Emit pre-expansion feature gate warnings for negative impls and specialization

compiler/rustc_parse/src/parser/item.rs

@@ -248,10 +248,18 @@ impl<'a> Parser<'a> {
             self.parse_use_item()?
         } else if self.check_fn_front_matter(check_pub, case) {
             // FUNCTION ITEM
+            let defaultness = def_();
+            if let Defaultness::Default(span) = defaultness {
+                // Default functions should only require feature `min_specialization`. We remove the
+                // `specialization` tag again as such spans *require* feature `specialization` to be
+                // enabled. In a later stage, we make `specialization` imply `min_specialization`.
+                self.psess.gated_spans.gate(sym::min_specialization, span);
+                self.psess.gated_spans.ungate_last(sym::specialization, span);
+            }
             let (ident, sig, generics, contract, body) =
                 self.parse_fn(attrs, fn_parse_mode, lo, vis, case)?;
             ItemKind::Fn(Box::new(Fn {
-                defaultness: def_(),
+                defaultness,
                 ident,
                 sig,
                 generics,
@@ -603,6 +611,7 @@ impl<'a> Parser<'a> {
     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 {
@@ -1015,6 +1024,7 @@ impl<'a> Parser<'a> {
         if self.check_keyword(exp!(Default))
             && self.look_ahead(1, |t| t.is_non_raw_ident_where(|i| i.name != kw::As))
         {
+            self.psess.gated_spans.gate(sym::specialization, self.token.span);
             self.bump(); // `default`
             Defaultness::Default(self.prev_token_uninterpolated_span())
         } else if self.eat_keyword(exp!(Final)) {

tests/ui/feature-gates/feature-gate-auto-traits.rs

@@ -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

@@ -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-auto_traits.rs

@@ -1,6 +1,6 @@
-// For historical reasons, auto traits 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.
+// For historical reasons, auto traits don't have an erroring pre-expansion feature gate.
+// We're now at least issuing a warning for those that only exist before macro expansion.
+// FIXME(#154045): Turn this pre-expansion warning into an error and remove the post-expansion gate.
 //                 As part of this, move these test cases into `feature-gate-auto-traits.rs`.
 //@ check-pass
 

tests/ui/feature-gates/soft-feature-gate-box_patterns.rs

@@ -1,6 +1,6 @@
-// For historical reasons, box patterns 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.
+// For historical reasons, box patterns don't have an erroring pre-expansion feature gate.
+// We're now at least issuing a warning for those that only exist before macro expansion.
+// FIXME(#154045): Turn this pre-expansion warning into an error and remove the post-expansion gate.
 //                 As part of this, move these test cases into `feature-gate-box_patterns.rs`.
 //@ check-pass
 

tests/ui/feature-gates/soft-feature-gate-decl_macro.rs

@@ -1,6 +1,6 @@
-// For historical reasons, decl macros 2.0 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.
+// For historical reasons, decl macros 2.0 don't have an erroring pre-expansion feature gate.
+// We're now at least issuing a warning for those that only exist before macro expansion.
+// FIXME(#154045): Turn this pre-expansion warning into an error and remove the post-expansion gate.
 //                 As part of this, move these test cases into `feature-gate-decl_macro.rs`.
 //@ check-pass
 

tests/ui/feature-gates/soft-feature-gate-negative_impls.rs

@@ -0,0 +1,12 @@
+// For historical reasons, negative impls don't have an erroring pre-expansion feature gate.
+// We're now at least issuing a warning for those that only exist before macro expansion.
+// FIXME(#154045): Turn this pre-expansion warning into an error and remove the post-expansion gate.
+//                 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

@@ -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/feature-gates/soft-feature-gate-trait_alias.rs

@@ -1,6 +1,6 @@
-// For historical reasons, trait aliases 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.
+// For historical reasons, trait aliases don't have an erroring pre-expansion feature gate.
+// We're now at least issuing a warning for those that only exist before macro expansion.
+// FIXME(#154045): Turn this pre-expansion warning into an error and remove the post-expansion gate.
 //                 As part of this, move these test cases into `feature-gate-trait-alias.rs`.
 //@ check-pass
 

tests/ui/feature-gates/soft-feature-gate-try_blocks.rs

@@ -1,6 +1,6 @@
-// For historical reasons, try blocks 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.
+// For historical reasons, try blocks don't have an erroring pre-expansion feature gate.
+// We're now at least issuing a warning for those that only exist before macro expansion.
+// FIXME(#154045): Turn this pre-expansion warning into an error and remove the post-expansion gate.
 //                 As part of this, move these test cases into `feature-gate-try_blocks.rs`.
 //@ edition: 2018
 //@ check-pass

tests/ui/impl-trait/precise-capturing/bound-modifiers.stderr

@@ -46,6 +46,16 @@ error[E0405]: cannot find trait `r#use` in this scope
 LL | fn binder() -> impl Sized + for<'a> use<> {}
    |                                     ^^^ not found in this scope
 
