Introduce FileEntryRef and use it when handling includes to report correct dependencies when the FileManager is reused across invocations

[arphaman]

Summary

This patch introduces a parallel API to FileManager's getFile: getFileEntryRef, which returns a reference to the FileEntry, and the name that was used to access the file.

The new API is adopted only in the HeaderSearch and Preprocessor for include file lookup, so that the accessed path can be propagated to SourceManager's FileInfo. SourceManager's FileInfo now can report this accessed path, using the new getName method. This API is then adopted in the dependency collector, which now correctly reports dependencies when a file is included both using a symlink and a real path in the case when the FileManager is reused across multiple Preprocessor invocations.

Note that this patch does not fix all dependency collector issues, as the same problem is still present in other cases when dependencies are obtained using FileSkipped, InclusionDirective, and HasInclude. This will be fixed in a follow-up patch.

[arphaman]

Fix a bug with dereferencing None File value in one call.

[arphaman]

I forgot I left a FIXME that I intended to fix in there, I need to resolve that first. I'll update the patch.

[arphaman]

Fix the FIXME.
The patch is now ready for review.

[Bigcheese]

clang/include/clang/Basic/FileManager.h

130

Isn't this incorrect in the case of symlinks?

249–251

LLVM_DEPRECATED()? (or w/e the name is of our depreciation attribute macro).

[Bigcheese]

clang/include/clang/Basic/SourceManager.h

1024

Invalid? I realize this is copied from above, but i'd fix the name.

clang/lib/Lex/PPDirectives.cpp

1757–1765

This lambda is huge and I only see it used once. Should this be a separate function?

[bruno]

clang/include/clang/Basic/FileManager.h

110

How does that work with the VFS? Will it keep the virtual path as the FileName to return with getName() or the external-content? Should it change when in face of use-external-names attribute?

249–251

Probably can't be done until we move all uses over? There's probably still enough of them that the warning would be very annoying?

clang/lib/Basic/FileManager.cpp

194

I know the surrounding functions are not consistent with capitalization, but maybe name and value here should?

[arphaman]

Address review comments and proper use-external-names support.

clang/include/clang/Basic/FileManager.h

110

Good catch. In the first patch getFileRef didn't honor use-external-names correctly (specifically once a file was opened once, for subsequent open of that file, it returned the VFS name, not the external name).

I fixed this issue by introducing a potential indirection to SeenFileEntries in the update patch. Now the getFileRef should always return the virtual path, unless use-external-names is specified, and then it will return the external path.

130

Right, I was planning to provide another way to get a directory with name. For now I'll just remove this method, so clients will have to call into FileEntry.

249–251

That's right, I can't mark the function as deprecated just yet, as you'll get a lot of warnings when building clang.

[arphaman]

remove accidentally include diff's .rej file.

[JamesNagurne]

@arphaman you disabled this test on Windows, but did not specify exactly how it fails.
My team works on an embedded ARM compiler (most similar to arm-none-eabi), and we're now seeing failures from DependencyScannerTest. I can't find a buildbot failure for this test so I can't cross-reference to see if we have the same issue.

Does this failure look similar to what you saw on Windows, or could it be an option we're adding as part of the Compilation setup?

[ RUN      ] DependencyScanner.ScanDepsReuseFilemanager
.../clang/unittests/Tooling/DependencyScannerTest.cpp:100: Failure
      Expected: Deps[1]
      Which is: "symlink.h"
To be equal to: "/root/symlink.h"
.../clang/unittests/Tooling/DependencyScannerTest.cpp:101: Failure
      Expected: Deps[2]
      Which is: "header.h"
To be equal to: "/root/header.h"
.../clang/unittests/Tooling/DependencyScannerTest.cpp:113: Failure
      Expected: Deps[1]
      Which is: "symlink.h"
To be equal to: "/root/symlink.h"
.../clang/unittests/Tooling/DependencyScannerTest.cpp:114: Failure
      Expected: Deps[2]
      Which is: "header.h"
To be equal to: "/root/header.h"
[  FAILED  ] DependencyScanner.ScanDepsReuseFilemanager (5 ms)

[arphaman]

In D65907#1643364, @JamesNagurne wrote:

@arphaman you disabled this test on Windows, but did not specify exactly how it fails.
My team works on an embedded ARM compiler (most similar to arm-none-eabi), and we're now seeing failures from DependencyScannerTest. I can't find a buildbot failure for this test so I can't cross-reference to see if we have the same issue.

Does this failure look similar to what you saw on Windows, or could it be an option we're adding as part of the Compilation setup?

[ RUN      ] DependencyScanner.ScanDepsReuseFilemanager
.../clang/unittests/Tooling/DependencyScannerTest.cpp:100: Failure
      Expected: Deps[1]
      Which is: "symlink.h"
To be equal to: "/root/symlink.h"
.../clang/unittests/Tooling/DependencyScannerTest.cpp:101: Failure
      Expected: Deps[2]
      Which is: "header.h"
To be equal to: "/root/header.h"
.../clang/unittests/Tooling/DependencyScannerTest.cpp:113: Failure
      Expected: Deps[1]
      Which is: "symlink.h"
To be equal to: "/root/symlink.h"
.../clang/unittests/Tooling/DependencyScannerTest.cpp:114: Failure
      Expected: Deps[2]
      Which is: "header.h"
To be equal to: "/root/header.h"
[  FAILED  ] DependencyScanner.ScanDepsReuseFilemanager (5 ms)

No the windows test failure was different, there were no Deps at all. I'm currently investigating it on a windows VM.

@JamesNagurne I think there's some issue with the working directory, which is not added in your case. Which platform are you running your build/test on? Which cmake options are you using?

[JamesNagurne]

In D65907#1643650, @arphaman wrote:

No the windows test failure was different, there were no Deps at all. I'm currently investigating it on a windows VM.

@JamesNagurne I think there's some issue with the working directory, which is not added in your case. Which platform are you running your build/test on? Which cmake options are you using?

I apologize for not giving such information in the first reply. Unfortunately this isn't an easy remote reproduction, as our ToolChain and some integral changes aren't upstreamed. This is an embedded ARM cross-compiled on Linux. Might be able to reproduce with arm-none-none-eabi.
LLVM is built as an external project. Looking at the build system, it looks like we have the CMAKE_ARGS:

-DLLVM_DEFAULT_TARGET_TRIPLE=arm-ti-none-eabi
-DLLVM_EXTERNAL_CLANG_SOURCE_DIR=${CMAKE_SOURCE_DIR}/llvm-project/clang
-DLLVM_TARGETS_TO_BUILD=ARM
-DCMAKE_BUILD_TYPE=Release
-DCMAKE_CXX_COMPILER=clang++
-DCMAKE_C_COMPILER=clang
-DLLVM_USE_LINKER=gold
-GNinja

Nothing suspicious, except maybe the default triple and ARM target.
Looking at our (not upstream) toolchain file, we do have some RTLibs, LibInternal, libcxx, and System include changes, along with a -nostdsysteminc to avoid pulling host includes into our cross compiler. However, none of this should affect general "#include" behavior, correct?
Another glance at your changes don't seem to affect any target-specific handling either, at least directly.

I might have to just bite the bullet and drop into the test with a debugger.

[arphaman]

In D65907#1643800, @JamesNagurne wrote:

In D65907#1643650, @arphaman wrote:

No the windows test failure was different, there were no Deps at all. I'm currently investigating it on a windows VM.

@JamesNagurne I think there's some issue with the working directory, which is not added in your case. Which platform are you running your build/test on? Which cmake options are you using?

I apologize for not giving such information in the first reply. Unfortunately this isn't an easy remote reproduction, as our ToolChain and some integral changes aren't upstreamed. This is an embedded ARM cross-compiled on Linux. Might be able to reproduce with arm-none-none-eabi.
LLVM is built as an external project. Looking at the build system, it looks like we have the CMAKE_ARGS:

-DLLVM_DEFAULT_TARGET_TRIPLE=arm-ti-none-eabi
-DLLVM_EXTERNAL_CLANG_SOURCE_DIR=${CMAKE_SOURCE_DIR}/llvm-project/clang
-DLLVM_TARGETS_TO_BUILD=ARM
-DCMAKE_BUILD_TYPE=Release
-DCMAKE_CXX_COMPILER=clang++
-DCMAKE_C_COMPILER=clang
-DLLVM_USE_LINKER=gold
-GNinja

Nothing suspicious, except maybe the default triple and ARM target.
Looking at our (not upstream) toolchain file, we do have some RTLibs, LibInternal, libcxx, and System include changes, along with a -nostdsysteminc to avoid pulling host includes into our cross compiler. However, none of this should affect general "#include" behavior, correct?
Another glance at your changes don't seem to affect any target-specific handling either, at least directly.

Yes, I don't see anything in your changes that is an obvious thing to blame.

I might have to just bite the bullet and drop into the test with a debugger.

I fixed the Windows issue, and it was completely unrelated to your issue. It looks like the FileManager isn't constructing absolute paths when accessing the files, which is somewhat unexpected. It would be useful to debug invocations of getFileEntryRef, to see if the InterndFilename in the function is getting changed into an absolute path or not.

[JamesNagurne]

In D65907#1645474, @arphaman wrote:

In D65907#1643800, @JamesNagurne wrote:

In D65907#1643650, @arphaman wrote:

No the windows test failure was different, there were no Deps at all. I'm currently investigating it on a windows VM.

@JamesNagurne I think there's some issue with the working directory, which is not added in your case. Which platform are you running your build/test on? Which cmake options are you using?

I apologize for not giving such information in the first reply. Unfortunately this isn't an easy remote reproduction, as our ToolChain and some integral changes aren't upstreamed. This is an embedded ARM cross-compiled on Linux. Might be able to reproduce with arm-none-none-eabi.
LLVM is built as an external project. Looking at the build system, it looks like we have the CMAKE_ARGS:

-DLLVM_DEFAULT_TARGET_TRIPLE=arm-ti-none-eabi
-DLLVM_EXTERNAL_CLANG_SOURCE_DIR=${CMAKE_SOURCE_DIR}/llvm-project/clang
-DLLVM_TARGETS_TO_BUILD=ARM
-DCMAKE_BUILD_TYPE=Release
-DCMAKE_CXX_COMPILER=clang++
-DCMAKE_C_COMPILER=clang
-DLLVM_USE_LINKER=gold
-GNinja

Nothing suspicious, except maybe the default triple and ARM target.
Looking at our (not upstream) toolchain file, we do have some RTLibs, LibInternal, libcxx, and System include changes, along with a -nostdsysteminc to avoid pulling host includes into our cross compiler. However, none of this should affect general "#include" behavior, correct?
Another glance at your changes don't seem to affect any target-specific handling either, at least directly.

Yes, I don't see anything in your changes that is an obvious thing to blame.

I might have to just bite the bullet and drop into the test with a debugger.

I fixed the Windows issue, and it was completely unrelated to your issue. It looks like the FileManager isn't constructing absolute paths when accessing the files, which is somewhat unexpected. It would be useful to debug invocations of getFileEntryRef, to see if the InterndFilename in the function is getting changed into an absolute path or not.

We found and fixed the issue on our end. Turns out we had a nefarious little piece of code in AddClangSystemIncludeArgs:

if (!DriverArgs.hasArg(options::OPT_nostdlibinc)) {
  SmallString<128> Dir(getDriver().SysRoot);
  llvm::sys::path::append(Dir, "include");
  addSystemInclude(DriverArgs, CC1Args, Dir.str());
}

Turns out that, as a cross compiler, we had set SysRoot to the empty string. So, we were adding "-internal-isystem" "include" to the cc1 arguments, which somehow caused the test to fail. I don't know precisely why it exposes issues in your test, but the code is clearly busted, so we've removed it.

