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Fixed more &x ->&mut x suggestions#157032

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nullie:borrowck-deref-pattern-mut-suggestion-fix
May 30, 2026
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Fixed more &x ->&mut x suggestions#157032
rust-bors[bot] merged 2 commits into
rust-lang:mainfrom
nullie:borrowck-deref-pattern-mut-suggestion-fix

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@nullie nullie commented May 27, 2026 •
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This PR fixes additional issues related to #148467, i.e. compiler still suggests incorrect fixes for adding mut to deref patterns (needing additional parens) in other bindings besides for loop

fn let_deref(num_ref: &u32) -> u32 {
    let &num = num_ref;

    num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

    num
}

fn deref_inside_pattern(option_num_ref: Option<&u32>) {
    if let Some(&num) = option_num_ref {
        num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

        println!("{num}");
    }
}
...
help: consider making this binding mutable
  |
2 |     let &mut num = num_ref;
  |          +++
...
help: consider making this binding mutable
   |
10 |     if let Some(&mut num) = option_num_ref {
   |                  +++

@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 May 27, 2026
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rustbot commented May 27, 2026

r? @nnethercote

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nnethercote
nnethercote reviewed May 29, 2026
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Can you merge the three commits? There is no need for them to be separate, they logically belong together. r=me once that is done.

(For next time: a nice way to do error message PRs is to add/change tests in a first commit, and then make the code changes in a second commit. That way the improvements in the diagnostics are easy to see in the second commit.)

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@nullie nullie force-pushed the borrowck-deref-pattern-mut-suggestion-fix branch from a0f000a to a5b0416 Compare May 29, 2026 12:51
@nullie nullie force-pushed the borrowck-deref-pattern-mut-suggestion-fix branch from a5b0416 to 9bef677 Compare May 29, 2026 13:34
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nullie commented May 29, 2026

r? @nnethercote regrouped into two commits as you suggested

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Requested reviewer is already assigned to this pull request.

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nnethercote approved these changes May 29, 2026
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Thank you! Splitting it that way is really helpful, and makes reviewing much easier.

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nnethercote commented May 29, 2026

@bors r+ rollup

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rust-bors Bot commented May 29, 2026

📌 Commit 9bef677 has been approved by nnethercote

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 1. This pull request will be tested once the tree is reopened.

@rust-bors rust-bors Bot 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 May 29, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 30, 2026
@JonathanBrouwer
Rollup merge of rust-lang#157032 - nullie:borrowck-deref-pattern-mut-…
d3ca59d 
…suggestion-fix, r=nnethercote

Fixed more &x ->&mut x suggestions

This PR fixes additional issues related to rust-lang#148467, i.e. compiler still suggests incorrect fixes for adding mut to deref patterns (needing additional parens) in other bindings besides for loop

```rust
fn let_deref(num_ref: &u32) -> u32 {
    let &num = num_ref;

    num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

    num
}

fn deref_inside_pattern(option_num_ref: Option<&u32>) {
    if let Some(&num) = option_num_ref {
        num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

        println!("{num}");
    }
}
```

```
...
help: consider making this binding mutable
  |
2 |     let &mut num = num_ref;
  |          +++
...
help: consider making this binding mutable
   |
10 |     if let Some(&mut num) = option_num_ref {
   |                  +++
```
@JonathanBrouwer JonathanBrouwer mentioned this pull request May 30, 2026
Closed
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 30, 2026
@JonathanBrouwer
Rollup merge of rust-lang#157032 - nullie:borrowck-deref-pattern-mut-…
455ecb5 
…suggestion-fix, r=nnethercote

Fixed more &x ->&mut x suggestions

This PR fixes additional issues related to rust-lang#148467, i.e. compiler still suggests incorrect fixes for adding mut to deref patterns (needing additional parens) in other bindings besides for loop

```rust
fn let_deref(num_ref: &u32) -> u32 {
    let &num = num_ref;

    num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

    num
}

fn deref_inside_pattern(option_num_ref: Option<&u32>) {
    if let Some(&num) = option_num_ref {
        num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

        println!("{num}");
    }
}
```

```
...
help: consider making this binding mutable
  |
2 |     let &mut num = num_ref;
  |          +++
...
help: consider making this binding mutable
   |
10 |     if let Some(&mut num) = option_num_ref {
   |                  +++
```
This was referenced May 30, 2026
Closed
Merged
rust-bors Bot pushed a commit that referenced this pull request May 30, 2026
@bors
Auto merge of #157149 - JonathanBrouwer:rollup-JIG4HGr, r=JonathanBro…
a857d06 
…uwer

Rollup of 12 pull requests

Successful merges:

 - #154591 (Remove `will_cache_on_disk_for_key_fn`)
 - #156672 (Misc improvements to coroutine transform code)
 - #157027 (HIR ty lowering: Move some things into submodules)
 - #157051 (Allow two object files for a single CGU in CompiledModule)
 - #157100 (Some more per owner things)
 - #153497 (Use `trait_object_dummy_self` more & heavily fix+update related docs)
 - #155638 (Fix tupled closure signature in `AsyncFn` arg mismatch diagnostic)
 - #156826 (style: Clarify nullary call and `()` no-break rule applies past max width)
 - #157004 (Remove unused functions in `value_analysis.rs`)
 - #157032 (Fixed more &x ->&mut x suggestions)
 - #157033 (Note irrefutable while let in loop type errors)
 - #157139 (compiler: `ops::RangeInclusive` → `range::RangeInclusive`)

Failed merges:

 - #156875 (Correct and document semantics of `yield` terminator)
@rust-bors rust-bors Bot merged commit 6717454 into rust-lang:main May 30, 2026
12 checks passed
@rustbot rustbot added this to the 1.98.0 milestone May 30, 2026
rust-timer added a commit that referenced this pull request May 30, 2026
@rust-timer
Unrolled build for #157032
5529a89 
Rollup merge of #157032 - nullie:borrowck-deref-pattern-mut-suggestion-fix, r=nnethercote

Fixed more &x ->&mut x suggestions

This PR fixes additional issues related to #148467, i.e. compiler still suggests incorrect fixes for adding mut to deref patterns (needing additional parens) in other bindings besides for loop

```rust
fn let_deref(num_ref: &u32) -> u32 {
    let &num = num_ref;

    num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

    num
}

fn deref_inside_pattern(option_num_ref: Option<&u32>) {
    if let Some(&num) = option_num_ref {
        num *= 2; //~ ERROR cannot assign twice to immutable variable `num`

        println!("{num}");
    }
}
```

```
...
help: consider making this binding mutable
  |
2 |     let &mut num = num_ref;
  |          +++
...
help: consider making this binding mutable
   |
10 |     if let Some(&mut num) = option_num_ref {
   |                  +++
```
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