Problems creating a GIT worktree

Question

I have a GIT repository which I would like to create a worktree from. The repository looks like:

alpha
  .git
  Part a
  Part b

I execute the command git worktree add ../beta beta (beta is a branch in alpha). I get:

beta
  .git
  alpha
    Part a
    Part b

I want the copy worktree to look like the original, only with branch beta checked out:

beta
  .git
  Part a
  Part b

What am I doing wrong?

Answer 1

It could be that the alpha repository is broken.

As commented, git fsck is the right tool to check if anything is amiss.

With Git 2.41 (Q2 2023), "git fsck"^(man) learned to check the index files in other worktrees, just like "git gc"^(man) honors them as anchoring points.

See commit 8d3e7ea (26 Feb 2023), and commit 592ec63, commit fb64ca5, commit 8840069 (24 Feb 2023) by Jeff King (peff).
^{(Merged by Junio C Hamano -- gitster -- in commit 2d019f4, 17 Mar 2023)}

fsck: mention file path for index errors

^{Signed-off-by: Jeff King}

If we encounter an error in an index file, we may say something like:

error: 1234abcd: invalid sha1 pointer in resolve-undo

But if you have multiple worktrees, each with its own index, it can be very helpful to know which file had the problem.

So let's pass that path down through the various index-fsck functions and use it where appropriate.
After this patch you should get something like:

error: 1234abcd: invalid sha1 pointer in resolve-undo of .git/worktrees/wt/index

That's a bit verbose, but since the point is that you shouldn't see this normally, we're better to err on the side of more details.

I've also added the index filename to the name used by "fsck --name-objects", which will show up if we find the object to be missing, etc.
This is bending the rules a little there, as the option claims to write names that can be fed to rev-parse.
But there is no revision syntax to access the index of another worktree, so the best we can do is make up something that a human will probably understand.

I did take care to retain the existing ":file" syntax for the current worktree.
So the uglier output should kick in only when it's actually necessary.

---

With Git 2.42 (Q3 2023), this is clarified:

See commit 6e6a529 (29 Jun 2023) by Eric Sunshine (sunshineco).
^{(Merged by Junio C Hamano -- gitster -- in commit b00ec25, 08 Jul 2023)}

fsck: avoid misleading variable name

^{Signed-off-by: Eric Sunshine
Acked-by: Jeff King}

When reporting a problem, git fsck^(man) emits a message such as:

missing blob 1234abcd (:file)

However, this can be ambiguous when the problem is detected in the index of a worktree other than the one in which git fsck was invoked.
To address this shortcoming, 592ec63 ("fsck: mention file path for index errors", 2023-02-24, Git v2.41.0-rc0 -- merge listed in batch #2) enhanced the output to mention the path of the index when the problem is detected in some other worktree:

missing blob 1234abcd (.git/worktrees/wt/index:file)

Unfortunately, the variable in fsck_index() which controls whether the index path should be shown is misleadingly named "is_main_index" which can be misunderstood as referring to the main worktree (i.e.
the one housing the .git/ repository) rather than to the current worktree (i.e. the one in which git fsck was invoked).
Avoid such potential confusion by choosing a name more reflective of its actual purpose.