home-manager/modules/lib-bash/activation-init.sh

# Moves the existing profile from /nix to ~ to match changed behavior in Nix
# 2.14. See https://github.com/NixOS/nix/pull/5226.
#
# Note, this function is intentionally unused for now. There remains a few open
# questions about backwards compatibility and support from
# `nix-collect-garbage`.
function migrateProfile() {
    declare -r stateHome="${XDG_STATE_HOME:-$HOME/.local/state}"
    declare -r hmStateDir="$stateHome/home-manager"
    declare -r nixStateDir="${NIX_STATE_DIR:-/nix/var/nix}"

    declare -r newProfilesDir="$hmStateDir/profiles"
    declare -r oldProfilesDir="$nixStateDir/profiles/per-user/$USER"

    if [[ ! -d $newProfilesDir ]]; then
        _i 'Migrating profiles from %s to %s' "$oldProfilesDir" "$newProfilesDir"
        mkdir -p "$newProfilesDir"
        for p in "$oldProfilesDir"/home-manager-*; do
            declare -r name="${p##*/}"
            nix-store --realise "$p" --add-root "$newProfilesDir/$name" > /dev/null
        done
        cp -P "$oldProfilesDir/home-manager" "$newProfilesDir"
    fi

    rm "$oldProfilesDir"/home-manager-*
}

function setupVars() {
    declare -r nixStateDir="${NIX_STATE_DIR:-/nix/var/nix}"
    declare -r globalProfilesDir="$nixStateDir/profiles/per-user/$USER"
    declare -r globalGcrootsDir="$nixStateDir/gcroots/per-user/$USER"

    declare -r stateHome="${XDG_STATE_HOME:-$HOME/.local/state}"
    declare -r hmStateDir="$stateHome/home-manager"
    declare -r hmGcrootsDir="$hmStateDir/gcroots"

    # If the global profiles path exists or we can create it, then place the HM
    # profile there. Otherwise place it in the HM data directory. We prefer to
    # use the global location since it makes it visible to
    # `nix-collect-garbage`.
    #
    # In the future we may perform a one-shot migration to the new location.
    #
    # shellcheck disable=2174
    if [[ -d "$globalProfilesDir" ]] || mkdir -m 0755 -p "$globalProfilesDir" 2>/dev/null; then
        declare -r hmProfilesDir="$globalProfilesDir"
    else
        declare -r hmProfilesDir="$hmStateDir/profiles"
        mkdir -m 0755 -p "$hmProfilesDir"
    fi

    declare -gr genProfilePath="$hmProfilesDir/home-manager"
    declare -gr newGenPath="@GENERATION_DIR@";
    declare -gr newGenGcPath="$hmGcrootsDir/current-home"
    declare -gr legacyGenGcPath="$globalGcrootsDir/current-home"

    declare greatestGenNum
    greatestGenNum=$( \
        nix-env --list-generations --profile "$genProfilePath" \
            | tail -1 \
            | sed -E 's/ *([[:digit:]]+) .*/\1/')

    if [[ -n $greatestGenNum ]] ; then
        declare -gr oldGenNum=$greatestGenNum
        declare -gr newGenNum=$((oldGenNum + 1))
    else
        declare -gr newGenNum=1
    fi

    if [[ -e $genProfilePath ]] ; then
        declare -g oldGenPath
        oldGenPath="$(readlink -e "$genProfilePath")"
    fi

    $VERBOSE_RUN _i "Sanity checking oldGenNum and oldGenPath"
    if [[ -v oldGenNum && ! -v oldGenPath
            || ! -v oldGenNum && -v oldGenPath ]]; then
        _i $'The previous generation number and path are in conflict! These\nmust be either both empty or both set but are now set to\n\n    \'%s\' and \'%s\'\n\nIf you don\'t mind losing previous profile generations then\nthe easiest solution is probably to run\n\n   rm %s/home-manager*\n   rm %s/current-home\n\nand trying home-manager switch again. Good luck!' \
           "${oldGenNum:-}" "${oldGenPath:-}" \
           "$hmProfilesDir" "$hmGcrootsDir"
        exit 1
    fi
}

if [[ -v VERBOSE ]]; then
    export VERBOSE_ECHO=echo
    export VERBOSE_ARG="--verbose"
    export VERBOSE_RUN=""
else
    export VERBOSE_ECHO=true
    export VERBOSE_ARG=""
    export VERBOSE_RUN=true
fi

_i "Starting Home Manager activation"

# Verify that we can connect to the Nix store and/or daemon. This will
# also create the necessary directories in profiles and gcroots.
$VERBOSE_RUN _i "Sanity checking Nix"
nix-build --expr '{}' --no-out-link

setupVars

if [[ -v DRY_RUN ]] ; then
    _i "This is a dry run"
    export DRY_RUN_CMD=echo
    export DRY_RUN_NULL=/dev/stdout
else
    $VERBOSE_RUN _i "This is a live run"
    export DRY_RUN_CMD=""
    export DRY_RUN_NULL=/dev/null

fi

if [[ -v VERBOSE ]]; then
    _i 'Using Nix version: %s' "$(nix-env --version)"
fi

$VERBOSE_RUN _i "Activation variables:"
if [[ -v oldGenNum ]] ; then
    $VERBOSE_ECHO "  oldGenNum=$oldGenNum"
    $VERBOSE_ECHO "  oldGenPath=$oldGenPath"
else
    $VERBOSE_ECHO "  oldGenNum undefined (first run?)"
    $VERBOSE_ECHO "  oldGenPath undefined (first run?)"
fi
$VERBOSE_ECHO "  newGenPath=$newGenPath"
$VERBOSE_ECHO "  newGenNum=$newGenNum"
$VERBOSE_ECHO "  genProfilePath=$genProfilePath"
$VERBOSE_ECHO "  newGenGcPath=$newGenGcPath"
$VERBOSE_ECHO "  legacyGenGcPath=$legacyGenGcPath"