Entering the main source file in the preprocessor can fail if the
source file has been changed. Handle that failure more gracefully.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@98727 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/Preprocessor.cpp b/lib/Lex/Preprocessor.cpp
index a86799a..917a2e7 100644
--- a/lib/Lex/Preprocessor.cpp
+++ b/lib/Lex/Preprocessor.cpp
@@ -488,7 +488,7 @@
 
 /// EnterMainSourceFile - Enter the specified FileID as the main source file,
 /// which implicitly adds the builtin defines etc.
-void Preprocessor::EnterMainSourceFile() {
+bool Preprocessor::EnterMainSourceFile() {
   // We do not allow the preprocessor to reenter the main file.  Doing so will
   // cause FileID's to accumulate information from both runs (e.g. #line
   // information) and predefined macros aren't guaranteed to be set properly.
@@ -497,8 +497,8 @@
 
   // Enter the main file source buffer.
   std::string ErrorStr;
-  bool Res = EnterSourceFile(MainFileID, 0, ErrorStr);
-  assert(!Res && "Entering main file should not fail!");
+  if (EnterSourceFile(MainFileID, 0, ErrorStr))
+    return true;
 
   // Tell the header info that the main file was entered.  If the file is later
   // #imported, it won't be re-entered.
@@ -515,8 +515,7 @@
   assert(!FID.isInvalid() && "Could not create FileID for predefines?");
 
   // Start parsing the predefines.
-  Res = EnterSourceFile(FID, 0, ErrorStr);
-  assert(!Res && "Entering predefines should not fail!");
+  return EnterSourceFile(FID, 0, ErrorStr);
 }