fix(package-deps-hash): strip GIT_DIR/GIT_WORK_TREE in git subprocess calls to fix build cache in linked worktrees

When a git pre-commit hook runs in a linked worktree, git sets GIT_DIR to the
per-worktree metadata directory (.git/worktrees/{name}) without setting
GIT_WORK_TREE. With GIT_DIR set this way, `git rev-parse --show-toplevel`
returns the CWD (e.g. the rushJsonFolder subdirectory) instead of the actual
worktree root, causing all subsequent git calls to use the wrong root directory.
This makes `git status -u` miss the top-level .gitignore, surfacing node_modules
symlinks as untracked files, which then causes `git hash-object` to fail on
symlink-to-directory entries and ultimately breaks the build cache.

Fix: strip GIT_DIR and GIT_WORK_TREE from the environment in getRepoRoot,
spawnGitAsync, and getRepoChanges so git auto-discovers the correct repo root
from the working directory regardless of hook-injected env vars.

Author: istateside

libraries/package-deps-hash/src/getRepoState.ts

@@ -33,9 +33,28 @@ const STANDARD_GIT_OPTIONS: readonly string[] = [
 // `git hash-object` aborts the process. Such files are typically untracked artifacts left behind
 // by tooling (e.g. stray `nul` from a shell redirect).
 const WINDOWS_RESERVED_BASENAMES: ReadonlySet<string> = new Set([
-  'CON', 'PRN', 'AUX', 'NUL',
-  'COM1', 'COM2', 'COM3', 'COM4', 'COM5', 'COM6', 'COM7', 'COM8', 'COM9',
-  'LPT1', 'LPT2', 'LPT3', 'LPT4', 'LPT5', 'LPT6', 'LPT7', 'LPT8', 'LPT9'
+  'CON',
+  'PRN',
+  'AUX',
+  'NUL',
+  'COM1',
+  'COM2',
+  'COM3',
+  'COM4',
+  'COM5',
+  'COM6',
+  'COM7',
+  'COM8',
+  'COM9',
+  'LPT1',
+  'LPT2',
+  'LPT3',
+  'LPT4',
+  'LPT5',
+  'LPT6',
+  'LPT7',
+  'LPT8',
+  'LPT9'
 ]);
 
 /**
@@ -254,6 +273,14 @@ export function parseGitStatus(output: string): Map<string, boolean> {
 
 const repoRootCache: Map<string, string> = new Map();
 
+// Strip GIT_DIR/GIT_WORK_TREE: git hooks in linked worktrees set GIT_DIR to the per-worktree metadata dir, causing rev-parse --show-toplevel to return CWD instead of the worktree root.
+function getCleanGitEnvironment(): NodeJS.ProcessEnv {
+  const env: NodeJS.ProcessEnv = { ...process.env };
+  delete env.GIT_DIR;
+  delete env.GIT_WORK_TREE;
+  return env;
+}
+
 /**
  * Finds the root of the current Git repository
  *
@@ -270,7 +297,8 @@ export function getRepoRoot(currentWorkingDirectory: string, gitPath?: string):
       gitPath || 'git',
       ['--no-optional-locks', 'rev-parse', '--show-toplevel'],
       {
-        currentWorkingDirectory
+        currentWorkingDirectory,
+        environment: getCleanGitEnvironment()
       }
     );
 
@@ -305,7 +333,8 @@ async function spawnGitAsync(
 ): Promise<string> {
   const spawnOptions: IExecutableSpawnOptions = {
     currentWorkingDirectory,
-    stdio: ['pipe', 'pipe', 'pipe']
+    stdio: ['pipe', 'pipe', 'pipe'],
+    environment: getCleanGitEnvironment()
   };
 
   let stdout: string = '';
@@ -591,7 +620,8 @@ export function getRepoChanges(
       '--'
     ]),
     {
-      currentWorkingDirectory: rootDirectory
+      currentWorkingDirectory: rootDirectory,
+      environment: getCleanGitEnvironment()
     }
   );
 

libraries/package-deps-hash/src/test/getRepoDeps.test.ts

@@ -45,6 +45,24 @@ describe(getRepoRoot.name, () => {
     const expectedRoot: string = path.resolve(__dirname, '../../../..').replace(/\\/g, '/');
     expect(root).toEqual(expectedRoot);
   });
+
+  it(`ignores GIT_DIR set by git hooks in linked worktrees`, () => {
+    // GIT_DIR pointing to a non-existent path causes git rev-parse to fail unless stripped.
+    const originalGitDir: string | undefined = process.env.GIT_DIR;
+    try {
+      process.env.GIT_DIR = '/nonexistent-fake-gitdir-worktrees-for-testing';
+      const testCwd: string = path.resolve(SOURCE_PATH, '..');
+      const root: string = getRepoRoot(testCwd);
+      const expectedRoot: string = path.resolve(__dirname, '../../../..').replace(/\\/g, '/');
+      expect(root).toEqual(expectedRoot);
+    } finally {
+      if (originalGitDir === undefined) {
+        delete process.env.GIT_DIR;
+      } else {
+        process.env.GIT_DIR = originalGitDir;
+      }
+    }
+  });
 });
 
 describe(parseGitLsTree.name, () => {