[PATCH v2 0/4] difftool refactoring + remove OPT_ARGUMENT() macro

We've only ever used parse-option.c's OPT_ARGUMENT() in one place, as it turns out we can use an OPT_BOOL there instead. and get a net reduction in code & complexity.

I think this v2 should address the comments Jeff King had in https://lore.kernel.org/git/YT6BnnXeAWn8BycF@coredump.intra.peff.net/; there's now an amended version of his proposed patch as part of this, but I prepended it with another one to prepare the "struct child_process" in cmd_difftool().

Doing so nicely gets around the question of the strvec memory management, since we can trust the run-command.c API to do that for us, but couldn't in my v1 when we'd copy our own "struct strvec *" to its "args".

Jeff King (1):
  difftool: prepare "diff" cmdline in cmd_difftool()

Ævar Arnfjörð Bjarmason (3):
  difftool: prepare "struct child_process" in cmd_difftool()
  difftool: use run_command() API in run_file_diff()
  parse-options API: remove OPTION_ARGUMENT feature

 Documentation/technical/api-parse-options.txt |  5 --
 builtin/difftool.c                            | 51 ++++++++++---------
 parse-options.c                               | 13 -----
 parse-options.h                               |  3 --
 t/helper/test-parse-options.c                 |  1 -
 t/t0040-parse-options.sh                      |  5 --
 6 files changed, 26 insertions(+), 52 deletions(-)

Range-diff against v1:
1:  e7481eb0c0c ! 1:  f57c6c9b069 difftool: use "struct strvec" API in run_{dir,file}_diff()
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    difftool: use "struct strvec" API in run_{dir,file}_diff()
    +    difftool: prepare "struct child_process" in cmd_difftool()
     
    -    The underlying run_command() API can take either the "struct strvec
    -    args", or a "const char **argv". Let's move to the former to use the
    -    more "native" version of run_command() in both of these functions.
    -
    -    This change probably isn't worth in on its own, but sets us up to
    -    simplify API use even more in a subsequent commit.
    +    Move the preparation of the "struct child_process" from run_dir_diff()
    +    to its only caller, cmd_difftool(). This is in preparation for
    +    migrating run_file_diff() to using the run_command() API directly, and
    +    to move more of the shared setup of the two to cmd_difftool().
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
    @@ builtin/difftool.c: static int checkout_path(unsigned mode, struct object_id *oi
      
      static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
     -			int argc, const char **argv)
    -+			struct strvec *args)
    ++			int argc, const char **argv,
    ++			struct child_process *child)
      {
      	char tmpdir[PATH_MAX];
      	struct strbuf info = STRBUF_INIT, lpath = STRBUF_INIT;
     @@ builtin/difftool.c: static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
    - 	child.clean_on_exit = 1;
    - 	child.dir = prefix;
    - 	child.out = -1;
    + 	struct index_state wtindex;
    + 	struct checkout lstate, rstate;
    + 	int rc, flags = RUN_GIT_CMD, err = 0;
    +-	struct child_process child = CHILD_PROCESS_INIT;
    + 	const char *helper_argv[] = { "difftool--helper", NULL, NULL, NULL };
    + 	struct hashmap wt_modified, tmp_modified;
    + 	int indices_loaded = 0;
    +@@ builtin/difftool.c: static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
    + 	rdir_len = rdir.len;
    + 	wtdir_len = wtdir.len;
    + 
    +-	child.no_stdin = 1;
    +-	child.git_cmd = 1;
    +-	child.use_shell = 0;
    +-	child.clean_on_exit = 1;
    +-	child.dir = prefix;
    +-	child.out = -1;
     -	strvec_pushl(&child.args, "diff", "--raw", "--no-abbrev", "-z",
    --		     NULL);
    --	for (i = 0; i < argc; i++)
    ++	child->no_stdin = 1;
    ++	child->git_cmd = 1;
    ++	child->use_shell = 0;
    ++	child->clean_on_exit = 1;
    ++	child->dir = prefix;
    ++	child->out = -1;
    ++	strvec_pushl(&child->args, "diff", "--raw", "--no-abbrev", "-z",
    + 		     NULL);
    + 	for (i = 0; i < argc; i++)
     -		strvec_push(&child.args, argv[i]);
    -+	child.argv = args->v;
    -+
    - 	if (start_command(&child))
    +-	if (start_command(&child))
    ++		strvec_push(&child->args, argv[i]);
    ++	if (start_command(child))
      		die("could not obtain raw diff");
    - 	fp = xfdopen(child.out, "r");
    -@@ builtin/difftool.c: static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
    - 	strbuf_release(&rdir);
    - 	strbuf_release(&wtdir);
    - 	strbuf_release(&buf);
    -+	strvec_clear(args);
    - 
    - 	return ret;
    - }
    +-	fp = xfdopen(child.out, "r");
    ++	fp = xfdopen(child->out, "r");
      
