lib/types: Introduce types.raw for unprocessed values

lib/tests/modules.sh

···
 checkConfigError 'The option .int.a. is used but not defined' config.int.a ./emptyValues.nix
 checkConfigError 'The option .nonEmptyList.a. is used but not defined' config.nonEmptyList.a ./emptyValues.nix
 
+## types.raw
+checkConfigOutput "{ foo = <CODE>; }" config.unprocessedNesting ./raw.nix
+checkConfigOutput "10" config.processedToplevel ./raw.nix
+checkConfigError "The option .multiple. is defined multiple times" config.multiple ./raw.nix
+checkConfigOutput "bar" config.priorities ./raw.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass

lib/tests/modules/raw.nix

···
+{ lib, ... }: {
+
+  options = {
+    processedToplevel = lib.mkOption {
+      type = lib.types.raw;
+    };
+    unprocessedNesting = lib.mkOption {
+      type = lib.types.raw;
+    };
+    multiple = lib.mkOption {
+      type = lib.types.raw;
+    };
+    priorities = lib.mkOption {
+      type = lib.types.raw;
+    };
+  };
+
+  config = {
+    processedToplevel = lib.mkIf true 10;
+    unprocessedNesting.foo = throw "foo";
+    multiple = lib.mkMerge [
+      "foo"
+      "foo"
+    ];
+    priorities = lib.mkMerge [
+      "foo"
+      (lib.mkForce "bar")
+    ];
+  };
+}

lib/types.nix

···
   # nixos/doc/manual/development/option-types.xml!
   types = rec {
 
+    raw = mkOptionType rec {
+      name = "raw";
+      description = "raw value";
+      check = value: true;
+      merge = mergeOneOption;
+    };
+
     anything = mkOptionType {
       name = "anything";
       description = "anything";

nixos/doc/manual/development/option-types.section.md

···
     ```
     :::
 
+`types.raw`
+
+:   A type which doesn't do any checking, merging or nested evaluation. It
+    accepts a single arbitrary value that is not recursed into, making it
+    useful for values coming from outside the module system, such as package
+    sets or arbitrary data. Options of this type are still evaluated according
+    to priorities and conditionals, so `mkForce`, `mkIf` and co. still work on
+    the option value itself, but not for any value nested within it. This type
+    should only be used when checking, merging and nested evaluation are not
+    desirable.
+
 `types.attrs`
 
 :   A free-form attribute set.

nixos/doc/manual/from_md/development/option-types.section.xml

···
       </varlistentry>
       <varlistentry>
         <term>
+          <literal>types.raw</literal>
+        </term>
+        <listitem>
+          <para>
+            A type which doesn’t do any checking, merging or nested
+            evaluation. It accepts a single arbitrary value that is not
+            recursed into, making it useful for values coming from
+            outside the module system, such as package sets or arbitrary
+            data. Options of this type are still evaluated according to
+            priorities and conditionals, so <literal>mkForce</literal>,
+            <literal>mkIf</literal> and co. still work on the option
+            value itself, but not for any value nested within it. This
+            type should only be used when checking, merging and nested
+            evaluation are not desirable.
+          </para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>
           <literal>types.attrs</literal>
         </term>
         <listitem>