GitComet/README.md

GitComet

Fast, resource-efficient, fully open source Git GUI written in Rust, targeting GitKraken/SourceTree/GitHub Desktop-class workflows using gpui for the UI.

Goals

• Pure Rust Git backend (recommended: gix/gitoxide backend).
• Fast UI for very large repositories (virtualized lists, incremental loading, caching).
• Modular architecture with clear boundaries, to support benchmarking and testing.
• Drop-in replacement for git difftool and git mergetool with CLI compatibility for Meld and KDiff3.

Workspace layout

• crates/gitcomet-core: domain types, merge algorithm, conflict session, text utils.
• crates/gitcomet-git: Git abstraction + no-op backend.
• crates/gitcomet-git-gix: gix/gitoxide backend implementation.
• crates/gitcomet-state: MVU state store, reducers, effects, conflict session management.
• crates/gitcomet-ui: UI model/state (toolkit-independent).
• crates/gitcomet-ui-gpui: gpui views/components (focused diff/merge windows, conflict resolver, word diff).
• crates/gitcomet-app: binary entrypoint, CLI (clap), difftool/mergetool/setup modes.

Getting started

Offline-friendly default build (does not build the UI or the Git backend):

cargo build

To build the actual app you'll enable features (requires network for dependencies):

cargo build -p gitcomet-app --features ui,gix

To also compile the gpui-based UI crate:

cargo build -p gitcomet-app --features ui-gpui,gix

Run (opens the repo passed as the first arg, or falls back to the current directory):

cargo run -p gitcomet-app --features ui-gpui,gix -- /path/to/repo

Using as a Git difftool / mergetool

GitComet can be used as a standalone diff and merge tool invoked by git difftool and git mergetool. It supports both headless (algorithm-only) and GUI (interactive GPUI window) modes.

Automatic setup

The built-in setup command configures Git globally:

gitcomet-app setup

This registers both headless and GUI tool variants with guiDefault=auto, so Git automatically picks the GUI tool when a display is available and falls back to headless otherwise.

Manual setup

GITGPUI_BIN="/absolute/path/to/gitcomet-app"

# Headless tool — algorithm-only merge/diff for CI, scripts, and no-display environments
git config --global merge.tool gitcomet
git config --global mergetool.gitcomet.cmd \
  "'$GITGPUI_BIN' mergetool --base \"\$BASE\" --local \"\$LOCAL\" --remote \"\$REMOTE\" --merged \"\$MERGED\""
git config --global mergetool.gitcomet.trustExitCode true
git config --global mergetool.prompt false

git config --global diff.tool gitcomet
git config --global difftool.gitcomet.cmd \
  "'$GITGPUI_BIN' difftool --local \"\$LOCAL\" --remote \"\$REMOTE\" --path \"\$MERGED\""
git config --global difftool.gitcomet.trustExitCode true
git config --global difftool.prompt false

# GUI tool — opens focused GPUI windows for interactive diff/merge
git config --global merge.guitool gitcomet-gui
git config --global mergetool.gitcomet-gui.cmd \
  "'$GITGPUI_BIN' mergetool --gui --base \"\$BASE\" --local \"\$LOCAL\" --remote \"\$REMOTE\" --merged \"\$MERGED\""
git config --global mergetool.gitcomet-gui.trustExitCode true

git config --global diff.guitool gitcomet-gui
git config --global difftool.gitcomet-gui.cmd \
  "'$GITGPUI_BIN' difftool --gui --local \"\$LOCAL\" --remote \"\$REMOTE\" --path \"\$MERGED\""
git config --global difftool.gitcomet-gui.trustExitCode true

# Auto-select GUI tool when DISPLAY is available, headless otherwise
git config --global mergetool.guiDefault auto
git config --global difftool.guiDefault auto

CLI modes

Difftool:

gitcomet-app difftool --local <path> --remote <path> [--path <display_name>] [--label-left <label>] [--label-right <label>]

Also reads LOCAL/REMOTE from environment as a fallback when invoked by Git.

Mergetool:

gitcomet-app mergetool --local <path> --remote <path> --merged <path> [--base <path>] [--label-local <label>] [--label-remote <label>] [--label-base <label>]

Also reads LOCAL/REMOTE/MERGED/BASE from environment. Base is optional for add/add conflicts.

Compatibility

KDiff3 and Meld invocation forms are supported (--L1/--L2/--L3, -o/--output/--out, --base, positional arguments), so GitComet can be a drop-in replacement.

Exit codes

Code	Meaning
0	User completed the action and the result was saved
1	User canceled or closed with unresolved result
>=2	Input, I/O, or internal error

Testing

Full headless test suite (CI mode):

cargo test --workspace --no-default-features --features gix

Clippy (CI mode):

cargo clippy --workspace --no-default-features --features gix -- -D warnings

The test suite covers:

• Core merge algorithm (ported from Git t6403/t6427)
• KDiff3-style fixture harness with permutation corpus
• Meld algorithm parity tests
• Git mergetool and difftool E2E integration
• Standalone tool mode (CLI arg/env parsing, compatibility forms, exit codes)
• State management (reducers, effects, conflict sessions)
• UI components (focused merge/diff windows, word diff, conflict resolver)

Profiling (Callgrind)

To profile the app with Valgrind Callgrind (interactive on/off instrumentation):

bash scripts/profile-callgrind.sh --open -- /path/to/repo

Crash logs

If the app crashes due to a Rust panic, GitComet writes a crash log to:

• Linux: $XDG_STATE_HOME/gitcomet/crashes/ (fallback: ~/.local/state/gitcomet/crashes/)
• macOS: ~/Library/Logs/gitcomet/crashes/
• Windows: %LOCALAPPDATA%\gitcomet\crashes\ (fallback: %APPDATA%\gitcomet\crashes\)

On next startup, GitComet can prompt you to report the crash as a prefilled GitHub issue in Auto-Explore/GitComet, including app version, platform, panic details, and a trimmed backtrace.

Roadmap (high level)

• Open repositories; show status + commit history timeline.
• Branch/remote tracking; pull/push; fetch with progress.
• Stash create/apply/drop; discard changes; stage/unstage.
• Visualize branch/merge topology from refs (commit graph lanes).
• Benchmarks for log/graph/status/diff on large repos.

License

GitComet is licensed under the GNU Affero General Public License Version 3 (AGPL-3.0-only). See LICENSE-AGPL-3.0.

Copyright (C) 2026 AutoExplore Oy
Contact: info@autoexplore.ai