nixos/etc: Replace make-etc.sh with nix and bash

The main goal of this commit is to replace the rather fragile passing of
multiple arrays which could break in cases like #130935.
While I could have just added proper shell escaping to the variables
being passed, I opted for the more painful approach of replacing the
fragile and somewhat strange construct with the 5 bash lists. While
there are currently no more problems present with the current approach
(at least none that I know of), the new approach seems more solid and
might get around problems that could arise in the future stemming from
either the multiple-lists situation or from the absence of proper shell
quoting all over the script.

nixos/modules/system/boot/systemd.nix

@@ -1045,7 +1045,7 @@ in
           done
         '' + concatMapStrings (name: optionalString (hasPrefix "tmpfiles.d/" name) ''
           rm -f $out/${removePrefix "tmpfiles.d/" name}
-        '') config.system.build.etc.targets;
+        '') config.system.build.etc.passthru.targets;
       }) + "/*";
 
       "systemd/system-generators" = { source = hooks "generators" cfg.generators; };

nixos/modules/system/etc/etc.nix

@@ -8,21 +8,61 @@ let
 
   etc' = filter (f: f.enable) (attrValues config.environment.etc);
 
-  etc = pkgs.stdenvNoCC.mkDerivation {
-    name = "etc";
-
-    builder = ./make-etc.sh;
-
+  etc = pkgs.runCommand "etc" {
     preferLocalBuild = true;
     allowSubstitutes = false;
 
-    /* !!! Use toXML. */
-    sources = map (x: x.source) etc';
-    targets = map (x: x.target) etc';
-    modes = map (x: x.mode) etc';
-    users  = map (x: x.user) etc';
-    groups  = map (x: x.group) etc';
-  };
+    # This is needed for the systemd module
+    passthru.targets = map (x: x.target) etc';
+  } /* sh */ ''
+    set -euo pipefail
+
+    makeEtcEntry() {
+      src="$1"
+      target="$2"
+      mode="$3"
+      user="$4"
+      group="$5"
+
+      if [[ "$src" = *'*'* ]]; then
+        # If the source name contains '*', perform globbing.
+        mkdir -p "$out/etc/$target"
+        for fn in $src; do
+            ln -s "$fn" "$out/etc/$target/"
+        done
+      else
+
+        mkdir -p "$out/etc/$(dirname "$target")"
+        if ! [ -e "$out/etc/$target" ]; then
+          ln -s "$src" "$out/etc/$target"
+        else
+          echo "duplicate entry $target -> $src"
+          if [ "$(readlink "$out/etc/$target")" != "$src" ]; then
+            echo "mismatched duplicate entry $(readlink "$out/etc/$target") <-> $src"
+            ret=1
+
+            continue
+          fi
+        fi
+
+        if [ "$mode" != symlink ]; then
+          echo "$mode" > "$out/etc/$target.mode"
+          echo "$user" > "$out/etc/$target.uid"
+          echo "$group" > "$out/etc/$target.gid"
+        fi
+      fi
+    }
+
+    mkdir -p "$out/etc"
+    ${concatMapStringsSep "\n" (etcEntry: escapeShellArgs [
+      "makeEtcEntry"
+      etcEntry.source
+      etcEntry.target
+      etcEntry.mode
+      etcEntry.user
+      etcEntry.group
+    ]) etc'}
+  '';
 
 in
 

nixos/modules/system/etc/make-etc.sh

@@ -1,45 +0,0 @@
-source $stdenv/setup
-
-mkdir -p $out/etc
-
-set -f
-sources_=($sources)
-targets_=($targets)
-modes_=($modes)
-users_=($users)
-groups_=($groups)
-set +f
-
-for ((i = 0; i < ${#targets_[@]}; i++)); do
-    source="${sources_[$i]}"
-    target="${targets_[$i]}"
-
-    if [[ "$source" =~ '*' ]]; then
-
-        # If the source name contains '*', perform globbing.
-        mkdir -p $out/etc/$target
-        for fn in $source; do
-            ln -s "$fn" $out/etc/$target/
-        done
-
-    else
-
-        mkdir -p $out/etc/$(dirname $target)
-        if ! [ -e $out/etc/$target ]; then
-            ln -s $source $out/etc/$target
-        else
-            echo "duplicate entry $target -> $source"
-            if test "$(readlink $out/etc/$target)" != "$source"; then
-                echo "mismatched duplicate entry $(readlink $out/etc/$target) <-> $source"
-                exit 1
-            fi
-        fi
-
-        if test "${modes_[$i]}" != symlink; then
-            echo "${modes_[$i]}"  > $out/etc/$target.mode
-            echo "${users_[$i]}"  > $out/etc/$target.uid
-            echo "${groups_[$i]}" > $out/etc/$target.gid
-        fi
-
-    fi
-done