+error[E0658]: const trait impls are experimental
+  --> $DIR/bound-modifiers.rs:12:32
+   |
+LL | fn constness() -> impl Sized + const use<> {}
+   |                                ^^^^^
+   |
+   = note: see issue #143874 <https://github.com/rust-lang/rust/issues/143874> for more information
+   = help: add `#![feature(const_trait_impl)]` 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]: `async` trait bounds are unstable
   --> $DIR/bound-modifiers.rs:7:32
    |
@@ -57,16 +67,6 @@ LL | fn asyncness() -> impl Sized + async use<> {}
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
    = help: use the desugared name of the async trait, such as `AsyncFn`
 
-error[E0658]: const trait impls are experimental
-  --> $DIR/bound-modifiers.rs:12:32
-   |
-LL | fn constness() -> impl Sized + const use<> {}
-   |                                ^^^^^
-   |
-   = note: see issue #143874 <https://github.com/rust-lang/rust/issues/143874> for more information
-   = help: add `#![feature(const_trait_impl)]` 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 10 previous errors
 
 Some errors have detailed explanations: E0405, E0658.

tests/ui/macros/stringify.rs

@@ -9,12 +9,13 @@
 #![feature(const_trait_impl)]
 #![feature(coroutines)]
 #![feature(decl_macro)]
+#![feature(macro_guard_matcher)]
 #![feature(more_qualified_paths)]
 #![feature(never_patterns)]
+#![feature(specialization)]
 #![feature(trait_alias)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
-#![feature(macro_guard_matcher)]
 #![deny(unused_macros)]
 
 // These macros force the use of AST pretty-printing by converting the input to

tests/ui/parser/trait-item-with-defaultness-pass.rs

@@ -1,4 +1,5 @@
 //@ check-pass
+#![feature(specialization)]
 
 fn main() {}
 

tests/ui/specialization/feature-gate-specialization.rs

@@ -0,0 +1,21 @@
+trait Trait {
+    type Ty;
+    const CT: ();
+    fn fn_(&self);
+}
+
+impl<T> Trait for T {
+    default type Ty = (); //~ ERROR specialization is experimental
+    default const CT: () = (); //~ ERROR specialization is experimental
+    default fn fn_(&self) {} //~ ERROR specialization is experimental
+}
+
+trait OtherTrait {
+    fn fn_();
+}
+
+default impl<T> OtherTrait for T { //~ ERROR specialization is experimental
+    fn fn_() {}
+}
+
+fn main() {}

tests/ui/specialization/feature-gate-specialization.stderr

@@ -0,0 +1,45 @@
+error[E0658]: specialization is experimental
+  --> $DIR/feature-gate-specialization.rs:8:5
+   |
+LL |     default type Ty = ();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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]: specialization is experimental
+  --> $DIR/feature-gate-specialization.rs:9:5
+   |
+LL |     default const CT: () = ();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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]: specialization is experimental
+  --> $DIR/feature-gate-specialization.rs:10:5
+   |
+LL |     default fn fn_(&self) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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]: specialization is experimental
+  --> $DIR/feature-gate-specialization.rs:17:1
+   |
+LL | / default impl<T> OtherTrait for T {
+LL | |     fn fn_() {}
+LL | | }
+   | |_^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/specialization/soft-feature-gate-specialization.default.stderr

@@ -0,0 +1,62 @@
+warning: specialization is experimental
+  --> $DIR/soft-feature-gate-specialization.rs:21:5
+   |
+LL |     default type Ty = ();
+   |     ^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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: specialization is experimental
+  --> $DIR/soft-feature-gate-specialization.rs:24:5
+   |
+LL |     default const CT: () = ();
+   |     ^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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: specialization is experimental
+  --> $DIR/soft-feature-gate-specialization.rs:40:1
+   |
+LL | default impl Trait for () {}
+   | ^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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: specialization is experimental
+  --> $DIR/soft-feature-gate-specialization.rs:27:5
+   |
+LL |     default fn fn_();
+   |     ^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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: specialization is experimental
+  --> $DIR/soft-feature-gate-specialization.rs:35:1
+   |
+LL | default fn fn_() {}
+   | ^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: add `#![feature(specialization)]` 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: 5 warnings emitted
+