✓ Stable v0.1.0

🔀 fit

Terminal-based merge conflict resolver written in Fortran

fit is a modern terminal-based tool for resolving Git merge conflicts. Features a three-pane TUI with side-by-side incoming/local comparison and live preview of the resolved file. Supports both interactive resolution and automated CI/CD workflows with command-line flags.

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Installation

fit is available for Fedora/RHEL, Arch Linux (AUR), macOS (Homebrew), and can be built from source using Make or the Fortran Package Manager (fpm).

Fedora / RHEL 9

# Add the musicsian repository (first time only) sudo dnf config-manager --add-repo https://repos.musicsian.com/musicsian.repo # Install fit sudo dnf install fit

Arch Linux (AUR)

# Install via AUR helper yay -S fit

macOS (Homebrew)

# Tap the repository and install brew tap FortranGoingOnForty/fit brew install fit

From Source

# Prerequisites: gfortran >= 4.8 sudo dnf install gcc-gfortran make # Clone and build git clone https://github.com/FortranGoingOnForty/fit.git cd fit make sudo make install # Install to /usr/bin

Quick Start

Open a file with merge conflicts to start resolving:

# After a merge with conflicts git merge feature-branch # Open fit to resolve fit conflicted-file.txt # In the TUI: # - Press 'i' to choose incoming (remote) # - Press 'l' to choose local (your branch) # - Press 'b' to keep both versions # - Press 'n' to go to next conflict # - Press 's' to save and exit

Git Integration

Configure fit as your default merge tool:

# Configure fit as merge tool git config --global merge.tool fit git config --global mergetool.fit.cmd 'fit "$MERGED"' git config --global mergetool.fit.trustExitCode true # Then use during merge conflicts git merge feature-branch git mergetool # Opens fit for each conflicted file

Dependencies

Build: gfortran ≥ 4.8, make
Runtime: glibc, git

Command-Line Options

Option	Type	Default	Description
`fit <file>`	command	-	Open file in interactive TUI mode
`--incoming, -i`	flag	-	Auto-resolve all conflicts with incoming (remote) version
`--local, -l`	flag	-	Auto-resolve all conflicts with local (current) version
`--both, -b`	flag	-	Auto-resolve all conflicts with both versions combined

Exit Codes

0 - Success (file resolved and saved)
1 - Error (file not found, parse error, or quit without saving)

Git Mergetool Configuration

Configure fit as your default merge tool by adding to ~/.gitconfig:

[merge] tool = fit [mergetool "fit"] cmd = fit "$MERGED" trustExitCode = true

Environment Variables

fit does not use environment variables. Terminal dimensions are auto-detected via stty size. ANSI color support is assumed (256-color terminal recommended).

Terminal Requirements

Minimum size: 80 columns x 24 rows
Color support: 256-color recommended
ANSI escape codes: Required

Tested on: Linux terminals (xterm, GNOME Terminal, Konsole), macOS Terminal, iTerm2, SSH sessions, tmux, and screen.

Overview

fit is a terminal-based merge conflict resolver designed as a lightweight alternative to vimdiff and meld. It provides an intuitive three-pane interface for visual side-by-side conflict comparison and interactive resolution.

Key Features

Three-Pane Display: Incoming, local, and live preview
Keyboard-Driven: Simple single-key commands
Scrollable Panes: Navigate large conflicts easily
Auto-Resolution: CLI flags for CI/CD automation
Git Integration: Works as a git mergetool
Lightweight: ~2MB binary, fast startup

Three-Pane Interface

Layout

The TUI displays conflicts in a split-screen layout:

┌───────────────────────────────────────────────────────┐
│ INCOMING                    │ LOCAL                    │
│ (from remote/HEAD)          │ (current branch)         │
├───────────────────────────────────────────────────────┤
│ PREVIEW - Live resolution showing resolved file       │
│                                                        │
├───────────────────────────────────────────────────────┤
│ [i]ncoming [l]ocal [b]oth | [n]ext [p]rev | [s]ave   │
└───────────────────────────────────────────────────────┘

Top panes (40%): Side-by-side incoming and local versions
Bottom pane (60%): Full-file preview with all conflicts resolved
Status bar: Keybindings and conflict counter

Pane Navigation

Use arrow keys to switch between panes and scroll within them:

← / → - Switch to previous/next pane
↑ / ↓ - Scroll within active pane

The active pane is highlighted with a yellow border and ◀ indicator. Each pane has independent scrolling.

Color Coding

Incoming pane: Green + prefix on conflict lines
Local pane: Red - prefix on conflict lines
Preview pane: Bold cyan for resolved content
Context lines: Dimmed gray (non-conflict portions)

Comparison to Other Tools

Feature	fit	vimdiff	meld
Terminal-based	Yes	Yes	No
Three-pane view	Yes	Yes	Yes
Auto-resolve flags	Yes	No	No
Simple keybindings	Yes	Complex	N/A
Binary size	~2MB	Large	Large
No X11 required	Yes	Yes	No

System Overview

fit is implemented in approximately 3,500 lines of modern Fortran across 6 specialized modules. The architecture follows a clean separation of concerns: terminal control, conflict parsing, resolution logic, and TUI rendering.

