Re: [PATCH] refs: introduce API function to write invalid null ref

On Sun, Feb 21, 2021 at 8:20 PM Eric Sunshine [off-list ref] wrote:

The reason I ask is that the bit of code in
builtin/worktree.c:add_worktree() which this patch targets is itself a
hack to work around the shortcoming in which is_git_directory() won't
consider the newly-created worktree as being legitimate if it doesn't
have a well-formed HEAD ref. [...]

By the way, the only reason the hack of creating a temporary HEAD
(containing arbitrary OID) is needed is that add_worktree() shells out
to invoke one of git-update-ref or git-symbolic-ref. It is that
shell-out to invoke a Git command which triggers the necessity of
pacifying is_git_directory()...

On the other hand, I could see this as acceptable if "invalid" is
removed from the function name and if it accepts an OID to write
rather than unconditionally writing a zero-ID. In that case, it would
become a generally useful function without the bad smells associated
with the too-special-purpose write_invalid_head_ref().

... so, a much cleaner fix would be to stop shelling out to set up
HEAD in the newly-created worktree, and instead call C API to perform
those functions (update-ref and symbolic-ref) directly. If that C API
does not yet exist, then it should be added.