feat: Added support for backend-specific layouts

lua/code-preview/diff.lua

@@ -127,6 +127,17 @@ local function active_count()
   return n
 end
 
+local function layout_for_backend(cfg, backend)
+  local diff_cfg = (cfg and cfg.diff) or {}
+  local layouts = diff_cfg.layouts or {}
+
+  if backend and layouts[backend] then
+    return layouts[backend]
+  end
+
+  return diff_cfg.layout or "tab"
+end
+
 function M.is_open(file_path)
   if file_path and file_path ~= "" then
     local entry = active_diffs[file_path]
@@ -416,12 +427,14 @@ local function show_inline_diff(original_path, proposed_path, real_file_path, cf
   return { tab = tab, bufs = { buf }, inline_win = win }
 end
 
-function M.show_diff(original_path, proposed_path, real_file_path, abs_file_path, action)
+function M.show_diff(original_path, proposed_path, real_file_path, abs_file_path, action, backend)
   local file_key = abs_file_path or real_file_path
   local cfg = require("code-preview").config
-  log.info(log.fmt("show_diff: file=%s layout=%s active=%d",
+  local layout = layout_for_backend(cfg, backend)
+  log.info(log.fmt("show_diff: file=%s layout=%s backend=%s active=%d",
     file_key or "nil",
-    (cfg.diff and cfg.diff.layout) or "tab",
+    layout,
+    backend or "nil",
     active_count()))
 
   -- If a diff for this SAME file is already open, close it first (re-edit)
@@ -434,7 +447,7 @@ function M.show_diff(original_path, proposed_path, real_file_path, abs_file_path
   mark_change_and_reveal(abs_file_path, action)
 
   -- Inline layout
-  if cfg.diff.layout == "inline" then
+  if layout == "inline" then
     local result = show_inline_diff(original_path, proposed_path, real_file_path, cfg)
     active_diffs[file_key] = result
     -- Force terminal redraw so RPC-triggered tab creation is visible (see force_redraw).
@@ -449,7 +462,7 @@ function M.show_diff(original_path, proposed_path, real_file_path, abs_file_path
   local labels = cfg.diff.labels or { current = "CURRENT", proposed = "PROPOSED" }
   local ft = vim.filetype.match({ filename = real_file_path }) or ""
 
-  if cfg.diff.layout == "vsplit" then
+  if layout == "vsplit" then
     vim.cmd("vsplit")
   else
     vim.cmd("tabnew")

lua/code-preview/init.lua

@@ -7,6 +7,7 @@ local default_config = {
   debug = false,  -- enable debug logging to stdpath("log")/code-preview.log
   diff = {
     layout = "tab",        -- "tab", "vsplit", or "inline"
+    layouts = {},          -- override layout per backend: { opencode = "tab", codex = "vsplit" }
     labels = { current = "CURRENT", proposed = "PROPOSED" },
     equalize = true,
     full_file = true,

lua/code-preview/pre_tool/init.lua

@@ -146,7 +146,7 @@ M.display_path = display_path  -- exposed for testing
 -- to diff.show_diff (or skip when visible_only excludes the file). The only
 -- per-tool variation is how `proposed_content` is computed, so each handler
 -- below is a one-liner around this helper.
-local function present_single_file(file_path, proposed_content, input, cfg)
+local function present_single_file(file_path, proposed_content, input, cfg, backend)
   local id = next_id()
   local orig = tmpdir() .. "/code-preview-diff-original-" .. id
   local prop = tmpdir() .. "/code-preview-diff-proposed-" .. id
@@ -159,29 +159,29 @@ local function present_single_file(file_path, proposed_content, input, cfg)
     return
   end
 
-  diff.show_diff(orig, prop, display_path(file_path, input.cwd), file_path, nil)
+  diff.show_diff(orig, prop, display_path(file_path, input.cwd), file_path, nil, backend)
 end
 
-local function handle_edit(input, cfg)
+local function handle_edit(input, cfg, backend)
   local fp = input.tool_input.file_path
   local content = apply_edit.apply(
     fp,
     input.tool_input.old_string or "",
     input.tool_input.new_string or "",
     input.tool_input.replace_all == true
   )
-  present_single_file(fp, content, input, cfg)
+  present_single_file(fp, content, input, cfg, backend)
 end
 
-local function handle_write(input, cfg)
+local function handle_write(input, cfg, backend)
   local fp = input.tool_input.file_path
-  present_single_file(fp, input.tool_input.content or "", input, cfg)
+  present_single_file(fp, input.tool_input.content or "", input, cfg, backend)
 end
 
