API Refactor template layer into its own module

Includes the following large-scale changes:
- Impoved barrier between model and view layers
- Improved casting of scalar to relevant DBField types
- Improved capabilities for rendering arbitrary data in templates

_config/view.yml

@@ -0,0 +1,6 @@
+---
+Name: view-config
+---
+SilverStripe\Core\Injector\Injector:
+  SilverStripe\View\TemplateEngine:
+    class: 'SilverStripe\View\SSTemplateEngine'

src/Control/ContentNegotiator.php

@@ -225,7 +225,7 @@ public function html(HTTPResponse $response)
         // Fix base tag
         $content = preg_replace(
             '/<base href="([^"]*)" \/>/',
-            '<base href="$1"><!--[if lte IE 6]></base><![endif]-->',
+            '<base href="$1">',
             $content ?? ''
         );
 

src/Control/Controller.php

@@ -3,11 +3,14 @@
 namespace SilverStripe\Control;
 
 use SilverStripe\Core\ClassInfo;
+use SilverStripe\Core\Injector\Injector;
 use SilverStripe\Dev\Debug;
+use SilverStripe\Model\ModelData;
 use SilverStripe\ORM\FieldType\DBHTMLText;
 use SilverStripe\Security\Member;
 use SilverStripe\Security\Security;
 use SilverStripe\View\SSViewer;
+use SilverStripe\View\TemplateEngine;
 use SilverStripe\View\TemplateGlobalProvider;
 
 /**
@@ -87,6 +90,8 @@ class Controller extends RequestHandler implements TemplateGlobalProvider
         'handleIndex',
     ];
 
+    protected ?TemplateEngine $templateEngine = null;
+
     public function __construct()
     {
         parent::__construct();
@@ -400,7 +405,7 @@ public function getViewer($action)
             $templates = array_unique(array_merge($actionTemplates, $classTemplates));
         }
 
-        return SSViewer::create($templates);
+        return SSViewer::create($templates, $this->getTemplateEngine());
     }
 
     /**
@@ -452,9 +457,10 @@ protected function definingClassForAction($action)
         }
 
         $class = static::class;
-        while ($class != 'SilverStripe\\Control\\RequestHandler') {
+        $engine = $this->getTemplateEngine();
+        while ($class !== RequestHandler::class) {
             $templateName = strtok($class ?? '', '_') . '_' . $action;
-            if (SSViewer::hasTemplate($templateName)) {
+            if ($engine->hasTemplate($templateName)) {
                 return $class;
             }
 
@@ -486,17 +492,25 @@ public function hasActionTemplate($action)
             $parentClass = get_parent_class($parentClass ?? '');
         }
 
-        return SSViewer::hasTemplate($templates);
+        $engine = $this->getTemplateEngine();
+        return $engine->hasTemplate($templates);
+    }
+
+    public function renderWith($template, ModelData|array $customFields = []): DBHTMLText
+    {
+        // Ensure template engine is used, unless the viewer was already explicitly instantiated
+        if (!($template instanceof SSViewer)) {
+            $template = SSViewer::create($template, $this->getTemplateEngine());
+        }
+        return parent::renderWith($template, $customFields);
     }
 
     /**
      * Render the current controller with the templates determined by {@link getViewer()}.
      *
      * @param array $params
-     *
-     * @return string
      */
-    public function render($params = null)
+    public function render($params = null): DBHTMLText
     {
         $template = $this->getViewer($this->getAction());
 
@@ -735,4 +749,12 @@ public static function get_template_global_variables()
             'CurrentPage' => 'curr',
         ];
     }
+
+    protected function getTemplateEngine(): TemplateEngine
+    {
+        if (!$this->templateEngine) {
+            $this->templateEngine = Injector::inst()->create(TemplateEngine::class);
+        }
+        return $this->templateEngine;
+    }
 }

src/Control/Email/Email.php

@@ -46,7 +46,7 @@ class Email extends SymfonyEmail
     private static string|array $admin_email = '';
 
