feat(renderer): highlight mentions in output

This was fairly tricky for two reasons:

1. The part that needs highlighting has already been rendered when we
   get the part that contains the range so we have to rerender the first
   part.

2. Sometimes Opencode sends back a range that starts with 0. In that
   case, we fallback to searching for the string of the mention.

Author: cameronr

lua/opencode/ui/formatter.lua

@@ -5,6 +5,7 @@ local Output = require('opencode.ui.output')
 local state = require('opencode.state')
 local config = require('opencode.config')
 local snapshot = require('opencode.snapshot')
+local mention = require('opencode.ui.mention')
 
 local M = {}
 
@@ -314,14 +315,37 @@ end
 
 ---@param output Output Output object to write to
 ---@param text string
-function M._format_user_prompt(output, text)
+---@param message? OpencodeMessage Optional message object to extract mentions from
+function M._format_user_prompt(output, text, message)
   local start_line = output:get_line_count()
 
   output:add_lines(vim.split(text, '\n'))
 
   local end_line = output:get_line_count()
-  require('opencode.ui.mention').highlight_mentions(output)
-  M._add_vertical_border(output, start_line, end_line, 'OpencodeMessageRoleUser', -3)
+
+  local end_line_extmark_offset = 0
+
+  local mentions = {}
+  if message and message.parts then
+    -- message.parts will only be filled out on a re-render
+    -- we need to collect the mentions here
+    for _, part in ipairs(message.parts) do
+      if part.type == 'file' then
+        -- we're rerendering this part and we have files, the space after the user prompt
+        -- also needs an extmark
+        end_line_extmark_offset = 1
+        if part.source and part.source.text then
+          table.insert(mentions, part.source.text)
+        end
+      end
+    end
+  end
+
+  if #mentions > 0 then
+    mention.highlight_mentions_in_output(output, text, mentions, start_line)
+  end
+
+  M._add_vertical_border(output, start_line, end_line + end_line_extmark_offset, 'OpencodeMessageRoleUser', -3)
 end
 
 ---@param output Output Output object to write to
@@ -654,19 +678,20 @@ end
 
 ---Formats a single message part and returns the resulting output object
 ---@param part MessagePart The part to format
----@param role 'user'|'assistant'|'system' The role, user or assistant, that created this part
+---@param message? OpencodeMessage Optional message object to extract role and mentions from
 ---@return Output
-function M.format_part(part, role)
+function M.format_part(part, message)
   local output = Output.new()
 
   local content_added = false
+  local role = message and message.info and message.info.role
 
   if role == 'user' then
     if part.type == 'text' and part.text then
       if part.synthetic == true then
         M._format_selection_context(output, part)
       else
-        M._format_user_prompt(output, vim.trim(part.text))
+        M._format_user_prompt(output, vim.trim(part.text), message)
         content_added = true
       end
     elseif part.type == 'file' then

lua/opencode/ui/mention.lua

@@ -1,3 +1,5 @@
+local config = require('opencode.config')
+
 local M = {}
 
 local mentions_namespace = vim.api.nvim_create_namespace('OpencodeMentions')
@@ -40,24 +42,61 @@ function M.highlight_all_mentions(buf, callback)
   end
 end
 
