feature: allow different source in the current picker depending on the input

[kristijanhusak]

Did you check the docs?

• I have read all the snacks.nvim docs

Is your feature request related to a problem? Please describe.

I'm aware this is a very complex feature, but I'll write it down in case you ever get to it.

Sublime text has this neat feature where you find files, and once you press @ it switches to "symbols" mode. For example, in snacks repo, doing preview@ would open up lua/snacks/picker/preview.lua in the background while picker is still visible, and start showing lsp symbols results in the same picker, which can also be fuzzy matched.
Here's a short recording:

sublime-file-symbol-picker.mp4

Describe the solution you'd like

I'd like to be able to create a custom picker that would achieve something similar, or ideally the same thing.

For starters, it would be good enough to be able to hook into something like on_prompt_change hook to get the input prompt value, and get the last "valid" item in a more graceful way.

Describe alternatives you've considered

Currently, I hacked this up, where it opens up the files picker, and once @ is typed, it closes the files picker with the last selected file, and opens up lsp_symbols picker.

    vim.keymap.set('n', '<C-p>', function()
      local should_open_symbols = false
      -- Last valid item selected. Once `@` is typed, current item in the `confirm` callback is no longer valid
      local last_item = nil
      local main_picker = Snacks.picker.files({
        on_change = function(_, item)
          if item then
            last_item = item
          end
        end,
        confirm = function(picker, item)
          if last_item and should_open_symbols then
            picker:close()
            vim.schedule(function()
              vim.cmd(('e %s'):format(last_item.cwd .. '/' .. last_item.file))
              Snacks.picker.lsp_symbols()
            end)
            return
          end
          vim.cmd(('e %s'):format(item.cwd .. '/' .. item.file))
        end,
      })

      local win = main_picker.input.win
      win:on(
        { 'TextChangedI' },
        Snacks.util.throttle(function()
          local line = win:line()
          if line:match('@$') then
            should_open_symbols = true
            main_picker:action('confirm')
            return
          end
        end, { ms = 30 })
      )
    end)

Additional context

No response