experimental: renderer

examples/counter.lua

@@ -0,0 +1,65 @@
+local tracker = require 'u.tracker'
+local Buffer = require 'u.buffer'
+local h = require('u.renderer').h
+
+-- Create an buffer for the UI
+vim.cmd.vnew()
+local ui_buf = Buffer.current()
+ui_buf:set_tmp_options()
+
+local s_count = tracker.create_signal(0, 'counter_signal')
+
+-- Effect: Render
+-- Setup the effect for rendering the UI whenever dependencies are updated
+tracker.create_effect(function()
+  -- Calling `Signal:get()` in an effect registers the given signal as a
+  -- dependency of the current effect. Whenever that signal (or any other
+  -- dependency) changes, the effect will rerun. In this particular case,
+  -- rendering the UI is an effect that depends on one signal.
+  local count = s_count:get()
+
+  -- Markup is hyperscript, which is just 1) text, and 2) tags (i.e.,
+  -- constructed with `h(...)` calls). To help organize the markup, text and
+  -- tags can be nested in tables at any depth. Line breaks must be specified
+  -- manually, with '\n'.
+  ui_buf:render {
+    'Reactive Counter Example\n',
+    '========================\n\n',
+
+    { 'Counter: ', tostring(count), '\n' },
+
+    '\n',
+
+    {
+      h('text', {
+        hl = 'DiffDelete',
+        on_key = {
+          ['\r'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            s_count:update(function(n) return n - 1 end)
+            -- Also equivalent: s_count:set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Decrement '),
+      ' ',
+      h('text', {
+        hl = 'DiffAdd',
+        on_key = {
+          ['\r'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            s_count:update(function(n) return n + 1 end)
+            -- Also equivalent: s_count:set(s_count:get() + 1)
+            return ''
+          end,
+        },
+      }, ' Increment '),
+    },
+
+    '\n',
+    '\n',
+    { 'Press <CR> on each "button" above to increment/decrement the counter.' },
+  }
+end)

examples/picker.lua

@@ -0,0 +1,881 @@
+local utils = require 'u.utils'
+local Buffer = require 'u.buffer'
+local Renderer = require('u.renderer').Renderer
+local h = require('u.renderer').h
+local TreeBuilder = require('u.renderer').TreeBuilder
+local tracker = require 'u.tracker'
+
+local M = {}
+
+local S_EDITOR_DIMENSIONS = tracker.create_signal(utils.get_editor_dimensions(), 's:editor_dimensions')
+vim.api.nvim_create_autocmd('VimResized', {
+  callback = function()
+    local new_dim = utils.get_editor_dimensions()
+    S_EDITOR_DIMENSIONS:set(new_dim)
+  end,
+})
+
+--- @param low number
+---@param x number
+---@param high number
+local function clamp(low, x, high)
+  x = math.max(low, x)
+  x = math.min(x, high)
+  return x
+end
+
+--- @generic T
+--- @param arr `T`[]
+--- @return T[]
+local function shallow_copy_arr(arr) return vim.iter(arr):totable() end
+
+--------------------------------------------------------------------------------
+-- BEGIN create_picker
+--
+-- This is the star of the show (in this file, anyway).
+-- In summary, the outline of this function is:
+-- 1. Setup signals/memos for computing the picker size, and window positions
+-- 2. Create the two windows:
+--   a. The picker input. This is where the filter is typed
+--   b. The picker list. This is where the items are displayed
+-- 3. Setup event handlers that respond to user input
+-- 4. Render the list. After all the prework above, this is probably the
+--    shortest portion of this function.
