systemd: use sd-switch

This makes the systemd module use the sd-switch application to perform
the unit switch during a generation activation.

Since the closure of sd-switch is relatively lightweight we
unconditionally pull it in as a dependency. We simultaneously remove
the `systemd.user.startServices` option and perform the switch action
automatically.

PR #1388

modules/systemd-activate.sh

@@ -1,114 +0,0 @@
-#!/usr/bin/env bash
-
-function isStartable() {
-  local service="$1"
-  [[ $(systemctl --user show -p RefuseManualStart "$service") == *=no ]]
-}
-
-function isStoppable() {
-  if [[ -v oldGenPath ]] ; then
-    local service="$1"
-    [[ $(systemctl --user show -p RefuseManualStop "$service") == *=no ]]
-  fi
-}
-
-function systemdPostReload() {
-  local workDir
-  workDir="$(mktemp -d)"
-
-  if [[ -v oldGenPath ]] ; then
-    local oldUserServicePath="$oldGenPath/home-files/.config/systemd/user"
-  fi
-
-  local newUserServicePath="$newGenPath/home-files/.config/systemd/user"
-  local oldServiceFiles="$workDir/old-files"
-  local newServiceFiles="$workDir/new-files"
-  local servicesDiffFile="$workDir/diff-files"
-
-  if [[ ! (-v oldUserServicePath && -d "$oldUserServicePath") \
-      && ! -d "$newUserServicePath" ]]; then
-    return
-  fi
-
-  if [[ ! (-v oldUserServicePath && -d "$oldUserServicePath") ]]; then
-    touch "$oldServiceFiles"
-  else
-    find "$oldUserServicePath" \
-      -maxdepth 1 -name '*.service' -exec basename '{}' ';' \
-      | sort \
-      > "$oldServiceFiles"
-  fi
-
-  if [[ ! -d "$newUserServicePath" ]]; then
-    touch "$newServiceFiles"
-  else
-    find "$newUserServicePath" \
-      -maxdepth 1 -name '*.service' -exec basename '{}' ';' \
-      | sort \
-      > "$newServiceFiles"
-  fi
-
-  diff \
-    --new-line-format='+%L' \
-    --old-line-format='-%L' \
-    --unchanged-line-format=' %L' \
-    "$oldServiceFiles" "$newServiceFiles" \
-    > "$servicesDiffFile" || true
-
-  local -a maybeRestart=( $(grep '^ ' "$servicesDiffFile" | cut -c2-) )
-  local -a maybeStop=( $(grep '^-' "$servicesDiffFile" | cut -c2-) )
-  local -a maybeStart=( $(grep '^+' "$servicesDiffFile" | cut -c2-) )
-  local -a toRestart=( )
-  local -a toStop=( )
-  local -a toStart=( )
-
-  for f in "${maybeRestart[@]}" ; do
-    if isStoppable "$f" \
-        && isStartable "$f" \
-        && systemctl --quiet --user is-active "$f" \
-        && ! cmp --quiet \
-            "$oldUserServicePath/$f" \
-            "$newUserServicePath/$f" ; then
-      toRestart+=("$f")
-    fi
-  done
-
-  for f in "${maybeStop[@]}" ; do
-    if isStoppable "$f" ; then
-      toStop+=("$f")
-    fi
-  done
-
-  for f in "${maybeStart[@]}" ; do
-    if isStartable "$f" ; then
-      toStart+=("$f")
-    fi
-  done
-
-  rm -r "$workDir"
-
-  local sugg=""
-
-  if [[ -n "${toRestart[@]}" ]] ; then
-    sugg="${sugg}systemctl --user restart ${toRestart[@]}\n"
-  fi
-
-  if [[ -n "${toStop[@]}" ]] ; then
-    sugg="${sugg}systemctl --user stop ${toStop[@]}\n"
-  fi
-
-  if [[ -n "${toStart[@]}" ]] ; then
-    sugg="${sugg}systemctl --user start ${toStart[@]}\n"
-  fi
-
-  if [[ -n "$sugg" ]] ; then
-    echo "Suggested commands:"
-    echo -n -e "$sugg"
-  fi
-}
-
-oldGenPath="$1"
-newGenPath="$2"
-
-$DRY_RUN_CMD systemctl --user daemon-reload
-systemdPostReload