feat(core): implement non-recursive watcher to avoid unnecessary watchers being registered

[MaxKless]

Current Behavior

The Nx native file watcher uses watchexec (v3.0.1) which internally calls notify::INotifyWatcher with RecursiveMode::Recursive. This walks every subdirectory in the
workspace and registers an OS-level watch on each one. The ignore patterns (node_modules/, .git/, .nx/, etc.) are only applied as event filters via the watchexec Filterer
trait — they don't prevent the watch registration itself.

In practice, a typical node_modules contains 30-50k+ subdirectories. All of these get watches registered, even though every event from them is immediately filtered out and
discarded. This causes two problems:

1. Linux (inotify): Blows past the default max_user_watches limit (usually 8192-65536), causing the watcher to fail with ENOSPC: System limit for number of file watchers
   reached.
2. All platforms: Wastes OS resources tracking events for tens of thousands of directories whose events will never be used.

On the Nx repo itself: 59,568 directories get watches, of which 46,086 are ignored (node_modules, .git, .nx).

Expected Behavior

The watcher only registers watches for directories that aren't ignored. Using the Nx repo as a benchmark:

• Before: ~59,568 watches (every directory)
• After: ~13,482 watches (only non-ignored directories)
• Reduction: 77%

For typical user projects with larger node_modules trees, the reduction will be even greater.

The NAPI API surface is unchanged — TypeScript consumers see no difference.

Approach

Upgrade watchexec from 3.0.1 to 4.1.0, which introduces WatchedPath::non_recursive(). Instead of passing a single recursive root path to watchexec, we walk the directory
tree ourselves using ignore::WalkBuilder (the same crate and pattern already used in walker.rs) and pass each non-ignored directory as a WatchedPath::non_recursive().

Key design decisions

1. All platforms, not just Linux. While inotify's hard max_user_watches limit makes Linux the most acute case, registering watches for 50k+ ignored directories is wasteful
   everywhere. Same code path on all platforms keeps things simple.
2. walk_directories() reuses the walker.rs pattern. Uses ignore::WalkBuilder with the same gitignore/nxignore/glob handling as the existing file walker —
   parent_gitignore_files() for git boundary detection, .nxignore support, and filter_entry for the watcher's static ignore globs.
3. Dynamic directory creation handling. With non-recursive watches, newly created directories aren't automatically watched. The on_action callback detects
   CreateKind::Folder events and re-walks the workspace to update the watch set. This required removing the #[cfg(target_os = "linux")] guard on directory events in the
   filterer — previously directory events were only allowed through on Linux (for inotify race condition handling), but now all platforms need them to detect new directories.
4. Weak to avoid circular references. The on_action closure needs access to watchexec.config.pathset() to update watches. Using Arc::downgrade() avoids a
   circular Arc reference (Watchexec → Config → on_action closure → Arc) that would prevent cleanup.
5. Full re-walk on directory creation rather than incremental updates. config.pathset() replaces the entire path set (no "add" API). Rather than maintaining a separate
   tracking structure, we re-walk the workspace on directory creation. This is simple, correct, and fast since WalkBuilder skips ignored directories.

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☁️ Nx Cloud last updated this comment at 2026-02-05 17:56:42 UTC

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[FrozenPandaz]

I'll handle this in #34329

[github-actions]

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