1 files changed, 38 insertions, 4 deletions
diff --git a/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp b/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
index 7436c7256327..b4d5a29ca695 100644
--- a/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
+++ b/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
@@ -122,6 +122,32 @@ DependencyScanningFilesystemSharedCache::get(StringRef Key) {
   return It.first->getValue();
 }
 
+/// Whitelist file extensions that should be minimized, treating no extension as
+/// a source file that should be minimized.
+///
+/// This is kinda hacky, it would be better if we knew what kind of file Clang
+/// was expecting instead.
+static bool shouldMinimize(StringRef Filename) {
+  StringRef Ext = llvm::sys::path::extension(Filename);
+  if (Ext.empty())
+    return true; // C++ standard library
+  return llvm::StringSwitch<bool>(Ext)
+    .CasesLower(".c", ".cc", ".cpp", ".c++", ".cxx", true)
+    .CasesLower(".h", ".hh", ".hpp", ".h++", ".hxx", true)
+    .CasesLower(".m", ".mm", true)
+    .CasesLower(".i", ".ii", ".mi", ".mmi", true)
+    .CasesLower(".def", ".inc", true)
+    .Default(false);
+}
+
+
+static bool shouldCacheStatFailures(StringRef Filename) {
+  StringRef Ext = llvm::sys::path::extension(Filename);
+  if (Ext.empty())
+    return false; // This may be the module cache directory.
+  return shouldMinimize(Filename); // Only cache stat failures on source files.
+}
+
 llvm::ErrorOr<const CachedFileSystemEntry *>
 DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(
     const StringRef Filename) {
@@ -132,7 +158,8 @@ DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(
   // FIXME: Handle PCM/PCH files.
   // FIXME: Handle module map files.
 
-  bool KeepOriginalSource = IgnoredFiles.count(Filename);
+  bool KeepOriginalSource = IgnoredFiles.count(Filename) ||
+                            !shouldMinimize(Filename);
   DependencyScanningFilesystemSharedCache::SharedFileSystemEntry
       &SharedCacheEntry = SharedCache.get(Filename);
   const CachedFileSystemEntry *Result;
@@ -143,9 +170,16 @@ DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(
     if (!CacheEntry.isValid()) {
       llvm::vfs::FileSystem &FS = getUnderlyingFS();
       auto MaybeStatus = FS.status(Filename);
-      if (!MaybeStatus)
-        CacheEntry = CachedFileSystemEntry(MaybeStatus.getError());
-      else if (MaybeStatus->isDirectory())
+      if (!MaybeStatus) {
+        if (!shouldCacheStatFailures(Filename))
+          // HACK: We need to always restat non source files if the stat fails.
+          //   This is because Clang first looks up the module cache and module
+          //   files before building them, and then looks for them again. If we
+          //   cache the stat failure, it won't see them the second time.
+          return MaybeStatus.getError();
+        else
+          CacheEntry = CachedFileSystemEntry(MaybeStatus.getError());
+      } else if (MaybeStatus->isDirectory())
         CacheEntry = CachedFileSystemEntry::createDirectoryEntry(
             std::move(*MaybeStatus));
       else