Re: [PATCH v5 3/3] ls-files.c: add --deduplicate option

From: Junio C Hamano <gitster@pobox.com>
To: 胡哲宁 <adlternative@gmail.com>
Cc: ZheNing Hu via GitGitGadget <gitgitgadget@gmail.com>,
	Git List <git@vger.kernel.org>,
	Eric Sunshine <sunshine@sunshineco.com>
Subject: Re: [PATCH v5 3/3] ls-files.c: add --deduplicate option
Date: Thu, 21 Jan 2021 12:45:16 -0800	[thread overview]
Message-ID: <xmqq1reec943.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <CAOLTT8R=fF00WCVBSTDKHG_3p5RcZaxM2AU-cUj1sNWvy=mhCQ@mail.gmail.com> (=?utf-8?B?IuiDoeWTsuWugSIncw==?= message of "Thu, 21 Jan 2021 19:00:42 +0800")

胡哲宁 <adlternative@gmail.com> writes:

>> OK.  When show_stage is set, skipping_duplicates is automatically
>> turned off (and show_unmerged is automatically covered as it turns
>> show_stage on automatically).  So this feature has really become
>> "are we showing only names, and if so, did we show an entry of the
>> same name before?".
> Yeah,showing only names,so I yesterday ask such question :)
>>
>> >                       if (!show_unmerged || ce_stage(ce))
>> >                               show_ce(repo, dir, ce, fullname.buf,
>> >                                       ce_stage(ce) ? tag_unmerged :
>> >                                       (ce_skip_worktree(ce) ? tag_skip_worktree :
>> >                                               tag_cached));
>> > +                     if (show_cached && skipping_duplicates)
>> > +                             last_shown_ce = ce;
>>
>> The code that calls show_ce() belonging to a totally separate if()
>> statement makes my stomach hurt---how are we going to guarantee that
>> "last shown" really will keep track of what was shown last?
>>
>> Shouldn't the above be more like this?
>>
>> -                       if (!show_unmerged || ce_stage(ce))
>> +                       if (!show_unmerged || ce_stage(ce)) {
>>                                 show_ce(repo, dir, ce, fullname.buf,
>>                                         ce_stage(ce) ? tag_unmerged :
>>                                         (ce_skip_worktree(ce) ? tag_skip_worktree :
>>                                                 tag_cached));
>> +                               last_shown_ce = ce;
>> +                       }
>>
> well,I am also thinking about this question :"last_shown_ce" is not true
> last shown ce,but may be If "last_shown_ce" truly seen every last shown
> ce ,We may need more cumbersome logic to make the program correct.
> I have tried the processing method of your above code before, but found
>  that some errors may have occurred.

I think judicious use of "goto" without introducing the last_shown
would probably result in a much more maintainable code.  It may look
somewhat like so:

	for (i = 0; i < repo->index->cache_nr; i++) {
		const struct cache_entry *ce = repo->index->cache[i];
		struct stat st;
		int stat_err;

		construct_fullname(&fullname, repo, ce);

		if ((dir->flags & DIR_SHOW_IGNORED) &&
			!ce_excluded(dir, repo->index, fullname.buf, ce))
			continue;
		if (ce->ce_flags & CE_UPDATE)
			continue;
		if ((show_cached || show_stage) &&
		    (!show_unmerged || ce_stage(ce))) {
			show_ce(repo, dir, ce, fullname.buf,
				ce_stage(ce) ? tag_unmerged :
				(ce_skip_worktree(ce) ? tag_skip_worktree :
				 tag_cached));
			if (skip_duplicates)
				goto skip_to_next_name;
		}

		if (!show_deleted && !show_modified)
			continue;
		if (ce_skip_worktree(ce))
			continue;
		stat_err = lstat(fullname.buf, &st);
		if (stat_err && (errno != ENOENT && errno != ENOTDIR))
			error_errno("cannot lstat '%s'", fullname.buf);

		if (show_deleted) {
			show_ce(repo, dir, ce, fullname.buf, tag_removed);
			if (skip_duplicates)
				goto skip_to_next_name;
		}
		if (show_modified &&
		    (stat_err || ie_modified(repo->index, ce, &st, 0)))
			show_ce(repo, dir, ce, fullname.buf, tag_modified);
		continue;

	skip_to_next_name:
		{
			int j;
			const struct cache_entry **cache = repo->index->cache;
			for (j = i + 1; j < repo->index->cache_nr; j++)
				if (strcmp(ce->ce_name, cache[j]->ce_name))
					break;
			i = j - 1; /* compensate for outer for loop */
		}
	}