feat: toggle layout, welcome page improvements, stale buffer fixes (#307)

## Summary

### Toggle between inline and side-by-side layout (`t` key)
Press `t` in any diff view to toggle between side-by-side and inline
layout. The current file is re-rendered in the new layout automatically.
Works in explorer, history, and standalone modes.

- `toggle.lua`: Orchestrates layout switch (normalize windows → rerender
current file)
- Uses existing `single_pane` mechanism and `rerender_current()` to
replay file selection
- Conflict mode blocks toggle (not applicable)
- Configurable: `keymaps.view.toggle_layout = "t"`

Closes #292
Closes #302
Closes the runtime toggle aspect of #146.

### Welcome page improvements
- Fixed flicker: guard against re-creating welcome buffer on every
refresh cycle
- Fixed stale selection highlight persisting after welcome page shown
- Fixed missing `welcome` module require (regression from toggle
refactoring)

### Stale buffer fix improvements
- Cross-platform git helpers in all test files (fixes Windows CI)
- Double-quoted commit messages for Windows cmd.exe compatibility

### Code cleanup
- Removed `display_state` / `diff_config` abstractions (toggle works
purely through existing session fields)
- Removed dead code: `reset_diff_panes`, `show_single_file_preview`,
`current_layout` wrapper
- Renamed for consistency: `rerender_current_source` →
`rerender_current_file`
- Toggle always commits layout change (no rollback desync)

### Documentation
- README: toggle feature in features list + keymaps config
- vimdoc: new `codediff-toggle-layout` section
- Tags regenerated

### Testing
- Layout toggle test suite (`layout_toggle_spec.lua`)
- All existing tests pass (Linux + Windows CI)

Author: esmuellert

README.md

@@ -25,6 +25,7 @@ https://github.com/user-attachments/assets/64c41f01-dffe-4318-bce4-16eec8de356e
   - Deep/dark character-level highlights showing exact changes within lines
 - **Side-by-side diff view** in a new tab with synchronized scrolling
 - **Inline (unified) diff view** — single-window layout with deleted lines as virtual overlays, with treesitter syntax highlighting
+- **Toggle layout** — switch between side-by-side and inline layout at runtime with `t`
 - **Git integration**: Compare between any git revision (HEAD, commits, branches, tags)
 - **Same implementation as VSCode's diff engine**, providing identical visual highlighting for most scenarios
 - **Fast C-based diff computation** using FFI with **multi-core parallelization** (OpenMP)
@@ -155,6 +156,7 @@ https://github.com/user-attachments/assets/64c41f01-dffe-4318-bce4-16eec8de356e
         hunk_textobject = "ih",      -- Textobject for hunk (vih to select, yih to yank, etc.)
         show_help = "g?",   -- Show floating window with available keymaps
         align_move = "gm", -- Temporarily align moved code blocks across panes
+        toggle_layout = "t", -- Toggle between side-by-side and inline layout
       },
       explorer = {
         select = "<CR>",    -- Open diff for selected file

VERSION

@@ -1 +1 @@
-2.42.0
+2.43.0

doc/codediff.txt

@@ -153,6 +153,23 @@ The `gm` keymap disables scrollbind and positions both panes so the moved
 block appears at the same visual row. Moving the cursor outside the block
 or switching windows restores normal scrollbind.
 
+TOGGLING LAYOUT                                   *codediff-toggle-layout*
+
+Press `t` in a diff view to toggle between side-by-side and inline layout.
+The current file is re-rendered in the new layout automatically. This works
+in all modes (explorer, history, standalone).
+
+The toggle keymap can be customized:
+>lua
+  require("codediff").setup({
+    keymaps = {
+      view = {
+        toggle_layout = "t",  -- or false to disable
+      },
+    },
+  })
+<
+
 Setup entry point:
 >lua
   require("codediff").setup({
@@ -216,6 +233,7 @@ Setup entry point:
         hunk_textobject = "ih",
         show_help = "g?",
         align_move = "gm",
+        toggle_layout = "t",
       },
       explorer = {
         select = "<CR>",

