Specify focused item when opening a Picker

[noomly]

It would be nice if we could specify what item we want focused by default when opening a picker. For example, instead of doing Snacks.picker.lsp_references({ focus = "list" }), we could do Snacks.picker.lsp_references({ focus = "current" }) which would automatically focus the current reference in the list. It's easy to get lost when there are many references, and this would allow to quickly jump to neighboring references in the same file and make navigation much smoother.

This would also be very useful to navigate lsp symbols in a big file. For example: Snacks.picker.lsp_symbols({ focus = "nearest" }) could focus the nearest item on the list from our current position in the file and allow us to kind of quickly "zoom out", locate ourselves, and move around.

To make this a more generic feature, maybe focus could instead accept a function that takes in the list of items and returns the index for the item that should be focused.

[noomly]

So, looking closer at the doc I realized that it is already possible to do what I described using the on_show option. Here's an example for lsp_references:

--- @param picker snacks.Picker
local function find_current_reference(picker)
    local items = picker:items()
    local filter = picker.finder and picker.finder.filter
    if not filter then
        return
    end

    -- Get the source buffer and window
    local bufnr = filter.current_buf
    local win = filter.current_win

    -- Get the cursor position from the original window
    local cursor_pos = vim.api.nvim_win_get_cursor(win)
    local cursor_row, cursor_col = cursor_pos[1], cursor_pos[2]
    local filename = vim.api.nvim_buf_get_name(bufnr)

    -- Find the item that matches the current position
    for i, item in ipairs(items) do
        if item.file and item.pos then
            local item_filename = item.file

            -- Check if the file matches
            if item.buf == bufnr or item_filename == filename then
                local start_line, start_col = item.pos[1], item.pos[2]
                local end_line = item.end_pos and item.end_pos[1] or start_line
                local end_col = item.end_pos and item.end_pos[2] or (start_col + 1)

                -- Check if cursor is within the range
                if
                    (cursor_row == start_line and cursor_col >= start_col)
                    or (cursor_row == end_line and cursor_col <= end_col)
                    or (cursor_row > start_line and cursor_row < end_line)
                then
                    picker.list:view(i)
                    Snacks.picker.actions.list_scroll_center(picker)
                    return
                end
            end
        end
    end
end

Snacks.picker.lsp_references({
    focus = "list",
    include_current = true,
    on_show = find_current_reference,
})