mozilla / mozilla/cbindgen

[Question] Why does parse.expand use an unstable flag to rustc?

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Dominant language
Rust
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Description

Currently, [parse.expand] uses the -Z unstable pretty=expand option to rustc. This requires using the nightly rustc compiler. There is nothing in the documentation that mentions why this is required, and there isn't much discussion as to why. If macro expansion is needed, is there a reason that cbindgen can't just do cargo expand which does not require any nightly rustc options?

I think that macro expansion is a relatively common requirement, and gating it behind having to use a nightly toolchain is a big cost.

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Research direction

Trace the implementation of the parse.expand option and its rustc invocation, then compare that behavior with cargo expand and its toolchain requirements. Determine whether macro expansion can use the proposed approach without losing supported behavior; document the rationale or define the required change and validation criteria.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
tooling
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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