feature #21455 [DI] Allow to count on lazy collection arguments (ogizanagi)

This PR was merged into the 3.3-dev branch.

Discussion
----------

[DI] Allow to count on lazy collection arguments

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony/pull/21450#issuecomment-275931764
| License       | MIT
| Doc PR        | todo (with https://github.com/symfony/symfony-docs/issues/7336)

When using the new iterator feature of the DI component to lazy load collection, we always know the number of arguments in the collection (only the invalidBehavior set to `IGNORE_ON_INVALID_REFERENCE` may change this number). So we are able to generate and use a `RewindableGenerator` implementing `\Countable` by computing this value ahead.

So, in a service accepting `array|iterable`, like in the `GuardAuthenticationListener` (see #21450):

```php
class GuardAuthenticationListener implements ListenerInterface
{
    private $guardAuthenticators;

    /**
       * @param iterable|GuardAuthenticatorInterface[]  $guardAuthenticators   The authenticators, with keys that match what's passed to GuardAuthenticationProvider
       * @param LoggerInterface                         $logger                A LoggerInterface instance
    */
    public function __construct($guardAuthenticators, LoggerInterface $logger = null)
    {
          // ...
    }

    public function handle(GetResponseEvent $event)
    {
        if (null !== $this->logger) {
            $context = array()
            if (is_array($this->guardAuthenticators) || $this->guardAuthenticators instanceof \Countable) {
                $context['authenticators'] = count($this->guardAuthenticators);
            }
            $this->logger->debug('Checking for guard authentication credentials.', $context);
        }
        // ...
    }
}
```

we still keep the ability to call count without loosing the lazy load benefits.

Commits
-------

f23e460 [DI] Allow to count on lazy collection arguments

src/Symfony/Component/DependencyInjection/Argument/RewindableGenerator.php

@@ -14,13 +14,19 @@ namespace Symfony\Component\DependencyInjection\Argument;
 /**
  * @internal
  */
-class RewindableGenerator implements \IteratorAggregate
+class RewindableGenerator implements \IteratorAggregate, \Countable
 {
     private $generator;
+    private $count;
 
-    public function __construct(callable $generator)
+    /**
+     * @param callable     $generator
+     * @param int|callable $count
+     */
+    public function __construct(callable $generator, $count)
     {
         $this->generator = $generator;
+        $this->count = $count;
     }
 
     public function getIterator()
@@ -29,4 +35,13 @@ class RewindableGenerator implements \IteratorAggregate
 
         return $g();
     }
+
+    public function count()
+    {
+        if (is_callable($count = $this->count)) {
+            $this->count = $count();
+        }
+
+        return $this->count;
+    }
 }

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

@@ -1002,6 +1002,19 @@ class ContainerBuilder extends Container implements TaggedContainerInterface
 
                     yield $k => $this->resolveServices($parameterBag->unescapeValue($parameterBag->resolveValue($v)));
                 }
+            }, function () use ($value) {
+                $count = 0;
+                foreach ($value->getValues() as $v) {
+                    foreach (self::getServiceConditionals($v) as $s) {
+                        if (!$this->has($s)) {
+                            continue 2;
+                        }
+                    }
+
+                    ++$count;
+                }
+
+                return $count;
             });
         } elseif ($value instanceof ClosureProxyArgument) {
             $parameterBag = $this->getParameterBag();

src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php

@@ -1362,19 +1362,36 @@ EOF;
      */
     private function wrapServiceConditionals($value, $code, &$isUnconditional = null, $containerRef = '$this')
     {
-        if ($isUnconditional = !$services = ContainerBuilder::getServiceConditionals($value)) {
+        if ($isUnconditional = !$condition = $this->getServiceConditionals($value, $containerRef)) {
             return $code;
         }
 
+        // re-indent the wrapped code
+        $code = implode("\n", array_map(function ($line) { return $line ? '    '.$line : $line; }, explode("\n", $code)));
+
+        return sprintf("        if (%s) {\n%s        }\n", $condition, $code);
+    }
+
+    /**
+     * Get the conditions to execute for conditional services.
+     *
+     * @param string $value
+     * @param string $containerRef
+     *
+     * @return null|string
+     */
+    private function getServiceConditionals($value, $containerRef = '$this')
+    {
+        if (!$services = ContainerBuilder::getServiceConditionals($value)) {
+            return null;
+        }
+
         $conditions = array();
         foreach ($services as $service) {
             $conditions[] = sprintf("%s->has('%s')", $containerRef, $service);
         }
 
-        // re-indent the wrapped code
-        $code = implode("\n", array_map(function ($line) { return $line ? '    '.$line : $line; }, explode("\n", $code)));
-
-        return sprintf("        if (%s) {\n%s        }\n", implode(' && ', $conditions), $code);
+        return implode(' && ', $conditions);
     }
 
