feat: add option to show the context with the **folded** current buffer

[atusy]

By using the folded current buffer, the content (including extmark!) is automatically synced among the edit window and the context window.

This allows label-based motion plugins (e.g., nvim-treehopper, flash.nvim, treemonkey.nvim) to show the label on the context without hacks.
See example below.

[lewis6991]

Sorry this isn't something I want to support, at least in this way.

[atusy]

hmmm... alright...

[lewis6991]

Looking at this a bit more closely, I think a similar implementation that I'd be more open to would be to create a separate window per context and setting the bufnr as you've done here. Then as you've pointed out this would sync all the extmarks.

I'm not a fan of any of the fold stuff, at least for now.

If neovim/neovim#20750 gets merged, we could leverage that here so we only need one floating window.

[atusy]

Thank you for the comments.

If neovim/neovim#20750 gets merged, we could leverage that here so we only need one floating window.

This sounds good.
For now, I get context from treesitter-context directly from my plugin, and explicitly adds extmarks.

https://github.com/atusy/treemonkey.nvim/blob/4226ea69f6b84673eafdfe0ce5f1eafb1d648a1f/lua/treemonkey.lua?plain=1#L92-L104

Just to add a context, I liked the folding because users have oppotunity to customize foldtext.
For example, we can show context line like local function foo(a, b) from the following buffer.

local function foo(
  a,
  b
)
  local res = {a, b}  -- window's topline at here
  return res  -- cursor at here
end