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Rollup merge of #100838 - hkmatsumoto:move-gen-args-to-trait-when-appropriate, r=davidtwco
Suggest moving redundant generic args of an assoc fn to its trait Closes #89064
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‎compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs‎

Lines changed: 118 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -523,6 +523,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
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if self.not_enough_args_provided() {
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self.suggest_adding_args(err);
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} else if self.too_many_args_provided() {
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self.suggest_moving_args_from_assoc_fn_to_trait(err);
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self.suggest_removing_args_or_generics(err);
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} else {
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unreachable!();
@@ -653,6 +654,123 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
653654
}
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}
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/// Suggests moving redundant argument(s) of an associate function to the
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/// trait it belongs to.
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///
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/// ```compile_fail
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/// Into::into::<Option<_>>(42) // suggests considering `Into::<Option<_>>::into(42)`
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/// ```
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fn suggest_moving_args_from_assoc_fn_to_trait(&self, err: &mut Diagnostic) {
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let trait_ = match self.tcx.trait_of_item(self.def_id) {
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Some(def_id) => def_id,
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None => return,
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};
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// Skip suggestion when the associated function is itself generic, it is unclear
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// how to split the provided parameters between those to suggest to the trait and
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// those to remain on the associated type.
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let num_assoc_fn_expected_args =
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self.num_expected_type_or_const_args() + self.num_expected_lifetime_args();
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if num_assoc_fn_expected_args > 0 {
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return;
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}
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let num_assoc_fn_excess_args =
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self.num_excess_type_or_const_args() + self.num_excess_lifetime_args();
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let trait_generics = self.tcx.generics_of(trait_);
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let num_trait_generics_except_self =
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trait_generics.count() - if trait_generics.has_self { 1 } else { 0 };
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let msg = format!(
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"consider moving {these} generic argument{s} to the `{name}` trait, which takes up to {num} argument{s}",
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these = pluralize!("this", num_assoc_fn_excess_args),
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s = pluralize!(num_assoc_fn_excess_args),
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name = self.tcx.item_name(trait_),
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num = num_trait_generics_except_self,
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);
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if let Some(hir_id) = self.path_segment.hir_id
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&& let Some(parent_node) = self.tcx.hir().find_parent_node(hir_id)
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&& let Some(parent_node) = self.tcx.hir().find(parent_node)
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&& let hir::Node::Expr(expr) = parent_node {
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match expr.kind {
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hir::ExprKind::Path(ref qpath) => {
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self.suggest_moving_args_from_assoc_fn_to_trait_for_qualified_path(
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err,
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qpath,
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msg,
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num_assoc_fn_excess_args,
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num_trait_generics_except_self
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)
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},
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hir::ExprKind::MethodCall(..) => {
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self.suggest_moving_args_from_assoc_fn_to_trait_for_method_call(
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err,
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trait_,
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expr,
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msg,
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num_assoc_fn_excess_args,
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num_trait_generics_except_self
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)
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},
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_ => return,
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}
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}
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}
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fn suggest_moving_args_from_assoc_fn_to_trait_for_qualified_path(
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&self,
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err: &mut Diagnostic,
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qpath: &'tcx hir::QPath<'tcx>,
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msg: String,
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num_assoc_fn_excess_args: usize,
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num_trait_generics_except_self: usize,
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) {
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if let hir::QPath::Resolved(_, path) = qpath
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&& let Some(trait_path_segment) = path.segments.get(0) {
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let num_generic_args_supplied_to_trait = trait_path_segment.args().num_generic_params();
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if num_assoc_fn_excess_args == num_trait_generics_except_self - num_generic_args_supplied_to_trait {
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if let Some(span) = self.gen_args.span_ext()
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&& let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
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let sugg = vec![
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(self.path_segment.ident.span, format!("{}::{}", snippet, self.path_segment.ident)),
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(span.with_lo(self.path_segment.ident.span.hi()), "".to_owned())
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];
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err.multipart_suggestion(
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msg,
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sugg,
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Applicability::MaybeIncorrect
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);
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}
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}
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}
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}
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fn suggest_moving_args_from_assoc_fn_to_trait_for_method_call(
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&self,
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err: &mut Diagnostic,
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trait_: DefId,
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expr: &'tcx hir::Expr<'tcx>,
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msg: String,
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num_assoc_fn_excess_args: usize,
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num_trait_generics_except_self: usize,
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) {
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if let hir::ExprKind::MethodCall(_, args, _) = expr.kind {
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assert_eq!(args.len(), 1);
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if num_assoc_fn_excess_args == num_trait_generics_except_self {
764+
if let Some(gen_args) = self.gen_args.span_ext()
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&& let Ok(gen_args) = self.tcx.sess.source_map().span_to_snippet(gen_args)
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&& let Ok(args) = self.tcx.sess.source_map().span_to_snippet(args[0].span) {
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let sugg = format!("{}::{}::{}({})", self.tcx.item_name(trait_), gen_args, self.tcx.item_name(self.def_id), args);
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err.span_suggestion(expr.span, msg, sugg, Applicability::MaybeIncorrect);
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}
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}
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}
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}
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/// Suggests to remove redundant argument(s):
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///
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/// ```text

