Subject: Re: [PATCH v2] grep: improve errors for unmatched ( and )

From: Junio C Hamano <[email-masked]>
Date: Sat, 23 Mar 2024 11:06:53 -0700

Ahelenia Ziemiańska <[email-masked]> writes:

> Imagine you want to grep for (. Easy:
>
>   $ git grep '('
>   fatal: unmatched parenthesis
>
> uhoh. This is plainly wrong. Unless you know specifically that
> (a) git grep has expression groups and that
> (b) the only way to work around them is by doing -- '(' or -e '('
>
> Similarly,
>
>   $ git grep ')'
>   fatal: incomplete pattern expression: )
>
> is somehow worse. ")" is a complete regular expression pattern.
> Of course, the error wants to say "group" here.
> In this case it's also not "incomplete", it's unmatched.
> But whatever.
>
> Make them return
>
>   $ ./git grep '('
>   fatal: unmatched ( for expression group
>   $ ./git grep ')'
>   fatal: incomplete pattern expression group: )
>
> which hopefully are clearer in indicating that it's not the expression
> that's wrong (since no pattern had been parsed at all), but rather that
> it's been misconstrued as a grouping operator.
>
> Link: https://bugs.debian.org/1051205
> Signed-off-by: Ahelenia Ziemiańska <[email-masked]>
> ---
> On Fri, Mar 22, 2024 at 09:41:40AM -0700, Junio C Hamano wrote:
>> Ahelenia Ziemiańska <[email-masked]> writes:
>> > uhoh. This is plainly wrong. Unless you know specifically that
>> > (a) git grep has expression groups and that
>> > (b) the only way to work around them is by doing -- '(' or -e '('
>> I do not think "--" (end of options and beginning of pathspec)
>> marker would work for that purpose, UNLESS you are talking about a
>> file whose name is an open parenthesis.
> False. -- turns all subsequent parameters into arguments, and if
> there is no -e, the first argument is the pattern, and all the
> subsequent ones are paths. This is normal [git] grep behaviour.

Ah, thanks.  

I forgot that "git grep" was a oddball that allows revs come after
"--" in some cases.  As long as the user understands this may not
work for other commands, it is OK.  "-e" is the only officially
supported way (which is why I mentioned it in the review comments I
gave you here), so guiding users in that direction would be a better
idea anyway, though.

Thanks.

> diff --git a/grep.c b/grep.c
> index 5f23d1a..ac34bfe 100644
> --- a/grep.c
> +++ b/grep.c
> @@ -621,7 +621,7 @@ static struct grep_expr *compile_pattern_atom(struct grep_pat **list)
>  		*list = p->next;
>  		x = compile_pattern_or(list);
>  		if (!*list || (*list)->token != GREP_CLOSE_PAREN)
> -			die("unmatched parenthesis");
> +			die("unmatched ( for expression group");
>  		*list = (*list)->next;
>  		return x;
>  	default:
> @@ -792,7 +792,7 @@ void compile_grep_patterns(struct grep_opt *opt)
>  	if (p)
>  		opt->pattern_expression = compile_pattern_expr(&p);
>  	if (p)
> -		die("incomplete pattern expression: %s", p->pattern);
> +		die("incomplete pattern expression group: %s", p->pattern);
>  
>  	if (opt->no_body_match && opt->pattern_expression)
>  		opt->pattern_expression = grep_not_expr(opt->pattern_expression);