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Implement use associated items of traits
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‎compiler/rustc_error_codes/src/error_codes/E0253.md

+6-6
Original file line numberDiff line numberDiff line change
@@ -1,19 +1,19 @@
1-
Attempt was made to import an unimportable value. This can happen when trying
2-
to import a method from a trait.
1+
Attempt was made to import an unimportable type. This can happen when trying
2+
to import a type from a trait.
33

44
Erroneous code example:
55

66
```compile_fail,E0253
77
mod foo {
88
pub trait MyTrait {
9-
fn do_something();
9+
type SomeType;
1010
}
1111
}
1212
13-
use foo::MyTrait::do_something;
14-
// error: `do_something` is not directly importable
13+
use foo::MyTrait::SomeType;
14+
// error: `SomeType` is not directly importable
1515
1616
fn main() {}
1717
```
1818

19-
It's invalid to directly import methods belonging to a trait or concrete type.
19+
It's invalid to directly import types belonging to a trait.

‎compiler/rustc_feature/src/unstable.rs

+2
Original file line numberDiff line numberDiff line change
@@ -519,6 +519,8 @@ declare_features! (
519519
(unstable, impl_trait_in_bindings, "1.64.0", Some(63065)),
520520
/// Allows `impl Trait` as output type in `Fn` traits in return position of functions.
521521
(unstable, impl_trait_in_fn_trait_return, "1.64.0", Some(99697)),
522+
/// Allows `use` associated functions from traits.
523+
(unstable, import_trait_associated_functions, "CURRENT_RUSTC_VERSION", Some(134691)),
522524
/// Allows associated types in inherent impls.
523525
(incomplete, inherent_associated_types, "1.52.0", Some(8995)),
524526
/// Allow anonymous constants from an inline `const` block in pattern position

‎compiler/rustc_resolve/src/diagnostics.rs

+5-1
Original file line numberDiff line numberDiff line change
@@ -1183,7 +1183,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
11831183
let in_module_is_extern = !in_module.def_id().is_local();
11841184
in_module.for_each_child(self, |this, ident, ns, name_binding| {
11851185
// avoid non-importable candidates
1186-
if !name_binding.is_importable() {
1186+
if !name_binding.is_importable()
1187+
// FIXME(import_trait_associated_functions): remove this when `import_trait_associated_functions` is stable
1188+
|| name_binding.is_assoc_const_or_fn()
1189+
&& !this.tcx.features().import_trait_associated_functions()
1190+
{
11871191
return;
11881192
}
11891193

‎compiler/rustc_resolve/src/imports.rs

+13-1
Original file line numberDiff line numberDiff line change
@@ -17,9 +17,10 @@ use rustc_session::lint::builtin::{
1717
AMBIGUOUS_GLOB_REEXPORTS, HIDDEN_GLOB_REEXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE,
1818
REDUNDANT_IMPORTS, UNUSED_IMPORTS,
1919
};
20+
use rustc_session::parse::feature_err;
2021
use rustc_span::edit_distance::find_best_match_for_name;
2122
use rustc_span::hygiene::LocalExpnId;
22-
use rustc_span::{Ident, Span, Symbol, kw};
23+
use rustc_span::{Ident, Span, Symbol, kw, sym};
2324
use smallvec::SmallVec;
2425
use tracing::debug;
2526

@@ -829,6 +830,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
829830
// Don't update the resolution, because it was never added.
830831
Err(Determined) if target.name == kw::Underscore => {}
831832
Ok(binding) if binding.is_importable() => {
833+
if binding.is_assoc_const_or_fn()
834+
&& !this.tcx.features().import_trait_associated_functions()
835+
{
836+
feature_err(
837+
this.tcx.sess,
838+
sym::import_trait_associated_functions,
839+
import.span,
840+
"`use` associated items of traits is unstable",
841+
)
842+
.emit();
843+
}
832844
let imported_binding = this.import(binding, import);
833845
target_bindings[ns].set(Some(imported_binding));
834846
this.define(parent, target, ns, imported_binding);

