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Fix rust-lang#90970, doesn't address rust-lang#87437 
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8 files changed

+115
-6
lines changed

8 files changed

+115
-6
lines changed

‎compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

+73-6
Original file line numberDiff line numberDiff line change
@@ -2,10 +2,11 @@ pub mod on_unimplemented;
22
pub mod suggestions;
33

44
use super::{
5-
EvaluationResult, FulfillmentContext, FulfillmentError, FulfillmentErrorCode,
6-
MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
7-
OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
8-
PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
5+
DerivedObligationCause, EvaluationResult, FulfillmentContext, FulfillmentError,
6+
FulfillmentErrorCode, ImplDerivedObligationCause, MismatchedProjectionTypes, Obligation,
7+
ObligationCause, ObligationCauseCode, OnUnimplementedDirective, OnUnimplementedNote,
8+
OutputTypeParameterMismatch, Overflow, PredicateObligation, SelectionContext, SelectionError,
9+
TraitNotObjectSafe,
910
};
1011

1112
use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
@@ -654,11 +655,77 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
654655
} else if !suggested {
655656
// Can't show anything else useful, try to find similar impls.
656657
let impl_candidates = self.find_similar_impl_candidates(trait_ref);
657-
self.report_similar_impl_candidates(
658+
if !self.report_similar_impl_candidates(
658659
impl_candidates,
659660
trait_ref,
660661
&mut err,
661-
);
662+
) {
663+
// This is *almost* equivalent to
664+
// `obligation.cause.code().peel_derives()`, but it gives us the
665+
// trait predicate for that corresponding root obligation. This
666+
// lets us get a derived obligation from a type parameter, like
667+
// when calling `string.strip_suffix(p)` where `p` is *not* an
668+
// implementer of `Pattern<'_>`.
669+
let mut code = obligation.cause.code();
670+
let mut trait_pred = trait_predicate;
671+
let mut peeled = false;
672+
loop {
673+
match &*code {
674+
ObligationCauseCode::FunctionArgumentObligation {
675+
parent_code,
676+
..
677+
} => {
678+
code = &parent_code;
679+
}
680+
ObligationCauseCode::ImplDerivedObligation(
681+
box ImplDerivedObligationCause {
682+
derived:
683+
DerivedObligationCause {
684+
parent_code,
685+
parent_trait_pred,
686+
},
687+
..
688+
},
689+
)
690+
| ObligationCauseCode::BuiltinDerivedObligation(
691+
DerivedObligationCause {
692+
parent_code,
693+
parent_trait_pred,
694+
},
695+
)
696+
| ObligationCauseCode::DerivedObligation(
697+
DerivedObligationCause {
698+
parent_code,
699+
parent_trait_pred,
700+
},
701+
) => {
702+
peeled = true;
703+
code = &parent_code;
704+
trait_pred = *parent_trait_pred;
705+
}
706+
_ => break,
707+
};
708+
}
709+
let def_id = trait_pred.def_id();
710+
// Mention *all* the `impl`s for the *top most* obligation, the
711+
// user might have meant to use one of them, if any found. We skip
712+
// auto-traits or fundamental traits that might not be exactly what
713+
// the user might expect to be presented with. Instead this is
714+
// useful for less general traits.
715+
if peeled
716+
&& !self.tcx.trait_is_auto(def_id)
717+
&& !self.tcx.lang_items().items().contains(&Some(def_id))
718+
{
719+
let trait_ref = trait_pred.to_poly_trait_ref();
720+
let impl_candidates =
721+
self.find_similar_impl_candidates(trait_ref);
722+
self.report_similar_impl_candidates(
723+
impl_candidates,
724+
trait_ref,
725+
&mut err,
726+
);
727+
}
728+
}
662729
}
663730

664731
// Changing mutability doesn't make a difference to whether we have

‎src/test/ui/const-generics/generic_const_exprs/issue-85848.stderr

+1
Original file line numberDiff line numberDiff line change
@@ -6,6 +6,7 @@ LL | writes_to_specific_path(&cap);
66
| |
77
| required by a bound introduced by this call
88
|
9+
= help: the trait `Delegates<U>` is implemented for `T`
910
note: required because of the requirements on the impl of `Contains<(), true>` for `&C`
1011
--> $DIR/issue-85848.rs:21:12
1112
|

‎src/test/ui/impl-trait/cross-return-site-inference.stderr

+1
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,7 @@ LL | Err("whoops")?;
77
| ^ the trait `From<&str>` is not implemented for `impl Debug`
88
|
99
= note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
10+
= help: the trait `FromResidual<Result<Infallible, E>>` is implemented for `Result<T, F>`
1011
= note: required because of the requirements on the impl of `FromResidual<Result<Infallible, &str>>` for `Result<(), impl Debug>`
1112

