0.0"),
-          optional: false,
+          satisfied: false,
         },
       ],
     },
@@ -46,25 +43,66 @@ Deno.test("Can get peer dependencies", async () => {
 
 Deno.test("Can get optional peer dependencies", async () => {
   const peer_deps = await fetch_peer_dependencies([
-    { name: "@guardian/libs", version: new SemVer("12.0.0"), peers: [] },
+    { name: "@guardian/libs", range: new Range("12.0.0") },
   ]);
 
   assertEquals(peer_deps, [
     {
       name: "@guardian/libs",
-      version: new SemVer("12.0.0"),
+      range: new Range("12.0.0"),
+      versions: [new SemVer("12.0.0")],
       peers: [
         {
           name: "tslib",
           range: new Range("^2.4.1"),
-          optional: false,
+          satisfied: false,
         },
         {
           name: "typescript",
           range: new Range("^4.3.2"),
-          optional: true,
+          satisfied: true,
         },
       ],
     },
   ]);
 });
+
+Deno.test("Will fail on optional dependencies that are defined locally", async () => {
+  const peer_deps = await fetch_peer_dependencies([
+    { name: "@guardian/libs", range: new Range("12.0.0") },
+    { name: "tslib", range: new Range("2.4.1") },
+    { name: "typescript", range: new Range("4.2.2") },
+  ]);
+
+  assertEquals(peer_deps, [
+    {
+      name: "@guardian/libs",
+      range: new Range("12.0.0"),
+      versions: [new SemVer("12.0.0")],
+      peers: [
+        {
+          name: "tslib",
+          range: new Range("^2.4.1"),
+          satisfied: true,
+        },
+        {
+          name: "typescript",
+          range: new Range("^4.3.2"),
+          satisfied: false,
+        },
+      ],
+    },
+    {
+      name: "tslib",
+      range: new Range("2.4.1"),
+      versions: [new SemVer("2.4.1")],
+      peers: [],
+    },
+    {
+      name: "typescript",
+      range: new Range("4.2.2"),
+      versions: [new SemVer("4.2.2")],
+      peers: [],
+    },
+  ]);
+});
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index b9bbb53..cbd6d5a 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -1,32 +1,96 @@
-import { literal, object, Range, record, string } from "./deps.ts";
-import { Dependency, PeerDependency } from "./types.ts";
+import { colour } from "./colours.ts";
+import {
+  literal,
+  minVersion,
+  object,
+  Range,
+  record,
+  satisfies,
+  SemVer,
+  string,
+} from "./deps.ts";
+import type { Dependency, RegistryDependency } from "./types.ts";
 
 const { parseAsync: parse_peers } = object({
-  peerDependencies: record(string()).optional(),
-  peerDependenciesMeta: record(object({ optional: literal(true) })).optional(),
+  versions: record(object({
+    version: string(),
+    dependencies: record(string()).optional(),
+    peerDependencies: record(string()).optional(),
+    peerDependenciesMeta: record(object({ optional: literal(true) }))
+      .optional(),
+  })),
 });
 
 export const fetch_peer_dependencies = (
   dependencies: Dependency[],
-): Promise<Dependency[]> =>
+): Promise<RegistryDependency[]> =>
   Promise.all(
     dependencies.map((dependency) =>
       fetch(
         new URL(
-          `${dependency.name}@${dependency.version.version}/package.json`,
-          "https://esm.sh/",
+          encodeURIComponent(dependency.name),
+          "https://registry.npmjs.org/",
         ),
       )
         .then((res) => res.json())
         .then(parse_peers)
-        .then(({ peerDependencies = {}, peerDependenciesMeta }) => ({
-          ...dependency,
-          peers: Object.entries(peerDependencies).map(([name, range]) => ({
-            name,
-            range: new Range(range),
-            optional: !!peerDependenciesMeta?.[name]?.optional,
-          })),
-        }))
+        .then((registry) => {
+          const [version, ...versions] = Object.values(registry.versions)
+            .filter(({ version }) => satisfies(version, dependency.range));
+
+          if (!version) {
+            throw new Error(
+              `Could not find ${dependency.name}@${dependency.range.range}`,
+            );
+          }
+
+          if (Object.keys(version.dependencies ?? {}).length > 0) {
+            console.warn(
+              "🔍 Further dependencies not analysed for",
+              colour.dependency(dependency.name),
+              colour.subdued("@"),
+              colour.version(version.version),
+            );
+          }
+
+          const peers = version.peerDependencies
+            ? Object.entries(version.peerDependencies).map((
+              [name, range],
+            ) => {
+              const local_version = dependencies.find((dependency) =>
+                dependency.name === name
+              )?.range;
+
+              const local_min_version = local_version
+                ? minVersion(local_version)
+                : null;
+              const local_version_matches = local_min_version
+                ? satisfies(local_min_version, range)
+                : false;
+
+              const is_optional = !!version.peerDependenciesMeta?.[name]
+                ?.optional;
+
+              const satisfied = local_version
+                ? local_version_matches
+                : is_optional;
+
+              return ({
+                name,
+                range: new Range(range),
+                satisfied,
+              });
+            })
+            : [];
+
+          return ({
+            ...dependency,
+            peers,
+            versions: [version, ...versions].map(({ version }) =>
+              new SemVer(version)
+            ),
+          });
+        })
         .catch((error) => {
           console.error("🚨 Failed to parse package.json for", dependency.name);
           throw error;
diff --git a/find_mismatches.test.ts b/find_mismatches.test.ts
index 2c4f013..129f63a 100644
--- a/find_mismatches.test.ts
+++ b/find_mismatches.test.ts
@@ -1,69 +1,62 @@
-import { assertEquals } from "./deps.ts";
-import { SemVer, Range } from "./deps.ts";
-import { find_mismatched_peer_dependencies } from "./find_mismatches.ts";
+import { assertEquals, Range, SemVer } from "./deps.ts";
 
-Deno.test("Works when all depencies are matches", () => {
+import { count_unsatisfied_peer_dependencies } from "./find_mismatches.ts";
+
+Deno.test("Works when all dependencies are matched", () => {
   assertEquals(
-    find_mismatched_peer_dependencies([
+    count_unsatisfied_peer_dependencies([
       {
         name: "one",
-        version: new SemVer("1.0.0"),
+        range: new Range("1.0.0"),
+        versions: [new SemVer("1.0.0")],
         peers: [
           {
             name: "two",
-            optional: false,
+            satisfied: true,
             range: new Range("^2.0.0"),
           },
-        ],
-      },
-      { name: "two", version: new SemVer("2.0.2"), peers: [] },
-    ]),
-    []
-  );
-});
-
-Deno.test("Fails on invalid range", () => {
-  assertEquals(
-    find_mismatched_peer_dependencies([
-      {
-        name: "one",
-        version: new SemVer("1.0.0"),
-        peers: [
           {
-            name: "two",
-            optional: false,
-            range: new Range("^2.0.3"),
+            name: "three",
+            satisfied: true,
+            range: new Range("^3.0.0"),
           },
         ],
       },
-      { name: "two", version: new SemVer("2.0.2"), peers: [] },
-    ]),
-    [
       {
         name: "two",
-        optional: false,
-        range: new Range("^2.0.3"),
-        required_by: "one",
+        range: new Range("2.0.2"),
+        versions: [new SemVer("2.0.2")],
+        peers: [
+          { name: "four", satisfied: true, range: new Range("^4") },
+        ],
       },
-    ]
+    ]),
+    0,
   );
 });
 
-Deno.test("Allows optional deps to fail if absent", () => {
+Deno.test("Fails on invalid range", () => {
   assertEquals(
-    find_mismatched_peer_dependencies([
+    count_unsatisfied_peer_dependencies([
       {
         name: "one",
-        version: new SemVer("1.0.0"),
+        range: new Range("1.0.0"),
+        versions: [new SemVer("1.0.0")],
         peers: [
           {
             name: "two",
-            optional: true,
+            satisfied: false,
             range: new Range("^2.0.3"),
           },
         ],
       },
+      {
+        name: "two",
+        range: new Range("2.0.2"),
+        versions: [new SemVer("2.0.2")],
+        peers: [],
+      },
     ]),
-    []
+    1,
   );
 });
diff --git a/find_mismatches.ts b/find_mismatches.ts
index 323ea60..221fd41 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -1,46 +1,47 @@
 import { colour } from "./colours.ts";
-import { satisfies } from "./deps.ts";
-import { Dependency } from "./types.ts";
+import { Dependency, RegistryDependency } from "./types.ts";
 
-export const find_mismatched_peer_dependencies = (
-  dependencies: Dependency[],
-) => {
-  const peers = dependencies.flatMap(({ name, peers }) =>
-    peers.map((peer) => ({ ...peer, required_by: name }))
-  );
+interface Matching {
+  name: string;
+  peers?: never;
+}
 
-  const mismatched = peers.filter((peer_dependency) => {
-    const local_version = dependencies.find(
-      ({ name }) => name === peer_dependency.name,
-    );
-    if (!local_version) {
-      return !peer_dependency.optional;
-    }
-    return !satisfies(local_version.version, peer_dependency.range);
-  });
+interface Missing {
+  name: string;
+  peers: Dependency[];
+}
+
+export const count_unsatisfied_peer_dependencies = (
+  dependencies: RegistryDependency[],
+) =>
+  dependencies.map(({ name, peers }) => {
+    const { length: unsatisfied } = peers.filter((peer) => !peer.satisfied);
 
-  if (mismatched.length === 0) {
-    console.info(`✅ All ${colour.file("peerDependencies")} satisfied}`);
-  } else {
-    console.error(
-      `🚨 The following ${colour.file("peerDependencies")} are unsatisfied:`,
-    );
+    if (unsatisfied === 0) {
+      console.info(
+        `✅ All ${colour.file("peerDependencies")} satisfied for ${
+          colour.dependency(name)
+        }`,
+      );
+    } else {
+      console.error(
+        `🚨 Not all ${colour.file("peerDependencies")} are satisfied for ${
+          colour.dependency(name)
+        }:`,
+      );
+    }
 
-    for (const { name, range, required_by } of mismatched) {
+    for (const { name, range, satisfied } of peers) {
       console.error(
-        `   - ${
+        `   - ${satisfied ? "✅" : "🚨"} ${
           [
             colour.dependency(name),
             colour.subdued("@"),
             colour.version(range.raw),
-            " (from ",
-            colour.dependency(required_by),
-            " )",
           ].join("")
         }`,
       );
     }
-  }
 
-  return mismatched;
-};
+    return unsatisfied;
+  }).reduce((acc, curr) => acc + curr);
diff --git a/main.ts b/main.ts
index f0b57e6..88d6231 100644
--- a/main.ts
+++ b/main.ts
@@ -1,7 +1,7 @@
 import { parse_declared_dependencies } from "./parse_dependencies.ts";
 import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
 import { colour } from "./colours.ts";
-import { find_mismatched_peer_dependencies } from "./find_mismatches.ts";
+import { count_unsatisfied_peer_dependencies } from "./find_mismatches.ts";
 
 const [package_file] = Deno.args;
 
@@ -30,14 +30,18 @@ if (dependencies.length === 0) {
 
 const dependencies_with_peers = await fetch_peer_dependencies(dependencies);
 
-const { length: number_of_mismatched_deps } = find_mismatched_peer_dependencies(
+const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(
   dependencies_with_peers,
 );
 
 if (number_of_mismatched_deps === 0) {
   console.info("✅ Everything is fine with your dependencies");
 } else {
-  console.info("🚨 This shal");
+  console.info(
+    `🚨 There are ${
+      colour.file(String(number_of_mismatched_deps))
+    } unsatisfied peer dependencies`,
+  );
 }
 
 Deno.exit(number_of_mismatched_deps);
diff --git a/parse_dependencies.test.ts b/parse_dependencies.test.ts
index a3b9d38..3b36d5b 100644
--- a/parse_dependencies.test.ts
+++ b/parse_dependencies.test.ts
@@ -1,4 +1,4 @@
-import { assertEquals, assertThrows, SemVer } from "./deps.ts";
+import { assertEquals, assertThrows, Range } from "./deps.ts";
 import { parse_declared_dependencies } from "./parse_dependencies.ts";
 
 Deno.test("Handles valid package.json", () => {
@@ -18,23 +18,19 @@ Deno.test("Handles valid package.json", () => {
   assertEquals(parse_declared_dependencies(json), [
     {
       name: "one",
-      version: new SemVer("1.0.0"),
-      peers: [],
+      range: new Range("1.0.0"),
     },
     {
       name: "two",
-      version: new SemVer("1.1.0"),
-      peers: [],
+      range: new Range("~1.1.0"),
     },
     {
       name: "three",
-      version: new SemVer("1.1.1"),
-      peers: [],
+      range: new Range("^1.1.1"),
     },
     {
       name: "four",
-      version: new SemVer("0.0.1"),
-      peers: [],
+      range: new Range("0.0.1"),
     },
   ]);
 });
diff --git a/parse_dependencies.ts b/parse_dependencies.ts
index be6fc9a..3fdd091 100644
--- a/parse_dependencies.ts
+++ b/parse_dependencies.ts
@@ -1,4 +1,4 @@
-import { object, record, string, coerce } from "./deps.ts";
+import { object, Range, record, string } from "./deps.ts";
 import { colour } from "./colours.ts";
 import { Dependency } from "./types.ts";
 
@@ -9,12 +9,11 @@ const { parse } = object({
 
 const parse_dependencies = (o: Record<string, string>): Dependency[] =>
   Object.entries(o).map(([name, version]) => {
-    const semver = coerce(version);
-    if (!semver) throw new Error(`Could not parse semver: ${version}`);
+    const range = new Range(version);
+    if (!range) throw new Error(`Could not parse semver: ${version}`);
     return {
       name,
-      version: semver,
-      peers: [],
+      range,
     };
   });
 
@@ -32,7 +31,7 @@ const find_duplicates = (deps: Dependency[]): string[] => {
 
 export const parse_declared_dependencies = (contents: string): Dependency[] => {
   const { dependencies = {}, devDependencies = {} } = parse(
-    JSON.parse(contents)
+    JSON.parse(contents),
   );
 
   const deps = [dependencies, devDependencies].map(parse_dependencies).flat();
diff --git a/types.ts b/types.ts
index e5bb9a5..d632ff9 100644
--- a/types.ts
+++ b/types.ts
@@ -1,13 +1,15 @@
-import { SemVer, Range } from "./deps.ts";
+import { Range, SemVer } from "./deps.ts";
 
 export interface Dependency {
   name: string;
-  version: SemVer;
+  range: Range;
+}
+
+export interface RegistryDependency extends Dependency {
+  versions: SemVer[];
   peers: PeerDependency[];
 }
 
-export interface PeerDependency {
-  name: string;
-  range: Range;
-  optional: boolean;
+export interface PeerDependency extends Dependency {
+  satisfied: boolean;
 }

From 5eaf930568e0c6b30b2c8ec18cd46a8850587691 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Mon, 23 Jan 2023 15:43:43 +0000
Subject: [PATCH 03/28] docs: update to-do list

---
 README.md | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 0255bb7..749738d 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,10 @@ Validate your NPM dependencies without installing Node (WIP)
 
 ## Todo
 
-- [X] Make it functional and composable
-- [X] Handle peer dependencies
+- [x] Make it functional and composable
+- [x] Handle peer dependencies
 - [ ] Handle lock files? (probably not)
-- [ ] Great error messaging
+- [x] Great error messaging
+- [ ] Investigate direct dependencies of dependencies, which may have peers
+      themselves
+- [ ] Give insight into possible resolution steps, including intersects

