Contributing Workflow for mathlib

A guide for the contribution process to mathlib4, the standard library for Lean 4.

Quick Start

One-time Setup

# Fork and clone using GitHub CLI (recommended)
gh repo fork leanprover-community/mathlib4 --default-branch-only --clone
cd mathlib4

# Or manually:
# 1. Fork on GitHub
# 2. Clone your fork: git clone https://github.com/YOUR_USERNAME/mathlib4.git
# 3. Add upstream: git remote add upstream https://github.com/leanprover-community/mathlib4.git

Daily Workflow

# Update master
git switch master
git pull

# Create feature branch
git switch -c my-feature-branch

# Make changes, commit, push
git add .
git commit -m "feat: add theorem X"
git push

# Open PR on GitHub or via CLI
gh pr create --fill

What to Contribute

Welcome Contributions

• Small fixes: docstring fixes, typo corrections
• Single lemma additions: to existing theories
• Extended theories: new theorems extending existing areas
• New theories: if within mathlib's scope

Scope Check

Ask before contributing new theories:

1. Is this typically taught in a mathematics department?
2. Does it align with maintainers' mathematical interests?
3. Can you find a reviewer?

If unsure, ask on Zulip in #mathlib.

External Projects

Consider creating a standalone repository with mathlib as a dependency if your work is outside scope.

Communication

• Use Zulip to discuss before and during work
• Add GitHub username to Zulip profile
• Set display name to real name

PR Conventions

Title Format

<type>(<optional-scope>): <subject>

Types: feat, fix, doc, style, refactor, test, chore, perf, ci

Examples:

feat(Data/Nat): add factorial function
fix(Algebra/Group): resolve instance synthesis issue
doc: improve module documentation

Description

• Use imperative, present tense
• Explain motivation and contrast with previous behavior
• Include : for breaking changes

Dependencies

Depends on: #1234

Git Workflow

Setup Remotes

git remote -v
# Should show:
# origin    https://github.com/YOUR_USERNAME/mathlib4.git
# upstream  https://github.com/leanprover-community/mathlib4.git

Creating PRs

# Keep master updated
git switch master
git pull

# Create branch
git switch -c my-feature

# Push and create PR
git push
gh pr create --fill

Working on Others' PRs

# Via GitHub CLI
gh pr checkout 1234

# Manually
git remote add contributor https://github.com/USERNAME/mathlib4.git
git fetch contributor
git checkout contributor/branch-name

Review Process

Finding Reviewers

• Anyone can review - not just maintainers
• Seek out reviewers yourself
• Partial reviews are helpful
• History of reviews → eligibility for reviewer/maintainer teams

What Reviewers Check

1. Style - follows naming, formatting
2. Documentation - doc strings present
3. Location - correct file/module
4. Improvements - can be simplified
5. Library integration - fits with existing API

Being Reviewed

• Be respectful and encouraging
• Leave room for alternative approaches
• Recognize you may be wrong
• Helpful reviews criteria for maintainer eligibility

Performance

Benchmarking

• Comment !bench on PR to trigger benchmarking
• Significant changes need proactive benchmarking:
  • New classes/instances
  • New simp lemmas
  • Changed imports
  • New definitions

Avoiding Regressions

• Profile before submitting
• Check impact on compilation time

Resources

• Main Contribution Guide
• Git Guide
• Commit Conventions
• PR Review Guide
• Zulip Chat
• Loogle (Declaration Search)
• mathlib4 Docs