Tracking Issue for `--print=supported-crate-types`

[jieyouxu]

This is a tracking issue for the compiler print request --print=supported-crate-types.
This print request is currently unstable, gated behind -Zunstable-options.

About tracking issues

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They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
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Steps

• Draft and accept an MCP: Add --print=supported-crate-types compiler-team#836
• Implement the print request as an unstable print option: Add unstable --print=supported-crate-types option #138641
• Adjust documentation (see instructions on rustc-dev-guide): Add unstable --print=supported-crate-types option #138641
• Stabilization PR (see instructions on rustc-dev-guide): TODO; after some baking

Unresolved Questions

• (Bikeshedding) Is supported-crate-types the best name for the print request?

Design decision history

None yet, since initial implementation.

Implementation history

• Add unstable --print=supported-crate-types option #138641

[weihanglo]

Just realized this won't help remove Cargo's hack on parsing error messages. Basically, Cargo is looking for something like these

___.wasm
lib___.rlib
___.wasm
lib___.a

in order to learn what file prefix/suffix a crate-type will emit.

Unless we have one more print option like --print prefix-suffix, cargo doesn't really benefit from this. That said, Cargo can o spawn an extra rustc invocation first to get supported crate-types, though it is costly and hurts startup time, and is alwasy a thing we want to avoid in Cargo in general.

[tgross35]

Could the json output include more information rust-lang/compiler-team#860? So --print=supported-crate-types:json would return:

{"supported-crate-types", "value": [{"type": "staticlib", "prefix": "lib", "extension":"a"}, {"type": "rlib", "prefix": "lib", "extension":"rlib"}, {"type": "bin", "prefix": "", "extension":""}]}

[jieyouxu]

@tgross35 yes, but I originally kinda intended for that to be a separate print request (something like --print=file-name-prefix-suffix-per-crate-type). However, I suppose that's technically a "superset" of this flag (in the current form), and you could easily derive --print=supported-crate-types from that richer form. I'm open to changing this flag to output the more "rich" version (I don't want to have the json vs non-json form differ, I think just outputting what you propose here seems more useful). (I just haven't gotten around to this.)

cf. https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/rustc.20--print-json.20shape/near/511302120