receive.denyCurrentBranch updateInstead issues when using separate git dir

Hey there, I think I found a bug, it's a bit of an edge case when the repository has a separate git dir. Here's the filled-in output of git bugreport:

What did you do before the bug happened? (Steps to reproduce your issue) The `receive.denyCurrentBranch updateInstead` configuration behaves differently when cloning using a --separate-git-dir flag.

What did you expect to happen? (Expected behavior) The documentation for `receive.denyCurrentBranch updateInstead` indicates that the `push-to-checkout` hook should be configured to run `git read-tree -u -m HEAD "$1"`, however, the tree still contains files from the original commit. This only happens when the receiving repository uses a separate git dir. When the .git dir is inside the repository it updates the work tree correctly.

What happened instead? (Actual behavior) The work tree still had files from the original commit when they should have gotten deleted.

What's different between what you expected and what actually happened? I was expecting the work tree to be updated after the push-to-checkout hook ran git read-tree

Anything else you want to add: I wrote this script to reproduce the issue. I tested it on 2.29.0, v2.29.2-334-gfaefdd61ec, and v2.29.2-505-g04529851e5 ``` #!/usr/bin/env bash

function create {
        git init --quiet one
        cd one
        touch file1
        git add file1
        git commit --quiet -am 'added file1'
        cd ..
}

function allow-updateInstead {
        cd two
        git config receive.denyCurrentBranch updateInstead
        echo 'git read-tree -u -m HEAD "$1"' > $(git rev-parse
--git-dir)/hooks/push-to-checkout
        chmod 755 $(git rev-parse --git-dir)/hooks/push-to-checkout
        cd ..
}

function push-changes {
        cd one
        touch file2
        git rm --quiet file1
        git add file2
        git commit --quiet -am 'removed file1, add file 2'
        git push --quiet ../two HEAD
}

function check-status {
        cd ../two
        git status
}

pushd $(mktemp -d) create git clone --quiet one two allow-updateInstead push-changes echo echo WITH REGULAR CLONE check-status echo GIT STATUS WAS EMPTY echo popd

pushd $(mktemp -d) create git clone --quiet --separate-git-dir two.git one two allow-updateInstead push-changes echo echo WITH SEPARATE GIT DIR CLONE check-status echo GIT STATUS WAS NOT EMPTY echo popd ```

[System Info] git version: git version 2.29.0 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Linux 4.4.0-1117-aws #131-Ubuntu SMP Tue Oct 6 20:45:33 UTC 2020 x86_64 compiler info: gnuc: 5.4 libc info: glibc: 2.23 $SHELL (typically, interactive shell): /bin/bash

[Enabled Hooks] push-to-checkout