[Bug preprocessor/8270] [4.8/4.9/5 Regression] back-slash white space newline with comments, no warning

["ktietz at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8270

Kai Tietz <ktietz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ktietz at gcc dot gnu.org

--- Comment #55 from Kai Tietz <ktietz at gcc dot gnu.org> ---
Well, by looking into the standard ISO/IEC 9899:TC3 I found the following
statement:

5.1.12 Translation phase
"2. Each instance of a backslash character (\) immediately followed by a
new-line
character is deleted, splicing physical source lines to form logical source
lines.
Only the last backslash on any physical source line shall be eligible for being
part of such a splice. A source file that is not empty shall end in a new-line
character, which shall not be immediately preceded by a backslash character
before any such splicing takes place."

For ISO/IEC 14882:2003 we see at topic "2 Lexical Convention"

"2 Each instance of a new-line character and an immediately preceding backslash
character is deleted, splicing physical source lines to form logical source
lines. If, as a result, a character sequence that matches the syntax of a
universal-character-name is produced, the behavior is undefined. If a source
file that is not empty does not end in a new-line character, or ends in a
new-line character immediately preceded by a backslash character, the behavior
is undefined."

So the handling of backslash whitespace newline is clearly a gnu-extension and
not part of the standard.

I suggest something like this patch for fixing standard-requirement. 
Additionally we could check here for cpp_option lang being gnu-style for
allowing 'backslash,whitespaces,newling' too.

Index: lex.c
===================================================================
--- lex.c       (Revision 221514)
+++ lex.c       (Arbeitskopie)
@@ -896,6 +896,11 @@ _cpp_clean_line (cpp_reader *pfile)
        p--;
       if (p - 1 != pbackslash)
        goto done;
+      if (p != d)
+       {
+         ++p;
+         goto done;
+       }

       /* Have an escaped newline; process it and proceed to
         the slow path.  */
@@ -917,13 +922,19 @@ _cpp_clean_line (cpp_reader *pfile)
              if (s == buffer->rlimit)
                break;

-             /* Escaped?  */
+             /* Escaped?
+                But make sure it isn't a backslash followed by a
+                whitespace.  */
              p = d;
              while (p != buffer->next_line && is_nvspace (p[-1]))
                p--;
              if (p == buffer->next_line || p[-1] != '\\')
                break;
-
+             if (p != d)
+               {
+                 ++p;
+                 break;
+               }
              add_line_note (buffer, p - 1, p != d ? ' ': '\\');
              d = p - 2;
              buffer->next_line = p - 1;