perf(changed-files): limit git and hg commands to specified roots (jestjs#6732)

## Summary

Given a monorepo setup under git version control, we saw `jest --watch` commands take significantly longer in a Docker container host mount (`rw:cached`) than when on the host directly. Tracked the issue down to the fact that `git` and `hg` command used to determine `lastCommit` changes were traversing the entire repository, and not just paths specified in the Jest config `roots` values. Given the mounted container latency, things like basic `lstat` gathering be intensive in a large repository. The `roots` we had specified are rather shallow themselves and only contain things we want to test with Jest. When limiting the scope of the `git` command to just the `roots` paths, we saw change determination drop from 2.5m to 3s in our container.

This implementation seem to align more closely with the [`roots` documentation](https://jestjs.io/docs/en/configuration#roots-array-string) which indicates:

> A list of paths to directories that Jest should use to search for files in.

It did seem a little unexpected that Jest would be traversing our entire repo.

Author: booleanbetrayal

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## master
 
+### Performance
+
+- `[jest-changed-files]` limit git and hg commands to specified roots ([#6732](https://github.com/facebook/jest/pull/6732))
+
 ### Fixes
 
 - `[babel-jest]` Make `getCacheKey()` take into account `createTransformer` options ([#6699](https://github.com/facebook/jest/pull/6699))

e2e/__tests__/jest_changed_files.test.js

@@ -224,6 +224,25 @@ test('gets changed files for git', async () => {
   ).toEqual(['file5.txt']);
 });
 
+test('monitors only root paths for git', async () => {
+  writeFiles(DIR, {
+    'file1.txt': 'file1',
+    'nested_dir/file2.txt': 'file2',
+    'nested_dir/second_nested_dir/file3.txt': 'file3',
+  });
+
+  run(`${GIT} init`, DIR);
+
+  const roots = [path.resolve(DIR, 'nested_dir')];
+
+  const {changedFiles: files} = await getChangedFilesForRoots(roots, {});
+  expect(
+    Array.from(files)
+      .map(filePath => path.basename(filePath))
+      .sort(),
+  ).toEqual(['file2.txt', 'file3.txt']);
+});
+
 test('gets changed files for hg', async () => {
   if (process.env.CI) {
     // Circle and Travis have very old version of hg (v2, and current
@@ -326,3 +345,29 @@ test('gets changed files for hg', async () => {
       .sort(),
   ).toEqual(['file5.txt']);
 });
+
+test('monitors only root paths for hg', async () => {
+  if (process.env.CI) {
+    // Circle and Travis have very old version of hg (v2, and current
+    // version is v4.2) and its API changed since then and not compatible
+    // any more. Changing the SCM version on CIs is not trivial, so we'll just
+    // skip this test and run it only locally.
+    return;
+  }
+  writeFiles(DIR, {
+    'file1.txt': 'file1',
+    'nested_dir/file2.txt': 'file2',
+    'nested_dir/second_nested_dir/file3.txt': 'file3',
+  });
+
+  run(`${HG} init`, DIR);
+
+  const roots = [path.resolve(DIR, 'nested_dir')];
+
+  const {changedFiles: files} = await getChangedFilesForRoots(roots, {});
+  expect(
+    Array.from(files)
+      .map(filePath => path.basename(filePath))
+      .sort(),
+  ).toEqual(['file2.txt', 'file3.txt']);
+});

packages/jest-changed-files/src/git.js

@@ -51,28 +51,40 @@ const adapter: SCMAdapter = {
     const changedSince: ?string =
       options && (options.withAncestor ? 'HEAD^' : options.changedSince);
 
+    const includePaths: Array<Path> = (options && options.includePaths) || [];
+
     if (options && options.lastCommit) {
       return await findChangedFilesUsingCommand(
-        ['show', '--name-only', '--pretty=%b', 'HEAD'],
+        ['show', '--name-only', '--pretty=%b', 'HEAD'].concat(includePaths),
         cwd,
       );
     } else if (changedSince) {
       const committed = await findChangedFilesUsingCommand(
-        ['log', '--name-only', '--pretty=%b', 'HEAD', `^${changedSince}`],
+        [
+          'log',
+          '--name-only',
+          '--pretty=%b',
+          'HEAD',
+          `^${changedSince}`,
+        ].concat(includePaths),
         cwd,
       );
       const staged = await findChangedFilesUsingCommand(
-        ['diff', '--cached', '--name-only'],
+        ['diff', '--cached', '--name-only'].concat(includePaths),
         cwd,
       );
       const unstaged = await findChangedFilesUsingCommand(
-        ['ls-files', '--other', '--modified', '--exclude-standard'],
+        ['ls-files', '--other', '--modified', '--exclude-standard'].concat(
+          includePaths,
+        ),
         cwd,
       );
       return [...committed, ...staged, ...unstaged];
     } else {
       return await findChangedFilesUsingCommand(
-        ['ls-files', '--other', '--modified', '--exclude-standard'],
+        ['ls-files', '--other', '--modified', '--exclude-standard'].concat(
+          includePaths,
+        ),
         cwd,
       );
     }

packages/jest-changed-files/src/hg.js

@@ -34,14 +34,17 @@ const adapter: SCMAdapter = {
     options: Options,
   ): Promise<Array<Path>> =>
     new Promise((resolve, reject) => {
-      let args = ['status', '-amnu'];
+      const includePaths: Array<Path> = (options && options.includePaths) || [];
+
+      const args = ['status', '-amnu'];
       if (options && options.withAncestor) {
         args.push('--rev', `ancestor(${ANCESTORS.join(', ')})`);
       } else if (options && options.changedSince) {
         args.push('--rev', `ancestor(., ${options.changedSince})`);
       } else if (options && options.lastCommit === true) {
-        args = ['tip', '--template', '{files%"{file}\n"}'];
+        args.push('-A');
       }
+      args.push(...includePaths);
       const child = childProcess.spawn('hg', args, {cwd, env});
       let stdout = '';
       let stderr = '';

packages/jest-changed-files/src/index.js

@@ -27,12 +27,14 @@ export const getChangedFilesForRoots = async (
 ): ChangedFilesPromise => {
   const repos = await findRepos(roots);
 
+  const changedFilesOptions = Object.assign({}, {includePaths: roots}, options);
+
   const gitPromises = Array.from(repos.git).map(repo =>
-    git.findChangedFiles(repo, options),
+    git.findChangedFiles(repo, changedFilesOptions),
   );
 
   const hgPromises = Array.from(repos.hg).map(repo =>
-    hg.findChangedFiles(repo, options),
+    hg.findChangedFiles(repo, changedFilesOptions),
   );
 
   const changedFiles = (await Promise.all(

types/ChangedFiles.js

@@ -13,6 +13,7 @@ export type Options = {|
   lastCommit?: boolean,
   withAncestor?: boolean,
   changedSince?: string,
+  includePaths?: Array<Path>,
 |};
 
 export type ChangedFiles = Set<Path>;