Goss Geppert [off-list ref] writes:

Please see the commit message for a description. Effectively, since
8d92fb2927 (dir: replace exponential algorithm with a linear one,
2020-04-01) the following no longer does what it used to do:

test_repo="$(mktemp -d /tmp/git-test-XXXXXXX)"
cd "$test_repo"
>test-file
git init
git config core.worktree /tmp
git add test-file

And this is supposed to add a new entry to the index at
"git-test-123456/test-file"?

If it added a new index entry 'test-file', that means "git config
core.worktree" is completely ignored, because we are not treating
"/tmp" as the root of the working tree as it is instructed and that
sounds like a bug.  Is that what you mean by "no longer does what it
used to do"?

Thanks for raising an issue (although it is not quite clear yet to
me what the issue is, exactly ;-).