Re: [PATCH v2 09/11] bisect: libify `check_good_are_ancestors_of_bad` and its dependents

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Jan 30, 2020, 13:46 UTC
Message-ID: <nycvar.QRO.7.76.6.2001301341100.46@tvgsbejvaqbjf.bet>
In-Reply-To: <20200128144026.53128-10-mirucam@gmail.com>

Hi Miriam,

On Tue, 28 Jan 2020, Miriam Rubio wrote:

Show 16 quoted lines

> @@ -893,18 +901,20 @@ static void check_good_are_ancestors_of_bad(struct repository *r,
>  	if (check_ancestors(r, rev_nr, rev, prefix))
>  		res = check_merge_bases(rev_nr, rev, no_checkout);
>  	free(rev);
> -	if (res)
> -		exit(res == -11 ? 0 : -res);
>
> -	/* Create file BISECT_ANCESTORS_OK. */
> -	fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
> -	if (fd < 0)
> -		warning_errno(_("could not create file '%s'"),
> -			      filename);
> -	else
> -		close(fd);
> +	if (!res)
> +	{

Please move the opening `{` to the same line as the `if (!res)`.

Show 8 quoted lines

> +		/* Create file BISECT_ANCESTORS_OK. */
> +		fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
> +		if (fd < 0)
> +			warning_errno(_("could not create file '%s'"),
> +				      filename);
> +		else
> +			close(fd);
> +	}

I wonder whether this would be easier to read:

	if (res == -11)
		res = 0;
	else if (res)
		; /* error out */
	else if ((fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600)) < 0)
		res = warning_errno(_("could not create file '%s'"), filename);
	else
		close(fd);

Note: my code explicitly assigns `res = -1` if the file could not be
created, which is technically a change in behavior, but I think it is
actually a bug fix.

Show 9 quoted lines

>   done:
>  	free(filename);
> +	return res;
>  }
>
>  /*
> @@ -975,7 +985,9 @@ int bisect_next_all(struct repository *r, const char *prefix, int no_checkout)
>  	if (read_bisect_refs())
>  		die(_("reading bisect refs failed"));

I see that there is still a `die()` here, and you left it alone in this patch because at this point, only the callers of `check_good_are_ancestors_of_bad()` need to be addressed. Good.

At a later point, this will have to be dealt with, of course.

Another thing will need to be handled, too: while I was looking at the code whether any resources need to be released (returning a negative integer does not release memory or close file handles, unlike `die()`), I stumbled across the fact that `term_bad` and `term_good` are file-local variables. They will need to be made attributes of a `struct` and will need to be released properly, i.e. the ownership will have to be clarified (is a failed `bisect_next_all()` responsible for releasing the memory it allocated via `read_bisect_terms()`, or its caller?).

Just something to keep in mind. Or better: to jot down in a TODO list.

Show 33 quoted lines

>
> -	check_good_are_ancestors_of_bad(r, prefix, no_checkout);
> +	res = check_good_are_ancestors_of_bad(r, prefix, no_checkout);
> +	if (res)
> +		return res;
>
>  	bisect_rev_setup(r, &revs, prefix, "%s", "^%s", 1);
>  	revs.limited = 1;
> diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c
> index 826fcba2ed..3442bfe2cb 100644
> --- a/builtin/bisect--helper.c
> +++ b/builtin/bisect--helper.c
> @@ -666,7 +666,8 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
>
>  	switch (cmdmode) {
>  	case NEXT_ALL:
> -		return bisect_next_all(the_repository, prefix, no_checkout);
> +		res = bisect_next_all(the_repository, prefix, no_checkout);
> +		break;
>  	case WRITE_TERMS:
>  		if (argc != 2)
>  			return error(_("--write-terms requires two arguments"));
> @@ -713,5 +714,12 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
>  		return error("BUG: unknown subcommand '%d'", cmdmode);
>  	}
>  	free_terms(&terms);
> -	return !!res;
> +	/*
> +	 * Handle early success
> +	 * From check_merge_bases > check_good_are_ancestors_of_bad > bisect_next_all
> +	 */
> +	if (res == -11)
> +		res = 0;

Hmm. Is this the correct place, though? Should `bisect_next_all()` not be the function that already turns `-11` into `0`? In other words, _which_ code are we supposed to skip over when `check_good_are_ancestors_of_bad()` returns `-11`? In other words, where would the `catch` of the `try`/`catch` be, if we had portable exceptions in C?

> +
> +	return res < 0 ? -res : res;

This is a change in behavior, though: previously we guaranteed that the exit code is either 0 on success or 1 upon failure. I am not quite sure that we want to change that behavior.

Ciao, Dscho

Show 5 quoted lines

>  }
> --
> 2.21.1 (Apple Git-122.3)
>
>