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This commit is contained in:
Esteban Küber 2019-12-22 17:53:50 -08:00
parent eb0f4d51df
commit 3811232190
6 changed files with 24 additions and 46 deletions
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58
src/librustc_infer/infer/error_reporting/nice_region_error/trait_impl_difference.rs
View file

@ -63,22 +63,25 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
err.span_label(trait_sp, &format!("expected {:?}", expected));
let trait_fn_sig = tcx.fn_sig(trait_def_id);
// Check the `trait`'s method's output to look for type parameters that might have
// unconstrained lifetimes. If the method returns a type parameter and the `impl` has a
// borrow as the type parameter being implemented, the lifetimes will not match because
// a new lifetime is being introduced in the `impl` that is not present in the `trait`.
// Because this is confusing as hell the first time you see it, we give a short message
// explaining the situation and proposing constraining the type param with a named lifetime
// so that the `impl` will have one to tie them together.
struct AssocTypeFinder(FxHashSet<ty::ParamTy>);
impl<'tcx> ty::fold::TypeVisitor<'tcx> for AssocTypeFinder {
fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
debug!("assoc type finder ty {:?} {:?}", ty, ty.kind);
match ty.kind {
ty::Param(param) => {
self.0.insert(param);
}
_ => {}
if let ty::Param(param) = ty.kind {
self.0.insert(param);
}
ty.super_visit_with(self)
}
}
let mut visitor = AssocTypeFinder(FxHashSet::default());
trait_fn_sig.output().visit_with(&mut visitor);
if let Some(id) = tcx.hir().as_local_hir_id(trait_def_id) {
let parent_id = tcx.hir().get_parent_item(id);
let trait_item = tcx.hir().expect_item(parent_id);
@ -86,8 +89,8 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
for param_ty in visitor.0 {
if let Some(generic) = generics.get_named(param_ty.name) {
err.span_label(generic.span, &format!(
"in order for `impl` items to be able to implement the method, this \
type parameter might need a lifetime restriction like `{}: 'a`",
"for `impl` items to implement the method, this type parameter might \
need a lifetime restriction like `{}: 'a`",
param_ty.name,
));
}
@ -95,46 +98,21 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
}
}
struct EarlyBoundRegionHighlighter(FxHashSet<DefId>);
impl<'tcx> ty::fold::TypeVisitor<'tcx> for EarlyBoundRegionHighlighter {
fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
match *r {
ty::ReFree(free) => {
self.0.insert(free.scope);
}
ty::ReEarlyBound(bound) => {
self.0.insert(bound.def_id);
}
_ => {}
}
r.super_visit_with(self)
}
}
let mut visitor = EarlyBoundRegionHighlighter(FxHashSet::default());
expected.visit_with(&mut visitor);
let note = !visitor.0.is_empty();
if let Some((expected, found)) = self
.tcx()
if let Some((expected, found)) = tcx
.infer_ctxt()
.enter(|infcx| infcx.expected_found_str_ty(&ExpectedFound { expected, found }))
{
// Highlighted the differences when showing the "expected/found" note.
err.note_expected_found(&"", expected, &"", found);
} else {
// This fallback shouldn't be necessary, but let's keep it in just in case.
err.note(&format!("expected `{:?}`\n found `{:?}`", expected, found));
}
if note {
err.note(
"the lifetime requirements from the `trait` could not be fulfilled by the `impl`",
);
err.help(
"verify the lifetime relationships in the `trait` and `impl` between the \
`self` argument, the other inputs and its output",
);
}
err.note("the lifetime requirements from the `trait` could not be satisfied by the `impl`");
err.help(
"verify the lifetime relationships in the `trait` and `impl` between the `self` \
argument, the other inputs and its output",
);
err.emit();
}
}

2
src/test/ui/in-band-lifetimes/mismatched_trait_impl-2.stderr
View file

@ -11,7 +11,7 @@ LL | fn deref(&self) -> &Self::Target;
|
= note: expected `fn(&Struct) -> &(dyn Trait + 'static)`
found `fn(&Struct) -> &dyn Trait`
= note: the lifetime requirements from the `trait` could not be fulfilled by the `impl`
= note: the lifetime requirements from the `trait` could not be satisfied by the `impl`
= help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
error: aborting due to previous error

2
src/test/ui/in-band-lifetimes/mismatched_trait_impl.nll.stderr
View file

@ -9,7 +9,7 @@ LL | fn foo(&self, x: &u32, y: &'a u32) -> &'a u32 {
|
= note: expected `fn(&i32, &'a u32, &u32) -> &'a u32`
found `fn(&i32, &u32, &u32) -> &u32`
= note: the lifetime requirements from the `trait` could not be fulfilled by the `impl`
= note: the lifetime requirements from the `trait` could not be satisfied by the `impl`
= help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
error: aborting due to previous error

2
src/test/ui/in-band-lifetimes/mismatched_trait_impl.stderr
View file

@ -9,7 +9,7 @@ LL | fn foo(&self, x: &u32, y: &'a u32) -> &'a u32 {
|
= note: expected `fn(&i32, &'a u32, &u32) -> &'a u32`
found `fn(&i32, &u32, &u32) -> &u32`
= note: the lifetime requirements from the `trait` could not be fulfilled by the `impl`
= note: the lifetime requirements from the `trait` could not be satisfied by the `impl`
= help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
error[E0623]: lifetime mismatch

2
src/test/ui/lifetimes/lifetime-mismatch-between-trait-and-impl.stderr
View file

@ -9,7 +9,7 @@ LL | fn foo<'a>(x: &'a i32, y: &'a i32) -> &'a i32 {
|
= note: expected `fn(&i32, &'a i32) -> &'a i32`
found `fn(&i32, &i32) -> &i32`
= note: the lifetime requirements from the `trait` could not be fulfilled by the `impl`
= note: the lifetime requirements from the `trait` could not be satisfied by the `impl`
= help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
error: aborting due to previous error

4
src/test/ui/traits/trait-param-without-lifetime-constraint.stderr
View file

@ -2,7 +2,7 @@ error: `impl` item signature doesn't match `trait` item signature
--> $DIR/trait-param-without-lifetime-constraint.rs:14:5
|
LL | pub trait HaveRelationship<To> {
| -- in order for `impl` items to be able to implement the method, this type parameter might need a lifetime restriction like `To: 'a`
| -- for `impl` items to implement the method, this type parameter might need a lifetime restriction like `To: 'a`
LL | fn get_relation(&self) -> To;
| ----------------------------- expected fn(&Article) -> &ProofReader
...
@ -11,7 +11,7 @@ LL | fn get_relation(&self) -> &ProofReader {
|
= note: expected `fn(&Article) -> &ProofReader`
found `fn(&Article) -> &ProofReader`
= note: the lifetime requirements from the `trait` could not be fulfilled by the `impl`
= note: the lifetime requirements from the `trait` could not be satisfied by the `impl`
= help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
error: aborting due to previous error