Re: bug: setting GIT_DIR to $(git rev-parse --git-dir) changes behavior

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 25, 2021, 18:29 UTC
Message-ID: <xmqqtuq0uhkg.fsf@gitster.g>
In-Reply-To: <alpine.LSU.2.20.2102251549330.20742@cpza.bfz-tzou.qr>

Martin Nicolay <m.nicolay@osm-ag.de> writes:

> What did you do before the bug happened? (Steps to reproduce your issue)

Thanks for concise and clear descriptions for us to learn everything you did. I wish all the reports were written like this one.

> $ env | grep GIT
> $ git --version
> git version 2.30.1

Showed there is no funny environment variable involved and the version. Good.

Show 6 quoted lines

> $ git init t
> Initialized empty Git repository in /tmp/t/.git/
> $ mkdir t/foo
> $ cd t/foo
> $ git rev-parse --show-toplevel
> /tmp/t

The root of the working tree is at /tmp/t/, the repository at /tmp/t/.git/, and you are in the foo/ subdirectory. When you ask "where is the top level of the working tree in this state, because you do not have GIT_DIR or GIT_WORK_TREE environment variables, you are asking Git to "discover" both the .git/ directory and the top of the working tree, by starting at the current directory, i.e. /tmp/t/foo, which is where you are.

First Git looks to see /tmp/t/foo/.git/ exists and is a repository; it is not. So it goes one level up and does so for /tmp/t/.git/ and it finds that it is the repository. The directory in which the repository was discovered is the top of the working tree, hence you get /tmp/t back.

> $ GIT_DIR=$(git rev-parse --git-dir) git rev-parse --show-toplevel
> /tmp/t/foo

When you give the GIT_DIR environment variable, you are telling Git not to perform the repository discovery, AND also you are telling Git that you are at the top-level of the working tree. So this is quite expected (it is a feature that is used by folks who want to have their repository data in a distant and unrelated directory from their working tree).

In other words, this is 100% expected behaviour.

If you want to also tell Git where the top-level of your working tree is, you can export GIT_WORK_TREE at the same time.

    Side note: the latter environment variable was invented for this
    exact reason.  Back when only GIT_DIR existed as a way to tell
    Git where the distant repository is, those who wanted to use the
    "split" layout had to stay at the top-level of their working
    tree, and they got tired of not being able to work from a
    subdirectory.  GIT_WORK_TREE was introduced to tell where the
    top-level is separately from GIT_DIR when GIT_DIR environment
    variable is in use.

> $ git rev-parse --git-dir
> /tmp/t/.git