From 27720fb9694e6a645d99dccd000227db04089555 Mon Sep 17 00:00:00 2001
From: Elizabeth Craig <elcraig@microsoft.com>
Date: Thu, 29 Jul 2021 23:32:48 -0700
Subject: [PATCH] Add caching of changed packages

---
 ...-1cc40d1b-98c5-48b9-8387-c6a7f1dbf6a1.json |  7 +++
 src/__e2e__/multiMonorepo.test.ts             |  3 +-
 src/changefile/getChangedPackages.ts          | 62 ++++++++++++-------
 3 files changed, 48 insertions(+), 24 deletions(-)
 create mode 100644 change/beachball-1cc40d1b-98c5-48b9-8387-c6a7f1dbf6a1.json

diff --git a/change/beachball-1cc40d1b-98c5-48b9-8387-c6a7f1dbf6a1.json b/change/beachball-1cc40d1b-98c5-48b9-8387-c6a7f1dbf6a1.json
new file mode 100644
index 000000000..95dd6a84d
--- /dev/null
+++ b/change/beachball-1cc40d1b-98c5-48b9-8387-c6a7f1dbf6a1.json
@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "Add caching of changed packages",
+  "packageName": "beachball",
+  "email": "elcraig@microsoft.com",
+  "dependentChangeType": "patch"
+}
diff --git a/src/__e2e__/multiMonorepo.test.ts b/src/__e2e__/multiMonorepo.test.ts
index 089ea3cc4..681ccf040 100644
--- a/src/__e2e__/multiMonorepo.test.ts
+++ b/src/__e2e__/multiMonorepo.test.ts
@@ -1,7 +1,7 @@
 import fs from 'fs-extra';
 import path from 'path';
 import { RepositoryFactory } from '../fixtures/repository';
-import { getChangedPackages } from '../changefile/getChangedPackages';
+import { getChangedPackages, resetChangedPackagesCache } from '../changefile/getChangedPackages';
 import { writeChangeFiles } from '../changefile/writeChangeFiles';
 import { git } from 'workspace-tools';
 import { bump } from '../commands/bump';
@@ -14,6 +14,7 @@ describe('changed files', () => {
   let repositoryFactory: RepositoryFactory | undefined;
 
   afterEach(() => {
+    resetChangedPackagesCache();
     if (repositoryFactory) {
       repositoryFactory.cleanUp();
       repositoryFactory = undefined;
diff --git a/src/changefile/getChangedPackages.ts b/src/changefile/getChangedPackages.ts
index d6488109a..e311eca1a 100644
--- a/src/changefile/getChangedPackages.ts
+++ b/src/changefile/getChangedPackages.ts
@@ -7,6 +7,17 @@ import { getScopedPackages } from '../monorepo/getScopedPackages';
 import { BeachballOptions } from '../types/BeachballOptions';
 import { PackageInfos } from '../types/PackageInfo';
 
+let cachedPackages: { [key: string]: ReadonlyArray<string> } = {};
+
+function getCacheKey(options: BeachballOptions) {
+  return [options.path, options.branch, options.fetch].join('-');
+}
+
+/** Reset the cache for `getChangedPackages` */
+export function resetChangedPackagesCache() {
+  cachedPackages = {};
+}
+
 /**
  * Gets all the changed packages, regardless of the change files
  */
@@ -17,30 +28,28 @@ function getAllChangedPackages(options: BeachballOptions, packageInfos: PackageI
   const scopedPackages = getScopedPackages(options, packageInfos);
   const ignoredFiles = ['CHANGELOG.md', 'CHANGELOG.json'];
   const packageRoots: { [pathName: string]: string } = {};
-  if (changes) {
-    // Discover package roots from modded files (ignores the CHANGELOG file because that's generated by beachball)
-    changes
-      .filter(name => !ignoredFiles.includes(path.basename(name)))
-      .forEach(moddedFile => {
-        const root = findPackageRoot(path.join(cwd, path.dirname(moddedFile)));
-
-        if (root && !packageRoots[root]) {
-          try {
-            const packageJson = fs.readJSONSync(path.join(root, 'package.json'));
-
-            if (!packageJson.private && (!packageJson.beachball || packageJson.beachball.shouldPublish !== false)) {
-              const packageName = packageJson.name;
-
-              if (scopedPackages.includes(packageName)) {
-                packageRoots[root] = packageName;
-              }
+  // Discover package roots from modded files (ignores the CHANGELOG file because that's generated by beachball)
+  changes
+    .filter(name => !ignoredFiles.includes(path.basename(name)))
+    .forEach(moddedFile => {
+      const root = findPackageRoot(path.join(cwd, path.dirname(moddedFile)));
+
+      if (root && !packageRoots[root]) {
+        try {
+          const packageJson = fs.readJSONSync(path.join(root, 'package.json'));
+
+          if (!packageJson.private && (!packageJson.beachball || packageJson.beachball.shouldPublish !== false)) {
+            const packageName = packageJson.name;
+
+            if (scopedPackages.includes(packageName)) {
+              packageRoots[root] = packageName;
             }
-          } catch (e) {
-            // Ignore JSON errors
           }
+        } catch (e) {
+          // Ignore JSON errors
         }
-      });
-  }
+      }
+    });
 
   return Object.values(packageRoots);
 }
@@ -50,6 +59,11 @@ function getAllChangedPackages(options: BeachballOptions, packageInfos: PackageI
  */
 export function getChangedPackages(options: BeachballOptions, packageInfos: PackageInfos) {
   const { fetch, path: cwd, branch } = options;
+  const cacheKey = getCacheKey(options);
+
+  if (cachedPackages[cacheKey]) {
+    return cachedPackages[cacheKey];
+  }
 
   const changePath = getChangePath(cwd);
 
@@ -59,7 +73,7 @@ export function getChangedPackages(options: BeachballOptions, packageInfos: Pack
     fetchRemoteBranch(remote, remoteBranch, cwd);
   }
 
-  const changedPackages = getAllChangedPackages(options, packageInfos);
+  let changedPackages = getAllChangedPackages(options, packageInfos);
 
   const changeFilesResult = git(
     ['diff', '--name-only', '--relative', '--no-renames', '--diff-filter=A', `${branch}...`],
@@ -67,6 +81,7 @@ export function getChangedPackages(options: BeachballOptions, packageInfos: Pack
   );
 
   if (!changePath || !fs.existsSync(changePath) || !changeFilesResult.success) {
+    cachedPackages[cacheKey] = changedPackages;
     return changedPackages;
   }
 
@@ -94,5 +109,6 @@ export function getChangedPackages(options: BeachballOptions, packageInfos: Pack
     );
   }
 
-  return changedPackages.filter(pkgName => !changeFilePackageSet.has(pkgName));
+  changedPackages = cachedPackages[cacheKey] = changedPackages.filter(pkgName => !changeFilePackageSet.has(pkgName));
+  return changedPackages;
 }