feat(ui): inline diff in chat (#2934)

Author: olimorris

CLAUDE.md

@@ -13,9 +13,10 @@ Neovim plugin (Lua) providing LLM-powered coding assistance: chat, inline transf
 
 - **Naming:** snake_case for files/functions, PascalCase for classes, underscore prefix for private functions
 - **Explicit names:** `pattern` not `pat`, `should_include` not `include_ok`
+- **Readable code:** names, variables, and control flow should read like clean English. Prefer `threshold_met` over a long inline condition. Avoid generic names like `ctx` — use domain-specific names (`permission`, `request`, `source`)
 - **Function params:** prefer a single table argument over positional args
 - **Error handling:** `pcall` + `log:error()`, return nil on failure
-- **Type annotations:** LuaCATS for public APIs
+- **Type annotations:** LuaCATS for public APIs. Keep doc blocks concise — one description line, params should be self-explanatory without inline comments
 - **Functions:** keep under 50 lines
 - **Globals:** avoid; use module-local state
 - **Code blocks:** use four backticks with language spec

doc/codecompanion.txt

@@ -1,4 +1,4 @@
-*codecompanion.txt*          For NVIM v0.11         Last change: 2026 March 24
+*codecompanion.txt*          For NVIM v0.11         Last change: 2026 March 26
 
 ==============================================================================
 Table of Contents                            *codecompanion-table-of-contents*
@@ -1980,7 +1980,13 @@ plugin. If you utilize the `insert_edit_into_file` tool or use an ACP adapter,
 then the plugin will update files and buffers, displaying the changes in a
 floating window.
 
-There are a number of configuration option available to you:
+For small changes, the diff is shown directly in the chat buffer. This can be
+controlled by `threshold_for_chat`, which corresponds to the size of the diff
+in terms of changed lines. For larger changes, the diff will automatically open
+in a floating window when the chat buffer is active. Or, you will be prompted
+to view the diff manually (`gv` by default).
+
+There are a number of configuration options available to you:
 
 
 

doc/configuration/chat-buffer.md

@@ -209,7 +209,9 @@ vim.api.nvim_create_autocmd("User", {
 
 CodeCompanion has a built-in diff engine that's leveraged throughout the plugin. If you utilize the `insert_edit_into_file` tool or use an ACP adapter, then the plugin will update files and buffers, displaying the changes in a floating window.
 
-There are a number of configuration option available to you:
+For small changes, the diff is shown directly in the chat buffer. This can be controlled by `threshold_for_chat`, which corresponds to the size of the diff in terms of changed lines. For larger changes, the diff will automatically open in a floating window when the chat buffer is active. Or, you will be prompted to view the diff manually (`gv` by default).
+
+There are a number of configuration options available to you:
 
 ::: code-group
 
@@ -218,6 +220,10 @@ require("codecompanion").setup({
   display = {
     diff = {
       enabled = true,
+
+      -- At or below this diff size, always display the diff in the chat buffer
+      threshold_for_chat = 6,
+
       word_highlights = {
         additions = true,
         deletions = true,

lua/codecompanion/config.lua

@@ -1121,6 +1121,8 @@ The user is working on a %s machine. Please respond with system specific command
 
     diff = {
       enabled = true,
+      threshold_for_chat = 6, -- At or below this, always display the diff in the chat buffer
+
       -- Options for any diff windows (extends from floating_window)
       window = {
         opts = {},

lua/codecompanion/diff/utils.lua

@@ -234,4 +234,35 @@ function M.split_words(str)
   return ret
 end
 
+---Count the number of changed lines (additions + deletions)
+---@param from_lines string[]
+---@param to_lines string[]
+---@return number
+function M.changed_lines(from_lines, to_lines)
+  local hunks = require("codecompanion.diff")._diff(from_lines, to_lines)
+
+  local count = 0
+  for _, hunk in ipairs(hunks) do
+    count = count + hunk[2] + hunk[4]
+  end
+
+  return count
+end
+
+---Generate a unified diff string suitable for inline display
+---@param from_lines string[]
+---@param to_lines string[]
+---@return string
+function M.unified(from_lines, to_lines)
+  ---@diagnostic disable-next-line: deprecated
+  local diff_fn = vim.text.diff or vim.diff
+  local result =
+    diff_fn(table.concat(from_lines, "\n"), table.concat(to_lines, "\n"), { result_type = "unified", ctxlen = 3 })
+
+  -- Strip the newline marker
+  result = (result or ""):gsub("\n?\\ No newline at end of file%s*", ""):gsub("\n$", "")
+
+  return result
+end
+
 return M

lua/codecompanion/interactions/chat/acp/request_permission.lua

@@ -1,8 +1,13 @@
+local config = require("codecompanion.config")
+local diff_utils = require("codecompanion.diff.utils")
 local log = require("codecompanion.utils.log")
+local ui_utils = require("codecompanion.utils.ui")
 local utils = require("codecompanion.utils")
 
 local labels = require("codecompanion.interactions.chat.tools.labels")
 