From 808aa784dce55229bd11d807fc56e29e0d798e73 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Mon, 23 Jan 2023 17:30:34 +0000
Subject: [PATCH 04/28] feat: handle edge cases and quiet mode

---
 deps.ts                    |  2 +-
 fetch_peer_dependencies.ts |  7 ++---
 find_mismatches.ts         | 53 +++++++++++++++++++++++---------------
 main.ts                    | 18 +++++++++----
 parse_dependencies.ts      | 27 ++++++++++++++++---
 5 files changed, 73 insertions(+), 34 deletions(-)

diff --git a/deps.ts b/deps.ts
index 245a4d1..3ce103d 100644
--- a/deps.ts
+++ b/deps.ts
@@ -1,4 +1,4 @@
-export { literal, object, record, string } from "https://esm.sh/zod@3.20.2";
+export { boolean, object, record, string } from "https://esm.sh/zod@3.20.2";
 export * from "https://esm.sh/semver@7.3.8";
 
 export {
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index cbd6d5a..5a4a4d2 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -1,6 +1,6 @@
 import { colour } from "./colours.ts";
 import {
-  literal,
+  boolean,
   minVersion,
   object,
   Range,
@@ -16,13 +16,14 @@ const { parseAsync: parse_peers } = object({
     version: string(),
     dependencies: record(string()).optional(),
     peerDependencies: record(string()).optional(),
-    peerDependenciesMeta: record(object({ optional: literal(true) }))
+    peerDependenciesMeta: record(object({ optional: boolean() }))
       .optional(),
   })),
 });
 
 export const fetch_peer_dependencies = (
   dependencies: Dependency[],
+  verbose = true,
 ): Promise<RegistryDependency[]> =>
   Promise.all(
     dependencies.map((dependency) =>
@@ -44,7 +45,7 @@ export const fetch_peer_dependencies = (
             );
           }
 
-          if (Object.keys(version.dependencies ?? {}).length > 0) {
+          if (verbose && Object.keys(version.dependencies ?? {}).length > 0) {
             console.warn(
               "🔍 Further dependencies not analysed for",
               colour.dependency(dependency.name),
diff --git a/find_mismatches.ts b/find_mismatches.ts
index 221fd41..34ed793 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -13,35 +13,46 @@ interface Missing {
 
 export const count_unsatisfied_peer_dependencies = (
   dependencies: RegistryDependency[],
+  verbose = true,
 ) =>
   dependencies.map(({ name, peers }) => {
+    if (peers.length === 0) return 0;
+
     const { length: unsatisfied } = peers.filter((peer) => !peer.satisfied);
 
     if (unsatisfied === 0) {
-      console.info(
-        `✅ All ${colour.file("peerDependencies")} satisfied for ${
-          colour.dependency(name)
-        }`,
-      );
-    } else {
-      console.error(
-        `🚨 Not all ${colour.file("peerDependencies")} are satisfied for ${
-          colour.dependency(name)
-        }:`,
-      );
+      if (verbose) {
+        console.info(
+          `✅ All ${colour.file("peerDependencies")} satisfied for ${
+            colour.dependency(name)
+          }`,
+        );
+      }
+      return 0;
     }
 
+    console.error(
+      `🚨 Not all ${colour.file("peerDependencies")} are satisfied for ${
+        colour.dependency(name)
+      }:`,
+    );
+
     for (const { name, range, satisfied } of peers) {
-      console.error(
-        `   - ${satisfied ? "✅" : "🚨"} ${
-          [
-            colour.dependency(name),
-            colour.subdued("@"),
-            colour.version(range.raw),
-          ].join("")
-        }`,
-      );
-    }
+      const dependency = [
+        colour.dependency(name),
+        colour.subdued("@"),
+        colour.version(range.raw),
+      ].join("");
 
+      if (satisfied) {
+        if (verbose) {
+          console.info(`   - ✅ ${dependency}`);
+        }
+      } else {
+        console.error(
+          `   - 🚨 ${dependency}`,
+        );
+      }
+    }
     return unsatisfied;
   }).reduce((acc, curr) => acc + curr);
diff --git a/main.ts b/main.ts
index 88d6231..ecdce97 100644
--- a/main.ts
+++ b/main.ts
@@ -3,7 +3,9 @@ import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
 import { colour } from "./colours.ts";
 import { count_unsatisfied_peer_dependencies } from "./find_mismatches.ts";
 
-const [package_file] = Deno.args;
+const [package_file, quiet] = Deno.args;
+
+const verbose = quiet !== "--quiet";
 
 if (!package_file) {
   console.error("🚨 No package.json passed as argument");
@@ -15,7 +17,7 @@ const filename = Deno.cwd() + "/" + package_file;
 const package_content = await Deno.readTextFile(filename).catch(() => "");
 
 if (package_content) {
-  console.info(`✅ Found package.json file`);
+  if (verbose) console.info(`✅ Found package.json file`);
 } else {
   console.error("🚨 No package.json found at", colour.file(filename));
   Deno.exit(1);
@@ -24,18 +26,24 @@ if (package_content) {
 const dependencies = parse_declared_dependencies(package_content);
 
 if (dependencies.length === 0) {
-  console.info("✅ You have no dependencies and therefore no issues!");
+  if (verbose) {
+    console.info("✅ You have no dependencies and therefore no issues!");
+  }
   Deno.exit();
 }
 
-const dependencies_with_peers = await fetch_peer_dependencies(dependencies);
+const dependencies_with_peers = await fetch_peer_dependencies(
+  dependencies,
+  verbose,
+);
 
 const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(
   dependencies_with_peers,
+  verbose,
 );
 
 if (number_of_mismatched_deps === 0) {
-  console.info("✅ Everything is fine with your dependencies");
+  if (verbose) console.info("✅ Everything is fine with your dependencies");
 } else {
   console.info(
     `🚨 There are ${
diff --git a/parse_dependencies.ts b/parse_dependencies.ts
index 3fdd091..16b2984 100644
--- a/parse_dependencies.ts
+++ b/parse_dependencies.ts
@@ -8,12 +8,10 @@ const { parse } = object({
 });
 
 const parse_dependencies = (o: Record<string, string>): Dependency[] =>
-  Object.entries(o).map(([name, version]) => {
-    const range = new Range(version);
-    if (!range) throw new Error(`Could not parse semver: ${version}`);
+  Object.entries(o).map(([name, range]) => {
     return {
       name,
-      range,
+      range: new Range(range),
     };
   });
 
@@ -34,6 +32,27 @@ export const parse_declared_dependencies = (contents: string): Dependency[] => {
     JSON.parse(contents),
   );
 
+  for (
+    const [name, range] of Object.entries({
+      ...dependencies,
+      ...devDependencies,
+    })
+  ) {
+    try {
+      new Range(range);
+    } catch (error: unknown) {
+      if (error instanceof Error) console.error(error.message);
+      console.warn(
+        "🚨 Ignored peer dependency",
+        colour.dependency(name),
+        colour.subdued("@"),
+        colour.version(range),
+      );
+      delete dependencies[name];
+      delete devDependencies[name];
+    }
+  }
+
   const deps = [dependencies, devDependencies].map(parse_dependencies).flat();
 
   const duplicates = find_duplicates(deps);

From 203301c1bacc1b954de1d330b877126b16e01c4b Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 09:49:30 +0000
Subject: [PATCH 05/28] feat: add caching option

---
 cache.ts                   | 17 +++++++++++++++++
 deps.ts                    |  2 +-
 fetch_peer_dependencies.ts | 32 +++++++++++++++++++++++++++-----
 find_mismatches.ts         | 12 +-----------
 main.ts                    | 10 ++++++----
 5 files changed, 52 insertions(+), 21 deletions(-)
 create mode 100644 cache.ts

diff --git a/cache.ts b/cache.ts
new file mode 100644
index 0000000..2f14832
--- /dev/null
+++ b/cache.ts
@@ -0,0 +1,17 @@
+const name = "NPM registry";
+
+const cache = await caches.open(name);
+
+export const get = async (url: URL, use_cache: boolean) => {
+  if (!use_cache) {
+    cache.delete(url);
+    return fetch(url);
+  }
+
+  const found = await cache.match(url);
+  if (found) return found;
+
+  const response = await fetch(url);
+  cache.put(url, response.clone());
+  return response;
+};
diff --git a/deps.ts b/deps.ts
index 3ce103d..bda89cd 100644
--- a/deps.ts
+++ b/deps.ts
@@ -4,4 +4,4 @@ export * from "https://esm.sh/semver@7.3.8";
 export {
   assertEquals,
   assertThrows,
-} from "https://deno.land/std@0.156.0/testing/asserts.ts";
+} from "https://deno.land/std@0.168.0/testing/asserts.ts";
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index 5a4a4d2..792b269 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -1,3 +1,4 @@
+import { get } from "./cache.ts";
 import { colour } from "./colours.ts";
 import {
   boolean,
@@ -23,15 +24,16 @@ const { parseAsync: parse_peers } = object({
 
 export const fetch_peer_dependencies = (
   dependencies: Dependency[],
-  verbose = true,
+  { verbose = false, cache = false } = {},
 ): Promise<RegistryDependency[]> =>
   Promise.all(
     dependencies.map((dependency) =>
-      fetch(
+      get(
         new URL(
           encodeURIComponent(dependency.name),
           "https://registry.npmjs.org/",
         ),
+        cache,
       )
         .then((res) => res.json())
         .then(parse_peers)
@@ -48,9 +50,11 @@ export const fetch_peer_dependencies = (
           if (verbose && Object.keys(version.dependencies ?? {}).length > 0) {
             console.warn(
               "🔍 Further dependencies not analysed for",
-              colour.dependency(dependency.name),
-              colour.subdued("@"),
-              colour.version(version.version),
+              [
+                colour.dependency(dependency.name),
+                colour.subdued("@"),
+                colour.version(version.version),
+              ].join(""),
             );
           }
 
@@ -98,3 +102,21 @@ export const fetch_peer_dependencies = (
         })
     ),
   );
+
+Deno.bench("Fetch with cache", async () => {
+  await fetch_peer_dependencies([
+    {
+      name: "@guardian/core-web-vitals",
+      range: new Range("2.0.2"),
+    },
+  ], { cache: true });
+});
+
+Deno.bench("Fetch without cache", async () => {
+  await fetch_peer_dependencies([
+    {
+      name: "@guardian/core-web-vitals",
+      range: new Range("2.0.2"),
+    },
+  ], { cache: false });
+});
diff --git a/find_mismatches.ts b/find_mismatches.ts
index 34ed793..d832ba1 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -1,15 +1,5 @@
 import { colour } from "./colours.ts";
-import { Dependency, RegistryDependency } from "./types.ts";
-
-interface Matching {
-  name: string;
-  peers?: never;
-}
-
-interface Missing {
-  name: string;
-  peers: Dependency[];
-}
+import { RegistryDependency } from "./types.ts";
 
 export const count_unsatisfied_peer_dependencies = (
   dependencies: RegistryDependency[],
diff --git a/main.ts b/main.ts
index ecdce97..030f4cd 100644
--- a/main.ts
+++ b/main.ts
@@ -2,10 +2,12 @@ import { parse_declared_dependencies } from "./parse_dependencies.ts";
 import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
 import { colour } from "./colours.ts";
 import { count_unsatisfied_peer_dependencies } from "./find_mismatches.ts";
+import { parse } from "https://deno.land/std@0.168.0/flags/mod.ts";
 
-const [package_file, quiet] = Deno.args;
-
-const verbose = quiet !== "--quiet";
+const { _: [package_file], verbose, cache } = parse(Deno.args, {
+  boolean: ["verbose", "cache"],
+  default: { verbose: false, cache: true },
+});
 
 if (!package_file) {
   console.error("🚨 No package.json passed as argument");
@@ -34,7 +36,7 @@ if (dependencies.length === 0) {
 
 const dependencies_with_peers = await fetch_peer_dependencies(
   dependencies,
-  verbose,
+  { verbose, cache },
 );
 
 const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(

From 2b84c6c2faa8de4ab701f3c17dee2e64d20bfdcd Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 10:26:36 +0000
Subject: [PATCH 06/28] refactor: extract formatting

---
 colours.ts                 |  9 +++++++++
 fetch_peer_dependencies.ts | 11 ++++-------
 find_mismatches.ts         | 26 ++++++++++----------------
 3 files changed, 23 insertions(+), 23 deletions(-)

diff --git a/colours.ts b/colours.ts
index a8af971..7d40644 100644
--- a/colours.ts
+++ b/colours.ts
@@ -5,9 +5,18 @@ import {
   yellow,
 } from "https://deno.land/std@0.171.0/fmt/colors.ts";
 
+import { Range } from "./deps.ts";
+
 export const colour = {
   dependency: blue,
   file: cyan,
   subdued: gray,
   version: yellow,
 };
+
+export const format = (name: string, range: Range) =>
+  [
+    colour.dependency(name),
+    colour.subdued("@"),
+    colour.version(range.raw),
+  ].join("");
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index 792b269..f8e21ae 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -1,5 +1,5 @@
 import { get } from "./cache.ts";
-import { colour } from "./colours.ts";
+import { format } from "./colours.ts";
 import {
   boolean,
   minVersion,
@@ -49,12 +49,9 @@ export const fetch_peer_dependencies = (
 
           if (verbose && Object.keys(version.dependencies ?? {}).length > 0) {
             console.warn(
-              "🔍 Further dependencies not analysed for",
-              [
-                colour.dependency(dependency.name),
-                colour.subdued("@"),
-                colour.version(version.version),
-              ].join(""),
+              `🔍 ${
+                format(dependency.name, dependency.range)
+              } – futher deps not analysed`,
             );
           }
 
diff --git a/find_mismatches.ts b/find_mismatches.ts
index d832ba1..62e255f 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -1,11 +1,11 @@
-import { colour } from "./colours.ts";
+import { colour, format } from "./colours.ts";
 import { RegistryDependency } from "./types.ts";
 
 export const count_unsatisfied_peer_dependencies = (
   dependencies: RegistryDependency[],
   verbose = true,
 ) =>
-  dependencies.map(({ name, peers }) => {
+  dependencies.map(({ name, range, peers }) => {
     if (peers.length === 0) return 0;
 
     const { length: unsatisfied } = peers.filter((peer) => !peer.satisfied);
@@ -13,34 +13,28 @@ export const count_unsatisfied_peer_dependencies = (
     if (unsatisfied === 0) {
       if (verbose) {
         console.info(
-          `✅ All ${colour.file("peerDependencies")} satisfied for ${
-            colour.dependency(name)
-          }`,
+          `✅ ${format(name, range)} – all ${
+            colour.file("peerDependencies")
+          } satisfied`,
         );
       }
       return 0;
     }
 
     console.error(
-      `🚨 Not all ${colour.file("peerDependencies")} are satisfied for ${
-        colour.dependency(name)
-      }:`,
+      `🚨 ${format(name, range)} – unsatisfied ${
+        colour.file("peerDependencies")
+      }`,
     );
 
     for (const { name, range, satisfied } of peers) {
-      const dependency = [
-        colour.dependency(name),
-        colour.subdued("@"),
-        colour.version(range.raw),
-      ].join("");
-
       if (satisfied) {
         if (verbose) {
-          console.info(`   - ✅ ${dependency}`);
+          console.info(`   - ✅ ${format(name, range)}`);
         }
       } else {
         console.error(
-          `   - 🚨 ${dependency}`,
+          `   - 🚨 ${format(name, range)}`,
         );
       }
     }

