Recipe: Git Commit Messages

This recipe creates a custom lectic commit subcommand that generates commit messages from your staged changes.

The Subcommand

Lectic looks for executables named lectic-<command> in your config directory, data directory, or PATH. Create ~/.config/lectic/lectic-commit:

#!/bin/bash
set -euo pipefail

# Check for staged changes
if git diff --cached --quiet; then
  echo "No staged changes" >&2
  exit 1
fi

lectic -f ~/.config/lectic/commit-prompt.lec -S

Make it executable:

chmod +x ~/.config/lectic/lectic-commit

The Prompt Template

Create ~/.config/lectic/commit-prompt.lec:

---
interlocutor:
  name: Assistant
  prompt: |
    You write git commit messages following the Conventional Commits
    specification. Output ONLY the commit message, nothing else.
    
    Format:
    <type>[optional scope]: <description>
    
    [optional body]
    
    Types: feat, fix, docs, style, refactor, perf, test, chore
    
    Rules:
    - Subject line max 50 characters
    - Use imperative mood ("add" not "added")
    - Body wraps at 72 characters
    - Explain what and why, not how
  provider: anthropic
  model: claude-3-haiku-20240307
  max_tokens: 500
---

Write a commit message for this diff:

:cmd[git diff --cached]

The :cmd[git diff --cached] directive runs git diff --cached and includes the output in the context sent to the LLM.

Usage

Stage your changes and run:

git add -p
lectic commit

Output:

feat(auth): add password strength validation

Implement zxcvbn-based password strength checking during registration.
Reject passwords scoring below 3 and display feedback to users.

Pipe directly to git

lectic commit | git commit -F -

Interactive edit before commit

lectic commit | git commit -eF -

Variations

Include recent commits for context

Modify the prompt to show recent history:

Recent commits for context:
:cmd[git log --oneline -5]

Write a commit message for this diff:
:cmd[git diff --cached]

Different styles

Create multiple prompt files for different projects:

• commit-prompt-conventional.lec — Conventional Commits
• commit-prompt-gitmoji.lec — Gitmoji style
• commit-prompt-simple.lec — Plain descriptions

Then modify the subcommand to accept an argument:

#!/bin/bash
set -euo pipefail

STYLE="${1:-conventional}"
PROMPT="$HOME/.config/lectic/commit-prompt-$STYLE.lec"

if [[ ! -f "$PROMPT" ]]; then
  echo "Unknown style: $STYLE" >&2
  exit 1
fi

if git diff --cached --quiet; then
  echo "No staged changes" >&2
  exit 1
fi

lectic -f "$PROMPT" -S

Usage: lectic commit gitmoji

Batch mode for multiple commits

Generate messages for each file separately:

#!/bin/bash
for file in $(git diff --cached --name-only); do
  echo "=== $file ==="
  # Create a temporary prompt with just this file's diff
  cat > /tmp/commit-single.lec << EOF
---
interlocutor:
  name: Assistant
  prompt: Write a conventional commit message for this change. Output only the message.
  model: claude-3-haiku-20240307
  max_tokens: 200
---

:cmd[git diff --cached -- "$file"]
EOF
  lectic -f /tmp/commit-single.lec -S
  echo
done