Set window height for "autocmd window" when using nvim_buf_call

[chipsenkbeil]

This is connected to my attempt to address #27940.

Is there a way to set the size of the temporary window created when using nvim_buf_call if there is no window already hosting the buffer?

Following along the code for nvim_buf_call, I can see where and how it allocates a new window. I noticed this because I was using a temporary buffer to add some lines of text, have them rendered based on filetype (org), and grab the extmarks to apply elsewhere; my way to selecting a range in a buffer and apply highlights to it as a different filetype.

Code pointer

To get the above to work, I have to use nvim_buf_call where I re-detect the filetype using filetype detect and then force a redraw using redraw!. Because the window is only 5 rows high, if I have a longer set of lines (say 7), then only the first 5 lines have extmarks applied in my situation.

neovim/src/nvim/window.c

Lines 4030 to 4040 in d9235ef

	void win_alloc_aucmd_win(int idx)
	{
	Error err = ERROR_INIT;
	WinConfig fconfig = WIN_CONFIG_INIT;
	fconfig.width = Columns;
	fconfig.height = 5;
	fconfig.focusable = false;
	aucmd_win[idx].auc_win = win_new_float(NULL, true, fconfig, &err);
	aucmd_win[idx].auc_win->w_buffer->b_nwindows--;
	RESET_BINDING(aucmd_win[idx].auc_win);
	}

Code Sample

-- Create a scratch buffer to house lines of orgmode text we want to highlight
local scratch_buffer = vim.api.nvim_create_buf(false, true)
assert(scratch_buffer ~= 0, "failed to create scratch buffer")

local name = vim.fn.tempname() .. ".org"
vim.api.nvim_buf_set_name(scratch_buffer, name)
vim.api.nvim_buf_set_option(scratch_buffer, "filetype", "org")

-- Read a subset of lines from our non-org buffer into our scratch buffer
local start, end_ = range[1], range[2]
local lines = vim.api.nvim_buf_get_lines(buffer, start, end_, false)
vim.api.nvim_buf_set_lines(scratch_buffer, 0, -1, true, lines)

-- Force a redraw of the scratch buffer to get extmarks to apply
-- NOTE: I think this is a specific need for nvim-orgmode, but I could be wrong
vim.api.nvim_buf_call(scratch_buffer, function()
    vim.cmd("filetype detect")
    vim.cmd("redraw!")
end)

-- Read all highlights from the buffer (extmark_id, line, col, details), zero-indexed
---@type {[1]:integer, [2]:integer, [3]:integer, [4]:table}[]
local extmarks = vim.api.nvim_buf_get_extmarks(scratch_buffer, -1, 0, -1, {
    details = true,
})