From c53b6468c9e6c2fc0d6bdd553c518b8bd3cae39d Mon Sep 17 00:00:00 2001
From: Fabien Potencier <fabien@potencier.org>
Date: Fri, 11 Sep 2026 06:10:11 -0700
Subject: [PATCH] Resolve constant parent templates once instead of on every
 lookup

---
 CHANGELOG                     |  1 +
 src/Node/ModuleNode.php       | 19 ++++++++++---------
 tests/Node/ModuleTest.php     |  2 +-
 tests/TemplateWrapperTest.php | 13 +++++++++++++
 4 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 7b222909e..b0fb15187 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -8,6 +8,7 @@
  * Fix `TemplateWrapper::streamBlock()`, `TemplateWrapper::hasBlock()`, and `TemplateWrapper::getBlockNames()` omitting environment globals
  * Fix exceptions from dynamic parent expressions escaping without template context
  * Add the `BlockChain` class to compose blocks from multiple templates without using template internals
+ * Fix `TemplateWrapper::hasBlock()` and `TemplateWrapper::getBlockNames()` losing the `extends` line when the parent template does not exist
  * Fix an output buffer leak when a parent block rendered in an expression throws in non-yield mode
  * Add the `HtmlExtension::htmlAttrValue()` method to resolve a single HTML attribute value the way the `html_attr` function renders it
  * Fix `html_attr` JSON encoding a `Stringable` value in a `data-*` attribute instead of using its string representation
diff --git a/src/Node/ModuleNode.php b/src/Node/ModuleNode.php
index ca2b0b9c2..13eef99ad 100644
--- a/src/Node/ModuleNode.php
+++ b/src/Node/ModuleNode.php
@@ -143,17 +143,18 @@ final class ModuleNode extends Node implements CoercesChildrenToStringInterface
         ;
 
         if ($parent instanceof ConstantExpression) {
-            $compiler->subcompile($parent);
-        } else {
-            $compiler
-                ->raw('$this->load(')
-                ->subcompile($parent)
-                ->raw(', ')
-                ->repr($parent->getTemplateLine())
-                ->raw(')')
-            ;
+            // a constant parent never depends on the context, so resolve it once
+            $compiler->raw('$this->parent ??= ');
         }
 
+        $compiler
+            ->raw('$this->load(')
+            ->subcompile($parent)
+            ->raw(', ')
+            ->repr($parent->getTemplateLine())
+            ->raw(')')
+        ;
+
         $compiler
             ->raw(";\n")
             ->outdent()
diff --git a/tests/Node/ModuleTest.php b/tests/Node/ModuleTest.php
index c3cbad02d..670309367 100644
--- a/tests/Node/ModuleTest.php
+++ b/tests/Node/ModuleTest.php
@@ -232,7 +232,7 @@ class __TwigTemplate_%x extends Template
     protected function doGetParent(array \$context): bool|string|Template|TemplateWrapper
     {
         // line 1
-        return "layout.twig";
+        return \$this->parent ??= \$this->load("layout.twig", 1);
     }
 
     protected function doDisplay(array \$context, array \$blocks = []): iterable
diff --git a/tests/TemplateWrapperTest.php b/tests/TemplateWrapperTest.php
index b5a8b6be3..197e3aa13 100644
--- a/tests/TemplateWrapperTest.php
+++ b/tests/TemplateWrapperTest.php
@@ -139,6 +139,19 @@ class TemplateWrapperTest extends TestCase
         yield 'exception thrown by parent expression' => ['{% extends boom() %}', new TwigFunction('boom', static function (): never { throw new \DomainException('kaboom'); }), \DomainException::class];
     }
 
+    public function testBlockIntrospectionReportsTheExtendsLineForAMissingParent(): void
+    {
+        $twig = new Environment(new ArrayLoader(['index' => "\n\n{% extends 'missing' %}"]));
+
+        try {
+            $twig->load('index')->hasBlock('foo');
+            $this->fail('Introspecting a template with a missing parent must fail.');
+        } catch (LoaderError $e) {
+            $this->assertSame('Template "missing" is not defined.', $e->getRawMessage());
+            $this->assertSame(3, $e->getTemplateLine());
+        }
+    }
+
     public function testRenderBlock(): void
     {
         $twig = new Environment(new ArrayLoader([