lib/utils: add nestedLiteral and nestedLiteralLua

`nestedLiteral` converts a `literalExpression` into a `toPretty` style
pretty-printer.

`nestedLiteralLua` composes `nestedLiteral` and `literalLua` together.

lib/default.nix

@@ -97,6 +97,8 @@ lib.fix (
       mkIfNonNull'
       mkRaw
       mkRawKey
+      nestedLiteral
+      nestedLiteralLua
       override
       overrideDerivation
       toRawKeys

lib/utils.nix

@@ -155,6 +155,64 @@ rec {
     in
     lib.literalExpression exp;
 
+  /**
+    Convert the given string into a `__pretty` printed mkRaw expression.
+
+    For use in nested values that will be printed by `lib.generators.toPretty`,
+    or `lib.options.renderOptionValue`.
+
+    # Example
+
+    ```nix
+    nestedLiteralLua "print('hi')"
+    => nestedLiteral (literalLua "print('hi')")
+    => {
+      __pretty = lib.getAttr "text";
+      val = literalLua "print('hi')";
+    }
+    ```
+
+    # Type
+    ```
+    nestedLiteralLua :: String -> AttrSet
+    ```
+  */
+  nestedLiteralLua = r: nestedLiteral (literalLua r);
+
+  /**
+    Convert the given string or literalExpression into a `__pretty` printed expression.
+
+    For use in nested values that will be printed by `lib.generators.toPretty`,
+    or `lib.options.renderOptionValue`.
+
+    # Examples
+
+    ```nix
+    nestedLiteral "example"
+    => {
+      __pretty = lib.getAttr "text";
+      val = literalExpression "example";
+    }
+    ```
+
+    ```nix
+    nestedLiteral (literalExpression ''"hello, world"'')
+    => {
+      __pretty = lib.getAttr "text";
+      val = literalExpression ''"hello, world"'';
+    }
+    ```
+
+    # Type
+    ```
+    nestedLiteral :: (String | literalExpression) -> AttrSet
+    ```
+  */
+  nestedLiteral = val: {
+    __pretty = lib.getAttr "text";
+    val = if val._type or null == "literalExpression" then val else lib.literalExpression val;
+  };
+
   wrapDo = string: ''
     do
       ${string}

tests/lib-tests.nix

@@ -331,6 +331,34 @@ let
       };
     };
 
+    # Integration test for nestedLiteral and renderOptionValue
+    testNestedLiteral_withRenderOptionValue = {
+      expr =
+        builtins.mapAttrs
+          (
+            _: v:
+            (lib.options.renderOptionValue {
+              literal = helpers.nestedLiteral v;
+            }).text
+          )
+          {
+            empty = "";
+            sum = "1 + 1";
+            print = ''lib.mkRaw "print('hi')"'';
+          };
+      expected =
+        builtins.mapAttrs
+          (_: literal: ''
+            {
+              literal = ${literal};
+            }'')
+          {
+            empty = "";
+            sum = "1 + 1";
+            print = ''lib.mkRaw "print('hi')"'';
+          };
+    };
+
     testUpperFirstChar = {
       expr = map helpers.upperFirstChar [
         "foo"