Tracking Issue for -Z crate-attr

[jyn514]

This is a tracking issue for the -Z crate-attr unstable option (RFC 3791).

About tracking issues

Tracking issues are used to record the overall progress of implementation.
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.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
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Steps

• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• this likely needs an RFC, since it landed without much discussion? i am tentatively planning to do this at the same time as an RFC for #![register_tool].
• probably we will want to limit the syntax? for example, -Z crate-attr='crate_name= /* foo */ "test"' is currently accepted without warning, and -Z crate-attr='crate_name=/*' gives an error about an unterminated block comment.
• fix interactions with doctests: rustdoc --test does not respect -Zcrate-attr #138491
• we should improve diagnostics; currently we treat the attribute as surrounded by #![ /*...*/ ], but don't show the surrounding code in the error:

; rustc src/main.rs -Z crate-attr='#![crate_name="test"]'
error: expected identifier, found `#`
 --> <crate attribute>:1:1
  |
1 | #![crate_name="test"]
  | ^ expected identifier

Implementation history

• Initial implementation: Add the -Zcrate-attr=foo unstable rustc option #52355
• Recommended in other diagnostics: fix #113702 emit a proper diagnostic message for unstable lints passed from CLI #114959
• Documentation and tests: Document -Z crate-attr #138288
• Improve diagnostics for crate-attr itself: Improve -Z crate-attr diagnostics #138336

[jyn514]

some places where this has been mentioned as useful:

• doc(html_no_source): Add an option to exclude source code from docs #75497
• enabling unstable lints: Unstable lints passed on command line can only be ungated from source code #113702
• test frameworks: Add the -Zcrate-attr=foo unstable rustc option #52355 (comment)
• i think this could be useful for register_tool: Tracking issue for #![register_tool] #66079 (comment)
• in general, we have a bunch of attributes that are duplicated as flags (-A/W/D/F, --crate-name, --crate-type). -Z crate-attr allows us not to have to decide between an attribute, flag, or both, because adding an attribute automatically allows it to be specified as a flag.

[fmease]

we have a bunch of attributes that are duplicated as flags

--edition

Not edition, there's no #![edition = …] (but it used to exist a long time ago for a brief period iirc)