apply Eli's patch to fix PR4008, with a testcase. Thanks Eli!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@69750 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Lex/TokenConcatenation.cpp

@@ -126,6 +126,14 @@ static char GetFirstChar(Preprocessor &PP, const Token &Tok) {
 /// don't want to track enough to tell "x.." from "...".
 bool TokenConcatenation::AvoidConcat(const Token &PrevTok,
                                      const Token &Tok) const {
+  // First, check to see if the tokens were directly adjacent in the original
+  // source.  If they were, it must be okay to stick them together: if there
+  // were an issue, the tokens would have been lexed differently.
+  if (PrevTok.getLocation().isFileID() && Tok.getLocation().isFileID() &&
+      PrevTok.getLocation().getFileLocWithOffset(PrevTok.getLength()) == 
+        Tok.getLocation())
+    return false;
+  
   tok::TokenKind PrevKind = PrevTok.getKind();
   if (PrevTok.getIdentifierInfo())  // Language keyword or named operator.
     PrevKind = tok::identifier;

test/Preprocessor/output_paste_avoid.c

@@ -1,18 +1,23 @@
-// RUN: clang-cc -E %s | grep '+ + - - + + = = =' &&
-// RUN: clang-cc -E %s | not grep -F '...' &&
-// RUN: clang-cc -E %s | not grep -F 'L"str"'
-
+// RUN: clang-cc -E %s -o %t &&
 // This should print as ".. ." to avoid turning into ...
+// RUN: grep -F 'A: . . .' %t &&
 #define y(a) ..a
-y(.)
+A: y(.)
+
+// RUN: grep -F 'C: .. .' %t &&
+#define DOT .
+C: ..DOT
+
 
+// RUN: grep -F 'D: + + - - + + = = =' %t &&
 #define PLUS +
 #define EMPTY
 #define f(x) =x=
-+PLUS -EMPTY- PLUS+ f(=)
+D: +PLUS -EMPTY- PLUS+ f(=)
 
+// RUN: grep -F 'E: L "str"' %t
 
 // Should expand to L "str" not L"str"
 #define test(x) L#x
-test(str)
+E: test(str)