bug #4924 Resolve constant parent templates once instead of on every lookup (fabpot)

This PR was merged into the 3.x branch.

Discussion
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Resolve constant parent templates once instead of on every lookup

Currently, `Template::$parent` is only memoized by the compiled `doDisplay()`. Anything that reaches a template through `getParent()` without rendering it (`TemplateWrapper::hasBlock()`, `getBlockNames()`, `renderBlock()`, `yieldParentBlock()`, `MacroNamespace::getParent()`) re-evaluates `doGetParent()` and re-runs the sandbox check on every call, even when the parent is a string literal.

`doGetParent()` now does `$this->parent ??= $this->load("name", $line)` for a constant parent, which is what `doDisplay()` already does one line later. Dynamic parents are untouched and still resolve per context.

This also fixes a bug: `getParent()` loaded a constant parent with line `-1`, so a missing parent reported through `hasBlock()`/`getBlockNames()` lost its line number, while `render()` reported the `{% extends %}` line. All three now agree.

Commits
-------

c53b6468c9 Resolve constant parent templates once instead of on every lookup

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

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()

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

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([