fix(admin): support Mustache 3.2 dotted-name lookup in AssetsHelpers

packages/admin/src/Charcoal/Admin/Mustache/AssetsHelpers.php

@@ -76,12 +76,23 @@ protected function reset()
     /**
      * Magic: Render the Mustache section.
      *
+     * Mustache 3+ may invoke callables while resolving dotted names
+     * (e.g. `assets.output.css`) with zero arguments. In that case,
+     * return `$this` so `__get()` can continue.
+     *
+     * Mustache 3.2 interpolates the final dotted-name value instead of
+     * invoking it as a lambda. `__toString()` runs the pending action.
+     *
      * @param  string            $text   The translation key.
      * @param  LambdaHelper|null $helper For rendering strings in the current context.
-     * @return string
+     * @return string|self
      */
     public function __invoke($text = null, LambdaHelper $helper = null)
     {
+        if (func_num_args() === 0 || $this->action === null) {
+            return $this;
+        }
+
         if ($helper) {
             $text = (string)$helper->render($text);
         }
@@ -97,6 +108,23 @@ public function __invoke($text = null, LambdaHelper $helper = null)
         return $text;
     }
 
+    /**
+     * Magic: Render the pending action when Mustache interpolates this helper.
+     *
+     * @return string
+     */
+    public function __toString(): string
+    {
+        if ($this->action === null) {
+            return '';
+        }
+
+        $return = $this->{$this->action}($this->collection, '');
+        $this->reset();
+
+        return (string)$return;
+    }
+
     /**
      * Magic: Determine if a property is set and is not NULL.
      *

packages/admin/tests/Charcoal/Admin/Mustache/AssetsHelpersTest.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace Charcoal\Tests\Admin\Mustache;
+
+use Assetic\Asset\AssetCollection;
+use Assetic\Asset\StringAsset;
+use Assetic\AssetManager;
+use Charcoal\Admin\Mustache\AssetsHelpers;
+use Charcoal\Tests\AbstractTestCase;
+use Mustache\Engine as MustacheEngine;
+
+/**
+ *
+ */
+class AssetsHelpersTest extends AbstractTestCase
+{
+    /**
+     * @var AssetsHelpers
+     */
+    private $obj;
+
+    /**
+     * @var AssetManager
+     */
+    private $assets;
+
+    /**
+     * @return void
+     */
+    public function setUp(): void
+    {
+        $this->assets = new AssetManager();
+        $this->assets->set('css', new AssetCollection([
+            new StringAsset('.login { color: red; }'),
+        ]));
+
+        $this->obj = new AssetsHelpers([
+            'assets' => $this->assets,
+        ]);
+    }
+
+    /**
+     * @return void
+     */
+    public function testDottedOutputWithMustache()
+    {
+        $mustache = new MustacheEngine([
+            'helpers'          => $this->obj->toArray(),
+            'strict_callables' => true,
+        ]);
+
+        $this->assertEquals(
+            '{{=<<<<% %>>>>=}}.login { color: red; }<<<<%={{ }}=%>>>>',
+            $mustache->render('{{& assets.output.css }}')
+        );
+    }
+
+    /**
+     * @return void
+     */
+    public function testInvokeWithoutArgumentsReturnsSelf()
+    {
+        $this->assertSame($this->obj, ($this->obj)());
+    }
+}