Add impl_constness query

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -959,6 +959,10 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         self.get_impl_data(id).defaultness
     }
 
+    fn get_impl_constness(&self, id: DefIndex) -> hir::Constness {
+        self.get_impl_data(id).constness
+    }
+
     fn get_coerce_unsized_info(&self, id: DefIndex) -> Option<ty::adjustment::CoerceUnsizedInfo> {
         self.get_impl_data(id).coerce_unsized_info
     }

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -168,6 +168,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     is_no_builtins => { cdata.root.no_builtins }
     symbol_mangling_version => { cdata.root.symbol_mangling_version }
     impl_defaultness => { cdata.get_impl_defaultness(def_id.index) }
+    impl_constness => { cdata.get_impl_constness(def_id.index) }
     reachable_non_generics => {
         let reachable_non_generics = tcx
             .exported_symbols(cdata.cnum)

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1412,7 +1412,7 @@ impl EncodeContext<'a, 'tcx> {
                     adt_def.repr,
                 )
             }
-            hir::ItemKind::Impl(hir::Impl { defaultness, .. }) => {
+            hir::ItemKind::Impl(hir::Impl { defaultness, constness, .. }) => {
                 let trait_ref = self.tcx.impl_trait_ref(def_id);
                 let polarity = self.tcx.impl_polarity(def_id);
                 let parent = if let Some(trait_ref) = trait_ref {
@@ -1437,8 +1437,13 @@ impl EncodeContext<'a, 'tcx> {
                     }
                 });
 
-                let data =
+                let data = ImplData {
-                    ImplData { polarity, defaultness, parent_impl: parent, coerce_unsized_info };
+                    polarity,
+                    defaultness,
+                    constness,
+                    parent_impl: parent,
+                    coerce_unsized_info,
+                };
 
                 EntryKind::Impl(self.lazy(data))
             }

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -390,6 +390,7 @@ struct TraitData {
 #[derive(TyEncodable, TyDecodable)]
 struct ImplData {
     polarity: ty::ImplPolarity,
+    constness: hir::Constness,
     defaultness: hir::Defaultness,
     parent_impl: Option<DefId>,
 

compiler/rustc_middle/src/query/mod.rs

@@ -1136,6 +1136,10 @@ rustc_queries! {
         desc { |tcx| "looking up whether `{}` is a default impl", tcx.def_path_str(def_id) }
     }
 
+    query impl_constness(def_id: DefId) -> hir::Constness {
+        desc { |tcx| "looking up whether `{}` is a default impl", tcx.def_path_str(def_id) }
+    }
+
     query check_item_well_formed(key: LocalDefId) -> () {
         desc { |tcx| "checking that `{}` is well-formed", tcx.def_path_str(key.to_def_id()) }
     }

compiler/rustc_ty_utils/src/ty.rs

@@ -168,6 +168,16 @@ fn impl_defaultness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Defaultness {
     }
 }
 
+fn impl_constness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Constness {
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
+    let item = tcx.hir().expect_item(hir_id);
+    if let hir::ItemKind::Impl(impl_) = &item.kind {
+        impl_.constness
+    } else {
+        bug!("`impl_constness` called on {:?}", item);
+    }
+}
+
 /// Calculates the `Sized` constraint.
 ///
 /// In fact, there are only a few options for the types in the constraint:
@@ -535,6 +545,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
         instance_def_size_estimate,
         issue33140_self_ty,
         impl_defaultness,
+        impl_constness,
         conservative_is_privately_uninhabited: conservative_is_privately_uninhabited_raw,
         ..*providers
     };