From 2f2b82b31b9d07a75efe79c74779f86b39219abb Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 11:14:25 +0000
Subject: [PATCH 07/28] fix: clean up code

---
 main.ts | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/main.ts b/main.ts
index 030f4cd..c20bcee 100644
--- a/main.ts
+++ b/main.ts
@@ -6,10 +6,9 @@ import { parse } from "https://deno.land/std@0.168.0/flags/mod.ts";
 
 const { _: [package_file], verbose, cache } = parse(Deno.args, {
   boolean: ["verbose", "cache"],
-  default: { verbose: false, cache: true },
 });
 
-if (!package_file) {
+if (typeof package_file !== "string") {
   console.error("🚨 No package.json passed as argument");
   Deno.exit(1);
 }

From ce37682beea184a17e33e1e84af83e9d7014fe4a Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 12:14:50 +0000
Subject: [PATCH 08/28] refactor: better tree shaping

---
 colours.ts                      |  4 ++
 fetch_peer_dependencies.test.ts | 15 ++++--
 fetch_peer_dependencies.ts      | 85 ++++++++++++++++-----------------
 find_mismatches.test.ts         | 12 +++--
 find_mismatches.ts              | 51 +++++++++++---------
 fixtures/package.json           |  2 +
 fixtures/package_valid.json     |  2 +
 main.ts                         | 54 ++++++++++++++-------
 parse_dependencies.ts           | 16 ++++++-
 types.ts                        |  3 +-
 10 files changed, 149 insertions(+), 95 deletions(-)

diff --git a/colours.ts b/colours.ts
index 7d40644..6ac01ac 100644
--- a/colours.ts
+++ b/colours.ts
@@ -2,6 +2,8 @@ import {
   blue,
   cyan,
   gray,
+  green,
+  red,
   yellow,
 } from "https://deno.land/std@0.171.0/fmt/colors.ts";
 
@@ -12,6 +14,8 @@ export const colour = {
   file: cyan,
   subdued: gray,
   version: yellow,
+  valid: green,
+  invalid: red,
 };
 
 export const format = (name: string, range: Range) =>
diff --git a/fetch_peer_dependencies.test.ts b/fetch_peer_dependencies.test.ts
index fa9aab9..7e7bae7 100644
--- a/fetch_peer_dependencies.test.ts
+++ b/fetch_peer_dependencies.test.ts
@@ -14,7 +14,8 @@ Deno.test("Can get peer dependencies", async () => {
     {
       name: "@guardian/core-web-vitals",
       range: new Range("2.0.2"),
-      versions: [new SemVer("2.0.2")],
+      version: new SemVer("2.0.2"),
+      dependencies: [],
       peers: [
         {
           name: "@guardian/libs",
@@ -50,7 +51,8 @@ Deno.test("Can get optional peer dependencies", async () => {
     {
       name: "@guardian/libs",
       range: new Range("12.0.0"),
-      versions: [new SemVer("12.0.0")],
+      version: new SemVer("12.0.0"),
+      dependencies: [],
       peers: [
         {
           name: "tslib",
@@ -78,7 +80,8 @@ Deno.test("Will fail on optional dependencies that are defined locally", async (
     {
       name: "@guardian/libs",
       range: new Range("12.0.0"),
-      versions: [new SemVer("12.0.0")],
+      version: new SemVer("12.0.0"),
+      dependencies: [],
       peers: [
         {
           name: "tslib",
@@ -95,13 +98,15 @@ Deno.test("Will fail on optional dependencies that are defined locally", async (
     {
       name: "tslib",
       range: new Range("2.4.1"),
-      versions: [new SemVer("2.4.1")],
+      version: new SemVer("2.4.1"),
+      dependencies: [],
       peers: [],
     },
     {
       name: "typescript",
       range: new Range("4.2.2"),
-      versions: [new SemVer("4.2.2")],
+      version: new SemVer("4.2.2"),
+      dependencies: [],
       peers: [],
     },
   ]);
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index f8e21ae..a298e9b 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -13,18 +13,19 @@ import {
 import type { Dependency, RegistryDependency } from "./types.ts";
 
 const { parseAsync: parse_peers } = object({
-  versions: record(object({
-    version: string(),
-    dependencies: record(string()).optional(),
-    peerDependencies: record(string()).optional(),
-    peerDependenciesMeta: record(object({ optional: boolean() }))
-      .optional(),
-  })),
+  versions: record(
+    object({
+      version: string(),
+      dependencies: record(string()).optional(),
+      peerDependencies: record(string()).optional(),
+      peerDependenciesMeta: record(object({ optional: boolean() })).optional(),
+    }),
+  ),
 });
 
 export const fetch_peer_dependencies = (
   dependencies: Dependency[],
-  { verbose = false, cache = false } = {},
+  { cache = false } = {},
 ): Promise<RegistryDependency[]> =>
   Promise.all(
     dependencies.map((dependency) =>
@@ -38,29 +39,20 @@ export const fetch_peer_dependencies = (
         .then((res) => res.json())
         .then(parse_peers)
         .then((registry) => {
-          const [version, ...versions] = Object.values(registry.versions)
-            .filter(({ version }) => satisfies(version, dependency.range));
+          const version = Object.values(registry.versions).find(({ version }) =>
+            satisfies(version, dependency.range)
+          );
 
           if (!version) {
             throw new Error(
-              `Could not find ${dependency.name}@${dependency.range.range}`,
-            );
-          }
-
-          if (verbose && Object.keys(version.dependencies ?? {}).length > 0) {
-            console.warn(
-              `🔍 ${
-                format(dependency.name, dependency.range)
-              } – futher deps not analysed`,
+              `Could not find ${format(dependency.name, dependency.range)}`,
             );
           }
 
           const peers = version.peerDependencies
-            ? Object.entries(version.peerDependencies).map((
-              [name, range],
-            ) => {
-              const local_version = dependencies.find((dependency) =>
-                dependency.name === name
+            ? Object.entries(version.peerDependencies).map(([name, range]) => {
+              const local_version = dependencies.find(
+                (dependency) => dependency.name === name,
               )?.range;
 
               const local_min_version = local_version
@@ -77,21 +69,22 @@ export const fetch_peer_dependencies = (
                 ? local_version_matches
                 : is_optional;
 
-              return ({
+              return {
                 name,
                 range: new Range(range),
                 satisfied,
-              });
+              };
             })
             : [];
 
-          return ({
+          return {
             ...dependency,
-            peers,
-            versions: [version, ...versions].map(({ version }) =>
-              new SemVer(version)
+            dependencies: Object.entries(version.dependencies ?? {}).map(
+              ([name, range]) => ({ name, range: new Range(range) }),
             ),
-          });
+            peers,
+            version: new SemVer(version.version),
+          };
         })
         .catch((error) => {
           console.error("🚨 Failed to parse package.json for", dependency.name);
@@ -101,19 +94,25 @@ export const fetch_peer_dependencies = (
   );
 
 Deno.bench("Fetch with cache", async () => {
-  await fetch_peer_dependencies([
-    {
-      name: "@guardian/core-web-vitals",
-      range: new Range("2.0.2"),
-    },
-  ], { cache: true });
+  await fetch_peer_dependencies(
+    [
+      {
+        name: "@guardian/core-web-vitals",
+        range: new Range("2.0.2"),
+      },
+    ],
+    { cache: true },
+  );
 });
 
 Deno.bench("Fetch without cache", async () => {
-  await fetch_peer_dependencies([
-    {
-      name: "@guardian/core-web-vitals",
-      range: new Range("2.0.2"),
-    },
-  ], { cache: false });
+  await fetch_peer_dependencies(
+    [
+      {
+        name: "@guardian/core-web-vitals",
+        range: new Range("2.0.2"),
+      },
+    ],
+    { cache: false },
+  );
 });
diff --git a/find_mismatches.test.ts b/find_mismatches.test.ts
index 129f63a..695f2f4 100644
--- a/find_mismatches.test.ts
+++ b/find_mismatches.test.ts
@@ -8,7 +8,8 @@ Deno.test("Works when all dependencies are matched", () => {
       {
         name: "one",
         range: new Range("1.0.0"),
-        versions: [new SemVer("1.0.0")],
+        version: new SemVer("1.0.0"),
+        dependencies: [],
         peers: [
           {
             name: "two",
@@ -25,7 +26,8 @@ Deno.test("Works when all dependencies are matched", () => {
       {
         name: "two",
         range: new Range("2.0.2"),
-        versions: [new SemVer("2.0.2")],
+        version: new SemVer("2.0.2"),
+        dependencies: [],
         peers: [
           { name: "four", satisfied: true, range: new Range("^4") },
         ],
@@ -41,7 +43,8 @@ Deno.test("Fails on invalid range", () => {
       {
         name: "one",
         range: new Range("1.0.0"),
-        versions: [new SemVer("1.0.0")],
+        version: new SemVer("1.0.0"),
+        dependencies: [],
         peers: [
           {
             name: "two",
@@ -53,7 +56,8 @@ Deno.test("Fails on invalid range", () => {
       {
         name: "two",
         range: new Range("2.0.2"),
-        versions: [new SemVer("2.0.2")],
+        version: new SemVer("2.0.2"),
+        dependencies: [],
         peers: [],
       },
     ]),
diff --git a/find_mismatches.ts b/find_mismatches.ts
index 62e255f..87e2296 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -3,40 +3,45 @@ import { RegistryDependency } from "./types.ts";
 
 export const count_unsatisfied_peer_dependencies = (
   dependencies: RegistryDependency[],
-  verbose = true,
 ) =>
-  dependencies.map(({ name, range, peers }) => {
-    if (peers.length === 0) return 0;
+  dependencies.map(({ peers }) =>
+    peers.filter((peer) => !peer.satisfied).length
+  )
+    .reduce((acc, curr) => acc + curr);
 
-    const { length: unsatisfied } = peers.filter((peer) => !peer.satisfied);
+export const format_dependencies = (
+  dependencies: RegistryDependency[],
+  verbose = true,
+): void => {
+  dependencies.map(({ name, range, dependencies, peers }) => {
+    console.info(
+      `├─ ${format(name, range)}`,
+    );
 
-    if (unsatisfied === 0) {
-      if (verbose) {
-        console.info(
-          `✅ ${format(name, range)} – all ${
-            colour.file("peerDependencies")
-          } satisfied`,
-        );
-      }
-      return 0;
+    let count = dependencies.length;
+    for (const dependency of dependencies) {
+      const angle = peers.length === 0 && --count === 0 ? "╰" : "├";
+      console.warn(
+        `│  ${angle}─ ${colour.version("▲")} ${
+          format(dependency.name, dependency.range)
+        } – futher ${colour.file("dependencies")} not analysed`,
+      );
     }
 
-    console.error(
-      `🚨 ${format(name, range)} – unsatisfied ${
-        colour.file("peerDependencies")
-      }`,
-    );
-
+    count = peers.length;
     for (const { name, range, satisfied } of peers) {
+      const angle = --count === 0 ? "╰" : "├";
       if (satisfied) {
         if (verbose) {
-          console.info(`   - ✅ ${format(name, range)}`);
+          console.info(
+            `│  ${angle}─ ${colour.valid("○")} ${format(name, range)}`,
+          );
         }
       } else {
         console.error(
-          `   - 🚨 ${format(name, range)}`,
+          `│  ${angle}─ ${colour.invalid("✕")} ${format(name, range)}`,
         );
       }
     }
-    return unsatisfied;
-  }).reduce((acc, curr) => acc + curr);
+  });
+};
diff --git a/fixtures/package.json b/fixtures/package.json
index 2850bb8..5a0d1d7 100644
--- a/fixtures/package.json
+++ b/fixtures/package.json
@@ -1,4 +1,6 @@
 {
+  "name": "npm-dependencies",
+  "version": "0.0.1",
   "dependencies": {
     "@guardian/source-foundations": "8.0.0",
     "@guardian/core-web-vitals": "2.0.2"
diff --git a/fixtures/package_valid.json b/fixtures/package_valid.json
index 4a194d9..69268b2 100644
--- a/fixtures/package_valid.json
+++ b/fixtures/package_valid.json
@@ -1,4 +1,6 @@
 {
+  "name": "npm-dependencies",
+  "version": "0.0.1",
   "dependencies": {
     "@guardian/ab-core": "2.0.0",
     "@guardian/core-web-vitals": "2.0.2",
diff --git a/main.ts b/main.ts
index c20bcee..390d8fc 100644
--- a/main.ts
+++ b/main.ts
@@ -1,7 +1,13 @@
-import { parse_declared_dependencies } from "./parse_dependencies.ts";
+import {
+  parse_declared_dependencies,
+  parse_package_info,
+} from "./parse_dependencies.ts";
 import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
-import { colour } from "./colours.ts";
-import { count_unsatisfied_peer_dependencies } from "./find_mismatches.ts";
+import { colour, format } from "./colours.ts";
+import {
+  count_unsatisfied_peer_dependencies,
+  format_dependencies,
+} from "./find_mismatches.ts";
 import { parse } from "https://deno.land/std@0.168.0/flags/mod.ts";
 
 const { _: [package_file], verbose, cache } = parse(Deno.args, {
@@ -15,41 +21,55 @@ if (typeof package_file !== "string") {
 
 const filename = Deno.cwd() + "/" + package_file;
 
-const package_content = await Deno.readTextFile(filename).catch(() => "");
+const package_content: unknown = await Deno.readTextFile(filename).catch(() =>
+  ""
+).then(
+  (contents) => JSON.parse(contents),
+);
 
-if (package_content) {
-  if (verbose) console.info(`✅ Found package.json file`);
-} else {
+if (!package_content) {
   console.error("🚨 No package.json found at", colour.file(filename));
   Deno.exit(1);
 }
 
-const dependencies = parse_declared_dependencies(package_content);
+const { name, range } = parse_package_info(package_content);
+
+console.info(`${format(name, range)}`);
 
-if (dependencies.length === 0) {
+const dependencies_from_package = parse_declared_dependencies(package_content);
+
+if (dependencies_from_package.length === 0) {
   if (verbose) {
     console.info("✅ You have no dependencies and therefore no issues!");
   }
   Deno.exit();
 }
 
-const dependencies_with_peers = await fetch_peer_dependencies(
-  dependencies,
-  { verbose, cache },
+const dependencies_from_registry = await fetch_peer_dependencies(
+  dependencies_from_package,
+  { cache },
 );
 
-const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(
-  dependencies_with_peers,
+format_dependencies(
+  dependencies_from_registry,
   verbose,
 );
 
+const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(
+  dependencies_from_registry,
+);
+
 if (number_of_mismatched_deps === 0) {
-  if (verbose) console.info("✅ Everything is fine with your dependencies");
+  if (verbose) console.info("✅ Dependencies are in good shape");
+} else if (number_of_mismatched_deps === 1) {
+  console.error(
+    `🚨 There is ${colour.file("1")} dependencies problem`,
+  );
 } else {
-  console.info(
+  console.error(
     `🚨 There are ${
       colour.file(String(number_of_mismatched_deps))
-    } unsatisfied peer dependencies`,
+    } dependencies problems`,
   );
 }
 
diff --git a/parse_dependencies.ts b/parse_dependencies.ts
index 16b2984..e1fea1d 100644
--- a/parse_dependencies.ts
+++ b/parse_dependencies.ts
@@ -27,9 +27,21 @@ const find_duplicates = (deps: Dependency[]): string[] => {
   return [...duplicates];
 };
 
