SourceManager: Change SourceManager::isMainFile to take a FileEntry, NFC

[dexonsmith]

Summary

SourceManager::isMainFile does not use the filename, so it doesn't
need the full FileEntryRef; in fact, it's misleading to take the name
because that makes it look relevant. Simplify the API, and in the
process remove some calls to FileEntryRef::FileEntryRef in the unit
tests (which were blocking making that private to SourceManager).

clang/include/clang/Basic/SourceManager.h

public:
   /// Set the file ID for the main source file.
   void setMainFileID(FileID FID) {
     MainFileID = FID;
   }
 
   /// Returns true when the given FileEntry corresponds to the main file.
   ///
   /// The main file should be set prior to calling this function.
-  bool isMainFile(FileEntryRef SourceFile);
+  bool isMainFile(const FileEntry &SourceFile);
 
   /// Set the file ID for the precompiled preamble.
   void setPreambleFileID(FileID Preamble) {
     assert(PreambleFileID.isInvalid() && "PreambleFileID already set!");
     PreambleFileID = Preamble;
   }
 
   /// Get the file ID for the precompiled preamble if there is one.

clang/lib/Basic/SourceManager.cpp

if (LineTable)
     LineTable->clear();
 
   // Use up FileID #0 as an invalid expansion.
   NextLocalOffset = 0;
   CurrentLoadedOffset = MaxLoadedOffset;
   createExpansionLoc(SourceLocation(), SourceLocation(), SourceLocation(), 1);
 }
 
-bool SourceManager::isMainFile(FileEntryRef SourceFile) {
+bool SourceManager::isMainFile(const FileEntry &SourceFile) {
   assert(MainFileID.isValid() && "expected initialized SourceManager");
-  auto FE = getFileEntryRefForID(MainFileID);
-  if (!FE)
-    return false;
+  if (auto *FE = getFileEntryForID(MainFileID))
     return FE->getUID() == SourceFile.getUID();
+  return false;
 }
 
 void SourceManager::initializeForReplay(const SourceManager &Old) {
   assert(MainFileID.isInvalid() && "expected uninitialized SourceManager");
 
   auto CloneContentCache = [&](const ContentCache *Cache) -> ContentCache * {
     auto *Clone = new (ContentCacheAlloc.Allocate<ContentCache>()) ContentCache;
     Clone->OrigEntry = Cache->OrigEntry;

clang/lib/Lex/PPDirectives.cpp

#endif
   }
 
   // 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 (Action == Enter && File && PreambleConditionalStack.isRecording() &&
-      SourceMgr.isMainFile(*File)) {
+      SourceMgr.isMainFile(File->getFileEntry())) {
     Diag(FilenameTok.getLocation(),
          diag::err_pp_including_mainfile_in_preamble);
     return {ImportAction::None};
   }
 
   if (Callbacks && !IsImportDecl) {
     // Notify the callback object that we've seen an inclusion directive.
     // FIXME: Use a different callback for a pp-import?

clang/unittests/Basic/SourceManagerTest.cpp

std::unique_ptr<llvm::MemoryBuffer> Buf2 =
       llvm::MemoryBuffer::getMemBuffer(Source);
   const FileEntry *SecondFile =
       FileMgr.getVirtualFile("file2.cpp", Buf2->getBufferSize(), 0);
   SourceMgr.overrideFileContents(SecondFile, std::move(Buf2));
 
   FileID MainFileID = SourceMgr.getOrCreateFileID(SourceFile, SrcMgr::C_User);
   SourceMgr.setMainFileID(MainFileID);
 
-  EXPECT_TRUE(SourceMgr.isMainFile(FileEntryRef("mainFile.cpp", *SourceFile)));
-  EXPECT_TRUE(
-      SourceMgr.isMainFile(FileEntryRef("anotherName.cpp", *SourceFile)));
-  EXPECT_FALSE(SourceMgr.isMainFile(FileEntryRef("mainFile.cpp", *SecondFile)));
+  EXPECT_TRUE(SourceMgr.isMainFile(*SourceFile));
+  EXPECT_TRUE(SourceMgr.isMainFile(*SourceFile));
+  EXPECT_FALSE(SourceMgr.isMainFile(*SecondFile));
 }
 
 #endif
 
 } // anonymous namespace