[Jake Bailey (jakebailey)]

Caught this in an audit.

Fixes #64037 (which I did not realize before making this fix)

[Copilot]

🟡 Changes recommended

Watch mode can miss valid new inputs due to inconsistent extension casing and suppression of files never emitted, while regression tests do not cover same-directory output loops.

3 open issues

• Test same-directory outputs do not trigger recompilation · New
• Match mapper extensions using filesystem case sensitivity · New
• Track only successfully emitted files to avoid hiding new inputs · New

What changed in this PR

Updates the native compiler’s single-project watch mode to prevent emitted files from triggering repeated builds, addressing #64037.

Changes:

• Filters file events using tracked dependencies, supported extensions, and predicted output paths.
• Tracks dependency directories so directory deletions invalidate the build.
• Adds tests for output filtering, new source discovery, and directory events.

File	Description
tsc/​internal/​execute/​watcher.go	Adds output-aware event filtering and dependency-directory tracking.
tsc/​internal/​execute/​tsctests/​watch_shallow_test.go	Tests ignored file events and relevant source and directory changes.

_{Review effort: Balanced}

[Copilot]

🟡 Changes recommended

The append-only emittedFiles set retains stale output paths, causing watch mode to miss recreated independent declarations; entries need lifecycle-aware cleanup and regression coverage.

1 open issue

• Retire stale emitted-file records to avoid suppressing discovery · New

3 resolved since last review

• Track only successfully emitted files to avoid hiding new inputs
• Match mapper extensions using filesystem case sensitivity
• Test same-directory outputs do not trigger recompilation

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Directory-replacement updates can retain stale source contents and resolutions, while excluded-directory and restored-output events can still trigger unnecessary watch rebuilds.

No open issues 🎉

3 previously missed issues

In code that hasn't changed since last review

Force full rebuild when tracked dependency directories are replaced

tsc/​internal/​execute/​watcher.go:324

A directory replacement can be coalesced into EventUpdate, so this delete-only guard leaves program reuse enabled. If the root filenames stay unchanged and another source is edited in the same batch, the single-file fast path can retain stale contents and resolutions from the replaced directory. Invalidate cached descendants and force a full rebuild for updates to directories containing tracked dependencies; add a regression covering that mixed event batch.

Filter excluded output-directory events from watch cycles

tsc/​internal/​execute/​watcher.go:418

The macOS repro in #64037 still passes this filter: with include: ["**/*"], exclude: ["build"], and tsBuildInfoFile: "./build/tsconfig.tsbuildinfo", the backend delivers updates for both /repro/build and the build-info file. Although the file event is now removed, the directory event survives solely because it is under the recursive watch, so DoCycle still reports a change and rebuilds after emission. Please filter excluded output-directory events too, while preserving directories containing genuine dependencies or discoverable inputs, and add a regression test delivering this pair of events.

Track outputs restored from build info to avoid spurious rebuilds

tsc/​internal/​execute/​watcher.go:709

Outputs restored from build info are never registered here if incremental emission skips their writes. For example, prebuild a composite project that emits declarations alongside its sources, then start --watch without changing the inputs: the existing .d.ts files remain active outputs, but emittedFiles starts empty and this callback is not invoked for them. An event for one of those declarations therefore passes filterRelevantChanges as a new wildcard input and triggers an unnecessary rebuild. Initialize output tracking from confirmed restored emission state as well as successful writes, and add a prebuild/restart regression case; do not blanket-register potential outputs that were never emitted.

1 resolved since last review

• Retire stale emitted-file records to avoid suppressing discovery

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Human assessment is needed to evaluate a watcher edge case where a coalesced directory-to-file update can leave removed sources in the program.

No open issues 🎉

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

The added tests inject mocked events, leaving native directory-event coalescing—especially kqueue child-directory updates—without the OS-level validation needed to rule out emitted-file rebuild loops.

No open issues 🎉

_{Review effort: Balanced}