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/ASTConsumers.cpp b/Driver/ASTConsumers.cpp
index 9487a05..6729746 100644
--- a/Driver/ASTConsumers.cpp
+++ b/Driver/ASTConsumers.cpp
@@ -903,10 +903,10 @@
       return;
     
     SourceManager& SourceMgr = TU.getContext().getSourceManager();
-    unsigned ID = SourceMgr.getMainFileID();
-    assert (ID && "MainFileID not set!");
+    FileID ID = SourceMgr.getMainFileID();
+    assert(!ID.isInvalid() && "MainFileID not set!");
     const FileEntry* FE = SourceMgr.getFileEntryForID(ID);
-    assert (FE && "No FileEntry for main file.");
+    assert(FE && "No FileEntry for main file.");
     
     // FIXME: This is not portable to Windows.
     // FIXME: This logic should probably be moved elsewhere later.