+--------------------------------------------------------------------------------
+
+--- @alias SelectController {
+---   get_items: fun(): T[];
+---   set_items: fun(items: T[]);
+---   set_filter_text: fun(filter_text: string);
+---   get_selected_indices: fun(): number[];
+---   get_selected_items: fun(): T[];
+---   set_selected_indices: fun(indicies: number[], ephemeral?: boolean);
+---   close: fun();
+--- }
+--- @alias SelectOpts<T> {
+---   items: `T`[];
+---   multi?: boolean;
+---   format_item?: fun(item: T[]): Tree;
+---   on_finish?: fun(items: T[], indicies: number[]);
+---   on_selection_changed?: fun(items: T[], indicies: number[]);
+---   mappings?: table<string, fun(select: SelectController)>;
+--- }
+
+--- @generic T
+--- @param opts SelectOpts<T>
+function M.create_picker(opts)
+  local is_in_insert_mode = vim.api.nvim_get_mode().mode:sub(1, 1) == 'i'
+  local stopinsert = not is_in_insert_mode
+
+  if opts.multi == nil then opts.multi = false end
+
+  local H = {}
+
+  --- Runs a function `fn`, and if it fails, cleans up the UI by calling
+  --- `H.finish`
+  ---
+  --- @generic T
+  --- @param fn fun(): `T`
+  --- @return T
+  local function safe_run(fn, ...)
+    local ok, result_or_error = pcall(fn, ...)
+    if not ok then
+      pcall(H.finish, true, result_or_error)
+      error(result_or_error .. '\n' .. debug.traceback())
+    end
+    return result_or_error
+  end
+
+  --- Creates a function that safely calls the given function, cleaning up the
+  --- UI if it ever fails
+  ---
+  --- @generic T
+  --- @param fn `T`
+  --- @return T
+  local function safe_wrap(fn)
+    return function(...) return safe_run(fn, ...) end
+  end
+
+  --
+  -- Compute the positions of the input bar and the list:
+  --
+
+  -- Reactively compute the space available for the picker based on the size of
+  -- the editor
+  local s_editor_dimensions = S_EDITOR_DIMENSIONS:clone()
+  local s_picker_space_available = tracker.create_memo(safe_wrap(function()
+    local editor_dim = s_editor_dimensions:get()
+    local width = math.floor(editor_dim.width * 0.75)
+    local height = math.floor(editor_dim.height * 0.75)
+    local row = math.floor((editor_dim.height - height) / 2)
+    local col = math.floor((editor_dim.width - width) / 2)
+    return { width = width, height = height, row = row, col = col }
+  end))
+
+  -- Reactively compute the size of the prompt (input) bar
+  local s_w_input_coords = tracker.create_memo(safe_wrap(function()
+    local picker_coords = s_picker_space_available:get()
+    return {
+      width = picker_coords.width,
+      height = 1,
+      row = picker_coords.row,
+      col = picker_coords.col,
+    }
+  end))
+
+  -- Reactively compute the size of the list view
+  local s_w_list_coords = tracker.create_memo(safe_wrap(function()
+    local picker_coords = s_picker_space_available:get()
+    return {
+      width = picker_coords.width,
+      height = picker_coords.height - 3,
+      row = picker_coords.row + 3,
+      col = picker_coords.col,
+    }
+  end))
+
+  --
+  -- Create resources (i.e., windows):
+  --
+
+  local w_input_cfg = {
+    width = s_w_input_coords:get().width,
+    height = s_w_input_coords:get().height,
+    row = s_w_input_coords:get().row,
+    col = s_w_input_coords:get().col,
+    relative = 'editor',
+    focusable = true,
+    border = 'rounded',
+  }
+  local w_input_buf = Buffer.create(false, true)
+  local w_input = vim.api.nvim_open_win(w_input_buf.buf, false, w_input_cfg)
+  vim.wo[w_input].number = false
+  vim.wo[w_input].relativenumber = false
+
+  -- The following option is a signal to other plugins like 'cmp' to not mess
+  -- with this buffer:
+  vim.bo[w_input_buf.buf].buftype = 'prompt'
+  vim.fn.prompt_setprompt(w_input_buf.buf, '')
+
+  vim.api.nvim_set_current_win(w_input)
+  tracker.create_effect(safe_wrap(function()
+    -- update window position/size every time the editor is resized:
+    w_input_cfg = vim.tbl_deep_extend('force', w_input_cfg, s_w_input_coords:get())
+    vim.api.nvim_win_set_config(w_input, w_input_cfg)
+  end))
+
+  local w_list_cfg = {
+    width = s_w_list_coords:get().width,
+    height = s_w_list_coords:get().height,
+    row = s_w_list_coords:get().row,
+    col = s_w_list_coords:get().col,
+    relative = 'editor',
+    focusable = true,
+    border = 'rounded',
+  }
+  local w_list_buf = Buffer.create(false, true)
+  local w_list = vim.api.nvim_open_win(w_list_buf.buf, false, w_list_cfg)
+  vim.wo[w_list].number = false
+  vim.wo[w_list].relativenumber = false
+  vim.wo[w_list].scrolloff = 0
+  tracker.create_effect(safe_wrap(function()
+    -- update window position/size every time the editor is resized:
+    w_list_cfg = vim.tbl_deep_extend('force', w_list_cfg, s_w_list_coords:get())
+    vim.api.nvim_win_set_config(w_list, w_list_cfg)
+  end))
+
+  -- Now that we have created the window with the prompt in it, start insert
+  -- mode so that the user can type immediately:
+  vim.cmd.startinsert()
+
+  --
+  -- State:
+  --
+
+  local s_items_raw = tracker.create_signal(opts.items, 's:items')
+  local s_items = s_items_raw:debounce(100)
+  local s_selected_indices = tracker.create_signal({}, 's:selected_indices')
+  local s_top_offset = tracker.create_signal(0, 's:top_offset')
+  local s_cursor_index = tracker.create_signal(1, 's:cursor_index')
+
+  local s_filter_text_undebounced = tracker.create_signal('', 's:filter_text')
+  w_input_buf:autocmd('TextChangedI', {
+    callback = safe_wrap(function() s_filter_text_undebounced:set(vim.api.nvim_get_current_line()) end),
+  })
+  local s_filter_text = s_filter_text_undebounced:debounce(50)
+
+  --
+  -- Derived State:
+  --
+
+  local s_formatted_items = tracker.create_memo(function()
+    local function _format_item(item) return opts.format_item and opts.format_item(item) or tostring(item) end
+
+    local items = s_items:get()
+    return vim.iter(items):map(function(item) return { item = item, formatted = _format_item(item) } end):totable()
+  end)
+
+  -- When the filter text changes, update the filtered items:
+  local s_filtered_items = tracker.create_memo(
+    safe_wrap(function()
+      local formatted_items = s_formatted_items:get()
+      local filter_text = vim.trim(s_filter_text:get())
+      local filter_pattern = (#formatted_items > 250 and #filter_text <= 3) and (filter_text:gsub('%.', '%%.'))
+        or vim.iter(vim.split(filter_text, '')):map(function(c) return c .. '.*' end):join ''
+
+      local new_filtered_items = vim
+        .iter(formatted_items)
+        :enumerate()
+        :map(function(i, inf) return { orig_idx = i, item = inf.item, formatted = inf.formatted } end)
+        :filter(function(inf)
+          if filter_text == '' then return true end
+          local formatted_as_string = Renderer.markup_to_string { tree = inf.formatted }
+          local match = string.match(Renderer.markup_to_string { tree = formatted_as_string }, filter_pattern)
+          return match ~= nil
+        end)
+        :totable()
+
+      -- Don't do the levenshtein-sort if there are over 250 items:
+      if #new_filtered_items <= 250 then
+        table.sort(new_filtered_items, function(a_inf, b_inf)
+          local a = Renderer.markup_to_string { markup = a_inf.formatted }
+          local b = Renderer.markup_to_string { markup = b_inf.formatted }
+          if a == b then return false end
+
+          local lev_a = utils.levenshtein(vim.split(filter_text, ''), vim.split(a, ''))
+          local lev_b = utils.levenshtein(vim.split(filter_text, ''), vim.split(b, ''))
+          return #lev_a < #lev_b
+        end)
+      end
+
+      s_top_offset:set(0)
+      s_cursor_index:set(1)
+      return new_filtered_items
+    end),
+    'e:(filter_text=>filtered_items)'
+  )
+
+  -- Visible items, are _just_ the items that fit into the current viewport.
