Re: [PATCH] add: add --chmod=+x / --chmod=-x options

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: May 25, 2016, 12:19 UTC
Message-ID: <alpine.DEB.2.20.1605251406020.4449@virtualbox>
In-Reply-To: <xmqqh9dm37xk.fsf@gitster.mtv.corp.google.com>

Hi Junio,

On Wed, 25 May 2016, Junio C Hamano wrote:

>  * I am not familiar with life on filesystems with core.filemode=0;
>    do files people would want to be able to "add --chmod=+x" share
>    common trait that can be expressed with .gitattributes mechanism?

I think it is safe to say that the biggest example of core.filemode == 0 is Windows. On that platform, there simply is no executable bit in the sense of POSIX permissions. There are Access Control Lists that let you permit or deny certain users from executing certain files (and it is files only, directories are a never "executable" as in POSIX' scheme).

And on Windows, you certainly do not mark a file explicitly as executable when creating it. The file extension determines whether it is executable or not, and that's it.

In a sense, it is cleaner than POSIX' permission system: it separates between the permissions and the classification "is it executable"?

Side note: shell scripts in Git for Windows are a special type of animal. They *cannot* be made executable by Windows because there is just no concept of free-form scripts that can choose whatever interpreter they want to run in. In Git Bash, we have a special hack that is inherited transitively from Cygwin, where scripts are automatically marked as executable if their contents start with a shebang. This stops working as soon as you leave the Bash, of course. Due to Git's heavy dependence on shell scripting, we had to imitate that same concept in compat/mingw.c. It is ugly, it is slow, and we have to live with it.

As a consequence of this very different concept of an "executable bit", you will actually see quite a few Windows-only repositories that *never* mark their executables with 0755. In Git for Windows' own repositories, there are a couple of examples where scripts were introduced and only much later did I realize that they were not marked executable (and then I ran `git update-index --chmod=+x` on them).

All that means that the `--chmod` option is really useful only to cross-platform projects, and only with careful developers. (And those developers could use update-index, as you pointed out.)

I still like Ed's idea and would love to have it: it is murky waters to require users to call plumbing only because our porcelain isn't up to par.

Ciao, Dscho