Traverse upwards for single context projects

[nojaf]

This resolves the upwards traversal as discussed in #7117 (comment)

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commit: bdac509

[Copilot]

Pull Request Overview

This PR implements upward directory traversal for package resolution in single context projects, allowing ReScript to find dependencies in parent node_modules directories when building standalone packages in workspace setups.

Key changes include:

• Added upward traversal logic that searches parent directories for node_modules when dependencies aren't found locally
• Implemented caching mechanism to optimize repeated path existence checks during traversal
• Added comprehensive test coverage for standalone package builds

Reviewed Changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rewatch/src/helpers.rs	Core implementation of upward traversal logic with caching for package resolution
rewatch/tests/compile.sh	Added test case for standalone package building via rescript command
rewatch/testrepo/packages/standalone/*	Test fixtures for standalone package with dependency on @testrepo/dep01
rewatch/testrepo/package.json	Added standalone package to workspace and updated scripts to use rescript instead of rewatch
CHANGELOG.md	Documented the new upward traversal feature

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[cknitt]

👍 LGTM, but would be great if someone else could review, too.

[cknitt]

@codex review

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

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[jfrolich]

can we not put this in the build state instead of a static value?

[nojaf]

It is used before BuildState is created, packages::make already needs it.
I was able to move it to ProjectContext:

• Key point: ProjectContext exists before BuildState. We resolve packages (e.g. helpers::try_package_path) during config/dependency reading, which happens pre-BuildState, and those call sites already have a &ProjectContext.

• Correct scope/lifetime: The cache models workspace layout (node_modules existence), not per-build artifacts. BuildState may be recreated in watch cycles; ProjectContext persists, so the cache isn’t thrown away.

• Concurrency and isolation: A per-ProjectContext RwLock allows concurrent reads and avoids process-wide statics and cross-project cache bleed.

• Lower coupling/less churn: Callers already pass ProjectContext; using it avoids threading BuildState through config.rs and build/packages.rs and reduces borrow/contention with the highly mutable BuildState.

[jfrolich]

Great!

[nojaf]

I'm also incorporating the changes of #7890 as it is a similar cache.

[Copilot]

Pull Request Overview

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

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