+local fmt = string.format
+
 ---Ref: https://agentclientprotocol.com/protocol/schema#permissionoptionkind
 local ACP_OPTIONS = {
   allow_once = { label = labels.accept, keymap = "accept" },
@@ -14,10 +19,10 @@ local ACP_OPTIONS = {
 local M = {}
 
 ---Find the first reject option from the request options
----@param options table
+---@param opts table
 ---@return string|nil optionId
-local function find_reject_option(options)
-  for _, opt in ipairs(options or {}) do
+local function find_reject_option(opts)
+  for _, opt in ipairs(opts or {}) do
     if opt.kind:find("^reject", 1, true) then
       return opt.optionId
     end
@@ -26,11 +31,11 @@ local function find_reject_option(options)
 end
 
 ---Build a map of kind -> optionId for easy lookup
----@param options table
+---@param opts table
 ---@return table<string, string> kind -> optionId
-local function build_kind_map(options)
+local function build_kind_map(opts)
   local map = {}
-  for _, opt in ipairs(options or {}) do
+  for _, opt in ipairs(opts or {}) do
     if type(opt.kind) == "string" and type(opt.optionId) == "string" then
       map[opt.kind] = opt.optionId
     end
@@ -40,7 +45,7 @@ end
 
 ---Get the shared keymap key for an ACP option kind
 ---@param kind string
----@param keys table Resolved keymaps from labels.keymaps()
+---@param keys table
 ---@return string|nil
 local function key_for_kind(kind, keys)
   local opt = ACP_OPTIONS[kind]
@@ -51,8 +56,8 @@ local function key_for_kind(kind, keys)
 end
 
 ---Build the banner displayed in the diff window winbar
----@param kind_map table<string, string> kind -> optionId
----@param keys table Resolved keymaps from labels.keymaps()
+---@param kind_map table<string, string>
+---@param keys table
 ---@return string
 local function build_banner(kind_map, keys)
   local parts = {}
@@ -63,11 +68,11 @@ local function build_banner(kind_map, keys)
     local lhs = key_for_kind(kind, keys)
     if lhs then
       local label = (ACP_OPTIONS[kind] and ACP_OPTIONS[kind].label) or kind:gsub("_", " ")
-      table.insert(parts, string.format("%s %s", lhs, label))
+      table.insert(parts, fmt("%s %s", lhs, label))
     end
   end
 
-  table.insert(parts, string.format("%s/%s Next/Prev", keys.next_hunk, keys.previous_hunk))
+  table.insert(parts, fmt("%s/%s Next/Prev", keys.next_hunk, keys.previous_hunk))
   table.insert(parts, "q Close")
 
   return table.concat(parts, " | ")
@@ -150,28 +155,26 @@ local function setup_diff_keymaps(opts)
   })
 end
 
----Display the diff preview and resolve permission by user decision
----@param opts { chat: CodeCompanion.Chat, request: table, on_done: fun(choice_label: string) }
----@return nil
-local function show_diff(opts)
-  local d = get_diff(opts.request.tool_call)
+---Open the floating diff view for an ACP permission request
+---@param permission table
+local function open_diff_view(permission)
+  local d = get_diff(permission.request.tool_call)
 
-  local diff_id = math.random(1000000)
-  local kind_map = build_kind_map(opts.request.options)
+  local kind_map = build_kind_map(permission.request.options)
   local keys = labels.keymaps()
 
   local diff_ui = require("codecompanion.helpers").show_diff({
     from_lines = vim.split(d.old or "", "\n", { plain = true }),
     to_lines = vim.split(d.new or "", "\n", { plain = true }),
     banner = build_banner(kind_map, keys),
-    chat_bufnr = opts.chat.bufnr,
-    diff_id = diff_id,
+    chat_bufnr = permission.chat.bufnr,
+    diff_id = math.random(1000000),
     ft = vim.filetype.match({ filename = d.path }) or "text",
     keymaps = {
       on_reject = function()
-        opts.on_done(labels.reject)
-        local rejected = find_reject_option(opts.request.options)
-        opts.request.respond(rejected, false)
+        permission.on_done(labels.reject)
+        local rejected = find_reject_option(permission.request.options)
+        permission.request.respond(rejected, false)
       end,
     },
     skip_default_keymaps = true,
@@ -182,53 +185,40 @@ local function show_diff(opts)
     diff_ui = diff_ui,
     kind_map = kind_map,
     keys = keys,
-    request = opts.request,
-    on_done = opts.on_done,
+    request = permission.request,
+    on_done = permission.on_done,
   })
 end
 
