Change Twig template loading fallbacks

Previously:
- registered Laravel view file
- attempt to load file as a CMS partial

Now:
- registered Laravel view file
- valid CMS partials
- any file that Twig can access (from the project root) rendered as a plain twig template (but with support for the CMS twig environment)

Fixes 80aab47f04 (commitcomment-42223643), https://github.com/octobercms/october/issues/5261#issuecomment-691235167

modules/cms/twig/Loader.php

@@ -27,7 +27,9 @@ class Loader extends LoaderBase implements TwigLoaderInterface
 
     /**
      * Sets a CMS object to load the template from.
+     *
      * @param \Cms\Contracts\CmsObject $obj Specifies the CMS object.
+     * @return void
      */
     public function setObject(CmsObject $obj)
     {
@@ -37,6 +39,9 @@ class Loader extends LoaderBase implements TwigLoaderInterface
     /**
      * Returns the Twig content string.
      * This step is cached internally by Twig.
+     *
+     * @param string $name The template name
+     * @return TwigSource
      */
     public function getSourceContext($name)
     {
@@ -65,6 +70,9 @@ class Loader extends LoaderBase implements TwigLoaderInterface
 
     /**
      * Returns the Twig cache key.
+     *
+     * @param string $name The template name
+     * @return string
      */
     public function getCacheKey($name)
     {
@@ -77,6 +85,10 @@ class Loader extends LoaderBase implements TwigLoaderInterface
 
     /**
      * Determines if the content is fresh.
+     *
+     * @param string $name The template name
+     * @param mixed $time The time to check against the template
+     * @return bool
      */
     public function isFresh($name, $time)
     {
@@ -89,6 +101,9 @@ class Loader extends LoaderBase implements TwigLoaderInterface
 
     /**
      * Returns the file name of the loaded template.
+     *
+     * @param string $name The template name
+     * @return string
      */
     public function getFilename($name)
     {
@@ -101,6 +116,9 @@ class Loader extends LoaderBase implements TwigLoaderInterface
 
     /**
      * Checks that the template exists.
+     *
+     * @param string $name The template name
+     * @return bool
      */
     public function exists($name)
     {
@@ -115,11 +133,12 @@ class Loader extends LoaderBase implements TwigLoaderInterface
      * Internal method that checks if the template name matches
      * the loaded object, with fallback support to partials.
      *
+     * @param string $name The template name to validate
      * @return bool
      */
     protected function validateCmsObject($name)
     {
-        if ($name === $this->obj->getFilePath()) {
+        if ($this->obj && $name === $this->obj->getFilePath()) {
             return true;
         }
 
@@ -133,18 +152,29 @@ class Loader extends LoaderBase implements TwigLoaderInterface
 
     /**
      * Looks up a fallback CMS partial object.
-     * @return Cms\Classes\Partial
+     *
+     * @param string $name The filename to attempt to load a fallback CMS partial for
+     * @return Cms\Classes\Partial|bool Returns false if a CMS partial can't be found
      */
     protected function findFallbackObject($name)
     {
+        // Ignore Laravel views
         if (strpos($name, '::') !== false) {
             return false;
         }
 
+        // Check the cache
         if (array_key_exists($name, $this->fallbackCache)) {
             return $this->fallbackCache[$name];
         }
 
-        return $this->fallbackCache[$name] = CmsPartial::find($name);
+        // Attempt to load the path as a CMS Partial object
+        try {
+            $partial = CmsPartial::find($name);
+        } catch (\Exception $e) {
+            return false;
+        }
+
+        return $this->fallbackCache[$name] = $partial;
     }
 }