Re: [PATCH 10/9] ref-filter: fix leak with unterminated %(if) atoms

> When parsing `%(if)` atoms we expect a few other atoms to exist to
> complete it, like `%(then)` and `%(end)`. Whether or not we have seen
> these other atoms is tracked in an allocated `if_then_else` structure,
> which gets free'd by the `if_then_else_handler()` once we have parsed
> the complete conditional expression.
> 
> This results in a memory leak when the `%(if)` atom is not terminated
> correctly and thus incomplete. We never end up executing its handler and
> thus don't end up freeing the structure.
> 
> Plug this memory leak by introducing a new `at_end_data_free` callback
> function. If set, we'll execute it in `pop_stack_element()` and pass it
> the `at_end_data` variable with the intent to free its state. Wire it up
> for the `%(if)` atom accordingly.

> @@ -1169,6 +1170,8 @@ static void pop_stack_element(struct ref_formatting_stack **stack)
>  	if (prev)
>  		strbuf_addbuf(&prev->output, &current->output);
>  	strbuf_release(&current->output);
> +	if (current->at_end_data_free)
> +		current->at_end_data_free(current->at_end_data);
>  	free(current);
>  	*stack = prev;
>  }

> @@ -1228,15 +1231,13 @@ static void if_then_else_handler(struct ref_formatting_stack **stack)
>  	}
>  
>  	*stack = cur;
> -	free(if_then_else);
>  }