Commit Hygiene

┌─────────────────────────────────────────────────────────────────┐
│  ATOMIC COMMITS                                                  │
│  ─────────────────────────────────────────────────────────────  │
│  One logical change per commit.                                  │
│  Each commit should be self-contained and deployable.            │
│  If you need "and" to describe it, split it.                     │
├─────────────────────────────────────────────────────────────────┤
│  SMALL PRS WIN                                                   │
│  ─────────────────────────────────────────────────────────────  │
│  < 400 lines changed = reviewed in < 1 hour                      │
│  > 1000 lines = likely rubber-stamped or abandoned               │
│  Smaller PRs = faster reviews, fewer bugs, easier reverts        │
├─────────────────────────────────────────────────────────────────┤
│  COMMIT EARLY, COMMIT OFTEN                                      │
│  ─────────────────────────────────────────────────────────────  │
│  Working code? Commit it.                                        │
│  Test passing? Commit it.                                        │
│  Don't wait for "done" - commit at every stable point.           │
└─────────────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────────────┐
│  IDEAL COMMIT                                                    │
│  ─────────────────────────────────────────────────────────────  │
│  Files: 1-5                                                      │
│  Lines: 50-200 total changes                                     │
│  Scope: Single logical unit of work                              │
│  Message: Describes ONE thing                                    │
└─────────────────────────────────────────────────────────────────┘

# See what's changed (staged + unstaged)
git status --short

# Count files and lines changed
git diff --stat
git diff --cached --stat  # Staged only

# Get totals
git diff --shortstat
# Example output: 8 files changed, 245 insertions(+), 32 deletions(-)

# Full diff summary with file names
git diff --stat HEAD

# Just the numbers
git diff --numstat HEAD | awk '{add+=$1; del+=$2} END {print "+"add" -"del" total:"add+del}'

# Files changed count
git status --porcelain | wc -l

#!/bin/bash
# scripts/check-commit-size.sh

# Thresholds
MAX_FILES=10
MAX_LINES=400
WARN_FILES=5
WARN_LINES=200

# Get stats
FILES=$(git status --porcelain | wc -l | tr -d ' ')
STATS=$(git diff --shortstat HEAD 2>/dev/null)
INSERTIONS=$(echo "$STATS" | grep -oE '[0-9]+ insertion' | grep -oE '[0-9]+' || echo 0)
DELETIONS=$(echo "$STATS" | grep -oE '[0-9]+ deletion' | grep -oE '[0-9]+' || echo 0)
TOTAL=$((INSERTIONS + DELETIONS))

echo "📊 Current changes: $FILES files, +$INSERTIONS -$DELETIONS ($TOTAL total lines)"

# Check thresholds
if [ "$FILES" -gt "$MAX_FILES" ] || [ "$TOTAL" -gt "$MAX_LINES" ]; then
    echo "🔴 RED ZONE: Commit immediately! Changes are too large."
    echo "   Consider splitting into multiple commits."
    exit 1
elif [ "$FILES" -gt "$WARN_FILES" ] || [ "$TOTAL" -gt "$WARN_LINES" ]; then
    echo "🟡 WARNING: Changes getting large. Commit soon."
    exit 0
else
    echo "🟢 OK: Changes are within healthy limits."
    exit 0
fi

✅ "Add email validation to signup form"
   - 3 files: validator.ts, signup.tsx, signup.test.ts
   - 120 lines changed
   - Single purpose: email validation

✅ "Fix null pointer in user lookup"
   - 2 files: userService.ts, userService.test.ts
   - 25 lines changed
   - Single purpose: fix one bug

✅ "Refactor: Extract PaymentProcessor class"
   - 4 files: payment.ts → paymentProcessor.ts + types
   - 180 lines changed
   - Single purpose: refactoring

❌ "Add authentication, fix bugs, update styles"
   - 25 files changed
   - 800 lines changed
   - Multiple purposes mixed

❌ "WIP"
   - Unknown scope
   - No clear purpose
   - Hard to review/revert

❌ "Updates"
   - 15 files changed
   - Mix of features, fixes, refactors
   - Impossible to review properly

Instead of one commit with:
  - API endpoint + database migration + frontend + tests

Split into:
  1. "Add users table migration"
  2. "Add User model and repository"
  3. "Add GET /users endpoint"
  4. "Add UserList component"
  5. "Add integration tests for user flow"

Instead of one commit with:
  - All CRUD operations for users

Split into:
  1. "Add create user functionality"
  2. "Add read user functionality"
  3. "Add update user functionality"
  4. "Add delete user functionality"

Instead of:
  - Feature + refactoring mixed

Split into:
  1. "Refactor: Extract validation helpers" (no behavior change)
  2. "Add email validation using new helpers" (new feature)

Instead of:
  - Safe changes + risky changes together

Split into:
  1. "Update dependencies" (safe, isolated)
  2. "Migrate to new API version" (risky, separate)

┌─────────────────────────────────────────────────────────────────┐
│  RESEARCH FINDINGS (Google, Microsoft studies)                  │
│  ─────────────────────────────────────────────────────────────  │
│  PRs < 200 lines: 15% defect rate                               │
│  PRs 200-400 lines: 23% defect rate                             │
│  PRs > 400 lines: 40%+ defect rate                              │
│                                                                 │
│  Review quality drops sharply after 200-400 lines.              │
│  Large PRs get "LGTM" rubber stamps, not real reviews.          │
└─────────────────────────────────────────────────────────────────┘

# Check PR size before creating
git diff main --stat
git diff main --shortstat

# If too large, consider:
# 1. Split into multiple PRs (stacked PRs)
# 2. Create feature flag and merge incrementally
# 3. Use draft PR for early feedback

<type>: <description> (50 chars max)

[optional body - wrap at 72 chars]

[optional footer]

feat: Add email validation to signup form

fix: Prevent null pointer in user lookup

refactor: Extract PaymentProcessor class

test: Add integration tests for checkout flow

chore: Update dependencies to latest versions