[Cache] Emit cache-hit remark for diagnostics

Author: cachemeifyoucan

lib/Frontend/CachingUtils.cpp

@@ -244,6 +244,10 @@ bool replayCachedCompilerOutputs(
     Diag.diagnose(SourceLoc(), diag::error_replay_cached_diag,
                   toString(std::move(E)));
     return false;
+  } else {
+    if (CacheRemarks)
+      Diag.diagnose(SourceLoc(), diag::replay_output, "<cached-diagnostics>",
+                    DiagnosticsOutput->Key);
   }
 
   // Replay the result only when everything is resolved.

test/CAS/cache_replay.swift

@@ -18,7 +18,9 @@
 // RUN:  -module-name Test -o %t/test.o -cas-path %t/cas -allow-unstable-cache-key-for-testing 2>&1 | %FileCheck --allow-empty --check-prefix=SKIP-CACHE %s
 
 // CACHE-MISS: remark: cache miss output file
-// CACHE-HIT: remark: replay output file
+// CACHE-HIT: remark: replay output file '<cached-diagnostics>': key 'llvmcas://{{.*}}'
+// CACHE-HIT: remark: replay output file '{{.*}}{{/|\\}}test.o': key 'llvmcas://{{.*}}'
+// CACHE-HIT: remark: replay output file '{{.*}}{{/|\\}}Test.swiftmodule': key 'llvmcas://{{.*}}'
 // SKIP-CACHE-NOT: remark:
 
 func testFunc() {}