Reject a Template instance created by another environment when resolving templates

CHANGELOG

@@ -1,5 +1,6 @@
 # 3.30.1 (2026-XX-XX)
 
+ * Reject a deprecated `Template` instance created by another environment in `Environment::resolveTemplate()`
  * Speed up reading object attributes backed by getters or class constants
 
 # 3.30.0 (2026-09-25)

src/Environment.php

@@ -514,6 +514,10 @@ class Environment
             if ($name instanceof Template) {
                 trigger_deprecation('twig/twig', '3.9', 'Passing a "%s" instance to "%s" is deprecated.', Template::class, __METHOD__);
 
+                if (!$name->isOwnedBy($this)) {
+                    throw new RuntimeError(\sprintf('A "%s" can only be used with the "%s" that created it.', Template::class, self::class));
+                }
+
                 return new TemplateWrapper($this, $name);
             }
             if ($name instanceof TemplateWrapper) {

tests/EnvironmentTest.php

@@ -96,6 +96,22 @@ class EnvironmentTest extends TestCase
         $twig->load($foreign->load('index'));
     }
 
+    /**
+     * @group legacy
+     */
+    #[Group('legacy')]
+    public function testResolveTemplateRejectsTemplateFromAnotherEnvironment(): void
+    {
+        $foreign = new Environment(new ArrayLoader(['index' => 'foreign']));
+        $twig = new Environment(new ArrayLoader());
+
+        $this->expectDeprecation('Since twig/twig 3.9: Passing a "Twig\Template" instance to "Twig\Environment::resolveTemplate" is deprecated.');
+        $this->expectException(RuntimeError::class);
+        $this->expectExceptionMessage('A "Twig\Template" can only be used with the "Twig\Environment" that created it.');
+
+        $twig->resolveTemplate([$foreign->load('index')->unwrap($foreign)]);
+    }
+
     /**
      * @group legacy
      */