Fix nested block() resolution when a directly rendered block calls parent()

CHANGELOG

@@ -1,5 +1,6 @@
 # 3.27.2 (2026-XX-XX)
 
+ * Fix nested `block()` calls to resolve against the overriding template when a block rendered through `block(name, template)` calls `parent()`
  * Stop reporting a skipped test in `IntegrationTestCase` when there is no legacy test to run
  * Make the `IntegrationTestCase` and `NodeTestCase` test helpers compatible with PHPUnit 11
  * Cast printed expressions to string so values that cannot be converted to a string (arrays, non-`Stringable` objects, ...) report a usable stack trace at the print location

src/Template.php

@@ -440,6 +440,8 @@ abstract class Template
         } elseif (isset($this->blocks[$name])) {
             $template = $this->blocks[$name][0];
             $block = $this->blocks[$name][1];
+            // expose this template's own blocks so nested block() calls resolve against them when the block is rendered directly (e.g. block(name, template))
+            $blocks = array_merge($this->blocks, $blocks);
         } else {
             $template = null;
             $block = null;

tests/Fixtures/functions/block_with_template_parent.test

@@ -0,0 +1,28 @@
+--TEST--
+"block" function with a template argument resolves nested "block" calls against the overriding template through parent()
+--TEMPLATE--
+{{ block('block1', 'theme.html.twig') }}
+--TEMPLATE(theme.html.twig)--
+{% extends 'base.html.twig' %}
+
+{%- block block1 -%}
+    {{- parent() -}}
+    BLOCK1THEME/
+{%- endblock -%}
+
+{%- block block2 -%}
+    BLOCK2THEME/
+{%- endblock -%}
+--TEMPLATE(base.html.twig)--
+{%- block block1 -%}
+    BLOCK1BASE/
+    {{- block('block2') -}}
+{%- endblock -%}
+
+{%- block block2 -%}
+    BLOCK2BASE/
+{%- endblock -%}
+--DATA--
+return []
+--EXPECT--
+BLOCK1BASE/BLOCK2THEME/BLOCK1THEME/