`sl ghstack land PRURL` crashes when previous ghstack PR landed from GitHub UI

[francois]

Using ghstack land crashes after merging a ghstack-generated PR:

sl clone $SCRATCH_URL
cd $( basename $SCRATCH_URL )
date > foo && sl add foo && sl commit -m foo
date > bar && sl add bar && sl commit -m bar
sl ghstack
# merge `foo` PR from GitHub UI
sl pull # STDOUT says "marked 1 commit as landed"
sl ghstack land $BAR_PR_URL # crash

I suspect this is not an intended use-case, but can the crash be prevented and appropriate remediation actions be proposed?

╰─○ sl ghstack land https://github.com/francois/scratch/pull/15
pulling from https://github.com/francois/scratch
** Sapling SCM (version 0.1.20221118-210929-cfbb68aa) has crashed:
Traceback (most recent call last):
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/__init__.py", line 106, in run
    dispatch.run(args, fin, fout, ferr, config)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 161, in run
    status = (dispatch(req) or 0) & 255
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 503, in dispatch
    ret = _runcatch(req)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 712, in _runcatch
    return _callcatch(ui, req, _runcatchfunc)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 721, in _callcatch
    return scmutil.callcatch(ui, req, func)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/scmutil.py", line 147, in callcatch
    return func()
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 683, in _runcatchfunc
    return _dispatch(req)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 1218, in _dispatch
    ret = runcommand(
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/ext/undo.py", line 146, in _runcommandwrapper
    result = orig(lui, repo, cmd, fullargs, *args)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/ext/journal.py", line 80, in runcommand
    return orig(lui, repo, cmd, fullargs, *args)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/ext/sparse.py", line 504, in _tracktelemetry
    res = runcommand(lui, repo, *args)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/ext/copytrace.py", line 173, in _runcommand
    return orig(lui, repo, cmd, fullargs, ui, *args, **kwargs)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 913, in runcommand
    ret = _runcommand(ui, options, cmd, d)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 1259, in _runcommand
    return cmdfunc()
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/dispatch.py", line 1217, in <lambda>
    d = lambda: util.checksignature(func)(ui, *args, **strcmdopt)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/util.py", line 1285, in check
    return func(*args, **kwargs)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/edenscm/ext/ghstack/__init__.py", line 149, in land_cmd
    ghstack.land.main(
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/ghstack/land.py", line 19, in main
    return ghstack.sapling_land.main(pull_request, remote_name, github, sh, github_url)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/ghstack/sapling_land.py", line 105, in main
    ghstack.github_utils.update_ref(github=github, repo_id=repo_id, ref=base_ref, target_ref=head_ref)
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/ghstack/github_utils.py", line 300, in update_ref
    data = github.graphql(
  File "/opt/homebrew/Cellar/[email protected]/3.8.15/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/ghstack/github_cli_endpoint.py", line 48, in graphql
    raise RuntimeError(result.error)
RuntimeError: {
 "data": {
  "updateRef": null
 },
 "errors": [
  {
   "type": "UNPROCESSABLE",
   "path": [
    "updateRef"
   ],
   "locations": [
    {
     "line": 3,
     "column": 13
    }
   ],
   "message": "Refusing to perform non-fast-foward update when `force=false`."
  }
 ]
}