-export const parse_declared_dependencies = (contents: string): Dependency[] => {
+const package_parser = object({
+  name: string(),
+  version: string(),
+});
+
+export const parse_package_info = (contents: unknown): Dependency => {
+  const { name, version } = package_parser.parse(contents);
+  return { name, range: new Range(version) };
+};
+
+export const parse_declared_dependencies = (
+  contents: unknown,
+): Dependency[] => {
   const { dependencies = {}, devDependencies = {} } = parse(
-    JSON.parse(contents),
+    contents,
   );
 
   for (
diff --git a/types.ts b/types.ts
index d632ff9..891d82e 100644
--- a/types.ts
+++ b/types.ts
@@ -6,7 +6,8 @@ export interface Dependency {
 }
 
 export interface RegistryDependency extends Dependency {
-  versions: SemVer[];
+  version: SemVer;
+  dependencies: Dependency[]
   peers: PeerDependency[];
 }
 

From 860fe75ad863833ab92cba981d5f5ee436843e5e Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 14:29:58 +0000
Subject: [PATCH 09/28] fix: handle invalid ranges

---
 fetch_peer_dependencies.ts | 12 +++++++++++-
 find_mismatches.ts         | 39 ++++++++++++++++++++++----------------
 2 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index a298e9b..ab89b8f 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -79,7 +79,17 @@ export const fetch_peer_dependencies = (
 
           return {
             ...dependency,
-            dependencies: Object.entries(version.dependencies ?? {}).map(
+            dependencies: Object.entries(version.dependencies ?? {}).filter(
+              ([name, range]) => {
+                try {
+                  new Range(range);
+                  return true;
+                } catch {
+                  console.warn("Invalid range:", `${name}@${range}`);
+                }
+                return false;
+              },
+            ).map(
               ([name, range]) => ({ name, range: new Range(range) }),
             ),
             peers,
diff --git a/find_mismatches.ts b/find_mismatches.ts
index 87e2296..87d16c2 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -10,26 +10,31 @@ export const count_unsatisfied_peer_dependencies = (
     .reduce((acc, curr) => acc + curr);
 
 export const format_dependencies = (
-  dependencies: RegistryDependency[],
+  registry_dependencies: RegistryDependency[],
   verbose = true,
 ): void => {
-  dependencies.map(({ name, range, dependencies, peers }) => {
-    console.info(
-      `├─ ${format(name, range)}`,
-    );
+  for (const { name, range, dependencies, peers } of registry_dependencies) {
+    const unsatisfied = peers.filter(({ satisfied }) => !satisfied);
+    if (verbose || unsatisfied.length > 0) {
+      console.info(
+        `├─ ${format(name, range)}`,
+      );
+    }
 
     let count = dependencies.length;
-    for (const dependency of dependencies) {
-      const angle = peers.length === 0 && --count === 0 ? "╰" : "├";
-      console.warn(
-        `│  ${angle}─ ${colour.version("▲")} ${
-          format(dependency.name, dependency.range)
-        } – futher ${colour.file("dependencies")} not analysed`,
-      );
+    if (verbose) {
+      for (const dependency of dependencies) {
+        const angle = peers.length === 0 && --count === 0 ? "╰" : "├";
+        console.warn(
+          `│  ${angle}─ ${colour.version("▲")} ${
+            format(dependency.name, dependency.range)
+          } – futher ${colour.file("dependencies")} not analysed`,
+        );
+      }
     }
 
-    count = peers.length;
-    for (const { name, range, satisfied } of peers) {
+    count = verbose ? peers.length : unsatisfied.length;
+    for (const { name, range, satisfied } of verbose ? peers : unsatisfied) {
       const angle = --count === 0 ? "╰" : "├";
       if (satisfied) {
         if (verbose) {
@@ -39,9 +44,11 @@ export const format_dependencies = (
         }
       } else {
         console.error(
-          `│  ${angle}─ ${colour.invalid("✕")} ${format(name, range)}`,
+          `│  ${angle}─ ${colour.invalid("✕")} ${
+            format(name, range)
+          } – unsatisfied peer dependency`,
         );
       }
     }
-  });
+  }
 };

From 7490588f7b932068118dcf49c6421374aedd57fb Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 15:04:27 +0000
Subject: [PATCH 10/28] feat: breathe a little

add more breathing room to CLI output
---
 find_mismatches.ts | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/find_mismatches.ts b/find_mismatches.ts
index 87d16c2..aea53f6 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -16,9 +16,8 @@ export const format_dependencies = (
   for (const { name, range, dependencies, peers } of registry_dependencies) {
     const unsatisfied = peers.filter(({ satisfied }) => !satisfied);
     if (verbose || unsatisfied.length > 0) {
-      console.info(
-        `├─ ${format(name, range)}`,
-      );
+      console.info(`│`);
+      console.info(`├─ ${format(name, range)}`);
     }
 
     let count = dependencies.length;
@@ -44,9 +43,7 @@ export const format_dependencies = (
         }
       } else {
         console.error(
-          `│  ${angle}─ ${colour.invalid("✕")} ${
-            format(name, range)
-          } – unsatisfied peer dependency`,
+          `│  ${angle}─ ${colour.invalid("✕")} ${format(name, range)}`,
         );
       }
     }

From e4083dd7e7e88811171808cb06077f241459acbd Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 15:15:38 +0000
Subject: [PATCH 11/28] feat: indicate the reason for mismatch

---
 fetch_peer_dependencies.ts       |  1 +
 find_mismatches.ts               | 12 ++++++++++--
 fixtures/package_duplicate.json  |  2 ++
 fixtures/package_typescript.json |  2 ++
 types.ts                         |  3 ++-
 5 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index ab89b8f..149c7a5 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -73,6 +73,7 @@ export const fetch_peer_dependencies = (
                 name,
                 range: new Range(range),
                 satisfied,
+                local: local_version,
               };
             })
             : [];
diff --git a/find_mismatches.ts b/find_mismatches.ts
index aea53f6..950d67d 100644
--- a/find_mismatches.ts
+++ b/find_mismatches.ts
@@ -33,7 +33,9 @@ export const format_dependencies = (
     }
 
     count = verbose ? peers.length : unsatisfied.length;
-    for (const { name, range, satisfied } of verbose ? peers : unsatisfied) {
+    for (
+      const { name, range, satisfied, local } of verbose ? peers : unsatisfied
+    ) {
       const angle = --count === 0 ? "╰" : "├";
       if (satisfied) {
         if (verbose) {
@@ -42,8 +44,14 @@ export const format_dependencies = (
           );
         }
       } else {
+        const reason = local
+          ? `locally specified to ${colour.version(local.raw)}`
+          : "locally missing";
+
         console.error(
-          `│  ${angle}─ ${colour.invalid("✕")} ${format(name, range)}`,
+          `│  ${angle}─ ${colour.invalid("✕")} ${
+            format(name, range)
+          } – ${reason}`,
         );
       }
     }
diff --git a/fixtures/package_duplicate.json b/fixtures/package_duplicate.json
index 9eded57..ff6e348 100644
--- a/fixtures/package_duplicate.json
+++ b/fixtures/package_duplicate.json
@@ -1,4 +1,6 @@
 {
+  "name": "npm-dependencies-duplicate",
+  "version": "0.0.2",
   "dependencies": {
     "@guardian/source-foundations": "8.0.0",
     "@guardian/libs": "^12"
diff --git a/fixtures/package_typescript.json b/fixtures/package_typescript.json
index 306a2d6..dde15e4 100644
--- a/fixtures/package_typescript.json
+++ b/fixtures/package_typescript.json
@@ -1,4 +1,6 @@
 {
+  "name": "npm-dependencies-typescript",
+  "version": "0.0.1",
   "dependencies": {
     "@guardian/source-foundations": "8.0.0"
   },
diff --git a/types.ts b/types.ts
index 891d82e..9669db5 100644
--- a/types.ts
+++ b/types.ts
@@ -7,10 +7,11 @@ export interface Dependency {
 
 export interface RegistryDependency extends Dependency {
   version: SemVer;
-  dependencies: Dependency[]
+  dependencies: Dependency[];
   peers: PeerDependency[];
 }
 
 export interface PeerDependency extends Dependency {
   satisfied: boolean;
+  local?: Range;
 }

From d5d7af389e47599c7197dfea13503ca3bb409f00 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 18:09:37 +0000
Subject: [PATCH 12/28] refactor: extract benchmark

---
 fetch_peer_dependencies.bench.ts | 26 ++++++++++++++++++++++++++
 fetch_peer_dependencies.ts       | 24 ------------------------
 2 files changed, 26 insertions(+), 24 deletions(-)
 create mode 100644 fetch_peer_dependencies.bench.ts

diff --git a/fetch_peer_dependencies.bench.ts b/fetch_peer_dependencies.bench.ts
new file mode 100644
index 0000000..9ce0ea4
--- /dev/null
+++ b/fetch_peer_dependencies.bench.ts
@@ -0,0 +1,26 @@
+import { Range } from "./deps.ts";
+import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
+
+Deno.bench("Fetch with cache", async () => {
+  await fetch_peer_dependencies(
+    [
+      {
+        name: "@guardian/core-web-vitals",
+        range: new Range("2.0.2"),
+      },
+    ],
+    { cache: true },
+  );
+});
+
+Deno.bench("Fetch without cache", async () => {
+  await fetch_peer_dependencies(
+    [
+      {
+        name: "@guardian/core-web-vitals",
+        range: new Range("2.0.2"),
+      },
+    ],
+    { cache: false },
+  );
+});
diff --git a/fetch_peer_dependencies.ts b/fetch_peer_dependencies.ts
index 149c7a5..8f3e750 100644
--- a/fetch_peer_dependencies.ts
+++ b/fetch_peer_dependencies.ts
@@ -103,27 +103,3 @@ export const fetch_peer_dependencies = (
         })
     ),
   );
-
-Deno.bench("Fetch with cache", async () => {
-  await fetch_peer_dependencies(
-    [
-      {
-        name: "@guardian/core-web-vitals",
-        range: new Range("2.0.2"),
-      },
-    ],
-    { cache: true },
-  );
-});
-
-Deno.bench("Fetch without cache", async () => {
-  await fetch_peer_dependencies(
-    [
-      {
-        name: "@guardian/core-web-vitals",
-        range: new Range("2.0.2"),
-      },
-    ],
-    { cache: false },
-  );
-});

From 9832ba9ce3d3c9a071a16bd300592fb7dba9f8ce Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Tue, 24 Jan 2023 18:09:47 +0000
Subject: [PATCH 13/28] feat: add lock file

---
 lock.json | 197 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 197 insertions(+)
 create mode 100644 lock.json

diff --git a/lock.json b/lock.json
new file mode 100644
index 0000000..feec490
--- /dev/null
+++ b/lock.json
@@ -0,0 +1,197 @@
+{
+  "version": "2",
+  "remote": {
+    "https://deno.land/std@0.168.0/_util/asserts.ts": "d0844e9b62510f89ce1f9878b046f6a57bf88f208a10304aab50efcb48365272",
+    "https://deno.land/std@0.168.0/flags/mod.ts": "4f50ec6383c02684db35de38b3ffb2cd5b9fcfcc0b1147055d1980c49e82521c",
+    "https://deno.land/std@0.168.0/fmt/colors.ts": "03ad95e543d2808bc43c17a3dd29d25b43d0f16287fe562a0be89bf632454a12",
+    "https://deno.land/std@0.168.0/testing/_diff.ts": "a23e7fc2b4d8daa3e158fa06856bedf5334ce2a2831e8bf9e509717f455adb2c",
+    "https://deno.land/std@0.168.0/testing/_format.ts": "cd11136e1797791045e639e9f0f4640d5b4166148796cad37e6ef75f7d7f3832",
+    "https://deno.land/std@0.168.0/testing/asserts.ts": "51353e79437361d4b02d8e32f3fc83b22231bc8f8d4c841d86fd32b0b0afe940",
+    "https://deno.land/std@0.171.0/fmt/colors.ts": "938c5d44d889fb82eff6c358bea8baa7e85950a16c9f6dae3ec3a7a729164471",
+    "https://deno.land/std@0.173.0/_util/asserts.ts": "178dfc49a464aee693a7e285567b3d0b555dc805ff490505a8aae34f9cfb1462",
+    "https://deno.land/std@0.173.0/_util/os.ts": "d932f56d41e4f6a6093d56044e29ce637f8dcc43c5a90af43504a889cf1775e3",
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+    "https://deno.land/std@0.173.0/async/pool.ts": "fd082bd4aaf26445909889435a5c74334c017847842ec035739b4ae637ae8260",
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+    "https://deno.land/std@0.173.0/node/_events.d.ts": "1347437fd6b084d7c9a4e16b9fe7435f00b030970086482edeeb3b179d0775af",
+    "https://deno.land/std@0.173.0/node/_events.mjs": "d4ba4e629abe3db9f1b14659fd5c282b7da8b2b95eaf13238eee4ebb142a2448",
+    "https://deno.land/std@0.173.0/node/_global.d.ts": "2d88342f38b4083b858998e27c706725fb03a74aa14ef8d985dc18438b5188e4",
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+    "https://deno.land/std@0.173.0/node/_process/process.ts": "c96bb1f6253824c372f4866ee006dcefda02b7050d46759736e403f862d91051",
+    "https://deno.land/std@0.173.0/node/_process/stdio.mjs": "cf17727eac8da3a665851df700b5aca6a12bacc3ebbf33e63e4b919f80ba44a6",
+    "https://deno.land/std@0.173.0/node/_process/streams.mjs": "c1461c4dbf963a93a0ca8233467573a685bbde347562573761cc9435fd7080f6",
+    "https://deno.land/std@0.173.0/node/_stream.d.ts": "112e1a0677cd6db932c3ce0e6e5bbdc7a2ac1874572f449044ecc82afcf5ee2e",
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+    "https://deno.land/std@0.173.0/node/internal/crypto/_keys.ts": "8f3c3b5a141aa0331a53c205e9338655f1b3b307a08085fd6ff6dda6f7c4190b",
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+    "https://deno.land/std@0.173.0/node/internal/validators.mjs": "e02f2b02dd072a5d623970292588d541204dc82207b4c58985d933a5f4b382e6",
+    "https://deno.land/std@0.173.0/node/internal_binding/_libuv_winerror.ts": "30c9569603d4b97a1f1a034d88a3f74800d5ea1f12fcc3d225c9899d4e1a518b",
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+    "https://deno.land/std@0.173.0/node/internal_binding/_timingSafeEqual.ts": "7d9732464d3c669ff07713868ce5d25bc974a06112edbfb5f017fc3c70c0853e",
+    "https://deno.land/std@0.173.0/node/internal_binding/_utils.ts": "7c58a2fbb031a204dee9583ba211cf9c67922112fe77e7f0b3226112469e9fe1",
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+    "https://esm.sh/v104/yallist@4.0.0/deno/yallist.js": "55a926cdcbd6f8b54bb87a8b07589f02aa45ff136a51fc7f0c671a08e7d5c6f8",
+    "https://esm.sh/v104/zod@3.20.2/deno/zod.js": "4e1c7e6ae3b866c33bfebc0c6886cb22ce577dd9ebf53cebdbd8fa8a7ab4d739",
+    "https://esm.sh/v104/zod@3.20.2/index.d.ts": "b51c954b9557b1dcb03b2bf34cd136e710cb9aa276e686cac0e291249590a52a",
+    "https://esm.sh/v104/zod@3.20.2/lib/ZodError.d.ts": "c53bb6e3d82b7813bed0096be4185d253c8f7d32db9c8960bc7f06980f86261e",
+    "https://esm.sh/v104/zod@3.20.2/lib/errors.d.ts": "5ec2790f877581637c058eb5bbb72e855a078620d0781d2a6a8f308fe1d5436f",
+    "https://esm.sh/v104/zod@3.20.2/lib/external.d.ts": "91cec2fe1e1fb2574812a29a57ad2c39a1e69b0fa1179547382c92649fc5c66e",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/enumUtil.d.ts": "f672c876c1a04a223cf2023b3d91e8a52bb1544c576b81bf64a8fec82be9969c",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/errorUtil.d.ts": "98a9cc18f661d28e6bd31c436e1984f3980f35e0f0aa9cf795c54f8ccb667ffe",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/parseUtil.d.ts": "d3dbfc2f2fbf2c1bdea72db72f9f5c95d2ca5b4d32c9e229764ebaba0920203c",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/partialUtil.d.ts": "7da6f1e431746c5364ebe6703f5d3a844ab0495e2a8cedc0a29cced52d6284a1",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/typeAliases.d.ts": "5487b97cfa28b26b4a9ef0770f872bdbebd4c46124858de00f242c3eed7519f4",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/util.d.ts": "bb98c05ae5cb9bd7cb7ad76fe517251a661787a6f24337b842f47faf393f79c7",
+    "https://esm.sh/v104/zod@3.20.2/lib/index.d.ts": "0f86f053aecd06054359e146b6cd800fee9bf82905f8afb47f1fe774fd37311e",
+    "https://esm.sh/v104/zod@3.20.2/lib/locales/en.d.ts": "f8ec1611afb8d132c6c71822718805866890cf2071025153af97508eff24e4b6",
+    "https://esm.sh/v104/zod@3.20.2/lib/types.d.ts": "744e3c65de31c5f7f8e79f9a37e1e372c9043a5ca130ec1038180ba4c9941f1f",
+    "https://esm.sh/zod@3.20.2": "5da460955f749f7688ad10d15edfefd8eaa41d8a7ed54e65f6abd10d8d879128"
+  }
+}

