If preprocessing results in a token with leading whitespace that was expanded

from a macro in column 0, ensure that we print whitespace before it in the -E
output. Patch by Harald van Dijk!

llvm-svn: 202070

clang/lib/Frontend/PrintPreprocessedOutput.cpp

@@ -521,6 +521,13 @@ bool PrintPPOutputPPCallbacks::HandleFirstTokOnLine(Token &Tok) {
   // indented for easy reading.
   unsigned ColNo = SM.getExpansionColumnNumber(Tok.getLocation());
 
+  // The first token on a line can have a column number of 1, yet still expect
+  // leading white space, if a macro expansion in column 1 starts with an empty
+  // macro argument, or an empty nested macro expansion. In this case, move the
+  // token to column 2.
+  if (ColNo == 1 && Tok.hasLeadingSpace())
+    ColNo = 2;
+
   // This hack prevents stuff like:
   // #define HASH #
   // HASH define foo bar

clang/test/Preprocessor/macro_expand_empty.c

@@ -17,5 +17,5 @@ IDENTITY0()
 #define FOO() BAR() second
 #define BAR()
 first // CHECK: {{^}}first{{$}}
-FOO() // CHECK: second
+FOO() // CHECK: {{^}} second{{$}}
 third // CHECK: {{^}}third{{$}}