‎src/test/ui/const-generics/invalid-const-arg-for-type-param.stderr‎

Lines changed: 10 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2,15 +2,22 @@ error[E0107]: this associated function takes 0 generic arguments but 1 generic a
22
--> $DIR/invalid-const-arg-for-type-param.rs:6:23
33
|
44
LL | let _: u32 = 5i32.try_into::<32>().unwrap();
5-
| ^^^^^^^^------ help: remove these generics
6-
| |
7-
| expected 0 generic arguments
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| ^^^^^^^^ expected 0 generic arguments
86
|
97
note: associated function defined here, with 0 generic parameters
108
--> $SRC_DIR/core/src/convert/mod.rs:LL:COL
119
|
1210
LL | fn try_into(self) -> Result<T, Self::Error>;
1311
| ^^^^^^^^
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help: consider moving this generic argument to the `TryInto` trait, which takes up to 1 argument
13+
|
14+
LL | let _: u32 = TryInto::<32>::try_into(5i32).unwrap();
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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help: remove these generics
17+
|
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LL - let _: u32 = 5i32.try_into::<32>().unwrap();
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LL + let _: u32 = 5i32.try_into().unwrap();
20+
|
1421

1522
error[E0599]: no method named `f` found for struct `S` in the current scope
1623
--> $DIR/invalid-const-arg-for-type-param.rs:9:7

‎src/test/ui/suggestions/issue-89064.rs‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,35 @@
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use std::convert::TryInto;
2+
3+
trait A<T> {
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fn foo() {}
5+
}
6+
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trait B<T, U> {
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fn bar() {}
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}
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struct S;
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impl<T> A<T> for S {}
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impl<T, U> B<T, U> for S {}
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fn main() {
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let _ = A::foo::<S>();
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//~^ ERROR
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//~| HELP remove these generics
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//~| HELP consider moving this generic argument
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22+
let _ = B::bar::<S, S>();
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//~^ ERROR
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//~| HELP remove these generics
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//~| HELP consider moving these generic arguments
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let _ = A::<S>::foo::<S>();
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//~^ ERROR
29+
//~| HELP remove these generics
30+
31+
let _ = 42.into::<Option<_>>();
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//~^ ERROR
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//~| HELP remove these generics
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//~| HELP consider moving this generic argument
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}

‎src/test/ui/suggestions/issue-89064.stderr‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,82 @@
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error[E0107]: this associated function takes 0 generic arguments but 1 generic argument was supplied
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--> $DIR/issue-89064.rs:17:16
3+
|
4+
LL | let _ = A::foo::<S>();
5+
| ^^^ expected 0 generic arguments
6+
|
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note: associated function defined here, with 0 generic parameters
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--> $DIR/issue-89064.rs:4:8
9+
|
10+
LL | fn foo() {}
11+
| ^^^
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help: consider moving this generic argument to the `A` trait, which takes up to 1 argument
13+
|
14+
LL - let _ = A::foo::<S>();
15+
LL + let _ = A::<S>::foo();
16+
|
17+
help: remove these generics
18+
|
19+
LL - let _ = A::foo::<S>();
20+
LL + let _ = A::foo();
21+
|
22+
23+
error[E0107]: this associated function takes 0 generic arguments but 2 generic arguments were supplied
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--> $DIR/issue-89064.rs:22:16
25+
|
26+
LL | let _ = B::bar::<S, S>();
27+
| ^^^ expected 0 generic arguments
28+
|
29+
note: associated function defined here, with 0 generic parameters
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--> $DIR/issue-89064.rs:8:8
31+
|
32+
LL | fn bar() {}
33+
| ^^^
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help: consider moving these generic arguments to the `B` trait, which takes up to 2 arguments
35+
|
36+
LL - let _ = B::bar::<S, S>();
37+
LL + let _ = B::<S, S>::bar();
38+
|
39+
help: remove these generics
40+
|
41+
LL - let _ = B::bar::<S, S>();
42+
LL + let _ = B::bar();
43+
|
44+
45+
error[E0107]: this associated function takes 0 generic arguments but 1 generic argument was supplied
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--> $DIR/issue-89064.rs:27:21
47+
|
48+
LL | let _ = A::<S>::foo::<S>();
49+
| ^^^----- help: remove these generics
50+
| |
51+
| expected 0 generic arguments
52+
|
53+
note: associated function defined here, with 0 generic parameters
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--> $DIR/issue-89064.rs:4:8
55+
|
56+
LL | fn foo() {}
57+
| ^^^
58+
59+
error[E0107]: this associated function takes 0 generic arguments but 1 generic argument was supplied
60+
--> $DIR/issue-89064.rs:31:16
61+
|
62+
LL | let _ = 42.into::<Option<_>>();
63+
| ^^^^ expected 0 generic arguments
64+
|
65+
note: associated function defined here, with 0 generic parameters
66+
--> $SRC_DIR/core/src/convert/mod.rs:LL:COL
67+
|
68+
LL | fn into(self) -> T;
69+
| ^^^^
70+
help: consider moving this generic argument to the `Into` trait, which takes up to 1 argument
71+
|
72+
LL | let _ = Into::<Option<_>>::into(42);
73+
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~
74+
help: remove these generics
75+
|
76+
LL - let _ = 42.into::<Option<_>>();
77+
LL + let _ = 42.into();
78+
|
79+
80+
error: aborting due to 4 previous errors
81+
82+
For more information about this error, try `rustc --explain E0107`.

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