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Rework how the disallowed qualifier in function type diagnostics are generated #142302

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Rework how the disallowed qualifier in function type diagnostics are generated #142302

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@JonathanBrouwer JonathanBrouwer commented Jun 10, 2025 •
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This pull request fixes two independent issues:

  1. When qualifiers of a function type ptr are in the wrong order and one of them is async/const (not permitted on function types), the diagnostic suggests removing the incorrect qualifier. Fixes invalid token removal suggested on unsafe const fn() type #142268, which is an issue created by Trim extra whitespace in fn ptr suggestion span #133151. This is fixed by moving the check into parse_fn_front_matter, where better span information is available to generate the right suggestions.
  2. When qualifiers of a function type ptr are in the wrong order and one of them is async/const (not permitted on function types), cargo fix crashes because "cannot replace slice of data that was already replaced". This is fixed by not generating a suggestion for the "wrong order" diagnostic if the "disallowed qualifier" diagnostic is triggered.

There is a commit with failing tests so the test diff is clearer
r? @jdonszelmann

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 10, 2025
@JonathanBrouwer JonathanBrouwer changed the title Invalid const token Rework how the disallowed qualifier lints are generated Jun 10, 2025
@JonathanBrouwer JonathanBrouwer changed the title Rework how the disallowed qualifier lints are generated Rework how the disallowed qualifier in function type lints are generated Jun 10, 2025
@JonathanBrouwer JonathanBrouwer changed the title Rework how the disallowed qualifier in function type lints are generated Rework how the disallowed qualifier in function type diagnostics are generated Jun 10, 2025
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jdonszelmann reviewed Jun 11, 2025
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@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 12, 2025
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rustbot commented Jun 12, 2025

Reminder, once the PR becomes ready for a review, use @rustbot ready.

@JonathanBrouwer JonathanBrouwer force-pushed the invalid-const-token branch 2 times, most recently from f4135a4 to 8cfeeb8 Compare June 13, 2025 10:33
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@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 13, 2025
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compiler/rustc_parse/messages.ftl Outdated

parse_fn_pointer_cannot_be_const = an `fn` pointer type cannot be `const`
.label = `const` because of this
.suggestion = remove the `const` qualifier
.note = allowed qualifiers are: `unsafe`, `extern`
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could you say

unsafe and extern
?

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@JonathanBrouwer JonathanBrouwer Jun 13, 2025 •
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Fixed.
I decided to keep the : in the allowed qualifiers are: 'unsafe' and 'extern', but if you want to remove that lmk

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r=me after that

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@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 13, 2025
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Rework how the disallowed qualifier lints are generated
b131b6f 
Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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@rustbot ready
Fixed comment & rebased on master

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 13, 2025
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bors-r-plus

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bors commented Jun 13, 2025

📌 Commit b131b6f has been approved by jdonszelmann

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 13, 2025
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invalid token removal suggested on unsafe const fn() type
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