hit-enter prompt with vim.err_write with redraw before last line (deoplete)

[blueyed]

The following will not trigger a hit-enter prompt:

:py3 import vim; vim.err_write('\n'.join(str(x) for x in range(10))+'\n'); vim.command('redraw'); vim.err_write('last\n')

It displays the lines 0-9, then waits for a short time, and displays "last".
This is good/useful when wanting to add a traceback/more info for :messages, but have the actual error in the end (without a large red blob).

But for some reason similar code in deoplete will not (when adding a redraw command before the last line) - it displays all of it at once, causing a hit-enter prompt: https://github.com/Shougo/deoplete.nvim/blob/57d3f0c3cdfcfc1d91901a6d59d08f9008abd166/rplugin/python3/deoplete/util.py#L94-L101

This might be related to how deoplete integrates with neovim-python-client (https://github.com/Shougo/deoplete.nvim/blob/master/rplugin/python3/deoplete/parent.py#L96-L102).

[justinmk]

I'm not sure why the first case "waits". That seems like an accident, doesn't it?

[blueyed]

Agreed. I've thought that it might be intentional, but I also think that it should not wait.
The main issue is that the second case even triggers the hit-enter prompt though.

[justinmk]

I don't understand why it's a problem for an error message to trigger hit-enter? Isn't that normal?

[blueyed]

The trick that deoplete uses is to first use echom for additional info (traceback), then redraw and then echom for the main msg.
This way you have it in :messages, but are not bothered with the full blob initially.
I've noticed that this does not work as expected when using vim.err_write.

[justinmk]

Try nvim_call_atomic or server-side VimL/Lua ?

[blueyed]

@justinmk
Please elaborate.
Do you mean to do this from deoplete's error_tb (Python)? (https://github.com/Shougo/deoplete.nvim/blob/57d3f0c3cdfcfc1d91901a6d59d08f9008abd166/rplugin/python3/deoplete/util.py#L94-L101)
deoplete uses rpcnotify to trigger the Python code.