I appreciate the responses as we've worked through the problems on our end!

clang/include/clang/Basic/FileManager.h

void closeFile() const {
     File.reset(); // rely on destructor to close File
   }
 
   // Only for use in tests to see if deferred opens are happening, rather than
   // relying on RealPathName being empty.
   bool isOpenForTests() const { return File != nullptr; }
 };
 
+/// A reference to a \c FileEntry that includes the name of the file as it was
+/// accessed by the FileManager's client.
+class FileEntryRef {
+public:
+  FileEntryRef(StringRef Name, const FileEntry &Entry)
+      : Name(Name), Entry(Entry) {}
+
+  const StringRef getName() const { return Name; }
+
+  const FileEntry &getFileEntry() const { return Entry; }
+
+  off_t getSize() const { return Entry.getSize(); }
+
+  unsigned getUID() const { return Entry.getUID(); }
+
+  const llvm::sys::fs::UniqueID &getUniqueID() const {
+    return Entry.getUniqueID();
+  }
+
+  time_t getModificationTime() const { return Entry.getModificationTime(); }
+
+  const DirectoryEntry *getDir() const { return Entry.getDir(); }
+
+private:
+  StringRef Name;
+  const FileEntry &Entry;
+};
+
 /// Implements support for file system lookup, file system caching,
 /// and directory search management.
 ///
 /// This also handles more advanced properties, such as uniquing files based
 /// on "inode", so that a file with two names (e.g. symlinked) will be treated
 /// as a single file.
 ///
 class FileManager : public RefCountedBase<FileManager> {
public:
   ///
   /// \param statCache the new stat cache to install. Ownership of this
   /// object is transferred to the FileManager.
   void setStatCache(std::unique_ptr<FileSystemStatCache> statCache);
 
   /// Removes the FileSystemStatCache object from the manager.
   void clearStatCache();
 
+  /// Returns the number of unique real file entries cached by the file manager.
+  size_t getNumUniqueRealFiles() const { return UniqueRealFiles.size(); }
+
   /// Lookup, cache, and verify the specified directory (real or
   /// virtual).
   ///
   /// This returns a \c std::error_code if there was an error reading the
   /// directory. If there is no error, the DirectoryEntry is guaranteed to be
   /// non-NULL.
   ///
   /// \param CacheFailure If true and the file does not exist, we'll cache
   /// the failure to find this file.
   llvm::ErrorOr<const DirectoryEntry *>
   getDirectory(StringRef DirName, bool CacheFailure = true);
 
   /// Lookup, cache, and verify the specified file (real or
   /// virtual).
   ///
+  /// This function is deprecated and will be removed at some point in the
+  /// future, new clients should use
+  ///  \c getFileRef.
+  ///
   /// This returns a \c std::error_code if there was an error loading the file.
   /// If there is no error, the FileEntry is guaranteed to be non-NULL.
   ///
   /// \param OpenFile if true and the file exists, it will be opened.
   ///
   /// \param CacheFailure If true and the file does not exist, we'll cache
   /// the failure to find this file.
   llvm::ErrorOr<const FileEntry *>
   getFile(StringRef Filename, bool OpenFile = false, bool CacheFailure = true);
 
+  /// Lookup, cache, and verify the specified file (real or virtual). Return the
+  /// reference to the file entry together with the exact path that was used to
+  /// access a file by a particular call to getFileRef.
+  ///
+  /// This returns a \c std::error_code if there was an error loading the file,
+  /// or a \c FileEntryRef otherwise.
+  ///
+  /// \param OpenFile if true and the file exists, it will be opened.
+  ///
+  /// \param CacheFailure If true and the file does not exist, we'll cache
+  /// the failure to find this file.
+  llvm::ErrorOr<FileEntryRef> getFileRef(StringRef Filename,
+                                         bool OpenFile = false,
+                                         bool CacheFailure = true);
+
   /// Returns the current file system options
   FileSystemOptions &getFileSystemOpts() { return FileSystemOpts; }
   const FileSystemOptions &getFileSystemOpts() const { return FileSystemOpts; }
 
   llvm::vfs::FileSystem &getVirtualFileSystem() const { return *FS; }
 
   /// Retrieve a file entry for a "virtual" file that acts as
   /// if there were a file with the given name on disk.

clang/include/clang/Basic/SourceManager.h

class FileInfo {
 
     /// Whether this FileInfo has any \#line directives.
     unsigned HasLineDirectives : 1;
 
     /// The content cache and the characteristic of the file.
     llvm::PointerIntPair<const ContentCache*, 3, CharacteristicKind>
         ContentAndKind;
 
+    /// The filename that is used to access the file entry represented by the
+    /// content cache.
+    StringRef Filename;
+
   public:
     /// Return a FileInfo object.
     static FileInfo get(SourceLocation IL, const ContentCache *Con,
-                        CharacteristicKind FileCharacter) {
+                        CharacteristicKind FileCharacter, StringRef Filename) {
       FileInfo X;
       X.IncludeLoc = IL.getRawEncoding();
       X.NumCreatedFIDs = 0;
       X.HasLineDirectives = false;
       X.ContentAndKind.setPointer(Con);
       X.ContentAndKind.setInt(FileCharacter);
+      X.Filename = Filename;
       return X;
     }
 
     SourceLocation getIncludeLoc() const {
       return SourceLocation::getFromRawEncoding(IncludeLoc);
     }
 
     const ContentCache *getContentCache() const {
       return ContentAndKind.getPointer();
     }
 
     /// Return whether this is a system header or not.
     CharacteristicKind getFileCharacteristic() const {
       return ContentAndKind.getInt();
     }
 
     /// Return true if this FileID has \#line directives in it.
     bool hasLineDirectives() const { return HasLineDirectives; }
 
     /// Set the flag that indicates that this FileID has
     /// line table entries associated with it.
     void setHasLineDirectives() {
       HasLineDirectives = true;
     }
+
+    /// Returns the name of the file that was used when the file was loaded from
+    /// the underlying file system.
+    StringRef getName() const { return Filename; }
   };
 
   /// Each ExpansionInfo encodes the expansion location - where
   /// the token was ultimately expanded, and the SpellingLoc - where the actual
   /// character data for the token came from.
   class ExpansionInfo {
     // Really these are all SourceLocations.
 
public:
   ///
   /// This translates NULL into standard input.
   FileID createFileID(const FileEntry *SourceFile, SourceLocation IncludePos,
                       SrcMgr::CharacteristicKind FileCharacter,
                       int LoadedID = 0, unsigned LoadedOffset = 0) {
     const SrcMgr::ContentCache *IR =
         getOrCreateContentCache(SourceFile, isSystem(FileCharacter));
     assert(IR && "getOrCreateContentCache() cannot return NULL");
-    return createFileID(IR, IncludePos, FileCharacter, LoadedID, LoadedOffset);
+    return createFileID(IR, SourceFile->getName(), IncludePos, FileCharacter,
+                        LoadedID, LoadedOffset);
+  }
+
+  FileID createFileID(FileEntryRef SourceFile, SourceLocation IncludePos,
+                      SrcMgr::CharacteristicKind FileCharacter,
+                      int LoadedID = 0, unsigned LoadedOffset = 0) {
+    const SrcMgr::ContentCache *IR = getOrCreateContentCache(
+        &SourceFile.getFileEntry(), isSystem(FileCharacter));
+    assert(IR && "getOrCreateContentCache() cannot return NULL");
+    return createFileID(IR, SourceFile.getName(), IncludePos, FileCharacter,
+                        LoadedID, LoadedOffset);
   }
 
   /// Create a new FileID that represents the specified memory buffer.
   ///
   /// This does no caching of the buffer and takes ownership of the
   /// MemoryBuffer, so only pass a MemoryBuffer to this once.
   FileID createFileID(std::unique_ptr<llvm::MemoryBuffer> Buffer,
                       SrcMgr::CharacteristicKind FileCharacter = SrcMgr::C_User,
                       int LoadedID = 0, unsigned LoadedOffset = 0,
                       SourceLocation IncludeLoc = SourceLocation()) {
+    StringRef Name = Buffer->getBufferIdentifier();
     return createFileID(
         createMemBufferContentCache(Buffer.release(), /*DoNotFree*/ false),
-        IncludeLoc, FileCharacter, LoadedID, LoadedOffset);
+        Name, IncludeLoc, FileCharacter, LoadedID, LoadedOffset);
   }
 
   enum UnownedTag { Unowned };
 
   /// Create a new FileID that represents the specified memory buffer.
   ///
   /// This does not take ownership of the MemoryBuffer. The memory buffer must
   /// outlive the SourceManager.
   FileID createFileID(UnownedTag, const llvm::MemoryBuffer *Buffer,
                       SrcMgr::CharacteristicKind FileCharacter = SrcMgr::C_User,
                       int LoadedID = 0, unsigned LoadedOffset = 0,
                       SourceLocation IncludeLoc = SourceLocation()) {
-    return createFileID(createMemBufferContentCache(Buffer, /*DoNotFree*/true),
-                        IncludeLoc, FileCharacter, LoadedID, LoadedOffset);
+    return createFileID(createMemBufferContentCache(Buffer, /*DoNotFree*/ true),
+                        Buffer->getBufferIdentifier(), IncludeLoc,
+                        FileCharacter, LoadedID, LoadedOffset);
   }
 
   /// Get the FileID for \p SourceFile if it exists. Otherwise, create a
   /// new FileID for the \p SourceFile.
   FileID getOrCreateFileID(const FileEntry *SourceFile,
                            SrcMgr::CharacteristicKind FileCharacter) {
     FileID ID = translateFile(SourceFile);
     return ID.isValid() ? ID : createFileID(SourceFile, SourceLocation(),
if (MyInvalid || !Entry.isFile())
       return nullptr;
 
     const SrcMgr::ContentCache *Content = Entry.getFile().getContentCache();
     if (!Content)
       return nullptr;
     return Content->OrigEntry;
   }
 
+  /// Returns the FileEntryRef for the provided FileID.
+  Optional<FileEntryRef> getFileEntryRefForID(FileID FID) const {
+    bool MyInvalid = false;
+    const SrcMgr::SLocEntry &Entry = getSLocEntry(FID, &MyInvalid);
+    if (MyInvalid || !Entry.isFile())
+      return None;
+
+    const SrcMgr::ContentCache *Content = Entry.getFile().getContentCache();
+    if (!Content || !Content->OrigEntry)
+      return None;
+    return FileEntryRef(Entry.getFile().getName(), *Content->OrigEntry);
+  }
+
   /// Returns the FileEntry record for the provided SLocEntry.
   const FileEntry *getFileEntryForSLocEntry(const SrcMgr::SLocEntry &sloc) const
   {
     const SrcMgr::ContentCache *Content = sloc.getFile().getContentCache();
     if (!Content)
       return nullptr;
     return Content->OrigEntry;
   }
private:
   /// no next one.
   FileID getNextFileID(FileID FID) const;
 
   /// Create a new fileID for the specified ContentCache and
   /// include position.
   ///
   /// This works regardless of whether the ContentCache corresponds to a
   /// file or some other input source.
-  FileID createFileID(const SrcMgr::ContentCache* File,
+  FileID createFileID(const SrcMgr::ContentCache *File, StringRef Filename,
                       SourceLocation IncludePos,
-                      SrcMgr::CharacteristicKind DirCharacter,
-                      int LoadedID, unsigned LoadedOffset);
+                      SrcMgr::CharacteristicKind DirCharacter, int LoadedID,
+                      unsigned LoadedOffset);
 
   const SrcMgr::ContentCache *
     getOrCreateContentCache(const FileEntry *SourceFile,
                             bool isSystemFile = false);
 
   /// Create a new ContentCache for the specified  memory buffer.
   const SrcMgr::ContentCache *
   createMemBufferContentCache(const llvm::MemoryBuffer *Buf, bool DoNotFree);

clang/include/clang/Lex/DirectoryLookup.h

public:
   /// user-specified to be treated as a system framework.
   ///
   /// \param [out] IsFrameworkFound For a framework directory set to true if
   /// specified '.framework' directory is found.
   ///
   /// \param [out] MappedName if this is a headermap which maps the filename to
   /// a framework include ("Foo.h" -> "Foo/Foo.h"), set the new name to this
   /// vector and point Filename to it.
-  const FileEntry *LookupFile(StringRef &Filename, HeaderSearch &HS,
-                              SourceLocation IncludeLoc,
-                              SmallVectorImpl<char> *SearchPath,
-                              SmallVectorImpl<char> *RelativePath,
-                              Module *RequestingModule,
-                              ModuleMap::KnownHeader *SuggestedModule,
-                              bool &InUserSpecifiedSystemFramework,
-                              bool &IsFrameworkFound,
-                              bool &HasBeenMapped,
-                              SmallVectorImpl<char> &MappedName) const;
+  Optional<FileEntryRef>
+  LookupFile(StringRef &Filename, HeaderSearch &HS, SourceLocation IncludeLoc,
+             SmallVectorImpl<char> *RelativePath, Module *RequestingModule,
+             bool &InUserSpecifiedSystemFramework, bool &IsFrameworkFound,
+             bool &HasBeenMapped, SmallVectorImpl<char> &MappedName) const;
 
 private:
-  const FileEntry *DoFrameworkLookup(
-      StringRef Filename, HeaderSearch &HS,
-      SmallVectorImpl<char> *SearchPath,
-      SmallVectorImpl<char> *RelativePath,
-      Module *RequestingModule,
+  Optional<FileEntryRef> DoFrameworkLookup(
+      StringRef Filename, HeaderSearch &HS, SmallVectorImpl<char> *SearchPath,
+      SmallVectorImpl<char> *RelativePath, Module *RequestingModule,
       ModuleMap::KnownHeader *SuggestedModule,
-      bool &InUserSpecifiedSystemFramework,
-      bool &IsFrameworkFound) const;
-
+      bool &InUserSpecifiedSystemFramework, bool &IsFrameworkFound) const;
 };
 
