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Recover from incorrect replacement of & for types and expressions - #162376

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KevinA-cpu:c-style-reference-recovery
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Recover from incorrect replacement of & for types and expressions#162376
KevinA-cpu wants to merge 1 commit into
rust-lang:mainfrom
KevinA-cpu:c-style-reference-recovery

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@KevinA-cpu

@KevinA-cpu KevinA-cpu commented Sep 6, 2026 •
edited by rustbot
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  • Suggest from T& to &T
  • Suggest from mut& to &mut
  • Suggest from mut &'a u8 to &'a mut u8
  • Suggest from expr& to &expr
  • Suggest from expr &mut to &mut expr

Guards:

  • check for may_recover() to avoid breaking macros
  • can_begin_type/can_begin_expr to avoid breaking u8 & u8 and tests/ui/consts/closure-type-error-during-const-eval-66706.rs
  • Binary/Cast guards are in-place to prevent making wrong suggestions in complicated lhs

Does not touch the following areas:

#101487

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rustbot commented Sep 6, 2026

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The parser was modified, potentially altering the grammar of (stable) Rust
which would be a breaking change.

cc @fmease

@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 Sep 6, 2026
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r? @nnethercote

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@KevinA-cpu
Add c-style-reference recovery for types and expressions
bea1b70 
- Suggest from `T&` to `&T`
- Suggest from `mut&` to `&mut`
- Suggest from `mut &'a u8` to `&'a mut u8`
- Suggest from `expr&` to `&expr`
- Suggest from `expr &mut` to `&mut expr`

Guards:
- check for may_recover() to avoid breaking macros
- can_begin_type/can_begin_expr to avoid breaking `u8 & u8` and tests/ui/consts/closure-type-error-during-const-eval-66706.rs
- Binary/Cast guards are in-place to prevent making wrong suggestions in complicated `lhs`

Does not touch the following areas:

- const& T: overlapping with open issue 146122
- i32&&: C++'s T&& is an rvalue reference and Rust doesn't have the same thing currently
- u8 &mut
- x as u8&
@KevinA-cpu
KevinA-cpu force-pushed the c-style-reference-recovery branch from bba988b to bea1b70 Compare September 6, 2026 15:19
fmease
fmease reviewed Sep 6, 2026
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Comment thread tests/ui/did_you_mean/c-style-reference-exprs-issue-101487.rs

@fmease fmease Sep 6, 2026 •
edited by rustbot
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We're in an expression context here, so "reference types" isn't correct terminology. You're looking for "borrow expression".

However, stepping back, expr& is not a thing in C/C++, so I'm not so sure if it's worth trying to recover from it. Do you think that anybody is really going to accidentally type expr& when they meant &expr? Re. expr &mut I'm 99.9% confident nobody has ever written that by accident.

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fmease
fmease reviewed Sep 6, 2026
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Comment thread tests/ui/did_you_mean/c-style-reference-types-issue-101487.rs

@fmease fmease Sep 6, 2026 •
edited by rustbot
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I'm wondering whether we should say &mut /* Type */ instead to make it crystal clear what is a placeholder and what isn't.

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fmease
fmease reviewed Sep 6, 2026
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Comment thread tests/ui/did_you_mean/c-style-reference-types-issue-101487.rs

@fmease fmease Sep 6, 2026 •
edited by rustbot
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Thanks for making sure this is well-tested. However, personally I think it's a tinge excessive for such a niche recovery 🤷

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nnethercote commented Sep 6, 2026

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r? @fmease

@rustbot rustbot assigned fmease and unassigned nnethercote Sep 6, 2026
@fmease fmease 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 Sep 7, 2026
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rust-bors Bot commented Sep 8, 2026

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☔ The latest upstream changes (presumably #162269) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

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