this massive patch introduces a simple new abstraction: it makes
"FileID" a concept that is now enforced by the compiler's type checker
instead of yet-another-random-unsigned floating around.

This is an important distinction from the "FileID" currently tracked by
SourceLocation.  *That* FileID may refer to the start of a file or to a
chunk within it.  The new FileID *only* refers to the file (and its 
#include stack and eventually #line data), it cannot refer to a chunk.

FileID is a completely opaque datatype to all clients, only SourceManager
is allowed to poke and prod it.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@62407 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Driver/RewriteMacros.cpp b/Driver/RewriteMacros.cpp
index fb423c6..ecf4b41 100644
--- a/Driver/RewriteMacros.cpp
+++ b/Driver/RewriteMacros.cpp
@@ -65,7 +65,7 @@
   
   // Create a lexer to lex all the tokens of the main file in raw mode.  Even
   // though it is in raw mode, it will not return comments.
-  Lexer RawLex(SourceLocation::getFileLoc(SM.getMainFileID(), 0),
+  Lexer RawLex(SM.getLocForStartOfFile(SM.getMainFileID()),
                PP.getLangOptions(), File.first, File.second);
 
   // Switch on comment lexing because we really do want them.