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Fix invalid mut T suggestion for &mut T in missing lifetime error

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* Find ref prefix span for owned suggestions
* Improve missing lifetime suggestions for `&mut str`
This commit is contained in:
reddevilmidzy 2026-02-17 10:18:08 +00:00
parent 466ea4e6c3
commit e0d9d470df
3 changed files with 231 additions and 13 deletions
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78
compiler/rustc_resolve/src/late/diagnostics.rs
View file

@ -3837,25 +3837,32 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
"instead, you are more likely to want"
};
let mut owned_sugg = lt.kind == MissingLifetimeKind::Ampersand;
let mut sugg_is_str_to_string = false;
let mut sugg = vec![(lt.span, String::new())];
if let Some((kind, _span)) = self.diag_metadata.current_function
&& let FnKind::Fn(_, _, ast::Fn { sig, .. }) = kind
&& let ast::FnRetTy::Ty(ty) = &sig.decl.output
{
let mut lt_finder =
LifetimeFinder { lifetime: lt.span, found: None, seen: vec![] };
lt_finder.visit_ty(&ty);
if let [Ty { span, kind: TyKind::Ref(_, mut_ty), .. }] =
&lt_finder.seen[..]
{
// We might have a situation like
// fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()>
// but `lt.span` only points at `'_`, so to suggest `-> Option<()>`
// we need to find a more accurate span to end up with
// fn g<'a>(mut x: impl Iterator<Item = &'_ ()>) -> Option<()>
sugg = vec![(span.with_hi(mut_ty.ty.span.lo()), String::new())];
owned_sugg = true;
for param in &sig.decl.inputs {
lt_finder.visit_ty(&param.ty);
}
if let ast::FnRetTy::Ty(ret_ty) = &sig.decl.output {
lt_finder.visit_ty(ret_ty);
let mut ret_lt_finder =
LifetimeFinder { lifetime: lt.span, found: None, seen: vec![] };
ret_lt_finder.visit_ty(ret_ty);
if let [Ty { span, kind: TyKind::Ref(_, mut_ty), .. }] =
&ret_lt_finder.seen[..]
{
// We might have a situation like
// fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()>
// but `lt.span` only points at `'_`, so to suggest `-> Option<()>`
// we need to find a more accurate span to end up with
// fn g<'a>(mut x: impl Iterator<Item = &'_ ()>) -> Option<()>
sugg = vec![(span.with_hi(mut_ty.ty.span.lo()), String::new())];
owned_sugg = true;
}
}
if let Some(ty) = lt_finder.found {
if let TyKind::Path(None, path) = &ty.kind {
@ -3875,6 +3882,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
lt.span.with_hi(ty.span.hi()),
"String".to_string(),
)];
sugg_is_str_to_string = true;
}
Some(Res::PrimTy(..)) => {}
Some(Res::Def(
@ -3901,6 +3909,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
lt.span.with_hi(ty.span.hi()),
"String".to_string(),
)];
sugg_is_str_to_string = true;
}
Res::PrimTy(..) => {}
Res::Def(
@ -3935,6 +3944,12 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
}
}
if owned_sugg {
if let Some(span) =
self.find_ref_prefix_span_for_owned_suggestion(lt.span)
&& !sugg_is_str_to_string
{
sugg = vec![(span, String::new())];
}
err.multipart_suggestion_verbose(
format!("{pre} to return an owned value"),
sugg,
@ -3961,6 +3976,23 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
}
}
}
fn find_ref_prefix_span_for_owned_suggestion(&self, lifetime: Span) -> Option<Span> {
let mut finder = RefPrefixSpanFinder { lifetime, span: None };
if let Some(item) = self.diag_metadata.current_item {
finder.visit_item(item);
} else if let Some((kind, _span)) = self.diag_metadata.current_function
&& let FnKind::Fn(_, _, ast::Fn { sig, .. }) = kind
{
for param in &sig.decl.inputs {
finder.visit_ty(&param.ty);
}
if let ast::FnRetTy::Ty(ret_ty) = &sig.decl.output {
finder.visit_ty(ret_ty);
}
}
finder.span
}
}
fn mk_where_bound_predicate(
@ -4058,6 +4090,26 @@ impl<'ast> Visitor<'ast> for LifetimeFinder<'ast> {
}
}
struct RefPrefixSpanFinder {
lifetime: Span,
span: Option<Span>,
}
impl<'ast> Visitor<'ast> for RefPrefixSpanFinder {
fn visit_ty(&mut self, t: &'ast Ty) {
if self.span.is_some() {
return;
}
if let TyKind::Ref(_, mut_ty) | TyKind::PinnedRef(_, mut_ty) = &t.kind
&& t.span.lo() == self.lifetime.lo()
{
self.span = Some(t.span.with_hi(mut_ty.ty.span.lo()));
return;
}
walk_ty(self, t);
}
}
/// Shadowing involving a label is only a warning for historical reasons.
//FIXME: make this a proper lint.
pub(super) fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {