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Rollup merge of #84544 - RalfJung:const_fn_in_trait, r=oli-obk
Always reject `const fn` in `trait` during parsing. 'const fn' in trait are rejected in the AST: https://github.com/rust-lang/rust/blob/b78c0d8a4d5af91a4a55d029293e3ecb879ec142/compiler/rustc_ast_passes/src/ast_validation.rs#L1411 So this feature gate check is a NOP and we can just remove it. The src/test/ui/feature-gates/feature-gate-min_const_fn.rs and src/test/ui/feature-gates/feature-gate-const_fn.rs tests ensure that we still reject `const fn` in `trait` Cc #84510 r? ``@oli-obk``
2 parents 9063dc6 + 8a961a5 commit 5f946b1

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8 files changed

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lines changed

‎compiler/rustc_ast_passes/src/feature_gate.rs

Lines changed: 1 addition & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -586,12 +586,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
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fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
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let is_fn = match i.kind {
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ast::AssocItemKind::Fn(box ast::FnKind(_, ref sig, _, _)) => {
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if let (ast::Const::Yes(_), AssocCtxt::Trait) = (sig.header.constness, ctxt) {
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gate_feature_post!(&self, const_fn, i.span, "const fn is unstable");
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}
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true
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}
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ast::AssocItemKind::Fn(_) => true,
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ast::AssocItemKind::TyAlias(box ast::TyAliasKind(_, ref generics, _, ref ty)) => {
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if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
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gate_feature_post!(

‎compiler/rustc_error_codes/src/error_codes/E0379.md

Lines changed: 0 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3,8 +3,6 @@ A trait method was declared const.
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Erroneous code example:
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```compile_fail,E0379
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#![feature(const_fn)]
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trait Foo {
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const fn bar() -> u32; // error!
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}

‎compiler/rustc_error_codes/src/error_codes/E0764.md

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Original file line numberDiff line numberDiff line change
@@ -3,7 +3,6 @@ A mutable reference was used in a constant.
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Erroneous code example:
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```compile_fail,E0764
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#![feature(const_fn)]
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#![feature(const_mut_refs)]
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fn main() {
@@ -27,7 +26,6 @@ Remember: you cannot use a function call inside a constant or static. However,
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you can totally use it in constant functions:
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```
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#![feature(const_fn)]
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#![feature(const_mut_refs)]
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const fn foo(x: usize) -> usize {

‎src/test/ui/consts/const-fn-not-in-trait.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
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// Test that const fn is illegal in a trait declaration, whether or
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// not a default is provided.
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// not a default is provided, and even with the feature gate.
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#![feature(const_fn)]
55

‎src/test/ui/feature-gates/feature-gate-const_fn.rs

Lines changed: 2 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -3,10 +3,8 @@
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const fn foo() -> usize { 0 } // ok
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trait Foo {
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const fn foo() -> u32; //~ ERROR const fn is unstable
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//~| ERROR functions in traits cannot be declared const
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const fn bar() -> u32 { 0 } //~ ERROR const fn is unstable
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//~| ERROR functions in traits cannot be declared const
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const fn foo() -> u32; //~ ERROR functions in traits cannot be declared const
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const fn bar() -> u32 { 0 } //~ ERROR functions in traits cannot be declared const
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}
119

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impl Foo for u32 {

‎src/test/ui/feature-gates/feature-gate-const_fn.stderr

Lines changed: 4 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -5,36 +5,17 @@ LL | const fn foo() -> u32;
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| ^^^^^ functions in traits cannot be const
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error[E0379]: functions in traits cannot be declared const
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--> $DIR/feature-gate-const_fn.rs:8:5
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--> $DIR/feature-gate-const_fn.rs:7:5
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|
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LL | const fn bar() -> u32 { 0 }
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| ^^^^^ functions in traits cannot be const
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error[E0379]: functions in traits cannot be declared const
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--> $DIR/feature-gate-const_fn.rs:13:5
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--> $DIR/feature-gate-const_fn.rs:11:5
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|
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LL | const fn foo() -> u32 { 0 }
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| ^^^^^ functions in traits cannot be const
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error[E0658]: const fn is unstable
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--> $DIR/feature-gate-const_fn.rs:6:5
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|
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LL | const fn foo() -> u32;
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| ^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
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= help: add `#![feature(const_fn)]` to the crate attributes to enable
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error[E0658]: const fn is unstable
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--> $DIR/feature-gate-const_fn.rs:8:5
30-
|
31-
LL | const fn bar() -> u32 { 0 }
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
35-
= help: add `#![feature(const_fn)]` to the crate attributes to enable
36-
37-
error: aborting due to 5 previous errors
19+
error: aborting due to 3 previous errors
3820

39-
Some errors have detailed explanations: E0379, E0658.
40-
For more information about an error, try `rustc --explain E0379`.
21+
For more information about this error, try `rustc --explain E0379`.

‎src/test/ui/feature-gates/feature-gate-min_const_fn.rs

Lines changed: 2 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -3,10 +3,8 @@
33
const fn foo() -> usize { 0 } // stabilized
44

55
trait Foo {
6-
const fn foo() -> u32; //~ ERROR const fn is unstable
7-
//~| ERROR functions in traits cannot be declared const
8-
const fn bar() -> u32 { 0 } //~ ERROR const fn is unstable
9-
//~| ERROR functions in traits cannot be declared const
6+
const fn foo() -> u32; //~ ERROR functions in traits cannot be declared const
7+
const fn bar() -> u32 { 0 } //~ ERROR functions in traits cannot be declared const
108
}
119

1210
impl Foo for u32 {

‎src/test/ui/feature-gates/feature-gate-min_const_fn.stderr

Lines changed: 4 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -5,36 +5,17 @@ LL | const fn foo() -> u32;
55
| ^^^^^ functions in traits cannot be const
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77
error[E0379]: functions in traits cannot be declared const
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--> $DIR/feature-gate-min_const_fn.rs:8:5
8+
--> $DIR/feature-gate-min_const_fn.rs:7:5
99
|
1010
LL | const fn bar() -> u32 { 0 }
1111
| ^^^^^ functions in traits cannot be const
1212

1313
error[E0379]: functions in traits cannot be declared const
14-
--> $DIR/feature-gate-min_const_fn.rs:13:5
14+
--> $DIR/feature-gate-min_const_fn.rs:11:5
1515
|
1616
LL | const fn foo() -> u32 { 0 }
1717
| ^^^^^ functions in traits cannot be const
1818

19-
error[E0658]: const fn is unstable
20-
--> $DIR/feature-gate-min_const_fn.rs:6:5
21-
|
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LL | const fn foo() -> u32;
23-
| ^^^^^^^^^^^^^^^^^^^^^^
24-
|
25-
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
26-
= help: add `#![feature(const_fn)]` to the crate attributes to enable
27-
28-
error[E0658]: const fn is unstable
29-
--> $DIR/feature-gate-min_const_fn.rs:8:5
30-
|
31-
LL | const fn bar() -> u32 { 0 }
32-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
33-
|
34-
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
35-
= help: add `#![feature(const_fn)]` to the crate attributes to enable
36-
37-
error: aborting due to 5 previous errors
19+
error: aborting due to 3 previous errors
3820

39-
Some errors have detailed explanations: E0379, E0658.
40-
For more information about an error, try `rustc --explain E0379`.
21+
For more information about this error, try `rustc --explain E0379`.

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