doc/tags

@@ -13,6 +13,7 @@ codediff-lua-api	codediff.txt	/*codediff-lua-api*
 codediff-moved-code	codediff.txt	/*codediff-moved-code*
 codediff-quickstart	codediff.txt	/*codediff-quickstart*
 codediff-see-also	codediff.txt	/*codediff-see-also*
+codediff-toggle-layout	codediff.txt	/*codediff-toggle-layout*
 codediff-usage	codediff.txt	/*codediff-usage*
 codediff.nvim	codediff.txt	/*codediff.nvim*
 codediff.txt	codediff.txt	/*codediff.txt*

lua/codediff/config.lua

@@ -99,6 +99,7 @@ M.defaults = {
       discard_hunk = "<leader>hr", -- Discard the hunk under cursor (working tree only)
       hunk_textobject = "ih", -- Textobject for hunk (vih to select, yih to yank, etc.)
       align_move = "gm", -- Temporarily align other pane to show paired moved code
+      toggle_layout = "t", -- Toggle diff layout for the current codediff session
       show_help = "g?", -- Show floating window with available keymaps
     },
     explorer = {

lua/codediff/ui/explorer/init.lua

@@ -9,6 +9,8 @@ local actions = require("codediff.ui.explorer.actions")
 
 -- Delegate to render module
 M.create = render.create
+M.rerender_current = render.rerender_current
+M.show_welcome_page = render.show_welcome_page
 
 -- Delegate to refresh module
 M.setup_auto_refresh = refresh.setup_auto_refresh

lua/codediff/ui/explorer/refresh.lua

@@ -4,7 +4,6 @@ local M = {}
 local config = require("codediff.config")
 local tree_module = require("codediff.ui.explorer.tree")
 local welcome = require("codediff.ui.welcome")
-
 -- Setup auto-refresh triggers for explorer
 -- Returns a cleanup function that should be called when the explorer is destroyed
 function M.setup_auto_refresh(explorer, tabpage)
@@ -256,38 +255,24 @@ function M.refresh(explorer)
       local function clear_current_file()
         explorer.current_file_path = nil
         explorer.current_file_group = nil
-      end
-
-      -- Helper: show the welcome page in the diff panes
-      local function show_welcome_page()
-        local lifecycle = require("codediff.ui.lifecycle")
-        local session = lifecycle.get_session(explorer.tabpage)
-        if session and not welcome.is_welcome_buffer(session.modified_bufnr) then
-          local mod_win = session.modified_win
-          if mod_win and vim.api.nvim_win_is_valid(mod_win) then
-            if session.layout == "inline" then
-              local w = vim.api.nvim_win_get_width(mod_win)
-              local h = vim.api.nvim_win_get_height(mod_win)
-              local welcome_buf = welcome.create_buffer(w, h)
-              require("codediff.ui.view.inline_view").show_welcome(explorer.tabpage, welcome_buf)
-            else
-              local orig_win = session.original_win
-              if orig_win and vim.api.nvim_win_is_valid(orig_win) then
-                local w = vim.api.nvim_win_get_width(orig_win) + vim.api.nvim_win_get_width(mod_win) + 1
-                local h = vim.api.nvim_win_get_height(orig_win)
-                local welcome_buf = welcome.create_buffer(w, h)
-                require("codediff.ui.view.side_by_side").show_welcome(explorer.tabpage, welcome_buf)
-              end
-            end
-          end
+        explorer.current_selection = nil
+        if explorer.clear_selection then
+          explorer.clear_selection()
         end
       end
 
-      -- Show welcome page when all files are clean
+      local show_welcome_page = require("codediff.ui.explorer.render").show_welcome_page
+
+      -- Show welcome page when all files are clean (skip if already showing)
       local total_files = #(status_result.unstaged or {}) + #(status_result.staged or {}) + #(status_result.conflicts or {})
       if total_files == 0 then
+        local lifecycle = require("codediff.ui.lifecycle")
+        local session = lifecycle.get_session(explorer.tabpage)
+        local already_welcome = session and welcome.is_welcome_buffer(session.modified_bufnr)
         clear_current_file()
-        show_welcome_page()
+        if not already_welcome then
+          show_welcome_page(explorer)
+        end
       end
 
