twain

"…and never the twain shall meet." — Rudyard Kipling

A simple diff tool. Side-by-side file diff with intra-line highlighting, side-by-side folder tree compare with synced expand/scroll/selection, and click-arrow-to-merge editing.

Build

Requires Qt 6 (Widgets) and CMake.

make build

The binary lands at build/twain.

Usage

twain                       # empty workspace; use File > Open to load
twain left right            # auto-detect: two files or two directories
twain -h                    # CLI help
twain --version

Folder pair vs file pair

If both arguments are directories, twain opens the folder-compare view (synced two-pane tree, blue for orphans, red for different). Otherwise it opens the file-diff view (side-by-side text with red change highlights).

Tabs and shortcuts

Each opened pair is a tab. Drilling into a differing file from a folder tab opens it in a new tab.

Shortcut	Action
Ctrl+O	Open file pair
Ctrl+Shift+O	Open folder pair
Ctrl+W	Close current tab
Ctrl+S	Save edits in the current diff tab
F5	Refresh
F7 / Ctrl+N	Next difference (or next differing file in a tree)
Shift+F7 / Ctrl+P	Previous difference
Ctrl+M	Jump to the next differing file

In a diff tab, click a yellow arrow in the gutter to copy that hunk to the other side. Then save (Ctrl+S) to write both files to disk.

git integration

twain is designed to drop in as a git difftool. Print the config commands and pipe them through sh:

build/twain --git-config | sh

That sets:

git config --global diff.tool twain
git config --global difftool.twain.cmd '/abs/path/to/twain "$LOCAL" "$REMOTE"'
git config --global difftool.prompt false

Drop --global to set per-repo only.

Then use it:

git difftool -d              # tree view: all changed files at once
git difftool -d HEAD~1       # tree view vs a revision
git difftool -d HEAD~1 HEAD  # what a commit changed (like 'git show')
git difftool                 # one file at a time (default)

The -d / --dir-diff flag is what gives you the side-by-side folder tree. Without it, git invokes the difftool once per changed file.

A handy alias for the tree view:

git config --global alias.dd 'difftool --dir-diff'

The same info is available in-app under Help → Configure as git difftool….

Editing

Direct typing works in either pane (Phase B): edit, Ctrl+S to save. Undo/redo (Ctrl+Z / Ctrl+Y) works during a typing session and clears on the next diff rebuild (after save or refresh).

Yellow merge arrows in the gutter copy a whole hunk from one side to the other; the destination rows are marked with a yellow vertical bar so you can see what was just changed.

View options

Under the View menu:

• Ignore Case — fold case for diff matching
• Ignore Whitespace — collapse whitespace runs and strip leading/trailing
• Ignore Blank Lines — drop blank lines before diffing

These are persisted across sessions and apply to all open diff tabs.

License

MIT — see LICENSE.