feature #23915 [DI] Allow get available services from service locator (Koc)

This PR was merged into the 3.4 branch.

Discussion
----------

[DI] Allow get available services from service locator

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

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Sometimes we are using service locators and throw context specific exceptions if service not found inside it. Would be nice inform user about available services in our custom exception, like:

```php
try {
    return $this->transports->get($transport);
} catch (NotFoundExceptionInterface $e) {
    $availableTransports = method_exists($e, 'getAlternatives') ? $e->getAlternatives() : [];

    throw TransportNotFoundException::create($transport, $availableTransports, $e);
}
```

Commits
-------

4993b1c14c Allow to get alternatives when ServiceNotFoundException occurs.

src/Symfony/Component/DependencyInjection/Exception/ServiceNotFoundException.php

@@ -22,6 +22,7 @@ class ServiceNotFoundException extends InvalidArgumentException implements NotFo
 {
     private $id;
     private $sourceId;
+    private $alternatives;
 
     public function __construct($id, $sourceId = null, \Exception $previous = null, array $alternatives = array())
     {
@@ -44,6 +45,7 @@ class ServiceNotFoundException extends InvalidArgumentException implements NotFo
 
         $this->id = $id;
         $this->sourceId = $sourceId;
+        $this->alternatives = $alternatives;
     }
 
     public function getId()
@@ -55,4 +57,9 @@ class ServiceNotFoundException extends InvalidArgumentException implements NotFo
     {
         return $this->sourceId;
     }
+
+    public function getAlternatives()
+    {
+        return $this->alternatives;
+    }
 }

src/Symfony/Component/DependencyInjection/Tests/ServiceLocatorTest.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\DependencyInjection\Tests;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
 use Symfony\Component\DependencyInjection\ServiceLocator;
 
 class ServiceLocatorTest extends TestCase
@@ -58,7 +59,7 @@ class ServiceLocatorTest extends TestCase
 
     /**
      * @expectedException        \Psr\Container\NotFoundExceptionInterface
-     * @expectedExceptionMessage You have requested a non-existent service "dummy"
+     * @expectedExceptionMessage You have requested a non-existent service "dummy". Did you mean one of these: "foo", "bar"?
      */
     public function testGetThrowsOnUndefinedService()
     {
@@ -67,7 +68,13 @@ class ServiceLocatorTest extends TestCase
             'bar' => function () { return 'baz'; },
         ));
 
-        $locator->get('dummy');
+        try {
+            $locator->get('dummy');
+        } catch (ServiceNotFoundException $e) {
+            $this->assertSame(array('foo', 'bar'), $e->getAlternatives());
+
+            throw $e;
+        }
     }
 
     public function testInvoke()