Problem: Bulking message lines to write in a single API call is
complicated and still not correct w.r.t. overwriting
highlights.
Solution: Write each chunk pattern separately with it's highlight
such that it will be spliced correctly for message chunks
that contain a carriage return. Go with correctness over
performance until this proves to be too inefficient.
Also add an identifying name to the various extui buffers.
Problem: Unable to discern windows used by the extui interface
to configure their local options.
'winblend' may be detrimental to legibility depending on the
colorscheme and 'background'.
Solution: Assign the "cmdline", "msgmore", "msgprompt" and "msgbox"
'filetype' to the respective windows.
Don't set 'winblend' for the message "box" window.
Problem: Moving the "more" (or any extui)-window to a split with
`wincmd L` does not invalidate it as a tracked window.
Solution: Drop an extui window that is no longer floating.
Problem: The cmdline popupmenu is hidden behind extui windows.
'showmode' message is drawn over the cmdline.
Changing the 'cmdheight' to accommodate space for the text in
the cmdline may change the current cursor position.
Solution: Ensure kZIndexMessages < zindex < kZIndexCmdlinePopupMenu.
Clear the 'showmode' message when the cmdline level is negative.
Temporarily set 'splitkeep' = "screen" when changing the 'cmdheight'.
Problem: We have an unmaintained Vimscript parser and cmdline
highlighting mechanism, with which it is hard to leverage the
treesitter highlighter. Long messages result in a hit-enter-prompt.
Solution: Implement a vim.ui_attach() UI, that replaces the message
grid (orphaning some 3000+ LOC core C code). Introduce an experimental
vim._extui module, because removing the message grid at the same time is
too risky. The new UI leverages the bundled treesitter highlighter and
parser for Vimscript, as well as the matchparen plugin, to highlight the
cmdline. Messages are truncated in the cmdline area, or placed in a
floating message box in the bottom right corner. Special ("list_cmd")
messages and the message history are shown in a, "more prompt" (now a
fully interactive regular window). Various default UI elements ('showcmd',
'ruler') are also placed in the cmdline area, as virtual text.
`require('vim._extui').enable({})` enables the experimental UI.
`{ msg.pos = 'box' }` or `:set cmdheight=0` enables the message
box variant.
Followup:
- Come to a consensus for how best to represent messages (by default).
- Start removing message grid when this is deemed a successful replacement.
When that is finished, make this new UI the default and update a lot of tests.
