mergers

A visual diff and merge tool written in Rust with GTK4, inspired by Meld.

WARNING: This software is alpha-quality and under active development. It may eat your files, corrupt your data, or silently discard changes. Always keep backups and use version control. You have been warned.

Features

• Two-way file comparison with syntax highlighting (GtkSourceView 5)
• Three-way merge for resolving conflicts
• Directory comparison with recursive scanning and async background diffing
• Git integration — run mergers . to view uncommitted changes
• Inline word-level diff highlighting
• Ignore whitespace / blank lines options (with persistent defaults in preferences)
• Find & Replace within panes
• Go to line (Ctrl+L)
• Undo / Redo
• Chunk navigation with keyboard shortcuts (with optional wrap-around)
• Synchronized scrolling — chunk-aware vertical sync keeps corresponding lines aligned
• Chunk map — visual overview strips alongside each pane with viewport indicator
• Patch export (unified diff format)
• Refresh (Ctrl+R / F5) — reload files from disk with unsaved-changes confirmation
• Open externally (Ctrl+Shift+O) — open focused file in system default app
• Save As (Ctrl+Shift+S) — save focused pane to a new path
• Save All (Ctrl+Shift+L) — save all dirty panes at once
• Blank Comparison — start with empty panes for quick scratch diffs
• New Comparison (Ctrl+N) — open a new comparison tab from any window
• Tab navigation — Ctrl+Alt+PageUp/Down and Alt+1-9 to switch tabs
• Swap panes
• Custom pane labels via -L flag
• Directory copy/delete operations
• File watcher — auto-reloads when files change on disk
• Configurable folder filters (exclude patterns like node_modules, .git, etc.)
• Insert spaces instead of tabs option
• Show whitespace characters (spaces, tabs, newlines)
• Keyboard shortcuts reference — accessible from the preferences dialog
• Preferences dialog — font, color scheme, tab width, editor & comparison defaults, filters, with live preview
• Binary file detection — prevents loading binary files into text buffers

Installation

macOS (Homebrew)

brew install joske/mergers/mergers

This downloads a pre-built binary (apple silicon - on intel it will build from source) and pulls in GTK4 and GtkSourceView 5 automatically.

Linux (Arch)

mergers is in the AUR, use your AUR helper of choice:

yay -S mergers

Linux (AppImage)

Download the latest AppImage from GitHub Releases:

chmod +x mergers-x86_64.AppImage
./mergers-x86_64.AppImage

Windows (x86_64 & aarch64)

Download the latest build from GitHub Releases:

From crates.io

Requires GTK4 and GtkSourceView 5 development libraries (see Building).

cargo install mergers

From source

See Building below.

Usage

# Compare two files
mergers file1.txt file2.txt

# Compare two directories
mergers dir1/ dir2/

# Three-way merge (left, merged, right)
mergers local.txt merged.txt remote.txt

# View uncommitted git changes
mergers .

# Custom labels
mergers file1.txt file2.txt -L "Original" -L "Modified"

Git Mergetool

To use mergers as your git merge tool:

git config --global merge.tool mergers
git config --global mergetool.mergers.cmd 'mergers "$LOCAL" "$MERGED" "$REMOTE"'
git config --global mergetool.mergers.trustExitCode true

Then resolve conflicts with:

git mergetool

Comparison with Similar Tools

Building

Requires GTK4 and GtkSourceView 5 development libraries.

# Debian/Ubuntu
sudo apt install libgtk-4-dev libgtksourceview-5-dev

# Fedora
sudo dnf install gtk4-devel gtksourceview5-devel

# Arch
sudo pacman -S gtk4 gtksourceview5

# macOS
brew install gtk4 gtksourceview5

# Build
cargo build --release

Testing

mergers uses a three-layer testing strategy:

Layer 1 — Pure unit tests (Rust)

Core algorithms (Myers diff, chunk navigation, merge logic, gutter hit-testing, chunk-map geometry) are extracted into pure functions in src/ui/diff_state.rs and src/ui/merge_state.rs and covered by cargo test. These run headlessly on every CI push — no display server needed.

cargo test

Layer 2 — UI integration tests (dogtail / AT-SPI)

Higher-level tests drive the real GTK4 application via the AT-SPI accessibility bus using dogtail. They exercise file comparison, directory comparison, VCS mode, and keyboard shortcuts end-to-end. An X virtual framebuffer (Xvfb) is used so tests run headlessly in CI.

Test files live in tests/ui_integration/. Dependencies are managed in a local venv:

# First time — sets up the venv and installs dogtail
make test-release

# Subsequent runs
make test-release

make test-release runs cargo test followed by pytest tests/ui_integration/ -v under dbus-run-session + xvfb-run.

Required system packages (Debian/Ubuntu)

sudo apt install \
  libgtksourceview-5-dev \
  xvfb \
  fonts-dejavu-core \
  at-spi2-core \
  gir1.2-atspi-2.0 \
  gir1.2-gtk-3.0 \
  dbus-x11 \
  xdotool \
  python3-pip \
  python3-gi

Running UI tests manually (with a display)

source tests/ui_integration/.venv/bin/activate
pytest tests/ui_integration/ -v

Layer 3 — Benchmarks (Criterion)

Performance-critical paths are benchmarked with Criterion at large-project scale (50k–500k lines). Benchmarks cover Myers diff, chunk navigation, conflict detection, VCS parsing, and merge state operations. Property tests (proptest) verify optimized algorithms match naive reference implementations.

cargo bench

Benchmarks run automatically on pull requests via .github/workflows/bench.yml.

CI

The .github/workflows/ui-tests.yml workflow runs the full suite on every push, installing at-spi2-core and xdotool from the system package manager before invoking make test-release.

License

GPL-2.0