Pre-expansion gate 'default'.

Author: Centril

src/libsyntax/feature_gate.rs

@@ -1980,19 +1980,13 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
+            ast::ItemKind::Impl(_, polarity, ..) => {
                 if polarity == ast::ImplPolarity::Negative {
                     gate_feature_post!(&self, optin_builtin_traits,
                                        i.span,
                                        "negative trait bounds are not yet fully implemented; \
                                         use marker types for now");
                 }
-
-                if let ast::Defaultness::Default = defaultness {
-                    gate_feature_post!(&self, specialization,
-                                       i.span,
-                                       "specialization is unstable");
-                }
             }
 
             ast::ItemKind::Trait(ast::IsAuto::Yes, ..) => {
@@ -2231,12 +2225,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     }
 
     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
-        if ii.defaultness == ast::Defaultness::Default {
-            gate_feature_post!(&self, specialization,
-                              ii.span,
-                              "specialization is unstable");
-        }
-
         match ii.node {
             ast::ImplItemKind::Method(..) => {}
             ast::ImplItemKind::OpaqueTy(..) => {
@@ -2451,6 +2439,7 @@ pub fn check_crate(krate: &ast::Crate,
     gate_all!(async_closure, "async closures are unstable");
     gate_all!(yields, generators, "yield syntax is experimental");
     gate_all!(or_patterns, "or-patterns syntax is experimental");
+    gate_all!(specialization, "specialization is unstable");
 
     let visitor = &mut PostExpansionVisitor {
         context: &ctx,

src/libsyntax/parse/mod.rs

@@ -53,6 +53,8 @@ pub struct GatedSpans {
     pub yields: Lock<Vec<Span>>,
     /// Spans collected for gating `or_patterns`, e.g. `Some(Foo | Bar)`.
     pub or_patterns: Lock<Vec<Span>>,
+    /// Spans collected for gating the `default` qualifier for `specialization`.
+    pub specialization: Lock<Vec<Span>>,
 }
 
 /// Info about a parsing session.

src/libsyntax/parse/parser/item.rs

@@ -833,6 +833,7 @@ impl<'a> Parser<'a> {
             ])
         {
             self.bump(); // `default`
+            self.sess.gated_spans.specialization.borrow_mut().push(self.prev_span);
             Defaultness::Default
         } else {
             Defaultness::Final

src/test/ui/specialization/defaultimpl/specialization-feature-gate-default.stderr

@@ -1,10 +1,8 @@
 error[E0658]: specialization is unstable
   --> $DIR/specialization-feature-gate-default.rs:7:1
    |
-LL | / default impl<T> Foo for T {
-LL | |     fn foo(&self) {}
-LL | | }
-   | |_^
+LL | default impl<T> Foo for T {
+   | ^^^^^^^
    |
    = note: for more information, see https://github.com/rust-lang/rust/issues/31844
    = help: add `#![feature(specialization)]` to the crate attributes to enable

src/test/ui/specialization/specialization-feature-gate-default.rs

@@ -6,8 +6,16 @@ trait Foo {
     fn foo(&self);
 }
 
+#[cfg(FALSE)]
 impl<T> Foo for T {
-    default fn foo(&self) {} //~ ERROR specialization is unstable
+    default //~ ERROR specialization is unstable
+    fn foo(&self) {}
+}
+
+#[cfg(FALSE)]
+default //~ ERROR specialization is unstable
+impl<T> Foo for T {
+    fn foo(&self) {}
 }
 
 fn main() {}

src/test/ui/specialization/specialization-feature-gate-default.stderr

@@ -1,12 +1,21 @@
 error[E0658]: specialization is unstable
-  --> $DIR/specialization-feature-gate-default.rs:10:5
+  --> $DIR/specialization-feature-gate-default.rs:11:5
    |
-LL |     default fn foo(&self) {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     default
+   |     ^^^^^^^
    |
    = note: for more information, see https://github.com/rust-lang/rust/issues/31844
    = help: add `#![feature(specialization)]` to the crate attributes to enable
 
-error: aborting due to previous error
+error[E0658]: specialization is unstable
+  --> $DIR/specialization-feature-gate-default.rs:16:1
+   |
+LL | default
+   | ^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/31844
+   = help: add `#![feature(specialization)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.