       -- Re-select the currently viewed file after refresh.
@@ -339,7 +324,7 @@ function M.refresh(explorer)
         else
           -- File was committed/removed — show welcome
           clear_current_file()
-          show_welcome_page()
+          show_welcome_page(explorer)
         end
       end
     end)

lua/codediff/ui/explorer/render.lua

@@ -8,6 +8,48 @@ local nodes_module = require("codediff.ui.explorer.nodes")
 local tree_module = require("codediff.ui.explorer.tree")
 local keymaps_module = require("codediff.ui.explorer.keymaps")
 local refresh_module = require("codediff.ui.explorer.refresh")
+local welcome = require("codediff.ui.welcome")
+
+local function should_show_welcome(explorer)
+  if not explorer or not explorer.git_root or explorer.dir1 or explorer.dir2 then
+    return false
+  end
+
+  local status = explorer.status_result or {}
+  local total_files = #(status.unstaged or {}) + #(status.staged or {}) + #(status.conflicts or {})
+  return total_files == 0
+end
+
+local function show_welcome_page(explorer)
+  local lifecycle = require("codediff.ui.lifecycle")
+  local session = lifecycle.get_session(explorer.tabpage)
+  if not session then
+    return false
+  end
+
+  local mod_win = session.modified_win
+  if not mod_win or not vim.api.nvim_win_is_valid(mod_win) then
+    return false
+  end
+
+  if session.layout == "inline" then
+    local welcome_buf = welcome.create_buffer(vim.api.nvim_win_get_width(mod_win), vim.api.nvim_win_get_height(mod_win))
+    require("codediff.ui.view.inline_view").show_welcome(explorer.tabpage, welcome_buf)
+    return true
+  end
+
+  local orig_win = session.original_win
+  local width = vim.api.nvim_win_get_width(mod_win)
+  local height = vim.api.nvim_win_get_height(mod_win)
+  if orig_win and vim.api.nvim_win_is_valid(orig_win) then
+    width = vim.api.nvim_win_get_width(orig_win) + width + 1
+    height = vim.api.nvim_win_get_height(orig_win)
+  end
+
+  local welcome_buf = welcome.create_buffer(width, height)
+  require("codediff.ui.view.side_by_side").show_welcome(explorer.tabpage, welcome_buf)
+  return true
+end
 
 function M.create(status_result, git_root, tabpage, width, base_revision, target_revision, opts)
   opts = opts or {}
@@ -132,12 +174,14 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
     on_file_select = nil, -- Will be set below
     current_file_path = nil, -- Track currently selected file
     current_file_group = nil, -- Track currently selected file's group (staged/unstaged)
+    current_selection = nil, -- Full file selection used to replay current state
     is_hidden = false, -- Track visibility state
     visible_groups = vim.deepcopy(explorer_config.visible_groups or { staged = true, unstaged = true, conflicts = true }),
   }
 
   -- File selection callback - manages its own lifecycle
-  local function on_file_select(file_data)
+  local function on_file_select(file_data, opts)
+    opts = opts or {}
     local git = require("codediff.core.git")
     local view = require("codediff.ui.view")
     local lifecycle = require("codediff.ui.lifecycle")
@@ -164,7 +208,7 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
 
       -- Check if already displaying same file
       local session = lifecycle.get_session(tabpage)
-      if session and session.original_path == original_path and session.modified_path == modified_path then
+      if not opts.force and session and session.original_path == original_path and session.modified_path == modified_path then
         return
       end
 
@@ -190,7 +234,9 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
       vim.schedule(function()
         local sess = lifecycle.get_session(tabpage)
         if sess and sess.layout == "inline" then
-          require("codediff.ui.view.inline_view").show_single_file(tabpage, abs_path)
+          require("codediff.ui.view.inline_view").show_single_file(tabpage, abs_path, {
+            side = "modified",
+          })
         else
           require("codediff.ui.view.side_by_side").show_untracked_file(tabpage, abs_path)
         end
@@ -206,19 +252,31 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
 
