Add initial section of activation script

The initial section creates some useful variables for use by later
activation sections.

modules/activation-init.sh

@@ -0,0 +1,46 @@
+function setupVars() {
+    local profilesPath="/nix/var/nix/profiles/per-user/$USER"
+    local gcPath="/nix/var/nix/gcroots/per-user/$USER"
+    local greatestGenNum
+
+    greatestGenNum=$( \
+        find "$profilesPath" -name 'home-manager-*-link' \
+            | sed 's/^.*-\([0-9]*\)-link$/\1/' \
+            | sort -rn \
+            | head -1)
+
+    if [[ -n "$greatestGenNum" ]] ; then
+        oldGenNum=$greatestGenNum
+        newGenNum=$((oldGenNum + 1))
+    else
+        newGenNum=1
+    fi
+
+    if [[ -e "$gcPath/current-home" ]] ; then
+        oldGenPath="$(readlink -e "$gcPath/current-home")"
+    fi
+
+    newGenPath="@GENERATION_DIR@";
+    newGenProfilePath="$profilesPath/home-manager-$newGenNum-link"
+    newGenGcPath="$gcPath/current-home"
+}
+
+setupVars
+
+echo "Starting home manager activation"
+
+if [[ $DRY_RUN ]] ; then
+  echo "This is a dry run"
+  export DRY_RUN_CMD=echo
+else
+  echo "This is a live run"
+  unset DRY_RUN_CMD
+fi
+
+echo "Activation variables:"
+echo "  oldGenNum=$oldGenNum"
+echo "  newGenNum=$newGenNum"
+echo "  oldGenPath=$oldGenPath"
+echo "  newGenPath=$newGenPath"
+echo "  newGenProfilePath=$newGenProfilePath"
+echo "  newGenGcPath=$newGenGcPath"

modules/home-environment.nix

@@ -202,7 +202,7 @@ in
         //
         (maybeSet "LC_TIME" cfg.language.time);
 
-    home.activation.linkages =
+    home.activation.linkGeneration =
       let
         link = pkgs.writeText "link" ''
           newGenFiles="$1"
@@ -234,42 +234,6 @@ in
         '';
       in
         ''
-          function setupVars() {
-            local profilesPath="/nix/var/nix/profiles/per-user/$(whoami)"
-            local gcPath="/nix/var/nix/gcroots/per-user/$(whoami)"
-            local greatestGenNum=( \
-              $(find "$profilesPath" -name 'home-manager-*-link' \
-                | sed 's/^.*-\([0-9]*\)-link$/\1/' \
-                | sort -rn \
-                | head -1) \
-            )
-
-            if [[ -n "$greatestGenNum" ]] ; then
-              oldGenNum=$greatestGenNum
-              newGenNum=$(($oldGenNum + 1))
-            else
-              newGenNum=1
-            fi
-
-            if [[ -e "$gcPath/current-home" ]] ; then
-              oldGenPath="$(readlink -e "$gcPath/current-home")"
-            fi
-
-            newGenPath="@GENERATION_DIR@";
-            newGenProfilePath="$profilesPath/home-manager-$newGenNum-link"
-            newGenGcPath="$gcPath/current-home"
-          }
-
-          # Set some vars, these can be used later on as well.
-          setupVars
-
-          echo oldGenNum=$oldGenNum
-          echo newGenNum=$newGenNum
-          echo oldGenPath=$oldGenPath
-          echo newGenPath=$newGenPath
-          echo newGenProfilePath=$newGenProfilePath
-          echo newGenGcPath=$newGenGcPath
-
           function linkNewGen() {
             local newGenFiles
             newGenFiles="$(readlink -e "$newGenPath/home-files")"
@@ -324,13 +288,9 @@ in
         sf = pkgs.writeText "activation-script" ''
           #!${pkgs.stdenv.shell}
 
-          if [[ $DRY_RUN ]] ; then
-            echo "Performing dry run"
-            export DRY_RUN_CMD=echo
-          else
-            echo "Performing live run"
-            unset DRY_RUN_CMD
-          fi
+          set -e
+
+          ${builtins.readFile ./activation-init.sh}
 
           ${activationCmds}
         '';

modules/systemd.nix

@@ -69,7 +69,7 @@ in
         (buildServices "timer" config.systemd.user.timers)
       );
 
-    home.activation.reloadSystemD = stringAfter ["linkages"] ''
+    home.activation.reloadSystemD = ''
       function systemdPostReload() {
         local servicesDiffFile="$(mktemp)"
         local oldUserServicePath="$oldGenPath/home-files/.config/systemd/user"