Issue #5303 has been reported by Michael Edgar.

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Bug #5303: parse.y relies on $$ = $1 before action routines [PATCH]
http://redmine.ruby-lang.org/issues/5303

Author: Michael Edgar
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: ruby 1.9.3dev (2011-08-21 revision 33020) [x86_64-darwin11.1.0]


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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