Multiple use of ast node in parser

I'm playing around with some syntactic sugar for PHP and when trying to implement
:$foo
as equivalent for
'foo' => $foo
I ran into the problem of having only having one ast node but trying to use it twice.

My first attempt was
| ':' T_VARIABLE
{ $$ = zend_ast_create(ZEND_AST_ARRAY_ELEM, zend_ast_create(ZEND_AST_VAR, $2), $2); }
but that results in corrupted memory because of the double usage.

Trying something like
| ':' T_VARIABLE
{ $$ = zend_ast_create(ZEND_AST_ARRAY_ELEM, zend_ast_create(ZEND_AST_VAR, GC_AST(zend_ast_copy($2))), $2); }
works but leaks memory because the copied ast is not freed.

Is there a proper way to do something like this ast transformation inside the parser?

Regards,

• Chris