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

Thank you for filling out a Git bug report! Please answer the following questions to help us understand your issue.

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

$ env | grep GIT $ git --version git version 2.30.1 $ git init t Initialized empty Git repository in /tmp/t/.git/ $ mkdir t/foo $ cd t/foo $ git rev-parse --show-toplevel /tmp/t $ GIT_DIR=$(git rev-parse --git-dir) git rev-parse --show-toplevel /tmp/t/foo $ git rev-parse --git-dir /tmp/t/.git

What did you expect to happen? (Expected behavior)

"git rev-parse --show-toplevel" should be the same in both invocation.

What happened instead? (Actual behavior)

"git rev-parse --show-toplevel" shows the current working directory if GIT_DIR is set.

What's different between what you expected and what actually happened?

Setting GIT_DIR to $(git rev-parse --git-dir) should not change anything.

Anything else you want to add:

Please review the rest of the bug report below. You can delete any lines you don't wish to share.

[System Info] git version: git version 2.30.1 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Linux 5.3.18-22-default #1 SMP Wed Jun 3 12:16:43 UTC 2020 (720aeba) x86_64 compiler info: gnuc: 9.1 libc info: glibc: 2.26 $SHELL (typically, interactive shell): /opt/local/bin/bash

[Enabled Hooks]

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

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

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

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.

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.