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Rollup merge of rust-lang#91818 - camelid:unused-result-type, r=jackh726
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Show the unused type for `unused_results` lint

I think it's helpful to know what type was unused when looking at these
warnings. The type will likely determine whether the result *should* be
used, or whether it should just be ignored.

Including the type also matches the behavior of the `must_use` lint:
unused `SomeType` that must be used.
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matthiaskrgr authored Dec 17, 2021
2 parents 34dc0d0 + f53e489 commit aeca000
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Showing 3 changed files with 5 additions and 3 deletions.
4 changes: 3 additions & 1 deletion compiler/rustc_lint/src/unused.rs
Original file line number Diff line number Diff line change
Expand Up @@ -169,7 +169,9 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
}

if !(type_permits_lack_of_use || fn_warned || op_warned) {
cx.struct_span_lint(UNUSED_RESULTS, s.span, |lint| lint.build("unused result").emit());
cx.struct_span_lint(UNUSED_RESULTS, s.span, |lint| {
lint.build(&format!("unused result of type `{}`", ty)).emit()
});
}

// Returns whether an error has been emitted (and thus another does not need to be later).
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2 changes: 1 addition & 1 deletion src/test/ui/lint/unused/unused-result.rs
Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ fn test2() {
}

fn main() {
foo::<isize>(); //~ ERROR: unused result
foo::<isize>(); //~ ERROR: unused result of type `isize`
foo::<MustUse>(); //~ ERROR: unused `MustUse` that must be used
foo::<MustUseMsg>(); //~ ERROR: unused `MustUseMsg` that must be used
//~^ NOTE: some message
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2 changes: 1 addition & 1 deletion src/test/ui/lint/unused/unused-result.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ LL | foo::<MustUseMsg>();
|
= note: some message

error: unused result
error: unused result of type `isize`
--> $DIR/unused-result.rs:34:5
|
LL | foo::<isize>();
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