From 4cdf264e6fe58325dcedb2f571cbac4aed095eb7 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 9 Sep 2022 15:34:11 +0000
Subject: [PATCH] cache collect_trait_impl_trait_tys

---
 compiler/rustc_middle/src/arena.rs             | 2 +-
 compiler/rustc_middle/src/query/mod.rs         | 3 ++-
 compiler/rustc_query_impl/src/on_disk_cache.rs | 6 ++++++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 9b1fedd0b533c..6bdf5a023b6c3 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -102,7 +102,7 @@ macro_rules! arena_types {
 
             [] dep_kind: rustc_middle::dep_graph::DepKindStruct<'tcx>,
 
-            [] trait_impl_trait_tys: rustc_data_structures::fx::FxHashMap<rustc_hir::def_id::DefId, rustc_middle::ty::Ty<'tcx>>,
+            [decode] trait_impl_trait_tys: rustc_data_structures::fx::FxHashMap<rustc_hir::def_id::DefId, rustc_middle::ty::Ty<'tcx>>,
         ]);
     )
 }
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 0fe22a26cd503..5cc2b7984d709 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -164,7 +164,8 @@ rustc_queries! {
     query collect_trait_impl_trait_tys(key: DefId)
         -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed>
     {
-        desc { "better description please" }
+        desc { "compare an impl and trait method signature, inferring any hidden `impl Trait` types in the process" }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
diff --git a/compiler/rustc_query_impl/src/on_disk_cache.rs b/compiler/rustc_query_impl/src/on_disk_cache.rs
index 5ef95911f562d..0e93f3ce1d646 100644
--- a/compiler/rustc_query_impl/src/on_disk_cache.rs
+++ b/compiler/rustc_query_impl/src/on_disk_cache.rs
@@ -798,6 +798,12 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx FxHashSet<LocalDefId>
     }
 }
 
+impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx FxHashMap<DefId, Ty<'tcx>> {
+    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {
+        RefDecodable::decode(d)
+    }
+}
+
 impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>>
     for &'tcx IndexVec<mir::Promoted, mir::Body<'tcx>>
 {