feat(ui/renderer): add virtualized renderer, caching, and components

Refactor formatter to accept an explicit render context and expose render_*
APIs while keeping legacy wrappers for backwards compatibility.
Add renderer modules: backend, cache, components (message, part, overlays),
measure, scheduler, session_view, viewport, and virtualize to support
virtualized rendering and block-level caching/measurement.
Add unit tests for formatter and renderer (cache, components, overlays).

Author: sudo-tee

lua/opencode/ui/formatter.lua

@@ -17,9 +17,76 @@ M.separator = {
   '',
 }
 
+local function default_win_width()
+  local output_win = state.windows and state.windows.output_win
+  if output_win and vim.api.nvim_win_is_valid(output_win) then
+    return vim.api.nvim_win_get_width(output_win)
+  end
+
+  if type(config.ui.window_width) == 'number' and config.ui.window_width > 1 then
+    return config.ui.window_width
+  end
+
+  return 80
+end
+
+local function resolve_render_ctx(render_ctx)
+  render_ctx = render_ctx or {}
+
+  local current_messages = render_ctx.messages
+  if current_messages == nil then
+    current_messages = state.messages or {}
+  end
+
+  local permission_renderer = render_ctx.permission_renderer
+  if permission_renderer == nil then
+    permission_renderer = function(output)
+      permission_window.format_display(output)
+    end
+  end
+
+  local question_renderer = render_ctx.question_renderer
+  if question_renderer == nil then
+    question_renderer = function(output)
+      require('opencode.ui.question_window').format_display(output)
+    end
+  end
+
+  local show_reasoning_output = config.ui.output.tools.show_reasoning_output
+  if render_ctx.show_reasoning_output ~= nil then
+    show_reasoning_output = render_ctx.show_reasoning_output
+  end
+
+  local show_debug_ids = config.debug.show_ids
+  if render_ctx.show_debug_ids ~= nil then
+    show_debug_ids = render_ctx.show_debug_ids
+  end
+
+  local revert_info = state.active_session and state.active_session.revert or nil
+  if render_ctx.revert_info ~= nil then
+    revert_info = render_ctx.revert_info
+  end
+
+  return {
+    messages = current_messages,
+    current_mode = render_ctx.current_mode ~= nil and render_ctx.current_mode or state.current_mode,
+    show_reasoning_output = show_reasoning_output,
+    show_debug_ids = show_debug_ids,
+    win_width = render_ctx.win_width or default_win_width(),
+    get_child_parts = render_ctx.get_child_parts,
+    child_session_parts = render_ctx.child_session_parts,
+    permission_renderer = permission_renderer,
+    question_renderer = question_renderer,
+    revert_info = revert_info,
+    is_last_part = render_ctx.is_last_part == true,
+  }
+end
+
 ---@param output Output
 ---@param part OpencodeMessagePart
-function M._format_reasoning(output, part)
+---@param render_ctx? table
+function M._format_reasoning(output, part, render_ctx)
+  render_ctx = resolve_render_ctx(render_ctx)
   local text = vim.trim(part.text or '')
 
   local start_line = output:get_line_count() + 1
@@ -35,7 +102,7 @@ function M._format_reasoning(output, part)
 
   format_utils.format_action(output, icons.get('reasoning'), title, '')
 
-  if config.ui.output.tools.show_reasoning_output and text ~= '' then
+  if render_ctx.show_reasoning_output and text ~= '' then
     output:add_empty_line()
     output:add_lines(vim.split(text, '\n'))
     output:add_empty_line()
@@ -54,10 +121,12 @@ end
 ---Format the revert callout with statistics
 ---@param session_data OpencodeMessage[] All messages in the session
 ---@param start_idx number Index of the message where revert occurred
+---@param render_ctx? table
 ---@return Output output object representing the lines, extmarks, and actions
-function M._format_revert_message(session_data, start_idx)
+function M.render_revert_message(session_data, start_idx, render_ctx)
+  render_ctx = resolve_render_ctx(render_ctx)
   local output = Output.new()
-  local stats = format_utils.calculate_revert_stats(session_data, start_idx, state.active_session.revert)
+  local stats = format_utils.calculate_revert_stats(session_data, start_idx, render_ctx.revert_info)
   local message_text = stats.messages == 1 and 'message' or 'messages'
   local tool_text = stats.tool_calls == 1 and 'tool call' or 'tool calls'
 
@@ -98,6 +167,8 @@ function M._format_revert_message(session_data, start_idx)
   return output
 end
 
+M._format_revert_message = M.render_revert_message
+
 local function add_action(output, text, action_type, args, key, line)
   -- actions use api-indexing (e.g. 0 indexed)
   line = (line or output:get_line_count()) - 1
@@ -150,8 +221,10 @@ function M._format_error(output, message)
 end
 
 ---@param message OpencodeMessage
+---@param render_ctx? table
 ---@return Output
-function M.format_message_header(message)
+function M.render_message_header(message, render_ctx)
+  render_ctx = resolve_render_ctx(render_ctx)
   local output = Output.new()
 
   output:add_lines(M.separator)
@@ -162,7 +235,7 @@ function M.format_message_header(message)
   local role_hl = 'OpencodeMessageRole' .. role:sub(1, 1):upper() .. role:sub(2)
   local model_text = message.info.modelID and ' ' .. message.info.modelID or ''
 
-  local debug_text = config.debug.show_ids and ' [' .. message.info.id .. ']' or ''
+  local debug_text = render_ctx.show_debug_ids and ' [' .. message.info.id .. ']' or ''
 
   local display_name
   if role == 'assistant' then
@@ -172,9 +245,10 @@ function M.format_message_header(message)
     else
       -- For the most recent assistant message, show current_mode if mode is missing
       -- This handles new messages that haven't been stamped yet
-      local is_last_message = #state.messages == 0 or message.info.id == state.messages[#state.messages].info.id
-      if is_last_message and state.current_mode and state.current_mode ~= '' then
-        display_name = state.current_mode:upper()
+      local messages = render_ctx.messages or {}
+      local is_last_message = #messages == 0 or message.info.id == messages[#messages].info.id
+      if is_last_message and render_ctx.current_mode and render_ctx.current_mode ~= '' then
+        display_name = render_ctx.current_mode:upper()
       else
         display_name = 'ASSISTANT'
       end
@@ -222,16 +296,21 @@ function M.format_message_header(message)
   return output
 end
 
+---@param message OpencodeMessage
+---@return Output
+function M.format_message_header(message)
+  return M.render_message_header(message)
+end
+
 ---@param output Output Output object to write to
 ---@param callout string Callout type (e.g., 'ERROR', 'TODO')
 ---@param text string Callout text content
 ---@param title? string Optional title for the callout
-function M._format_callout(output, callout, text, title)
+---@param render_ctx? table
+function M._format_callout(output, callout, text, title, render_ctx)
+  render_ctx = resolve_render_ctx(render_ctx)
   title = title and title .. ' ' or ''
-  local win_width = (state.windows and state.windows.output_win and vim.api.nvim_win_is_valid(state.windows.output_win))
-      and vim.api.nvim_win_get_width(state.windows.output_win)
-    or config.ui.window_width
-    or 80
+  local win_width = render_ctx.win_width
   if #text > win_width - 4 then
     local ok, substituted = pcall(vim.fn.substitute, text, '\v(.{' .. (win_width - 8) .. '})', '\1\n', 'g')
     text = ok and substituted or text
@@ -470,10 +549,10 @@ end
 ---Formats a single message part and returns the resulting output object
 ---@param part OpencodeMessagePart The part to format
 ---@param message? OpencodeMessage Optional message object to extract role and mentions from
----@param is_last_part? boolean Whether this is the last part in the message, used to show an error if there is one
----@param get_child_parts? fun(session_id: string): OpencodeMessagePart[]?
+---@param render_ctx? { is_last_part?: boolean, get_child_parts?: fun(session_id: string): OpencodeMessagePart[]?, child_session_parts?: OpencodeMessagePart[]?, show_reasoning_output?: boolean, permission_renderer?: fun(output: Output), question_renderer?: fun(output: Output), win_width?: integer, messages?: OpencodeMessage[], current_mode?: string, show_debug_ids?: boolean }
 ---@return Output
-function M.format_part(part, message, is_last_part, get_child_parts)
+function M.render_part(part, message, render_ctx)
+  render_ctx = resolve_render_ctx(render_ctx)
   local output = Output.new()
 
   if not message or not message.info or not message.info.role then
@@ -505,9 +584,24 @@ function M.format_part(part, message, is_last_part, get_child_parts)
       M._format_assistant_message(output, vim.trim(part.text), part.messageID)
       content_added = true
     elseif part.type == 'reasoning' then
-      M._format_reasoning(output, part)
+      M._format_reasoning(output, part, render_ctx)
       content_added = true
     elseif part.type == 'tool' then
+      local get_child_parts = render_ctx.get_child_parts
+      if render_ctx.child_session_parts ~= nil then
+        local child_session_parts = render_ctx.child_session_parts
+        local child_session_id = part.state and part.state.metadata and part.state.metadata.sessionId
+        get_child_parts = function(session_id)
+          if child_session_id and session_id == child_session_id then
+            return child_session_parts
+          end
+          if type(render_ctx.get_child_parts) == 'function' then
+            return render_ctx.get_child_parts(session_id)
+          end
+          return nil
+        end
+      end
+
       M.format_tool(output, part, get_child_parts)
       content_added = true
     elseif part.type == 'patch' and part.hash then
@@ -516,27 +610,39 @@ function M.format_part(part, message, is_last_part, get_child_parts)
     end
   elseif role == 'system' then
     if part.type == 'permissions-display' then
-      permission_window.format_display(output)
-      content_added = true
+      render_ctx.permission_renderer(output)
+      content_added = output:get_line_count() > 0
     elseif part.type == 'questions-display' then
-      local question_window = require('opencode.ui.question_window')
-      question_window.format_display(output)
-      content_added = true
+      render_ctx.question_renderer(output)
+      content_added = output:get_line_count() > 0
     end
   end
 
   if content_added then
     output:add_empty_line()
   end
 
-  if is_last_part and role == 'assistant' and message.info.error and message.info.error ~= '' then
+  if render_ctx.is_last_part and role == 'assistant' and message.info.error and message.info.error ~= '' then
     local error = message.info.error
     local error_message = error.data and error.data.message or vim.inspect(error)
-    M._format_callout(output, 'ERROR', error_message)
+    M._format_callout(output, 'ERROR', error_message, nil, render_ctx)
     output:add_empty_line()
   end
 
   return output
 end
 
+---Formats a single message part and returns the resulting output object
+---@param part OpencodeMessagePart The part to format
+---@param message? OpencodeMessage Optional message object to extract role and mentions from
+---@param is_last_part? boolean Whether this is the last part in the message, used to show an error if there is one
+---@param get_child_parts? fun(session_id: string): OpencodeMessagePart[]?
+---@return Output
+function M.format_part(part, message, is_last_part, get_child_parts)
+  return M.render_part(part, message, {
+    is_last_part = is_last_part,
+    get_child_parts = get_child_parts,
+  })
+end
+
 return M

lua/opencode/ui/renderer/backend.lua

@@ -0,0 +1,7 @@
+local M = {}
+
+function M.apply_full(visible_render)
+  return visible_render
+end
+
+return M