 }  // end namespace clang
 
 #endif

clang/include/clang/Lex/HeaderSearch.h

public:
   ///
   /// \param IsMapped If non-null, and the search involved header maps, set to
   /// true.
   ///
   /// \param IsFrameworkFound If non-null, will be set to true if a framework is
   /// found in any of searched SearchDirs. Will be set to false if a framework
   /// is found only through header maps. Doesn't guarantee the requested file is
   /// found.
-  const FileEntry *LookupFile(
+  Optional<FileEntryRef> LookupFile(
       StringRef Filename, SourceLocation IncludeLoc, bool isAngled,
       const DirectoryLookup *FromDir, const DirectoryLookup *&CurDir,
       ArrayRef<std::pair<const FileEntry *, const DirectoryEntry *>> Includers,
       SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
       Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule,
       bool *IsMapped, bool *IsFrameworkFound, bool SkipCache = false,
       bool BuildSystemModule = false);
 
   /// Look up a subframework for the specified \#include file.
   ///
   /// For example, if \#include'ing <HIToolbox/HIToolbox.h> from
   /// within ".../Carbon.framework/Headers/Carbon.h", check to see if
   /// HIToolbox is a subframework within Carbon.framework.  If so, return
   /// the FileEntry for the designated file, otherwise return null.
-  const FileEntry *LookupSubframeworkHeader(
+  Optional<FileEntryRef> LookupSubframeworkHeader(
       StringRef Filename, const FileEntry *ContextFileEnt,
       SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
       Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule);
 
   /// Look up the specified framework name in our framework cache.
   /// \returns The DirectoryEntry it is in if we know, null otherwise.
   FrameworkCacheEntry &LookupFrameworkCache(StringRef FWName) {
     return FrameworkMap[FWName];
private:
   /// \return \c true if the file can be used, \c false if we are not permitted to
   ///         find this file due to requirements from \p RequestingModule.
   bool findUsableModuleForFrameworkHeader(
       const FileEntry *File, StringRef FrameworkName, Module *RequestingModule,
       ModuleMap::KnownHeader *SuggestedModule, bool IsSystemFramework);
 
   /// Look up the file with the specified name and determine its owning
   /// module.
-  const FileEntry *
+  Optional<FileEntryRef>
   getFileAndSuggestModule(StringRef FileName, SourceLocation IncludeLoc,
                           const DirectoryEntry *Dir, bool IsSystemHeaderDir,
                           Module *RequestingModule,
                           ModuleMap::KnownHeader *SuggestedModule);
 
 public:
   /// Retrieve the module map.
   ModuleMap &getModuleMap() { return ModMap; }

clang/include/clang/Lex/Preprocessor.h

public:
   /// when this method decides to use a different buffer.
   ///
   /// \returns true if the input filename was in <>'s or false if it was
   /// in ""'s.
   bool GetIncludeFilenameSpelling(SourceLocation Loc,StringRef &Buffer);
 
   /// Given a "foo" or \<foo> reference, look up the indicated file.
   ///
-  /// Returns null on failure.  \p isAngled indicates whether the file
+  /// Returns None on failure.  \p isAngled indicates whether the file
   /// reference is for system \#include's or not (i.e. using <> instead of "").
-  const FileEntry *LookupFile(SourceLocation FilenameLoc, StringRef Filename,
-                              bool isAngled, const DirectoryLookup *FromDir,
-                              const FileEntry *FromFile,
-                              const DirectoryLookup *&CurDir,
-                              SmallVectorImpl<char> *SearchPath,
-                              SmallVectorImpl<char> *RelativePath,
-                              ModuleMap::KnownHeader *SuggestedModule,
-                              bool *IsMapped, bool *IsFrameworkFound,
-                              bool SkipCache = false);
+  Optional<FileEntryRef>
+  LookupFile(SourceLocation FilenameLoc, StringRef Filename, bool isAngled,
+             const DirectoryLookup *FromDir, const FileEntry *FromFile,
+             const DirectoryLookup *&CurDir, SmallVectorImpl<char> *SearchPath,
+             ModuleMap::KnownHeader *SuggestedModule, bool *IsMapped,
+             bool *IsFrameworkFound, bool SkipCache = false);
 
   /// Get the DirectoryLookup structure used to find the current
   /// FileEntry, if CurLexer is non-null and if applicable.
   ///
   /// This allows us to implement \#include_next and find directory-specific
   /// properties.
   const DirectoryLookup *GetCurDirLookup() { return CurDirLookup; }
 

clang/lib/Basic/FileManager.cpp

if (UDE.getName().empty()) {
     UDE.Name  = InterndDirName;
   }
 
   return &UDE;
 }
 
 llvm::ErrorOr<const FileEntry *>
 FileManager::getFile(StringRef Filename, bool openFile, bool CacheFailure) {
+  auto Result = getFileRef(Filename, openFile, CacheFailure);
+  if (Result)
+    return &Result->getFileEntry();
+  return Result.getError();
+}
+
+static llvm::ErrorOr<FileEntryRef>
+promoteFileRef(StringRef name, llvm::ErrorOr<FileEntry &> value) {
+  if (value)
+    return FileEntryRef(name, *value);
+  return value.getError();
+}
+
+llvm::ErrorOr<FileEntryRef>
+FileManager::getFileRef(StringRef Filename, bool openFile, bool CacheFailure) {
   ++NumFileLookups;
 
   // See if there is already an entry in the map.
   auto SeenFileInsertResult =
       SeenFileEntries.insert({Filename, std::errc::no_such_file_or_directory});
   if (!SeenFileInsertResult.second)
-    return promoteInnerReference(SeenFileInsertResult.first->second);
+    return promoteFileRef(SeenFileInsertResult.first->first(),
+                          SeenFileInsertResult.first->second);
 
   // We've not seen this before. Fill it in.
   ++NumFileCacheMisses;
   auto &NamedFileEnt = *SeenFileInsertResult.first;
   assert(!NamedFileEnt.second && "should be newly-created");
 
   // Get the null-terminated file name as stored as the key of the
   // SeenFileEntries map.
if (UFE.isValid()) { // Already have an entry with this inode, return it.
     if (DirInfo != UFE.Dir && Status.IsVFSMapped)
       UFE.Dir = DirInfo;
 
     // Always update the name to use the last name by which a file was accessed.
     // FIXME: Neither this nor always using the first name is correct; we want
     // to switch towards a design where we return a FileName object that
     // encapsulates both the name by which the file was accessed and the
     // corresponding FileEntry.
+    // FIXME: The Name should be removed from FileEntry once all clients
+    // adopt FileEntryRef.
     UFE.Name = InterndFileName;
 
-    return &UFE;
+    return FileEntryRef(InterndFileName, UFE);
   }
 
   // Otherwise, we don't have this file yet, add it.
   UFE.Name    = InterndFileName;
   UFE.Size    = Status.getSize();
   UFE.ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
   UFE.Dir     = DirInfo;
   UFE.UID     = NextFileUID++;
   UFE.UniqueID = Status.getUniqueID();
   UFE.IsNamedPipe = Status.getType() == llvm::sys::fs::file_type::fifo_file;
   UFE.File = std::move(F);
   UFE.IsValid = true;
 
   if (UFE.File) {
     if (auto PathName = UFE.File->getName())
       fillRealPathName(&UFE, *PathName);
   } else if (!openFile) {
     // We should still fill the path even if we aren't opening the file.
     fillRealPathName(&UFE, InterndFileName);
   }
-  return &UFE;
+  return FileEntryRef(InterndFileName, UFE);
 }
 
 const FileEntry *
 FileManager::getVirtualFile(StringRef Filename, off_t Size,
                             time_t ModificationTime) {
   ++NumFileLookups;
 
   // See if there is already an entry in the map for an existing file.

clang/lib/Basic/SourceManager.cpp

const SrcMgr::SLocEntry &SourceManager::loadSLocEntry(unsigned Index,
                                                       bool *Invalid) const {
   assert(!SLocEntryLoaded[Index]);
   if (ExternalSLocEntries->ReadSLocEntry(-(static_cast<int>(Index) + 2))) {
     if (Invalid)
       *Invalid = true;
     // If the file of the SLocEntry changed we could still have loaded it.
     if (!SLocEntryLoaded[Index]) {
       // Try to recover; create a SLocEntry so the rest of clang can handle it.
-      LoadedSLocEntryTable[Index] = SLocEntry::get(0,
-                                 FileInfo::get(SourceLocation(),
-                                               getFakeContentCacheForRecovery(),
-                                               SrcMgr::C_User));
+      LoadedSLocEntryTable[Index] = SLocEntry::get(
+          0, FileInfo::get(SourceLocation(), getFakeContentCacheForRecovery(),
+                           SrcMgr::C_User, ""));
     }
   }
 
   return LoadedSLocEntryTable[Index];
 }
 
 std::pair<int, unsigned>
 SourceManager::AllocateLoadedSLocEntries(unsigned NumSLocEntries,

 
 //===----------------------------------------------------------------------===//
 // Methods to create new FileID's and macro expansions.
 //===----------------------------------------------------------------------===//
 
 /// createFileID - Create a new FileID for the specified ContentCache and
 /// include position.  This works regardless of whether the ContentCache
 /// corresponds to a file or some other input source.
-FileID SourceManager::createFileID(const ContentCache *File,
+FileID SourceManager::createFileID(const ContentCache *File, StringRef Filename,
                                    SourceLocation IncludePos,
                                    SrcMgr::CharacteristicKind FileCharacter,
                                    int LoadedID, unsigned LoadedOffset) {
   if (LoadedID < 0) {
     assert(LoadedID != -1 && "Loading sentinel FileID");
     unsigned Index = unsigned(-LoadedID) - 2;
     assert(Index < LoadedSLocEntryTable.size() && "FileID out of range");
     assert(!SLocEntryLoaded[Index] && "FileID already loaded");
-    LoadedSLocEntryTable[Index] = SLocEntry::get(LoadedOffset,
-        FileInfo::get(IncludePos, File, FileCharacter));
+    LoadedSLocEntryTable[Index] = SLocEntry::get(
+        LoadedOffset, FileInfo::get(IncludePos, File, FileCharacter, Filename));
     SLocEntryLoaded[Index] = true;
     return FileID::get(LoadedID);
   }
-  LocalSLocEntryTable.push_back(SLocEntry::get(NextLocalOffset,
-                                               FileInfo::get(IncludePos, File,
-                                                             FileCharacter)));
+  LocalSLocEntryTable.push_back(
+      SLocEntry::get(NextLocalOffset,
+                     FileInfo::get(IncludePos, File, FileCharacter, Filename)));
   unsigned FileSize = File->getSize();
   assert(NextLocalOffset + FileSize + 1 > NextLocalOffset &&
          NextLocalOffset + FileSize + 1 <= CurrentLoadedOffset &&
          "Ran out of source locations!");
   // We do a +1 here because we want a SourceLocation that means "the end of the
   // file", e.g. for the "no newline at the end of the file" diagnostic.
   NextLocalOffset += FileSize + 1;
 

clang/lib/Frontend/CompilerInstance.cpp

assert(SourceMgr.getMainFileID().isValid() &&
            "Couldn't establish MainFileID!");
     return true;
   }
 
   StringRef InputFile = Input.getFile();
 
   // Figure out where to get and map in the main file.
   if (InputFile != "-") {
-    auto FileOrErr = FileMgr.getFile(InputFile, /*OpenFile=*/true);
+    auto FileOrErr = FileMgr.getFileRef(InputFile, /*OpenFile=*/true);
     if (!FileOrErr) {
       Diags.Report(diag::err_fe_error_reading) << InputFile;
       return false;
     }
-    auto File = *FileOrErr;
+    FileEntryRef File = *FileOrErr;
 
     // The natural SourceManager infrastructure can't currently handle named
     // pipes, but we would at least like to accept them for the main
     // file. Detect them here, read them with the volatile flag so FileMgr will
     // pick up the correct size, and simply override their contents as we do for
     // STDIN.
-    if (File->isNamedPipe()) {
-      auto MB = FileMgr.getBufferForFile(File, /*isVolatile=*/true);
+    if (File.getFileEntry().isNamedPipe()) {
+      auto MB =
+          FileMgr.getBufferForFile(&File.getFileEntry(), /*isVolatile=*/true);
       if (MB) {
         // Create a new virtual file that will have the correct size.
-        File = FileMgr.getVirtualFile(InputFile, (*MB)->getBufferSize(), 0);
-        SourceMgr.overrideFileContents(File, std::move(*MB));
+        const FileEntry *FE =
+            FileMgr.getVirtualFile(InputFile, (*MB)->getBufferSize(), 0);
+        SourceMgr.overrideFileContents(FE, std::move(*MB));
+        SourceMgr.setMainFileID(
+            SourceMgr.createFileID(FE, SourceLocation(), Kind));
       } else {
         Diags.Report(diag::err_cannot_open_file) << InputFile
                                                  << MB.getError().message();
         return false;
       }
-    }
-
+    } else {
       SourceMgr.setMainFileID(
           SourceMgr.createFileID(File, SourceLocation(), Kind));
+    }
   } else {
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> SBOrErr =
         llvm::MemoryBuffer::getSTDIN();
     if (std::error_code EC = SBOrErr.getError()) {
       Diags.Report(diag::err_fe_error_reading_stdin) << EC.message();
       return false;
     }
     std::unique_ptr<llvm::MemoryBuffer> SB = std::move(SBOrErr.get());

clang/lib/Frontend/DependencyFile.cpp

void FileChanged(SourceLocation Loc, FileChangeReason Reason,
                    SrcMgr::CharacteristicKind FileType,
                    FileID PrevFID) override {
     if (Reason != PPCallbacks::EnterFile)
       return;
 
