Directly encode Defaultness in metadata.

Author: cjgillot

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1450,7 +1450,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 }))
             }
             hir::ItemKind::Impl(hir::Impl { defaultness, constness, .. }) => {
-                record!(self.tables.impl_defaultness[def_id] <- defaultness);
+                self.tables.impl_defaultness.set(def_id.index, defaultness);
                 self.tables.impl_constness.set(def_id.index, constness);
 
                 let trait_ref = self.tcx.impl_trait_ref(def_id);

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -312,7 +312,7 @@ define_tables! {
     impl_parent: Table<DefIndex, Lazy!(DefId)>,
     impl_polarity: Table<DefIndex, ty::ImplPolarity>,
     impl_constness: Table<DefIndex, hir::Constness>,
-    impl_defaultness: Table<DefIndex, Lazy!(hir::Defaultness)>,
+    impl_defaultness: Table<DefIndex, hir::Defaultness>,
     // FIXME(eddyb) perhaps compute this on the fly if cheap enough?
     coerce_unsized_info: Table<DefIndex, Lazy!(ty::adjustment::CoerceUnsizedInfo)>,
     mir_const_qualif: Table<DefIndex, Lazy!(mir::ConstQualifs)>,

compiler/rustc_metadata/src/rmeta/table.rs

@@ -120,6 +120,14 @@ fixed_size_enum! {
     }
 }
 
+fixed_size_enum! {
+    hir::Defaultness {
+        ( Final                        )
+        ( Default { has_value: false } )
+        ( Default { has_value: true }  )
+    }
+}
+
 // NOTE(eddyb) there could be an impl for `usize`, which would enable a more
 // generic `Lazy<T>` impl, but in the general case we might not need / want to
 // fit every `usize` in `u32`.