Validate Container configuration references valid class instances

Author: clue

docs/best-practices/controllers.md

@@ -262,9 +262,14 @@ This can be useful in these cases:
 
 The configured container instance can be passed into the application like any
 other middleware request handler. In most cases this means you create a single
-`Container` instance with a number of factory methods and pass this instance as
+`Container` instance with a number of factory functions and pass this instance as
 the first argument to the `App`.
 
+In its most common form, each entry in the container configuration maps a class
+name to a factory function that will be invoked when this class is first
+requested. The factory function is responsible for returning an instance that
+implements the given class name.
+
 ### PSR-11 compatibility
 
 > ⚠️ **Feature preview**

src/Container.php

@@ -15,6 +15,11 @@ class Container
     /** @var array<class-string,callable():object | object> */
     public function __construct(array $map = [])
     {
+        foreach ($map as $name => $value) {
+            if (!$value instanceof \Closure && !$value instanceof $name) {
+                throw new \BadMethodCallException('Map for ' . $name . ' contains unexpected ' . (is_object($value) ? get_class($value) : gettype($value)));
+            }
+        }
         $this->container = $map;
     }
 
@@ -81,7 +86,13 @@ private function load(string $name, int $depth = 64)
     {
         if (isset($this->container[$name])) {
             if ($this->container[$name] instanceof \Closure) {
-                $this->container[$name] = ($this->container[$name])();
+                $value = ($this->container[$name])();
+
+                if (!$value instanceof $name) {
+                    throw new \BadMethodCallException('Factory for ' . $name . ' returned unexpected ' . (is_object($value) ? get_class($value) : gettype($value)));
+                }
+
+                $this->container[$name] = $value;
             }
 
             return $this->container[$name];

tests/ContainerTest.php

@@ -132,6 +132,31 @@ public function __invoke(ServerRequestInterface $request)
         $this->assertEquals('{"num":1}', (string) $response->getBody());
     }
 
+    public function testCtorThrowsWhenMapContainsInvalidInteger()
+    {
+        $this->expectException(\BadMethodCallException::class);
+        $this->expectExceptionMessage('Map for stdClass contains unexpected integer');
+
+        new Container([
+            \stdClass::class => 42
+        ]);
+    }
+
+    public function testCallableReturnsCallableThatThrowsWhenFactoryReturnsInvalidInteger()
+    {
+        $request = new ServerRequest('GET', 'http://example.com/');
+
+        $container = new Container([
+            \stdClass::class => function () { return 42; }
+        ]);
+
+        $callable = $container->callable(\stdClass::class);
+
+        $this->expectException(\BadMethodCallException::class);
+        $this->expectExceptionMessage('Factory for stdClass returned unexpected integer');
+        $callable($request);
+    }
+
     public function testInvokeContainerAsMiddlewareReturnsFromNextRequestHandler()
     {
         $request = new ServerRequest('GET', 'http://example.com/');