From 6802082039285bc07736f8c9900a0410b5c1e7dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 15:08:03 +0200
Subject: [PATCH] Hash all of the import_ids for the TraitCandidate.

---
 src/librustc/ich/impls_hir.rs                 | 12 ++++++------
 src/librustc_data_structures/stable_hasher.rs | 12 ++++++++++++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/librustc/ich/impls_hir.rs b/src/librustc/ich/impls_hir.rs
index 5bd359ba1f6..5b2a1e783c0 100644
--- a/src/librustc/ich/impls_hir.rs
+++ b/src/librustc/ich/impls_hir.rs
@@ -7,6 +7,7 @@ use crate::hir::def_id::{DefId, LocalDefId, CrateNum, CRATE_DEF_INDEX};
 use crate::ich::{StableHashingContext, NodeIdHashingMode, Fingerprint};
 use rustc_data_structures::stable_hasher::{HashStable, ToStableHashKey,
                                            StableHasher, StableHasherResult};
+use smallvec::SmallVec;
 use std::mem;
 use syntax::ast;
 use syntax::attr;
@@ -397,14 +398,13 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::TraitCandidate {
             } = self;
 
             def_id.hash_stable(hcx, hasher);
-            // We only use the outermost import NodeId as key
-            import_ids.first().hash_stable(hcx, hasher);
+            import_ids.hash_stable(hcx, hasher);
         });
     }
 }
 
 impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
-    type KeyType = (DefPathHash, Option<(DefPathHash, hir::ItemLocalId)>);
+    type KeyType = (DefPathHash, SmallVec<[(DefPathHash, hir::ItemLocalId); 1]>);
 
     fn to_stable_hash_key(&self,
                           hcx: &StableHashingContext<'a>)
@@ -414,10 +414,10 @@ impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
             import_ids,
         } = self;
 
-        let first_import_id = import_ids.first().map(|node_id| hcx.node_to_hir_id(*node_id))
+        let import_keys = import_ids.iter().map(|node_id| hcx.node_to_hir_id(*node_id))
                                            .map(|hir_id| (hcx.local_def_path_hash(hir_id.owner),
-                                                          hir_id.local_id));
-        (hcx.def_path_hash(*def_id), first_import_id)
+                                                          hir_id.local_id)).collect();
+        (hcx.def_path_hash(*def_id), import_keys)
     }
 }
 
diff --git a/src/librustc_data_structures/stable_hasher.rs b/src/librustc_data_structures/stable_hasher.rs
index 19343a9250d..c777f1fa829 100644
--- a/src/librustc_data_structures/stable_hasher.rs
+++ b/src/librustc_data_structures/stable_hasher.rs
@@ -1,6 +1,7 @@
 use std::hash::{Hash, Hasher, BuildHasher};
 use std::marker::PhantomData;
 use std::mem;
+use smallvec::SmallVec;
 use crate::sip128::SipHasher128;
 use crate::indexed_vec;
 use crate::bit_set;
@@ -318,6 +319,17 @@ impl<T: HashStable<CTX>, CTX> HashStable<CTX> for Vec<T> {
     }
 }
 
+impl<A, CTX> HashStable<CTX> for SmallVec<[A; 1]> where A: HashStable<CTX> {
+    #[inline]
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          ctx: &mut CTX,
+                                          hasher: &mut StableHasher<W>) {
+        for item in self {
+            item.hash_stable(ctx, hasher);
+        }
+    }
+}
+
 impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for Box<T> {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,