fix(watcher): don't write output or emit events after close()

[situ2001]

Fixed #8937

Have tried my best to align the behavior in Rollup: https://github.com/rollup/rollup/blob/52b9e786b32220cbb1fb9760b03c4819cb9343b2/src/watch/watch.ts

[codspeed-hq]

Merging this PR will not alter performance

✅ 4 untouched benchmarks
⏩ 10 skipped benchmarks¹

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_{Comparing situ2001:situ/cancelable-build (b8d67cf) with main (c389bd7)}

Footnotes

1. 10 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

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[Copilot]

Pull request overview

Aligns watcher.close() with Rollup by introducing a shared closed flag observed during in-progress builds so that the output is discarded when close is requested mid-build, rather than always waiting for the build to write its bundle.

Changes:

• Add a shared Arc<AtomicBool> closed flag on Watcher, propagated to every WatchTask, set by Watcher::close() before sending WatcherMsg::Close.
• In WatchTask::build, after scan_modules completes, check the flag and short-circuit with a new BuildOutcome::Closed, skipping bundle_generate/bundle_write; the coordinator handles Closed by returning early from initial build / rebuild sequences.
• Add a regression test asserting that watcher.close() invoked during an in-progress build prevents BUNDLE_END/END events and produces no output file.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
crates/rolldown_watcher/src/watcher.rs	Adds shared closed AtomicBool; close() sets it before signaling the coordinator; threads it through create_tasks.
crates/rolldown_watcher/src/watch_task.rs	Stores the closed flag in each task; checks it between scan and write phases; introduces BuildOutcome::Closed.
crates/rolldown_watcher/src/watch_coordinator.rs	Handles BuildOutcome::Closed in both initial and rebuild loops by returning early, allowing the close path to proceed.
packages/rolldown/tests/watch/watch.test.ts	Adds a regression test for cancelling an in-progress build via watcher.close().

[hyf0]

Thank you!