Create & manage GHC package environment files

cabal-env.sh

#!/bin/bash

set -e

show_usage () {
    cat <<EOF
Usage: $0 [-n <env-name>] (-r | -l | [DEP]+)"

Creates GHC package environment named '<env-name>' (default = 'default')
containing the specified deps.

Flags:

  -n <env-name>   set environment name to operate on;
                  use the special env-name '.' to create a
                  local '.ghc.environment' file in the current folder.
                  (default: 'default')

  -r              deletes the specified environment (via -n)

  -l              lists available environments for current 'ghc'
                  (cannot be combined with other flags)

  -i              create temporary environment and invoke GHCi with it
                  (cannot be combined with other flags)


GHC Package environments are supported since GHC 8.0.2 and Cabal 2.2;
By default, the environment named 'default' is loaded by GHC and GHCi
if it exists.

You can select a specific package environment for GHC(i) via e.g.
'ghci -package-env myenv' or by setting an environment variable
'GHC_ENVIRONMENT=myenv ghci'

Examples:

  $0 -n lens 'lens == 4.15.*' 'lens-aeson == 1.0.*' http-streams

  $0 unordered-containers QuickCheck quickcheck-instances

EOF
    exit 1
}

get_ghc_triplet () {
    GHC_TARGET=$(ghc --print-target-platform)
    GHC_VER=$(ghc --numeric-version)
    trip_pat="([^-]*)-([^-]*)-(.*)"

    [[ $GHC_TARGET =~ $trip_pat ]]

    TRIPLET="${BASH_REMATCH[1]}-${BASH_REMATCH[3]}-${GHC_VER}"

    ENVSDIR="${HOME}/.ghc/${TRIPLET}/environments/"
}

remove=false
list=false
run_ghci=false

envname="default"

while getopts lrin: flag; do
    case $flag in
        n) envname="$OPTARG"
           ;;

        r) remove=true
           ;;

        l) list=true
           ;;

        i) run_ghci=true
           ;;

        ?) show_usage
           ;;
    esac
done

shift $((OPTIND - 1))

if $list; then
    if [ $# -ge 1 ]; then
        show_usage
    fi

    get_ghc_triplet

    echo ""

    # TODO: walk up folder hierarchy Git-style
    if [ -e ".ghc.environment.${TRIPLET}" ]; then
        echo "Local environment detected in '$(pwd)':"
        echo "- .ghc.environment.${TRIPLET}"
        echo ""
    fi

    if [ -d "$ENVSDIR" ]; then
        echo "Environments available in '$ENVSDIR':"
        cd "$ENVSDIR"
        find . -type f | sed 's,^[.][/],- ,'
        echo ""
    else
        echo "Environment folder $ENVSDIR does not exist"
    fi

    exit 0
fi

if $remove; then
    if [ $# -ge 1 ]; then
        show_usage
    fi

    get_ghc_triplet

    if [ "${envname}" = "." ]; then
        envfn=".ghc.environment.${TRIPLET}"
    else
        envfn="${ENVSDIR}${envname}"
    fi

    if [ -f "$envfn" ]; then
        echo "removing '$envfn'"
        rm "$envfn"
    else
        echo "Environemnt file '$envfn' doesn't exist; nothing to do"
    fi

    exit 0
fi

if [ $# -lt 1 ]; then
    show_usage
fi

echo "Using environment-name = '$envname'"

TMPDIR=$(mktemp -d)

PWD0=$(pwd)

pushd "$TMPDIR"

{
  cat <<EOF
name: z
version: 0
cabal-version:>=1.8
build-type: Simple

library
  build-depends: base
EOF

  for DEP in "$@";
  do
      echo "  build-depends: $DEP"
  done
} > z.cabal

cat > cabal.project <<EOF
packages: .
EOF

cabal new-build all

for ENVFN in .ghc.environment.*-*-*; do true; done

if [ -z "$ENVFN" ]; then
    echo "ERROR: no GHC environment file found. You need at least cabal 2.1 (or later) and GHC 8.0.2 (or later)."
    exit 1
fi

echo "Found '$ENVFN'"

TRIPLET=${ENVFN#.ghc.environment.}

if $run_ghci; then
    cat "$ENVFN" | grep -v '^package-db dist-newstyle/' | grep -v '^package-id z-0-inplace' > "ghci.env"
    popd
    ghci -package-env "$TMPDIR/ghci.env"
    RC=$?

    rm -rf "$TMPDIR"
    echo "cabal-env: temporary environment destroyed again"
    exit $RC
fi

if [ "${envname}" = "." ]; then
    cat "$ENVFN" | grep -v '^package-db dist-newstyle/' | grep -v '^package-id z-0-inplace' > "$PWD0/$ENVFN"
    popd

    rm -rf "$TMPDIR"

    echo ""
    echo "Succesfully created local '$PWD0/$ENVFN' pkg environment!"
else
    #echo "$TRIPLET"

    ENVSDIR="${HOME}/.ghc/${TRIPLET}/environments/"

    mkdir -v -p "${ENVSDIR}"

    ENVSDIRFN="${ENVSDIR}${envname}"

    cat "$ENVFN" | grep -v '^package-db dist-newstyle/' | grep -v '^package-id z-0-inplace' > "$ENVSDIRFN"

    popd

    rm -rf "$TMPDIR"

    echo ""
    echo "Succesfully created '$ENVSDIRFN' pkg environment;"
    echo "use 'ghci -package-env $envname' or 'GHC_ENVIRONMENT=$envname ghci' to select."
    echo "(The 'default' package env is used by default. Try ':show packages' inside GHCi.)"
fi