[5.6] Required If Rule based on a clousure or boolean value

src/Illuminate/Validation/Rule.php

@@ -73,4 +73,15 @@ public static function unique($table, $column = 'NULL')
     {
         return new Rules\Unique($table, $column);
     }
+
+    /**
+     * Get a required_if constraint builder instance.
+     *
+     * @param  \Closure  $callback
+     * @return \Illuminate\Validation\Rules\RequiredIf
+     */
+    public static function requiredIf($callback)
+    {
+        return new Rules\RequiredIf($callback);
+    }
 }

src/Illuminate/Validation/Rules/RequiredIf.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace Illuminate\Validation\Rules;
+
+use Closure;
+
+class RequiredIf
+{
+    /**
+     * The name of the rule.
+     */
+    protected $rule = 'required';
+
+    /**
+     * The condition that validates the attribute.
+     *
+     * @var bool|\Closure
+     */
+    public $condition;
+
+    /**
+     * Create a new required validation rule based on a condition.
+     *
+     * @param  bool|\Closure  $condition
+     * @return void
+     */
+    public function __construct($condition)
+    {
+        $this->condition = $condition;
+    }
+
+    /**
+     * Convert the rule to a validation string.
+     *
+     * @return string
+     */
+    public function __toString()
+    {
+        if ($this->condition instanceof Closure) {
+            return $this->condition->__invoke() ? $this->rule : '';
+        }
+
+        return $this->condition ? $this->rule : '';
+    }
+}

tests/Validation/ValidationRequiredIfTest.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Illuminate\Tests\Validation;
+
+use PHPUnit\Framework\TestCase;
+use Illuminate\Validation\Rules\RequiredIf;
+
+class ValidationRequiredIfTest extends TestCase
+{
+    public function testItClousureReturnsFormatsAStringVersionOfTheRule()
+    {
+        $rule = new RequiredIf(function () {
+            return true;
+        });
+
+        $this->assertEquals('required', (string) $rule);
+
+        $rule = new RequiredIf(function () {
+            return false;
+        });
+
+        $this->assertEquals('', (string) $rule);
+
+        $rule = new RequiredIf(true);
+
+        $this->assertEquals('required', (string) $rule);
+
+        $rule = new RequiredIf(false);
+
+        $this->assertEquals('', (string) $rule);
+    }
+}