clang/{Format,Rewrite}: Stop using SourceManager::getBuffer, NFC

Update clang/lib/Format and clang/lib/Rewrite to use a `MemoryBufferRef`
from `getBufferOrFake` instead of `MemoryBuffer*` from `getBuffer`.

No functionality change here, since the call sites weren't checking if
the buffer was valid.

Differential Revision: https://reviews.llvm.org/D89406

clang/lib/Format/FormatTokenLexer.cpp

@@ -763,7 +763,7 @@ bool FormatTokenLexer::tryMergeConflictMarkers() {
   unsigned FirstInLineOffset;
   std::tie(ID, FirstInLineOffset) = SourceMgr.getDecomposedLoc(
       Tokens[FirstInLineIndex]->getStartOfNonWhitespace());
-  StringRef Buffer = SourceMgr.getBuffer(ID)->getBuffer();
+  StringRef Buffer = SourceMgr.getBufferOrFake(ID).getBuffer();
   // Calculate the offset of the start of the current line.
   auto LineOffset = Buffer.rfind('\n', FirstInLineOffset);
   if (LineOffset == StringRef::npos) {

clang/lib/Rewrite/HTMLRewrite.cpp

@@ -107,9 +107,9 @@ void html::HighlightRange(RewriteBuffer &RB, unsigned B, unsigned E,
 void html::EscapeText(Rewriter &R, FileID FID,
                       bool EscapeSpaces, bool ReplaceTabs) {
 
-  const llvm::MemoryBuffer *Buf = R.getSourceMgr().getBuffer(FID);
-  const char* C = Buf->getBufferStart();
-  const char* FileEnd = Buf->getBufferEnd();
+  llvm::MemoryBufferRef Buf = R.getSourceMgr().getBufferOrFake(FID);
+  const char* C = Buf.getBufferStart();
+  const char* FileEnd = Buf.getBufferEnd();
 
   assert (C <= FileEnd);
 
@@ -226,9 +226,9 @@ static void AddLineNumber(RewriteBuffer &RB, unsigned LineNo,
 
 void html::AddLineNumbers(Rewriter& R, FileID FID) {
 
-  const llvm::MemoryBuffer *Buf = R.getSourceMgr().getBuffer(FID);
-  const char* FileBeg = Buf->getBufferStart();
-  const char* FileEnd = Buf->getBufferEnd();
+  llvm::MemoryBufferRef Buf = R.getSourceMgr().getBufferOrFake(FID);
+  const char* FileBeg = Buf.getBufferStart();
+  const char* FileEnd = Buf.getBufferEnd();
   const char* C = FileBeg;
   RewriteBuffer &RB = R.getEditBuffer(FID);
 
@@ -274,9 +274,9 @@ void html::AddLineNumbers(Rewriter& R, FileID FID) {
 void html::AddHeaderFooterInternalBuiltinCSS(Rewriter &R, FileID FID,
                                              StringRef title) {
 
-  const llvm::MemoryBuffer *Buf = R.getSourceMgr().getBuffer(FID);
-  const char* FileStart = Buf->getBufferStart();
-  const char* FileEnd = Buf->getBufferEnd();
+  llvm::MemoryBufferRef Buf = R.getSourceMgr().getBufferOrFake(FID);
+  const char* FileStart = Buf.getBufferStart();
+  const char* FileEnd = Buf.getBufferEnd();
 
   SourceLocation StartLoc = R.getSourceMgr().getLocForStartOfFile(FID);
   SourceLocation EndLoc = StartLoc.getLocWithOffset(FileEnd-FileStart);