unknown error on startup with FixCursorHold.nvim and fzf.vim

[antoinemadec]

Describe the bug
I am the maintainer of FixCursorHold.nvim, an issue explaining the problem was created here: antoinemadec/FixCursorHold.nvim#7

My plugin reimplements CursorHold autocmd to avoid a performance bug.
Doing so seems to sometimes create a race condition on vim-ultest's end.

Error: Error: vim-ultest encountered an unknown error on startup, check v:exception

v:exception value:

Vim(let):Error invoking '/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest:function:_ultest_get_nearest_test' on channel 4 (python3-rplugin-host):
error caught in request handler '/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest:function:_ultest_get_nearest_test [[2, "term://~/toto//8265:'/home/antoine/toto/plug/fzf/bin/fzf'  '+m' '--tiebreak=index' '--multi' '--prompt' 'BLines> ' '--ansi' '--extended' '--nth=2..' '--tabstop=1' --expect=ctrl-v,ctrl-x,ctrl-t --no-height --border=rounded > /tmp/nvimeU62jz/1;#FZF", True]]':
Traceback (most recent call last):
  File "/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest/__init__.py", line 103, in _get_nearest_test
      return self.handler.get_nearest_test_dict(*args)
        File "/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest/handler/__init__.py", line 221, in get_nearest_test_dict
	    test = self.get_nearest_position(line, file_name, strict)
	      File "/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest/handler/__init__.py", line 212, in get_nearest_position
	          positions = self._tracker.file_positions(file_name)
		    File "/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest/handler/tracker.py", line 93, in file_positions
		        absolute_path = self._vim.sync_call("fnamemodify", file, ":p")
			  File "/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest/vim_client/__init__.py", line 121, in sync_call
			      return self._eval(expr, sync=True)
			        File "/home/antoine/toto/plug/vim-ultest/rplugin/python3/ultest/vim_client/__init__.py", line 134, in _eval
				    return self._vim.eval(expr, async_=not sync)
				      File "/usr/lib/python3.9/site-packages/pynvim/api/nvim.py", line 295, in eval
				          return self.request('nvim_eval', string, **kwargs)
					    File "/usr/lib/python3.9/site-packages/pynvim/api/nvim.py", line 182, in request
					        res = self._session.request(name, *args, **kwargs)
						  File "/usr/lib/python3.9/site-packages/pynvim/msgpack_rpc/session.py", line 102, in request
						      raise self.error_wrapper(err)
						      pynvim.api.common.NvimError: Vim:E121: Undefined variable: home

To Reproduce
See antoinemadec/FixCursorHold.nvim#7

Expected behavior
No error at startup.

Additional context
This kind of race condition seems to have already been a concern according to this comment in handler.vim's s:Call() definition:

      " Send twice because first one isn't shown if triggered during startup

However s:update_warn_sent value is 0 when the error is printed. Indicating that s:Call() was not sent twice at startup.
The if condition seems wrong to me, shouldn't it be "if error happened at least twice, then display the error message" ?

[rcarriga]

Hey thanks for looking into this, sorry for the trouble! This actually has nothing to do with your plugin, I'm assuming they it was only noticed because the updatetime before was longer and so the issue was never noticed. Basically what's happening is a bad string conversion of the terminal buffer name. I've added a change to avoid the issue happening.

The if condition seems wrong to me, shouldn't it be "if error happened at least twice, then display the error message" ?
No the condition is just there to stop messages being spammed in case of large amounts of errors