         if base_revision and target_revision and target_revision ~= "WORKING" then
           if is_inline then
-            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, { revision = target_revision, git_root = git_root, rel_path = file_path })
+            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, {
+              revision = target_revision,
+              git_root = git_root,
+              rel_path = file_path,
+              side = "modified",
+            })
           else
             require("codediff.ui.view.side_by_side").show_added_virtual_file(tabpage, git_root, file_path, target_revision)
           end
         elseif group == "staged" then
           if is_inline then
-            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, { revision = ":0", git_root = git_root, rel_path = file_path })
+            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, {
+              revision = ":0",
+              git_root = git_root,
+              rel_path = file_path,
+              side = "modified",
+            })
           else
             require("codediff.ui.view.side_by_side").show_added_virtual_file(tabpage, git_root, file_path, ":0")
           end
         else
           if is_inline then
-            require("codediff.ui.view.inline_view").show_single_file(tabpage, abs_path)
+            require("codediff.ui.view.inline_view").show_single_file(tabpage, abs_path, {
+              side = "modified",
+            })
           else
             require("codediff.ui.view.side_by_side").show_untracked_file(tabpage, abs_path)
           end
@@ -235,14 +293,24 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
 
         if base_revision and target_revision and target_revision ~= "WORKING" then
           if is_inline then
-            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, { revision = base_revision, git_root = git_root, rel_path = file_path })
+            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, {
+              revision = base_revision,
+              git_root = git_root,
+              rel_path = file_path,
+              side = "original",
+            })
           else
             require("codediff.ui.view.side_by_side").show_deleted_virtual_file(tabpage, git_root, file_path, base_revision)
           end
         else
           if is_inline then
             local revision = (group == "staged") and "HEAD" or ":0"
-            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, { revision = revision, git_root = git_root, rel_path = file_path })
+            require("codediff.ui.view.inline_view").show_single_file(tabpage, file_path, {
+              revision = revision,
+              git_root = git_root,
+              rel_path = file_path,
+              side = "original",
+            })
           else
             require("codediff.ui.view.side_by_side").show_deleted_file(tabpage, git_root, file_path, abs_path, group)
           end
@@ -257,7 +325,7 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
     if session then
       local is_same_file = (session.modified_path == abs_path or (session.git_root and session.original_path == file_path))
 
-      if is_same_file then
+      if is_same_file and not opts.force then
         -- Check if it's the same diff comparison
         local is_staged_diff = group == "staged"
         local current_is_staged = session.modified_revision == ":0"
@@ -391,13 +459,21 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
   end
 
   -- Wrap on_file_select to track current file and group
-  explorer.on_file_select = function(file_data)
+  explorer.on_file_select = function(file_data, opts)
     explorer.current_file_path = file_data.path
     explorer.current_file_group = file_data.group
+    explorer.current_selection = vim.deepcopy(file_data)
     selected_path = file_data.path
     selected_group = file_data.group
     tree:render()
-    on_file_select(file_data)
+    on_file_select(file_data, opts)
+  end
+
+  -- Clear selection highlight (used when showing welcome page)
+  explorer.clear_selection = function()
+    selected_path = nil
+    selected_group = nil
+    tree:render()
   end
 
   -- Setup keymaps (delegated to keymaps module)
@@ -485,6 +561,31 @@ function M.create(status_result, git_root, tabpage, width, base_revision, target
   return explorer
 end
 
+function M.rerender_current(explorer)
+  if not explorer then
+    return false
+  end
+
+  if explorer.current_selection then
+    explorer.on_file_select(vim.deepcopy(explorer.current_selection), { force = true })
+    return true
+  end
+
+  local lifecycle = require("codediff.ui.lifecycle")
+  local session = lifecycle.get_session(explorer.tabpage)
+  if not session then
+    return false
+  end
+
+  if should_show_welcome(explorer) and show_welcome_page(explorer) then
+    return true
+  end
+
+  return false
+end
+
+M.show_welcome_page = show_welcome_page
+
 -- Setup auto-refresh on file save and focus
 
 return M

lua/codediff/ui/history/init.lua

@@ -11,6 +11,7 @@ local render = require("codediff.ui.history.render")
 -- width: optional width override
 -- opts: { range, path, ... } original options
 M.create = render.create
+M.rerender_current = render.rerender_current
 
 -- Navigation (files within expanded commits)
 M.navigate_next = render.navigate_next