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, 1 insertions, 16 deletions

diff --git a/gcc/tree.c b/gcc/tree.c
index e845fc7..2bee1d2 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -68,6 +68,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "regs.h"
 #include "tree-vector-builder.h"
 #include "gimple-fold.h"
+#include "escaped_string.h"
 
 /* Tree code classes.  */
 
@@ -13225,22 +13226,6 @@ typedef_variant_p (const_tree type)
   return is_typedef_decl (TYPE_NAME (type));
 }
 
-/* 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 (const char *) m_str; }
-  void escape (const char *);
- private:
-  char *m_str;
-  bool  m_owned;
-};
-
 /* PR 84195: Replace control characters in "unescaped" with their
    escaped equivalents.  Allow newlines if -fmessage-length has
    been set to a non-zero value.  This is done here, rather than