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diagnostics: Box<dyn Trait> suggestion with multiple matching impl

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The two altered expectation messages both seem like improvements:

- `coerce-expect-unsized-ascribed.stderr` says you can go
  `Box<char> -> Box<dyn Debug>`, which you can.
- `upcast_soundness_bug.stderr` used to say that you could go
  `Box<dyn Trait<u8, u8>> -> Box<dyn Trait>`, which you can't,
  because the type parameters are missing in the destination
  and the only ones that work aren't what's needed.
This commit is contained in:
Michael Howell 2024-08-06 18:18:15 -07:00
parent 1b587a6e76
commit 20c833c632
3 changed files with 13 additions and 16 deletions
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24
compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
View File

@ -313,11 +313,9 @@ fn foo(&self, x: T) -> T { x }
(ty::Dynamic(t, _, ty::DynKind::Dyn), _)
if let Some(def_id) = t.principal_def_id() =>
{
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, values.found, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let has_non_blanket_impl =
tcx.non_blanket_impls_for_ty(def_id, values.found).next().is_some();
if has_non_blanket_impl {
let trait_name = tcx.item_name(def_id);
diag.help(format!(
"`{}` implements `{trait_name}` so you could box the found value \
@ -330,11 +328,9 @@ fn foo(&self, x: T) -> T { x }
(_, ty::Dynamic(t, _, ty::DynKind::Dyn))
if let Some(def_id) = t.principal_def_id() =>
{
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, values.expected, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let has_non_blanket_impl =
tcx.non_blanket_impls_for_ty(def_id, values.expected).next().is_some();
if has_non_blanket_impl {
let trait_name = tcx.item_name(def_id);
diag.help(format!(
"`{}` implements `{trait_name}` so you could change the expected \
@ -346,11 +342,9 @@ fn foo(&self, x: T) -> T { x }
(ty::Dynamic(t, _, ty::DynKind::DynStar), _)
if let Some(def_id) = t.principal_def_id() =>
{
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, values.found, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let has_non_blanket_impl =
tcx.non_blanket_impls_for_ty(def_id, values.found).next().is_some();
if has_non_blanket_impl {
let trait_name = tcx.item_name(def_id);
diag.help(format!(
"`{}` implements `{trait_name}`, `#[feature(dyn_star)]` is likely \

4
tests/ui/coercion/coerce-expect-unsized-ascribed.stderr
View File

@ -42,6 +42,7 @@ LL | let _ = type_ascribe!(Box::new( if true { false } else { true }), Box<d
|
= note: expected struct `Box<dyn Debug>`
found struct `Box<bool>`
= help: `bool` implements `Debug` so you could box the found value and coerce it to the trait object `Box<dyn Debug>`, you will have to change the expected type as well
error[E0308]: mismatched types
--> $DIR/coerce-expect-unsized-ascribed.rs:16:27
@ -51,6 +52,7 @@ LL | let _ = type_ascribe!(Box::new( match true { true => 'a', false => 'b'
|
= note: expected struct `Box<dyn Debug>`
found struct `Box<char>`
= help: `char` implements `Debug` so you could box the found value and coerce it to the trait object `Box<dyn Debug>`, you will have to change the expected type as well
error[E0308]: mismatched types
--> $DIR/coerce-expect-unsized-ascribed.rs:18:27
@ -96,6 +98,7 @@ LL | let _ = type_ascribe!(&if true { false } else { true }, &dyn Debug);
|
= note: expected reference `&dyn Debug`
found reference `&bool`
= help: `bool` implements `Debug` so you could box the found value and coerce it to the trait object `Box<dyn Debug>`, you will have to change the expected type as well
error[E0308]: mismatched types
--> $DIR/coerce-expect-unsized-ascribed.rs:24:27
@ -105,6 +108,7 @@ LL | let _ = type_ascribe!(&match true { true => 'a', false => 'b' }, &dyn D
|
= note: expected reference `&dyn Debug`
found reference `&char`
= help: `char` implements `Debug` so you could box the found value and coerce it to the trait object `Box<dyn Debug>`, you will have to change the expected type as well
error[E0308]: mismatched types
--> $DIR/coerce-expect-unsized-ascribed.rs:26:27

1
tests/ui/traits/upcast_soundness_bug.stderr
View File

@ -6,7 +6,6 @@ LL | let p = p as *const dyn Trait<u8, u16>; // <- this is bad!
|
= note: expected trait object `dyn Trait<u8, u8>`
found trait object `dyn Trait<u8, u16>`
= help: `dyn Trait<u8, u16>` implements `Trait` so you could box the found value and coerce it to the trait object `Box<dyn Trait>`, you will have to change the expected type as well
error: aborting due to 1 previous error