From 4e728f7a8faf310198774c2b5178828d1c0cf705 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 11:29:44 +0000
Subject: [PATCH 14/28] refactor: check package in a single pass

---
 fetch_peer_dependencies.test.ts |  8 +++++
 main.test.ts                    |  3 --
 parse_dependencies.test.ts      | 38 ++++++++---------------
 parse_dependencies.ts           | 54 +++++++++++----------------------
 types.ts                        |  5 +++
 5 files changed, 44 insertions(+), 64 deletions(-)
 delete mode 100644 main.test.ts

diff --git a/fetch_peer_dependencies.test.ts b/fetch_peer_dependencies.test.ts
index 7e7bae7..ce4b567 100644
--- a/fetch_peer_dependencies.test.ts
+++ b/fetch_peer_dependencies.test.ts
@@ -21,21 +21,25 @@ Deno.test("Can get peer dependencies", async () => {
           name: "@guardian/libs",
           range: new Range("^12.0.0"),
           satisfied: false,
+          local: undefined,
         },
         {
           name: "tslib",
           range: new Range("^2.4.1"),
           satisfied: false,
+          local: undefined,
         },
         {
           name: "typescript",
           range: new Range("^4.3.2"),
           satisfied: true,
+          local: undefined,
         },
         {
           name: "web-vitals",
           range: new Range("^2.0.0"),
           satisfied: false,
+          local: undefined,
         },
       ],
     },
@@ -58,11 +62,13 @@ Deno.test("Can get optional peer dependencies", async () => {
           name: "tslib",
           range: new Range("^2.4.1"),
           satisfied: false,
+          local: undefined,
         },
         {
           name: "typescript",
           range: new Range("^4.3.2"),
           satisfied: true,
+          local: undefined,
         },
       ],
     },
@@ -87,11 +93,13 @@ Deno.test("Will fail on optional dependencies that are defined locally", async (
           name: "tslib",
           range: new Range("^2.4.1"),
           satisfied: true,
+          local: new Range("2.4.1"),
         },
         {
           name: "typescript",
           range: new Range("^4.3.2"),
           satisfied: false,
+          local: new Range("4.2.2"),
         },
       ],
     },
diff --git a/main.test.ts b/main.test.ts
deleted file mode 100644
index 10da7df..0000000
--- a/main.test.ts
+++ /dev/null
@@ -1,3 +0,0 @@
-Deno.test("Parses package.json", () => {
-  return;
-});
diff --git a/parse_dependencies.test.ts b/parse_dependencies.test.ts
index 3b36d5b..f654f0c 100644
--- a/parse_dependencies.test.ts
+++ b/parse_dependencies.test.ts
@@ -2,20 +2,14 @@ import { assertEquals, assertThrows, Range } from "./deps.ts";
 import { parse_declared_dependencies } from "./parse_dependencies.ts";
 
 Deno.test("Handles valid package.json", () => {
-  const json = `
-  {
-    "dependencies": {
-      "one": "1.0.0",
-      "two": "~1.1.0"
-    },
-    "devDependencies": {
-      "three": "^1.1.1",
-      "four": "0.0.1"
-    }
-  }
-  `;
+  const tuples = [
+    ["one", "1.0.0"],
+    ["two", "~1.1.0"],
+    ["three", "^1.1.1"],
+    ["four", "0.0.1"],
+  ] satisfies [string, string][];
 
-  assertEquals(parse_declared_dependencies(json), [
+  assertEquals(parse_declared_dependencies(tuples), [
     {
       name: "one",
       range: new Range("1.0.0"),
@@ -36,17 +30,11 @@ Deno.test("Handles valid package.json", () => {
 });
 
 Deno.test("Warns on duplicate dependencies", () => {
-  const json = `
-  {
-    "dependencies": {
-      "one": "1.0.1",
-      "two": "2.0.1"
-    },
-    "devDependencies": {
-      "two": "2.0.2"
-    }
-  }
-  `;
+  const tuples = [
+    ["one", "1.0.1"],
+    ["two", "2.0.1"],
+    ["two", "2.0.2"],
+  ] satisfies [string, string][];
 
-  assertThrows(() => parse_declared_dependencies(json));
+  assertThrows(() => parse_declared_dependencies(tuples));
 });
diff --git a/parse_dependencies.ts b/parse_dependencies.ts
index e1fea1d..e1b19b4 100644
--- a/parse_dependencies.ts
+++ b/parse_dependencies.ts
@@ -1,25 +1,12 @@
 import { object, Range, record, string } from "./deps.ts";
 import { colour } from "./colours.ts";
-import { Dependency } from "./types.ts";
+import { Dependency, UnrefinedDependency } from "./types.ts";
 
-const { parse } = object({
-  dependencies: record(string()).optional(),
-  devDependencies: record(string()).optional(),
-});
-
-const parse_dependencies = (o: Record<string, string>): Dependency[] =>
-  Object.entries(o).map(([name, range]) => {
-    return {
-      name,
-      range: new Range(range),
-    };
-  });
-
-const find_duplicates = (deps: Dependency[]): string[] => {
+const find_duplicates = (dependencies: Dependency[]): string[] => {
   const seen = new Set<string>();
   const duplicates = new Set<string>();
 
-  for (const { name } of deps) {
+  for (const { name } of dependencies) {
     if (seen.has(name)) duplicates.add(name);
     seen.add(name);
   }
@@ -30,28 +17,26 @@ const find_duplicates = (deps: Dependency[]): string[] => {
 const package_parser = object({
   name: string(),
   version: string(),
+  dependencies: record(string()).optional(),
+  devDependencies: record(string()).optional(),
 });
 
-export const parse_package_info = (contents: unknown): Dependency => {
-  const { name, version } = package_parser.parse(contents);
-  return { name, range: new Range(version) };
+export const parse_package_info = (contents: unknown): UnrefinedDependency => {
+  const { name, version, dependencies = {}, devDependencies = {} } =
+    package_parser.parse(
+      contents,
+    );
+  return { name, range: new Range(version), dependencies, devDependencies };
 };
 
+const isDefined = <T>(_: T): _ is NonNullable<T> => typeof _ !== "undefined";
+
 export const parse_declared_dependencies = (
-  contents: unknown,
+  dependencies: [name: string, range: string][],
 ): Dependency[] => {
-  const { dependencies = {}, devDependencies = {} } = parse(
-    contents,
-  );
-
-  for (
-    const [name, range] of Object.entries({
-      ...dependencies,
-      ...devDependencies,
-    })
-  ) {
+  const deps = dependencies.map(([name, range]) => {
     try {
-      new Range(range);
+      return { name, range: new Range(range) };
     } catch (error: unknown) {
       if (error instanceof Error) console.error(error.message);
       console.warn(
@@ -60,12 +45,9 @@ export const parse_declared_dependencies = (
         colour.subdued("@"),
         colour.version(range),
       );
-      delete dependencies[name];
-      delete devDependencies[name];
     }
-  }
-
-  const deps = [dependencies, devDependencies].map(parse_dependencies).flat();
+    return undefined;
+  }).filter(isDefined).flat();
 
   const duplicates = find_duplicates(deps);
 
diff --git a/types.ts b/types.ts
index 9669db5..738b852 100644
--- a/types.ts
+++ b/types.ts
@@ -5,6 +5,11 @@ export interface Dependency {
   range: Range;
 }
 
+export interface UnrefinedDependency extends Dependency {
+  dependencies: Record<string, string>;
+  devDependencies: Record<string, string>;
+}
+
 export interface RegistryDependency extends Dependency {
   version: SemVer;
   dependencies: Dependency[];

From 25097a9da45cfec1b51a319dc55dba4a50389cf8 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 11:30:01 +0000
Subject: [PATCH 15/28] feat: check @types/* packages

---
 check_types.test.ts   | 55 +++++++++++++++++++++++++++++++++++++++++++
 check_types.ts        | 40 +++++++++++++++++++++++++++++++
 main.ts               | 49 ++++++++++++++++++++++++++++++--------
 parse_dependencies.ts |  3 +--
 utils.ts              |  2 ++
 5 files changed, 137 insertions(+), 12 deletions(-)
 create mode 100644 check_types.test.ts
 create mode 100644 check_types.ts
 create mode 100644 utils.ts

diff --git a/check_types.test.ts b/check_types.test.ts
new file mode 100644
index 0000000..9d0dbdd
--- /dev/null
+++ b/check_types.test.ts
@@ -0,0 +1,55 @@
+import { assertEquals } from "./deps.ts";
+import { matched_types, mismatches } from "./check_types.ts";
+
+Deno.test("will not complain on types without an associated pacakge", () => {
+  const mismatches = matched_types([
+    ["@types/node", "~8.11"],
+    ["typescript", "^4.9"],
+  ]);
+
+  assertEquals(mismatches, []);
+});
+
+Deno.test("will find potential mismatches on types with an associated pacakge", () => {
+  const matched = matched_types([
+    ["@types/react", "~16.1"],
+    ["react", "^16.1"],
+  ]);
+
+  assertEquals(matched, [
+    { name: "react", range: "^16.1", type_range: "~16.1" },
+  ]);
+});
+
+Deno.test("will error on caret ranges", () => {
+  const mismatched = mismatches(matched_types([
+    ["@types/react", "^17"],
+    ["react", "^17"],
+  ]));
+
+  assertEquals(mismatched, [
+    ["react", "Invalid caret (^) notation. Use tilde (~) instead"],
+  ]);
+});
+
+Deno.test("will error on invalid major ranges", () => {
+  const mismatched = mismatches(matched_types([
+    ["@types/react", "~17.1"],
+    ["react", "~18.1"],
+  ]));
+
+  assertEquals(mismatched, [
+    ["react", "Mismatching major versions"],
+  ]);
+});
+
+Deno.test("will error on invalid minor ranges", () => {
+  const mismatched = mismatches(matched_types([
+    ["@types/react", "~17.1"],
+    ["react", "~17.0"],
+  ]));
+
+  assertEquals(mismatched, [
+    ["react", "Mismatching minor versions"],
+  ]);
+});
diff --git a/check_types.ts b/check_types.ts
new file mode 100644
index 0000000..e203b3a
--- /dev/null
+++ b/check_types.ts
@@ -0,0 +1,40 @@
+import { major, minor, minVersion } from "./deps.ts";
+import { isDefined } from "./utils.ts";
+
+export const filter_types = (dependencies: string[]) =>
+  dependencies.filter((dependency) => dependency.startsWith("@types/"));
+
+export const matched_types = (dependencies: [string, string][]) =>
+  dependencies.map(([name, range]) => {
+    const [, type_range] = dependencies.find(([other_name]) =>
+      other_name === `@types/${name}`
+    ) ?? [];
+
+    return type_range ? { name, range, type_range } : undefined;
+  }).filter(isDefined);
+
+export const mismatches = (dependencies: ReturnType<typeof matched_types>) =>
+  dependencies.map(({ name, range, type_range }) => {
+    if (range.startsWith("^") || type_range.startsWith("^")) {
+      return [
+        name,
+        "Invalid caret (^) notation. Use tilde (~) instead",
+      ] as const;
+    }
+
+    const main_min = minVersion(range);
+    const type_min = minVersion(type_range);
+
+    if (!main_min || !type_min) {
+      return [name, "Invalid range or version types"] as const;
+    }
+
+    if (major(main_min) !== major(type_min)) {
+      return [name, "Mismatching major versions"] as const;
+    }
+    if (minor(main_min) !== minor(type_min)) {
+      return [name, "Mismatching minor versions"] as const;
+    }
+
+    return undefined;
+  }).filter(isDefined);
diff --git a/main.ts b/main.ts
index 390d8fc..3580894 100644
--- a/main.ts
+++ b/main.ts
@@ -9,6 +9,7 @@ import {
   format_dependencies,
 } from "./find_mismatches.ts";
 import { parse } from "https://deno.land/std@0.168.0/flags/mod.ts";
+import { filter_types } from "./check_types.ts";
 
 const { _: [package_file], verbose, cache } = parse(Deno.args, {
   boolean: ["verbose", "cache"],
@@ -32,15 +33,34 @@ if (!package_content) {
   Deno.exit(1);
 }
 
-const { name, range } = parse_package_info(package_content);
+const { name, range, dependencies, devDependencies } = parse_package_info(
+  package_content,
+);
 
 console.info(`${format(name, range)}`);
 
-const dependencies_from_package = parse_declared_dependencies(package_content);
+const types_in_direct_dependencies = filter_types(Object.keys(dependencies));
+
+if (types_in_direct_dependencies.length > 0) {
+  console.error(
+    `├─ ${colour.invalid("✕")} ${
+      colour.dependency("@types/*")
+    } should only be present in devDependencies`,
+  );
+}
+
+const dependencies_tuple: [name: string, range: string][] = [
+  dependencies,
+  devDependencies,
+].map((_) => Object.entries(_)).flat();
+
+const dependencies_from_package = parse_declared_dependencies(
+  dependencies_tuple,
+);
 
 if (dependencies_from_package.length === 0) {
   if (verbose) {
-    console.info("✅ You have no dependencies and therefore no issues!");
+    console.info("╰ You have no dependencies and therefore no issues!");
   }
   Deno.exit();
 }
@@ -59,18 +79,27 @@ const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(
   dependencies_from_registry,
 );
 