+  -- This is an optimization so that we are not rendering thousands of lines of
+  -- items on each state-change.
+  local s_visible_items = tracker.create_memo(
+    safe_wrap(function()
+      return vim
+        .iter(s_filtered_items:get())
+        :enumerate()
+        :skip(s_top_offset:get())
+        :take(s_w_list_coords:get().height)
+        :map(
+          function(i, inf)
+            return {
+              filtered_idx = i,
+              orig_idx = inf.orig_idx,
+              item = inf.item,
+              formatted = inf.formatted,
+            }
+          end
+        )
+        :totable()
+    end),
+    'm:visible_items'
+  )
+
+  -- Track selection information:
+  local s_selection_info = tracker.create_memo(
+    safe_wrap(function()
+      local items = s_items:get()
+      local selected_indices = s_selected_indices:get()
+      --- @type { orig_idx: number; item: T }[]
+      local filtered_items = s_filtered_items:get()
+      local cursor_index = s_cursor_index:get()
+      local indices = shallow_copy_arr(selected_indices) -- shallow copy
+      if #indices == 0 and #filtered_items > 0 then indices = { filtered_items[cursor_index].orig_idx } end
+      return {
+        items = vim.iter(indices):map(function(i) return items[i] end):totable(),
+        indices = indices,
+      }
+    end),
+    'm:selection_info'
+  )
+
+  --- When it is time to close the picker, this is the main cleanup routine
+  --- that runs in all cases:
+  ---
+  --- @param esc? boolean Whether the user pressed <Esc> or not
+  --- @param err? any Any error that occurred
+  function H.finish(esc, err)
+    -- s_editor_dimensions is the only signal that is cloned from a global,
+    -- one. It is therefore the only one that needs to be manually disposed.
+    -- The other ones should get cleaned up by the GC
+    s_editor_dimensions:dispose()
+    -- If we happen to have any async state-changes coming down the pipeline,
+    -- we can say right now that we are done rendering new UI (to avoid
+    -- "invalid window ID" errors):
+    H.unsubscribe_render_effect()
+    -- buftype=prompt buffers are not "temporary", so delete the buffer manually:
+    vim.api.nvim_buf_delete(w_input_buf.buf, { force = true })
+    -- The following is not needed, since the buffer is deleted above:
+    -- vim.api.nvim_win_close(w_input, false)
+    vim.api.nvim_win_close(w_list, false)
+    if stopinsert then vim.cmd.stopinsert() end
+    local inf = s_selection_info:get()
+    if not err and opts.on_finish then
+      -- If on_finish opens another picker, the closing of this one can happen
+      -- in _too_ quick succession, so put a small delay in there.
+      --
+      -- TODO: figure out _why_ this is actually happening, and then a better
+      -- way to handle this.
+      vim.defer_fn(function()
+        if esc then
+          opts.on_finish({}, {})
+        else
+          opts.on_finish(inf.items, inf.indices)
+        end
+      end, 100)
+    end
+  end
+
+  -- On selection info changed:
+  tracker.create_effect(
+    safe_wrap(function()
+      local inf = s_selection_info:get()
+      if opts.on_selection_changed then opts.on_selection_changed(inf.items, inf.indices) end
+    end),
+    'e:selection_changed'
+  )
+
+  --
+  -- Public API (i.e., `controller`):
+  -- We will fill in the methods further down, but we need this variable in scope so that it can be
+  -- closed over by some of the event handlers:
+  --
+  local controller = {}
+
+  --
+  -- Events
+  --
+  vim.keymap.set('i', '<Esc>', function() H.finish(true) end, { buffer = w_input_buf.buf })
+
+  vim.keymap.set('i', '<CR>', function() H.finish() end, { buffer = w_input_buf.buf })
+
+  local function action_next_line()
+    local max_line = #s_filtered_items:get()
+    local next_cursor_index = clamp(1, s_cursor_index:get() + 1, max_line)
+    if next_cursor_index - s_top_offset:get() > s_w_list_coords:get().height then
+      s_top_offset:set(s_top_offset:get() + 1)
+    end
+    s_cursor_index:set(next_cursor_index)
+  end
+  vim.keymap.set('i', '<C-n>', safe_wrap(action_next_line), { buffer = w_input_buf.buf, desc = 'Picker: next' })
+
+  vim.keymap.set(
+    'i',
+    '<C-p>',
+    safe_wrap(function()
+      local max_line = #s_filtered_items:get()
+      local next_cursor_index = clamp(1, s_cursor_index:get() - 1, max_line)
+      if next_cursor_index - s_top_offset:get() < 1 then s_top_offset:set(s_top_offset:get() - 1) end
+      s_cursor_index:set(next_cursor_index)
+    end),
+    { buffer = w_input_buf.buf, desc = 'Picker: previous' }
+  )
+
+  vim.keymap.set(
+    'i',
+    '<Tab>',
+    safe_wrap(function()
+      if not opts.multi then return end
+
+      local index = s_filtered_items:get()[s_cursor_index:get()].orig_idx
+      if vim.tbl_contains(s_selected_indices:get(), index) then
+        s_selected_indices:set(vim.iter(s_selected_indices:get()):filter(function(i) return i ~= index end):totable())
+      else
+        local new_selected_indices = shallow_copy_arr(s_selected_indices:get())
+        table.insert(new_selected_indices, index)
+        s_selected_indices:set(new_selected_indices)
+      end
+      action_next_line()
+    end),
+    { buffer = w_input_buf.buf }
+  )
+
+  for key, fn in pairs(opts.mappings or {}) do
+    vim.keymap.set('i', key, safe_wrap(function() return fn(controller) end), { buffer = w_input_buf.buf })
+  end
+
+  -- Render:
+  H.unsubscribe_render_effect = tracker.create_effect(
+    safe_wrap(function()
+      local selected_indices = s_selected_indices:get()
+      local top_offset = s_top_offset:get()
+      local cursor_index = s_cursor_index:get()
+      --- @type { filtered_idx: number; orig_idx: number; item: T; formatted: string }[]
+      local visible_items = s_visible_items:get()
+
+      -- The above has to run in the execution context for the signaling to work, but
+      -- the following cannot run in a NeoVim loop-callback:
+      vim.schedule(function()
+        w_list_buf:render(TreeBuilder.new()
+          :nest(function(tb)
+            for loop_idx, inf in ipairs(visible_items) do
+              local is_cur_line = inf.filtered_idx == cursor_index
+              local is_selected = vim.tbl_contains(selected_indices, inf.orig_idx)
+
+              tb:put(loop_idx > 1 and '\n')
+              tb:put(is_cur_line and h('text', { hl = 'Structure' }, '❯') or ' ')
+              tb:put(is_selected and h('text', { hl = 'Comment' }, '* ') or '  ')
+              tb:put(inf.formatted)
+            end
+          end)
+          :tree())
+
+        -- set the window viewport to have the first line in view:
+        pcall(vim.api.nvim_win_call, w_list, function() vim.fn.winrestview { topline = 1 } end)
+        pcall(vim.api.nvim_win_set_cursor, w_list, { cursor_index - top_offset, 0 })
+      end)
+    end),
+    'e:render'
+  )
+
+  --
+  -- Populate the public API:
+  --
+  function controller.get_items()
+    return safe_run(function() return s_items_raw:get() end)
+  end
+
+  ---@param items T[]
+  function controller.set_items(items)
+    return safe_run(function() s_items_raw:set(items) end)
+  end
+
+  function controller.set_filter_text(filter_text)
+    return safe_run(function()
+      vim.api.nvim_win_call(w_input, function() vim.api.nvim_set_current_line(filter_text) end)
+    end)
+  end
+
+  function controller.get_selected_indices()
+    return safe_run(function() return s_selection_info:get().indices end)
+  end
+
+  function controller.get_selected_items()
+    return safe_run(function() return s_selection_info:get().items end)
+  end
+
+  --- @param indicies number[]
+  ---@param ephemeral? boolean
+  function controller.set_selected_indices(indicies, ephemeral)
+    return safe_run(function()
+      if ephemeral == nil then ephemeral = false end
+
+      if ephemeral and #indicies == 1 then
+        local matching_filtered_item_idx, _ = vim
+          .iter(s_filtered_items:get())
+          :enumerate()
+          :find(function(_idx, inf) return inf.orig_idx == indicies[1] end)
+        if matching_filtered_item_idx ~= nil then s_cursor_index:set(indicies[1]) end
+      else
+        if not opts.multi then
+          local err = 'Cannot set multiple selected indices on a single-select picker'
+          H.finish(true, err)
+          error(err)
+        end
+        s_selected_indices:set(indicies)
+      end
+    end)
+  end
+
+  function controller.close()
+    return safe_run(function() H.finish(true) end)
+  end
+
+  return controller --[[@as SelectController]]
+end
+
+--------------------------------------------------------------------------------
+-- END create_picker
+--------------------------------------------------------------------------------
+
+--------------------------------------------------------------------------------
+-- vim.ui.select override
+--------------------------------------------------------------------------------
+
+local ORIGINAL_UI_SELECT
+function M.register_ui_select()
+  ORIGINAL_UI_SELECT = vim.ui.select
+  --- @generic T
+  --- @param items `T`[]
+  --- @param opts { prompt?: string, kind?: any, format_item?: fun(item: T):string }
+  --- @param cb fun(item: T|nil):any
+  function vim.ui.select(items, opts, cb)
+    M.create_picker {
+      items = items,
+      format_item = function(item)
+        local s = opts.format_item and opts.format_item(item) or tostring(item)
+        s = s:gsub('<', '&lt;')
+        return s
+      end,
+      on_finish = function(sel_items)
+        if #sel_items == 0 then cb(nil) end
+        cb(sel_items[#sel_items])
+      end,
+    }
+  end
+end
+function M.unregister_ui_select() vim.ui.select = ORIGINAL_UI_SELECT end
+
+--------------------------------------------------------------------------------
+-- Built-in pickers
+-- 1. files
+-- 2. buffers
+-- 3. code-symbols
+--------------------------------------------------------------------------------
+
+--- @param opts? { limit?: number }
+function M.files(opts)
+  opts = opts or {}
+  opts.limit = opts.limit or 10000
+
+  local cmd = {}
+  if vim.fn.executable 'rg' then
+    cmd = {
+      'rg',
+      '--color=never',
+      '--files',
+      '--hidden',
+      '--follow',
+      '-g',
+      '!.git',
+      '-g',
+      '!node_modules',
+      '-g',
+      '!target',
+    }
+  elseif vim.fn.executable 'fd' then
+    cmd = {
+      'fd',
+      '--color=never',
+      '--type',
+      'f',
+      '--hidden',
+      '--follow',
+      '--exclude',
+      '.git',
+      '--exclude',
+      'node_modules',
+      '--exclude',
+      'target',
+    }
+  elseif vim.fn.executable 'find' then
+    cmd = {
+      'find',
+      '-type',
+      'f',
+      '-not',
+      '-path',
+      "'*/.git/*'",
+      '-not',
+      '-path',
+      "'*/node_modules/*'",
+      '-not',
+      '-path',
+      "'*/target/*'",
+      '-printf',
+      "'%P\n'",
+    }
+  end
+
+  if #cmd == 0 then
+    vim.notify('rg/fd/find executable not found: cannot list files', vim.log.levels.ERROR)
+    return
+  end
+
+  -- Keep track of the job that will list files independent from the picker. We
+  -- will stream lines from this process to the picker as they come in:
+  local job_inf = { id = 0, proc_lines = {}, notified_over_limit = false }
+
+  -- Initially, create the picker with no items:
+  local picker = M.create_picker {
+    multi = true,
+    items = {},
+
+    format_item = function(item)
+      local icon_inf = require('my.icons').get { filename = tostring(item) }
+      return { h('text', { hl = icon_inf.group }, icon_inf.icon), ' ', item }
+    end,
+
+    --- @params items string[]
+    on_finish = function(items)
+      pcall(vim.fn.jobstop, job_inf.id)
+
+      if #items == 0 then return end
+      if #items == 1 then
+        vim.cmd.edit(items[1])
+      else
+        -- populate quickfix:
+        vim.fn.setqflist(vim
+          .iter(items)
+          :map(
+            function(item)
+              return {
+                filename = item,
+                lnum = 1,
+                col = 1,
+              }
+            end
+          )
+          :totable())
+        vim.cmd.copen()
+      end
+    end,
+
+    mappings = {
+      ['<C-t>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in new tab:
+        for _, item in ipairs(items) do
+          vim.cmd.tabnew(item)
+        end
+      end,
+
+      ['<C-v>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in vertical split:
+        for _, item in ipairs(items) do
+          vim.cmd.vsplit(item)
+        end
+      end,
+
+      ['<C-s>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in horizontal split:
+        for _, item in ipairs(items) do
+          vim.cmd.split(item)
+        end
+      end,
+    },
+  }
+
+  -- Kick off the process that lists the files. As lines come in, send them to
+  -- the picker:
+  job_inf.id = vim.fn.jobstart(cmd, {
+    --- @param data string[]
+    on_stdout = vim.schedule_wrap(function(_chanid, data, _name)
+      local lines = job_inf.proc_lines
+      local function set_lines_as_items_state()
+        picker.set_items(vim
+          .iter(lines)
+          :enumerate()
+          :filter(function(idx, item)
+            -- Filter out an incomplete last line:
+            local is_last_line = idx == #lines
+            if is_last_line and item == '' then return false end
+            return true
+          end)
+          :map(function(_, item) return item end)
+          :totable())
+      end
+
+      -- It's just not a good idea to process large lists with Lua. The default
+      -- limit is 10,000 items, and even crunching through this is iffy on a
+      -- fast laptop. Show a warning and truncate the list in this case.
+      if #lines >= opts.limit then
+        if not job_inf.notified_over_limit then
+          vim.notify('Picker list is too large (truncating list to ' .. opts.limit .. ' items)', vim.log.levels.WARN)
+          job_inf.notified_over_limit = true
+        end
+        return
+      end
+
+      -- :help channel-lines
+
+      local eof = #data == 1 and data[1] == ''
+      if eof then set_lines_as_items_state() end
+
+      -- Complete the previous line:
+      if #lines > 0 then lines[#lines] = lines[#lines] .. table.remove(data, 1) end
+
+      for _, l in ipairs(data) do
+        table.insert(lines, l)
+      end
+
+      set_lines_as_items_state()
+    end),
+  })
+end
+
+function M.buffers()
+  local cwd = vim.fn.getcwd(0, 0)
+  -- ensure that `cwd` ends with a trailing slash:
+  if cwd[#cwd] ~= '/' then cwd = cwd .. '/' end
+
+  --- @type { name: string; changed: number; bufnr: number }[]
+  local bufs = vim.fn.getbufinfo { buflisted = 1 }
+
+  M.create_picker {
+    multi = true,
+    items = bufs,
+
+    --- @param item { name: string; changed: number; bufnr: number }
+    format_item = function(item)
+      local icon_inf = require('my.icons').get { filename = item.name }
+      local item_name = item.name
+      if item_name == '' then item_name = '[No Name]' end
+      -- trim leading `cwd` from the buffer name:
+      if item_name:sub(1, #cwd) == cwd then item_name = item_name:sub(#cwd + 1) end
+
+      return TreeBuilder.new()
+        :put(item.changed == 1 and '[+] ' or '    ')
+        :put({ h('text', { hl = icon_inf.group }, icon_inf.icon), ' ' })
+        :put(item_name)
+        :tree()
+    end,
+
+    --- @params items { bufnr: number }[]
+    on_finish = function(items)
+      if #items == 0 then return end
+      if #items == 1 then
+        vim.cmd.buffer(items[1].bufnr)
+      else
+        -- populate quickfix:
+        vim.fn.setqflist(vim
+          .iter(items)
+          :map(
+            function(item)
+              return {
+                bufnr = item.bufnr,
+                filename = item.name,
+                lnum = 1,
+                col = 1,
+              }
+            end
+          )
+          :totable())
+        vim.cmd.copen()
+      end
+    end,
+
+    mappings = {
+      ['<C-t>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in new tab:
+        for _, item in ipairs(items) do
+          vim.cmd.tabnew()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-v>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in new vertial split:
+        for _, item in ipairs(items) do
+          vim.cmd.vsplit()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-s>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in horizontal split:
+        for _, item in ipairs(items) do
+          vim.cmd.split()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-x>'] = function(sel)
+        local selected_items = sel.get_selected_items()
+        for _, item in ipairs(selected_items) do
+          -- delete the buffer
+          vim.cmd.bdelete(item.bufnr)
+        end
+
+        sel.set_selected_indices {}
+        sel.set_items(
+          vim
+            .iter(sel.get_items())
+            :filter(function(item) return not vim.tbl_contains(selected_items, item) end)
+            :totable()
+        )
+      end,
+    },
+  }
+end
+
+local IS_CODE_SYMBOL_RUNNING = false
+function M.lsp_code_symbols()
+  if IS_CODE_SYMBOL_RUNNING then return end
+  IS_CODE_SYMBOL_RUNNING = true
+
+  -- Avoid callback-hell with a wizard-based "steps"-system. Define each "step"
+  -- sequentially in the code, and wire up the callbacks to call the next step:
+  -- a simple, yet powerful, and easy to understand pattern/approach.
+  local STEPS = {}
+
+  --- @param info vim.lsp.LocationOpts.OnList
+  function STEPS._1_on_symbols(info)
+    M.create_picker {
+      items = info.items,
+      --- @param item { text: string }
+      format_item = function(item)
+        local s = item.text:gsub('<', '&lt;')
+        return s
+      end,
+      on_finish = STEPS._2_on_symbol_picked,
+    }
+  end
+
+  --- @param items { filename: string, lnum: integer, col: integer }[]
+  function STEPS._2_on_symbol_picked(items)
+    if #items == 0 then return STEPS._finally() end
+
+    local item = items[1]
+
+    -- Jump to the file/buffer:
+    local buf = vim.iter(vim.fn.getbufinfo { buflisted = 1 }):find(function(b) return b.name == item.filename end)
+    if buf ~= nil then
+      vim.api.nvim_win_set_buf(0, buf.bufnr)
+    else
+      vim.cmd.edit(item.filename)
+    end
+
+    -- Jump to the specific location:
+    vim.api.nvim_win_set_cursor(0, { item.lnum, item.col - 1 })
+    vim.cmd.normal 'zz'
+
+    STEPS._finally()
+  end
+
+  function STEPS._finally() IS_CODE_SYMBOL_RUNNING = false end
+
+  -- Kick off the async operation:
+  vim.lsp.buf.document_symbol { on_list = STEPS._1_on_symbols }
+end
+
+function M.setup()
+  utils.ucmd('Files', M.files)
+  utils.ucmd('Buffers', M.buffers)
+  utils.ucmd('Lspcodesymbols', M.lsp_code_symbols)
+  M.register_ui_select()
+end
+
+return M