Skip to content

Fix lifetime suggestion for type aliases with objects in them #110827

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
May 8, 2023
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 13 additions & 3 deletions compiler/rustc_borrowck/src/diagnostics/region_errors.rs
Original file line number Diff line number Diff line change
Expand Up @@ -845,7 +845,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
return;
}

let Some((alias_tys, alias_span)) = self
let Some((alias_tys, alias_span, lt_addition_span)) = self
.infcx
.tcx
.return_type_impl_or_dyn_traits_with_type_alias(suitable_region.def_id) else { return; };
Expand All @@ -858,10 +858,20 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
()
}
if let TyKind::TraitObject(_, lt, _) = alias_ty.kind {
spans_suggs.push((lt.ident.span.shrink_to_hi(), " + 'a".to_string()));
if lt.ident.name == kw::Empty {
spans_suggs.push((lt.ident.span.shrink_to_hi(), " + 'a".to_string()));
} else {
spans_suggs.push((lt.ident.span, "'a".to_string()));
}
}
}
spans_suggs.push((alias_span.shrink_to_hi(), "<'a>".to_string()));

if let Some(lt_addition_span) = lt_addition_span {
spans_suggs.push((lt_addition_span, "'a, ".to_string()));
} else {
spans_suggs.push((alias_span.shrink_to_hi(), "<'a>".to_string()));
}

diag.multipart_suggestion_verbose(
&format!(
"to declare that the trait object {captures}, you can add a lifetime parameter `'a` in the type alias"
Expand Down
8 changes: 5 additions & 3 deletions compiler/rustc_middle/src/ty/context.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1116,11 +1116,13 @@ impl<'tcx> TyCtxt<'tcx> {
v.0
}

/// Given a `DefId` for an `fn`, return all the `dyn` and `impl` traits in its return type and associated alias span when type alias is used
/// Given a `DefId` for an `fn`, return all the `dyn` and `impl` traits in
/// its return type, and the associated alias span when type alias is used,
/// along with a span for lifetime suggestion (if there are existing generics).
pub fn return_type_impl_or_dyn_traits_with_type_alias(
self,
scope_def_id: LocalDefId,
) -> Option<(Vec<&'tcx hir::Ty<'tcx>>, Span)> {
) -> Option<(Vec<&'tcx hir::Ty<'tcx>>, Span, Option<Span>)> {
let hir_id = self.hir().local_def_id_to_hir_id(scope_def_id);
let mut v = TraitObjectVisitor(vec![], self.hir());
// when the return type is a type alias
Expand All @@ -1134,7 +1136,7 @@ impl<'tcx> TyCtxt<'tcx> {
{
v.visit_ty(alias_ty);
if !v.0.is_empty() {
return Some((v.0, alias_generics.span));
return Some((v.0, alias_generics.span, alias_generics.span_for_lifetime_suggestion()));
}
}
return None;
Expand Down
11 changes: 11 additions & 0 deletions tests/ui/borrowck/suggest-lt-on-ty-alias-w-generics.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
type Lazy<T> = Box<dyn Fn() -> T + 'static>;

fn test(x: &i32) -> Lazy<i32> {
Box::new(|| {
//~^ ERROR lifetime may not live long enough
//~| ERROR closure may outlive the current function
*x
})
}

fn main() {}
43 changes: 43 additions & 0 deletions tests/ui/borrowck/suggest-lt-on-ty-alias-w-generics.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
error: lifetime may not live long enough
--> $DIR/suggest-lt-on-ty-alias-w-generics.rs:4:5
|
LL | fn test(x: &i32) -> Lazy<i32> {
| - let's call the lifetime of this reference `'1`
LL | / Box::new(|| {
LL | |
LL | |
LL | | *x
LL | | })
| |______^ returning this value requires that `'1` must outlive `'static`
|
help: to declare that the trait object captures data from argument `x`, you can add a lifetime parameter `'a` in the type alias
|
LL | type Lazy<'a, T> = Box<dyn Fn() -> T + 'a>;
| +++ ~~

error[E0373]: closure may outlive the current function, but it borrows `x`, which is owned by the current function
--> $DIR/suggest-lt-on-ty-alias-w-generics.rs:4:14
|
LL | Box::new(|| {
| ^^ may outlive borrowed value `x`
...
LL | *x
| -- `x` is borrowed here
|
note: closure is returned here
--> $DIR/suggest-lt-on-ty-alias-w-generics.rs:4:5
|
LL | / Box::new(|| {
LL | |
LL | |
LL | | *x
LL | | })
| |______^
help: to force the closure to take ownership of `x` (and any other referenced variables), use the `move` keyword
|
LL | Box::new(move || {
| ++++

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0373`.