-if (number_of_mismatched_deps === 0) {
-  if (verbose) console.info("✅ Dependencies are in good shape");
-} else if (number_of_mismatched_deps === 1) {
+const problems = number_of_mismatched_deps +
+  types_in_direct_dependencies.length;
+
+console.info("│");
+
+if (problems === 0) {
+  if (verbose) {
+    console.info(`╰─ ${colour.valid("○")} Dependencies are in good shape`);
+  }
+} else if (problems === 1) {
   console.error(
-    `🚨 There is ${colour.file("1")} dependencies problem`,
+    `╰─ ${colour.invalid("✕")} There is ${
+      colour.invalid("1")
+    } dependencies problem`,
   );
 } else {
   console.error(
-    `🚨 There are ${
-      colour.file(String(number_of_mismatched_deps))
+    `╰─ ${colour.invalid("✕")} There are ${
+      colour.invalid(String(problems))
     } dependencies problems`,
   );
 }
 
-Deno.exit(number_of_mismatched_deps);
+Deno.exit(problems);
diff --git a/parse_dependencies.ts b/parse_dependencies.ts
index e1b19b4..764ca80 100644
--- a/parse_dependencies.ts
+++ b/parse_dependencies.ts
@@ -1,6 +1,7 @@
 import { object, Range, record, string } from "./deps.ts";
 import { colour } from "./colours.ts";
 import { Dependency, UnrefinedDependency } from "./types.ts";
+import { isDefined } from "./utils.ts";
 
 const find_duplicates = (dependencies: Dependency[]): string[] => {
   const seen = new Set<string>();
@@ -29,8 +30,6 @@ export const parse_package_info = (contents: unknown): UnrefinedDependency => {
   return { name, range: new Range(version), dependencies, devDependencies };
 };
 
-const isDefined = <T>(_: T): _ is NonNullable<T> => typeof _ !== "undefined";
-
 export const parse_declared_dependencies = (
   dependencies: [name: string, range: string][],
 ): Dependency[] => {
diff --git a/utils.ts b/utils.ts
new file mode 100644
index 0000000..f7b0607
--- /dev/null
+++ b/utils.ts
@@ -0,0 +1,2 @@
+export const isDefined = <T>(_: T): _ is NonNullable<T> =>
+  typeof _ !== "undefined";

From 79c779e6bb9045823ad79586481b8259dfee0640 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 11:30:17 +0000
Subject: [PATCH 16/28] chore: change colours and add deno config

---
 colours.ts            | 6 +++---
 deno.jsonc            | 6 ++++++
 fixtures/package.json | 1 +
 3 files changed, 10 insertions(+), 3 deletions(-)
 create mode 100644 deno.jsonc

diff --git a/colours.ts b/colours.ts
index 6ac01ac..3980d36 100644
--- a/colours.ts
+++ b/colours.ts
@@ -1,17 +1,17 @@
 import {
-  blue,
   cyan,
   gray,
   green,
   red,
+  underline,
   yellow,
 } from "https://deno.land/std@0.171.0/fmt/colors.ts";
 
 import { Range } from "./deps.ts";
 
 export const colour = {
-  dependency: blue,
-  file: cyan,
+  dependency: cyan,
+  file: underline,
   subdued: gray,
   version: yellow,
   valid: green,
diff --git a/deno.jsonc b/deno.jsonc
new file mode 100644
index 0000000..d53c7e6
--- /dev/null
+++ b/deno.jsonc
@@ -0,0 +1,6 @@
+{
+  "compilerOptions": {
+    "noUncheckedIndexedAccess": true,
+    "lib": ["dom", "deno.ns"]
+  }
+}
diff --git a/fixtures/package.json b/fixtures/package.json
index 5a0d1d7..51cb61a 100644
--- a/fixtures/package.json
+++ b/fixtures/package.json
@@ -2,6 +2,7 @@
   "name": "npm-dependencies",
   "version": "0.0.1",
   "dependencies": {
+    "@types/node": "~18.11",
     "@guardian/source-foundations": "8.0.0",
     "@guardian/core-web-vitals": "2.0.2"
   },

From 24e15631d74c4d52602dfde4dfdb3d55bae14936 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 11:32:32 +0000
Subject: [PATCH 17/28] chore: vscode config

---
 .vscode/settings.json | 9 +++++++++
 1 file changed, 9 insertions(+)
 create mode 100644 .vscode/settings.json

diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..d2c12f0
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,9 @@
+{
+  "deno.enable": true,
+  "deno.unstable": true,
+  "editor.defaultFormatter": "denoland.vscode-deno",
+  "[typescript]": {
+    "editor.defaultFormatter": "denoland.vscode-deno"
+  },
+  "deno.suggest.completeFunctionCalls": true
+}

From 7952a8e389433cc17d656f30d59c80ed9c95618c Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:07:54 +0000
Subject: [PATCH 18/28] feat: add lock file

---
 deno.lock | 195 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 195 insertions(+)
 create mode 100644 deno.lock

diff --git a/deno.lock b/deno.lock
new file mode 100644
index 0000000..2205560
--- /dev/null
+++ b/deno.lock
@@ -0,0 +1,195 @@
+{
+  "version": "2",
+  "remote": {
+    "https://deno.land/std@0.168.0/fmt/colors.ts": "03ad95e543d2808bc43c17a3dd29d25b43d0f16287fe562a0be89bf632454a12",
+    "https://deno.land/std@0.168.0/testing/_diff.ts": "a23e7fc2b4d8daa3e158fa06856bedf5334ce2a2831e8bf9e509717f455adb2c",
+    "https://deno.land/std@0.168.0/testing/_format.ts": "cd11136e1797791045e639e9f0f4640d5b4166148796cad37e6ef75f7d7f3832",
+    "https://deno.land/std@0.168.0/testing/asserts.ts": "51353e79437361d4b02d8e32f3fc83b22231bc8f8d4c841d86fd32b0b0afe940",
+    "https://deno.land/std@0.171.0/fmt/colors.ts": "938c5d44d889fb82eff6c358bea8baa7e85950a16c9f6dae3ec3a7a729164471",
+    "https://deno.land/std@0.173.0/_util/asserts.ts": "178dfc49a464aee693a7e285567b3d0b555dc805ff490505a8aae34f9cfb1462",
+    "https://deno.land/std@0.173.0/_util/os.ts": "d932f56d41e4f6a6093d56044e29ce637f8dcc43c5a90af43504a889cf1775e3",
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+    "https://deno.land/std@0.173.0/path/_util.ts": "86c2375a996c1931b2f2ac71fefd5ddf0cf0e579fa4ab12d3e4c552d4223b8d8",
+    "https://deno.land/std@0.173.0/path/common.ts": "ee7505ab01fd22de3963b64e46cff31f40de34f9f8de1fff6a1bd2fe79380000",
+    "https://deno.land/std@0.173.0/path/glob.ts": "d479e0a695621c94d3fd7fe7abd4f9499caf32a8de13f25073451c6ef420a4e1",
+    "https://deno.land/std@0.173.0/path/mod.ts": "4b83694ac500d7d31b0cdafc927080a53dc0c3027eb2895790fb155082b0d232",
+    "https://deno.land/std@0.173.0/path/posix.ts": "0874b341c2c6968ca38d323338b8b295ea1dae10fa872a768d812e2e7d634789",
+    "https://deno.land/std@0.173.0/path/separator.ts": "0fb679739d0d1d7bf45b68dacfb4ec7563597a902edbaf3c59b50d5bcadd93b1",
+    "https://deno.land/std@0.173.0/path/win32.ts": "672942919dd66ce1b8c224e77d3447e2ad8254eaff13fe6946420a9f78fa141e",
+    "https://deno.land/std@0.173.0/streams/write_all.ts": "3b2e1ce44913f966348ce353d02fa5369e94115181037cd8b602510853ec3033",
+    "https://deno.land/std@0.173.0/types.d.ts": "220ed56662a0bd393ba5d124aa6ae2ad36a00d2fcbc0e8666a65f4606aaa9784",
+    "https://esm.sh/semver@7.3.8": "66cf5abf347faf6aacb50a0f1ee0ec9ac2c66e57fa1c5b975fd2cb56fe53c956",
+    "https://esm.sh/v104/@types/semver@7.3.13/classes/comparator.d.ts": "793bfebb9bb0a72aef35d56cf59fefc343c96c3c83f33e4b6133d9e520ea4969",
+    "https://esm.sh/v104/@types/semver@7.3.13/classes/range.d.ts": "70acf43190f9af19604401b079199cfc618082ddac3de48be2ee9694113f47e5",
+    "https://esm.sh/v104/@types/semver@7.3.13/classes/semver.d.ts": "d549806ef609c83125b75954e470a6f34335005fcbf81be87426b5a9e0d39608",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/clean.d.ts": "a5eb84f0ee2822d98b3d8516509352a33ce8688965eb9fac13cf0e21eda62845",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/cmp.d.ts": "d1e4d215126fe0db53e060245cf5e697e6002d7335a09cefbed4af9f3fb54a5e",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/coerce.d.ts": "19cddcbff1ce1d540aeaab143b0b9a71633ebe255ab08aaae0ad4f36bef49db0",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/compare-build.d.ts": "b5277ca0bdb12056c3687b8cee47734492f67bb0b58b4b7073e965ccbf708503",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/compare-loose.d.ts": "d19bbef11362960a463317e82f993dff44f656a87eb02bb7452ba0a862fe7e9e",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/compare.d.ts": "b6adb9d9ace09dba2b1cc582b551139e61e0e65d7da31f1cc9f30c3075d3e13d",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/diff.d.ts": "d39a11c79c625ca1ef1ce6f99fa08542c0b106bde116186cf45e97b6211aa9c7",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/eq.d.ts": "6f80724fa45cc52b273e3416b2484b98fc5c236fffa40d7218a4b6299b381b22",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/gt.d.ts": "54846f82c2156b18e41e6a1d62e074e76d7f01440bc1c641fc72e9f334d67c3b",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/gte.d.ts": "de60cee0c3cf3acf97636b73529129437b883e07190674389da683e1f48f8474",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/inc.d.ts": "bad52417b5275f8cd6dfe53c0d94b84bdf4735a676e0f7ce70cbe76cd29a2f02",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/lt.d.ts": "c9fb4feb61e5e39e482b1bd6438a0237e6b708f148b5827ce4332925576c5804",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/lte.d.ts": "0c57de12d88bf67cb888332a67b71d6dcf7e6a0f41e8c2768aea6ffcbbe0574a",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/major.d.ts": "d9f654955c3f42874a69c3993819f7eccd93fc191538252556b4b6b62250abdb",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/minor.d.ts": "0dadf77ef9211bd11deb83b28dc36210987fcf125118fcdceef2f250984f753e",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/neq.d.ts": "b57f145cb5c8cee6d2913186adab341ca1baa8addd81dc96e3b495b52ec60657",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/parse.d.ts": "7a47a862beeb12ebbb976e49d0cc4d95ad6aa07622c6953cb29b4d0623d456a6",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/patch.d.ts": "8bb0cc352dc68930a91100124413d20c4f088574c08619160a10a9af9e141291",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/prerelease.d.ts": "2144f4fcc33a321c10eed831c4748cda4fc0c9c5e648a71fa7899d36c8c00923",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/rcompare.d.ts": "cd9ddb89bed51980102fab0c3986f9ee7a64e27d117c1adbe3ca738fb0eea12a",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/rsort.d.ts": "b8e949f8075bfa126fae1c421da8c8e559a07c4c47840f355420e56b299c91bb",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/satisfies.d.ts": "eeddc303a4753825486dca6028f73b404419d49a0dac668495c8f71bce92d771",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/sort.d.ts": "e74717fa7ab44e65972cba3afe5db0fbb7c48a35346bd2072ca6c9f3749923d7",
+    "https://esm.sh/v104/@types/semver@7.3.13/functions/valid.d.ts": "30ed3b9abb6ae21e71bcdf23a44d1de33bdcd05445c6a748370cd21b756fc2f1",
+    "https://esm.sh/v104/@types/semver@7.3.13/index.d.ts": "bf2f2a19df95d88e17f96a3914a5024d9f61c9e874e0d744b3bc0e6223e9e328",
+    "https://esm.sh/v104/@types/semver@7.3.13/internals/identifiers.d.ts": "34baf65cfee92f110d6653322e2120c2d368ee64b3c7981dff08ed105c4f19b0",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/gtr.d.ts": "fa58a5179a81fb88b32a0f0f5604e9cdc915f8734b6e394ff59b734e1a068a8d",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/intersects.d.ts": "aa6958786e1a4d90c0ca301edc86e04bc737e0bd489f5f38187bc6587474845b",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/ltr.d.ts": "1d7789ee92780ac62c4d331138e922d325286fb1d78c8447addfec23925ddb0f",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/max-satisfying.d.ts": "13524ac8f9a3c501aa03a9949ba5c5f01c6c30e33ff5c3505e1d2dc7a384b973",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/min-satisfying.d.ts": "192af061294d60671545e7341ad69494e6921b69805a15eb619afdf71f7a17c5",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/min-version.d.ts": "b6ccc5b599a1bd2677cd3a516984467f413f7c201bfe01c2f174f6afcbf98d50",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/outside.d.ts": "cf6a2f381910c3dd0e9e4c69719589a850cf843589759d9182eb6421a6864a65",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/simplify.d.ts": "568f0867b37eb79d1ca33c9712c7ada9ef41d722ad59cb0e5f37e89298861554",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/subset.d.ts": "4f46d5b9fdf398aac809a233fdc756e8bf4e2b743b159d24c9cb8b3a32c35f9f",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/to-comparators.d.ts": "ed87996328ada2100faff62f857b05fcedd53d1303a1f9b40cc3750ff0df10e4",
+    "https://esm.sh/v104/@types/semver@7.3.13/ranges/valid.d.ts": "d717439745a1ab3fae112cdf7eaaf569304328039f8b6f1e1c508040c67e32e7",
+    "https://esm.sh/v104/lru-cache@6.0.0/deno/lru-cache.js": "fbacc9d1ad6bd5f2b957937d47d373f80707087ddc22e36148f0bee153f601df",
+    "https://esm.sh/v104/semver@7.3.8/deno/semver.js": "ebd99a9b9db10a5d2a18d53cb020825f316b25ffa131f2a287551c428e3aa52c",
+    "https://esm.sh/v104/yallist@4.0.0/deno/yallist.js": "55a926cdcbd6f8b54bb87a8b07589f02aa45ff136a51fc7f0c671a08e7d5c6f8",
+    "https://esm.sh/v104/zod@3.20.2/deno/zod.js": "4e1c7e6ae3b866c33bfebc0c6886cb22ce577dd9ebf53cebdbd8fa8a7ab4d739",
+    "https://esm.sh/v104/zod@3.20.2/index.d.ts": "b51c954b9557b1dcb03b2bf34cd136e710cb9aa276e686cac0e291249590a52a",
+    "https://esm.sh/v104/zod@3.20.2/lib/ZodError.d.ts": "c53bb6e3d82b7813bed0096be4185d253c8f7d32db9c8960bc7f06980f86261e",
+    "https://esm.sh/v104/zod@3.20.2/lib/errors.d.ts": "5ec2790f877581637c058eb5bbb72e855a078620d0781d2a6a8f308fe1d5436f",
+    "https://esm.sh/v104/zod@3.20.2/lib/external.d.ts": "91cec2fe1e1fb2574812a29a57ad2c39a1e69b0fa1179547382c92649fc5c66e",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/enumUtil.d.ts": "f672c876c1a04a223cf2023b3d91e8a52bb1544c576b81bf64a8fec82be9969c",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/errorUtil.d.ts": "98a9cc18f661d28e6bd31c436e1984f3980f35e0f0aa9cf795c54f8ccb667ffe",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/parseUtil.d.ts": "d3dbfc2f2fbf2c1bdea72db72f9f5c95d2ca5b4d32c9e229764ebaba0920203c",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/partialUtil.d.ts": "7da6f1e431746c5364ebe6703f5d3a844ab0495e2a8cedc0a29cced52d6284a1",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/typeAliases.d.ts": "5487b97cfa28b26b4a9ef0770f872bdbebd4c46124858de00f242c3eed7519f4",
+    "https://esm.sh/v104/zod@3.20.2/lib/helpers/util.d.ts": "bb98c05ae5cb9bd7cb7ad76fe517251a661787a6f24337b842f47faf393f79c7",
+    "https://esm.sh/v104/zod@3.20.2/lib/index.d.ts": "0f86f053aecd06054359e146b6cd800fee9bf82905f8afb47f1fe774fd37311e",
+    "https://esm.sh/v104/zod@3.20.2/lib/locales/en.d.ts": "f8ec1611afb8d132c6c71822718805866890cf2071025153af97508eff24e4b6",
+    "https://esm.sh/v104/zod@3.20.2/lib/types.d.ts": "744e3c65de31c5f7f8e79f9a37e1e372c9043a5ca130ec1038180ba4c9941f1f",
+    "https://esm.sh/zod@3.20.2": "5da460955f749f7688ad10d15edfefd8eaa41d8a7ed54e65f6abd10d8d879128"
+  }
+}

