Stacking a commit on top of someone else's stacked PR is failing

[rgommers]

Not sure if this is even possible or not?

ghstack checkout https://github.com/pytorch/pytorch/pull/38201
git switch -c mypy-stackme
git cherry-pick some-commit-id
ghstack

gives:

$ git remote get-url origin
$ git fetch origin
Enter passphrase for key '/home/rgommers/.ssh/id_rsa': 
$ git merge-base origin/master HEAD
$ git rev-list --header ^b579433bf7fc2d4cd333bfdacee6f08f5c7f30b1 HEAD
$ git rev-list --header ^b579433bf7fc2d4cd333bfdacee6f08f5c7f30b1^@ b579433bf7fc2d4cd333bfdacee6f08f5c7f30b1
$ git rev-list --max-count=1 --header origin/gh/rgommers/751/orig
fatal: ambiguous argument 'origin/gh/rgommers/751/orig': unknown revision or path not in the working tree.

Clear that that branch doesn't exist, it replaces the username of the original PR submitter with my username.

git lg output looks fine:

* 33b6c27182 - (HEAD -> mypy-stackme) Add type annotations for iinfo/finfo, run mypy on some test files (8 minutes ago)
* 6fde698cba - (origin/gh/ezyang/755/orig) Move torch/autograd/grad_mode.pyi stubs inline (17 hours ago)
* 90a2d0e4b6 - (origin/gh/ezyang/752/orig) Device and torch._C function cleanup (17 hours ago)
* df2cd3de05 - (origin/gh/ezyang/751/orig) Delete torch/__init__.pyi, deferring to direct extension stubs (17 hours ago)

[rgommers]

Not sure if this is even possible or not?

Confirmed by @ezyang: stacking on top of someone else's PR doesn't work.

Leaving this issue open, it would be very useful to have this capability. I'm not planning on looking into it though.

[ezyang]

This works now, but #29 is a follow up.