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matthiaskrgrmatthiaskrgr
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Rollup merge of rust-lang#116553 - gurry:116464-assoc-type-invalid-suggestion, r=compiler-errors
Do not suggest 'Trait<Assoc=arg>' when in trait impl Fixes rust-lang#116464 We now skip the suggestion if we're in an impl of the trait.
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‎compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs‎

Lines changed: 57 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -129,6 +129,44 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
129129
if self.missing_lifetimes() { "lifetime" } else { "generic" }
130130
}
131131

132+
/// Returns true if the generic type is a trait
133+
/// and is being referred to from one of its trait impls
134+
fn is_in_trait_impl(&self) -> bool {
135+
if self.tcx.is_trait(self.def_id) {
136+
// Here we check if the reference to the generic type
137+
// is from the 'of_trait' field of the enclosing impl
138+
139+
let parent = self.tcx.hir().get_parent(self.path_segment.hir_id);
140+
let parent_item = self
141+
.tcx
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.hir()
143+
.get_by_def_id(self.tcx.hir().get_parent_item(self.path_segment.hir_id).def_id);
144+
145+
// Get the HIR id of the trait ref
146+
let hir::Node::TraitRef(hir::TraitRef { hir_ref_id: trait_ref_id, .. }) = parent else {
147+
return false;
148+
};
149+
150+
// Get the HIR id of the 'of_trait' field of the impl
151+
let hir::Node::Item(hir::Item {
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kind:
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hir::ItemKind::Impl(hir::Impl {
154+
of_trait: Some(hir::TraitRef { hir_ref_id: id_in_of_trait, .. }),
155+
..
156+
}),
157+
..
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}) = parent_item
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else {
160+
return false;
161+
};
162+
163+
// Check that trait is referred to from the of_trait field of impl
164+
trait_ref_id == id_in_of_trait
165+
} else {
166+
false
167+
}
168+
}
169+
132170
fn num_provided_args(&self) -> usize {
133171
if self.missing_lifetimes() {
134172
self.num_provided_lifetime_args()
@@ -955,20 +993,26 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
955993
// If there is a single unbound associated type and a single excess generic param
956994
// suggest replacing the generic param with the associated type bound
957995
if provided_args_matches_unbound_traits && !unbound_types.is_empty() {
958-
let unused_generics = &self.gen_args.args[self.num_expected_type_or_const_args()..];
959-
let suggestions = iter::zip(unused_generics, &unbound_types)
960-
.map(|(potential, name)| (potential.span().shrink_to_lo(), format!("{name} = ")))
961-
.collect::<Vec<_>>();
996+
// Don't suggest if we're in a trait impl as
997+
// that would result in invalid syntax (fixes #116464)
998+
if !self.is_in_trait_impl() {
999+
let unused_generics = &self.gen_args.args[self.num_expected_type_or_const_args()..];
1000+
let suggestions = iter::zip(unused_generics, &unbound_types)
1001+
.map(|(potential, name)| {
1002+
(potential.span().shrink_to_lo(), format!("{name} = "))
1003+
})
1004+
.collect::<Vec<_>>();
9621005

963-
if !suggestions.is_empty() {
964-
err.multipart_suggestion_verbose(
965-
format!(
966-
"replace the generic bound{s} with the associated type{s}",
967-
s = pluralize!(unbound_types.len())
968-
),
969-
suggestions,
970-
Applicability::MaybeIncorrect,
971-
);
1006+
if !suggestions.is_empty() {
1007+
err.multipart_suggestion_verbose(
1008+
format!(
1009+
"replace the generic bound{s} with the associated type{s}",
1010+
s = pluralize!(unbound_types.len())
1011+
),
1012+
suggestions,
1013+
Applicability::MaybeIncorrect,
1014+
);
1015+
}
9721016
}
9731017
} else if remove_entire_generics {
9741018
let span = self

‎tests/ui/traits/associated_type_bound/116464-invalid-assoc-type-suggestion-in-trait-impl.rs‎

Lines changed: 43 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
1+
// Regression test for #116464
2+
// Checks that we do not suggest Trait<..., Assoc=arg> when the trait
3+
// is referred to from one of its impls but do so at all other places
4+
5+
pub trait Trait<T> {
6+
type Assoc;
7+
}
8+
9+
impl<T, S> Trait<T> for i32 {
10+
type Assoc = String;
11+
}
12+
13+
// Should not not trigger suggestion here...
14+
impl<T, S> Trait<T, S> for () {}
15+
//~^ ERROR trait takes 1 generic argument but 2 generic arguments were supplied
16+
17+
//... but should do so in all of the below cases except the last one
18+
fn func<T: Trait<u32, String>>(t: T) -> impl Trait<(), i32> {
19+
//~^ ERROR trait takes 1 generic argument but 2 generic arguments were supplied
20+
//~| ERROR trait takes 1 generic argument but 2 generic arguments were supplied
21+
3
22+
}
23+
24+
struct Struct<T: Trait<u32, String>> {
25+
//~^ ERROR trait takes 1 generic argument but 2 generic arguments were supplied
26+
a: T
27+
}
28+
29+
trait AnotherTrait<T: Trait<T, i32>> {}
30+
//~^ ERROR trait takes 1 generic argument but 2 generic arguments were supplied
31+
32+
impl<T: Trait<u32, String>> Struct<T> {}
33+
//~^ ERROR trait takes 1 generic argument but 2 generic arguments were supplied
34+
35+
// Test for self type. Should not trigger suggestion as it doesn't have an
36+
// associated type
37+
trait YetAnotherTrait {}
38+
impl<T: Trait<u32, Assoc=String>, U> YetAnotherTrait for Struct<T, U> {}
39+
//~^ ERROR struct takes 1 generic argument but 2 generic arguments were supplied
40+
41+
42+
fn main() {
43+
}

