Use git diff instead of git log for --changedSince

CHANGELOG.md

@@ -34,6 +34,7 @@
 - `[docs]` Add param to `setSystemTime` docs and remove preceding period from it and `getRealSystemTime` ([#10169](https://github.com/facebook/jest/pull/10169))
 - `[jest-snapshot, jest-util]` Replace `make-dir` with `fs.mkdir` ([#10136](https://github.com/facebook/jest/pull/10136))
 - `[docs]` Added parcel-bundler documentation inside readme.md file
+- `[jest-changed-files]` Use git diff instead of git log for --changedSince ([#10155](https://github.com/facebook/jest/pull/10155))
 
 ### Performance
 

e2e/__tests__/__snapshots__/jestChangedFiles.test.ts.snap

@@ -5,7 +5,7 @@ exports[`handles a bad revision for "changedSince", for git 1`] = `
 
   ● Test suite failed to run
 
-    fatal: bad revision '^blablabla'
+    fatal: bad revision '^blablabla...HEAD'
 
 `;
 

e2e/__tests__/jestChangedFiles.test.ts

@@ -254,6 +254,49 @@ test('monitors only root paths for git', async () => {
   ).toEqual(['file2.txt', 'file3.txt']);
 });
 
+it('does not find changes in files with no diff, for git', async () => {
+  const roots = [path.resolve(DIR)];
+
+  // create an empty file, commit it to "master"
+  writeFiles(DIR, {
+    'file1.txt': '',
+  });
+  run(`${GIT} init`, DIR);
+  run(`${GIT} add file1.txt`, DIR);
+  run(`${GIT} commit --no-gpg-sign -m "initial"`, DIR);
+
+  // check out a new branch, jestChangedFilesSpecBase, to use later in diff
+  run(`${GIT} checkout -b jestChangedFilesSpecBase`, DIR);
+
+  // check out second branch, jestChangedFilesSpecMod, modify file & commit
+  run(`${GIT} checkout -b jestChangedFilesSpecMod`, DIR);
+  writeFiles(DIR, {
+    'file1.txt': 'modified file1',
+  });
+  run(`${GIT} add file1.txt`, DIR);
+  run(`${GIT} commit --no-gpg-sign -m "modified"`, DIR);
+
+  // still on jestChangedFilesSpecMod branch, "revert" back to empty file and commit
+  writeFiles(DIR, {
+    'file1.txt': '',
+  });
+  run(`${GIT} add file1.txt`, DIR);
+  run(`${GIT} commit --no-gpg-sign -m "removemod"`, DIR);
+
+  // check that passing in no changedSince arg doesn't return any unstaged / other changes
+  const {changedFiles: files} = await getChangedFilesForRoots(roots, {});
+  expect(Array.from(files)).toEqual([]);
+
+  // check that in diff from `jestChangedFilesSpecBase` branch, no changed files are reported
+  const {changedFiles: filesExplicitBaseBranch} = await getChangedFilesForRoots(
+    roots,
+    {
+      changedSince: 'jestChangedFilesSpecBase',
+    },
+  );
+  expect(Array.from(filesExplicitBaseBranch)).toEqual([]);
+});
+
 test('handles a bad revision for "changedSince", for git', async () => {
   writeFiles(DIR, {
     '.watchmanconfig': '',
@@ -266,7 +309,7 @@ test('handles a bad revision for "changedSince", for git', async () => {
   run(`${GIT} add .`, DIR);
   run(`${GIT} commit --no-gpg-sign -m "first"`, DIR);
 
-  const {exitCode, stderr} = runJest(DIR, ['--changedSince=blablabla']);
+  const {exitCode, stderr} = runJest(DIR, ['--changedSince=^blablabla']);
 
   expect(exitCode).toBe(1);
   expect(wrap(stderr)).toMatchSnapshot();

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

@@ -54,13 +54,9 @@ const adapter: SCMAdapter = {
     if (changedSince) {
       const [committed, staged, unstaged] = await Promise.all([
         findChangedFilesUsingCommand(
-          [
-            'log',
-            '--name-only',
-            '--pretty=format:',
-            'HEAD',
-            `^${changedSince}`,
-          ].concat(includePaths),
+          ['diff', '--name-only', `${changedSince}...HEAD`].concat(
+            includePaths,
+          ),
           cwd,
         ),
         findChangedFilesUsingCommand(