----Show the permission request to the user and handle their response
----@param chat CodeCompanion.Chat
----@param request table
----@return nil
-function M.confirm(chat, request)
-  local approval_prompt = require("codecompanion.interactions.chat.helpers.approval_prompt")
-
-  local tool_call = request.tool_call
-  local prompt = string.format(
-    "%s: %s",
-    utils.capitalize(tool_call and tool_call.kind or "Permission"),
-    tool_call and tool_call.title or "Agent requested permission"
-  )
-
-  local has_diff = request.tool_call and requires_diff(request.tool_call)
+---Build the approval choices for an ACP permission request
+---@param permission table
+---@param has_diff boolean
+---@return CodeCompanion.Chat.ApprovalChoice[]
+local function build_choices(permission, has_diff)
   local keys = labels.keymaps()
-
   local choices = {}
 
-  local on_done
-
   if has_diff then
     table.insert(choices, {
       keymap = keys.view,
       label = labels.view,
       preview = true,
       callback = function()
         log:debug("[acp::request_permission] Opening diff for review")
-        show_diff({ chat = chat, request = request, on_done = on_done })
+        open_diff_view(permission)
       end,
     })
   end
 
-  for _, opt in ipairs(request.options or {}) do
+  for _, opt in ipairs(permission.request.options or {}) do
     local key = key_for_kind(opt.kind, keys)
     if key then
       table.insert(choices, {
         keymap = key,
         label = (ACP_OPTIONS[opt.kind] and ACP_OPTIONS[opt.kind].label) or opt.name,
         callback = function()
           log:debug("[acp::request_permission] User selected option %s", opt.optionId)
-          request.respond(opt.optionId, false)
+          permission.request.respond(opt.optionId, false)
         end,
       })
     end
@@ -239,17 +229,77 @@ function M.confirm(chat, request)
     label = labels.cancel,
     callback = function()
       log:debug("[acp::request_permission] User cancelled")
-      request.respond(nil, true)
+      permission.request.respond(nil, true)
     end,
   })
 
-  on_done = approval_prompt.request(chat, {
-    id = request.id,
-    name = tool_call and tool_call.kind or nil,
-    title = has_diff and "View Proposed Edits" or nil,
-    prompt = prompt,
+  return choices
+end
+
+---Allow the user to approve from within the chat buffer
+---@param permission table
+---@param choices CodeCompanion.Chat.ApprovalChoice[]
+---@param prompt_opts { title?: string, prompt: string }
+local function approve_in_chat(permission, choices, prompt_opts)
+  local approval_prompt = require("codecompanion.interactions.chat.helpers.approval_prompt")
+  permission.on_done = approval_prompt.request(permission.chat, {
     choices = choices,
+    id = permission.request.id,
+    name = permission.request.tool_call and permission.request.tool_call.kind or nil,
+    prompt = prompt_opts.prompt,
+    title = prompt_opts.title,
   })
 end
 
+---Show the permission request to the user and handle their response
+---@param chat CodeCompanion.Chat
+---@param request table
+---@return nil
+function M.confirm(chat, request)
+  local tool_call = request.tool_call
+  local has_diff = tool_call and requires_diff(tool_call)
+
+  local base_prompt = fmt(
+    "%s: %s",
+    utils.capitalize(tool_call and tool_call.kind or "Permission"),
+    tool_call and tool_call.title or "Agent requested permission"
+  )
+
+  local permission = { chat = chat, request = request }
+  local choices = build_choices(permission, has_diff)
+
+  if not has_diff then
+    return approve_in_chat(permission, choices, { prompt = base_prompt })
+  end
+
+  local d = get_diff(tool_call)
+  local from_lines = vim.split(d.old or "", "\n", { plain = true })
+  local to_lines = vim.split(d.new or "", "\n", { plain = true })
+  local changed_lines = diff_utils.changed_lines(from_lines, to_lines)
+  local threshold = config.display.diff.threshold_for_chat
+  local threshold_met = threshold and threshold > 0 and changed_lines > 0 and changed_lines <= threshold
+
+  if threshold_met then
+    -- Show small diffs in the chat buffer
+    local diff_text = diff_utils.unified(from_lines, to_lines)
+    local prompt = fmt(
+      [[%s
+
+`````diff
+%s
+`````]],
+      base_prompt,
+      diff_text
+    )
+    return approve_in_chat(permission, choices, { title = "Proposed Edits", prompt = prompt })
+  elseif ui_utils.buf_is_active(chat.bufnr) then
+    -- If the chat is active, show the diff in the floating window
+    approve_in_chat(permission, choices, { title = "View Proposed Edits", prompt = base_prompt })
+    return open_diff_view(permission)
+  else
+    -- Otherwise, don't force the diff on the user, just show the approval
+    return approve_in_chat(permission, choices, { title = "View Proposed Edits", prompt = base_prompt })
+  end
+end
+
 return M