[Bug c++/15180] New: compound literal syntax for POD structs gives parse error

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

PR#12615 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12615) dealt with
parsing bugs for compound literal expressions that are used as
initializer of a variable.

Most of this was fixed in G++ 3.4.0, however there is still one case
where g++ gives an unjustified error: when the compound literal expression
for a POD struct is used to initialze a variable of a subclass of non-
POD type.

=============================== bug1.cc ==================================
struct object
{
  unsigned long one_o;
  unsigned int allocstamp;
};
struct gcv_object_t
{ 
  unsigned long one_o;
  operator object () const;
  gcv_object_t (object obj);
  gcv_object_t ();
};

void gc_mark (object obj)
{
  object       target0 = ((object){one_o: 0, allocstamp: 0});
  gcv_object_t target1 = gcv_object_t ((object){one_o: 0, allocstamp: 0});
  gcv_object_t target2 = (gcv_object_t) ((object){one_o: 0, allocstamp: 0});
  gcv_object_t target3; target3 = ((object){one_o: 0, allocstamp: 0});
  gcv_object_t target4 = ((object){one_o: 0, allocstamp: 0});
}
==========================================================================

$ g++ -O -c bug1.cc
bug1.cc: In function `void gc_mark(object)':
bug1.cc:20: Fehler: `target4' must be initialized by constructor, not by `{...}'

I think this is a bug because
  1. The right hand side of the 'target4' initialization is an expression
     (the fact that it is allowed as right-hand-side of the 'target3'
     assignment proves this),
  2. The right hand side of the 'target4' initialization, to be parsed
     as a "initializer-clause" (see [dcl.init]), does not have the
     syntax of a "{ initializer-list ,opt }", but rather is an
     "assignment-expression", even a "primary-expression".
  3. The right hand side is a valid expression of type 'object',
     gcv_object_t has a constructor with argument type 'object', and
     therefore [class.expl.init] paragraph 1 allows the initialization
     of a gcv_object_t variable with an expression of type 'object'.

Environment:
System: Linux honolulu.ilog.fr 2.4.21-0.13mdk #1 Fri Mar 14 15:08:06 EST 2003 i686 unknown unknown GNU/Linux
Architecture: i686

	
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../gcc-3.4.0/configure --prefix=/home/haible/gnu/arch/linuxgcc34 --enable-shared --enable-threads --enable-__cxa_atexit --enable-languages=c,c++,f77,java,objc --enable-nls

How-To-Repeat:

See above.
------- Additional Comments From bruno at clisp dot org  2004-04-27 20:53 -------
Fix:

The syntaxes for target1, target2, target3 provide workarounds.

-- 
           Summary: compound literal syntax for POD structs gives parse
                    error
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bruno at clisp dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15180