     // Dependency generation really does want to go all the way to the
     // file entry for a source location to find out what is depended on.
     // We do not want #line markers to affect dependency generation!
-    const FileEntry *FE =
-        SM.getFileEntryForID(SM.getFileID(SM.getExpansionLoc(Loc)));
-    if (!FE)
+    Optional<FileEntryRef> File =
+        SM.getFileEntryRefForID(SM.getFileID(SM.getExpansionLoc(Loc)));
+    if (!File)
       return;
 
     StringRef Filename =
-        llvm::sys::path::remove_leading_dotslash(FE->getName());
+        llvm::sys::path::remove_leading_dotslash(File->getName());
 
     DepCollector.maybeAddDependency(Filename, /*FromModule*/false,
                                     isSystem(FileType),
                                     /*IsModuleFile*/false, /*IsMissing*/false);
   }
 
   void FileSkipped(const FileEntry &SkippedFile, const Token &FilenameTok,
                    SrcMgr::CharacteristicKind FileType) override {

clang/lib/Frontend/FrontendActions.cpp

bool GenerateHeaderModuleAction::BeginSourceFileAction(
     CompilerInstance &CI) {
   CI.getLangOpts().setCompilingModule(LangOptions::CMK_HeaderModule);
 
   // Synthesize a Module object for the given headers.
   auto &HS = CI.getPreprocessor().getHeaderSearchInfo();
   SmallVector<Module::Header, 16> Headers;
   for (StringRef Name : ModuleHeaders) {
     const DirectoryLookup *CurDir = nullptr;
-    const FileEntry *FE = HS.LookupFile(
-        Name, SourceLocation(), /*Angled*/ false, nullptr, CurDir,
-        None, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr);
+    Optional<FileEntryRef> FE = HS.LookupFile(
+        Name, SourceLocation(), /*Angled*/ false, nullptr, CurDir, None,
+        nullptr, nullptr, nullptr, nullptr, nullptr, nullptr);
     if (!FE) {
       CI.getDiagnostics().Report(diag::err_module_header_file_not_found)
         << Name;
       continue;
     }
-    Headers.push_back({Name, FE});
+    Headers.push_back({Name, &FE->getFileEntry()});
   }
   HS.getModuleMap().createHeaderModule(CI.getLangOpts().CurrentModule, Headers);
 
   return GenerateModuleAction::BeginSourceFileAction(CI);
 }
 
 std::unique_ptr<raw_pwrite_stream>
 GenerateHeaderModuleAction::CreateOutputFile(CompilerInstance &CI,

clang/lib/Frontend/Rewrite/InclusionRewriter.cpp

bool InclusionRewriter::HandleHasInclude(
   // FIXME: Subframeworks aren't handled here. Do we care?
   bool isAngled = PP.GetIncludeFilenameSpelling(Tok.getLocation(), Filename);
   const DirectoryLookup *CurDir;
   const FileEntry *FileEnt = PP.getSourceManager().getFileEntryForID(FileId);
   SmallVector<std::pair<const FileEntry *, const DirectoryEntry *>, 1>
       Includers;
   Includers.push_back(std::make_pair(FileEnt, FileEnt->getDir()));
   // FIXME: Why don't we call PP.LookupFile here?
-  const FileEntry *File = PP.getHeaderSearchInfo().LookupFile(
+  Optional<FileEntryRef> File = PP.getHeaderSearchInfo().LookupFile(
       Filename, SourceLocation(), isAngled, Lookup, CurDir, Includers, nullptr,
       nullptr, nullptr, nullptr, nullptr, nullptr);
 
-  FileExists = File != nullptr;
+  FileExists = File.hasValue();
   return true;
 }
 
 /// Use a raw lexer to analyze \p FileId, incrementally copying parts of it
 /// and including content of included files recursively.
 void InclusionRewriter::Process(FileID FileId,
                                 SrcMgr::CharacteristicKind FileType,
                                 const DirectoryLookup *DirLookup) {

clang/lib/Frontend/VerifyDiagnosticConsumer.cpp

if (!PH.Next("@")) {
         Marker = PH.Match();
       } else if (PP && PH.Search(":")) {
         // Specific source file.
         StringRef Filename(PH.C, PH.P-PH.C);
         PH.Advance();
 
         // Lookup file via Preprocessor, like a #include.
         const DirectoryLookup *CurDir;
-        const FileEntry *FE =
+        Optional<FileEntryRef> File =
             PP->LookupFile(Pos, Filename, false, nullptr, nullptr, CurDir,
                            nullptr, nullptr, nullptr, nullptr, nullptr);
-        if (!FE) {
+        if (!File) {
           Diags.Report(Pos.getLocWithOffset(PH.C-PH.Begin),
                        diag::err_verify_missing_file) << Filename << KindStr;
           continue;
         }
 
+        const FileEntry *FE = &File->getFileEntry();
         if (SM.translateFile(FE).isInvalid())
           SM.createFileID(FE, Pos, SrcMgr::C_User);
 
         if (PH.Next(Line) && Line > 0)
           ExpectedLoc = SM.translateFileLineCol(FE, Line, 1);
         else if (PH.Next("*")) {
           MatchAnyLine = true;
           ExpectedLoc = SM.translateFileLineCol(FE, 1, 1);

clang/lib/Lex/HeaderSearch.cpp

StringRef DirectoryLookup::getName() const {
   if (isNormalDir())
     return getDir()->getName();
   if (isFramework())
     return getFrameworkDir()->getName();
   assert(isHeaderMap() && "Unknown DirectoryLookup");
   return getHeaderMap()->getFileName();
 }
 
-const FileEntry *HeaderSearch::getFileAndSuggestModule(
+Optional<FileEntryRef> HeaderSearch::getFileAndSuggestModule(
     StringRef FileName, SourceLocation IncludeLoc, const DirectoryEntry *Dir,
     bool IsSystemHeaderDir, Module *RequestingModule,
     ModuleMap::KnownHeader *SuggestedModule) {
   // If we have a module map that might map this header, load it and
   // check whether we'll have a suggestion for a module.
-  auto File = getFileMgr().getFile(FileName, /*OpenFile=*/true);
+  auto File = getFileMgr().getFileRef(FileName, /*OpenFile=*/true);
   if (!File)
-    return nullptr;
+    return None;
 
   // If there is a module that corresponds to this header, suggest it.
-  if (!findUsableModuleForHeader(*File, Dir ? Dir : (*File)->getDir(),
-                                 RequestingModule, SuggestedModule,
-                                 IsSystemHeaderDir))
-    return nullptr;
+  if (!findUsableModuleForHeader(
+          &File->getFileEntry(), Dir ? Dir : File->getFileEntry().getDir(),
+          RequestingModule, SuggestedModule, IsSystemHeaderDir))
+    return None;
 
   return *File;
 }
 
 /// LookupFile - Lookup the specified file in this search path, returning it
 /// if it exists or returning null if not.
-const FileEntry *DirectoryLookup::LookupFile(
-    StringRef &Filename,
-    HeaderSearch &HS,
-    SourceLocation IncludeLoc,
-    SmallVectorImpl<char> *SearchPath,
-    SmallVectorImpl<char> *RelativePath,
-    Module *RequestingModule,
-    ModuleMap::KnownHeader *SuggestedModule,
-    bool &InUserSpecifiedSystemFramework,
-    bool &IsFrameworkFound,
-    bool &HasBeenMapped,
-    SmallVectorImpl<char> &MappedName) const {
+Optional<FileEntryRef> DirectoryLookup::LookupFile(
+    StringRef &Filename, HeaderSearch &HS, SourceLocation IncludeLoc,
+    SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
+    Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule,
+    bool &InUserSpecifiedSystemFramework, bool &IsFrameworkFound,
+    bool &HasBeenMapped, SmallVectorImpl<char> &MappedName) const {
   InUserSpecifiedSystemFramework = false;
   HasBeenMapped = false;
 
   SmallString<1024> TmpDir;
   if (isNormalDir()) {
     // Concatenate the requested file onto the directory.
     TmpDir = getDir()->getName();
     llvm::sys::path::append(TmpDir, Filename);
return DoFrameworkLookup(Filename, HS, SearchPath, RelativePath,
                              RequestingModule, SuggestedModule,
                              InUserSpecifiedSystemFramework, IsFrameworkFound);
 
   assert(isHeaderMap() && "Unknown directory lookup");
   const HeaderMap *HM = getHeaderMap();
   SmallString<1024> Path;
   StringRef Dest = HM->lookupFilename(Filename, Path);
   if (Dest.empty())
-    return nullptr;
+    return None;
 
-  const FileEntry *Result;
+  auto FixupSearchPath = [&]() {
+    if (SearchPath) {
+      StringRef SearchPathRef(getName());
+      SearchPath->clear();
+      SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
+    }
+    if (RelativePath) {
+      RelativePath->clear();
+      RelativePath->append(Filename.begin(), Filename.end());
+    }
+  };
 
   // Check if the headermap maps the filename to a framework include
   // ("Foo.h" -> "Foo/Foo.h"), in which case continue header lookup using the
   // framework include.
   if (llvm::sys::path::is_relative(Dest)) {
     MappedName.clear();
     MappedName.append(Dest.begin(), Dest.end());
     Filename = StringRef(MappedName.begin(), MappedName.size());
     HasBeenMapped = true;
-    Result = HM->LookupFile(Filename, HS.getFileMgr());
-  } else if (auto Res = HS.getFileMgr().getFile(Dest)) {
-    Result = *Res;
-  } else {
-    Result = nullptr;
+    // FIXME ULTRA: auto Result = HM->LookupFile(Filename, HS.getFileMgr());
+    // FixupSearchPath();
+  } else if (auto Res = HS.getFileMgr().getFileRef(Dest)) {
+    FixupSearchPath();
+    return *Res;
   }
 
-  if (Result) {
-    if (SearchPath) {
-      StringRef SearchPathRef(getName());
-      SearchPath->clear();
-      SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
-    }
-    if (RelativePath) {
-      RelativePath->clear();
-      RelativePath->append(Filename.begin(), Filename.end());
-    }
-  }
-  return Result;
+  return None;
 }
 
 /// Given a framework directory, find the top-most framework directory.
 ///
 /// \param FileMgr The file manager to use for directory lookups.
 /// \param DirName The name of the framework directory.
 /// \param SubmodulePath Will be populated with the submodule path from the
 /// returned top-level module to the originally named framework.

 static bool needModuleLookup(Module *RequestingModule,
                              bool HasSuggestedModule) {
   return HasSuggestedModule ||
          (RequestingModule && RequestingModule->NoUndeclaredIncludes);
 }
 
 /// DoFrameworkLookup - Do a lookup of the specified file in the current
 /// DirectoryLookup, which is a framework directory.
-const FileEntry *DirectoryLookup::DoFrameworkLookup(
+Optional<FileEntryRef> DirectoryLookup::DoFrameworkLookup(
     StringRef Filename, HeaderSearch &HS, SmallVectorImpl<char> *SearchPath,
     SmallVectorImpl<char> *RelativePath, Module *RequestingModule,
     ModuleMap::KnownHeader *SuggestedModule,
     bool &InUserSpecifiedSystemFramework, bool &IsFrameworkFound) const {
   FileManager &FileMgr = HS.getFileMgr();
 
   // Framework names must have a '/' in the filename.
   size_t SlashPos = Filename.find('/');
-  if (SlashPos == StringRef::npos) return nullptr;
+  if (SlashPos == StringRef::npos)
+    return None;
 
   // Find out if this is the home for the specified framework, by checking
   // HeaderSearch.  Possible answers are yes/no and unknown.
   FrameworkCacheEntry &CacheEntry =
     HS.LookupFrameworkCache(Filename.substr(0, SlashPos));
 
   // If it is known and in some other directory, fail.
   if (CacheEntry.Directory && CacheEntry.Directory != getFrameworkDir())
-    return nullptr;
+    return None;
 
   // Otherwise, construct the path to this framework dir.
 
