Keep watch alive after rebuild errors

[fhammerschmidt]

A config or source-layout change that made full rebuild initialization fail caused watch mode to panic or exit. Initialization errors now propagate through the build lock, are reported to the user, and keep the watcher alive for recovery.

After initialization fails, later source edits retry full initialization until the current configuration can be loaded. They cannot emit outputs using the previous suffix, dependencies, or compiler options. Malformed dependency configs also return errors instead of exiting the process, retaining their resolved directory so the watcher can observe a correction to a newly added dependency. Dependency resolution failures retain their package-tree context and dependency name when propagated to the CLI.

Dependency resolution and configuration failures now return exit code 1 instead of 2 from rescript build, clean, and format, using the CLI's normal error path. Dependency errors are reported once, retaining their package-tree context.

Recovery limit: installing a missing dependency or replacing a non-local dependency directory does not itself trigger a retry. After installation or replacement, edit a watched source file or touch rescript.json to retry initialization. Automatic detection of these installation changes remains a follow-up.

Add regressions for editing a source while the root config is invalid, recovering with a changed suffix, and fixing only a newly added workspace dependency's config. The invalid-config test waits for the edited source's event to select full reinitialization and for an initialization failure after that event, so delayed config events cannot satisfy the assertion. The integration tests use the shared platform-aware polling helpers and stop cleanup if watcher shutdown fails.

Validation:

• make passes with the native watcher backend.
• cargo test --manifest-path rewatch/Cargo.toml passes: 145 tests.
• All 41 build fixtures pass, including missing regular and development dependencies.
• Clippy with all targets/features and warnings denied, Rust formatting, and shell syntax checks pass.
• Both focused watcher integration scripts pass with an isolated polling-backend build that supplies native-style content-change events. Disabling full reinitialization after a source edit makes the strengthened invalid-config test fail and reproduces stale output. Native macOS filesystem events are unavailable in this environment, including outside the sandbox; native platform integration remains for CI.

[chatgpt-codex-connector]

Codex Review Summary

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

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-09T14:22:30.923223Z	f83cd4f	Manual request

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commit: fef2886

[fhammerschmidt]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 3377441a3d

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[fhammerschmidt]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

Reviewed commit: f83cd4ffd8

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• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

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[github-actions]

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-8641

[cknitt]

🤖 This review was generated by Claude (Claude Code) on behalf of @cknitt.

Verdict: approve with nits. No correctness bugs found in the watch loop. Init errors propagate instead of panicking. initialization_failed forces a full re-init rather than an incremental build on stale state. Every fallible step in initialize_build runs before cleanup_previous_build, so a failed init leaves nothing half-cleaned. Both new tests fail without the fix.

• Exit code change: the two process::exit(2) calls in packages.rs are gone and main.rs's exit_code returns 1. rescript build/clean/format now exit 1 instead of 2 when a dependency is missing or has a malformed config. weird_deps/weird_devdeps only assert != 0, so CI doesn't catch it. Please acknowledge it in the PR/changelog, or keep 2.
• Missing dependency dir gets no recovery watch: only DependencyConfigError adds one. Example: a dependency added to rescript.json before npm install. Finishing the install produces no event, so watch stays failed until a .res file or rescript.json is touched. The same happens when a non-local dependency with a bad config is reinstalled, because the directory is replaced. Still far better than exiting; could be documented, or the root node_modules watched non-recursively while init is failing.
• Duplicate test number: 07-watch-recovers-from-invalid-config.sh sits next to the existing 07-changed-interface-after-failed-implementation.sh. Renumber the new ones to 08/09.
• Test 07 can pass without proving anything: if the mv of the invalid config spans two debounce windows, a second init failure can bump initial_errors before the Test.res edit is processed, and the "no marker in Test.mjs" check then passes trivially. This can't cause a flaky failure, only a false pass. Waiting for a marker tied to the edit would tighten it.
• Nits:
  • With show_progress, dependency errors are printed twice (inspect_err in packages.rs, then eprintln!("{error:#}")).
  • The rustfmt re-indent in watcher.rs (~509-540) and packages.rs makes the diff noisier.
  • Out of scope, but other panics can still kill watch mode after a config change, e.g. "JSX version {v} is unsupported" (config.rs:834) and .expect("Could not canonicalize") (packages.rs:562). Possible follow-up.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.51%. Comparing base (8d51b9c) to head (fef2886).
⚠️ Report is 26 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8641      +/-   ##
==========================================
+ Coverage   80.40%   80.51%   +0.10%     
==========================================
  Files         447      447              
  Lines       60990    61060      +70     
==========================================
+ Hits        49042    49162     +120     
+ Misses      11948    11898      -50     

see 37 files with indirect coverage changes

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[fhammerschmidt]

The follow-ups document the exit-code change and dependency-install recovery limit, renumber the tests, and remove duplicate diagnostics. The recovery regression now waits for the source event and a subsequent initialization failure; disabling recovery makes it fail and reproduces stale output. Automatic detection of newly installed or replaced dependencies remains a follow-up; editing a watched source or touching rescript.json triggers recovery. CI, including the package-installation checks, coverage, and changelog validation now all pass.