[2.x] Introduce ProvidesInertiaProp interface

src/PropertyContext.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Inertia;
+
+use Illuminate\Http\Request;
+
+class PropertyContext
+{
+    public function __construct(
+        public string $key,
+        public array $props,
+        public Request $request
+    ) {
+        //
+    }
+}

src/ProvidesInertiaProperty.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace Inertia;
+
+interface ProvidesInertiaProperty
+{
+    public function toInertiaProperty(PropertyContext $prop): mixed;
+}

src/Response.php

@@ -254,7 +254,7 @@ public function resolveAlways(array $props): array
     /**
      * Resolve all necessary class instances in the given props.
      */
-    public function resolvePropertyInstances(array $props, Request $request): array
+    public function resolvePropertyInstances(array $props, Request $request, ?string $parentKey = null): array
     {
         foreach ($props as $key => $value) {
             $resolveViaApp = collect([
@@ -270,6 +270,12 @@ public function resolvePropertyInstances(array $props, Request $request): array
                 $value = App::call($value);
             }
 
+            $currentKey = $parentKey ? $parentKey.'.'.$key : $key;
+
+            if ($value instanceof ProvidesInertiaProperty) {
+                $value = $value->toInertiaProperty(new PropertyContext($currentKey, $props, $request));
+            }
+
             if ($value instanceof Arrayable) {
                 $value = $value->toArray();
             }
@@ -287,7 +293,7 @@ public function resolvePropertyInstances(array $props, Request $request): array
             }
 
             if (is_array($value)) {
-                $value = $this->resolvePropertyInstances($value, $request);
+                $value = $this->resolvePropertyInstances($value, $request, $currentKey);
             }
 
             $props[$key] = $value;

tests/ResponseTest.php

@@ -14,10 +14,12 @@
 use Illuminate\View\View;
 use Inertia\AlwaysProp;
 use Inertia\DeferProp;
+use Inertia\Inertia;
 use Inertia\LazyProp;
 use Inertia\MergeProp;
 use Inertia\Response;
 use Inertia\Tests\Stubs\FakeResource;
+use Inertia\Tests\Stubs\MergeWithSharedProp;
 use Mockery;
 
 class ResponseTest extends TestCase
@@ -820,6 +822,29 @@ public function test_always_props_are_included_on_partial_reload(): void
         $this->assertFalse(isset($page->props->user));
     }
 
+    public function test_inertia_response_type_prop(): void
+    {
+        $request = Request::create('/user/123', 'GET');
+
+        Inertia::share('items', ['foo']);
+        Inertia::share('deep.foo.bar', ['foo']);
+
+        $response = new Response('User/Edit', [
+            'items' => new MergeWithSharedProp(['bar']),
+            'deep' => [
+                'foo' => [
+                    'bar' => new MergeWithSharedProp(['baz']),
+                ],
+            ],
+        ], 'app', '123');
+        $response = $response->toResponse($request);
+        $view = $response->getOriginalContent();
+        $page = $view->getData()['page'];
+
+        $this->assertSame(['foo', 'bar'], $page['props']['items']);
+        $this->assertSame(['foo', 'baz'], $page['props']['deep']['foo']['bar']);
+    }
+
     public function test_top_level_dot_props_get_unpacked(): void
     {
         $props = [

tests/Stubs/MergeWithSharedProp.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Inertia\Tests\Stubs;
+
+use Inertia\Inertia;
+use Inertia\PropertyContext;
+use Inertia\ProvidesInertiaProperty;
+
+class MergeWithSharedProp implements ProvidesInertiaProperty
+{
+    public function __construct(protected array $items = []) {}
+
+    public function toInertiaProperty(PropertyContext $prop): mixed
+    {
+        return array_merge(Inertia::getShared($prop->key, []), $this->items);
+    }
+}