-local function handle_multi_edit(input, cfg)
+local function handle_multi_edit(input, cfg, backend)
   local fp = input.tool_input.file_path
   local content = apply_multi_edit.apply(fp, input.tool_input.edits or {})
-  present_single_file(fp, content, input, cfg)
+  present_single_file(fp, content, input, cfg, backend)
 end
 
 local function handle_bash(input)
@@ -214,7 +214,7 @@ local function handle_bash(input)
   end
 end
 
-local function handle_apply_patch(input, cfg)
+local function handle_apply_patch(input, cfg, backend)
   local patch_text = input.tool_input and input.tool_input.patch_text
   if not patch_text or patch_text == "" then
     log.info("pre_tool: ApplyPatch with empty patch_text")
@@ -250,7 +250,7 @@ local function handle_apply_patch(input, cfg)
       -- whatever the model wrote in the `*** Update File:` directive, and some
       -- codex models (e.g. GPT 5.3) write an absolute path there, which would
       -- render the tab as `D:\...` instead of a cwd-relative label.
-      diff.show_diff(orig, prop, display_path(file.path, input.cwd), file.path, file.action)
+      diff.show_diff(orig, prop, display_path(file.path, input.cwd), file.path, file.action, backend)
     else
       log.info(log.fmt("pre_tool: ApplyPatch skip %s (visible_only)", file.rel_path))
     end
@@ -261,7 +261,7 @@ local dispatchers = {
   Edit       = handle_edit,
   Write      = handle_write,
   MultiEdit  = handle_multi_edit,
-  Bash       = function(input, _cfg) handle_bash(input) end,
+  Bash       = function(input, _cfg, _backend) handle_bash(input) end,
   ApplyPatch = handle_apply_patch,
 }
 
@@ -280,7 +280,7 @@ function M.handle(raw, backend)
 
   local fn = dispatchers[tool_name]
   if fn then
-    local ok, err = pcall(fn, input, cfg)
+    local ok, err = pcall(fn, input, cfg, backend)
     if not ok then
       log.error("pre_tool: dispatch failed: " .. tostring(err))
     end

tests/plugin/diff_lifecycle_spec.lua

@@ -213,12 +213,15 @@ describe("diff lifecycle", function()
 end)
 
 describe("diff layouts", function()
-  -- Temporarily override the diff layout for one test, restoring it afterwards.
-  local function with_layout(layout, fn)
+  -- Temporarily override diff layout config for one test, restoring it afterwards.
+  local function with_layout(layout, fn, layouts)
     local saved = require("code-preview").config.diff.layout
+    local saved_layouts = vim.deepcopy(require("code-preview").config.diff.layouts or {})
     require("code-preview").config.diff.layout = layout
+    require("code-preview").config.diff.layouts = layouts or {}
     local ok, err = pcall(fn)
     require("code-preview").config.diff.layout = saved
+    require("code-preview").config.diff.layouts = saved_layouts
     if not ok then error(err, 2) end
   end
 
@@ -289,4 +292,45 @@ describe("diff layouts", function()
     os.remove(orig)
     os.remove(prop)
   end)
+
+  it("backend layout override wins over the default layout", function()
+    local orig = tmp_file("backend_vs_orig.txt", "alpha\nbeta")
+    local prop = tmp_file("backend_vs_prop.txt", "alpha\ngamma")
+
+    local tabs_before = #vim.api.nvim_list_tabpages()
+    local tab = vim.api.nvim_get_current_tabpage()
+    local wins_before = #vim.api.nvim_tabpage_list_wins(tab)
+
+    with_layout("tab", function()
+      diff.show_diff(orig, prop, "layout_backend_vsplit.txt", nil, nil, "codex")
+    end, { codex = "vsplit" })
+
+    assert.is_true(diff.is_open())
+    assert.equals(tabs_before, #vim.api.nvim_list_tabpages())
+    assert.equals(wins_before + 2, #vim.api.nvim_tabpage_list_wins(tab))
+
+    diff.close_diff()
+    os.remove(orig)
+    os.remove(prop)
+  end)
+
+  it("missing backend falls back to the default layout", function()
+    local orig = tmp_file("no_backend_orig.txt", "alpha\nbeta")
+    local prop = tmp_file("no_backend_prop.txt", "alpha\ngamma")
+
+    local tabs_before = #vim.api.nvim_list_tabpages()
+
+    with_layout("tab", function()
+      diff.show_diff(orig, prop, "layout_no_backend.txt")
+    end, { codex = "vsplit" })
+
+    assert.is_true(diff.is_open())
+    assert.equals(tabs_before + 1, #vim.api.nvim_list_tabpages())
+    local diff_tabpage = vim.api.nvim_get_current_tabpage()
+    assert.equals(2, #vim.api.nvim_tabpage_list_wins(diff_tabpage))
+
+    diff.close_diff()
+    os.remove(orig)
+    os.remove(prop)
+  end)
 end)