Fix PR3917: the location of a #line directive is the location of the first _.

llvm-svn: 69485

clang/lib/Lex/PPMacroExpansion.cpp

@@ -485,6 +485,10 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
     // be affected by #line.
     SourceLocation Loc = Tok.getLocation();
     
+    // Advance to the location of the first _, this might not be the first byte
+    // of the token if it starts with an escaped newline.
+    Loc = AdvanceToTokenCharacter(Loc, 0);
+    
     // One wrinkle here is that GCC expands __LINE__ to location of the *end* of
     // a macro instantiation.  This doesn't matter for object-like macros, but
     // can matter for a function-like macro that expands to contain __LINE__.

clang/test/Preprocessor/line-directive.c

@@ -79,3 +79,11 @@ typedef int w;  // expected-error {{redefinition of typedef 'w' is invalid in C}
 #line 010  // expected-warning {{#line directive interprets number as decimal, not octal}}
 extern int array[__LINE__ == 10 ? 1:-1];
 
+/* PR3917 */
+#line 41
+extern char array2[\
+_\
+_LINE__ == 42 ? 1: -1];  /* line marker is location of first _ */
+
+
+