Functions emulator file watcher silently ignores changes in git worktrees

[khevamann]

[REQUIRED] Environment info

firebase-tools: 15.9.0

Platform: macOS (Darwin 25.2.0)

[REQUIRED] Test case

The Functions emulator's chokidar file watcher is configured with a regex to ignore hidden (dot-prefixed) directories:

// lib/emulator/functionsEmulator.js — line ~270
const watcher = chokidar.watch(backend.functionsDir, {
    ignored: [
        /.+?[\\\/]node_modules[\\\/].+?/,
        /(^|[\/\\])\../,   // <-- matches .worktrees in absolute path
        /.+\.log/,
        /.+?[\\\/]venv[\\\/].+?/,
        ...(backend.ignore?.map((i) => `**/${i}`) ?? []),
    ],
    persistent: true,
});

Chokidar tests this regex against absolute file paths. When the project is in a git worktree, every path contains /.worktrees/, which matches /(^|[\/\\])\../ at the /.w position:

/Users/dev/project/.worktrees/my-feature/functions/lib/index.js
                   ^^^^^^^^^^
                   matches /(^|[\/\\])\../

This causes every file change event to be silently dropped.

[REQUIRED] Steps to reproduce

1. Create a git worktree: git worktree add .worktrees/my-feature
2. cd .worktrees/my-feature
3. Start the Functions emulator
4. Observe the emulator logs — you should see Watching "<path>" for Cloud Functions... confirming the watcher is set up
5. Edit a function source file and save
6. Observe that the emulator never reloads — no Loaded functions definitions from source message appears

[REQUIRED] Expected behavior

The Functions emulator should detect file changes in the functions source directory and reload triggers, regardless of whether the project is inside a git worktree (.worktrees/) directory. After saving a file change, the emulator should log Loaded functions definitions from source: ... and serve the updated code.

[REQUIRED] Actual behavior

All file change events are silently ignored by chokidar because the absolute path contains /.worktrees/, which matches the hidden directory regex /(^|[\/\\])\../. The emulator continues serving stale code with no error or warning. The change event listener and loadTriggers reload mechanism work correctly — the issue is purely that the ignored regex prevents chokidar from ever firing events.

This can be confirmed in a Node REPL:

const re = /(^|[\/\\])\../;
re.test("/Users/dev/project/.worktrees/feature/functions/lib/index.js");
// → true (matched "/.w" in "/.worktrees")

Suggested Fix

Add a negative lookahead to exclude .worktrees from the hidden directory pattern:

// Before:
/(^|[\/\\])\../

// After:
/(^|[\/\\])\.(?!worktrees[\/\\])/

This preserves the intent of ignoring hidden directories (.git, .cache, etc.) while allowing git worktree paths to function correctly.

[inlined]

I'm admittedly new to worktrees, but AFAICT this is not the best way to do them. I personally make worktree directories peers to my main repository, which makes IDEs and the firebase emulator clearly know which code to run without deep git integration.

In your proposed idea, the file system would notice all worktrees that exist and run multiple branches' code all at once, wouldn't it?

[khevamann]

@inlined Yes peer worktrees does avoid the issue since the path wouldn't have a dot-prefixed directory. That said, nested worktrees under .worktrees/ are pretty common (it's what git worktree add does by default), and it'd be nice if the emulator worked regardless of where the project lives on disk.

On the multiple branches concern, the emulator only watches the single functionsDir resolved from firebase.json's functions.source, not the repo root. That said, having written this I realize if someone has functions.source: "." (functions at the repo root), .worktrees/ would be inside the watched directory. A safer fix than the negative lookahead would be to test the hidden-dir regex against the relative path from functionsDir rather than the absolute path, that way .worktrees/ inside the watched dir stays ignored, but .worktrees/ in an ancestor path doesn't break the watcher:

(filePath) => {
  const rel = path.relative(backend.functionsDir, filePath);
  return /(^|[\/\\])\./.test(rel);
}

The underlying issue is really just that the ignored regex runs against absolute paths, so a dot-prefixed ancestor directory like /.worktrees/ gets caught by a pattern that's meant for things like .git/ and .cache/ within the watched directory. It'd affect any project path that happens to contain a dot-prefixed folder.