feat(diff): add option to show full diff with diff mode

Add new `full_diff` option to show_diff mapping which allows showing a full
diff view instead of unified diff view. When enabled, it will show the
modified file content side by side with original file using Vim's built-in
diff mode.

The full diff mode provides better visualization of changes and allows using
Vim's diff navigation commands to review changes.

Closes #705

lua/CopilotChat/config.lua

@@ -30,9 +30,12 @@ local utils = require('CopilotChat.utils')
 ---@field insert string?
 ---@field detail string?
 
----@class CopilotChat.config.mapping.register : CopilotChat.config.mapping
+---@class CopilotChat.config.mapping.yank_diff : CopilotChat.config.mapping
 ---@field register string?
 
+---@class CopilotChat.config.mapping.show_diff : CopilotChat.config.mapping
+---@field full_diff boolean?
+
 ---@class CopilotChat.config.mappings
 ---@field complete CopilotChat.config.mapping?
 ---@field close CopilotChat.config.mapping?
@@ -42,8 +45,8 @@ local utils = require('CopilotChat.utils')
 ---@field accept_diff CopilotChat.config.mapping?
 ---@field jump_to_diff CopilotChat.config.mapping?
 ---@field quickfix_diffs CopilotChat.config.mapping?
----@field yank_diff CopilotChat.config.mapping.register?
----@field show_diff CopilotChat.config.mapping?
+---@field yank_diff CopilotChat.config.mapping.yank_diff?
+---@field show_diff CopilotChat.config.mapping.show_diff?
 ---@field show_info CopilotChat.config.mapping?
 ---@field show_context CopilotChat.config.mapping?
 ---@field show_help CopilotChat.config.mapping?
@@ -391,10 +394,11 @@ return {
     },
     yank_diff = {
       normal = 'gy',
-      register = '"',
+      register = '"', -- Default register to use for yanking
     },
     show_diff = {
       normal = 'gd',
+      full_diff = false, -- Show full diff instead of unified diff when showing diff window
     },
     show_info = {
       normal = 'gi',

lua/CopilotChat/init.lua

@@ -6,11 +6,6 @@ local context = require('CopilotChat.context')
 local prompts = require('CopilotChat.prompts')
 local utils = require('CopilotChat.utils')
 
-local Chat = require('CopilotChat.ui.chat')
-local Diff = require('CopilotChat.ui.diff')
-local Overlay = require('CopilotChat.ui.overlay')
-local Debug = require('CopilotChat.ui.debug')
-
 local M = {}
 local PLUGIN_NAME = 'CopilotChat'
 local WORD = '([^%s]+)'
@@ -959,34 +954,38 @@ function M.setup(config)
   if state.overlay then
     state.overlay:delete()
   end
-  state.overlay = Overlay('copilot-overlay', overlay_help, function(bufnr)
+  state.overlay = require('CopilotChat.ui.overlay')('copilot-overlay', overlay_help, function(bufnr)
     map_key('close', bufnr, function()
       state.overlay:restore(state.chat.winnr, state.chat.bufnr)
     end)
   end)
 
   if not state.debug then
-    state.debug = Debug()
+    state.debug = require('CopilotChat.ui.debug')()
   end
 
   if state.diff then
     state.diff:delete()
   end
-  state.diff = Diff(diff_help, function(bufnr)
-    map_key('close', bufnr, function()
-      state.diff:restore(state.chat.winnr, state.chat.bufnr)
-    end)
+  state.diff = require('CopilotChat.ui.diff')(
+    M.config.mappings.show_diff.full_diff,
+    diff_help,
+    function(bufnr)
+      map_key('close', bufnr, function()
+        state.diff:restore(state.chat.winnr, state.chat.bufnr)
+      end)
 