   // FrameworkName = "/System/Library/Frameworks/"
   SmallString<1024> FrameworkName;
   FrameworkName += getFrameworkDir()->getName();
   if (FrameworkName.empty() || FrameworkName.back() != '/')
     FrameworkName.push_back('/');
 
   // FrameworkName = "/System/Library/Frameworks/Cocoa"
   StringRef ModuleName(Filename.begin(), SlashPos);
   FrameworkName += ModuleName;
 
   // FrameworkName = "/System/Library/Frameworks/Cocoa.framework/"
   FrameworkName += ".framework/";
 
   // If the cache entry was unresolved, populate it now.
   if (!CacheEntry.Directory) {
     HS.IncrementFrameworkLookupCount();
 
     // If the framework dir doesn't exist, we fail.
     auto Dir = FileMgr.getDirectory(FrameworkName);
-    if (!Dir) return nullptr;
+    if (!Dir)
+      return None;
 
     // Otherwise, if it does, remember that this is the right direntry for this
     // framework.
     CacheEntry.Directory = getFrameworkDir();
 
     // If this is a user search directory, check if the framework has been
     // user-specified as a system framework.
     if (getDirCharacteristic() == SrcMgr::C_User) {
Optional<FileEntryRef> DirectoryLookup::DoFrameworkLookup(
   if (SearchPath) {
     SearchPath->clear();
     // Without trailing '/'.
     SearchPath->append(FrameworkName.begin(), FrameworkName.end()-1);
   }
 
   FrameworkName.append(Filename.begin()+SlashPos+1, Filename.end());
 
-  const FileEntry *FE = nullptr;
-  if (auto File = FileMgr.getFile(FrameworkName, /*OpenFile=*/!SuggestedModule))
-    FE = *File;
+  llvm::ErrorOr<FileEntryRef> File =
+      FileMgr.getFileRef(FrameworkName, /*OpenFile=*/!SuggestedModule);
 
-  if (!FE) {
+  if (!File) {
     // Check "/System/Library/Frameworks/Cocoa.framework/PrivateHeaders/file.h"
     const char *Private = "Private";
     FrameworkName.insert(FrameworkName.begin()+OrigSize, Private,
                          Private+strlen(Private));
     if (SearchPath)
       SearchPath->insert(SearchPath->begin()+OrigSize, Private,
                          Private+strlen(Private));
 
-    if (auto File = FileMgr.getFile(FrameworkName, 
-                                    /*OpenFile=*/!SuggestedModule))
-      FE = *File;
+    File = FileMgr.getFileRef(FrameworkName, /*OpenFile=*/!SuggestedModule);
   }
 
   // If we found the header and are allowed to suggest a module, do so now.
-  if (FE && needModuleLookup(RequestingModule, SuggestedModule)) {
+  if (File && needModuleLookup(RequestingModule, SuggestedModule)) {
     // Find the framework in which this header occurs.
-    StringRef FrameworkPath = FE->getDir()->getName();
+    StringRef FrameworkPath = File->getFileEntry().getDir()->getName();
     bool FoundFramework = false;
     do {
       // Determine whether this directory exists.
       auto Dir = FileMgr.getDirectory(FrameworkPath);
       if (!Dir)
         break;
 
       // If this is a framework directory, then we're a subframework of this
       // framework.
       if (llvm::sys::path::extension(FrameworkPath) == ".framework") {
         FoundFramework = true;
         break;
       }
 
       // Get the parent directory name.
       FrameworkPath = llvm::sys::path::parent_path(FrameworkPath);
       if (FrameworkPath.empty())
         break;
     } while (true);
 
     bool IsSystem = getDirCharacteristic() != SrcMgr::C_User;
     if (FoundFramework) {
       if (!HS.findUsableModuleForFrameworkHeader(
-              FE, FrameworkPath, RequestingModule, SuggestedModule, IsSystem))
-        return nullptr;
-    } else {
-      if (!HS.findUsableModuleForHeader(FE, getDir(), RequestingModule,
-                                        SuggestedModule, IsSystem))
-        return nullptr;
+              &File->getFileEntry(), FrameworkPath, RequestingModule,
+        return None;
+    } else {
+      if (!HS.findUsableModuleForHeader(&File->getFileEntry(), getDir(),
+                                        RequestingModule, SuggestedModule,
+                                        IsSystem))
+        return None;
     }
   }
-  return FE;
+  if (File)
+    return *File;
+  return None;
 }
 
 void HeaderSearch::setTarget(const TargetInfo &Target) {
   ModMap.setTarget(Target);
 }
 
 //===----------------------------------------------------------------------===//
 // Header File Location.
Diags.Report(IncludeLoc, diag::warn_framework_include_private_from_public)
         << IncludeFilename;
 }
 
 /// LookupFile - Given a "foo" or \<foo> reference, look up the indicated file,
 /// return null on failure.  isAngled indicates whether the file reference is
 /// for system \#include's or not (i.e. using <> instead of ""). Includers, if
 /// non-empty, indicates where the \#including file(s) are, in case a relative
 /// search is needed. Microsoft mode will pass all \#including files.
-const FileEntry *HeaderSearch::LookupFile(
+Optional<FileEntryRef> HeaderSearch::LookupFile(
     StringRef Filename, SourceLocation IncludeLoc, bool isAngled,
     const DirectoryLookup *FromDir, const DirectoryLookup *&CurDir,
     ArrayRef<std::pair<const FileEntry *, const DirectoryEntry *>> Includers,
     SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
     Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule,
     bool *IsMapped, bool *IsFrameworkFound, bool SkipCache,
     bool BuildSystemModule) {
   if (IsMapped)
     *IsMapped = false;
 
   if (IsFrameworkFound)
     *IsFrameworkFound = false;
 
   if (SuggestedModule)
     *SuggestedModule = ModuleMap::KnownHeader();
 
   // If 'Filename' is absolute, check to see if it exists and no searching.
   if (llvm::sys::path::is_absolute(Filename)) {
     CurDir = nullptr;
 
     // If this was an #include_next "/absolute/file", fail.
-    if (FromDir) return nullptr;
+    if (FromDir)
+      return None;
 
     if (SearchPath)
       SearchPath->clear();
     if (RelativePath) {
       RelativePath->clear();
       RelativePath->append(Filename.begin(), Filename.end());
     }
     // Otherwise, just return the file.
     return getFileAndSuggestModule(Filename, IncludeLoc, nullptr,
                                    /*IsSystemHeaderDir*/false,
                                    RequestingModule, SuggestedModule);
   }
 
   // This is the header that MSVC's header search would have found.
-  const FileEntry *MSFE = nullptr;
   ModuleMap::KnownHeader MSSuggestedModule;
+  const FileEntry *MSFE_FE = nullptr;
+  StringRef MSFE_Name;
 
   // Unless disabled, check to see if the file is in the #includer's
   // directory.  This cannot be based on CurDir, because each includer could be
   // a #include of a subdirectory (#include "foo/bar.h") and a subsequent
   // include of "baz.h" should resolve to "whatever/foo/baz.h".
   // This search is not done for <> headers.
   if (!Includers.empty() && !isAngled && !NoCurDirSearch) {
     SmallString<1024> TmpDir;
for (const auto &IncluderAndDir : Includers) {
       // a container that could be reallocated across this call.
       //
       // If we have no includer, that means we're processing a #include
       // from a module build. We should treat this as a system header if we're
       // building a [system] module.
       bool IncluderIsSystemHeader =
           Includer ? getFileInfo(Includer).DirInfo != SrcMgr::C_User :
           BuildSystemModule;
-      if (const FileEntry *FE = getFileAndSuggestModule(
+      if (Optional<FileEntryRef> FE = getFileAndSuggestModule(
               TmpDir, IncludeLoc, IncluderAndDir.second, IncluderIsSystemHeader,
               RequestingModule, SuggestedModule)) {
         if (!Includer) {
           assert(First && "only first includer can have no file");
           return FE;
         }
 
         // Leave CurDir unset.
         // This file is a system header or C++ unfriendly if the old file is.
         //
         // Note that we only use one of FromHFI/ToHFI at once, due to potential
         // reallocation of the underlying vector potentially making the first
         // reference binding dangling.
         HeaderFileInfo &FromHFI = getFileInfo(Includer);
         unsigned DirInfo = FromHFI.DirInfo;
         bool IndexHeaderMapHeader = FromHFI.IndexHeaderMapHeader;
         StringRef Framework = FromHFI.Framework;
 
-        HeaderFileInfo &ToHFI = getFileInfo(FE);
+        HeaderFileInfo &ToHFI = getFileInfo(&FE->getFileEntry());
         ToHFI.DirInfo = DirInfo;
         ToHFI.IndexHeaderMapHeader = IndexHeaderMapHeader;
         ToHFI.Framework = Framework;
 
         if (SearchPath) {
           StringRef SearchPathRef(IncluderAndDir.second->getName());
           SearchPath->clear();
           SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
         }
         if (RelativePath) {
           RelativePath->clear();
           RelativePath->append(Filename.begin(), Filename.end());
         }
         if (First) {
           diagnoseFrameworkInclude(Diags, IncludeLoc,
                                    IncluderAndDir.second->getName(), Filename,
-                                   FE);
+                                   &FE->getFileEntry());
           return FE;
         }
 
         // Otherwise, we found the path via MSVC header search rules.  If
         // -Wmsvc-include is enabled, we have to keep searching to see if we
         // would've found this header in -I or -isystem directories.
         if (Diags.isIgnored(diag::ext_pp_include_search_ms, IncludeLoc)) {
           return FE;
         } else {
-          MSFE = FE;
+          MSFE_FE = &FE->getFileEntry();
+          MSFE_Name = FE->getName();
           if (SuggestedModule) {
             MSSuggestedModule = *SuggestedModule;
             *SuggestedModule = ModuleMap::KnownHeader();
           }
           break;
         }
       }
       First = false;
     }
   }
 
+  Optional<FileEntryRef> MSFE(MSFE_FE ? FileEntryRef(MSFE_Name, *MSFE_FE)
+                                      : Optional<FileEntryRef>());
+
   CurDir = nullptr;
 
   // If this is a system #include, ignore the user #include locs.
   unsigned i = isAngled ? AngledDirIdx : 0;
 
   // If this is a #include_next request, start searching after the directory the
   // file was found in.
   if (FromDir)
Optional<FileEntryRef> HeaderSearch::LookupFile(
 
   SmallString<64> MappedName;
 
   // Check each directory in sequence to see if it contains this file.
   for (; i != SearchDirs.size(); ++i) {
     bool InUserSpecifiedSystemFramework = false;
     bool HasBeenMapped = false;
     bool IsFrameworkFoundInDir = false;
-    const FileEntry *FE = SearchDirs[i].LookupFile(
+    Optional<FileEntryRef> File = SearchDirs[i].LookupFile(
         Filename, *this, IncludeLoc, SearchPath, RelativePath, RequestingModule,
         SuggestedModule, InUserSpecifiedSystemFramework, IsFrameworkFoundInDir,
         HasBeenMapped, MappedName);
     if (HasBeenMapped) {
       CacheLookup.MappedName =
           copyString(Filename, LookupFileCache.getAllocator());
       if (IsMapped)
         *IsMapped = true;
     }
     if (IsFrameworkFound)
       // Because we keep a filename remapped for subsequent search directory
       // lookups, ignore IsFrameworkFoundInDir after the first remapping and not
       // just for remapping in a current search directory.
       *IsFrameworkFound |= (IsFrameworkFoundInDir && !CacheLookup.MappedName);
-    if (!FE) continue;
+    if (!File)
+      continue;
 
     CurDir = &SearchDirs[i];
 
     // This file is a system header or C++ unfriendly if the dir is.
-    HeaderFileInfo &HFI = getFileInfo(FE);
+    HeaderFileInfo &HFI = getFileInfo(&File->getFileEntry());
     HFI.DirInfo = CurDir->getDirCharacteristic();
 
     // If the directory characteristic is User but this framework was
     // user-specified to be treated as a system framework, promote the
     // characteristic.
     if (HFI.DirInfo == SrcMgr::C_User && InUserSpecifiedSystemFramework)
       HFI.DirInfo = SrcMgr::C_System;
 
if (CurDir->isIndexHeaderMap()) {
       size_t SlashPos = Filename.find('/');
       if (SlashPos != StringRef::npos) {
         HFI.IndexHeaderMapHeader = 1;
         HFI.Framework = getUniqueFrameworkName(StringRef(Filename.begin(),
                                                          SlashPos));
       }
     }
 
