[cknitt]

The macOS leg of CI fails "Run rewatch snapshot tests" now and then (11 first attempts since 2026-11-08). Each time it's the quiet-watch case in rewatch-ocaml/tests/check_command_validation.sh: the same parse error is printed twice.

There are two causes:

• The watcher rebuilds when nothing changed. macOS can report one write twice, the second time after the 50 ms drain window. native_loop in watcher.ml re-read the file and rebuilt even when it matched the snapshot, so the error was printed again. update_entries now says whether anything differs (Unchanged, Updated, Not_in_snapshot), and the loop skips the build when nothing does. The polling and reconcile paths already did this. A file that can't be read still counts as changed, so its build still runs and reports the problem.
• The test's filter for repeated reports didn't work. It split the output at Syntax error!. Since Remove the Rust build system #9238 each report starts with a blank line, so the copies differed by one newline and were never merged. The split now goes before that blank line, and it also works with CRLF output.

New unit tests in watcher_tests.ml: re-reading an unchanged file returns Unchanged, before and after an update.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Kbf3gG8vKzkJGrU7AZ1CXQ

[github-actions]

Changelog

🐛 Bug fix

• Watch mode no longer rebuilds, and prints the same errors again, when one file change is reported twice.

Semantic Diff

1 commit · Full page

Skip watch rebuilds for files whose content didn't change

_{b5f76a2 · cknitt + Claude · Nov 14, 2026, 10:14 UTC}

Why

macOS can report one write twice, the second time after the 50 ms drain window. The native watch loop re-read the file and rebuilt even when nothing differed from its snapshot, so a parse error was printed twice. This made the quiet-watch case of check_command_validation.sh fail on macOS in about 4% of CI runs. The test's filter for repeated reports had stopped working with the new report format in #9238.

Diagnostic modified (repeated content event in watch mode)

let value =

diagnostic · Before

rescript watch --quiet after one save on macOS

  Syntax error!
  <ROOT>/src/A.res:1:12-2:0
…
  This let-binding misses an expression

  Syntax error!
  <ROOT>/src/A.res:1:12-2:0
…
  This let-binding misses an expression

diagnostic · After

  Syntax error!
  <ROOT>/src/A.res:1:12-2:0
…
  This let-binding misses an expression

Review

• Does a read error still rebuild? Yes. update_entries counts a kept entry as a change, as before, so the build reports the problem.
• Does touching a file still rebuild? Yes. The entry holds the modification time, as in the polling loop, so only an event for a file that is exactly as the snapshot recorded it is skipped.

[github-actions]

✅ Compiler benchmarks

Allocated words

In total: 640,949,305 → 640,950,354 (±0.00%).

Generated projects: 920,892,047 → 920,892,290 (±0.00%).

None of the 265 benchmarks changed by 0.1% or more.

Instructions

In total: 9,209,713,865 → 9,209,713,865 (±0.00%).

None of the 33 benchmarks changed by 0.1% or more.

Output size

In total: 25,843,406 → 25,843,406 (±0.00%).

None of the 13 benchmarks changed by 0.1% or more.

Pull request b5f76a2 compared with base 1efa212 in this run.

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commit: b5f76a2

[github-actions]

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-9305

[cknitt]

@codex review

[chatgpt-codex-connector]

Codex Review Summary: ✅ Completed

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-14T19:46:20.822375Z	b5f76a2	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: b5f76a2cf4

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