Implement __VA_OPT__

This implements __VA_OPT__, a new preprocessor feature added in C++2A.
The paper can be found here:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0306r4.html

gcc/ChangeLog

        * doc/cpp.texi (Variadic Macros): Document __VA_OPT__.

gcc/testsuite/ChangeLog

        * c-c++-common/cpp/va-opt-pedantic.c: New file.
        * c-c++-common/cpp/va-opt.c: New file.
        * c-c++-common/cpp/va-opt-error.c: New file.

libcpp/ChangeLog

        * pch.c (cpp_read_state): Set n__VA_OPT__.
        * macro.c (vaopt_state): New class.
        (_cpp_arguments_ok): Check va_opt flag.
        (replace_args, create_iso_definition): Use vaopt_state.
        * lex.c (lex_identifier_intern): Possibly issue errors for
        __VA_OPT__.
        (lex_identifier): Likewise.
        (maybe_va_opt_error): New function.
        * internal.h (struct lexer_state) <va_args_ok>: Update comment.
        (struct spec_nodes) <n__VA_OPT__>: New field.
        * init.c (struct lang_flags) <va_opt>: New field.
        (lang_defaults): Add entries for C++2A.  Update all entries for
        va_opt.
        (cpp_set_lang): Initialize va_opt.
        * include/cpplib.h (struct cpp_options) <va_opt>: New field.
        * identifiers.c (_cpp_init_hashtable): Initialize n__VA_OPT__.

From-SVN: r254707

1 files changed, 30 insertions, 0 deletions

diff --git a/libcpp/lex.c b/libcpp/lex.c
index 8af09e5..a8dc3ba 100644
--- a/libcpp/lex.c
+++ b/libcpp/lex.c
@@ -1352,6 +1352,28 @@ forms_identifier_p (cpp_reader *pfile, int first,
   return false;
 }
 
+/* Helper function to issue error about improper __VA_OPT__ use.  */
+static void
+maybe_va_opt_error (cpp_reader *pfile)
+{
+  if (CPP_PEDANTIC (pfile) && !CPP_OPTION (pfile, va_opt))
+    {
+      /* __VA_OPT__ should not be accepted at all, but allow it in
+	 system headers.  */
+      if (!cpp_in_system_header (pfile))
+	cpp_error (pfile, CPP_DL_PEDWARN,
+		   "__VA_OPT__ is not available until C++2a");
+    }
+  else if (!pfile->state.va_args_ok)
+    {
+      /* __VA_OPT__ should only appear in the replacement list of a
+	 variadic macro.  */
+      cpp_error (pfile, CPP_DL_PEDWARN,
+		 "__VA_OPT__ can only appear in the expansion"
+		 " of a C++2a variadic macro");
+    }
+}
+
 /* Helper function to get the cpp_hashnode of the identifier BASE.  */
 static cpp_hashnode *
 lex_identifier_intern (cpp_reader *pfile, const uchar *base)
@@ -1396,6 +1418,9 @@ lex_identifier_intern (cpp_reader *pfile, const uchar *base)
 		       " of a C99 variadic macro");
 	}
 
+      if (result == pfile->spec_nodes.n__VA_OPT__)
+	maybe_va_opt_error (pfile);
+
       /* For -Wc++-compat, warn about use of C++ named operators.  */
       if (result->flags & NODE_WARN_OPERATOR)
 	cpp_warning (pfile, CPP_W_CXX_OPERATOR_NAMES,
@@ -1485,6 +1510,11 @@ lex_identifier (cpp_reader *pfile, const uchar *base, bool starts_ucn,
 		       " of a C99 variadic macro");
 	}
 
+      /* __VA_OPT__ should only appear in the replacement list of a
+	 variadic macro.  */
+      if (result == pfile->spec_nodes.n__VA_OPT__)
+	maybe_va_opt_error (pfile);
+
       /* For -Wc++-compat, warn about use of C++ named operators.  */
       if (result->flags & NODE_WARN_OPERATOR)
 	cpp_warning (pfile, CPP_W_CXX_OPERATOR_NAMES,