strip UTF-8 BOM in -frewrite-includes (PR#15664)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195877 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Rewrite/Frontend/InclusionRewriter.cpp

@@ -367,6 +367,11 @@ bool InclusionRewriter::Process(FileID FileId,
   unsigned NextToWrite = 0;
   int Line = 1; // The current input file line number.
 
+  // Ignore UTF-8 BOM, otherwise it'd end up somewhere else than the start
+  // of the resulting file.
+  if (FromFile.getBuffer().startswith("\xEF\xBB\xBF"))
+    NextToWrite = 3;
+
   Token RawToken;
   RawLex.LexFromRawLexer(RawToken);
 

test/Frontend/Inputs/rewrite-includes-bom.h

+// This file starts with UTF-8 BOM marker.

test/Frontend/rewrite-includes-bom.c

+// RUN: %clang -E -frewrite-includes -I %S/Inputs %s -o - | %clang -fsyntax-only -Xclang -verify -x c -
+// expected-no-diagnostics
+
+#include "rewrite-includes-bom.h"