perf(linter/plugins): lazy deserialize comments array

[lilnasy]

Part of #14564.

Deserialize program.comments lazily upon first access, instead of eagerly, on assumption that most JS plugins won't access comments.

deserializeWith cleans up the buffer once deserializing AST is complete, so we keep a local copy of the buffer in scope of the comments getter, and restore it when the getter is triggered.

Buffers are reused, so the if (localAstId !== astId) check is required to make sure the AST in the buffer is same AST i.e. that the getter isn't accessed after the file has completed linting.

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[codspeed-hq]

CodSpeed Performance Report

Merging #14637 will not alter performance

_{Comparing lilnasy:perf/lazy-deserialize-comments (8469d57) with main (5858641)}

Summary

✅ 37 untouched

[lilnasy]

Not sure what's up with AST check CI. The generated code is up to date. CI's expected output is just different.

[overlookmotel]

Not sure what's up with AST check CI. The generated code is up to date. CI's expected output is just different.

Looks like dprint (which we use for formatting JS/TS code) requires 2 passes to get to a stable state with this code. That's a bug in dprint, but #14723 provides a workaround. I'll merge it if we decide to go forwards with this PR.

The problem on this PR was that the autofix CI job ran dprint and pushed a commit with the changes. But then the "AST Changes" job checks the code committed is identical to the output of cargo run -p oxc_ast_tools, which it's not because of that extra commit. 🔄

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Or just sidestep the formatting problem, by shortening the error message:

if (localAstId !== astId) throw new Error('Comments are only accessible while linting the file');

This is an edge case which shouldn't be hit in practice, so I don't think we need to provide too much explanation.

[lilnasy]

I tried that as well, dprint introduces a block in that case.

[overlookmotel]

Weird. I'm not seeing that locally. Anyway, it doesn't matter if it produces a block, only that it does so consistently.

[overlookmotel]

All nits...

[lilnasy]

Addressed the review comments in 09baebc.

[Copilot]

Pull Request Overview

Lazy-loads the Program.comments array to reduce upfront deserialization cost, guarding access with an AST session id and restoring buffers on demand.

• Introduces a global astId to gate comment access to the active lint session.
• Saves buffer references (uint32, uint8, sourceText) and adds a lazy getter for comments that deserializes on first access.

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tasks/ast_tools/src/generators/raw_transfer.rs	Adds astId initialization in the generated runtime to track the active AST session.
crates/oxc_ast/src/serialize/mod.rs	Implements lazy comments getter: captures buffer refs, increments astId per Program, restores buffers and deserializes comments on first access.

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[overlookmotel]

Thank you. I did warn you it might be tricky, but I underestimated!

[lilnasy]

Thanks for guiding me through this. I did not imagine a project of oxc's scope would neat and tidy, and I enjoyed this welcome tour!