Re: [PATCH v2] merge-recursive: symlink's descendants not in way

From: Junio C Hamano <gitster@pobox.com>
To: Jonathan Tan <jonathantanmy@google.com>
Cc: git@vger.kernel.org, newren@gmail.com, szeder.dev@gmail.com
Subject: Re: [PATCH v2] merge-recursive: symlink's descendants not in way
Date: Fri, 20 Sep 2019 10:15:25 -0700	[thread overview]
Message-ID: <xmqqzhiyvqhe.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20190918202738.57273-1-jonathantanmy@google.com> (Jonathan Tan's message of "Wed, 18 Sep 2019 13:27:38 -0700")

Jonathan Tan <jonathantanmy@google.com> writes:

> When the working tree has:
>  - bar (directory)
>  - bar/file (file)
>  - foo (symlink to .)
>
> (note that lstat() for "foo/bar" would tell us that it is a directory)
>
> and the user merges a commit that deletes the foo symlink and instead
> contains:
>  - bar (directory, as above)
>  - bar/file (file, as above)
>  - foo (directory)
>  - foo/bar (file)
>
> the merge should happen without requiring user intervention.

Thanks.  That clears my previous confusion.  It is clear that the
desired outcome is that bar/file will be merged with itself, foo
itself will resolve to "deleted", and foo/bar will be created.

> However, this does not happen.

OK.  We notice that we need to newly create foo/bar but we
incorrectly find that there is "foo/bar" already because of the
careless use of bare lstat(2) makes "bar" visible as if it were also
"foo/bar".  I wonder if the current code would be confused the same
way if the side branch added "foo/bar/file", or the confusion would
be even worse---it is not dir_in_way() and a different codepath
would be affected, no?

> diff --git a/merge-recursive.c b/merge-recursive.c
> index 6b812d67e3..22a12cfeba 100644
> --- a/merge-recursive.c
> +++ b/merge-recursive.c
> @@ -764,7 +764,8 @@ static int dir_in_way(struct index_state *istate, const char *path,
>  
>  	strbuf_release(&dirpath);
>  	return check_working_copy && !lstat(path, &st) && S_ISDIR(st.st_mode) &&
> -		!(empty_ok && is_empty_dir(path));
> +		!(empty_ok && is_empty_dir(path)) &&
> +		!has_symlink_leading_path(path, strlen(path));

As the new call is fairly heavyweight compared to everything else we
are doing, I think it is very sensible to have this at the end, like
this patch does.

Nicely done.  Thanks, will queue.