More specific exceptions

Per feedback, this patch makes exception throwing more consistent, and
more specific. Each of abstract factories, initializers, and delegator
factories now throw messages in the same manner, and differentiate
between inability to resolve a class name and non-callable/invalid type
factories.

Author: weierophinney

src/ServiceManager.php

@@ -274,11 +274,25 @@ protected function configure(array $config)
                     continue;
                 }
 
+                // Error condition; let's find out why.
+
+                // If we still have a string, we have a class name that does not resolve
+                if (is_string($abstractFactory)) {
+                    throw new InvalidArgumentException(sprintf(
+                        'An invalid abstract factory was registered; resolved to class "%s" '
+                        . 'which does not exist; please provide a valid class name resolving '
+                        . 'to an implementation of %s',
+                        $abstractFactory,
+                        AbstractFactoryInterface::class
+                    ));
+                }
+
+                // Otherwise, we have an invalid type.
                 throw new InvalidArgumentException(sprintf(
-                    'An invalid abstract factory was registered. An instance of "%s" was expected, '
+                    'An invalid abstract factory was registered. Expected an instance of "%s", '
                     . 'but "%s" was received',
                     AbstractFactoryInterface::class,
-                    is_object($abstractFactory) ? get_class($abstractFactory) : gettype($abstractFactory)
+                    (is_object($abstractFactory) ? get_class($abstractFactory) : gettype($abstractFactory))
                 ));
             }
         }
@@ -294,11 +308,25 @@ protected function configure(array $config)
                     continue;
                 }
 
+                // Error condition; let's find out why.
+
+                if (is_string($initializer)) {
+                    throw new InvalidArgumentException(sprintf(
+                        'An invalid initializer was registered; resolved to class or function "%s" '
+                        . 'which does not exist; please provide a valid function name or class '
+                        . 'name resolving to an implementation of %s',
+                        $initializer,
+                        InitializerInterface::class
+                    ));
+                }
+
+                // Otherwise, we have an invalid type.
                 throw new InvalidArgumentException(sprintf(
-                    'An invalid initializer was registered. A callable or an instance of "%s" was expected, but
-                    "%s" was received',
+                    'An invalid initializer was registered. Expected a callable, or an instance of '
+                    . '(or string class name resolving to) "%s", '
+                    . 'but "%s" was received',
                     InitializerInterface::class,
-                    is_object($initializer) ? get_class($initializer) : gettype($initializer)
+                    (is_object($initializer) ? get_class($initializer) : gettype($initializer))
                 ));
             }
         }
@@ -391,20 +419,21 @@ private function createDelegatorFromName($name, array $options = null)
                 $delegatorFactory = $this->createLazyServiceDelegatorFactory();
             }
 
-            if (is_string($delegatorFactory) && ! class_exists($delegatorFactory)) {
-                throw new ServiceNotCreatedException(sprintf(
-                    'An invalid delegator was provided. A callable or an instance of "%s" was expected, '
-                    . 'but "%s" was received',
-                    DelegatorFactoryInterface::class,
-                    $delegatorFactory
-                ));
-            }
-
-            if (is_string($delegatorFactory)) {
-                $delegatorFactory = $this->delegators[$name][$index] = new $delegatorFactory();
+            if (is_string($delegatorFactory) && class_exists($delegatorFactory)) {
+                $delegatorFactory = new $delegatorFactory();
             }
 
             if (! is_callable($delegatorFactory)) {
+                if (is_string($delegatorFactory)) {
+                    throw new ServiceNotCreatedException(sprintf(
+                        'An invalid delegator factory was registered; resolved to class or function "%s" '
+                        . 'which does not exist; please provide a valid function name or class name resolving '
+                        . 'to an implementation of %s',
+                        $delegatorFactory,
+                        DelegatorFactoryInterface::class
+                    ));
+                }
+
                 throw new ServiceNotCreatedException(sprintf(
                     'A non-callable delegator, "%s", was provided; expected a callable or '
                     . 'instance of "%s"',
@@ -413,6 +442,8 @@ private function createDelegatorFromName($name, array $options = null)
                 ));
             }
 
+            $this->delegators[$name][$index] = $delegatorFactory;
+
             $creationCallback = function () use ($delegatorFactory, $name, $creationCallback, $options) {
                 return $delegatorFactory($this->creationContext, $name, $creationCallback, $options);
             };