diagnostics: fix ICE in closure signature mismatch

[JonatanLindh]

Fixes #152331

Fixes an ICE where AdjustSignatureBorrow caused a panic because it attempted to set the len argument which was already defined by the parent diagnostic.

Both variants used len as argument name, but can both be present in a diagnostic. They now use different names for the argument.

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[Urgau]

The conflicting len argument comes from the same diagnostic who is emitted twice, but not with the same suggestion.

rust/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

Lines 5430 to 5436 in be4794c

	if !to_borrow.is_empty() {
	err.subdiagnostic(errors::AdjustSignatureBorrow::Borrow { to_borrow });
	}
	if !remove_borrow.is_empty() {
	err.subdiagnostic(errors::AdjustSignatureBorrow::RemoveBorrow { remove_borrow });
	}

[Urgau]

Thanks, the fix makes sense to me.

View changes since this review

[Urgau]

r? Urgau
@bors r+ rollup

[rust-bors]

📌 Commit fb55b5d has been approved by Urgau

It is now in the queue for this repository.

[Zalathar]

The test added by this PR does not demonstrate the underlying diagnostic bug.