    --static int run_file_diff(int prompt, const char *prefix,
    --			 int argc, const char **argv)
    -+static int run_file_diff(int prompt, const char *prefix, struct strvec *args)
    - {
    --	struct strvec args = STRVEC_INIT;
    --	const char *env[] = {
    --		"GIT_PAGER=", "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL,
    --		NULL
    --	};
    --	int i;
    -+	struct child_process cmd = CHILD_PROCESS_INIT;
    -+	int ret;
    - 
    -+	strvec_pushl(&cmd.env_array, "GIT_PAGER=",
    -+		     "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL);
    - 	if (prompt > 0)
    --		env[2] = "GIT_DIFFTOOL_PROMPT=true";
    -+		strvec_push(&cmd.env_array, "GIT_DIFFTOOL_PROMPT=true");
    - 	else if (!prompt)
    --		env[2] = "GIT_DIFFTOOL_NO_PROMPT=true";
    -+		strvec_push(&cmd.env_array, "GIT_DIFFTOOL_NO_PROMPT=true");
    - 
    -+	cmd.git_cmd = 1;
    -+	cmd.dir = prefix;
    -+	cmd.argv = args->v;
    - 
    --	strvec_push(&args, "diff");
    --	for (i = 0; i < argc; i++)
    --		strvec_push(&args, argv[i]);
    --	return run_command_v_opt_cd_env(args.v, RUN_GIT_CMD, prefix, env);
    -+	ret = run_command(&cmd);
    -+	strvec_clear(args);
    -+	return ret;
    - }
    + 	/* Build index info for left and right sides of the diff */
    + 	i = 0;
    +@@ builtin/difftool.c: static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
      
    - int cmd_difftool(int argc, const char **argv, const char *prefix)
    + 	fclose(fp);
    + 	fp = NULL;
    +-	if (finish_command(&child)) {
    ++	if (finish_command(child)) {
    + 		ret = error("error occurred running diff --raw");
    + 		goto finish;
    + 	}
     @@ builtin/difftool.c: int cmd_difftool(int argc, const char **argv, const char *prefix)
      		OPT_ARGUMENT("no-index", &no_index, N_("passed to `diff`")),
      		OPT_END()
      	};
    -+	struct strvec args = STRVEC_INIT;
    ++	struct child_process child = CHILD_PROCESS_INIT;
      
      	git_config(difftool_config, NULL);
      	symlinks = has_symlinks;
     @@ builtin/difftool.c: int cmd_difftool(int argc, const char **argv, const char *prefix)
    - 	 * will invoke a separate instance of 'git-difftool--helper' for
      	 * each file that changed.
      	 */
    -+	strvec_push(&args, "diff");
    -+	if (dir_diff)
    -+		strvec_pushl(&args, "--raw", "--no-abbrev", "-z", NULL);
    -+	strvec_pushv(&args, argv);
    -+
      	if (dir_diff)
     -		return run_dir_diff(extcmd, symlinks, prefix, argc, argv);
    --	return run_file_diff(prompt, prefix, argc, argv);
    -+		return run_dir_diff(extcmd, symlinks, prefix, &args);
    -+	return run_file_diff(prompt, prefix, &args);
    ++		return run_dir_diff(extcmd, symlinks, prefix, argc, argv, &child);
    + 	return run_file_diff(prompt, prefix, argc, argv);
      }
-:  ----------- > 2:  1c2794115c7 difftool: prepare "diff" cmdline in cmd_difftool()
-:  ----------- > 3:  2b093bd71fc difftool: use run_command() API in run_file_diff()
2:  28b43789b11 ! 4:  4fddce0a38d parse-options API: remove OPTION_ARGUMENT feature
    @@ builtin/difftool.c: int cmd_difftool(int argc, const char **argv, const char *pr
     +		OPT_BOOL(0, "no-index", &no_index, N_("passed to `diff`")),
      		OPT_END()
      	};
    - 	struct strvec args = STRVEC_INIT;
    + 	struct child_process child = CHILD_PROCESS_INIT;
     @@ builtin/difftool.c: int cmd_difftool(int argc, const char **argv, const char *prefix)
      	 * each file that changed.
      	 */
    - 	strvec_push(&args, "diff");
    + 	strvec_push(&child.args, "diff");
     +	if (no_index)
    -+		strvec_push(&args, "--no-index");
    ++		strvec_push(&child.args, "--no-index");
      	if (dir_diff)
    - 		strvec_pushl(&args, "--raw", "--no-abbrev", "-z", NULL);
    - 	strvec_pushv(&args, argv);
    + 		strvec_pushl(&child.args, "--raw", "--no-abbrev", "-z", NULL);
    + 	strvec_pushv(&child.args, argv);
     
      ## parse-options.c ##
     @@ parse-options.c: static enum parse_opt_result parse_long_opt(