bjoernager/rust
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Add note when FnPtr vs. FnDef impl trait

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I encountered an instance where an `FnPtr` implemented a trait, but I was passing an `FnDef`. To
the end user, there is really no way to differentiate each of them, but it is necessary to cast
to the generic function in order to compile. It is thus useful to suggest `as` in the help note,
(even if the Fn output implements the trait).
This commit is contained in:
kadmin 2023-01-10 06:08:18 +00:00
parent c0b8735959
commit 2de9d679ad
4 changed files with 111 additions and 17 deletions
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54
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
View file

@ -374,6 +374,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
})
}
}
impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
fn report_fulfillment_errors(
&self,
@ -852,6 +853,29 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
let mut suggested =
self.suggest_dereferences(&obligation, &mut err, trait_predicate);
suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
suggested = if let &[cand] = &impl_candidates[..] {
let cand = cand.trait_ref;
if let (ty::FnPtr(_), ty::FnDef(..)) =
(cand.self_ty().kind(), trait_ref.self_ty().skip_binder().kind())
{
err.span_suggestion(
span.shrink_to_hi(),
format!(
"the trait `{}` is implemented for fn pointer `{}`, try casting using `as`",
cand.print_only_trait_path(),
cand.self_ty(),
),
format!(" as {}", cand.self_ty()),
Applicability::MaybeIncorrect,
);
true
} else {
false
}
} else {
false
} || suggested;
suggested |=
self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
suggested |= self.suggest_semicolon_removal(
@ -1968,27 +1992,25 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
candidates.sort();
candidates.dedup();
let len = candidates.len();
if candidates.len() == 0 {
if candidates.is_empty() {
return false;
}
if candidates.len() == 1 {
let ty_desc = match candidates[0].self_ty().kind() {
ty::FnPtr(_) => Some("fn pointer"),
_ => None,
};
let the_desc = match ty_desc {
Some(desc) => format!(" implemented for {} `", desc),
None => " implemented for `".to_string(),
};
if let &[cand] = &candidates[..] {
let (desc, mention_castable) =
match (cand.self_ty().kind(), trait_ref.self_ty().skip_binder().kind()) {
(ty::FnPtr(_), ty::FnDef(..)) => {
(" implemented for fn pointer `", ", cast using `as`")
}
(ty::FnPtr(_), _) => (" implemented for fn pointer `", ""),
_ => (" implemented for `", ""),
};
err.highlighted_help(vec![
(
format!("the trait `{}` ", candidates[0].print_only_trait_path()),
Style::NoStyle,
),
(format!("the trait `{}` ", cand.print_only_trait_path()), Style::NoStyle),
("is".to_string(), Style::Highlight),
(the_desc, Style::NoStyle),
(candidates[0].self_ty().to_string(), Style::Highlight),
(desc.to_string(), Style::NoStyle),
(cand.self_ty().to_string(), Style::Highlight),
("`".to_string(), Style::NoStyle),
(mention_castable.to_string(), Style::NoStyle),
]);
return true;
}