     /**
-     * The name of the HTML template to render the email with (without *.ss extension)
+     * The name of the HTML template to render the email with
      */
     private string $HTMLTemplate = '';
 
@@ -398,26 +398,21 @@ public function removeData(string $name)
         return $this;
     }
 
-    public function getHTMLTemplate(): string
+    public function getHTMLTemplate(): string|array
     {
         if ($this->HTMLTemplate) {
             return $this->HTMLTemplate;
         }
 
-        return ThemeResourceLoader::inst()->findTemplate(
-            SSViewer::get_templates_by_class(static::class, '', Email::class),
-            SSViewer::get_themes()
-        );
+        return SSViewer::get_templates_by_class(static::class, '', Email::class);
     }
 
     /**
-     * Set the template to render the email with
+     * Set the template to render the email with.
+     * Do not include a file extension unless you are referencing a full absolute file path.
      */
     public function setHTMLTemplate(string $template): static
     {
-        if (substr($template ?? '', -3) == '.ss') {
-            $template = substr($template ?? '', 0, -3);
-        }
         $this->HTMLTemplate = $template;
         return $this;
     }
@@ -431,13 +426,11 @@ public function getPlainTemplate(): string
     }
 
     /**
-     * Set the template to render the plain part with
+     * Set the template to render the plain part with.
+     * Do not include a file extension unless you are referencing a full absolute file path.
      */
     public function setPlainTemplate(string $template): static
     {
-        if (substr($template ?? '', -3) == '.ss') {
-            $template = substr($template ?? '', 0, -3);
-        }
         $this->plainTemplate = $template;
         return $this;
     }

src/Control/HTTPResponse.php

@@ -444,8 +444,6 @@ public function isRedirect()
 
     /**
      * The HTTP response represented as a raw string
-     *
-     * @return string
      */
     public function __toString()
     {

src/Control/RSS/RSSFeed_Entry.php

@@ -47,7 +47,7 @@ class RSSFeed_Entry extends ModelData
      */
     public function __construct($entry, $titleField, $descriptionField, $authorField)
     {
-        $this->failover = $entry;
+        $this->setFailover($entry);
         $this->titleField = $titleField;
         $this->descriptionField = $descriptionField;
         $this->authorField = $authorField;
@@ -58,7 +58,7 @@ public function __construct($entry, $titleField, $descriptionField, $authorField
     /**
      * Get the description of this entry
      *
-     * @return DBField Returns the description of the entry.
+     * @return DBField|null Returns the description of the entry.
      */
     public function Title()
     {
@@ -68,7 +68,7 @@ public function Title()
     /**
      * Get the description of this entry
      *
-     * @return DBField Returns the description of the entry.
+     * @return DBField|null Returns the description of the entry.
      */
     public function Description()
     {
@@ -85,7 +85,7 @@ public function Description()
     /**
      * Get the author of this entry
      *
-     * @return DBField Returns the author of the entry.
+     * @return DBField|null Returns the author of the entry.
      */
     public function Author()
     {
@@ -96,7 +96,7 @@ public function Author()
      * Return the safely casted field
      *
      * @param string $fieldName Name of field
-     * @return DBField
+     * @return DBField|null
      */
     public function rssField($fieldName)
     {

src/Core/Manifest/ModuleResource.php

@@ -114,8 +114,6 @@ public function exists()
 
