Is there a way to find the work-tree of a Git repo, given its .git directory?

Question

I'm writing a script for some colleagues to use on their Git repositories, and I'm confused about how to reliably find the root of the repo's work-tree:

Typically, if the current directory is inside a work-tree, the commands...

git rev-parse --git-dir
git rev-parse --show-toplevel

...would return the roots of the .git directory and work-tree, respectively. However, if the current directory happens to be inside a .git directory, then only the first command works. The command git rev-parse --show-toplevel does not show the top-level of the work-tree (at least, not for me, using git 1.8.4.4 on Linux).

Assuming that git rev-parse --is-bare-repository returns false, I would normally guess that the parent directory of git rev-parse --git-dir is either the working directory (or somewhere inside the working directory), but if the user's GIT_DIR is set that the .git directory isn't inside the working directory, that won't work. (For example, when the user is working with submodules, their GIT_DIR might not be inside their work tree.)

What I find confusing is that, when run inside a GIT_DIR, git rev-parse --show-toplevel prints no error messages and returns 0:

$ cd $(git rev-parse --git-dir); git rev-parse --show-toplevel ; echo $?
0

Whereas running the same command somewhere that's clearly not a git repository returns an error code:

$ cd /; git rev-parse --show-toplevel ; echo $?
fatal: Not a git repository (or any of the parent directories): .git
128

If there'a a way to find the work-tree from the GIT_DIR, could someone tell me how...or if it's simply not possible to derive the location of the work tree from the .git directory, help me understand why, philosophically, the .git directory doesn't keep a reference to its work tree?

Thanks in advance for help/pointers!

Answer 1

why, philosophically, the .git directory doesn't keep a reference to its work tree?

Because you can set said work tree anywhere you want (with the --work-tree option or the GIT_WORK_TREE environment variable), including in a place which (and it is the goal) doesn't include the .git folder.

The git config man page does mention:

The value can be an absolute path or relative to the path to the .git directory, which is either specified by --git-dir or GIT_DIR, or automatically discovered.
If --git-dir or GIT_DIR is specified but none of --work-tree, GIT_WORK_TREE and core.worktree is specified, the current working directory is regarded as the top level of your working tree.

So it is more a convention based on the working tree folder (in order to find the .git) instead of the reverse (deducing working tree from the .git folder).

That being said, I list all the commands which can give you an idea of the working tree folder in "How to find the path of the local git repository when I am possibly in a subdirectory".