[modules] When explicitly importing a module, it's fine for the imported module

to be newer than we were expecting. That happens if .pcm's get moved between
file systems during a distributed build. (It's still not OK for them to actually
be different, though, so we still check the size and signature matches.)

llvm-svn: 222507

clang/lib/Serialization/ModuleManager.cpp

@@ -67,6 +67,13 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
   // Look for the file entry. This only fails if the expected size or
   // modification time differ.
   const FileEntry *Entry;
+  if (Type == MK_ExplicitModule) {
+    // 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
+    // contents, but we can't check that.)
+    ExpectedModTime = 0;
+  }
   if (lookupModuleFile(FileName, ExpectedSize, ExpectedModTime, Entry)) {
     ErrorStr = "module file out of date";
     return OutOfDate;