removed return type from Container::__call() again [Closes nette/utils#338]

The native `: mixed` return type was accidentally reintroduced on
Container::__call() by 7cbe717 ("added missing native types"),
reviving an incompatibility that had already been fixed once for
nette/utils#315 (commit 40afa80).

Nette\SmartObject::__call() in nette/utils intentionally declares no
native return type (it stays untyped for BC). As long as nobody
re-applies the trait, narrowing the inherited untyped __call() to
`: mixed` is allowed and everything loads fine - which is why the test
suite and Forms' own classes are unaffected.

The fatal error appears only when a subclass extends Form/Container AND
re-applies the SmartObject trait, e.g.:

	class MyForm extends Nette\Forms\Form { use Nette\SmartObject; }

Then the trait's untyped __call() overrides the already-typed
__call(): mixed, which PHP rejects as removing a return type:

	Declaration of Nette\SmartObject::__call(string $name, array $args)
	must be compatible with
	Nette\Forms\Container::__call(string $name, array $args): mixed

Re-applying SmartObject on top of a class that already has it is an
unusual, unexpected pattern, so the regression slipped through - but it
happens in the wild (e.g. via downstream component classes), breaks on
all PHP 8.1-8.5, and matches the report that 3.2.8 works but 3.2.9 does
not. Dropping the native return type (keeping it in phpDoc) restores
compatibility. A regression test covering the trait combination is added.

Author: dg

src/Forms/Container.php

@@ -604,8 +604,11 @@ public function addContainer(string|int $name): self
 	/********************* extension methods ****************d*g**/
 
 
-	/** @param mixed[] $args */
-	public function __call(string $name, array $args): mixed
+	/**
+	 * @param  mixed[]  $args
+	 * @return mixed
+	 */
+	public function __call(string $name, array $args)
 	{
 		if (isset(self::$extMethods[$name])) {
 			return (self::$extMethods[$name])($this, ...$args);

tests/Forms/Container.__call.smartObject.phpt

@@ -0,0 +1,25 @@
+<?php
+
+/**
+ * Test: A subclass that re-applies the Nette\SmartObject trait must remain
+ * compatible with Container::__call(). The trait declares __call() without a
+ * native return type, so Container::__call() must not declare one either,
+ * otherwise PHP raises a fatal "incompatible declaration" error at compile time.
+ * @see https://github.com/nette/utils/issues/338
+ */
+
+declare(strict_types=1);
+
+use Tester\Assert;
+
+
+require __DIR__ . '/../bootstrap.php';
+
+
+class FormWithSmartObject extends Nette\Forms\Form
+{
+	use Nette\SmartObject;
+}
+
+
+Assert::type(Nette\Forms\Form::class, new FormWithSmartObject);