1213
error[E0277]: the trait bound `impl Debug: From<&str>` is not satisfied

‎src/test/ui/impl-trait/nested_impl_trait.stderr

+2
Original file line numberDiff line numberDiff line change
@@ -52,6 +52,7 @@ error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfie
5252
LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
5353
| ^^^^^^^^^^^^^^^^^^^^^ the trait `From<impl Into<u32>>` is not implemented for `impl Debug`
5454
|
55+
= help: the trait `Into<U>` is implemented for `T`
5556
= note: required because of the requirements on the impl of `Into<impl Debug>` for `impl Into<u32>`
5657

5758
error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
@@ -60,6 +61,7 @@ error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfie
6061
LL | fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
6162
| ^^^^^^^^^^^^^^^^^^^^^ the trait `From<impl Into<u32>>` is not implemented for `impl Debug`
6263
|
64+
= help: the trait `Into<U>` is implemented for `T`
6365
= note: required because of the requirements on the impl of `Into<impl Debug>` for `impl Into<u32>`
6466

6567
error: aborting due to 8 previous errors

‎src/test/ui/issues/issue-32709.stderr

+1
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,7 @@ LL | Err(5)?;
77
| ^ the trait `From<{integer}>` is not implemented for `()`
88
|
99
= note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
10+
= help: the trait `FromResidual<Result<Infallible, E>>` is implemented for `Result<T, F>`
1011
= note: required because of the requirements on the impl of `FromResidual<Result<Infallible, {integer}>>` for `Result<i32, ()>`
1112

1213
error: aborting due to previous error

‎src/test/ui/kindck/kindck-impl-type-params.stderr

+2
Original file line numberDiff line numberDiff line change
@@ -80,6 +80,7 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
8080
LL | let a = t as Box<dyn Gettable<String>>;
8181
| ^ the trait `Copy` is not implemented for `String`
8282
|
83+
= help: the trait `Gettable<T>` is implemented for `S<T>`
8384
note: required because of the requirements on the impl of `Gettable<String>` for `S<String>`
8485
--> $DIR/kindck-impl-type-params.rs:14:32
8586
|
@@ -93,6 +94,7 @@ error[E0277]: the trait bound `Foo: Copy` is not satisfied
9394
LL | let a: Box<dyn Gettable<Foo>> = t;
9495
| ^ the trait `Copy` is not implemented for `Foo`
9596
|
97+
= help: the trait `Gettable<T>` is implemented for `S<T>`
9698
note: required because of the requirements on the impl of `Gettable<Foo>` for `S<Foo>`
9799
--> $DIR/kindck-impl-type-params.rs:14:32
98100
|

‎src/test/ui/traits/bound/assoc-fn-bound-root-obligation.rs

+12
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
1+
fn strip_lf(s: &str) -> &str {
2+
s.strip_suffix(b'\n').unwrap_or(s)
3+
//~^ ERROR expected a `FnMut<(char,)>` closure, found `u8`
4+
//~| NOTE expected an `FnMut<(char,)>` closure, found `u8`
5+
//~| NOTE required by a bound introduced by this call
6+
//~| HELP the trait `FnMut<(char,)>` is not implemented for `u8`
7+
//~| HELP the following other types implement trait `Pattern<'_>`:
8+
//~| NOTE required because of the requirements on the impl of `Pattern<'_>` for `u8`
9+
10+
}
11+
12+
fn main() {}

‎src/test/ui/traits/bound/assoc-fn-bound-root-obligation.stderr

+23
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,23 @@
1+
error[E0277]: expected a `FnMut<(char,)>` closure, found `u8`
2+
--> $DIR/assoc-fn-bound-root-obligation.rs:2:20
3+
|
4+
LL | s.strip_suffix(b'\n').unwrap_or(s)
5+
| ------------ ^^^^^ expected an `FnMut<(char,)>` closure, found `u8`
6+
| |
7+
| required by a bound introduced by this call
8+
|
9+
= help: the trait `FnMut<(char,)>` is not implemented for `u8`
10+
= help: the following other types implement trait `Pattern<'_>`:
11+
&'b String
12+
&'b [char; N]
13+
&'b [char]
14+
&'b str
15+
&'c &'b str
16+
[char; N]
17+
char
18+
pattern::MultiCharEqPattern<C>
19+
= note: required because of the requirements on the impl of `Pattern<'_>` for `u8`
20+
21+
error: aborting due to previous error
22+
23+
For more information about this error, try `rustc --explain E0277`.

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