statusline: reimplement default, include LSP progress

[justinmk]

Problem

the default 'statusline' is implemented in C, it doesn't use the 'statusline' DSL. And it isn't readable as a 'statusline' expression, so user configs/plugins can't augment it.

Expected behavior

• remove the C impl of 'statusline'. reimplement it as a 'statusline' expression
• show LspProgress in the default 'statusline' feat(lsp): redrawstatus on progress notifications #28569
• it should continue to be minimal and fast, but consider other useful things we can add

Related

• implement default titlestring using statusline #1248
• nvim_eval_statusline() can return the default statusline #28444

[yochem]

I would like to have a go with this, but I have a couple questions.

1. I'm unsure where I can find the current C implementation of the default statusline. I'm guessing it's src/nvim/statusline.c, but thus far I haven't found the part where the default is defined. Could someone give me a primer on this? here
2. Should the default statusline be defined in runtime/lua/vim/_defaults.lua by setting vim.o.statusline?
3. What should be the result of set statusline=? Current behaviour is showing the default statusline.
4. What would fall under "other useful things we can add"? Are there current discussions on possible components to add to the default statusline?

Current components (according to :h statusline)

• Relative file path (%f)
• Help flag (%h)
• Modified flag (%m)
• Readonly flag (%r)
• Left-right split (%=)
• line,col-VIRT (%l,%c%V)
• % of file / Top / Bot (%P)

Possible additions:

• Mode
• Filetype
• LspProgress
• Treesitter enabled for buf
• Diagnostics (only when there are any diagnostics)
• ...

Possible changes:

• line,col → line:col has been widely adopted as line + col representation. Could be line-line for V-line and line:col-line:col for V-block (or , instead of -)
• I do like the left-right split, but would also be possible to do three parts with filename centered in the midddle
• ...

Thanks in advance!

[yochem]

Rough example with components mode, filename, diagnostics, filetype, line:col, %file:

vim.o.statusline = '  %{luaeval("Mode()")} │ %f%m %=│ %{luaeval("Dia()")}│ %{&filetype} │ %l:%c │ %03(%p%)%%  '

Not sure if lua components can be made/used, and if so, how to do that without luaeval.

[justinmk]

Could be line-line for V-line and line:col-line:col for V-block (or , instead of -)

That is interesting because it avoids the need for 'ruler'.

The current example you showed looks like a good start. I wouldn't add anything else, it's better to start small, because the first major step is to move to a Lua/Vimscript impl and elminate the C impl. In fact, the first PR should look identical to the current default statusline, to avoid tons of churn in the tests. Then in a followup we can discuss how to offer an improved statusline.