Fish Shell: Generate a clean changelog between two Git revisions

changes.fish

function changes -d "Generate a Markdown changelog from conventional commits" -a target

    # Use fallback variables if no arguments were given.
    if test (count $argv) -eq 0
        set target master
    end

    # Include commit message, author name, and the short hash in parentheses.
    set -l log_format "%s (_%aN_) (%h)"

    # Compare against HEAD (the latest commit).
    set -l source "HEAD"

    # Filter to commits that pass the conventional commit format.
    # See: https://www.conventionalcommits.org/
    set -l commit_filter "^[a-z]+(\([a-z]+\))?:\s.+"

    # Prefix each line with '- ' to render a Markdown list.
    set -l prefix '{print "- " $0}'

    # Write changelog header
    echo -e "## `$target`\n\n"
    echo -e "Write your release notes on this line.\n\n"

    # Fill and sort the actual changelog
    git log --oneline --pretty=format:$log_format $source...$target \
    | grep -E "$commit_filter" \
    | sort -k1 \
    | awk "$prefix"

end