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Emit pre-expansion feature gate warning for negative impls

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This commit is contained in:
León Orell Valerian Liehr
2026-03-29 14:36:35 +02:00
parent dd96eff769
commit 394012bcd2
10 changed files with 46 additions and 52 deletions
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compiler/rustc_ast_passes/src/feature_gate.rs
+3 -2
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@@ -218,8 +218,8 @@ fn visit_item(&mut self, i: &'a ast::Item) {
self,
negative_impls,
span.to(of_trait.trait_ref.path.span),
"negative trait bounds are not fully implemented; \
use marker types for now"
"negative impls are experimental",
"use marker types for now"
);
}
@@ -614,6 +614,7 @@ macro_rules! soft_gate_all_legacy_dont_use {
soft_gate_all_legacy_dont_use!(auto_traits, "`auto` traits are unstable");
soft_gate_all_legacy_dont_use!(box_patterns, "box pattern syntax is experimental");
soft_gate_all_legacy_dont_use!(decl_macro, "`macro` is experimental");
soft_gate_all_legacy_dont_use!(negative_impls, "negative impls are experimental");
soft_gate_all_legacy_dont_use!(trait_alias, "trait aliases are experimental");
soft_gate_all_legacy_dont_use!(try_blocks, "`try` blocks are unstable");
// tidy-alphabetical-end
compiler/rustc_parse/src/parser/item.rs
+1
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@@ -603,6 +603,7 @@ fn is_async_fn(&self) -> bool {
fn parse_polarity(&mut self) -> ast::ImplPolarity {
// Disambiguate `impl !Trait for Type { ... }` and `impl ! { ... }` for the never type.
if self.check(exp!(Bang)) && self.look_ahead(1, |t| t.can_begin_type()) {
self.psess.gated_spans.gate(sym::negative_impls, self.token.span);
self.bump(); // `!`
ast::ImplPolarity::Negative(self.prev_token.span)
} else {
tests/ui/auto-traits/ungated-impl.rs
-7
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@@ -1,7 +0,0 @@
auto trait MyTrait {}
//~^ ERROR auto traits are experimental and possibly buggy
impl<T> !MyTrait for *mut T {}
//~^ ERROR negative trait bounds are not fully implemented
fn main() {}
tests/ui/auto-traits/ungated-impl.stderr
-23
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@@ -1,23 +0,0 @@
error[E0658]: auto traits are experimental and possibly buggy
--> $DIR/ungated-impl.rs:1:1
|
LL | auto trait MyTrait {}
| ^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #13231 <https://github.com/rust-lang/rust/issues/13231> for more information
= help: add `#![feature(auto_traits)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error[E0658]: negative trait bounds are not fully implemented; use marker types for now
--> $DIR/ungated-impl.rs:4:9
|
LL | impl<T> !MyTrait for *mut T {}
| ^^^^^^^^
|
= note: see issue #68318 <https://github.com/rust-lang/rust/issues/68318> for more information
= help: add `#![feature(negative_impls)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0658`.
tests/ui/feature-gates/feature-gate-auto-traits.rs
+2 -9
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@@ -1,12 +1,5 @@
// Test that default and negative trait implementations are gated by
// `auto_traits` feature gate
auto trait DummyAutoTrait {} //~ ERROR auto traits are experimental and possibly buggy
struct DummyStruct;
auto trait AutoDummyTrait {}
//~^ ERROR auto traits are experimental and possibly buggy
impl !AutoDummyTrait for DummyStruct {}
//~^ ERROR negative trait bounds are not fully implemented; use marker types for now
pub unsafe auto trait AnotherAutoTrait {} //~ ERROR auto traits are experimental and possibly buggy
fn main() {}
tests/ui/feature-gates/feature-gate-auto-traits.stderr
+8 -8
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@@ -1,21 +1,21 @@
error[E0658]: auto traits are experimental and possibly buggy
--> $DIR/feature-gate-auto-traits.rs:6:1
--> $DIR/feature-gate-auto-traits.rs:1:1
|
LL | auto trait AutoDummyTrait {}
LL | auto trait DummyAutoTrait {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #13231 <https://github.com/rust-lang/rust/issues/13231> for more information
= help: add `#![feature(auto_traits)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error[E0658]: negative trait bounds are not fully implemented; use marker types for now
--> $DIR/feature-gate-auto-traits.rs:9:6
error[E0658]: auto traits are experimental and possibly buggy
--> $DIR/feature-gate-auto-traits.rs:3:1
|
LL | impl !AutoDummyTrait for DummyStruct {}
| ^^^^^^^^^^^^^^^
LL | pub unsafe auto trait AnotherAutoTrait {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #68318 <https://github.com/rust-lang/rust/issues/68318> for more information
= help: add `#![feature(negative_impls)]` to the crate attributes to enable
= note: see issue #13231 <https://github.com/rust-lang/rust/issues/13231> for more information
= help: add `#![feature(auto_traits)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error: aborting due to 2 previous errors
tests/ui/feature-gates/soft-feature-gate-negative_impls.rs
+12
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@@ -0,0 +1,12 @@
// For historical reasons, negative impls don't have a proper pre-expansion feature gate.
// We're now at least issuing a *warning* for those that only exist before macro expansion.
// FIXME(#154045): Turn their post-expansion feature gate into a proper pre-expansion one.
// As part of this, move these test cases into `feature-gate-negative_impls.rs`.
//@ check-pass
#[cfg(false)]
impl !Trait for () {}
//~^ WARN negative impls are experimental
//~| WARN unstable syntax can change at any point in the future
fn main() {}
tests/ui/feature-gates/soft-feature-gate-negative_impls.stderr
+14
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@@ -0,0 +1,14 @@
warning: negative impls are experimental
--> $DIR/soft-feature-gate-negative_impls.rs:8:6
|
LL | impl !Trait for () {}
| ^
|
= note: see issue #68318 <https://github.com/rust-lang/rust/issues/68318> for more information
= help: add `#![feature(negative_impls)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
= warning: unstable syntax can change at any point in the future, causing a hard error!
= note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>
warning: 1 warning emitted
tests/ui/traits/negative-impls/feature-gate-negative_impls.rs
+3 -1
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@@ -1,3 +1,5 @@
trait MyTrait {}
impl !MyTrait for u32 {} //~ ERROR negative trait bounds are not fully implemented
impl !MyTrait for u32 {} //~ ERROR negative impls are experimental
fn main() {}
tests/ui/traits/negative-impls/feature-gate-negative_impls.stderr
+3 -2
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@@ -1,5 +1,5 @@
error[E0658]: negative trait bounds are not fully implemented; use marker types for now
--> $DIR/feature-gate-negative_impls.rs:2:6
error[E0658]: negative impls are experimental
--> $DIR/feature-gate-negative_impls.rs:3:6
|
LL | impl !MyTrait for u32 {}
| ^^^^^^^^
@@ -7,6 +7,7 @@ LL | impl !MyTrait for u32 {}
= note: see issue #68318 <https://github.com/rust-lang/rust/issues/68318> for more information
= help: add `#![feature(negative_impls)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
= help: use marker types for now
error: aborting due to 1 previous error