add support for appendable component attributes

src/Illuminate/View/AppendableAttributeValue.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Illuminate\View;
+
+class AppendableAttributeValue
+{
+    public $value;
+
+    public function __construct($value)
+    {
+        $this->value = $value;
+    }
+}

src/Illuminate/View/ComponentAttributeBag.php

@@ -171,31 +171,76 @@ public function exceptProps($keys)
      */
     public function merge(array $attributeDefaults = [], $escape = true)
     {
-        $attributes = [];
-
         $attributeDefaults = array_map(function ($value) use ($escape) {
-            if (! $escape || is_object($value) || is_null($value) || is_bool($value)) {
-                return $value;
-            }
-
-            return e($value);
+            return $this->shouldEscapeAttributeValue($escape, $value)
+                        ? e($value)
+                        : $value;
         }, $attributeDefaults);
 
-        foreach ($this->attributes as $key => $value) {
-            if ($key !== 'class') {
-                $attributes[$key] = $value;
+        [$appendableAttributes, $nonAppendableAttributes] = collect($this->attributes)
+                    ->partition(function ($value, $key) use ($attributeDefaults) {
+                        return $key === 'class' ||
+                               (isset($attributeDefaults[$key]) &&
+                                $attributeDefaults[$key] instanceof AppendableAttributeValue);
+                    });
 
-                continue;
-            }
+        $attributes = $appendableAttributes->mapWithKeys(function ($value, $key) use ($attributeDefaults, $escape) {
+            $defaultsValue = isset($attributeDefaults[$key]) && $attributeDefaults[$key] instanceof AppendableAttributeValue
+                        ? $this->resolveAppendableAttributeDefault($attributeDefaults, $key, $escape)
+                        : ($attributeDefaults[$key] ?? '');
 
-            $attributes[$key] = implode(' ', array_unique(
-                array_filter([$attributeDefaults[$key] ?? '', $value])
-            ));
-        }
+            return [$key => implode(' ', array_unique(array_filter([$defaultsValue, $value])))];
+        })->merge($nonAppendableAttributes)->all();
 
         return new static(array_merge($attributeDefaults, $attributes));
     }
 
+    /**
+     * Determine if the specific attribute value should be escaped.
+     *
+     * @param  bool  $escape
+     * @param  mixed  $value
+     * @return bool
+     */
+    protected function shouldEscapeAttributeValue($escape, $value)
+    {
+        if (! $escape) {
+            return false;
+        }
+
+        return ! is_object($value) &&
+               ! is_null($value) &&
+               ! is_bool($value);
+    }
+
+    /**
+     * Create a new appendable attribute value.
+     *
+     * @param  mixed  $value
+     * @return \Illuminate\View\AppendableAttributeValue
+     */
+    public function appends($value)
+    {
+        return new AppendableAttributeValue($value);
+    }
+
+    /**
+     * Resolve an appendable attribute value default value.
+     *
+     * @param  array  $attributeDefaults
+     * @param  string  $key
+     * @param  bool  $escape
+     * @return mixed
+     */
+    protected function resolveAppendableAttributeDefault($attributeDefaults, $key, $escape)
+    {
+        if ($this->shouldEscapeAttributeValue($escape, $value = $attributeDefaults[$key]->value)) {
+            $value = e($value);
+        }
+
+        return $value;
+    }
+
     /**
      * Get all of the raw attributes.
      *

tests/Integration/View/BladeTest.php

@@ -48,6 +48,15 @@ public function test_rendering_the_same_dynamic_component_with_different_attribu
 </span>', trim($view));
     }
 
+    public function test_appendable_attributes()
+    {
+        $view = View::make('uses-appendable-panel', ['name' => 'Taylor'])->render();
+
+        $this->assertEquals('<div class="mt-4 bg-gray-100" data-controller="inside-controller outside-controller" foo="bar">
+    Hello Taylor
+</div>', trim($view));
+    }
+
     protected function getEnvironmentSetUp($app)
     {
         $app['config']->set('view.paths', [__DIR__.'/templates']);

tests/Integration/View/templates/components/appendable-panel.blade.php

@@ -0,0 +1,5 @@
+@props(['name'])
+
+<div {{ $attributes->merge(['class' => 'mt-4', 'data-controller' => $attributes->appends('inside-controller')]) }}>
+    Hello {{ $name }}
+</div>

tests/Integration/View/templates/uses-appendable-panel.blade.php

@@ -0,0 +1,3 @@
+<x-appendable-panel class="bg-gray-100" :name="$name" data-controller="outside-controller" foo="bar">
+    Panel contents
+</x-appendable-panel>