Function run_external_diff

diff.c:4777–4835

An external diff command takes: * * diff-cmd name infile1 infile1-sha1 infile1-mode \ * infile2 infile2-sha1 infile2-mode [ rename-to ] * */

 *
 */
static void run_external_diff(const struct external_diff *pgm,
			      const char *name,
			      const char *other,
			      struct diff_filespec *one,
			      struct diff_filespec *two,
			      const char *xfrm_msg,
			      struct diff_options *o)
{
	struct child_process cmd = CHILD_PROCESS_INIT;
	struct diff_queue_struct *q = &diff_queued_diff;
	int rc;

	/*
	 * Trivial equality is handled by diff_unmodified_pair() before
	 * we get here.  If we don't need to show the diff and the
	 * external diff program lacks the ability to tell us whether
	 * it's empty then we consider it non-empty without even asking.
	 */
	if (!pgm->trust_exit_code && !o->file) {
		o->found_changes = 1;
		return;
	}

	strvec_push(&cmd.args, pgm->cmd);
	strvec_push(&cmd.args, name);

	if (one && two) {
		add_external_diff_name(o->repo, &cmd.args, one);
		add_external_diff_name(o->repo, &cmd.args, two);
		if (other) {
			strvec_push(&cmd.args, other);
			if (xfrm_msg)
				strvec_push(&cmd.args, xfrm_msg);
		}
	}

	strvec_pushf(&cmd.env, "GIT_DIFF_PATH_COUNTER=%d",
		     ++o->diff_path_counter);
	strvec_pushf(&cmd.env, "GIT_DIFF_PATH_TOTAL=%d", q->nr);

	diff_free_filespec_data(one);
	diff_free_filespec_data(two);
	cmd.use_shell = 1;
	if (!o->file)
		cmd.no_stdout = 1;
	else if (o->file != stdout)
		cmd.out = xdup(fileno(o->file));
	rc = run_command(&cmd);
	if (!pgm->trust_exit_code && rc == 0)
		o->found_changes = 1;
	else if (pgm->trust_exit_code && rc == 0)
		; /* nothing */
	else if (pgm->trust_exit_code && rc == 1)
		o->found_changes = 1;
	else
		die(_("external diff died, stopping at %s"), name);

	remove_tempfile();