-    map_key('accept_diff', bufnr, function()
-      apply_diff(state.diff:get_diff(), state.chat.config)
-    end)
-  end)
+      map_key('accept_diff', bufnr, function()
+        apply_diff(state.diff:get_diff(), state.chat.config)
+      end)
+    end
+  )
 
   if state.chat then
     state.chat:close(state.source and state.source.bufnr or nil)
     state.chat:delete()
   end
-  state.chat = Chat(
+  state.chat = require('CopilotChat.ui.chat')(
     M.config.question_header,
     M.config.answer_header,
     M.config.separator,

lua/CopilotChat/ui/diff.lua

@@ -14,13 +14,17 @@ local class = utils.class
 ---@class CopilotChat.ui.Diff : CopilotChat.ui.Overlay
 ---@field hl_ns number
 ---@field diff CopilotChat.ui.Diff.Diff?
-local Diff = class(function(self, help, on_buf_create)
+---@field augroup number
+---@field full_diff boolean
+local Diff = class(function(self, full_diff, help, on_buf_create)
   Overlay.init(self, 'copilot-diff', help, on_buf_create)
   self.hl_ns = vim.api.nvim_create_namespace('copilot-chat-highlights')
   vim.api.nvim_set_hl(self.hl_ns, '@diff.plus', { bg = utils.blend_color('DiffAdd', 20) })
   vim.api.nvim_set_hl(self.hl_ns, '@diff.minus', { bg = utils.blend_color('DiffDelete', 20) })
   vim.api.nvim_set_hl(self.hl_ns, '@diff.delta', { bg = utils.blend_color('DiffChange', 20) })
 
+  self.augroup = vim.api.nvim_create_augroup('CopilotChatDiff', { clear = true })
+  self.full_diff = full_diff
   self.diff = nil
 end, Overlay)
 
@@ -31,27 +35,74 @@ function Diff:show(diff, winnr)
   self:validate()
   vim.api.nvim_win_set_hl_ns(winnr, self.hl_ns)
 
-  Overlay.show(
-    self,
-    tostring(vim.diff(diff.reference, diff.change, {
-      result_type = 'unified',
-      ignore_blank_lines = true,
-      ignore_whitespace = true,
-      ignore_whitespace_change = true,
-      ignore_whitespace_change_at_eol = true,
-      ignore_cr_at_eol = true,
-      algorithm = 'myers',
-      ctxlen = #diff.reference,
-    })),
-    winnr,
-    diff.filetype,
-    'diff'
-  )
+  if not self.full_diff then
+    -- Create unified diff view
+    Overlay.show(
+      self,
+      tostring(vim.diff(diff.reference, diff.change, {
+        result_type = 'unified',
+        ignore_blank_lines = true,
+        ignore_whitespace = true,
+        ignore_whitespace_change = true,
+        ignore_whitespace_change_at_eol = true,
+        ignore_cr_at_eol = true,
+        algorithm = 'myers',
+        ctxlen = #diff.reference,
+      })),
+      winnr,
+      diff.filetype,
+      'diff'
+    )
+
+    return
+  end
+
+  -- Create modified version by applying the change
+  local modified = {}
+  if diff.bufnr and utils.buf_valid(diff.bufnr) then
+    modified = vim.api.nvim_buf_get_lines(diff.bufnr, 0, -1, false)
+  end
+  local change_lines = vim.split(diff.change, '\n')
+
+  -- Replace the lines in the modified content
+  if #modified > 0 then
+    local start_idx = diff.start_line - 1
+    local end_idx = diff.end_line - 1
+    for _ = start_idx, end_idx do
+      table.remove(modified, start_idx)
+    end
+    for i, line in ipairs(change_lines) do
+      table.insert(modified, start_idx + i - 1, line)
+    end
+  else
+    modified = change_lines
+  end
+
+  Overlay.show(self, table.concat(modified, '\n'), winnr, diff.filetype)
+
+  if diff.bufnr and vim.api.nvim_buf_is_valid(diff.bufnr) then
+    vim.cmd('diffthis')
+    vim.api.nvim_set_current_win(vim.fn.bufwinid(diff.bufnr))
+    vim.api.nvim_win_set_cursor(0, { diff.start_line, 0 })
+    vim.cmd('diffthis')
+    vim.api.nvim_set_current_win(winnr)
+    vim.api.nvim_win_set_cursor(winnr, { diff.start_line, 0 })
+
+    -- Link diff buffers lifecycle
+    vim.api.nvim_create_autocmd('BufWipeout', {
+      group = self.augroup,
+      buffer = self.bufnr,
+      callback = function()
+        vim.cmd('diffoff')
+      end,
+    })
+  end
 end
 
 ---@param winnr number
 ---@param bufnr number
 function Diff:restore(winnr, bufnr)
+  vim.cmd('diffoff')
   Overlay.restore(self, winnr, bufnr)
   vim.api.nvim_win_set_hl_ns(winnr, 0)
 end