From c79fa648943e0c3294dc6ea0b7cfe2b4fddee700 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:08:11 +0000
Subject: [PATCH 19/28] feat: add CI workflow

---
 .github/workflows/ci.yml | 94 ++++++++++++++++++++++++++++++++++++++++
 deno.lock                |  2 +
 2 files changed, 96 insertions(+)
 create mode 100644 .github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..5b56bf4
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,94 @@
+name: CI
+on:
+  pull_request:
+  workflow_dispatch:
+
+
+env:
+  DENO_DIR: my_cache_directory
+
+jobs:
+  health:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: denoland/setup-deno@v1
+        with:
+          deno-version: v1.x
+
+      - name: Cache Deno dependencies 
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.DENO_DIR }}
+          key: ${{ hashFiles('lock.json') }}
+      
+      - name: Format
+        run: deno fmt --check
+        
+      - name: Lint
+        run: deno lint
+
+      - name: Test
+        run: deno test --allow-net=registry.npmjs.org
+          
+  working_package:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: denoland/setup-deno@v1
+        with:
+          deno-version: v1.x
+
+      - name: Cache Deno dependencies 
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.DENO_DIR }}
+          key: ${{ hashFiles('lock.json') }}
+      
+      - run: |
+          deno run \
+            --allow-net=registry.npmjs.org \
+            --allow-read=. \
+            ./main.ts \
+            fixtures/package_valid.json  \
+            --verbose --cache
+  
+  failing_peer:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: denoland/setup-deno@v1
+        with:
+          deno-version: v1.x
+
+      - name: Cache Deno dependencies 
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.DENO_DIR }}
+          key: ${{ hashFiles('lock.json') }}
+
+      - run: |
+          deno run \
+            --allow-net=registry.npmjs.org \
+            --allow-read=. \
+            ./main.ts \
+            fixtures/package.json  \
+            --verbose --cache
+
+      - name: The job has failed, which is expected
+        if: ${{ failure() }}
+        run: exit 0
+
+      - name: The job has succeeded, which is wrong
+        if: ${{ success() }}
+        run: exit 1
+
+  final:
+    needs: [health, working_package, failing_peer]
+    runs-on: ubuntu-latest
+    steps:
+      - name: "All good"
+        run: exit 0
\ No newline at end of file
diff --git a/deno.lock b/deno.lock
index 2205560..feec490 100644
--- a/deno.lock
+++ b/deno.lock
@@ -1,6 +1,8 @@
 {
   "version": "2",
   "remote": {
+    "https://deno.land/std@0.168.0/_util/asserts.ts": "d0844e9b62510f89ce1f9878b046f6a57bf88f208a10304aab50efcb48365272",
+    "https://deno.land/std@0.168.0/flags/mod.ts": "4f50ec6383c02684db35de38b3ffb2cd5b9fcfcc0b1147055d1980c49e82521c",
     "https://deno.land/std@0.168.0/fmt/colors.ts": "03ad95e543d2808bc43c17a3dd29d25b43d0f16287fe562a0be89bf632454a12",
     "https://deno.land/std@0.168.0/testing/_diff.ts": "a23e7fc2b4d8daa3e158fa06856bedf5334ce2a2831e8bf9e509717f455adb2c",
     "https://deno.land/std@0.168.0/testing/_format.ts": "cd11136e1797791045e639e9f0f4640d5b4166148796cad37e6ef75f7d7f3832",

From e3d3bfcf1a3eb5e4dde4bb942b71959ae0ddbfef Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:15:33 +0000
Subject: [PATCH 20/28] fix: use cache @ v3

---
 .github/workflows/ci.yml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5b56bf4..e1d97c5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -18,7 +18,7 @@ jobs:
           deno-version: v1.x
 
       - name: Cache Deno dependencies 
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: ${{ env.DENO_DIR }}
           key: ${{ hashFiles('lock.json') }}
@@ -42,7 +42,7 @@ jobs:
           deno-version: v1.x
 
       - name: Cache Deno dependencies 
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: ${{ env.DENO_DIR }}
           key: ${{ hashFiles('lock.json') }}
@@ -65,7 +65,7 @@ jobs:
           deno-version: v1.x
 
       - name: Cache Deno dependencies 
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: ${{ env.DENO_DIR }}
           key: ${{ hashFiles('lock.json') }}

From b2d9ebe0255bb2cfb0f6b6d8d4bb61ea82ac2c04 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:20:28 +0000
Subject: [PATCH 21/28] refactor: move files to src

---
 .env                                                 |  1 +
 .github/workflows/ci.yml                             | 12 ++++++------
 .gitignore                                           |  1 +
 cache.ts => src/cache.ts                             |  0
 check_types.test.ts => src/check_types.test.ts       |  0
 check_types.ts => src/check_types.ts                 |  0
 colours.ts => src/colours.ts                         |  0
 deps.ts => src/deps.ts                               |  0
 .../fetch_peer_dependencies.bench.ts                 |  0
 .../fetch_peer_dependencies.test.ts                  |  0
 .../fetch_peer_dependencies.ts                       |  0
 .../find_mismatches.test.ts                          |  0
 find_mismatches.ts => src/find_mismatches.ts         |  0
 main.ts => src/main.ts                               |  0
 .../parse_dependencies.test.ts                       |  0
 parse_dependencies.ts => src/parse_dependencies.ts   |  0
 types.ts => src/types.ts                             |  0
 utils.ts => src/utils.ts                             |  0
 18 files changed, 8 insertions(+), 6 deletions(-)
 create mode 100644 .env
 create mode 100644 .gitignore
 rename cache.ts => src/cache.ts (100%)
 rename check_types.test.ts => src/check_types.test.ts (100%)
 rename check_types.ts => src/check_types.ts (100%)
 rename colours.ts => src/colours.ts (100%)
 rename deps.ts => src/deps.ts (100%)
 rename fetch_peer_dependencies.bench.ts => src/fetch_peer_dependencies.bench.ts (100%)
 rename fetch_peer_dependencies.test.ts => src/fetch_peer_dependencies.test.ts (100%)
 rename fetch_peer_dependencies.ts => src/fetch_peer_dependencies.ts (100%)
 rename find_mismatches.test.ts => src/find_mismatches.test.ts (100%)
 rename find_mismatches.ts => src/find_mismatches.ts (100%)
 rename main.ts => src/main.ts (100%)
 rename parse_dependencies.test.ts => src/parse_dependencies.test.ts (100%)
 rename parse_dependencies.ts => src/parse_dependencies.ts (100%)
 rename types.ts => src/types.ts (100%)
 rename utils.ts => src/utils.ts (100%)

diff --git a/.env b/.env
new file mode 100644
index 0000000..a5a446e
--- /dev/null
+++ b/.env
@@ -0,0 +1 @@
+DENO_DIR=.cache
\ No newline at end of file
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e1d97c5..5eb1447 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,7 +5,7 @@ on:
 
 
 env:
-  DENO_DIR: my_cache_directory
+  DENO_DIR: ./cache
 
 jobs:
   health:
@@ -24,13 +24,13 @@ jobs:
           key: ${{ hashFiles('lock.json') }}
       
       - name: Format
-        run: deno fmt --check
+        run: deno fmt src --check
         
       - name: Lint
-        run: deno lint
+        run: deno lint src
 
       - name: Test
-        run: deno test --allow-net=registry.npmjs.org
+        run: deno test src --allow-net=registry.npmjs.org
           
   working_package:
     runs-on: ubuntu-latest
@@ -51,7 +51,7 @@ jobs:
           deno run \
             --allow-net=registry.npmjs.org \
             --allow-read=. \
-            ./main.ts \
+            src/main.ts \
             fixtures/package_valid.json  \
             --verbose --cache
   
@@ -74,7 +74,7 @@ jobs:
           deno run \
             --allow-net=registry.npmjs.org \
             --allow-read=. \
-            ./main.ts \
+            src/main.ts \
             fixtures/package.json  \
             --verbose --cache
 
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1998c29
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.cache
\ No newline at end of file
diff --git a/cache.ts b/src/cache.ts
similarity index 100%
rename from cache.ts
rename to src/cache.ts
diff --git a/check_types.test.ts b/src/check_types.test.ts
similarity index 100%
rename from check_types.test.ts
rename to src/check_types.test.ts
diff --git a/check_types.ts b/src/check_types.ts
similarity index 100%
rename from check_types.ts
rename to src/check_types.ts
diff --git a/colours.ts b/src/colours.ts
similarity index 100%
rename from colours.ts
rename to src/colours.ts
diff --git a/deps.ts b/src/deps.ts
similarity index 100%
rename from deps.ts
rename to src/deps.ts
diff --git a/fetch_peer_dependencies.bench.ts b/src/fetch_peer_dependencies.bench.ts
similarity index 100%
rename from fetch_peer_dependencies.bench.ts
rename to src/fetch_peer_dependencies.bench.ts
diff --git a/fetch_peer_dependencies.test.ts b/src/fetch_peer_dependencies.test.ts
similarity index 100%
rename from fetch_peer_dependencies.test.ts
rename to src/fetch_peer_dependencies.test.ts
diff --git a/fetch_peer_dependencies.ts b/src/fetch_peer_dependencies.ts
similarity index 100%
rename from fetch_peer_dependencies.ts
rename to src/fetch_peer_dependencies.ts
diff --git a/find_mismatches.test.ts b/src/find_mismatches.test.ts
similarity index 100%
rename from find_mismatches.test.ts
rename to src/find_mismatches.test.ts
diff --git a/find_mismatches.ts b/src/find_mismatches.ts
similarity index 100%
rename from find_mismatches.ts
rename to src/find_mismatches.ts
diff --git a/main.ts b/src/main.ts
similarity index 100%
rename from main.ts
rename to src/main.ts
diff --git a/parse_dependencies.test.ts b/src/parse_dependencies.test.ts
similarity index 100%
rename from parse_dependencies.test.ts
rename to src/parse_dependencies.test.ts
diff --git a/parse_dependencies.ts b/src/parse_dependencies.ts
similarity index 100%
rename from parse_dependencies.ts
rename to src/parse_dependencies.ts
diff --git a/types.ts b/src/types.ts
similarity index 100%
rename from types.ts
rename to src/types.ts
diff --git a/utils.ts b/src/utils.ts
similarity index 100%
rename from utils.ts
rename to src/utils.ts

From 4c773af9a7fccfd2d53c45a4a79c1f91c1c8768d Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:30:07 +0000
Subject: [PATCH 22/28] feat: allow success if known number of errors

---
 .github/workflows/ci.yml | 10 +---------
 src/main.ts              |  9 ++++++++-
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5eb1447..a0f8433 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,15 +76,7 @@ jobs:
             --allow-read=. \
             src/main.ts \
             fixtures/package.json  \
-            --verbose --cache
-
-      - name: The job has failed, which is expected
-        if: ${{ failure() }}
-        run: exit 0
-
-      - name: The job has succeeded, which is wrong
-        if: ${{ success() }}
-        run: exit 1
+            --verbose --cache --errors=7
 
   final:
     needs: [health, working_package, failing_peer]
diff --git a/src/main.ts b/src/main.ts
index 3580894..7cbe454 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -11,8 +11,10 @@ import {
 import { parse } from "https://deno.land/std@0.168.0/flags/mod.ts";
 import { filter_types } from "./check_types.ts";
 
-const { _: [package_file], verbose, cache } = parse(Deno.args, {
+const { _: [package_file], verbose, cache, errors } = parse(Deno.args, {
   boolean: ["verbose", "cache"],
+  string: ["errors"],
+  default: { errors: "0" },
 });
 
 if (typeof package_file !== "string") {
@@ -101,5 +103,10 @@ if (problems === 0) {
     } dependencies problems`,
   );
 }
+if (errors === problems.toString()) {
+  // Pass if the number of problems matched the --errors flag
+  console.info(`\nAll ${errors} errors found – this is a success!`);
+  Deno.exit();
+}
 
 Deno.exit(problems);

From 3c00012014e431bd5790181c095a7d7a098ea46c Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:31:33 +0000
Subject: [PATCH 23/28] chore: remove unused final step

---
 .github/workflows/ci.yml | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a0f8433..6b6f67c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,11 +76,4 @@ jobs:
             --allow-read=. \
             src/main.ts \
             fixtures/package.json  \
-            --verbose --cache --errors=7
-
-  final:
-    needs: [health, working_package, failing_peer]
-    runs-on: ubuntu-latest
-    steps:
-      - name: "All good"
-        run: exit 0
\ No newline at end of file
+            --verbose --cache --errors=7
\ No newline at end of file

From dbef96cd2ce742c33d78db0377918d289d1bd123 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:39:47 +0000
Subject: [PATCH 24/28] feat: better error on duplicate

---
 .github/workflows/ci.yml  | 25 ++++++++++++++++++++++++-
 src/main.ts               | 12 +++++++++++-
 src/parse_dependencies.ts | 20 +++-----------------
 3 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6b6f67c..8233dfb 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,4 +76,27 @@ jobs:
             --allow-read=. \
             src/main.ts \
             fixtures/package.json  \
-            --verbose --cache --errors=7
\ No newline at end of file
+            --verbose --cache --errors=7
+
+  failing_duplicates:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: denoland/setup-deno@v1
+        with:
+          deno-version: v1.x
+
+      - name: Cache Deno dependencies 
+        uses: actions/cache@v3
+        with:
+          path: ${{ env.DENO_DIR }}
+          key: ${{ hashFiles('lock.json') }}
+
+      - run: |
+          deno run \
+            --allow-net=registry.npmjs.org \
+            --allow-read=. \
+            src/main.ts \
+            fixtures/package_duplicate.json  \
+            --verbose --cache --errors=3
\ No newline at end of file
diff --git a/src/main.ts b/src/main.ts
index 7cbe454..c96869c 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,4 +1,5 @@
 import {
+  find_duplicates,
   parse_declared_dependencies,
   parse_package_info,
 } from "./parse_dependencies.ts";
@@ -67,6 +68,15 @@ if (dependencies_from_package.length === 0) {
   Deno.exit();
 }
 
