Encode stability for default generic parameters

Author: varkor

src/librustc_metadata/rmeta/encoder.rs

@@ -1579,9 +1579,13 @@ impl EncodeContext<'tcx> {
                         EntryKind::TypeParam,
                         default.is_some(),
                     );
+                    if default.is_some() {
+                        self.encode_stability(def_id);
+                    }
                 }
                 GenericParamKind::Const { .. } => {
                     self.encode_info_for_generic_param(def_id, EntryKind::ConstParam, true);
+                    // FIXME(const_generics:defaults)
                 }
             }
         }

src/librustc_passes/stability.rs

@@ -138,13 +138,10 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             } else {
                 debug!("annotate: not found, parent = {:?}", self.parent_stab);
                 if let Some(stab) = self.parent_stab {
-                    // Instability (but not typically stability) is inherited from the parent.
-                    // If something is unstable, everything inside it should also be
-                    // considered unstable.
-                    // `AnnotationKind::Optional` items also inherit stability, as they may be
-                    // considered stable-by-default items, requiring an instability attribute to
-                    // override this.
-                    if stab.level.is_unstable() || kind == AnnotationKind::Optional {
+                    // Instability is inherited from the parent: if something is unstable,
+                    // everything inside it should also be considered unstable for the same
+                    // reason.
+                    if stab.level.is_unstable() {
                         self.index.stab_map.insert(hir_id, stab);
                     }
                 }
@@ -176,7 +173,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             // Propagate unstability.  This can happen even for non-staged-api crates in case
             // -Zforce-unstable-if-unmarked is set.
             if let Some(stab) = self.parent_stab {
-                if stab.level.is_unstable() || kind == AnnotationKind::Optional {
+                if stab.level.is_unstable() {
                     self.index.stab_map.insert(hir_id, stab);
                 }
             }

src/test/ui/stability-attribute/auxiliary/unstable_generic_param.rs

@@ -4,7 +4,13 @@
 #![stable(feature = "stable_test_feature", since = "1.0.0")]
 
 #[stable(feature = "stable_test_feature", since = "1.0.0")]
-pub trait Trait<#[unstable(feature = "ty", issue = "none")] T = ()> {
+pub trait Trait1<#[unstable(feature = "unstable_default", issue = "none")] T = ()> {
+    #[stable(feature = "stable_test_feature", since = "1.0.0")]
+    fn foo() -> T;
+}
+
+#[stable(feature = "stable_test_feature", since = "1.0.0")]
+pub trait Trait2<T = ()> {
     #[stable(feature = "stable_test_feature", since = "1.0.0")]
     fn foo() -> T;
 }

src/test/ui/stability-attribute/generics-default-stability.rs

@@ -2,14 +2,24 @@
 
 extern crate unstable_generic_param;
 
-use unstable_generic_param::Trait;
+use unstable_generic_param::{Trait1, Trait2};
+
+struct R;
+
+impl Trait1 for S {
+    fn foo() -> () { () } // ok
+}
 
 struct S;
 
-impl Trait<usize> for S {
+impl Trait1<usize> for S { //~ ERROR use of unstable library feature 'unstable_default'
     fn foo() -> usize { 0 }
 }
 
+impl Trait2<usize> for S {
+    fn foo() -> usize { 0 } // ok
+}
+
 fn main() {
     let _ = S;
 }

src/test/ui/stability-attribute/generics-default-stability.stderr

@@ -0,0 +1,11 @@
+error[E0658]: use of unstable library feature 'unstable_default'
+  --> $DIR/generics-default-stability.rs:15:13
+   |
+LL | impl Trait1<usize> for S {
+   |             ^^^^^
+   |
+   = help: add `#![feature(unstable_default)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.