‎compiler/rustc_resolve/src/lib.rs

+7-4
Original file line numberDiff line numberDiff line change
@@ -920,10 +920,13 @@ impl<'ra> NameBindingData<'ra> {
920920
}
921921

922922
fn is_importable(&self) -> bool {
923-
!matches!(
924-
self.res(),
925-
Res::Def(DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy, _)
926-
)
923+
!matches!(self.res(), Res::Def(DefKind::AssocTy, _))
924+
}
925+
926+
// FIXME(import_trait_associated_functions): associate `const` or `fn` are not importable unless
927+
// the feature `import_trait_associated_functions` is enable
928+
fn is_assoc_const_or_fn(&self) -> bool {
929+
matches!(self.res(), Res::Def(DefKind::AssocConst | DefKind::AssocFn, _))
927930
}
928931

929932
fn macro_kind(&self) -> Option<MacroKind> {

‎compiler/rustc_span/src/symbol.rs

+1
Original file line numberDiff line numberDiff line change
@@ -1093,6 +1093,7 @@ symbols! {
10931093
import,
10941094
import_name_type,
10951095
import_shadowing,
1096+
import_trait_associated_functions,
10961097
imported_main,
10971098
in_band_lifetimes,
10981099
include,

‎tests/ui/error-codes/E0253.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -1,10 +1,10 @@
11
mod foo {
22
pub trait MyTrait {
3-
fn do_something();
3+
type SomeType;
44
}
55
}
66

7-
use foo::MyTrait::do_something;
7+
use foo::MyTrait::SomeType;
88
//~^ ERROR E0253
99

1010
fn main() {}

‎tests/ui/error-codes/E0253.stderr

+3-3
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,8 @@
1-
error[E0253]: `do_something` is not directly importable
1+
error[E0253]: `SomeType` is not directly importable
22
--> $DIR/E0253.rs:7:5
33
|
4-
LL | use foo::MyTrait::do_something;
5-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot be imported directly
4+
LL | use foo::MyTrait::SomeType;
5+
| ^^^^^^^^^^^^^^^^^^^^^^ cannot be imported directly
66

77
error: aborting due to 1 previous error
88

‎tests/ui/feature-gates/feature-gate-import-trait-associated-functions.rs

+63
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,63 @@
1+
//@ edition:2018
2+
use std::collections::HashMap;
3+
4+
use A::{DEFAULT, new};
5+
//~^ ERROR `use` associated items of traits is unstable [E0658]
6+
//~| ERROR `use` associated items of traits is unstable [E0658]
7+
use Default::default;
8+
//~^ ERROR `use` associated items of traits is unstable [E0658]
9+
10+
struct S {
11+
a: HashMap<i32, i32>,
12+
}
13+
14+
impl S {
15+
fn new() -> S {
16+
S { a: default() }
17+
}
18+
}
19+
20+
trait A: Sized {
21+
const DEFAULT: Option<Self> = None;
22+
fn new() -> Self;
23+
fn do_something(&self);
24+
}
25+
26+
mod b {
27+
use super::A::{self, DEFAULT, new};
28+
//~^ ERROR `use` associated items of traits is unstable [E0658]
29+
//~| ERROR `use` associated items of traits is unstable [E0658]
30+
31+
struct B();
32+
33+
impl A for B {
34+
const DEFAULT: Option<Self> = Some(B());
35+
fn new() -> Self {
36+
B()
37+
}
38+
39+
fn do_something(&self) {}
40+
}
41+
42+
fn f() {
43+
let b: B = new();
44+
b.do_something();
45+
let c: B = DEFAULT.unwrap();
46+
}
47+
}
48+
49+
impl A for S {
50+
fn new() -> Self {
51+
S::new()
52+
}
53+
54+
fn do_something(&self) {}
55+
}
56+
57+
fn f() {
58+
let s: S = new();
59+
s.do_something();
60+
let t: Option<S> = DEFAULT;
61+
}
62+
63+
fn main() {}