     /**
      * Get relative path
-     *
-     * @return string
      */
     public function __toString()
     {

src/Dev/Backtrace.php

@@ -149,11 +149,11 @@ public static function full_func_name($item, $showArgs = false, $argCharLimit =
         if ($showArgs && isset($item['args'])) {
             $args = [];
             foreach ($item['args'] as $arg) {
-                if (!is_object($arg) || method_exists($arg, '__toString')) {
+                if (is_object($arg)) {
+                    $args[] = get_class($arg);
+                } else {
                     $sarg = is_array($arg) ? 'Array' : strval($arg);
                     $args[] = (strlen($sarg ?? '') > $argCharLimit) ? substr($sarg, 0, $argCharLimit) . '...' : $sarg;
-                } else {
-                    $args[] = get_class($arg);
                 }
             }
 

src/Dev/TestSession.php

@@ -4,6 +4,7 @@
 
 use Exception;
 use InvalidArgumentException;
+use LogicException;
 use SilverStripe\Control\Controller;
 use SilverStripe\Control\Cookie_Backend;
 use SilverStripe\Control\Director;
@@ -214,7 +215,7 @@ public function submitForm(string $formID, string $button = null, array $data =
                 $formCrawler = $page->filterXPath("//form[@id='$formID']");
                 $form = $formCrawler->form();
             } catch (InvalidArgumentException $e) {
-                user_error("TestSession::submitForm failed to find the form {$formID}");
+                throw new LogicException("TestSession::submitForm failed to find the form '{$formID}'");
             }
 
             foreach ($data as $fieldName => $value) {
@@ -235,7 +236,7 @@ public function submitForm(string $formID, string $button = null, array $data =
             if ($button) {
                 $btnXpath = "//button[@name='$button'] | //input[@name='$button'][@type='button' or @type='submit']";
                 if (!$formCrawler->children()->filterXPath($btnXpath)->count()) {
-                    throw new Exception("Can't find button '$button' to submit as part of test.");
+                    throw new LogicException("Can't find button '$button' to submit as part of test.");
                 }
                 $values[$button] = true;
             }

src/Forms/DropdownField.php

@@ -68,7 +68,7 @@
  * DropdownField::create(
  *   'Country',
  *   'Country',
- *   singleton(MyObject::class)->dbObject('Country')->enumValues()
+ *   singleton(MyObject::class)->dbObject('Country')?->enumValues()
  * );
  * </code>
  *

src/Forms/FieldGroup.php

@@ -154,7 +154,7 @@ public function getMessage()
         /** @var FormField $subfield */
         $messages = [];
         foreach ($dataFields as $subfield) {
-            $message = $subfield->obj('Message')->forTemplate();
+            $message = $subfield->obj('Message')?->forTemplate();
             if ($message) {
                 $messages[] = rtrim($message ?? '', ".");
             }

src/Forms/Form.php

@@ -82,7 +82,7 @@ class Form extends ModelData implements HasRequestHandler
     const ENC_TYPE_MULTIPART  = 'multipart/form-data';
 
     /**
-     * Accessed by Form.ss.
+     * Accessed by Form template.
      * A performance enhancement over the generate-the-form-tag-and-then-remove-it code that was there previously
      *
      * @var bool
@@ -159,7 +159,7 @@ class Form extends ModelData implements HasRequestHandler
     /**
      * Legend value, to be inserted into the
      * <legend> element before the <fieldset>
-     * in Form.ss template.
+     * in Form template.
      *
      * @var string|null
      */
@@ -888,7 +888,7 @@ public function setTarget($target)
 
     /**
      * Set the legend value to be inserted into
-     * the <legend> element in the Form.ss template.
+     * the <legend> element in the Form template.
      * @param string $legend
      * @return $this
      */
@@ -899,10 +899,10 @@ public function setLegend($legend)
     }
 
     /**
-     * Set the SS template that this form should use
+     * Set the template or template candidates that this form should use
      * to render with. The default is "Form".
      *
-     * @param string|array $template The name of the template (without the .ss extension) or array form
+     * @param string|array $template The name of the template (without the file extension) or array of candidates
      * @return $this
      */
     public function setTemplate($template)
@@ -1234,7 +1234,7 @@ public function getRecord()
 
     /**
      * Get the legend value to be inserted into the
-     * <legend> element in Form.ss
+     * <legend> element in Form template
      *
      * @return string
      */