Codebase Statistics

Total: ~3,500 lines of Fortran
Modules: 6 specialized modules
Build System: Makefile + fpm.toml
Binary Size: ~2MB (release build)

Module Structure

fit/
├── app/
│   └── main.f90              # Entry point, event loop
├── src/
│   ├── terminal_control.f90  # ANSI terminal control
│   ├── pane_state.f90        # Pane state and scrolling
│   ├── conflict_parser.f90   # Parse conflict markers
│   ├── resolution_engine.f90 # Write resolved files
│   ├── keyboard_input.f90    # Key detection
│   └── tui_layout.f90        # Three-pane rendering
└── test/                     # Test conflict files

Terminal Control

The terminal_control.f90 module handles ANSI terminal manipulation:

Screen clearing and cursor positioning
Color codes (foreground, background, styles)
Terminal size detection via stty size
Raw mode input enabling

Conflict Parser

The conflict_parser.f90 module extracts conflict data:

type conflict_t
    integer :: start_line, middle_line, end_line
    character(len=:), allocatable :: incoming_branch
    character(len=:), allocatable :: local_branch
    character(len=:), allocatable :: incoming_lines(:)
    character(len=:), allocatable :: local_lines(:)
    character(len=:), allocatable :: context_before(:)
    character(len=:), allocatable :: context_after(:)
    integer :: choice  ! 0=none, 1=incoming, 2=local, 3=both
end type

Uses two-pass parsing: first reads all lines, then identifies conflict markers and extracts components with 5 lines of context.

Resolution Engine

The resolution_engine.f90 module writes resolved files:

Validates all conflicts are resolved before writing
Single-pass file rewriting
Uses temporary file + atomic rename for safety

Data Flow

Input File
    ↓
┌─────────────────────────────────┐
│ conflict_parser                 │
│ Parse markers → conflict_t[]   │
└─────────────────────────────────┘
    ↓
┌─────────────────────────────────┐
│ Non-interactive mode?           │
│ → Set choices, write, exit      │
└─────────────────────────────────┘
    ↓
┌─────────────────────────────────┐
│ Event Loop                      │
│ 1. tui_layout: Draw panes       │
│ 2. keyboard_input: Wait for key │
│ 3. Process: Update choice/nav   │
│ 4. Loop                         │
└─────────────────────────────────┘
    ↓
┌─────────────────────────────────┐
│ resolution_engine               │
│ Write resolved file             │
└─────────────────────────────────┘

Resolution Selection

Option	Type	Default	Description
`i`	key	-	Select incoming (remote/HEAD) version
`l`	key	-	Select local (current branch) version
`b`	key	-	Select both versions (incoming then local)

Navigation

Option	Type	Default	Description
`n`	key	-	Go to next conflict
`p`	key	-	Go to previous conflict
`Arrow Left`	key	-	Switch to previous pane
`Arrow Right`	key	-	Switch to next pane
`Arrow Up`	key	-	Scroll up in active pane
`Arrow Down`	key	-	Scroll down in active pane

File Operations

Option	Type	Default	Description
`s`	key	-	Save resolved file and exit
`q`	key	-	Quit without saving
`ESC`	key	-	Same as q - quit without saving

Quick Reference

RESOLUTION i Select incoming (remote/HEAD) l Select local (current branch) b Select both (incoming then local) NAVIGATION n Next conflict p Previous conflict ←/→ Switch pane (incoming ↔ local ↔ preview) ↑/↓ Scroll within active pane FILE OPERATIONS s Save resolved file and exit q Quit without saving ESC Same as q

Status Bar

The bottom status bar shows:

[i/l/b] choose | [←→] pane | [↑↓] scroll | [n/p] conflict | [s]ave [q]uit  (1/5)

The right side shows the current conflict number (e.g., "1/5" = first of 5 conflicts).

🔀 fit

Installation

Fedora / RHEL 9

Arch Linux (AUR)

macOS (Homebrew)

From Source

Quick Start

Git Integration

Dependencies

Command-Line Options

Exit Codes

Git Mergetool Configuration

Environment Variables

Terminal Requirements

Overview

Key Features

Three-Pane Interface

Layout

Pane Navigation

Color Coding

Conflict Resolution

Incoming (i)

Local (l)

Both (b)

Workflow Examples

Interactive Resolution

CI/CD Automation

Comparison to Other Tools

System Overview

Codebase Statistics

Module Structure

Terminal Control

Conflict Parser

Resolution Engine

Data Flow

Conflict Detection

Resolution Selection

Navigation

File Operations

Quick Reference

Status Bar

Common Issues

Terminal display corrupted

File not found

"No merge conflicts found"

"Not all conflicts resolved" when saving

Keyboard input doesn't work

Git Integration Issues

fit not working as git mergetool

Performance

Known Limitations

Debugging