experiment query caching

Author: jdonszelmann

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -1,6 +1,6 @@
 use ast::StaticItem;
 use itertools::{Itertools, Position};
-use rustc_ast::{self as ast, EiiImpl, ModKind, ModKind, Safety, TraitAlias};
+use rustc_ast::{self as ast, EiiImpl, ModKind, Safety, TraitAlias};
 use rustc_span::Ident;
 
 use crate::pp::BoxMarker;

compiler/rustc_middle/src/query/mod.rs

@@ -2746,9 +2746,10 @@ rustc_queries! {
     }
 
     /// Returns a list of all `externally implementable items` crate.
-    query externally_implementable_items(_: CrateNum) -> &'tcx FxIndexMap<DefId, (EiiDecl, FxIndexMap<DefId, EiiImpl>)> {
+    query externally_implementable_items(cnum: CrateNum) -> &'tcx FxIndexMap<DefId, (EiiDecl, FxIndexMap<DefId, EiiImpl>)> {
         arena_cache
         desc { "looking up the externally implementable items of a crate" }
+        cache_on_disk_if { *cnum == LOCAL_CRATE }
         separate_provide_extern
     }
 }