Re: [PATCH] allow setting GIT_WORK_TREE to "no work tree"

> In setup_git_directory_gently, we have a special rule
> that says "if GIT_DIR is set but GIT_WORK_TREE is not, then
> use the current working directory as the work tree." This is
> the intended behavior for the user perspective.
> 
> However, setup_git_directory_gently sets GIT_DIR itself,
> meaning that further setups (either because we are executing
> a command via alias, or in a subprocess) will see the
> non-existent GIT_WORK_TREE and assume we fall into the
> "current working directory is the working tree" codepath.
> 
> Instead, we now use a special value of GIT_WORK_TREE to
> indicate that we have already checked for a worktree and
> that there isn't one, setting it when we set GIT_DIR and
> checking for it in the special case path.
> 
> The special value is a blank GIT_WORK_TREE; it could be any
> value, but this should not conflict with any user values
> (and as a bonus, you can now tell git "I don't have a work
> tree" with "GIT_WORK_TREE= git", though I suspect the use
> case for that is limited).