[8.x] Conditional rules

src/Illuminate/Validation/ConditionalRules.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Illuminate\Validation;
+
+class ConditionalRules
+{
+    /**
+     * The boolean condition indicating if the rules should be added to the attribute.
+     *
+     * @var callable|bool
+     */
+    protected $condition;
+
+    /**
+     * The rules to be added to the attribute.
+     *
+     * @var array
+     */
+    protected $rules;
+
+    /**
+     * Create a new conditional rules instance.
+     *
+     * @param  callable|bool  $condition
+     * @param  array|string  $rules
+     * @return void
+     */
+    public function __construct($condition, $rules)
+    {
+        $this->condition = $condition;
+        $this->rules = $rules;
+    }
+
+    /**
+     * Determine if the conditional rules should be added.
+     *
+     * @param  array  $data
+     * @return bool
+     */
+    public function passes(array $data = [])
+    {
+        return is_callable($this->condition)
+                    ? call_user_func($this->condition, $data)
+                    : $this->condition;
+    }
+
+    /**
+     * Get the rules.
+     *
+     * @return array
+     */
+    public function rules()
+    {
+        return is_string($this->rules) ? explode('|', $this->rules) : $this->rules;
+    }
+}

src/Illuminate/Validation/Rule.php

@@ -15,6 +15,18 @@ class Rule
 {
     use Macroable;
 
+    /**
+     * Create a new conditional rule set.
+     *
+     * @param  callable|bool  $condition
+     * @param  array|string  $rules
+     * @return \Illuminate\Validation\ConditionalRules
+     */
+    public static function when($condition, $rules)
+    {
+        return new ConditionalRules($condition, $rules);
+    }
+
     /**
      * Get a dimensions constraint builder instance.
      *

src/Illuminate/Validation/ValidationRuleParser.php

@@ -274,4 +274,33 @@ protected static function normalizeRule($rule)
                 return $rule;
         }
     }
+
+    /**
+     * Expand and conditional rules in the given array of rules.
+     *
+     * @param  array  $rules
+     * @param  array  $data
+     * @return array
+     */
+    public static function filterConditionalRules($rules, array $data = [])
+    {
+        return collect($rules)->mapWithKeys(function ($attributeRules, $attribute) use ($data) {
+            if (! is_array($attributeRules) &&
+                ! $attributeRules instanceof ConditionalRules) {
+                return [$attribute => $attributeRules];
+            }
+
+            if ($attributeRules instanceof ConditionalRules) {
+                return [$attribute => $attributeRules->passes($data) ? $attributeRules->rules() : null];
+            }
+
+            return [$attribute => collect($attributeRules)->map(function ($rule) use ($data) {
+                if (! $rule instanceof ConditionalRules) {
+                    return [$rule];
+                }
+
+                return $rule->passes($data) ? $rule->rules() : null;
+            })->filter()->flatten(1)->values()->all()];
+        })->filter()->all();
+    }
 }

src/Illuminate/Validation/Validator.php

@@ -1082,7 +1082,7 @@ public function addRules($rules)
         // of the explicit rules needed for the given data. For example the rule
         // names.* would get expanded to names.0, names.1, etc. for this data.
         $response = (new ValidationRuleParser($this->data))
-                            ->explode($rules);
+                            ->explode(ValidationRuleParser::filterConditionalRules($rules, $this->data));
 
         $this->rules = array_merge_recursive(
             $this->rules, $response->rules

tests/Validation/ValidationRuleParserTest.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Illuminate\Tests\Validation;
+
+use Illuminate\Validation\Rule;
+use Illuminate\Validation\ValidationRuleParser;
+use PHPUnit\Framework\TestCase;
+
+class ValidationRuleParserTest extends TestCase
+{
+    public function test_conditional_rules_are_properly_expanded_and_filtered()
+    {
+        $rules = ValidationRuleParser::filterConditionalRules([
+            'name' => Rule::when(true, ['required', 'min:2']),
+            'email' => Rule::when(false, ['required', 'min:2']),
+            'password' => Rule::when(true, 'required|min:2'),
+            'username' => ['required', Rule::when(true, ['min:2'])],
+            'address' => ['required', Rule::when(false, ['min:2'])],
+            'city' => ['required', Rule::when(function (array $input) {
+                return true;
+            }, ['min:2'])],
+        ]);
+
+        $this->assertEquals([
+            'name' => ['required', 'min:2'],
+            'password' => ['required', 'min:2'],
+            'username' => ['required', 'min:2'],
+            'address' => ['required'],
+            'city' => ['required', 'min:2'],
+        ], $rules);
+    }
+}