Re: [PATCH 4/8] use child_process member "args" instead of string array variable

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Thu, Oct 27 2022, René Scharfe wrote:

> @@ -729,20 +727,22 @@ static int is_expected_rev(const struct object_id *oid)
>  enum bisect_error bisect_checkout(const struct object_id *bisect_rev,
>  				  int no_checkout)
>  {
> -	char bisect_rev_hex[GIT_MAX_HEXSZ + 1];
>  	struct commit *commit;
>  	struct pretty_print_context pp = {0};
>  	struct strbuf commit_msg = STRBUF_INIT;
>
> -	oid_to_hex_r(bisect_rev_hex, bisect_rev);
>  	update_ref(NULL, "BISECT_EXPECTED_REV", bisect_rev, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
>
> -	argv_checkout[2] = bisect_rev_hex;
>  	if (no_checkout) {
>  		update_ref(NULL, "BISECT_HEAD", bisect_rev, NULL, 0,
>  			   UPDATE_REFS_DIE_ON_ERR);
>  	} else {
> -		if (run_command_v_opt(argv_checkout, RUN_GIT_CMD))
> +		struct child_process cmd = CHILD_PROCESS_INIT;
> +
> +		cmd.git_cmd = 1;
> +		strvec_pushl(&cmd.args, "checkout", "-q",
> +			     oid_to_hex(bisect_rev), "--", NULL);
> +		if (run_command(&cmd))
>  			/*
>  			 * Errors in `run_command()` itself, signaled by res < 0,
>  			 * and errors in the child process, signaled by res > 0

Perhaps I went overboard with it in my version, but it's probably worth
mentioning when converting some of these that the reason for the
pre-image of some is really not like the others.

Now that we're on C99 it perhaps make s no difference, but the pre-image
here is explicitly trying to avoid dynamic initializer elements, per
442c27dde78 (CodingGuidelines: mention dynamic C99 initializer elements,
2022-10-10).

Well, partially, some of it appears to just be based on a
misunderstanding of how our own APIs work, i.e. the use of
oid_to_hex_r() over oid_to_hex().

> diff --git a/builtin/am.c b/builtin/am.c
> index 39fea24833..20aea0d248 100644
> --- a/builtin/am.c
> +++ b/builtin/am.c
> @@ -2187,14 +2187,12 @@ static int show_patch(struct am_state *state, enum show_patch_type sub_mode)
>  	int len;
>
>  	if (!is_null_oid(&state->orig_commit)) {
> -		const char *av[4] = { "show", NULL, "--", NULL };
> -		char *new_oid_str;
> -		int ret;
> +		struct child_process cmd = CHILD_PROCESS_INIT;
>
> -		av[1] = new_oid_str = xstrdup(oid_to_hex(&state->orig_commit));
> -		ret = run_command_v_opt(av, RUN_GIT_CMD);
> -		free(new_oid_str);
> -		return ret;
> +		strvec_pushl(&cmd.args, "show", oid_to_hex(&state->orig_commit),
> +			     "--", NULL);
> +		cmd.git_cmd = 1;
> +		return run_command(&cmd);
>  	}

The same goes for this, FWIW I split this one out into its own commit (I
left the earlier one alone):
https://lore.kernel.org/git/patch-v2-04.10-5cfd6a94ce3-20221017T170316Z-avarab@gmail.com/;
It uses the same pattern

> diff --git a/builtin/difftool.c b/builtin/difftool.c
> index 4b10ad1a36..22bcc3444b 100644
> --- a/builtin/difftool.c
> +++ b/builtin/difftool.c
> @@ -360,8 +360,8 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
>  	struct pair_entry *entry;
>  	struct index_state wtindex;
>  	struct checkout lstate, rstate;
> -	int flags = RUN_GIT_CMD, err = 0;
> -	const char *helper_argv[] = { "difftool--helper", NULL, NULL, NULL };
> +	int err = 0;
> +	struct child_process cmd = CHILD_PROCESS_INIT;

In general, I like the disection of this series, but with this...

>  	struct hashmap wt_modified, tmp_modified;
>  	int indices_loaded = 0;
>
> @@ -563,16 +563,17 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
>  	}
>
>  	strbuf_setlen(&ldir, ldir_len);
> -	helper_argv[1] = ldir.buf;
>  	strbuf_setlen(&rdir, rdir_len);
> -	helper_argv[2] = rdir.buf;
>
>  	if (extcmd) {
> -		helper_argv[0] = extcmd;
> -		flags = 0;
> -	} else
> +		strvec_push(&cmd.args, extcmd);
> +	} else {
> +		strvec_push(&cmd.args, "difftool--helper");
> +		cmd.git_cmd = 1;

...and the frequent occurance of just e.g. "cmd.git_cmd = 1" and nothing
else I'm wondering if we're not throwing the baby out with the bath
water in having no convenience wrappers or macros at all.

A lot of your 3-lines would be 1 lines if we just had e.g. (untested,
and could be a function not a macro, but you get the idea):

	#define run_command_git_simple(__VA_ARGS__) \
		struct child_process cmd = CHILD_PROCESS_INIT; \
		cmd.git_cmd = 1; \
		strvec_pushl(&cmd.args, __VA_ARGS__); \
		run_command(&cmd);

But maybe nobody except me thinks that's worthwhile...

>  static void read_empty(const struct object_id *oid)
>  {
> -	int i = 0;
> -	const char *args[7];
> -
> -	args[i++] = "read-tree";
> -	args[i++] = "-m";
> -	args[i++] = "-u";
> -	args[i++] = empty_tree_oid_hex();
> -	args[i++] = oid_to_hex(oid);
> -	args[i] = NULL;
> +	struct child_process cmd = CHILD_PROCESS_INIT;
> +
> +	strvec_pushl(&cmd.args, "read-tree", "-m", "-u", empty_tree_oid_hex(),
> +		     oid_to_hex(oid), NULL);
> +	cmd.git_cmd = 1;
>
> -	if (run_command_v_opt(args, RUN_GIT_CMD))
> +	if (run_command(&cmd))
>  		die(_("read-tree failed"));
>  }
>
>  static void reset_hard(const struct object_id *oid)
>  {
> -	int i = 0;
> -	const char *args[6];
> -
> -	args[i++] = "read-tree";
> -	args[i++] = "-v";
> -	args[i++] = "--reset";
> -	args[i++] = "-u";
> -	args[i++] = oid_to_hex(oid);
> -	args[i] = NULL;
> +	struct child_process cmd = CHILD_PROCESS_INIT;
> +
> +	strvec_pushl(&cmd.args, "read-tree", "-v", "--reset", "-u",
> +		     oid_to_hex(oid), NULL);
> +	cmd.git_cmd = 1;
>
> -	if (run_command_v_opt(args, RUN_GIT_CMD))
> +	if (run_command(&cmd))
>  		die(_("read-tree failed"));
>  }

Two perfect examples, e.g. the former would just be:

	if (run_command_git_simple("read-tree", "-m", "-u", empty_tree_oid_hex(),
				   oid_to_hex(oid), NULL))
		die(...);