Implement C++20 P1301 [[nodiscard("should have a reason")]].

2019-10-17  JeanHeyd Meneide  <phdofthehouse@gmail.com>

gcc/
        * escaped_string.h (escaped_string): New header.
        * tree.c (escaped_string): Remove escaped_string class.

gcc/c-family
        * c-lex.c (c_common_has_attribute): Update nodiscard value.

gcc/cp/
        * tree.c (handle_nodiscard_attribute) Added C++2a nodiscard
	string message.
        (std_attribute_table) Increase nodiscard argument handling
	max_length from 0 to 1.
        * parser.c (cp_parser_check_std_attribute): Add requirement
	that nodiscard only be seen once in attribute-list.
        (cp_parser_std_attribute): Check that empty parenthesis lists are
        not specified for attributes that have max_length > 0 (e.g.
	[[attr()]]).
        * cvt.c (maybe_warn_nodiscard): Add nodiscard message to
	output, if applicable.
	(convert_to_void): Allow constructors to be nodiscard-able (P1771).

gcc/testsuite/g++.dg/cpp0x
        * gen-attrs-67.C: Test new error message for empty-parenthesis-list.

gcc/testsuite/g++.dg/cpp2a
        * nodiscard-construct.C: New test.
        * nodiscard-once.C: New test.
        * nodiscard-reason-nonstring.C: New test.
        * nodiscard-reason-only-one.C: New test.
        * nodiscard-reason.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

From-SVN: r277200

1 files changed, 43 insertions, 0 deletions

diff --git a/gcc/escaped_string.h b/gcc/escaped_string.h
new file mode 100644
index 0000000..b83e128
--- /dev/null
+++ b/gcc/escaped_string.h
@@ -0,0 +1,43 @@
+/* Shared escaped string class.
+   Copyright (C) 1999-2019 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_ESCAPED_STRING_H
+#define GCC_ESCAPED_STRING_H
+
+#include <cstdlib>
+
+/* A class to handle converting a string that might contain
+   control characters, (eg newline, form-feed, etc), into one
+   in which contains escape sequences instead.  */
+
+class escaped_string
+{
+ public:
+  escaped_string () { m_owned = false; m_str = NULL; };
+  ~escaped_string () { if (m_owned) free (m_str); }
+  operator const char *() const { return m_str; }
+  void escape (const char *);
+ private:
+  escaped_string(const escaped_string&) {}
+  escaped_string& operator=(const escaped_string&) { return *this; }
+  char *m_str;
+  bool  m_owned;
+};
+
+#endif /* ! GCC_ESCAPED_STRING_H */