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Add future-incompat warning against keywords in cfgs and add raw-idents #14671

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Add future-incompat warning against keywords in cfgs and add raw-idents #14671

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@Urgau Urgau commented Oct 11, 2024

What does this PR try to resolve?

This PR tries to address this thread #14649 (comment) in #14649 regarding cfg(true)/cfg(false) (and keywords more generally) which are wrongly accepted1 as ident.

To address this, this PR does two things:

  1. it introduce a future-incompatibility warning against those (wrongly) accepted keywords as ident
  2. it add parsing for raw-idents (r#true) add suggest-it in the warning

How should we test and review this PR?

This PR should be reviewed commit-by-commit.
Tests are included in preliminary commits.

Additional information

I added a new struct for representing Idents which is rawness aware.
Which implied updating cargo-platform to 0.2.0 due to the API changes.

r? @epage

Footnotes

  1. https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=ccfb9c894dbf14e791c8ae7e4798efd0 ↩

@rustbot rustbot added A-build-scripts Area: build.rs scripts A-cfg-expr Area: Platform cfg expressions A-manifest Area: Cargo.toml issues S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 11, 2024
@Urgau Urgau mentioned this pull request Oct 11, 2024
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@Urgau Urgau force-pushed the cfg-keyword-and-raw-idents branch 5 times, most recently from aa8bb59 to 0569db6 Compare October 11, 2024 13:42
epage
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@epage epage added the T-cargo Team: Cargo label Nov 1, 2024
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epage commented Nov 1, 2024

@rfcbot fcp merge

This PR adds a future-incompat warning for the use of true and false values in a cfg within Cargo. This is to make room supporting RFC3695 (see #14649) which we verbally confirmed approval for (see rust-lang/rfcs#3695 (comment))

The main focus of this FCP is insta-stabilizing support for raw identifiers (e.g. r#true) in cfgs in Cargo. The future-incompat warning (this PR) and support for true / false (#14649) is implemented in a way that mirrors rustc where true and false are considered keywords and to reference the identifers with those names you need to use raw identifiers.

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rfcbot commented Nov 1, 2024 •
edited by weihanglo
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Team member @epage has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

@rfcbot rfcbot added proposed-final-comment-period An FCP proposal has started, but not yet signed off. disposition-merge FCP with intent to merge labels Nov 1, 2024
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ehuss commented Nov 2, 2024

I'm not quite sure I understand the wording of the error message. Saying cfg(true) is deprecated and will become a hard error in a future doesn't seem correct, since when rust-lang/rust#131204 is stabilized, it will become a supported feature (and thus not deprecated, and will intentionally be supported), right?

Would it be possible to change the wording to be something more like:

warning: the meaning of cfg(true) may change in the future
Cargo used to erroneously allow cfg(true) and cfg(false), but both forms were interpreted as false unless manually overridden with --cfg. In the future these will be built-in defines that will have the corresponding true/false value. It is recommended to avoid using these values until they are properly supported. See rust-lang/rust#131204 for more information.

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Urgau commented Nov 2, 2024

[..] it will become a supported feature (and thus not deprecated, and will intentionally be supported), right?

Yes, cfg(true) and cfg(false) will have the right semantic after #14649 is stabilized.

Changed the wording as suggest.

@rfcbot rfcbot added final-comment-period FCP — a period for last comments before action is taken and removed proposed-final-comment-period An FCP proposal has started, but not yet signed off. labels Nov 15, 2024
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rfcbot commented Nov 15, 2024

🔔 This is now entering its final comment period, as per the review above. 🔔

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A-build-scripts Area: build.rs scripts A-cfg-expr Area: Platform cfg expressions A-manifest Area: Cargo.toml issues disposition-merge FCP with intent to merge final-comment-period FCP — a period for last comments before action is taken S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-cargo Team: Cargo
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