‎tests/ui/traits/associated_type_bound/116464-invalid-assoc-type-suggestion-in-trait-impl.stderr‎

Lines changed: 109 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,109 @@
1+
error[E0107]: trait takes 1 generic argument but 2 generic arguments were supplied
2+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:14:12
3+
|
4+
LL | impl<T, S> Trait<T, S> for () {}
5+
| ^^^^^ expected 1 generic argument
6+
|
7+
note: trait defined here, with 1 generic parameter: `T`
8+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:5:11
9+
|
10+
LL | pub trait Trait<T> {
11+
| ^^^^^ -
12+
13+
error[E0107]: trait takes 1 generic argument but 2 generic arguments were supplied
14+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:18:12
15+
|
16+
LL | fn func<T: Trait<u32, String>>(t: T) -> impl Trait<(), i32> {
17+
| ^^^^^ expected 1 generic argument
18+
|
19+
note: trait defined here, with 1 generic parameter: `T`
20+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:5:11
21+
|
22+
LL | pub trait Trait<T> {
23+
| ^^^^^ -
24+
help: replace the generic bound with the associated type
25+
|
26+
LL | fn func<T: Trait<u32, Assoc = String>>(t: T) -> impl Trait<(), i32> {
27+
| +++++++
28+
29+
error[E0107]: trait takes 1 generic argument but 2 generic arguments were supplied
30+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:18:46
31+
|
32+
LL | fn func<T: Trait<u32, String>>(t: T) -> impl Trait<(), i32> {
33+
| ^^^^^ expected 1 generic argument
34+
|
35+
note: trait defined here, with 1 generic parameter: `T`
36+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:5:11
37+
|
38+
LL | pub trait Trait<T> {
39+
| ^^^^^ -
40+
help: replace the generic bound with the associated type
41+
|
42+
LL | fn func<T: Trait<u32, String>>(t: T) -> impl Trait<(), Assoc = i32> {
43+
| +++++++
44+
45+
error[E0107]: trait takes 1 generic argument but 2 generic arguments were supplied
46+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:24:18
47+
|
48+
LL | struct Struct<T: Trait<u32, String>> {
49+
| ^^^^^ expected 1 generic argument
50+
|
51+
note: trait defined here, with 1 generic parameter: `T`
52+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:5:11
53+
|
54+
LL | pub trait Trait<T> {
55+
| ^^^^^ -
56+
help: replace the generic bound with the associated type
57+
|
58+
LL | struct Struct<T: Trait<u32, Assoc = String>> {
59+
| +++++++
60+
61+
error[E0107]: trait takes 1 generic argument but 2 generic arguments were supplied
62+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:29:23
63+
|
64+
LL | trait AnotherTrait<T: Trait<T, i32>> {}
65+
| ^^^^^ expected 1 generic argument
66+
|
67+
note: trait defined here, with 1 generic parameter: `T`
68+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:5:11
69+
|
70+
LL | pub trait Trait<T> {
71+
| ^^^^^ -
72+
help: replace the generic bound with the associated type
73+
|
74+
LL | trait AnotherTrait<T: Trait<T, Assoc = i32>> {}
75+
| +++++++
76+
77+
error[E0107]: trait takes 1 generic argument but 2 generic arguments were supplied
78+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:32:9
79+
|
80+
LL | impl<T: Trait<u32, String>> Struct<T> {}
81+
| ^^^^^ expected 1 generic argument
82+
|
83+
note: trait defined here, with 1 generic parameter: `T`
84+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:5:11
85+
|
86+
LL | pub trait Trait<T> {
87+
| ^^^^^ -
88+
help: replace the generic bound with the associated type
89+
|
90+
LL | impl<T: Trait<u32, Assoc = String>> Struct<T> {}
91+
| +++++++
92+
93+
error[E0107]: struct takes 1 generic argument but 2 generic arguments were supplied
94+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:38:58
95+
|
96+
LL | impl<T: Trait<u32, Assoc=String>, U> YetAnotherTrait for Struct<T, U> {}
97+
| ^^^^^^ - help: remove this generic argument
98+
| |
99+
| expected 1 generic argument
100+
|
101+
note: struct defined here, with 1 generic parameter: `T`
102+
--> $DIR/116464-invalid-assoc-type-suggestion-in-trait-impl.rs:24:8
103+
|
104+
LL | struct Struct<T: Trait<u32, String>> {
105+
| ^^^^^^ -
106+
107+
error: aborting due to 7 previous errors
108+
109+
For more information about this error, try `rustc --explain E0107`.

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