‎tests/ui/feature-gates/feature-gate-import-trait-associated-functions.stderr

+53
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,53 @@
1+
error[E0658]: `use` associated items of traits is unstable
2+
--> $DIR/feature-gate-import-trait-associated-functions.rs:4:9
3+
|
4+
LL | use A::{DEFAULT, new};
5+
| ^^^^^^^
6+
|
7+
= note: see issue #134691 <https://github.com/rust-lang/rust/issues/134691> for more information
8+
= help: add `#![feature(import_trait_associated_functions)]` to the crate attributes to enable
9+
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
10+
11+
error[E0658]: `use` associated items of traits is unstable
12+
--> $DIR/feature-gate-import-trait-associated-functions.rs:4:18
13+
|
14+
LL | use A::{DEFAULT, new};
15+
| ^^^
16+
|
17+
= note: see issue #134691 <https://github.com/rust-lang/rust/issues/134691> for more information
18+
= help: add `#![feature(import_trait_associated_functions)]` to the crate attributes to enable
19+
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
20+
21+
error[E0658]: `use` associated items of traits is unstable
22+
--> $DIR/feature-gate-import-trait-associated-functions.rs:7:5
23+
|
24+
LL | use Default::default;
25+
| ^^^^^^^^^^^^^^^^
26+
|
27+
= note: see issue #134691 <https://github.com/rust-lang/rust/issues/134691> for more information
28+
= help: add `#![feature(import_trait_associated_functions)]` to the crate attributes to enable
29+
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
30+
31+
error[E0658]: `use` associated items of traits is unstable
32+
--> $DIR/feature-gate-import-trait-associated-functions.rs:27:26
33+
|
34+
LL | use super::A::{self, DEFAULT, new};
35+
| ^^^^^^^
36+
|
37+
= note: see issue #134691 <https://github.com/rust-lang/rust/issues/134691> for more information
38+
= help: add `#![feature(import_trait_associated_functions)]` to the crate attributes to enable
39+
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
40+
41+
error[E0658]: `use` associated items of traits is unstable
42+
--> $DIR/feature-gate-import-trait-associated-functions.rs:27:35
43+
|
44+
LL | use super::A::{self, DEFAULT, new};
45+
| ^^^
46+
|
47+
= note: see issue #134691 <https://github.com/rust-lang/rust/issues/134691> for more information
48+
= help: add `#![feature(import_trait_associated_functions)]` to the crate attributes to enable
49+
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
50+
51+
error: aborting due to 5 previous errors
52+
53+
For more information about this error, try `rustc --explain E0658`.

‎tests/ui/imports/import-trait-method.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -2,6 +2,6 @@ trait Foo {
22
fn foo();
33
}
44

5-
use Foo::foo; //~ ERROR not directly importable
5+
use Foo::foo; //~ ERROR `use` associated items of traits is unstable [E0658]
66

7-
fn main() { foo(); }
7+
fn main() { foo(); } //~ ERROR type annotations needed

‎tests/ui/imports/import-trait-method.stderr

+17-4
Original file line numberDiff line numberDiff line change
@@ -1,9 +1,22 @@
1-
error[E0253]: `foo` is not directly importable
1+
error[E0658]: `use` associated items of traits is unstable
22
--> $DIR/import-trait-method.rs:5:5
33
|
44
LL | use Foo::foo;
5-
| ^^^^^^^^ cannot be imported directly
5+
| ^^^^^^^^
6+
|
7+
= note: see issue #134691 <https://github.com/rust-lang/rust/issues/134691> for more information
8+
= help: add `#![feature(import_trait_associated_functions)]` to the crate attributes to enable
9+
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
10+
11+
error[E0283]: type annotations needed
12+
--> $DIR/import-trait-method.rs:7:13
13+
|
14+
LL | fn main() { foo(); }
15+
| ^^^^^ cannot infer type
16+
|
17+
= note: cannot satisfy `_: Foo`
618

7-
error: aborting due to 1 previous error
19+
error: aborting due to 2 previous errors
820

9-
For more information about this error, try `rustc --explain E0253`.
21+
Some errors have detailed explanations: E0283, E0658.
22+
For more information about an error, try `rustc --explain E0283`.