     /**
@@ -1524,9 +1541,14 @@ EOF;
 
             return sprintf('array(%s)', implode(', ', $code));
         } elseif ($value instanceof IteratorArgument) {
+            $countCode = array();
+            $countCode[] = 'function () {';
+            $operands = array(0);
+
             $code = array();
-            $code[] = 'new RewindableGenerator(function() {';
+            $code[] = 'new RewindableGenerator(function () {';
             foreach ($value->getValues() as $k => $v) {
+                ($c = $this->getServiceConditionals($v)) ? $operands[] = "(int) ($c)" : ++$operands[0];
                 $v = $this->wrapServiceConditionals($v, sprintf("        yield %s => %s;\n", $this->dumpValue($k, $interpolate), $this->dumpValue($v, $interpolate)));
                 foreach (explode("\n", $v) as $v) {
                     if ($v) {
@@ -1534,7 +1556,11 @@ EOF;
                     }
                 }
             }
-            $code[] = '        })';
+
+            $countCode[] = sprintf('            return %s;', implode(' + ', $operands));
+            $countCode[] = '        }';
+
+            $code[] = sprintf('        }, %s)', count($operands) > 1 ? implode("\n", $countCode) : $operands[0]);
 
             return implode("\n", $code);
         } elseif ($value instanceof Definition) {

src/Symfony/Component/DependencyInjection/Tests/Argument/RewindableGeneratorTest.php

@@ -0,0 +1,52 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\DependencyInjection\Tests\Argument;
+
+use Symfony\Component\DependencyInjection\Argument\RewindableGenerator;
+
+class RewindableGeneratorTest extends \PHPUnit_Framework_TestCase
+{
+    public function testImplementsCountable()
+    {
+        $this->assertInstanceOf(\Countable::class, new RewindableGenerator(function () {
+            yield 1;
+        }, 1));
+    }
+
+    public function testCountUsesProvidedValue()
+    {
+        $generator = new RewindableGenerator(function () {
+            yield 1;
+        }, 3);
+
+        $this->assertCount(3, $generator);
+    }
+
+    public function testCountUsesProvidedValueAsCallback()
+    {
+        $called = 0;
+        $generator = new RewindableGenerator(function () {
+            yield 1;
+        }, function () use (&$called) {
+            ++$called;
+
+            return 3;
+        });
+
+        $this->assertSame(0, $called, 'Count callback is called lazily');
+        $this->assertCount(3, $generator);
+
+        count($generator);
+
+        $this->assertSame(1, $called, 'Count callback is called only once');
+    }
+}

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

@@ -423,6 +423,7 @@ class ContainerBuilderTest extends \PHPUnit_Framework_TestCase
 
         $lazyContext = $builder->get('lazy_context');
         $this->assertInstanceOf(RewindableGenerator::class, $lazyContext->lazyValues);
+        $this->assertCount(1, $lazyContext->lazyValues);
 
         $i = 0;
         foreach ($lazyContext->lazyValues as $k => $v) {

src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9.php

@@ -314,13 +314,13 @@ class ProjectServiceContainer extends Container
      */
     protected function getLazyContextService()
     {
-        return $this->services['lazy_context'] = new \LazyContext(new RewindableGenerator(function() {
+        return $this->services['lazy_context'] = new \LazyContext(new RewindableGenerator(function () {
             yield 0 => 'foo';
             yield 1 => ${($_ = isset($this->services['foo.baz']) ? $this->services['foo.baz'] : $this->get('foo.baz')) && false ?: '_'};
             yield 2 => array($this->getParameter('foo') => 'foo is '.$this->getParameter('foo').'', 'foobar' => $this->getParameter('foo'));
             yield 3 => true;
             yield 4 => $this;
-        }));
+        }, 5));
     }
 
     /**
@@ -333,11 +333,13 @@ class ProjectServiceContainer extends Container
      */
     protected function getLazyContextIgnoreInvalidRefService()
     {
-        return $this->services['lazy_context_ignore_invalid_ref'] = new \LazyContext(new RewindableGenerator(function() {
+        return $this->services['lazy_context_ignore_invalid_ref'] = new \LazyContext(new RewindableGenerator(function () {
             yield 0 => ${($_ = isset($this->services['foo.baz']) ? $this->services['foo.baz'] : $this->get('foo.baz')) && false ?: '_'};
             if ($this->has('invalid')) {
                 yield 1 => $this->get('invalid', ContainerInterface::NULL_ON_INVALID_REFERENCE);
             }
+        }, function () {
+            return 1 + (int) ($this->has('invalid'));
         }));
     }
 

src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_compiled.php

@@ -313,13 +313,13 @@ class ProjectServiceContainer extends Container
      */
     protected function getLazyContextService()
     {
-        return $this->services['lazy_context'] = new \LazyContext(new RewindableGenerator(function() {
+        return $this->services['lazy_context'] = new \LazyContext(new RewindableGenerator(function () {
             yield 0 => 'foo';
             yield 1 => ${($_ = isset($this->services['foo.baz']) ? $this->services['foo.baz'] : $this->get('foo.baz')) && false ?: '_'};
             yield 2 => array('bar' => 'foo is bar', 'foobar' => 'bar');
             yield 3 => true;
             yield 4 => $this;
-        }));
+        }, 5));
     }
 
     /**
@@ -332,9 +332,9 @@ class ProjectServiceContainer extends Container
      */
     protected function getLazyContextIgnoreInvalidRefService()
     {
-        return $this->services['lazy_context_ignore_invalid_ref'] = new \LazyContext(new RewindableGenerator(function() {
+        return $this->services['lazy_context_ignore_invalid_ref'] = new \LazyContext(new RewindableGenerator(function () {
             yield 0 => ${($_ = isset($this->services['foo.baz']) ? $this->services['foo.baz'] : $this->get('foo.baz')) && false ?: '_'};
-        }));
+        }, 1));
     }
 
     /**