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Rollup merge of #136412 - estebank:fn-ptr-cast-suggestion, r=jieyouxu

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Tweak fn pointer suggestion span

Use a more targeted span when suggesting casting an `fn` item to an `fn` pointer.

```
error[E0308]: cannot coerce functions which must be inlined to function pointers
  --> $DIR/cast.rs:10:33
   |
LL |     let _: fn(isize) -> usize = callee;
   |            ------------------   ^^^^^^ cannot coerce functions which must be inlined to function pointers
   |            |
   |            expected due to this
   |
   = note: expected fn pointer `fn(_) -> _`
                 found fn item `fn(_) -> _ {callee}`
   = note: fn items are distinct from fn pointers
help: consider casting to a fn pointer
   |
LL |     let _: fn(isize) -> usize = callee as fn(isize) -> usize;
   |                                        +++++++++++++++++++++
```
```
error[E0308]: mismatched types
  --> $DIR/fn-pointer-mismatch.rs:42:30
   |
LL |     let d: &fn(u32) -> u32 = foo;
   |            ---------------   ^^^ expected `&fn(u32) -> u32`, found fn item
   |            |
   |            expected due to this
   |
   = note: expected reference `&fn(_) -> _`
                found fn item `fn(_) -> _ {foo}`
help: consider using a reference
   |
LL |     let d: &fn(u32) -> u32 = &foo;
   |                              +
```
Previously we'd point at the whole expression for replacement, instead of marking what was being added.

We could also modify the suggestions for `&(name as fn())`, but for that we require storing more accurate spans than we have now.
This commit is contained in:
Matthias Krüger 2025-02-02 12:31:58 +01:00 • committed by GitHub
commit 44def58274
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GPG key ID: B5690EEEBB952194
4 changed files with 11 additions and 16 deletions
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9
compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
View file

@ -418,7 +418,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
};
let sugg = match (expected.is_ref(), found.is_ref()) {
(true, false) => FunctionPointerSuggestion::UseRef { span, fn_name },
(true, false) => {
FunctionPointerSuggestion::UseRef { span: span.shrink_to_lo() }
}
(false, true) => FunctionPointerSuggestion::RemoveRef { span, fn_name },
(true, true) => {
diag.subdiagnostic(FnItemsAreDistinct);
@ -426,7 +428,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
}
(false, false) => {
diag.subdiagnostic(FnItemsAreDistinct);
FunctionPointerSuggestion::Cast { span, fn_name, sig }
FunctionPointerSuggestion::Cast { span: span.shrink_to_hi(), sig }
}
};
diag.subdiagnostic(sugg);
@ -466,8 +468,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
}
} else {
FunctionPointerSuggestion::CastBoth {
span,
fn_name,
span: span.shrink_to_hi(),
found_sig: *found_sig,
expected_sig: *expected_sig,
}

12
compiler/rustc_trait_selection/src/errors.rs
View file

@ -1391,15 +1391,13 @@ pub struct OpaqueCapturesLifetime<'tcx> {
pub enum FunctionPointerSuggestion<'a> {
#[suggestion(
trait_selection_fps_use_ref,
code = "&{fn_name}",
code = "&",
style = "verbose",
applicability = "maybe-incorrect"
)]
UseRef {
#[primary_span]
span: Span,
#[skip_arg]
fn_name: String,
},
#[suggestion(
trait_selection_fps_remove_ref,
@ -1429,7 +1427,7 @@ pub enum FunctionPointerSuggestion<'a> {
},
#[suggestion(
trait_selection_fps_cast,
code = "{fn_name} as {sig}",
code = " as {sig}",
style = "verbose",
applicability = "maybe-incorrect"
)]
@ -1437,13 +1435,11 @@ pub enum FunctionPointerSuggestion<'a> {
#[primary_span]
span: Span,
#[skip_arg]
fn_name: String,
#[skip_arg]
sig: Binder<'a, FnSig<'a>>,
},
#[suggestion(
trait_selection_fps_cast_both,
code = "{fn_name} as {found_sig}",
code = " as {found_sig}",
style = "hidden",
applicability = "maybe-incorrect"
)]
@ -1451,8 +1447,6 @@ pub enum FunctionPointerSuggestion<'a> {
#[primary_span]
span: Span,
#[skip_arg]
fn_name: String,
#[skip_arg]
found_sig: Binder<'a, FnSig<'a>>,
expected_sig: Binder<'a, FnSig<'a>>,
},