‎tests/ui/suggestions/fn-to-method.import_trait_associated_functions.stderr

+39
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,39 @@
1+
error[E0425]: cannot find function `cmp` in this scope
2+
--> $DIR/fn-to-method.rs:12:13
3+
|
4+
LL | let x = cmp(&1, &2);
5+
| ^^^ not found in this scope
6+
|
7+
help: consider importing one of these associated functions
8+
|
9+
LL + use std::cmp::Ord::cmp;
10+
|
11+
LL + use std::iter::Iterator::cmp;
12+
|
13+
14+
error[E0425]: cannot find function `len` in this scope
15+
--> $DIR/fn-to-method.rs:16:13
16+
|
17+
LL | let y = len([1, 2, 3]);
18+
| ^^^ not found in this scope
19+
|
20+
help: consider importing this associated function
21+
|
22+
LL + use std::iter::ExactSizeIterator::len;
23+
|
24+
25+
error[E0425]: cannot find function `bar` in this scope
26+
--> $DIR/fn-to-method.rs:20:13
27+
|
28+
LL | let z = bar(Foo);
29+
| ^^^ not found in this scope
30+
|
31+
help: use the `.` operator to call the method `bar` on `Foo`
32+
|
33+
LL - let z = bar(Foo);
34+
LL + let z = Foo.bar();
35+
|
36+
37+
error: aborting due to 3 previous errors
38+
39+
For more information about this error, try `rustc --explain E0425`.

‎tests/ui/suggestions/fn-to-method.stderr ‎tests/ui/suggestions/fn-to-method.normal.stderr

+3-3
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
error[E0425]: cannot find function `cmp` in this scope
2-
--> $DIR/fn-to-method.rs:8:13
2+
--> $DIR/fn-to-method.rs:12:13
33
|
44
LL | let x = cmp(&1, &2);
55
| ^^^ not found in this scope
@@ -10,7 +10,7 @@ LL | let x = (&1).cmp(&2);
1010
| ~ ~~~~~~~~~
1111

1212
error[E0425]: cannot find function `len` in this scope
13-
--> $DIR/fn-to-method.rs:12:13
13+
--> $DIR/fn-to-method.rs:16:13
1414
|
1515
LL | let y = len([1, 2, 3]);
1616
| ^^^ not found in this scope
@@ -22,7 +22,7 @@ LL + let y = [1, 2, 3].len();
2222
|
2323

2424
error[E0425]: cannot find function `bar` in this scope
25-
--> $DIR/fn-to-method.rs:16:13
25+
--> $DIR/fn-to-method.rs:20:13
2626
|
2727
LL | let z = bar(Foo);
2828
| ^^^ not found in this scope

‎tests/ui/suggestions/fn-to-method.rs

+6-2
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,8 @@
1+
//@ revisions: normal import_trait_associated_functions
2+
#![cfg_attr(import_trait_associated_functions, feature(import_trait_associated_functions))]
13
struct Foo;
4+
//[import_trait_associated_functions]~^ HELP consider importing one of these associated functions
5+
//[import_trait_associated_functions]~| HELP consider importing this associated function
26

37
impl Foo {
48
fn bar(self) {}
@@ -7,11 +11,11 @@ impl Foo {
711
fn main() {
812
let x = cmp(&1, &2);
913
//~^ ERROR cannot find function `cmp` in this scope
10-
//~| HELP use the `.` operator to call the method `Ord::cmp` on `&{integer}`
14+
//[normal]~| HELP use the `.` operator to call the method `Ord::cmp` on `&{integer}`
1115

1216
let y = len([1, 2, 3]);
1317
//~^ ERROR cannot find function `len` in this scope
14-
//~| HELP use the `.` operator to call the method `len` on `&[{integer}]`
18+
//[normal]~| HELP use the `.` operator to call the method `len` on `&[{integer}]`
1519

1620
let z = bar(Foo);
1721
//~^ ERROR cannot find function `bar` in this scope

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