-    if (checkMSVCHeaderSearch(Diags, MSFE, FE, IncludeLoc)) {
+    if (checkMSVCHeaderSearch(Diags, MSFE ? &MSFE->getFileEntry() : nullptr,
+                              &File->getFileEntry(), IncludeLoc)) {
       if (SuggestedModule)
         *SuggestedModule = MSSuggestedModule;
       return MSFE;
     }
 
     bool FoundByHeaderMap = !IsMapped ? false : *IsMapped;
     if (!Includers.empty())
-      diagnoseFrameworkInclude(Diags, IncludeLoc,
-                               Includers.front().second->getName(), Filename,
-                               FE, isAngled, FoundByHeaderMap);
+      diagnoseFrameworkInclude(
+          Diags, IncludeLoc, Includers.front().second->getName(), Filename,
+          &File->getFileEntry(), isAngled, FoundByHeaderMap);
 
     // Remember this location for the next lookup we do.
     CacheLookup.HitIdx = i;
-    return FE;
+    return File;
   }
 
   // If we are including a file with a quoted include "foo.h" from inside
   // a header in a framework that is currently being built, and we couldn't
   // resolve "foo.h" any other way, change the include to <Foo/foo.h>, where
   // "Foo" is the name of the framework in which the including header was found.
   if (!Includers.empty() && Includers.front().first && !isAngled &&
       Filename.find('/') == StringRef::npos) {
     HeaderFileInfo &IncludingHFI = getFileInfo(Includers.front().first);
     if (IncludingHFI.IndexHeaderMapHeader) {
       SmallString<128> ScratchFilename;
       ScratchFilename += IncludingHFI.Framework;
       ScratchFilename += '/';
       ScratchFilename += Filename;
 
-      const FileEntry *FE = LookupFile(
+      Optional<FileEntryRef> File = LookupFile(
           ScratchFilename, IncludeLoc, /*isAngled=*/true, FromDir, CurDir,
           Includers.front(), SearchPath, RelativePath, RequestingModule,
           SuggestedModule, IsMapped, /*IsFrameworkFound=*/nullptr);
 
-      if (checkMSVCHeaderSearch(Diags, MSFE, FE, IncludeLoc)) {
+      if (checkMSVCHeaderSearch(Diags, MSFE ? &MSFE->getFileEntry() : nullptr,
+                                File ? &File->getFileEntry() : nullptr,
+                                IncludeLoc)) {
         if (SuggestedModule)
           *SuggestedModule = MSSuggestedModule;
         return MSFE;
       }
 
       LookupFileCacheInfo &CacheLookup = LookupFileCache[Filename];
       CacheLookup.HitIdx = LookupFileCache[ScratchFilename].HitIdx;
       // FIXME: SuggestedModule.
-      return FE;
+      return File;
     }
   }
 
-  if (checkMSVCHeaderSearch(Diags, MSFE, nullptr, IncludeLoc)) {
+  if (checkMSVCHeaderSearch(Diags, MSFE ? &MSFE->getFileEntry() : nullptr,
+                            nullptr, IncludeLoc)) {
     if (SuggestedModule)
       *SuggestedModule = MSSuggestedModule;
     return MSFE;
   }
 
   // Otherwise, didn't find it. Remember we didn't find this.
   CacheLookup.HitIdx = SearchDirs.size();
-  return nullptr;
+  return None;
 }
 
 /// LookupSubframeworkHeader - Look up a subframework for the specified
 /// \#include file.  For example, if \#include'ing <HIToolbox/HIToolbox.h> from
 /// within ".../Carbon.framework/Headers/Carbon.h", check to see if HIToolbox
 /// is a subframework within Carbon.framework.  If so, return the FileEntry
 /// for the designated file, otherwise return null.
-const FileEntry *HeaderSearch::
-LookupSubframeworkHeader(StringRef Filename,
-                         const FileEntry *ContextFileEnt,
-                         SmallVectorImpl<char> *SearchPath,
-                         SmallVectorImpl<char> *RelativePath,
-                         Module *RequestingModule,
-                         ModuleMap::KnownHeader *SuggestedModule) {
+Optional<FileEntryRef> HeaderSearch::LookupSubframeworkHeader(
+    StringRef Filename, const FileEntry *ContextFileEnt,
+    SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
+    Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule) {
   assert(ContextFileEnt && "No context file?");
 
   // Framework names must have a '/' in the filename.  Find it.
   // FIXME: Should we permit '\' on Windows?
   size_t SlashPos = Filename.find('/');
-  if (SlashPos == StringRef::npos) return nullptr;
+  if (SlashPos == StringRef::npos)
+    return None;
 
   // Look up the base framework name of the ContextFileEnt.
   StringRef ContextName = ContextFileEnt->getName();
 
   // If the context info wasn't a framework, couldn't be a subframework.
   const unsigned DotFrameworkLen = 10;
   auto FrameworkPos = ContextName.find(".framework");
   if (FrameworkPos == StringRef::npos ||
       (ContextName[FrameworkPos + DotFrameworkLen] != '/' &&
        ContextName[FrameworkPos + DotFrameworkLen] != '\\'))
-    return nullptr;
+    return None;
 
   SmallString<1024> FrameworkName(ContextName.data(), ContextName.data() +
                                                           FrameworkPos +
                                                           DotFrameworkLen + 1);
 
   // Append Frameworks/HIToolbox.framework/
   FrameworkName += "Frameworks/";
   FrameworkName.append(Filename.begin(), Filename.begin()+SlashPos);
   FrameworkName += ".framework/";
 
   auto &CacheLookup =
       *FrameworkMap.insert(std::make_pair(Filename.substr(0, SlashPos),
                                           FrameworkCacheEntry())).first;
 
   // Some other location?
   if (CacheLookup.second.Directory &&
       CacheLookup.first().size() == FrameworkName.size() &&
       memcmp(CacheLookup.first().data(), &FrameworkName[0],
              CacheLookup.first().size()) != 0)
-    return nullptr;
+    return None;
 
   // Cache subframework.
   if (!CacheLookup.second.Directory) {
     ++NumSubFrameworkLookups;
 
     // If the framework dir doesn't exist, we fail.
     auto Dir = FileMgr.getDirectory(FrameworkName);
-    if (!Dir) return nullptr;
+    if (!Dir)
+      return None;
 
     // Otherwise, if it does, remember that this is the right direntry for this
     // framework.
     CacheLookup.second.Directory = *Dir;
   }
 
-  const FileEntry *FE = nullptr;
 
   if (RelativePath) {
     RelativePath->clear();
     RelativePath->append(Filename.begin()+SlashPos+1, Filename.end());
   }
 
   // Check ".../Frameworks/HIToolbox.framework/Headers/HIToolbox.h"
   SmallString<1024> HeadersFilename(FrameworkName);
   HeadersFilename += "Headers/";
   if (SearchPath) {
     SearchPath->clear();
     // Without trailing '/'.
     SearchPath->append(HeadersFilename.begin(), HeadersFilename.end()-1);
   }
 
   HeadersFilename.append(Filename.begin()+SlashPos+1, Filename.end());
-  if (auto File = FileMgr.getFile(HeadersFilename, /*OpenFile=*/true))
-    FE = *File;
+  llvm::ErrorOr<FileEntryRef> File =
+      FileMgr.getFileRef(HeadersFilename, /*OpenFile=*/true);
 
-  if (!FE) {
+  if (!File) {
     // Check ".../Frameworks/HIToolbox.framework/PrivateHeaders/HIToolbox.h"
     HeadersFilename = FrameworkName;
     HeadersFilename += "PrivateHeaders/";
     if (SearchPath) {
       SearchPath->clear();
       // Without trailing '/'.
       SearchPath->append(HeadersFilename.begin(), HeadersFilename.end()-1);
     }
 
     HeadersFilename.append(Filename.begin()+SlashPos+1, Filename.end());
-    if (auto File = FileMgr.getFile(HeadersFilename, /*OpenFile=*/true))
-      FE = *File;
-  
-    if (!FE)
-      return nullptr;
+    File = FileMgr.getFileRef(HeadersFilename, /*OpenFile=*/true);
+    if (!File)
+      return None;
   }
 
   // This file is a system header or C++ unfriendly if the old file is.
   //
   // Note that the temporary 'DirInfo' is required here, as either call to
   // getFileInfo could resize the vector and we don't want to rely on order
   // of evaluation.
   unsigned DirInfo = getFileInfo(ContextFileEnt).DirInfo;
-  getFileInfo(FE).DirInfo = DirInfo;
+  getFileInfo(&File->getFileEntry()).DirInfo = DirInfo;
 
   FrameworkName.pop_back(); // remove the trailing '/'
-  if (!findUsableModuleForFrameworkHeader(FE, FrameworkName, RequestingModule,
-                                          SuggestedModule, /*IsSystem*/ false))
-    return nullptr;
+  if (!findUsableModuleForFrameworkHeader(&File->getFileEntry(), FrameworkName,
+                                          RequestingModule, SuggestedModule,
+                                          /*IsSystem*/ false))
+    return None;
 
-  return FE;
+  return *File;
 }
 
 //===----------------------------------------------------------------------===//
 // File Info Management.
 //===----------------------------------------------------------------------===//
 
 /// Merge the header file info provided by \p OtherHFI into the current
 /// header file info (\p HFI)

clang/lib/Lex/PPDirectives.cpp

if (!InTextualHeader)
       break;
 
     Loc = SM.getIncludeLoc(ID);
   }
 
   return nullptr;
 }
 
-const FileEntry *Preprocessor::LookupFile(
+Optional<FileEntryRef> Preprocessor::LookupFile(
     SourceLocation FilenameLoc, StringRef Filename, bool isAngled,
     const DirectoryLookup *FromDir, const FileEntry *FromFile,
     const DirectoryLookup *&CurDir, SmallVectorImpl<char> *SearchPath,
     SmallVectorImpl<char> *RelativePath,
     ModuleMap::KnownHeader *SuggestedModule, bool *IsMapped,
     bool *IsFrameworkFound, bool SkipCache) {
   Module *RequestingModule = getModuleForLocation(FilenameLoc);
   bool RequestingModuleIsModuleInterface = !SourceMgr.isInMainFile(FilenameLoc);
Optional<FileEntryRef> Preprocessor::LookupFile(
 
   CurDir = CurDirLookup;
 
   if (FromFile) {
     // We're supposed to start looking from after a particular file. Search
     // the include path until we find that file or run out of files.
     const DirectoryLookup *TmpCurDir = CurDir;
     const DirectoryLookup *TmpFromDir = nullptr;
-    while (const FileEntry *FE = HeaderInfo.LookupFile(
+    while (Optional<FileEntryRef> FE = HeaderInfo.LookupFile(
                Filename, FilenameLoc, isAngled, TmpFromDir, TmpCurDir,
                Includers, SearchPath, RelativePath, RequestingModule,
                SuggestedModule, /*IsMapped=*/nullptr,
                /*IsFrameworkFound=*/nullptr, SkipCache)) {
       // Keep looking as if this file did a #include_next.
       TmpFromDir = TmpCurDir;
       ++TmpFromDir;
-      if (FE == FromFile) {
+      if (&FE->getFileEntry() == FromFile) {
         // Found it.
         FromDir = TmpFromDir;
         CurDir = TmpCurDir;
         break;
       }
     }
   }
 
   // Do a standard file entry lookup.
-  const FileEntry *FE = HeaderInfo.LookupFile(
+  Optional<FileEntryRef> FE = HeaderInfo.LookupFile(
       Filename, FilenameLoc, isAngled, FromDir, CurDir, Includers, SearchPath,
       RelativePath, RequestingModule, SuggestedModule, IsMapped,
       IsFrameworkFound, SkipCache, BuildSystemModule);
   if (FE) {
     if (SuggestedModule && !LangOpts.AsmPreprocessor)
       HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
           RequestingModule, RequestingModuleIsModuleInterface, FilenameLoc,
-          Filename, FE);
+          Filename, &FE->getFileEntry());
     return FE;
   }
 
   const FileEntry *CurFileEnt;
   // Otherwise, see if this is a subframework header.  If so, this is relative
   // to one of the headers on the #include stack.  Walk the list of the current
   // headers on the #include stack and pass them to HeaderInfo.
   if (IsFileLexer()) {
     if ((CurFileEnt = CurPPLexer->getFileEntry())) {
-      if ((FE = HeaderInfo.LookupSubframeworkHeader(Filename, CurFileEnt,
-                                                    SearchPath, RelativePath,
-                                                    RequestingModule,
-                                                    SuggestedModule))) {
+      if (Optional<FileEntryRef> FE = HeaderInfo.LookupSubframeworkHeader(
+              Filename, CurFileEnt, SearchPath, RelativePath, RequestingModule,
+              SuggestedModule)) {
         if (SuggestedModule && !LangOpts.AsmPreprocessor)
           HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
               RequestingModule, RequestingModuleIsModuleInterface, FilenameLoc,
-              Filename, FE);
+              Filename, &FE->getFileEntry());
         return FE;
       }
     }
   }
 
   for (IncludeStackInfo &ISEntry : llvm::reverse(IncludeMacroStack)) {
     if (IsFileLexer(ISEntry)) {
       if ((CurFileEnt = ISEntry.ThePPLexer->getFileEntry())) {
-        if ((FE = HeaderInfo.LookupSubframeworkHeader(
+        if (Optional<FileEntryRef> FE = HeaderInfo.LookupSubframeworkHeader(
                 Filename, CurFileEnt, SearchPath, RelativePath,
-                RequestingModule, SuggestedModule))) {
+                RequestingModule, SuggestedModule)) {
           if (SuggestedModule && !LangOpts.AsmPreprocessor)
             HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
                 RequestingModule, RequestingModuleIsModuleInterface,
-                FilenameLoc, Filename, FE);
+                FilenameLoc, Filename, &FE->getFileEntry());
           return FE;
         }
       }
     }
   }
 
