Re: rev-parse --show-toplevel broken during exec'ed rebase?

>> Forgetting the code in git-sh-setup, are we?
>> 
>> git_dir_init() rather specifically set GIT_DIR to the absolute path, and
>> since that variable is already exported, the `exec` commands launched via
>> `git-rebase--interactive` all saw it.
>> 
>> That is the reason why the sequencer.c was taught to set GIT_DIR to an
>> absolute path rathern than not setting it: for backwards compatibility.
>
> GIT_DIR was not exported to 'exec' commands during an interactive
> rebase prior to 18633e1a22 (rebase -i: use the rebase--helper builtin,
> 2017-02-09) (nor was GIT_PREFIX):
>
>   $ git log -Sgit_dir_init master git-rebase*.sh
>   # Nothing.
>   $ git checkout 18633e1a22a6^ && make -j4 prefix=/tmp/BEFORE install
>   <....>
>   $ git checkout 18633e1a22a6 && make -j4 prefix=/tmp/AFTER install
>   <....>
>   $ GIT_EDITOR='sed -i -e "1ix set |grep ^GIT"' /tmp/BEFORE/bin/git rebase -i HEAD^
>   Executing: set |grep ^GIT
>   GIT_CHERRY_PICK_HELP=$'\nWhen you have resolved this problem, run "git rebase --continue".\nIf you prefer to skip this patch, run "git rebase --skip" instead.\nTo check out the original branch and stop rebasing, run "git rebase --abort".\n'
>   GIT_EDITOR='sed -i -e "1ix set |grep ^GIT"'
>   GIT_INTERNAL_GETTEXT_SH_SCHEME=gnu
>   GIT_REFLOG_ACTION='rebase -i (start): checkout HEAD^'
>   warning: notes ref refs/notes/commits is invalid
>   Successfully rebased and updated refs/heads/master.
>   $ GIT_EDITOR='sed -i -e "1ix set |grep ^GIT"' /tmp/AFTER/bin/git rebase -i HEAD^
>   Executing: set |grep ^GIT
>   GIT_CHERRY_PICK_HELP='
>   GIT_DIR='.git'
>   GIT_EDITOR='sed -i -e "1ix set |grep ^GIT"'
>   GIT_INTERNAL_GETTEXT_SH_SCHEME='gnu'
>   GIT_PREFIX=''
>   GIT_REFLOG_ACTION='rebase -i (start): checkout HEAD^'
>   warning: notes ref refs/notes/commits is invalid
>   Successfully rebased and updated refs/heads/master.
>
> And then recently came 226c0ddd0d (exec_cmd: RUNTIME_PREFIX on some
> POSIX systems, 2018-04-10), which then started to export GIT_EXEC_PATH
> to 'exec' commands as well...