prepare commit message for nixpkgs. put into .git/hooks/prepare-commit-msg

prepare-commit-msg.sh

#!/usr/bin/env bash

# shellcheck disable=SC2034
COMMIT_MSG_FILE=$1 # file which contains the commmit message
# shellcheck disable=SC2034
COMMIT_SOURCE=$2 # eg commit
# shellcheck disable=SC2034
SHA1=$3 # eg head

perl -i -ne 'print unless(m/^. Please enter the commit message/..m/^#$/)' "$COMMIT_MSG_FILE"

if [[ -z $SHA1 && -z $COMMIT_SOURCE ]] && type -P sponge &>/dev/null; then
  staged_files=$(git diff --cached --name-status | awk '{print $2}')
  staged_dirnames=()

  for line in $staged_files; do
    staged_dirnames+=("$(dirname "$line")")
  done

  if [[ $(echo "${staged_dirnames[@]}" | sed 's| |\n|g' | sort -u | wc -l) == 1 ]]; then
    changed_path=${staged_files[0]}

    # prefix   optional, gets prefixed to package
    # package  string to inject, a colon is added
    # message  whole message, no colon or prefix is added

    # nixpkgs
    if [[ $changed_path == nixos/modules/* ]]; then
      prefix="nixos/"
      package=$(basename "$staged_files" .nix)
    elif [[ $changed_path == pkgs/applications/kde/* ]]; then
      prefix="plasma5Packages."
      package=$(basename "$staged_files" .nix)
    elif [[ $changed_path == pkgs/applications/window-managers/i3/* ]]; then
      prefix="i3/"
      package=$(basename "$staged_files" .nix)
    elif [[ $changed_path == pkgs/applications/editors/vim/plugins/* ]]; then
      prefix="vimPlugins."
    elif [[ $changed_path == pkgs/desktops/gnome-3/* ]]; then
      prefix="gnome3."
    elif [[ $changed_path == pkgs/desktops/plasma-5/* ]]; then
      prefix="plasma5Packages."
    elif [[ $changed_path == pkgs/desktops/pantheon/* ]]; then
      prefix="pantheon."
    elif [[ $changed_path == pkgs/development/haskell-modules/* ]]; then
      prefix="haskellPackages"
    elif [[ $changed_path == pkgs/development/libraries/gstreamer/* ]]; then
      prefix="gst_all_1.gst-plugins-"
    elif [[ $changed_path == pkgs/development/libraries/kde-frameworks/* ]]; then
      prefix="kde-frameworks."
      package=$(basename "$staged_files" .nix)
    elif [[ $changed_path == pkgs/development/python-modules/* ]]; then
      prefix="python310Packages."
      package="$(basename "$(dirname "$changed_path")")"
    elif [[ $changed_path == pkgs/development/tools/ocaml/* ]]; then
      prefix="ocamlPackages."
    elif [[ $changed_path == ppkgs/development/tools/parsing/tree-sitter/grammars/* ]]; then
      message="tree-sitter: update grammars"
    elif [[ $changed_path == ppkgs/development/tools/parsing/tree-sitter/* ]]; then
      package="tree-sitter"
    elif [[ $changed_path == pkgs/misc/vscode-extensions/* ]]; then
      message="vscode-extensions."
    elif [[ $changed_path == pkgs/servers/monitoring/prometheus ]]; then
      prefix="prometheus."
      package=$(basename "$staged_files" .nix)
    elif [[ $changed_path == pkgs/top-level/perl-packages.nix ]]; then
      package="perlPackages."
    elif [[ $changed_path == pkgs/top-level/python-packages.nix ]]; then
      package="python310Packages"
    elif [[ $changed_path == pkgs/misc/vim-plugins/* ]]; then
      prefix="vimPlugins."
    elif [[ $changed_path == pkgs/* ]]; then
      package="$(basename "$(dirname "$changed_path")")"
    fi

    if [[ ! -v package ]]; then
      package=$(basename "$changed_path")
    fi

    if [[ ! -v message ]]; then
      # two spaces because core.editor vim trick puts us at the second last character for whatever reason
      message="$prefix$package: "
    fi

    echo -en "$message\n" | cat - "$COMMIT_MSG_FILE" | sponge "$COMMIT_MSG_FILE"
  fi
fi