determine-semver-from-conventional-commit.sh

#!/usr/bin/env bash

# Note on examples:
# - Uses null byte (%x00) as delimiter via git log --format=%B%x00
# - %B outputs the raw commit message body
# - read -d $'\0' reads until null byte, naturally handling multi-line commits
# - Works reliably with any commit message content (including special characters)

# Examples:
# Get change type for commits between v1.0.0 and HEAD
# git log v1.0.0..HEAD --format=%B%x00 | ./determine-semver-from-conventional-commit.sh

# Get change type for commits between two tags
# git log v1.0.0..v2.0.0 --format=%B%x00 | ./determine-semver-from-conventional-commit.sh

# Get change type for last 10 commits
# git log -10 --format=%B%x00 | ./determine-semver-from-conventional-commit.sh

# Function to determine change type for a single commit
get_change_type() {
    local COMMIT_MSG="$1"
    local FIRST_LINE=$(echo "$COMMIT_MSG" | head -n 1)
    local CHANGE_TYPE="patch"
    
    # Check for breaking changes (highest priority)
    if [[ "$FIRST_LINE" =~ ^[a-z]+(\([^\)]+\))?\!\:(.*) ]]; then
        CHANGE_TYPE="major"
    elif echo "$COMMIT_MSG" | grep -qE "^(BREAKING CHANGE:|BREAKING-CHANGE:)"; then
        CHANGE_TYPE="major"
    elif [[ "$FIRST_LINE" =~ ^feat(\([^\)]+\))?\: ]]; then
        CHANGE_TYPE="minor"
    fi
    
    echo "$CHANGE_TYPE"
}

# If argument provided, process single commit
if [ -n "$1" ]; then
    get_change_type "$1"
    exit 0
fi

# Otherwise, read multiple commits from stdin using null byte delimiter
HIGHEST="patch"

while IFS= read -r -d $'\0' commit; do
    # Skip empty commits
    [ -z "$commit" ] && continue
    
    TYPE=$(get_change_type "$commit")
    
    # Update highest if needed (major > minor > patch)
    if [ "$TYPE" = "major" ]; then
        HIGHEST="major"
        break  # Can't go higher than major
    elif [ "$TYPE" = "minor" ] && [ "$HIGHEST" = "patch" ]; then
        HIGHEST="minor"
    fi
done

echo "$HIGHEST"