Suggest mutable references for FnMut closure arguments

[chenyukang]

Fixes #118843

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[Albab-Hasan]

not sure if this case is in scope, but if the borrow comes from a macro body the suggestion lands inside the macro definition:

    macro_rules! call_it {
        ($f:expr) => { (0..100).for_each(&$f) };
    }
    fn main() {
        let mut value = 0;
        let mut func = |increment: usize| value += increment;
        call_it!(func);
    }

    help: consider changing this borrow's mutability
      |
    2 |     ($f:expr) => { (0..100).for_each(&mut $f) };
      |                                       +++

since its MachineApplicable and the new test has run-rustfix, cargo fix would rewrite the macro. master emits the same E0525 with no help line, so i think this comes in with the new call site rather than being pre existing.

would a from_expansion check on the arg be enough to rule it out?

verified both commits on master 5db7f4b

View changes since the review

[davidtwco]

@bors r+ rollup

[rust-bors]

📌 Commit 61d3b06 has been approved by davidtwco

It is now in the queue for this repository.

[rust-timer]

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (4c9aa76): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	1

Max RSS (memory usage)

Results (primary 1.4%, secondary -4.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.6%	[3.4%, 3.7%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-4.1%	[-4.1%, -4.1%]	1
All ❌✅ (primary)	1.4%	[-2.9%, 3.7%]	3

Cycles

Results (secondary -2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.1%, -2.0%]	2
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: missing data
Artifact size: 403.29 MiB -> 403.35 MiB (0.01%)