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Fix unused_variables typo suggestions for const patterns - #156904

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onehr:fix-unused-pattern-typo-147595
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Fix unused_variables typo suggestions for const patterns#156904
onehr wants to merge 1 commit into
rust-lang:mainfrom
onehr:fix-unused-pattern-typo-147595

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@onehr

@onehr onehr commented May 25, 2026

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Closes #147595

This fixes unused_variables typo suggestions that could print replacement
patterns which are not valid from the binding site.

The fix keeps the existing def_path_str output when it is already valid, but
adjusts two local-item cases:

  • items outside the binding module are printed with crate::...;
  • items nested inside the current body are printed relative to that body.

It also suppresses const typo suggestions for bare let x = ... bindings,
because replacing the binding with a const path creates a refutable pattern.
Unit ADT typo suggestions are left unchanged.

The regression test covers 2015 and 2021 editions, cross-module consts,
same-module consts, function-local consts, cross-module variants, and bare
let const initializers.

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 25, 2026
@onehr
onehr marked this pull request as ready for review May 25, 2026 09:59
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rustbot commented May 25, 2026

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Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

@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 May 25, 2026
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rustbot commented May 25, 2026

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r? @mejrs

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mejrs
mejrs requested changes May 26, 2026
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Thanks!

  • Please add a regression test for not suggesting path::_, like reported in the issue.
  • Please add explicit HELP annotations in the new tests.

It looks good otherwise but I'm not familiar enough here to tell whether or not corner cases are being missed, so

r? @fmease or @estebank

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@rustbot rustbot assigned fmease and unassigned mejrs May 26, 2026
@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 May 26, 2026
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rustbot commented May 26, 2026

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

@onehr
onehr force-pushed the fix-unused-pattern-typo-147595 branch from b6a1b9e to 518355f Compare May 26, 2026 17:15
@onehr

onehr commented May 26, 2026

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Thanks @mejrs for your comments, resolved.

@onehr

onehr commented May 26, 2026

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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 May 26, 2026
cjgillot
cjgillot reviewed May 30, 2026
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Comment thread compiler/rustc_mir_transform/src/liveness.rs
@onehr
onehr force-pushed the fix-unused-pattern-typo-147595 branch 2 times, most recently from 2de8a14 to 537deff Compare May 31, 2026 15:42
cjgillot
cjgillot reviewed Jun 6, 2026
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Comment thread compiler/rustc_mir_transform/src/liveness.rs Outdated
@onehr
onehr force-pushed the fix-unused-pattern-typo-147595 branch from 537deff to 189de55 Compare June 7, 2026 02:48
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onehr force-pushed the fix-unused-pattern-typo-147595 branch from 189de55 to 5632423 Compare June 7, 2026 06:14
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@apiraino

apiraino commented Aug 20, 2026

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Visiting during triage.

@onehr when you have a chance, feel free to rebase.
@cjgillot / @fmease for another look.

@rustbot author

thanks

@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 20, 2026
@rustbot rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Aug 20, 2026
@onehr
Fix unused_variables typo suggestions for const patterns
697b3ae 
When `unused_variables` finds a similarly named const or enum variant, it
suggests replacing the unused binding with a pattern matching that item. The
item was printed with a trimmed path, which is not necessarily resolvable from
the binding site, so the `MachineApplicable` suggestion could fail to compile.

Print the item with `with_crate_prefix!`: a `crate::`-rooted, re-export-aware
path that resolves from any binding site in the crate. A const declared inside
the current body has no such path, so it is printed by its bare in-scope name.

Also suppress const typo suggestions for bare `let x = ...` bindings, where a
const pattern would be refutable.
@onehr
onehr force-pushed the fix-unused-pattern-typo-147595 branch from 5632423 to 697b3ae Compare August 21, 2026 16:26
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rustbot commented Aug 21, 2026

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This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

@onehr

onehr commented Aug 21, 2026

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@apiraino rebased, thank you for reminding me!

@onehr
onehr requested a review from mejrs August 22, 2026 01:16
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Lint unused_variables's "typoed pattern" suggestion still suggests invalid and unrelated paths

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