[clang][Modules] Clarify error message when size check fails in lookupModuleFile

Author: cyndyishida

clang/lib/Serialization/ModuleManager.cpp

@@ -110,7 +110,9 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
   // Look for the file entry. This only fails if the expected size or
   // modification time differ.
   OptionalFileEntryRef Entry;
-  if (Type == MK_ExplicitModule || Type == MK_PrebuiltModule) {
+  const bool IgnoreModTime =
+      (Type == MK_ExplicitModule || Type == MK_PrebuiltModule);
+  if (IgnoreModTime) {
     // If we're not expecting to pull this file out of the module cache, it
     // might have a different mtime due to being moved across filesystems in
     // a distributed build. The size must still match, though. (As must the
@@ -120,7 +122,9 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
   // Note: ExpectedSize and ExpectedModTime will be 0 for MK_ImplicitModule
   // when using an ASTFileSignature.
   if (lookupModuleFile(FileName, ExpectedSize, ExpectedModTime, Entry)) {
-    ErrorStr = "module file has a different size or mtime than expected";
+    ErrorStr = IgnoreModTime
+                   ? "module file has a different size than expected"
+                   : "module file has a different size or mtime than expected";
     return OutOfDate;
   }
 

clang/test/Modules/explicit-build.cpp

@@ -199,6 +199,6 @@
 // RUN:            -fmodule-file=%t/c.pcm \
 // RUN:            %s -DHAVE_A -DHAVE_B -DHAVE_C 2>&1 | FileCheck --check-prefix=CHECK-MISMATCHED-B %s
 //
-// CHECK-MISMATCHED-B:      fatal error: module file '{{.*}}b.pcm' is out of date and needs to be rebuilt: module file has a different size or mtime than expected
+// CHECK-MISMATCHED-B:      fatal error: module file '{{.*}}b.pcm' is out of date and needs to be rebuilt: module file has a different size than expected
 // CHECK-MISMATCHED-B-NEXT: note: imported by module 'c'
 // CHECK-MISMATCHED-B-NOT:  note: