feat(reasoning): show reasoning output + toggle

This PR add reasoning output to the panel.

It cols be toggled with `/reasoning` or `/thinking`, `Opencode
toggle_reasoning_output ` or `<leader>otr`

This should resolve #138

Author: sudo-tee

README.md

@@ -127,6 +127,8 @@ require('opencode').setup({
       ['<leader>opa'] = { 'permission_accept' }, -- Accept permission request once
       ['<leader>opA'] = { 'permission_accept_all' }, -- Accept all (for current tool)
       ['<leader>opd'] = { 'permission_deny' }, -- Deny permission request once
+      ['<leader>ott'] = { 'toggle_tools_output' }, -- Toggle tools output (diffs, cmd output, etc.)
+      ['<leader>otr'] = { 'toggle_reasoning_output' }, -- Toggle reasoning output (thinking steps)
     },
     input_window = {
       ['<cr>'] = { 'submit_input_prompt', mode = { 'n', 'i' } }, -- Submit prompt (normal mode and insert mode)
@@ -191,6 +193,7 @@ require('opencode').setup({
     output = {
       tools = {
         show_output = true, -- Show tools output [diffs, cmd output, etc.] (default: true)
+        show_reasoning_output = true, -- Show reasoning/thinking steps output (default: true)
       },
       rendering = {
         markdown_debounce_ms = 250, -- Debounce time for markdown rendering on new data (default: 250ms)
@@ -389,7 +392,8 @@ The plugin provides the following actions that can be triggered via keymaps, com
 | Navigate to next prompt in history                        | `<down>`                              | -                                           | `require('opencode.api').next_history()`                               |
 | Toggle input/output panes                                 | `<tab>`                               | -                                           | -                                                                      |
 | Swap Opencode pane left/right                             | `<leader>ox`                          | `:Opencode swap position`                   | `require('opencode.api').swap_position()`                              |
-| Toggle tools output (diffs, cmd output, etc.)             | -                                     | `:Opencode toggle_tools_output`             | `require('opencode.api').toggle_tools_output()`                        |
+| Toggle tools output (diffs, cmd output, etc.)             | `<leader>ott`                         | `:Opencode toggle_tools_output`             | `require('opencode.api').toggle_tools_output()`                        |
+| Toggle reasoning output (thinking steps)                  | `<leader>otr`                         | `:Opencode toggle_reasoning_output`         | `require('opencode.api').toggle_reasoning_output()`                    |
 
 ---
 

lua/opencode/api.lua

@@ -904,10 +904,19 @@ function M.permission_deny()
 end
 
 function M.toggle_tool_output()
+  local action_text = config.ui.output.tools.show_output and 'Hiding' or 'Showing'
+  vim.notify(action_text .. ' tool output display', vim.log.levels.INFO)
   config.values.ui.output.tools.show_output = not config.ui.output.tools.show_output
   ui.render_output()
 end
 
+function M.toggle_reasoning_output()
+  local action_text = config.ui.output.tools.show_reasoning_output and 'Hiding' or 'Showing'
+  vim.notify(action_text .. ' reasoning output display', vim.log.levels.INFO)
+  config.values.ui.output.tools.show_reasoning_output = not config.ui.output.tools.show_reasoning_output
+  ui.render_output()
+end
+
 ---@type table<string, OpencodeUICommand>
 M.commands = {
   open = {
@@ -1210,6 +1219,11 @@ M.commands = {
     desc = 'Toggle tool output visibility in the output window',
     fn = M.toggle_tool_output,
   },
+
+  toggle_reasoning_output = {
+    desc = 'Toggle reasoning output visibility in the output window',
+    fn = M.toggle_reasoning_output,
+  },
   paste_image = {
     desc = 'Paste image from clipboard and add to context',
     fn = M.paste_image,
@@ -1234,6 +1248,8 @@ M.slash_commands_map = {
   ['/undo'] = { fn = M.undo, desc = 'Undo last action' },
   ['/unshare'] = { fn = M.unshare, desc = 'Unshare current session' },
   ['/rename'] = { fn = M.rename_session, desc = 'Rename current session' },
+  ['/thinking'] = { fn = M.toggle_reasoning_output, desc = 'Toggle reasoning output' },
+  ['/reasoning'] = { fn = M.toggle_reasoning_output, desc = 'Toggle reasoning output' },
 }
 
 M.legacy_command_map = {

lua/opencode/config.lua

@@ -41,6 +41,8 @@ M.defaults = {
       ['<leader>oPa'] = { 'permission_accept', desc = 'Accept permission' },
       ['<leader>oPA'] = { 'permission_accept_all', desc = 'Accept all permissions' },
       ['<leader>oPd'] = { 'permission_deny', desc = 'Deny permission' },
+      ['<leader>otr'] = { 'toggle_reasoning_output', desc = 'Toggle reasoning output' },
+      ['<leader>ott'] = { 'toggle_tool_output', desc = 'Toggle tool output' },
     },
     output_window = {
       ['<esc>'] = { 'close' },
@@ -118,6 +120,7 @@ M.defaults = {
       },
       tools = {
         show_output = true,
+        show_reasoning_output = true,
       },
       always_scroll_to_bottom = false,
     },

lua/opencode/types.lua

@@ -129,6 +129,10 @@
 ---@field output OpencodeUIOutputConfig
 ---@field input { text: { wrap: boolean } }
 ---@field completion OpencodeCompletionConfig
+---@field highlights? OpencodeHighlightConfig
+
+---@class OpencodeHighlightConfig
+---@field vertical_borders? { tool?: { fg?: string, bg?: string }, user?: { fg?: string, bg?: string }, assistant?: { fg?: string, bg?: string } }
 
 ---@class OpencodeUIOutputRenderingConfig
 ---@field markdown_debounce_ms number
@@ -137,7 +141,7 @@
 ---@field event_collapsing boolean
 
 ---@class OpencodeUIOutputConfig
----@field tools { show_output: boolean }
+---@field tools { show_output: boolean, show_reasoning_output: boolean }
 ---@field rendering OpencodeUIOutputRenderingConfig
 ---@field always_scroll_to_bottom boolean
 
@@ -382,7 +386,7 @@
 ---@field value string|nil
 
 ---@class OpencodeMessagePart
----@field type 'text'|'file'|'agent'|'tool'|'step-start'|'patch'|string
+---@field type 'text'|'file'|'agent'|'tool'|'step-start'|'patch'|'reasoning'|string
 ---@field id string|nil Unique identifier for tool use parts
 ---@field text string|nil
 ---@field tool string|nil Name of the tool being used
@@ -399,6 +403,7 @@
 ---@field callID string|nil Call identifier (used for tools)
 ---@field hash string|nil Hash identifier for patch parts
 ---@field files string[]|nil List of file paths for patch parts
+---@field time { start: number, end: number }|nil Timestamps for the part
 
 ---@class OpencodeModelModalities
 ---@field input ('text'|'image'|'audio'|'video')[] Supported input modalities

lua/opencode/ui/formatter.lua

@@ -14,6 +14,46 @@ M.separator = {
   '',
 }
 
+---@param output Output
+---@param part OpencodeMessagePart
+function M._format_reasoning(output, part)
+  local text = vim.trim(part.text or '')
+  if text == '' then
+    return
+  end
+
+  local start_line = output:get_line_count() + 1
+
+  local title = 'Reasoning'
+  local time = part.time
+  if time and type(time) == 'table' and time.start then
+    local start_text = util.format_time(time.start) or ''
+    local end_text = (time['end'] and util.format_time(time['end'])) or nil
+    if end_text and end_text ~= '' then
+      title = string.format('%s (%s - %s)', title, start_text, end_text)
+    elseif start_text ~= '' then
+      title = string.format('%s (%s)', title, start_text)
+    end
+  end
+
+  M._format_action(output, icons.get('reasoning') .. ' ' .. title, '')
+
+  if config.ui.output.tools.show_reasoning_output then
+    output:add_empty_line()
+    output:add_lines(vim.split(text, '\n'))
+    output:add_empty_line()
+  end
+
+  local end_line = output:get_line_count()
+  if end_line - start_line > 1 then
+    M._add_vertical_border(output, start_line, end_line, 'OpencodeToolBorder', -1, 'OpencodeReasoningText')
+  else
+    M.output:add_extmark(start_line - 1, {
+      line_hl_group = 'OpencodeReasoningText',
+    } --[[@as OutputExtmark]])
+  end
+end
+
 function M._handle_permission_request(output, part)
   if part.state and part.state.status == 'error' and part.state.error then
     if part.state.error:match('rejected permission') then
@@ -431,14 +471,15 @@ function M._format_assistant_message(output, text)
 end
 
 ---@param output Output Output object to write to
----@param type string Tool type (e.g., 'run', 'read', 'edit', etc.)
+---@param tool_type string Tool type (e.g., 'run', 'read', 'edit', etc.)
 ---@param value string Value associated with the action (e.g., filename, command)
-function M._format_action(output, type, value)
-  if not type or not value then
+function M._format_action(output, tool_type, value)
+  if not tool_type or not value then
     return
   end
+  local line = string.format('**%s** %s', tool_type, value and #value > 0 and ('`' .. value .. '`') or '')
 
-  output:add_line('**' .. type .. '** `' .. value .. '`')
+  output:add_line(line)
 end
 
 ---@param output Output Output object to write to
@@ -713,16 +754,24 @@ end
 ---@param output Output Output object to write to
 ---@param start_line number
 ---@param end_line number
----@param hl_group string
+---@param hl_group string Highlight group for the border character
 ---@param win_col number
-function M._add_vertical_border(output, start_line, end_line, hl_group, win_col)
+---@param text_hl_group? string Optional highlight group for the background/foreground of text lines
+function M._add_vertical_border(output, start_line, end_line, hl_group, win_col, text_hl_group)
   for line = start_line, end_line do
-    output:add_extmark(line - 1, {
+    local extmark_opts = {
       virt_text = { { require('opencode.ui.icons').get('border'), hl_group } },
       virt_text_pos = 'overlay',
       virt_text_win_col = win_col,
       virt_text_repeat_linebreak = true,
-    } --[[@as OutputExtmark]])
+    }
+
+    -- Add line highlight if text_hl_group is provided
+    if text_hl_group then
+      extmark_opts.line_hl_group = text_hl_group
+    end
+
+    output:add_extmark(line - 1, extmark_opts --[[@as OutputExtmark]])
   end
 end
 
@@ -762,6 +811,9 @@ function M.format_part(part, message, is_last_part)
     if part.type == 'text' and part.text then
       M._format_assistant_message(output, vim.trim(part.text))
       content_added = true
+    elseif part.type == 'reasoning' and part.text then
+      M._format_reasoning(output, part)
+      content_added = true
     elseif part.type == 'tool' then
       M._format_tool(output, part)
       content_added = true

lua/opencode/ui/highlight.lua

@@ -34,6 +34,7 @@ function M.setup()
     vim.api.nvim_set_hl(0, 'OpencodeContextSwitchOn', { link = '@label', default = true })
     vim.api.nvim_set_hl(0, 'OpencodePickerTime', { link = 'Comment', default = true })
     vim.api.nvim_set_hl(0, 'OpencodeDebugText', { link = 'Comment', default = true })
+    vim.api.nvim_set_hl(0, 'OpencodeReasoningText', { link = 'Comment', default = true })
   else
     vim.api.nvim_set_hl(0, 'OpencodeBorder', { fg = '#616161', default = true })
     vim.api.nvim_set_hl(0, 'OpencodeBackground', { link = 'Normal', default = true })
@@ -64,6 +65,7 @@ function M.setup()
     vim.api.nvim_set_hl(0, 'OpencodeContextSwitchOn', { link = '@label', default = true })
     vim.api.nvim_set_hl(0, 'OpencodePickerTime', { link = 'Comment', default = true })
     vim.api.nvim_set_hl(0, 'OpencodeDebugText', { link = 'Comment', default = true })
+    vim.api.nvim_set_hl(0, 'OpencodeReasoningText', { link = 'Comment', default = true })
   end
 end
 

lua/opencode/ui/icons.lua

@@ -25,6 +25,7 @@ local presets = {
     folder = ' ',
     attached_file = '󰌷 ',
     agent = '󰚩 ',
+    reasoning = '󰧑 ',
     -- statuses
     status_on = ' ',
     status_off = ' ',

tests/data/reasoning.expected.json

@@ -0,0 +1 @@
+{"lines":["----","","","Explain your plan, then provide the final title.","","----","","","**󰧑  Reasoning (2025-12-17 19:33:20 - 2025-12-17 19:33:21)** ","","The user is asking me to explain my plan and then provide a final title. I need to think through what they're asking for. It seems like they want me to demonstrate reasoning capabilities - showing my thought process before giving an answer. Let me break this down into steps.","","1. First, I should understand what kind of title they want - is this for a project, document, or something else?","2. Since they didn't specify the context, I should provide a general approach","3. I'll demonstrate my reasoning process transparently","4. Then I'll give them a concrete example title","","Given that this appears to be related to the OpenCode project (based on the file structure I can see), I should provide a title that reflects the nature of this AI coding assistant tool.","","Based on my reasoning above, here's my plan:","","1. Acknowledge the request for demonstrating reasoning","2. Show transparency in my thought process","3. Provide context-appropriate suggestions","","For the title, considering this is the OpenCode Neovim plugin - an AI-powered coding assistant - a good title would be:","","**\"OpenCode.nvim: AI-Powered Coding Assistant for Neovim\"**","","This title clearly identifies what the tool is (OpenCode), the platform it works with (Neovim), and its primary function (AI-powered coding assistance).","",""],"actions":[],"extmarks":[[1,1,0,{"virt_text":[["▌󰭻 ","OpencodeMessageRoleUser"],[" "],["USER","OpencodeMessageRoleUser"],["","OpencodeHint"],[" (2025-12-17 19:33:20)","OpencodeHint"],[" [msg_reason_user1]","OpencodeHint"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":10,"virt_text_repeat_linebreak":false,"right_gravity":true,"virt_text_win_col":-3,"ns_id":3}],[2,2,0,{"virt_text":[["▌","OpencodeMessageRoleUser"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"right_gravity":true,"virt_text_win_col":-3,"ns_id":3}],[3,3,0,{"virt_text":[["▌","OpencodeMessageRoleUser"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"right_gravity":true,"virt_text_win_col":-3,"ns_id":3}],[4,6,0,{"virt_text":[[" ","OpencodeMessageRoleAssistant"],[" "],["BUILD","OpencodeMessageRoleAssistant"],[" claude-sonnet-4","OpencodeHint"],[" (2025-12-17 19:33:20)","OpencodeHint"],[" [msg_reason_asst1]","OpencodeHint"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":10,"virt_text_repeat_linebreak":false,"right_gravity":true,"virt_text_win_col":-3,"ns_id":3}],[5,8,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[6,9,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[7,10,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[8,11,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[9,12,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[10,13,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[11,14,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[12,15,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[13,16,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[14,17,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}],[15,18,0,{"line_hl_group":"OpencodeReasoningText","right_gravity":true,"ns_id":3,"virt_text":[["▌","OpencodeToolBorder"]],"virt_text_pos":"win_col","virt_text_hide":false,"priority":4096,"virt_text_repeat_linebreak":true,"virt_text_win_col":-1}]],"timestamp":1766413340}