+const duplicates = find_duplicates(dependencies_from_package);
+
+if (duplicates.length > 0) {
+  console.error(`│  Duplicate dependencies found!`);
+  for (const name of duplicates) {
+    console.error(`│  ╰─ ${colour.invalid("✕")} ${colour.dependency(name)}`);
+  }
+}
+
 const dependencies_from_registry = await fetch_peer_dependencies(
   dependencies_from_package,
   { cache },
@@ -82,7 +92,7 @@ const number_of_mismatched_deps = count_unsatisfied_peer_dependencies(
 );
 
 const problems = number_of_mismatched_deps +
-  types_in_direct_dependencies.length;
+  types_in_direct_dependencies.length + duplicates.length;
 
 console.info("│");
 
diff --git a/src/parse_dependencies.ts b/src/parse_dependencies.ts
index 764ca80..ac33093 100644
--- a/src/parse_dependencies.ts
+++ b/src/parse_dependencies.ts
@@ -3,7 +3,7 @@ import { colour } from "./colours.ts";
 import { Dependency, UnrefinedDependency } from "./types.ts";
 import { isDefined } from "./utils.ts";
 
-const find_duplicates = (dependencies: Dependency[]): string[] => {
+export const find_duplicates = (dependencies: Dependency[]): string[] => {
   const seen = new Set<string>();
   const duplicates = new Set<string>();
 
@@ -32,8 +32,8 @@ export const parse_package_info = (contents: unknown): UnrefinedDependency => {
 
 export const parse_declared_dependencies = (
   dependencies: [name: string, range: string][],
-): Dependency[] => {
-  const deps = dependencies.map(([name, range]) => {
+): Dependency[] =>
+  dependencies.map(([name, range]) => {
     try {
       return { name, range: new Range(range) };
     } catch (error: unknown) {
@@ -47,17 +47,3 @@ export const parse_declared_dependencies = (
     }
     return undefined;
   }).filter(isDefined).flat();
-
-  const duplicates = find_duplicates(deps);
-
-  if (duplicates.length > 0) {
-    console.warn("🚨 Duplicate dependencies found:");
-    for (const duplicate of duplicates) {
-      console.warn(`   - ${colour.dependency(duplicate)}`);
-    }
-
-    throw new Error("Duplicates found");
-  }
-
-  return deps;
-};

From d646727588a547a1c2f1c69931068683069d16a8 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:58:30 +0000
Subject: [PATCH 25/28] refactor(cache): passe it around

---
 src/cache.ts                         |  9 ++-------
 src/fetch_peer_dependencies.bench.ts | 18 ++++++++++++++++--
 src/fetch_peer_dependencies.test.ts  |  6 +++---
 src/fetch_peer_dependencies.ts       |  2 +-
 src/main.ts                          |  2 +-
 src/parse_dependencies.test.ts       | 12 ++++++++----
 6 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/src/cache.ts b/src/cache.ts
index 2f14832..9653107 100644
--- a/src/cache.ts
+++ b/src/cache.ts
@@ -1,10 +1,5 @@
-const name = "NPM registry";
-
-const cache = await caches.open(name);
-
-export const get = async (url: URL, use_cache: boolean) => {
-  if (!use_cache) {
-    cache.delete(url);
+export const get = async (url: URL, cache?: Cache) => {
+  if (!cache) {
     return fetch(url);
   }
 
diff --git a/src/fetch_peer_dependencies.bench.ts b/src/fetch_peer_dependencies.bench.ts
index 9ce0ea4..21e3cad 100644
--- a/src/fetch_peer_dependencies.bench.ts
+++ b/src/fetch_peer_dependencies.bench.ts
@@ -1,6 +1,8 @@
 import { Range } from "./deps.ts";
 import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
 
+const cache = await caches.open("bench");
+
 Deno.bench("Fetch with cache", async () => {
   await fetch_peer_dependencies(
     [
@@ -9,7 +11,7 @@ Deno.bench("Fetch with cache", async () => {
         range: new Range("2.0.2"),
       },
     ],
-    { cache: true },
+    undefined,
   );
 });
 
@@ -21,6 +23,18 @@ Deno.bench("Fetch without cache", async () => {
         range: new Range("2.0.2"),
       },
     ],
-    { cache: false },
+    cache,
+  );
+});
+
+Deno.bench("Fetch large dependency with cache", async () => {
+  await fetch_peer_dependencies(
+    [
+      {
+        name: "typescript",
+        range: new Range("4.9.3"),
+      },
+    ],
+    cache,
   );
 });
diff --git a/src/fetch_peer_dependencies.test.ts b/src/fetch_peer_dependencies.test.ts
index ce4b567..7f820e3 100644
--- a/src/fetch_peer_dependencies.test.ts
+++ b/src/fetch_peer_dependencies.test.ts
@@ -8,7 +8,7 @@ Deno.test("Can get peer dependencies", async () => {
       name: "@guardian/core-web-vitals",
       range: new Range("2.0.2"),
     },
-  ]);
+  ], await caches.open("test"));
 
   assertEquals(with_peer_deps, [
     {
@@ -49,7 +49,7 @@ Deno.test("Can get peer dependencies", async () => {
 Deno.test("Can get optional peer dependencies", async () => {
   const peer_deps = await fetch_peer_dependencies([
     { name: "@guardian/libs", range: new Range("12.0.0") },
-  ]);
+  ], await caches.open("test"));
 
   assertEquals(peer_deps, [
     {
@@ -80,7 +80,7 @@ Deno.test("Will fail on optional dependencies that are defined locally", async (
     { name: "@guardian/libs", range: new Range("12.0.0") },
     { name: "tslib", range: new Range("2.4.1") },
     { name: "typescript", range: new Range("4.2.2") },
-  ]);
+  ], await caches.open("test"));
 
   assertEquals(peer_deps, [
     {
diff --git a/src/fetch_peer_dependencies.ts b/src/fetch_peer_dependencies.ts
index 8f3e750..ab188a3 100644
--- a/src/fetch_peer_dependencies.ts
+++ b/src/fetch_peer_dependencies.ts
@@ -25,7 +25,7 @@ const { parseAsync: parse_peers } = object({
 
 export const fetch_peer_dependencies = (
   dependencies: Dependency[],
-  { cache = false } = {},
+  cache?: Cache,
 ): Promise<RegistryDependency[]> =>
   Promise.all(
     dependencies.map((dependency) =>
diff --git a/src/main.ts b/src/main.ts
index c96869c..fb6470d 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -79,7 +79,7 @@ if (duplicates.length > 0) {
 
 const dependencies_from_registry = await fetch_peer_dependencies(
   dependencies_from_package,
-  { cache },
+  cache ? await caches.open("npm-registry-cache") : undefined,
 );
 
 format_dependencies(
diff --git a/src/parse_dependencies.test.ts b/src/parse_dependencies.test.ts
index f654f0c..f2e3733 100644
--- a/src/parse_dependencies.test.ts
+++ b/src/parse_dependencies.test.ts
@@ -1,5 +1,8 @@
 import { assertEquals, assertThrows, Range } from "./deps.ts";
-import { parse_declared_dependencies } from "./parse_dependencies.ts";
+import {
+  find_duplicates,
+  parse_declared_dependencies,
+} from "./parse_dependencies.ts";
 
 Deno.test("Handles valid package.json", () => {
   const tuples = [
@@ -30,11 +33,12 @@ Deno.test("Handles valid package.json", () => {
 });
 
 Deno.test("Warns on duplicate dependencies", () => {
-  const tuples = [
+  const dependencies = parse_declared_dependencies([
     ["one", "1.0.1"],
     ["two", "2.0.1"],
     ["two", "2.0.2"],
-  ] satisfies [string, string][];
+  ]);
+  const duplicates = find_duplicates(dependencies);
 
-  assertThrows(() => parse_declared_dependencies(tuples));
+  assertEquals(duplicates, ["two"]);
 });

From 628d47565a2e75dad4527a5da2d438655d552905 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 12:58:42 +0000
Subject: [PATCH 26/28] chore: remove unused import

---
 src/parse_dependencies.test.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/parse_dependencies.test.ts b/src/parse_dependencies.test.ts
index f2e3733..5c91877 100644
--- a/src/parse_dependencies.test.ts
+++ b/src/parse_dependencies.test.ts
@@ -1,4 +1,4 @@
-import { assertEquals, assertThrows, Range } from "./deps.ts";
+import { assertEquals, Range } from "./deps.ts";
 import {
   find_duplicates,
   parse_declared_dependencies,

From a26585a53416af4b83b97da89a53458bc3013d44 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 13:17:51 +0000
Subject: [PATCH 27/28] feat: use unpkg.com for speed
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Ran a benchmark to compare parsing `typescript`
and the results are incredible:
- registry.npmjs.org ~ 75ms
- unpkg.com ~ 150 µs (0.15ms)

Instead of getting all possible versions of a package,
it’s best to target a specific version directly.
---
 .github/workflows/ci.yml             |  8 ++---
 src/fetch_peer_dependencies.bench.ts |  4 +--
 src/fetch_peer_dependencies.ts       | 47 ++++++++++------------------
 3 files changed, 22 insertions(+), 37 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8233dfb..c5dd420 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,7 +30,7 @@ jobs:
         run: deno lint src
 
       - name: Test
-        run: deno test src --allow-net=registry.npmjs.org
+        run: deno test src --allow-net=unpkg.com
           
   working_package:
     runs-on: ubuntu-latest
@@ -49,7 +49,7 @@ jobs:
       
       - run: |
           deno run \
-            --allow-net=registry.npmjs.org \
+            --allow-net=unpkg.com \
             --allow-read=. \
             src/main.ts \
             fixtures/package_valid.json  \
@@ -72,7 +72,7 @@ jobs:
 
       - run: |
           deno run \
-            --allow-net=registry.npmjs.org \
+            --allow-net=unpkg.com \
             --allow-read=. \
             src/main.ts \
             fixtures/package.json  \
@@ -95,7 +95,7 @@ jobs:
 
       - run: |
           deno run \
-            --allow-net=registry.npmjs.org \
+            --allow-net=unpkg.com \
             --allow-read=. \
             src/main.ts \
             fixtures/package_duplicate.json  \
diff --git a/src/fetch_peer_dependencies.bench.ts b/src/fetch_peer_dependencies.bench.ts
index 21e3cad..02ffcd6 100644
--- a/src/fetch_peer_dependencies.bench.ts
+++ b/src/fetch_peer_dependencies.bench.ts
@@ -3,7 +3,7 @@ import { fetch_peer_dependencies } from "./fetch_peer_dependencies.ts";
 
 const cache = await caches.open("bench");
 
-Deno.bench("Fetch with cache", async () => {
+Deno.bench("Fetch without cache", async () => {
   await fetch_peer_dependencies(
     [
       {
@@ -15,7 +15,7 @@ Deno.bench("Fetch with cache", async () => {
   );
 });
 
-Deno.bench("Fetch without cache", async () => {
+Deno.bench("Fetch with cache", async () => {
   await fetch_peer_dependencies(
     [
       {
diff --git a/src/fetch_peer_dependencies.ts b/src/fetch_peer_dependencies.ts
index ab188a3..05660be 100644
--- a/src/fetch_peer_dependencies.ts
+++ b/src/fetch_peer_dependencies.ts
@@ -1,5 +1,4 @@
 import { get } from "./cache.ts";
-import { format } from "./colours.ts";
 import {
   boolean,
   minVersion,
@@ -12,15 +11,11 @@ import {
 } from "./deps.ts";
 import type { Dependency, RegistryDependency } from "./types.ts";
 
-const { parseAsync: parse_peers } = object({
-  versions: record(
-    object({
-      version: string(),
-      dependencies: record(string()).optional(),
-      peerDependencies: record(string()).optional(),
-      peerDependenciesMeta: record(object({ optional: boolean() })).optional(),
-    }),
-  ),
+const { parse } = object({
+  version: string(),
+  dependencies: record(string()).optional(),
+  peerDependencies: record(string()).optional(),
+  peerDependenciesMeta: record(object({ optional: boolean() })).optional(),
 });
 
 export const fetch_peer_dependencies = (
@@ -31,26 +26,16 @@ export const fetch_peer_dependencies = (
     dependencies.map((dependency) =>
       get(
         new URL(
-          encodeURIComponent(dependency.name),
-          "https://registry.npmjs.org/",
+          `${dependency.name}@${minVersion(dependency.range)}/package.json`,
+          "https://unpkg.com/",
         ),
         cache,
       )
-        .then((res) => res.json())
-        .then(parse_peers)
+        .then((res) => res.json() as unknown)
+        .then((json) => parse(json))
         .then((registry) => {
-          const version = Object.values(registry.versions).find(({ version }) =>
-            satisfies(version, dependency.range)
-          );
-
-          if (!version) {
-            throw new Error(
-              `Could not find ${format(dependency.name, dependency.range)}`,
-            );
-          }
-
-          const peers = version.peerDependencies
-            ? Object.entries(version.peerDependencies).map(([name, range]) => {
+          const peers = Object.entries(registry.peerDependencies ?? {}).map(
+            ([name, range]) => {
               const local_version = dependencies.find(
                 (dependency) => dependency.name === name,
               )?.range;
@@ -62,7 +47,7 @@ export const fetch_peer_dependencies = (
                 ? satisfies(local_min_version, range)
                 : false;
 
-              const is_optional = !!version.peerDependenciesMeta?.[name]
+              const is_optional = !!registry.peerDependenciesMeta?.[name]
                 ?.optional;
 
               const satisfied = local_version
@@ -75,12 +60,12 @@ export const fetch_peer_dependencies = (
                 satisfied,
                 local: local_version,
               };
-            })
-            : [];
+            },
+          );
 
           return {
             ...dependency,
-            dependencies: Object.entries(version.dependencies ?? {}).filter(
+            dependencies: Object.entries(registry.dependencies ?? {}).filter(
               ([name, range]) => {
                 try {
                   new Range(range);
@@ -94,7 +79,7 @@ export const fetch_peer_dependencies = (
               ([name, range]) => ({ name, range: new Range(range) }),
             ),
             peers,
-            version: new SemVer(version.version),
+            version: new SemVer(registry.version),
           };
         })
         .catch((error) => {

From 56db854f6732026b967dff7cfad3e83c3eaee286 Mon Sep 17 00:00:00 2001
From: Max Duval <max.duval@theguardian.com>
Date: Wed, 25 Jan 2023 13:31:50 +0000
Subject: [PATCH 28/28] fix: remove caches from tests

---
 src/fetch_peer_dependencies.test.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/fetch_peer_dependencies.test.ts b/src/fetch_peer_dependencies.test.ts
index 7f820e3..ce4b567 100644
--- a/src/fetch_peer_dependencies.test.ts
+++ b/src/fetch_peer_dependencies.test.ts
@@ -8,7 +8,7 @@ Deno.test("Can get peer dependencies", async () => {
       name: "@guardian/core-web-vitals",
       range: new Range("2.0.2"),
     },
-  ], await caches.open("test"));
+  ]);
 
   assertEquals(with_peer_deps, [
     {
@@ -49,7 +49,7 @@ Deno.test("Can get peer dependencies", async () => {
 Deno.test("Can get optional peer dependencies", async () => {
   const peer_deps = await fetch_peer_dependencies([
     { name: "@guardian/libs", range: new Range("12.0.0") },
-  ], await caches.open("test"));
+  ]);
 
   assertEquals(peer_deps, [
     {
@@ -80,7 +80,7 @@ Deno.test("Will fail on optional dependencies that are defined locally", async (
     { name: "@guardian/libs", range: new Range("12.0.0") },
     { name: "tslib", range: new Range("2.4.1") },
     { name: "typescript", range: new Range("4.2.2") },
-  ], await caches.open("test"));
+  ]);
 
   assertEquals(peer_deps, [
     {