Emit pre-expansion feature gate warning for item modifier default

Author: fmease

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -644,6 +644,24 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all_legacy_dont_use!(try_blocks, "`try` blocks are unstable");
     gate_all_legacy_dont_use!(auto_traits, "`auto` traits are unstable");
     gate_all_legacy_dont_use!(negative_impls, "negative impls are experimental");
+    gate_all_legacy_dont_use!(specialization, "specialization is experimental");
+
+    if let Some(spans) = spans.get(&sym::min_specialization) {
+        for &span in spans {
+            if !visitor.features.specialization()
+                && !visitor.features.min_specialization()
+                && !span.allows_unstable(sym::specialization)
+                && !span.allows_unstable(sym::min_specialization)
+            {
+                feature_warn(
+                    visitor.sess,
+                    sym::specialization,
+                    span,
+                    "specialization is experimental",
+                );
+            }
+        }
+    }
 
     visit::walk_crate(&mut visitor, krate);
 }

compiler/rustc_parse/src/parser/item.rs

@@ -248,10 +248,15 @@ 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 {
+                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,
@@ -1016,6 +1021,7 @@ 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/auto-traits/ungated-impl.rs

@@ -0,0 +1,7 @@
+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

@@ -0,0 +1,23 @@
+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/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/defaultimpl/specialization-feature-gate-default.rs

@@ -4,7 +4,7 @@ trait Foo {
     fn foo(&self);
 }
 
-default impl<T> Foo for T { //~ ERROR specialization is unstable
+default impl<T> Foo for T { //~ ERROR specialization is experimental
     fn foo(&self) {}
 }
 

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

@@ -1,4 +1,4 @@
-error[E0658]: specialization is unstable
+error[E0658]: specialization is experimental
   --> $DIR/specialization-feature-gate-default.rs:7:1
    |
 LL | / default impl<T> Foo for T {

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

@@ -0,0 +1,15 @@
+// The gate for `default impl` is exercised in `defaultimpl/specialization-feature-gate-default.rs`.
+
+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
+}
+
+fn main() {}

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

@@ -0,0 +1,33 @@
+error[E0658]: specialization is experimental
+  --> $DIR/feature-gate-specialization.rs:10:5
+   |
+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:11:5
+   |
+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:12:5
+   |
+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: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0658`.