Bug #5303
closed
parse.y relies on $$ = $1 before action routines [PATCH]
Description
In perusing parse.y, I came across this pair of action routines:
bv_decls : bvar
/%c%/
/%c
{
$$ = rb_ary_new3(1, $1);
}
%/
| bv_decls ',' bvar
/%c%/
/%c
{
rb_ary_push($$, $3);
}
%/
;
Here, the call to rb_ary_push($$, $3) is relying on the fact that yacc/bison prefaces each routine's execution with $$=$1. It does so in order to implement the default behavior for rules that have no action routine (the implicit $$ = $1 rule), and while I doubt that will ever change, I don't think it should be relied upon. At the very least, it's a bit confusing at first glance (using $$ before it is set). Notably, other instances of this idiom (undef_list -> fitem | undef_list ',' fitem; f_arg -> f_arg_item | f_arg ',' f_arg_item; f_block_optarg; f_optarg....) use this approach.
It is corrected by simply replacing $$ with $1. A patch is included. No behavior changes, so no test is included.
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