ENH Improve type safety to support refactored template layer

code/Controllers/ContentController.php

@@ -419,7 +419,7 @@ HTML;
         }
 
         // Find templates for the controller + action together - e.g. PageController_action.ss
-        $templatesFound[] = SSViewer::get_templates_by_class(static::class, $action, Controller::class);
+        $templatesFound[] = SSViewer::get_templates_by_class(static::class, $action ?? '', Controller::class);
 
         // Find templates for the record without an action - e.g. Page.ss
         if ($this->dataRecord instanceof SiteTree) {
@@ -427,9 +427,9 @@ HTML;
         }
 
         // Find the templates for the controller without an action - e.g. PageController.ss
-        $templatesFound[] = SSViewer::get_templates_by_class(static::class, "", Controller::class);
+        $templatesFound[] = SSViewer::get_templates_by_class(static::class, '', Controller::class);
 
         $templates = array_merge(...$templatesFound);
-        return SSViewer::create($templates);
+        return SSViewer::create($templates, $this->getTemplateEngine());
     }
 }

code/Model/SiteTree.php

@@ -1454,7 +1454,7 @@ class SiteTree extends DataObject implements PermissionProvider, i18nEntityProvi
 
         $tags['title'] = [
             'tag' => 'title',
-            'content' => $this->obj('Title')->forTemplate()
+            'content' => $this->obj('Title')?->forTemplate()
         ];
 
         $generator = $this->getGenerator();
@@ -1601,7 +1601,7 @@ class SiteTree extends DataObject implements PermissionProvider, i18nEntityProvi
 
         $tagString = implode("\n", $tags);
         if ($this->ExtraMeta) {
-            $tagString .= $this->obj('ExtraMeta')->forTemplate();
+            $tagString .= $this->obj('ExtraMeta')?->forTemplate();
         }
 
         $this->extend('updateMetaTags', $tagString);

tests/php/Controllers/ContentControllerTest.php

@@ -5,6 +5,8 @@ namespace SilverStripe\CMS\Tests\Controllers;
 use SilverStripe\CMS\Controllers\ContentController;
 use SilverStripe\CMS\Controllers\RootURLController;
 use SilverStripe\CMS\Model\SiteTree;
+use SilverStripe\CMS\Tests\Controllers\ContentControllerTest\DummyTemplateContentController;
+use SilverStripe\CMS\Tests\Controllers\ContentControllerTest\DummyTemplateEngine;
 use SilverStripe\Control\Director;
 use SilverStripe\Control\HTTPResponse_Exception;
 use SilverStripe\Core\Config\Config;
@@ -195,16 +197,23 @@ class ContentControllerTest extends FunctionalTest
             $response = $this->get($page->RelativeLink("testwithouttemplate"));
             $this->assertEquals("Page", trim($response->getBody() ?? ''));
 
-            // Test that an action with a template will render the both action template *and* the
+            // Test that an action with a template will render both the action template *and* the
             // correct parent template
-            $controller = new ContentController($page);
+            $controller = new DummyTemplateContentController($page);
             $viewer = $controller->getViewer('test');
-            $this->assertEquals(
+            /** @var DummyTemplateEngine $engine */
-                __DIR__
+            $engine = $viewer->getTemplateEngine();
-                . '/themes/controllertest/templates/SilverStripe/CMS/Tests/Controllers/'
+            $templateCandidates = $engine->getTemplates();
-                . 'ContentControllerTestPage_test.ss',
+            // Check for the action templates
-                $viewer->templates()['main']
+            $this->assertContains('SilverStripe\CMS\Tests\Controllers\ContentControllerTestPage_test', $templateCandidates);
-            );
+            $this->assertContains('SilverStripe\CMS\Model\SiteTree_test', $templateCandidates);
+            $this->assertContains('SilverStripe\CMS\Tests\Controllers\ContentControllerTest\DummyTemplateContentController_test', $templateCandidates);
+            $this->assertContains('SilverStripe\CMS\Controllers\ContentController_test', $templateCandidates);
+            // Check for the parent templates
+            $this->assertContains('SilverStripe\CMS\Tests\Controllers\ContentControllerTestPage', $templateCandidates);
+            $this->assertContains('SilverStripe\CMS\Model\SiteTree', $templateCandidates);
+            $this->assertContains('SilverStripe\CMS\Tests\Controllers\ContentControllerTest\DummyTemplateContentController', $templateCandidates);
+            $this->assertContains('SilverStripe\CMS\Controllers\ContentController', $templateCandidates);
         });
     }
 }

tests/php/Controllers/ContentControllerTest/DummyTemplateContentController.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace SilverStripe\CMS\Tests\Controllers\ContentControllerTest;
+
+use SilverStripe\CMS\Controllers\ContentController;
+use SilverStripe\Dev\TestOnly;
+use SilverStripe\View\TemplateEngine;
+
+class DummyTemplateContentController extends ContentController implements TestOnly
+{
+    protected function getTemplateEngine(): TemplateEngine
+    {
+        return new DummyTemplateEngine();
+    }
+}

tests/php/Controllers/ContentControllerTest/DummyTemplateEngine.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace SilverStripe\CMS\Tests\Controllers\ContentControllerTest;
+
+use SilverStripe\Dev\TestOnly;
+use SilverStripe\View\TemplateEngine;
+use SilverStripe\View\ViewLayerData;
+
+/**
+ * A dummy template renderer that doesn't actually render any templates.
+ */
+class DummyTemplateEngine implements TemplateEngine, TestOnly
+{
+    private string $output = '<html><head></head><body></body></html>';
+
+    private string|array $templates;
+
+    public function __construct(string|array $templateCandidates = [])
+    {
+        $this->templates = $templateCandidates;
+    }
+
+    public function setTemplate(string|array $templateCandidates): static
+    {
+        $this->templates = $templateCandidates;
+        return $this;
+    }
+
+    public function hasTemplate(string|array $templateCandidates): bool
+    {
+        return true;
+    }
+
+    public function renderString(string $template, ViewLayerData $model, array $overlay = [], bool $cache = true): string
+    {
+        return $this->output;
+    }
+
+    public function render(ViewLayerData $model, array $overlay = []): string
+    {
+        return $this->output;
+    }
+
+    public function setOutput(string $output): void
+    {
+        $this->output = $output;
+    }
+
+    /**
+     * Returns the template candidates that were passed to the constructor or to setTemplate()
+     */
+    public function getTemplates(): array
+    {
+        return $this->templates;
+    }
+}