SourceManager: getFileEntryRefForID => getNonBuiltinFilenameForID, NFC

[dexonsmith]

Summary

SourceManager::getFileEntryRefForID's remaining callers just want the
filename component, which is coming from the FileInfo. Replace the API
with getNonBuiltinFilenameForID, which also removes another use of
FileEntryRef::FileEntryRef outside of FileManager.

Both callers are collecting file dependencies, and one of them relied on
this API to filter out built-ins (as exposed by
clang/test/ClangScanDeps/modules-full.cpp). It seems nice to continue
providing that service.

[dexonsmith]

clang/lib/Basic/SourceManager.cpp

731–732

These ifs need to stay behind to detect whether the file is built-in.

clang/include/clang/Basic/SourceManager.h

public:
   /// Returns the FileEntry record for the provided FileID.
   const FileEntry *getFileEntryForID(FileID FID) const {
     if (auto *Entry = getSLocEntryForFile(FID))
       if (auto *Content = Entry->getFile().getContentCache())
         return Content->OrigEntry;
     return nullptr;
   }
 
-  /// Returns the FileEntryRef for the provided FileID.
-  Optional<FileEntryRef> getFileEntryRefForID(FileID FID) const;
+  /// Returns the filename for the provided FileID, unless it's a built-in
+  /// buffer that's not represented by a filename.
+  ///
+  /// Returns None for non-files and built-in files.
+  Optional<StringRef> getNonBuiltinFilenameForID(FileID FID) const;
 
   /// 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;

clang/lib/Basic/SourceManager.cpp

SourceManager::bypassFileContentsOverride(const FileEntry &File) {
   return FE;
 }
 
 void SourceManager::setFileIsTransient(const FileEntry *File) {
   const SrcMgr::ContentCache *CC = getOrCreateContentCache(File);
   const_cast<SrcMgr::ContentCache *>(CC)->IsTransient = true;
 }
 
-Optional<FileEntryRef> SourceManager::getFileEntryRefForID(FileID FID) const {
+Optional<StringRef>
+SourceManager::getNonBuiltinFilenameForID(FileID FID) const {
   if (const SrcMgr::SLocEntry *Entry = getSLocEntryForFile(FID))
     if (auto *Content = Entry->getFile().getContentCache())
       if (Content && Content->OrigEntry)
-        return FileEntryRef(Entry->getFile().getName(), *Content->OrigEntry);
+        return Entry->getFile().getName();
   return None;
 }
 
 StringRef SourceManager::getBufferData(FileID FID, bool *Invalid) const {
   auto B = getBufferDataOrNone(FID);
   if (Invalid)
     *Invalid = !B;
   return B ? *B : "<<<<<INVALID SOURCE LOCATION>>>>>";

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!
-    Optional<FileEntryRef> File =
-        SM.getFileEntryRefForID(SM.getFileID(SM.getExpansionLoc(Loc)));
-    if (!File)
-      return;
-
-    StringRef Filename =
-        llvm::sys::path::remove_leading_dotslash(File->getName());
-
-    DepCollector.maybeAddDependency(Filename, /*FromModule*/false,
-                                    isSystem(FileType),
-                                    /*IsModuleFile*/false, /*IsMissing*/false);
+    if (Optional<StringRef> Filename = SM.getNonBuiltinFilenameForID(
+            SM.getFileID(SM.getExpansionLoc(Loc))))
+      DepCollector.maybeAddDependency(
+          llvm::sys::path::remove_leading_dotslash(*Filename),
+          /*FromModule*/ false, isSystem(FileType), /*IsModuleFile*/ false,
+          /*IsMissing*/ false);
   }
 
   void FileSkipped(const FileEntryRef &SkippedFile, const Token &FilenameTok,
                    SrcMgr::CharacteristicKind FileType) override {
     StringRef Filename =
         llvm::sys::path::remove_leading_dotslash(SkippedFile.getName());
     DepCollector.maybeAddDependency(Filename, /*FromModule=*/false,
                                     /*IsSystem=*/isSystem(FileType),

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

if (MDC.ContextHash.empty()) {
     MDC.Consumer.handleContextHash(MDC.ContextHash);
   }
 
   SourceManager &SM = Instance.getSourceManager();
 
   // 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!
-  Optional<FileEntryRef> File =
-      SM.getFileEntryRefForID(SM.getFileID(SM.getExpansionLoc(Loc)));
-  if (!File)
-    return;
-
-  StringRef FileName =
-      llvm::sys::path::remove_leading_dotslash(File->getName());
-
-  MDC.MainDeps.push_back(std::string(FileName));
+  if (Optional<StringRef> Filename =
+          SM.getNonBuiltinFilenameForID(SM.getFileID(SM.getExpansionLoc(Loc))))
+    MDC.MainDeps.push_back(
+        std::string(llvm::sys::path::remove_leading_dotslash(*Filename)));
 }
 
 void ModuleDepCollectorPP::InclusionDirective(
     SourceLocation HashLoc, const Token &IncludeTok, StringRef FileName,
     bool IsAngled, CharSourceRange FilenameRange, const FileEntry *File,
     StringRef SearchPath, StringRef RelativePath, const Module *Imported,
     SrcMgr::CharacteristicKind FileType) {
   if (!File && !Imported) {