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matthiaskrgrmatthiaskrgr
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Rollup merge of #132487 - dianne:include-trait-args-in-suggestion, r=fmease
Provide placeholder generics for traits in "no method found for type parameter" suggestions In the diagnostics for the error ``no method named `method` found for type parameter `T` in the current scope [E0599]``, the compiler will suggest adding bounds on `T` for traits that define a method named `method`. However, these suggestions didn't include any generic arguments, so applying them would result in a `missing generics for trait` or `missing lifetime specifier` error. This PR adds placeholder arguments to the suggestion in such cases. Specifically, I tried to base the placeholders off of what's done in suggestions for when generics are missing or too few are provided: - The placeholder for a parameter without a default is the name of the parameter. - Placeholders are not provided for parameters with defaults. Placeholder arguments are enclosed in `/*` and `*/`, and the applicability of the suggestion is downgraded to `Applicability::HasPlaceholders` if any placeholders are provided. Fixes #132407
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4 files changed

+137
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‎compiler/rustc_hir_typeck/src/lib.rs‎

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Original file line numberDiff line numberDiff line change
@@ -4,6 +4,7 @@
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#![feature(array_windows)]
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#![feature(box_patterns)]
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#![feature(if_let_guard)]
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#![feature(iter_intersperse)]
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#![feature(let_chains)]
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#![feature(never_type)]
910
#![feature(try_blocks)]

‎compiler/rustc_hir_typeck/src/method/suggest.rs‎

Lines changed: 43 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -3874,22 +3874,52 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
38743874
param.name.ident(),
38753875
));
38763876
let bounds_span = hir_generics.bounds_span_for_suggestions(def_id);
3877+
let mut applicability = Applicability::MaybeIncorrect;
3878+
// Format the path of each suggested candidate, providing placeholders
3879+
// for any generic arguments without defaults.
3880+
let candidate_strs: Vec<_> = candidates
3881+
.iter()
3882+
.map(|cand| {
3883+
let cand_path = self.tcx.def_path_str(cand.def_id);
3884+
let cand_params = &self.tcx.generics_of(cand.def_id).own_params;
3885+
let cand_args: String = cand_params
3886+
.iter()
3887+
.skip(1)
3888+
.filter_map(|param| match param.kind {
3889+
ty::GenericParamDefKind::Type {
3890+
has_default: true,
3891+
..
3892+
}
3893+
| ty::GenericParamDefKind::Const {
3894+
has_default: true,
3895+
..
3896+
} => None,
3897+
_ => Some(param.name.as_str()),
3898+
})
3899+
.intersperse(", ")
3900+
.collect();
3901+
if cand_args.is_empty() {
3902+
cand_path
3903+
} else {
3904+
applicability = Applicability::HasPlaceholders;
3905+
format!("{cand_path}</* {cand_args} */>")
3906+
}
3907+
})
3908+
.collect();
3909+
38773910
if rcvr_ty.is_ref()
38783911
&& param.is_impl_trait()
38793912
&& let Some((bounds_span, _)) = bounds_span
38803913
{
38813914
err.multipart_suggestions(
38823915
msg,
3883-
candidates.iter().map(|t| {
3916+
candidate_strs.iter().map(|cand| {
38843917
vec![
38853918
(param.span.shrink_to_lo(), "(".to_string()),
3886-
(
3887-
bounds_span,
3888-
format!(" + {})", self.tcx.def_path_str(t.def_id)),
3889-
),
3919+
(bounds_span, format!(" + {cand})")),
38903920
]
38913921
}),
3892-
Applicability::MaybeIncorrect,
3922+
applicability,
38933923
);
38943924
return;
38953925
}
@@ -3905,16 +3935,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
39053935
(param.span.shrink_to_hi(), Introducer::Colon, None)
39063936
};
39073937

3908-
let all_suggs = candidates.iter().map(|cand| {
3909-
let suggestion = format!(
3910-
"{} {}",
3911-
match introducer {
3912-
Introducer::Plus => " +",
3913-
Introducer::Colon => ":",
3914-
Introducer::Nothing => "",
3915-
},
3916-
self.tcx.def_path_str(cand.def_id)
3917-
);
3938+
let all_suggs = candidate_strs.iter().map(|cand| {
3939+
let suggestion = format!("{} {cand}", match introducer {
3940+
Introducer::Plus => " +",
3941+
Introducer::Colon => ":",
3942+
Introducer::Nothing => "",
3943+
},);
39183944

39193945
let mut suggs = vec![];
39203946

@@ -3928,11 +3954,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
39283954
suggs
39293955
});
39303956

