chore: add no-external-code rule to Deno Style Guide lint plugin (#6562)

Author: iuioiua

_tools/lint_plugin.ts

@@ -56,6 +56,35 @@ export default {
         };
       },
     },
+    // https://docs.deno.com/runtime/contributing/style_guide/#do-not-depend-on-external-code.
+    "no-external-code": {
+      create(context) {
+        if (context.filename.includes("_tools")) {
+          // Tools are allowed to use external code
+          return {};
+        }
+        return {
+          ImportDeclaration(node) {
+            const resolvedSpecifier = import.meta.resolve(node.source.value);
+            if (
+              resolvedSpecifier.startsWith("file:") ||
+              resolvedSpecifier.startsWith("jsr:@std") ||
+              resolvedSpecifier.startsWith("jsr:/@std") ||
+              resolvedSpecifier.startsWith("node:")
+            ) {
+              return;
+            }
+            context.report({
+              node,
+              range: node.source.range,
+              message: "External imports are not allowed outside of tools",
+              hint:
+                'Use code from within `@std` instead of external code. E.g. Use `import { foo } from "@std/foo"` instead of `import { foo } from "https://deno.land/x/foo/mod.ts"`.',
+            });
+          },
+        };
+      },
+    },
     // https://docs.deno.com/runtime/contributing/style_guide/#naming-convention/
     "naming-convention": {
       create(context) {

_tools/lint_plugin_test.ts

@@ -56,6 +56,36 @@ class MyClass {
   );
 });
 
+Deno.test("deno-style-guide/no-external-code", {
+  ignore: !Deno.version.deno.startsWith("2"),
+}, () => {
+  // Good
+  assertLintPluginDiagnostics('import { walk } from "@std/fs/walk";', []);
+
+  // Bad
+  assertLintPluginDiagnostics(
+    `
+import { bad } from "https://deno.land/malicious-muffin/bad.ts";
+import { bad } from "jsr:@malicious-muffin/bad";
+    `,
+    [{
+      id: "deno-style-guide/no-external-code",
+      fix: [],
+      range: [1, 65],
+      message: "External imports are not allowed outside of tools",
+      hint:
+        'Use code from within `@std` instead of external code. E.g. Use `import { foo } from "@std/foo"` instead of `import { foo } from "https://deno.land/x/foo/mod.ts"`.',
+    }, {
+      id: "deno-style-guide/no-external-code",
+      fix: [],
+      range: [66, 114],
+      message: "External imports are not allowed outside of tools",
+      hint:
+        'Use code from within `@std` instead of external code. E.g. Use `import { foo } from "@std/foo"` instead of `import { foo } from "https://deno.land/x/foo/mod.ts"`.',
+    }],
+  );
+});
+
 Deno.test("deno-style-guide/naming-convention", {
   ignore: !Deno.version.deno.startsWith("2"),
 }, () => {

cli/_tools/compare_with_rust.ts

@@ -3,7 +3,7 @@
 
 import { unicodeWidth } from "../unicode_width.ts";
 import { fromFileUrl } from "../../path/mod.ts";
-import fc from "https://esm.sh/[email protected]";
+import fc from "npm:[email protected]";
 
 // Note: This test is optional. It requires the Rust code to be compiled locally
 Deno.test("fast-check equality with unicode_width Rust crate", async (t) => {