testsuite: Fix false FAIL in gdb.cp/casts.exp

testsuite: Fix false FAIL in gdb.cp/casts.exp

gcc-6.2.1-1.fc26.x86_64

gdb compile failed, /home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:40:10: error: expected primary-expression before 'int'
 decltype(int x)
          ^~~
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:40:10: error: expected ')' before 'int'
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:40:1: error: expected unqualified-id before 'decltype'
 decltype(int x)
 ^~~~~~~~
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc: In function 'int main(int, char**)':
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:59:14: error: expected primary-expression before 'decltype'
   double y = decltype(2);
              ^~~~~~~~

'decltype' is a registered keyword since C++11 which is now a default for GCC.

On Thu, 15 Sep 2016 14:06:56 +0200, Pedro Alves wrote:

Seems to be exercising the FLAG_SHADOW bits:

...
    {"__typeof__", TYPEOF, OP_TYPEOF, 0 },
    {"__typeof", TYPEOF, OP_TYPEOF, 0 },
    {"typeof", TYPEOF, OP_TYPEOF, FLAG_SHADOW },
    {"__decltype", DECLTYPE, OP_DECLTYPE, FLAG_CXX },
    {"decltype", DECLTYPE, OP_DECLTYPE, FLAG_CXX | FLAG_SHADOW },
...

/* This is used to associate some attributes with a token.  */

enum token_flag
{
...
  /* If this bit is set, the token is conditional: if there is a
     symbol of the same name, then the token is a symbol; otherwise,
     the token is a keyword.  */

  FLAG_SHADOW = 2
};

So perhaps a better fix is to move that particular test to a
separate testcase that force-compiles with -std=c++03.

gdb/testsuite/ChangeLog
2016-09-16  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.cp/casts.cc (decltype): Move it ...
	(main): ... with its call to ...
	* gdb.cp/casts03.cc: ... a new file.
	* gdb.cp/casts.exp: Add new file casts03.cc, move decltype test to it.