   // Otherwise, we really couldn't find the file.
-  return nullptr;
+  return None;
 }
 
 //===----------------------------------------------------------------------===//
 // Preprocessor Directive Handling.
 //===----------------------------------------------------------------------===//
 
 class Preprocessor::ResetMacroExpansionHelper {
 public:
Preprocessor::ImportAction Preprocessor::HandleHeaderIncludeOrImport(
   SourceLocation FilenameLoc = FilenameTok.getLocation();
   SmallString<128> NormalizedPath;
   if (LangOpts.MSVCCompat) {
     NormalizedPath = Filename.str();
 #ifndef _WIN32
     llvm::sys::path::native(NormalizedPath);
 #endif
   }
-  const FileEntry *File = LookupFile(
+
+  auto LookupHeaderFile = [&]() -> Optional<FileEntryRef> {
+    Optional<FileEntryRef> File = LookupFile(
         FilenameLoc, LangOpts.MSVCCompat ? NormalizedPath.c_str() : Filename,
         isAngled, LookupFrom, LookupFromFile, CurDir,
         Callbacks ? &SearchPath : nullptr, Callbacks ? &RelativePath : nullptr,
         &SuggestedModule, &IsMapped, &IsFrameworkFound);
+    if (File)
+      return File;
 
-  if (!File) {
     if (Callbacks) {
       // Give the clients a chance to recover.
       SmallString<128> RecoveryPath;
       if (Callbacks->FileNotFound(Filename, RecoveryPath)) {
         if (auto DE = FileMgr.getDirectory(RecoveryPath)) {
           // Add the recovery path to the list of search paths.
           DirectoryLookup DL(*DE, SrcMgr::C_User, false);
           HeaderInfo.AddSearchPath(DL, isAngled);
 
           // Try the lookup again, skipping the cache.
-          File = LookupFile(
+          Optional<FileEntryRef> File = LookupFile(
               FilenameLoc,
               LangOpts.MSVCCompat ? NormalizedPath.c_str() : Filename, isAngled,
               LookupFrom, LookupFromFile, CurDir, nullptr, nullptr,
               &SuggestedModule, &IsMapped, /*IsFrameworkFound=*/nullptr,
               /*SkipCache*/ true);
+          if (File)
+            return File;
         }
       }
     }
 
-    if (!SuppressIncludeNotFoundError) {
-      // If the file could not be located and it was included via angle
-      // brackets, we can attempt a lookup as though it were a quoted path to
-      // provide the user with a possible fixit.
-      if (isAngled) {
-        File = LookupFile(
-            FilenameLoc,
-            LangOpts.MSVCCompat ? NormalizedPath.c_str() : Filename, false,
-            LookupFrom, LookupFromFile, CurDir,
-            Callbacks ? &SearchPath : nullptr,
-            Callbacks ? &RelativePath : nullptr, &SuggestedModule, &IsMapped,
-            /*IsFrameworkFound=*/nullptr);
-        if (File) {
-          Diag(FilenameTok,
-               diag::err_pp_file_not_found_angled_include_not_fatal)
-              << Filename << IsImportDecl
-              << FixItHint::CreateReplacement(FilenameRange,
-                                              "\"" + Filename.str() + "\"");
-        }
-      }
+    if (SuppressIncludeNotFoundError)
+      return None;
+
+      Optional<FileEntryRef> File = LookupFile(
+          FilenameLoc, LangOpts.MSVCCompat ? NormalizedPath.c_str() : Filename,
+          false, LookupFrom, LookupFromFile, CurDir,
+        Diag(FilenameTok, diag::err_pp_file_not_found_angled_include_not_fatal)
+        return File;
 
-      // Check for likely typos due to leading or trailing non-isAlphanumeric
-      // characters
-      StringRef OriginalFilename = Filename;
-      if (LangOpts.SpellChecking && !File) {
-        // A heuristic to correct a typo file name by removing leading and
-        // trailing non-isAlphanumeric characters.
-        auto CorrectTypoFilename = [](llvm::StringRef Filename) {
-          Filename = Filename.drop_until(isAlphanumeric);
-          while (!Filename.empty() && !isAlphanumeric(Filename.back())) {
-            Filename = Filename.drop_back();
-          }
-          return Filename;
-        };
-        StringRef TypoCorrectionName = CorrectTypoFilename(Filename);
-        SmallString<128> NormalizedTypoCorrectionPath;
-        if (LangOpts.MSVCCompat) {
-          NormalizedTypoCorrectionPath = TypoCorrectionName.str();
+    if (LangOpts.SpellChecking) {
 #ifndef _WIN32
-          llvm::sys::path::native(NormalizedTypoCorrectionPath);
 #endif
-        }
-        File = LookupFile(
-            FilenameLoc,
-            LangOpts.MSVCCompat ? NormalizedTypoCorrectionPath.c_str()
-                                : TypoCorrectionName,
-            isAngled, LookupFrom, LookupFromFile, CurDir,
-            Callbacks ? &SearchPath : nullptr,
-            Callbacks ? &RelativePath : nullptr, &SuggestedModule, &IsMapped,
-            /*IsFrameworkFound=*/nullptr);
-        if (File) {
-          auto Hint =
-              isAngled
-                  ? FixItHint::CreateReplacement(
-                        FilenameRange, "<" + TypoCorrectionName.str() + ">")
-                  : FixItHint::CreateReplacement(
-                        FilenameRange, "\"" + TypoCorrectionName.str() + "\"");
-          Diag(FilenameTok, diag::err_pp_file_not_found_typo_not_fatal)
-              << OriginalFilename << TypoCorrectionName << Hint;
-          // We found the file, so set the Filename to the name after typo
-          // correction.
-          Filename = TypoCorrectionName;
-        }
-      }
+      Optional<FileEntryRef> File = LookupFile(
+        return File;
 
-      // If the file is still not found, just go with the vanilla diagnostic
-      if (!File) {
-        Diag(FilenameTok, diag::err_pp_file_not_found) << OriginalFilename
-                                                       << FilenameRange;
-        if (IsFrameworkFound) {
-          size_t SlashPos = OriginalFilename.find('/');
-          assert(SlashPos != StringRef::npos &&
-                 "Include with framework name should have '/' in the filename");
-          StringRef FrameworkName = OriginalFilename.substr(0, SlashPos);
-          FrameworkCacheEntry &CacheEntry =
-              HeaderInfo.LookupFrameworkCache(FrameworkName);
-          assert(CacheEntry.Directory && "Found framework should be in cache");
-          Diag(FilenameTok, diag::note_pp_framework_without_header)
-              << OriginalFilename.substr(SlashPos + 1) << FrameworkName
-              << CacheEntry.Directory->getName();
-        }
-      }
-    }
-  }
+    assert(!File.hasValue() && "expected missing file");
+    Diag(FilenameTok, diag::err_pp_file_not_found)
+        << OriginalFilename << FilenameRange;
+
+    return None;
+  };
+
+  Optional<FileEntryRef> File = LookupHeaderFile();
 
   if (usingPCHWithThroughHeader() && SkippingUntilPCHThroughHeader) {
-    if (isPCHThroughHeader(File))
+    if (File && isPCHThroughHeader(&File->getFileEntry()))
       SkippingUntilPCHThroughHeader = false;
     return {ImportAction::None};
   }
 
   // Check for circular inclusion of the main file.
   // We can't generate a consistent preamble with regard to the conditional
   // stack if the main file is included again as due to the preamble bounds
   // some directives (e.g. #endif of a header guard) will never be seen.
   // Since this will lead to confusing errors, avoid the inclusion.
   if (File && PreambleConditionalStack.isRecording() &&
-      SourceMgr.translateFile(File) == SourceMgr.getMainFileID()) {
+      SourceMgr.translateFile(&File->getFileEntry()) ==
+          SourceMgr.getMainFileID()) {
     Diag(FilenameTok.getLocation(),
          diag::err_pp_including_mainfile_in_preamble);
     return {ImportAction::None};
   }
 
   // Should we enter the source file? Set to Skip if either the source file is
   // known to have no effect beyond its effect on module visibility -- that is,
   // if it's got an include guard that is already defined, set to Import if it
   // is a modular header we've already built and should import.
   enum { Enter, Import, Skip, IncludeLimitReached } Action = Enter;
 
   if (PPOpts->SingleFileParseMode)
     Action = IncludeLimitReached;
 
   // If we've reached the max allowed include depth, it is usually due to an
   // include cycle. Don't enter already processed files again as it can lead to
   // reaching the max allowed include depth again.
   if (Action == Enter && HasReachedMaxIncludeDepth && File &&
-      HeaderInfo.getFileInfo(File).NumIncludes)
+      HeaderInfo.getFileInfo(&File->getFileEntry()).NumIncludes)
     Action = IncludeLimitReached;
 
   // Determine whether we should try to import the module for this #include, if
   // there is one. Don't do so if precompiled module support is disabled or we
   // are processing this module textually (because we're building the module).
   if (Action == Enter && File && SuggestedModule && getLangOpts().Modules &&
       !isForModuleBuilding(SuggestedModule.getModule(),
                            getLangOpts().CurrentModule,
#endif
   }
 
   // The #included file will be considered to be a system header if either it is
   // in a system include directory, or if the #includer is a system include
   // header.
   SrcMgr::CharacteristicKind FileCharacter =
       SourceMgr.getFileCharacteristic(FilenameTok.getLocation());
   if (File)
-    FileCharacter = std::max(HeaderInfo.getFileDirFlavor(File), FileCharacter);
+    FileCharacter = std::max(HeaderInfo.getFileDirFlavor(&File->getFileEntry()),
+                             FileCharacter);
 
   // If this is a '#import' or an import-declaration, don't re-enter the file.
   //
   // FIXME: If we have a suggested module for a '#include', and we've already
   // visited this file, don't bother entering it again. We know it has no
   // further effect.
   bool EnterOnce =
       IsImportDecl ||
       IncludeTok.getIdentifierInfo()->getPPKeywordID() == tok::pp_import;
 
   // Ask HeaderInfo if we should enter this #include file.  If not, #including
   // this file will have no effect.
   if (Action == Enter && File &&
-      !HeaderInfo.ShouldEnterIncludeFile(*this, File, EnterOnce,
-                                         getLangOpts().Modules,
+      !HeaderInfo.ShouldEnterIncludeFile(*this, &File->getFileEntry(),
+                                         EnterOnce, getLangOpts().Modules,
                                          SuggestedModule.getModule())) {
     // Even if we've already preprocessed this header once and know that we
     // don't need to see its contents again, we still need to import it if it's
     // modular because we might not have imported it from this submodule before.
     //
     // FIXME: We don't do this when compiling a PCH because the AST
     // serialization layer can't cope with it. This means we get local
     // submodule visibility semantics wrong in that case.
     Action = (SuggestedModule && !getLangOpts().CompilingPCH) ? Import : Skip;
   }
 
   if (Callbacks && !IsImportDecl) {
     // Notify the callback object that we've seen an inclusion directive.
     // FIXME: Use a different callback for a pp-import?
     Callbacks->InclusionDirective(
         HashLoc, IncludeTok,
         LangOpts.MSVCCompat ? NormalizedPath.c_str() : Filename, isAngled,
-        FilenameRange, File, SearchPath, RelativePath,
+        FilenameRange, &File->getFileEntry(), SearchPath, RelativePath,
         Action == Import ? SuggestedModule.getModule() : nullptr,
         FileCharacter);
     if (Action == Skip)
-      Callbacks->FileSkipped(*File, FilenameTok, FileCharacter);
+      Callbacks->FileSkipped(File->getFileEntry(), FilenameTok, FileCharacter);
   }
 
   if (!File)
     return {ImportAction::None};
 
   // If this is a C++20 pp-import declaration, diagnose if we didn't find any
   // module corresponding to the named header.
   if (IsImportDecl && !SuggestedModule) {
     Diag(FilenameTok, diag::err_header_import_not_header_unit)
       << OriginalFilename << File->getName();
     return {ImportAction::None};
   }
 
