don't encode only locally used attrs

compiler/rustc_middle/src/query/mod.rs

@@ -1072,6 +1072,9 @@ rustc_queries! {
         desc { |tcx| "checking whether `{}` is `doc(hidden)`", tcx.def_path_str(def_id) }
     }
 
+    /// Returns the attributes on the item at `def_id`.
+    ///
+    /// Do not use this directly, use `tcx.get_attrs` instead.
     query item_attrs(def_id: DefId) -> &'tcx [ast::Attribute] {
         desc { |tcx| "collecting attributes of `{}`", tcx.def_path_str(def_id) }
         separate_provide_extern

compiler/rustc_middle/src/ty/mod.rs

@@ -2187,6 +2187,10 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Gets the attributes of a definition.
+    ///
+    /// Note that attributes which are be relevant while
+    /// the current local crate are not stored in the crate metadata
+    /// and therefore cannot be accessed outside of that crate.
     pub fn get_attrs(self, did: DefId) -> Attributes<'tcx> {
         if let Some(did) = did.as_local() {
             self.hir().attrs(self.hir().local_def_id_to_hir_id(did))