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review comments: change wording and visual output

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This commit is contained in:
Esteban Küber 2020-05-27 20:58:05 -07:00
parent cb6408afc6
commit f213acf4db
6 changed files with 26 additions and 59 deletions
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63
src/librustc_infer/infer/error_reporting/nice_region_error/trait_impl_difference.rs
View file

@ -4,16 +4,13 @@ use crate::infer::error_reporting::nice_region_error::NiceRegionError;
use crate::infer::lexical_region_resolve::RegionResolutionError;
use crate::infer::{Subtype, TyCtxtInferExt, ValuePairs};
use crate::traits::ObligationCauseCode::CompareImplMethodObligation;
use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::ErrorReported;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::intravisit::Visitor;
use rustc_hir::ItemKind;
use rustc_middle::ty::error::ExpectedFound;
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_span::Span;
use rustc_span::{MultiSpan, Span};
impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
/// Print the error message for lifetime errors when the `impl` doesn't conform to the `trait`.
@ -63,41 +60,6 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
.struct_span_err(sp, "`impl` item signature doesn't match `trait` item signature");
err.span_label(sp, &format!("found `{:?}`", found));
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(FxIndexSet<ty::ParamTy>);
impl<'tcx> ty::fold::TypeVisitor<'tcx> for AssocTypeFinder {
fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
if let ty::Param(param) = ty.kind {
self.0.insert(param);
}
ty.super_visit_with(self)
}
}
let mut visitor = AssocTypeFinder(FxIndexSet::default());
trait_fn_sig.output().visit_with(&mut visitor);
if let Some(id) = trait_def_id.as_local().map(|id| tcx.hir().as_local_hir_id(id)) {
let parent_id = tcx.hir().get_parent_item(id);
let trait_item = tcx.hir().expect_item(parent_id);
if let ItemKind::Trait(_, _, generics, _, _) = &trait_item.kind {
for param_ty in &visitor.0 {
if let Some(generic) = generics.get_named(param_ty.name) {
err.span_label(
generic.span,
"this type parameter might not have a lifetime compatible with the \
`impl`",
);
}
}
}
}
// Get the span of all the used type parameters in the method.
let assoc_item = self.tcx().associated_item(trait_def_id);
@ -114,11 +76,12 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
}
_ => {}
}
for span in visitor.types {
err.span_label(
let mut type_param_span: MultiSpan =
visitor.types.iter().cloned().collect::<Vec<_>>().into();
for &span in &visitor.types {
type_param_span.push_span_label(
span,
"you might want to borrow this type parameter in the trait to make it match the \
`impl`",
"consider borrowing this type parameter in the trait".to_string(),
);
}
@ -132,11 +95,17 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
// This fallback shouldn't be necessary, but let's keep it in just in case.
err.note(&format!("expected `{:?}`\n found `{:?}`", expected, found));
}
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.span_help(
type_param_span,
"the lifetime requirements from the `impl` do not correspond to the requirements in \
the `trait`",
);
if visitor.types.is_empty() {
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 satisfied by the `impl`
= help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
= 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 satisfied by the `impl`
= help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
= 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 satisfied by the `impl`
= help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
= 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 satisfied by the `impl`
= help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
= 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

14
src/test/ui/traits/trait-param-without-lifetime-constraint.stderr
View file

@ -1,21 +1,19 @@
error: `impl` item signature doesn't match `trait` item signature
--> $DIR/trait-param-without-lifetime-constraint.rs:14:5
|
LL | pub trait HaveRelationship<To> {
| -- this type parameter might not have a lifetime compatible with the `impl`
LL | fn get_relation(&self) -> To;
| -----------------------------
| | |
| | you might want to borrow this type parameter in the trait to make it match the `impl`
| expected `fn(&Article) -> &ProofReader`
| ----------------------------- expected `fn(&Article) -> &ProofReader`
...
LL | fn get_relation(&self) -> &ProofReader {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(&Article) -> &ProofReader`
|
= note: expected `fn(&Article) -> &ProofReader`
found `fn(&Article) -> &ProofReader`
= 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
help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
--> $DIR/trait-param-without-lifetime-constraint.rs:10:31
|
LL | fn get_relation(&self) -> To;
| ^^ consider borrowing this type parameter in the trait
error: aborting due to previous error