Preprocessor: don't consider // to be a line comment in -E -std=c89 mode.

It's beneficial when compiling to treat // as the start of a line
comment even in -std=c89 mode, since it's not valid C code (with a few
rare exceptions) and is usually intended as such. We emit a pedantic
warning and then continue on as if line comments were enabled.
This has been our behavior for quite some time.

However, people use the preprocessor for things besides C source files.
In today's prompting example, the input contains (unquoted) URLs, which
contain // but should still be preserved.

This change instructs the lexer to treat // as a plain token if Clang is
in C90 mode and generating preprocessed output rather than actually compiling.

<rdar://problem/13338743>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176526 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 4 deletions

diff --git a/lib/Lex/Lexer.cpp b/lib/Lex/Lexer.cpp
index 65ea5e3996..e18953d448 100644
--- a/lib/Lex/Lexer.cpp
+++ b/lib/Lex/Lexer.cpp
@@ -3121,10 +3121,13 @@ LexNextToken:
       // this as "foo / bar" and langauges with Line comments would lex it as
       // "foo".  Check to see if the character after the second slash is a '*'.
       // If so, we will lex that as a "/" instead of the start of a comment.
-      // However, we never do this in -traditional-cpp mode.
-      if ((LangOpts.LineComment ||
-           getCharAndSize(CurPtr+SizeTmp, SizeTmp2) != '*') &&
-          !LangOpts.TraditionalCPP) {
+      // However, we never do this if we are just preprocessing.
+      bool TreatAsComment = LangOpts.LineComment && !LangOpts.TraditionalCPP;
+      if (!TreatAsComment)
+        if (!(PP && PP->isPreprocessedOutput()))
+          TreatAsComment = getCharAndSize(CurPtr+SizeTmp, SizeTmp2) != '*';
+
+      if (TreatAsComment) {
         if (SkipLineComment(Result, ConsumeChar(CurPtr, SizeTmp, Result)))
           return; // There is a token to return.