feature #21122 [ExpressionLanguage] Create an ExpressionFunction from a PHP function name (maidmaid)

This PR was squashed before being merged into the 3.3-dev branch (closes #21122).

Discussion
----------

[ExpressionLanguage] Create an ExpressionFunction from a PHP function name

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

When we [extend Expression Language](http://symfony.com/doc/current/components/expression_language/extending.html), we often need to add PHP functions whose code is repetitive and redundant at the compiler/evaluator level. This PR proposes a new way more generic which allows to add a PHP function.

currently:

```php
$el = new ExpressionLanguage();
$compiler = function ($str) {
    return sprintf('strtoupper(%s)', $str);
};
$evaluator = function ($arguments, $str) {
    return strtoupper($str);
};
$el->addFunction(new ExpressionFunction('strtoupper', $compiler, $evaluator));
$el->evaluate('strtoupper("hello")'); // return "HELLO"
```

with this PR:

```php
$el->addFunction(ExpressionFunction::fromPhp('strtoupper'));
$el->evaluate('strtoupper("hello")'); // return "HELLO"
```

It includes PHP namespaced function:

```php
$el->addFunction(ExpressionFunction::fromPhp('My\strtoupper', 'my_strtoupper'));
$el->evaluate('my_strtoupper("hello")'); // return "HELLO"
```

Commits
-------

44d67ed5f5 [ExpressionLanguage] Create an ExpressionFunction from a PHP function name

src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php

@@ -62,4 +62,41 @@ class ExpressionFunction
     {
         return $this->evaluator;
     }
+
+    /**
+     * Creates an ExpressionFunction from a PHP function name.
+     *
+     * @param string      $phpFunctionName        The PHP function name
+     * @param string|null $expressionFunctionName The expression function name (default: same than the PHP function name)
+     *
+     * @return self
+     *
+     * @throws \InvalidArgumentException if given PHP function name does not exist
+     * @throws \InvalidArgumentException if given PHP function name is in namespace
+     *                                   and expression function name is not defined
+     */
+    public static function fromPhp($phpFunctionName, $expressionFunctionName = null)
+    {
+        $phpFunctionName = ltrim($phpFunctionName, '\\');
+        if (!function_exists($phpFunctionName)) {
+            throw new \InvalidArgumentException(sprintf('PHP function "%s" does not exist.', $phpFunctionName));
+        }
+
+        $parts = explode('\\', $phpFunctionName);
+        if (!$expressionFunctionName && count($parts) > 1) {
+            throw new \InvalidArgumentException(sprintf('An expression function name must be defined when PHP function "%s" is namespaced.', $phpFunctionName));
+        }
+
+        $compiler = function () use ($phpFunctionName) {
+            return sprintf('\%s(%s)', $phpFunctionName, implode(', ', func_get_args()));
+        };
+
+        $evaluator = function () use ($phpFunctionName) {
+            $args = func_get_args();
+
+            return call_user_func_array($phpFunctionName, array_splice($args, 1));
+        };
+
+        return new self($expressionFunctionName ?: end($parts), $compiler, $evaluator);
+    }
 }

src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php

@@ -143,11 +143,7 @@ class ExpressionLanguage
 
     protected function registerFunctions()
     {
-        $this->register('constant', function ($constant) {
-            return sprintf('constant(%s)', $constant);
-        }, function (array $values, $constant) {
-            return constant($constant);
-        });
+        $this->addFunction(ExpressionFunction::fromPhp('constant'));
     }
 
     private function getLexer()

src/Symfony/Component/ExpressionLanguage/Tests/ExpressionFunctionTest.php

@@ -0,0 +1,44 @@
+<?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\ExpressionLanguage\Tests;
+
+use Symfony\Component\ExpressionLanguage\ExpressionFunction;
+
+/**
+ * Tests ExpressionFunction.
+ *
+ * @author Dany Maillard <danymaillard93b@gmail.com>
+ */
+class ExpressionFunctionTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage PHP function "fn_does_not_exist" does not exist.
+     */
+    public function testFunctionDoesNotExist()
+    {
+        ExpressionFunction::fromPhp('fn_does_not_exist');
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage An expression function name must be defined when PHP function "Symfony\Component\ExpressionLanguage\Tests\fn_namespaced" is namespaced.
+     */
+    public function testFunctionNamespaced()
+    {
+        ExpressionFunction::fromPhp('Symfony\Component\ExpressionLanguage\Tests\fn_namespaced');
+    }
+}
+
+function fn_namespaced()
+{
+}

src/Symfony/Component/ExpressionLanguage/Tests/ExpressionLanguageTest.php

@@ -109,7 +109,7 @@ class ExpressionLanguageTest extends TestCase
         $this->assertEquals(PHP_VERSION, $expressionLanguage->evaluate('constant("PHP_VERSION")'));
 
         $expressionLanguage = new ExpressionLanguage();
-        $this->assertEquals('constant("PHP_VERSION")', $expressionLanguage->compile('constant("PHP_VERSION")'));
+        $this->assertEquals('\constant("PHP_VERSION")', $expressionLanguage->compile('constant("PHP_VERSION")'));
     }
 
     public function testProviders()
@@ -117,6 +117,12 @@ class ExpressionLanguageTest extends TestCase
         $expressionLanguage = new ExpressionLanguage(null, array(new TestProvider()));
         $this->assertEquals('foo', $expressionLanguage->evaluate('identity("foo")'));
         $this->assertEquals('"foo"', $expressionLanguage->compile('identity("foo")'));
+        $this->assertEquals('FOO', $expressionLanguage->evaluate('strtoupper("foo")'));
+        $this->assertEquals('\strtoupper("foo")', $expressionLanguage->compile('strtoupper("foo")'));
+        $this->assertEquals('foo', $expressionLanguage->evaluate('strtolower("FOO")'));
+        $this->assertEquals('\strtolower("FOO")', $expressionLanguage->compile('strtolower("FOO")'));
+        $this->assertTrue($expressionLanguage->evaluate('fn_namespaced()'));
+        $this->assertEquals('\Symfony\Component\ExpressionLanguage\Tests\Fixtures\fn_namespaced()', $expressionLanguage->compile('fn_namespaced()'));
     }
 
     /**

src/Symfony/Component/ExpressionLanguage/Tests/Fixtures/TestProvider.php

@@ -13,6 +13,7 @@ namespace Symfony\Component\ExpressionLanguage\Tests\Fixtures;
 
 use Symfony\Component\ExpressionLanguage\ExpressionFunction;
 use Symfony\Component\ExpressionLanguage\ExpressionFunctionProviderInterface;
+use Symfony\Component\ExpressionLanguage\ExpressionPhpFunction;
 
 class TestProvider implements ExpressionFunctionProviderInterface
 {
@@ -24,6 +25,17 @@ class TestProvider implements ExpressionFunctionProviderInterface
             }, function (array $values, $input) {
                 return $input;
             }),
+
+            ExpressionFunction::fromPhp('strtoupper'),
+
+            ExpressionFunction::fromPhp('\strtolower'),
+
+            ExpressionFunction::fromPhp('Symfony\Component\ExpressionLanguage\Tests\Fixtures\fn_namespaced', 'fn_namespaced'),
         );
     }
 }
+
+function fn_namespaced()
+{
+    return true;
+}