----@param output Output
-function M.highlight_mentions(output)
-  local mention_pattern = '@[%w_%-%./][%w_%-%./]*'
-  for i, line in pairs(output:get_lines()) do
-    for mention in line:gmatch(mention_pattern) do
-      local col_start, col_end = line:find(mention, 1)
-      if col_start and col_end then
-        output:add_extmark(i, {
-          start_col = col_start - 1,
-          end_col = col_end,
-          hl_group = 'OpencodeMention',
-          priority = 1000,
-        })
+---Apply mention highlights from source.text data
+---@param output Output Output object to write to
+---@param text string The full text content
+---@param mentions OpencodeMessagePartSourceText[] Mention data with character offsets
+---@param start_line number The starting line index in the output (1-indexed)
+function M.highlight_mentions_in_output(output, text, mentions, start_line)
+  for _, mention in ipairs(mentions) do
+    local char_start = mention.start
+    local char_end = mention['end']
+
+    local char_count = 0
+
+    for i, line in ipairs(vim.split(text, '\n')) do
+      local line_start = char_count
+      local line_end = char_count + #line
+
+      if char_start == 0 and string.sub(text, 0, 1) ~= '@' then
+        -- Work around Opencode bug? where mentions sometimes have a 0 start
+        if config.debug.enabled then
+          vim.notify('Mention bug, falling back to search')
+        end
+
+        local start_pos, end_pos = string.find(line, mention.value, 1, true)
+
+        if start_pos then
+          output:add_extmark(start_line + i, {
+            start_col = start_pos - 1,
+            end_col = end_pos,
+            hl_group = 'OpencodeMention',
+            priority = 1000,
+          })
+          break
+        end
+      else
+        if char_start >= line_start and char_start < line_end then
+          local col_start = char_start - line_start
+          local col_end = math.min(char_end - line_start + 1, #line)
+
+          -- vim.notify('adding extmark, col_start: ' .. col_start .. ', col_end: ' .. col_end)
+          vim.notify('char: ' .. string.sub(line, col_start, col_start + 10))
+
+          output:add_extmark(start_line + i, {
+            start_col = col_start,
+            end_col = col_end,
+            hl_group = 'OpencodeMention',
+            priority = 1000,
+          })
+          break
+        end
+
+        char_count = line_end + 1
       end
     end
   end
 end
-
 local function insert_mention(windows, row, col, name)
   local current_line = vim.api.nvim_buf_get_lines(windows.input_buf, row - 1, row, false)[1]
 

lua/opencode/ui/renderer.lua

@@ -272,7 +272,7 @@ function M._replace_part_in_buffer(part_id, formatted_data)
 
   M._render_state:clear_actions(part_id)
 
-  output_window.clear_extmarks(cached.line_start, cached.line_end + 1)
+  output_window.clear_extmarks(cached.line_start - 1, cached.line_end + 1)
   output_window.set_lines(new_lines, cached.line_start, cached.line_end + 1)
 
   local new_line_end = cached.line_start + new_line_count - 1
@@ -465,7 +465,7 @@ function M.on_part_updated(properties, revert_index)
     M._render_state:update_part_data(part)
   end
 
-  local formatted = formatter.format_part(part, message.info.role)
+  local formatted = formatter.format_part(part, message)
 
   if revert_index and is_new_part then
     return
@@ -477,6 +477,15 @@ function M.on_part_updated(properties, revert_index)
     M._replace_part_in_buffer(part.id, formatted)
   end
 
+  if part.type == 'file' and part.source and part.source.text then
+    -- we have a mention, we need to rerender the early part to highlight
+    -- the mention.
+    local text_part_id = M._find_text_part_for_message(message)
+    if text_part_id then
+      M._rerender_part(text_part_id)
+    end
+  end
+
   M._scroll_to_bottom()
 end
 
@@ -657,6 +666,23 @@ function M._find_part_by_call_id(call_id, message_id)
   return M._render_state:get_part_by_call_id(call_id, message_id)
 end
 
+---Find the text part in a message
+---@param message OpencodeMessage The message containing the parts
+---@return string? text_part_id The ID of the text part
+function M._find_text_part_for_message(message)
+  if not message or not message.parts then
+    return nil
+  end
+
+  for _, part in ipairs(message.parts) do
+    if part.type == 'text' and not part.synthetic then
+      return part.id
+    end
+  end
+
+  return nil
+end
+
 ---Re-render existing part with current state
 ---Used for permission updates and other dynamic changes
 ---@param part_id string Part ID to re-render
@@ -673,7 +699,7 @@ function M._rerender_part(part_id)
   end
 
   local message = rendered_message.message
-  local formatted = formatter.format_part(part, message.info.role)
+  local formatted = formatter.format_part(part, message)
 
   M._replace_part_in_buffer(part_id, formatted)
 end

tests/data/diff.expected.json

@@ -1 +1 @@
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