   // Issue a diagnostic if the name of the file on disk has a different case
   // than the one we're about to open.
   const bool CheckIncludePathPortability =
-      !IsMapped && File && !File->tryGetRealPathName().empty();
+      !IsMapped && !File->getFileEntry().tryGetRealPathName().empty();
 
   if (CheckIncludePathPortability) {
     StringRef Name = LangOpts.MSVCCompat ? NormalizedPath.str() : Filename;
-    StringRef RealPathName = File->tryGetRealPathName();
+    StringRef RealPathName = File->getFileEntry().tryGetRealPathName();
     SmallVector<StringRef, 16> Components(llvm::sys::path::begin(Name),
                                           llvm::sys::path::end(Name));
 
     if (trySimplifyPath(Components, RealPathName)) {
       SmallString<128> Path;
       Path.reserve(Name.size()+2);
       Path.push_back(isAngled ? '<' : '"');
       bool isLeadingSeparator = llvm::sys::path::is_absolute(Name);
#endif
   }
 
   // Look up the file, create a File ID for it.
   SourceLocation IncludePos = FilenameTok.getLocation();
   // If the filename string was the result of macro expansions, set the include
   // position on the file where it will be included and after the expansions.
   if (IncludePos.isMacroID())
     IncludePos = SourceMgr.getExpansionRange(IncludePos).getEnd();
-  FileID FID = SourceMgr.createFileID(File, IncludePos, FileCharacter);
+  FileID FID = SourceMgr.createFileID(*File, IncludePos, FileCharacter);
   assert(FID.isValid() && "Expected valid file ID");
 
   // If all is good, enter the new file!
   if (EnterSourceFile(FID, CurDir, FilenameTok.getLocation()))
     return {ImportAction::None};
 
   // Determine if we're switching to building a new submodule, and which one.
   if (auto *M = SuggestedModule.getModule()) {

clang/lib/Lex/PPMacroExpansion.cpp

static bool EvaluateHasIncludeCommon(Token &Tok,
   bool isAngled = PP.GetIncludeFilenameSpelling(Tok.getLocation(), Filename);
   // If GetIncludeFilenameSpelling set the start ptr to null, there was an
   // error.
   if (Filename.empty())
     return false;
 
   // Search include directories.
   const DirectoryLookup *CurDir;
-  const FileEntry *File =
+  Optional<FileEntryRef> File =
       PP.LookupFile(FilenameLoc, Filename, isAngled, LookupFrom, LookupFromFile,
                     CurDir, nullptr, nullptr, nullptr, nullptr, nullptr);
 
   if (PPCallbacks *Callbacks = PP.getPPCallbacks()) {
     SrcMgr::CharacteristicKind FileType = SrcMgr::C_User;
     if (File)
-      FileType = PP.getHeaderSearchInfo().getFileDirFlavor(File);
-    Callbacks->HasInclude(FilenameLoc, Filename, isAngled, File, FileType);
+      FileType =
+          PP.getHeaderSearchInfo().getFileDirFlavor(&File->getFileEntry());
+    Callbacks->HasInclude(FilenameLoc, Filename, isAngled,
+                          File ? &File->getFileEntry() : nullptr, FileType);
   }
 
   // Get the result value.  A result of true means the file exists.
-  return File != nullptr;
+  return File.hasValue();
 }
 
 /// EvaluateHasInclude - Process a '__has_include("path")' expression.
 /// Returns true if successful.
 static bool EvaluateHasInclude(Token &Tok, IdentifierInfo *II,
                                Preprocessor &PP) {
   return EvaluateHasIncludeCommon(Tok, II, PP, nullptr, nullptr);
 }

clang/lib/Lex/Pragma.cpp

bool isAngled =
     GetIncludeFilenameSpelling(FilenameTok.getLocation(), Filename);
   // If GetIncludeFilenameSpelling set the start ptr to null, there was an
   // error.
   if (Filename.empty())
     return;
 
   // Search include directories for this file.
   const DirectoryLookup *CurDir;
-  const FileEntry *File =
+  Optional<FileEntryRef> File =
       LookupFile(FilenameTok.getLocation(), Filename, isAngled, nullptr,
                  nullptr, CurDir, nullptr, nullptr, nullptr, nullptr, nullptr);
   if (!File) {
     if (!SuppressIncludeNotFoundError)
       Diag(FilenameTok, diag::err_pp_file_not_found) << Filename;
     return;
   }
 

clang/lib/Lex/Preprocessor.cpp

void Preprocessor::EnterMainSourceFile() {
 
   // Start parsing the predefines.
   EnterSourceFile(FID, nullptr, SourceLocation());
 
   if (!PPOpts->PCHThroughHeader.empty()) {
     // Lookup and save the FileID for the through header. If it isn't found
     // in the search path, it's a fatal error.
     const DirectoryLookup *CurDir;
-    const FileEntry *File = LookupFile(
+    Optional<FileEntryRef> File = LookupFile(
         SourceLocation(), PPOpts->PCHThroughHeader,
         /*isAngled=*/false, /*FromDir=*/nullptr, /*FromFile=*/nullptr, CurDir,
         /*SearchPath=*/nullptr, /*RelativePath=*/nullptr,
         /*SuggestedModule=*/nullptr, /*IsMapped=*/nullptr,
         /*IsFrameworkFound=*/nullptr);
     if (!File) {
       Diag(SourceLocation(), diag::err_pp_through_header_not_found)
           << PPOpts->PCHThroughHeader;
       return;
     }
     setPCHThroughHeaderFileID(
-        SourceMgr.createFileID(File, SourceLocation(), SrcMgr::C_User));
+        SourceMgr.createFileID(*File, SourceLocation(), SrcMgr::C_User));
   }
 
   // Skip tokens from the Predefines and if needed the main file.
   if ((usingPCHWithThroughHeader() && SkippingUntilPCHThroughHeader) ||
       (usingPCHWithPragmaHdrStop() && SkippingUntilPragmaHdrStop))
     SkipTokensWhileUsingPCH();
 }
 

clang/lib/Serialization/ASTReader.cpp

case SM_SLOC_FILE_ENTRY: {
 
     SourceLocation IncludeLoc = ReadSourceLocation(*F, Record[1]);
     if (IncludeLoc.isInvalid() && F->Kind != MK_MainFile) {
       // This is the module's main file.
       IncludeLoc = getImportLocation(F);
     }
     SrcMgr::CharacteristicKind
       FileCharacter = (SrcMgr::CharacteristicKind)Record[2];
+    // FIXME: The FileID should be created from the FileEntryRef.
     FileID FID = SourceMgr.createFileID(File, IncludeLoc, FileCharacter,
                                         ID, BaseOffset + Record[0]);
     SrcMgr::FileInfo &FileInfo =
           const_cast<SrcMgr::FileInfo&>(SourceMgr.getSLocEntry(FID).getFile());
     FileInfo.NumCreatedFIDs = Record[5];
     if (Record[3])
       FileInfo.setHasLineDirectives();
 

clang/lib/Serialization/ASTWriter.cpp

RecordData::value_type Record[] = {
         INPUT_FILE,
         InputFileOffsets.size(),
         (uint64_t)Entry.File->getSize(),
         (uint64_t)getTimestampForOutput(Entry.File),
         Entry.BufferOverridden,
         Entry.IsTransient,
         Entry.IsTopLevelModuleMap};
 
+    // FIXME: The path should be taken from the FileEntryRef.
     EmitRecordWithPath(IFAbbrevCode, Record, Entry.File->getName());
   }
 
   Stream.ExitBlock();
 
   // Create input file offsets abbreviation.
   auto OffsetsAbbrev = std::make_shared<BitCodeAbbrev>();
   OffsetsAbbrev->Add(BitCodeAbbrevOp(INPUT_FILE_OFFSETS));

clang/unittests/Tooling/CMakeLists.txt

if (MSVC)
   set_source_files_properties(RecursiveASTVisitorTestExprVisitor.cpp PROPERTIES COMPILE_FLAGS /bigobj)
 endif()
 
 add_clang_unittest(ToolingTests
   ASTSelectionTest.cpp
   CastExprTest.cpp
   CommentHandlerTest.cpp
   CompilationDatabaseTest.cpp
+  DependencyScannerTest.cpp
   DiagnosticsYamlTest.cpp
   ExecutionTest.cpp
   FixItTest.cpp
   HeaderIncludesTest.cpp
   LexicallyOrderedRecursiveASTVisitorTest.cpp
   LookupTest.cpp
   QualTypeNamesTest.cpp
   RangeSelectorTest.cpp

clang/unittests/Tooling/DependencyScannerTest.cpp

+//===- unittest/Tooling/ToolingTest.cpp - Tooling unit tests --------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/DeclCXX.h"
+#include "clang/AST/DeclGroup.h"
+#include "clang/Frontend/ASTUnit.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendAction.h"
+#include "clang/Frontend/FrontendActions.h"
+#include "clang/Tooling/CompilationDatabase.h"
+#include "clang/Tooling/Tooling.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+#include "gtest/gtest.h"
+#include <algorithm>
+#include <string>
+
+namespace clang {
+namespace tooling {
+
+namespace {
+
+/// Prints out all of the gathered dependencies into a string.
+class TestFileCollector : public DependencyFileGenerator {
+public:
+  TestFileCollector(DependencyOutputOptions &Opts,
+                    std::vector<std::string> &Deps)
+      : DependencyFileGenerator(Opts), Deps(Deps) {}
+
+  void finishedMainFile(DiagnosticsEngine &Diags) override {
+    Deps = getDependencies();
+  }
+
+private:
+  std::vector<std::string> &Deps;
+};
+
+class TestDependencyScanningAction : public tooling::ToolAction {
+public:
+  TestDependencyScanningAction(std::vector<std::string> &Deps) : Deps(Deps) {}
+
+  bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
+                     FileManager *FileMgr,
+                     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
+                     DiagnosticConsumer *DiagConsumer) override {
+    CompilerInstance Compiler(std::move(PCHContainerOps));
+    Compiler.setInvocation(std::move(Invocation));
+    Compiler.setFileManager(FileMgr);
+
+    Compiler.createDiagnostics(DiagConsumer, /*ShouldOwnClient=*/false);
+    if (!Compiler.hasDiagnostics())
+      return false;
+
+    Compiler.createSourceManager(*FileMgr);
+    Compiler.addDependencyCollector(std::make_shared<TestFileCollector>(
+        Compiler.getInvocation().getDependencyOutputOpts(), Deps));
+
+    auto Action = llvm::make_unique<PreprocessOnlyAction>();
+    return Compiler.ExecuteAction(*Action);
+  }
+
+private:
+  std::vector<std::string> &Deps;
+};
+
+} // namespace
+
+TEST(DependencyScanner, ScanDepsReuseFilemanager) {
+  std::vector<std::string> Compilation = {"-c", "-E", "-MT", "test.cpp.o"};
+  StringRef CWD = "/root";
+  FixedCompilationDatabase CDB(CWD, Compilation);
+
+  auto VFS = new llvm::vfs::InMemoryFileSystem();
+  VFS->setCurrentWorkingDirectory(CWD);
+  VFS->addFile("/root/header.h", 0, llvm::MemoryBuffer::getMemBuffer("\n"));
+  VFS->addHardLink("/root/symlink.h", "/root/header.h");
+  VFS->addFile("/root/test.cpp", 0,
+               llvm::MemoryBuffer::getMemBuffer(
+                   "#include \"symlink.h\"\n#include \"header.h\"\n"));
+
+  ClangTool Tool(CDB, {"test.cpp"}, std::make_shared<PCHContainerOperations>(),
+                 VFS);
+  Tool.clearArgumentsAdjusters();
+  std::vector<std::string> Deps;
+  TestDependencyScanningAction Action(Deps);
+  Tool.run(&Action);
+  // The first invocation should return dependencies in order of access.
+  ASSERT_EQ(Deps.size(), 3u);
+  EXPECT_EQ(Deps[0], "/root/test.cpp");
+  EXPECT_EQ(Deps[1], "/root/symlink.h");
+  EXPECT_EQ(Deps[2], "/root/header.h");
+
+  // The file manager should still have two FileEntries, as one file is a
+  // hardlink.
+  FileManager &Files = Tool.getFiles();
+  EXPECT_EQ(Files.getNumUniqueRealFiles(), 2u);
+
+  Deps.clear();
+  Tool.run(&Action);
+  // The second invocation should have the same order of dependencies.
+  ASSERT_EQ(Deps.size(), 3u);
+  EXPECT_EQ(Deps[0], "/root/test.cpp");
+  EXPECT_EQ(Deps[1], "/root/symlink.h");
+  EXPECT_EQ(Deps[2], "/root/header.h");
+
+  EXPECT_EQ(Files.getNumUniqueRealFiles(), 2u);
+}
+
+} // end namespace tooling
+} // end namespace clang