3931-
err.multipart_suggestions(
3932-
msg,
3933-
all_suggs,
3934-
Applicability::MaybeIncorrect,
3935-
);
3957+
err.multipart_suggestions(msg, all_suggs, applicability);
39363958

39373959
return;
39383960
}

‎tests/ui/suggestions/no-method-found-suggest-trait-args.rs‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,30 @@
1+
/// Tests that suggestions to add trait bounds that would enable using a method include appropriate
2+
/// placeholder arguments for that trait.
3+
4+
trait Trait<I> {
5+
fn method(&self) {}
6+
}
7+
8+
trait Trait2<'a, A, const B: u8, C = (), const D: u8 = 0> {
9+
fn method2(&self) {}
10+
}
11+
12+
fn foo<T>(value: T) {
13+
//~^ SUGGESTION : Trait</* I */>
14+
//~| SUGGESTION : Trait2</* 'a, A, B */>
15+
value.method();
16+
//~^ ERROR no method named `method` found for type parameter `T` in the current scope [E0599]
17+
value.method2();
18+
//~^ ERROR no method named `method2` found for type parameter `T` in the current scope [E0599]
19+
}
20+
21+
fn bar(value: impl Copy) {
22+
//~^ SUGGESTION + Trait</* I */>
23+
//~| SUGGESTION + Trait2</* 'a, A, B */>
24+
value.method();
25+
//~^ ERROR no method named `method` found for type parameter `impl Copy` in the current scope [E0599]
26+
value.method2();
27+
//~^ ERROR no method named `method2` found for type parameter `impl Copy` in the current scope [E0599]
28+
}
29+
30+
fn main() {}

‎tests/ui/suggestions/no-method-found-suggest-trait-args.stderr‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,63 @@
1+
error[E0599]: no method named `method` found for type parameter `T` in the current scope
2+
--> $DIR/no-method-found-suggest-trait-args.rs:15:11
3+
|
4+
LL | fn foo<T>(value: T) {
5+
| - method `method` not found for this type parameter
6+
...
7+
LL | value.method();
8+
| ^^^^^^ method not found in `T`
9+
|
10+
= help: items from traits can only be used if the type parameter is bounded by the trait
11+
help: the following trait defines an item `method`, perhaps you need to restrict type parameter `T` with it:
12+
|
13+
LL | fn foo<T: Trait</* I */>>(value: T) {
14+
| ++++++++++++++++
15+
16+
error[E0599]: no method named `method2` found for type parameter `T` in the current scope
17+
--> $DIR/no-method-found-suggest-trait-args.rs:17:11
18+
|
19+
LL | fn foo<T>(value: T) {
20+
| - method `method2` not found for this type parameter
21+
...
22+
LL | value.method2();
23+
| ^^^^^^^ method not found in `T`
24+
|
25+
= help: items from traits can only be used if the type parameter is bounded by the trait
26+
help: the following trait defines an item `method2`, perhaps you need to restrict type parameter `T` with it:
27+
|
28+
LL | fn foo<T: Trait2</* 'a, A, B */>>(value: T) {
29+
| ++++++++++++++++++++++++
30+
31+
error[E0599]: no method named `method` found for type parameter `impl Copy` in the current scope
32+
--> $DIR/no-method-found-suggest-trait-args.rs:24:11
33+
|
34+
LL | fn bar(value: impl Copy) {
35+
| --------- method `method` not found for this type parameter
36+
...
37+
LL | value.method();
38+
| ^^^^^^ method not found in `impl Copy`
39+
|
40+
= help: items from traits can only be used if the type parameter is bounded by the trait
41+
help: the following trait defines an item `method`, perhaps you need to restrict type parameter `impl Copy` with it:
42+
|
43+
LL | fn bar(value: impl Copy + Trait</* I */>) {
44+
| ++++++++++++++++
45+
46+
error[E0599]: no method named `method2` found for type parameter `impl Copy` in the current scope
47+
--> $DIR/no-method-found-suggest-trait-args.rs:26:11
48+
|
49+
LL | fn bar(value: impl Copy) {
50+
| --------- method `method2` not found for this type parameter
51+
...
52+
LL | value.method2();
53+
| ^^^^^^^ method not found in `impl Copy`
54+
|
55+
= help: items from traits can only be used if the type parameter is bounded by the trait
56+
help: the following trait defines an item `method2`, perhaps you need to restrict type parameter `impl Copy` with it:
57+
|
58+
LL | fn bar(value: impl Copy + Trait2</* 'a, A, B */>) {
59+
| ++++++++++++++++++++++++
60+
61+
error: aborting due to 4 previous errors
62+
63+
For more information about this error, try `rustc --explain E0599`.

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