Option to watch fs events for subdirs separately from root dir#1329
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bvinc wants to merge 4 commits into
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Option to watch fs events for subdirs separately from root dir#1329bvinc wants to merge 4 commits into
bvinc wants to merge 4 commits into
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When set, the notify file watcher registers a recursive watch for each non-ignored top-level subdirectory of the project root rather than a single recursive watch on the root itself. Ignored top-level directories (e.g. buck-out) are never registered with the watcher backend. Defaults to false; existing behavior is unchanged.
When watch-included-root-dirs-only is enabled, `rescan_root` runs on every sync and tracks (size, mtime) of non-ignored top-level files. Modifications, creations, and removals at the project root are synthesized as events and merged into notify's stream. New top-level directories created mid-session are picked up by the same scan and registered for recursive watching. Adds two debug logs: * a new root subdirectory has a watch registered * a root-level file was modified
Cover the state transitions: ignored dir filtered at startup, ignored dir appearing mid-session stays invisible, new top-level dir is reported with a watch, root file modified/removed, top-level dir removed, no-op on a clean rescan.
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May 28, 2026
| let watch_included_root_dirs_only = root_config | ||
| .parse::<bool>(BuckconfigKeyRef { | ||
| section: "project", | ||
| property: "watch-included-root-dirs-only", |
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Snake case for buckconfig keys isn't it? Also maybe bike shed it a bit more
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I really wish you could grep BuckconfigKeyRef::new and get a big list of all of them to see where you might put a new one and what you might name it. But it ain't so.
`rescan_root` already detects when a previously-watched top-level subdirectory disappears and emits a synthetic `Remove(Folder)` event, but the matching `notify` watch was never released. On Linux this is masked by inotify auto-removing the watch in response to `IN_IGNORED`. On macOS (fsevent) and Windows (ReadDirectoryChangesW) there is no such auto-cleanup, so a long-running daemon would slowly leak watch handles as workspace subdirs are created and destroyed. Have `rescan_root` return the set of vanished directories alongside the existing `new_watches`, and unwatch them from `sync2`. Swallow `WatchNotFound` since it's the expected case on Linux. Bundle the return values into a `RescanResult` struct so the signature scales to a future fourth field without breaking call sites.
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This creates a new project setting "watch-included-root-dirs-only" which watches subdirectories at the root level separately. This allows real ignoring of the buck-out folder, which makes the possibility of missing fs change events much less likely.
This is the most important on mac, where fsevent has no knobs to turn, and no way to really ignore the buck-out folder. Without this change, large builds will easily and consistently overflow the internal fsevent buffers and cause file system events to be missed. After this change, almost no events happen, as changes outside of the buck-out folder are rare.
Unfortunately, this requires manual non-recursive polling of the root directory occasionally. I chose to put this in calls to sync2, which usually happen once at the beginning of a build.