feat: add field_exists rule

Author: kenjis

system/Validation/Rules.php

@@ -425,4 +425,22 @@ public function required_without(
 
         return true;
     }
+
+    /**
+     * The field exists in $data.
+     *
+     * @param array|bool|float|int|object|string|null $value The field value.
+     * @param string|null                             $param The rule's parameter.
+     * @param array                                   $data  The data to be validated.
+     * @param string|null                             $field The field name.
+     */
+    public function field_exists(
+        $value = null,
+        ?string $param = null,
+        array $data = [],
+        ?string $error = null,
+        ?string $field = null
+    ): bool {
+        return (bool) (array_key_exists($field, $data));
+    }
 }

system/Validation/StrictRules/Rules.php

@@ -373,4 +373,22 @@ public function required_without(
     ): bool {
         return $this->nonStrictRules->required_without($str, $otherFields, $data, $error, $field);
     }
+
+    /**
+     * The field exists in $data.
+     *
+     * @param array|bool|float|int|object|string|null $value The field value.
+     * @param string|null                             $param The rule's parameter.
+     * @param array                                   $data  The data to be validated.
+     * @param string|null                             $field The field name.
+     */
+    public function field_exists(
+        $value = null,
+        ?string $param = null,
+        array $data = [],
+        ?string $error = null,
+        ?string $field = null
+    ): bool {
+        return (bool) (array_key_exists($field, $data));
+    }
 }

system/Validation/Validation.php

@@ -323,8 +323,9 @@ protected function processRules(
                         continue;
                     }
 
-                    $found  = true;
-                    $passed = $param === false
+                    $found = true;
+
+                    $passed = ($param === false && $rule !== 'field_exists')
                         ? $set->{$rule}($value, $error)
                         : $set->{$rule}($value, $param, $data, $error, $field);
 

tests/system/Validation/RulesTest.php

@@ -830,4 +830,44 @@ public static function provideRequiredWithoutMultipleWithoutFields(): iterable
             ],
         ];
     }
+
+    /**
+     * @dataProvider provideFieldExists
+     */
+    public function testFieldExists(array $rules, array $data, bool $expected): void
+    {
+        $this->validation->setRules($rules);
+        $this->assertSame($expected, $this->validation->run($data));
+    }
+
+    public static function provideFieldExists(): iterable
+    {
+        yield from [
+            [
+                ['foo' => 'field_exists'],
+                ['foo' => ''],
+                true,
+            ],
+            [
+                ['foo' => 'field_exists'],
+                ['foo' => null],
+                true,
+            ],
+            [
+                ['foo' => 'field_exists'],
+                ['foo' => false],
+                true,
+            ],
+            [
+                ['foo' => 'field_exists'],
+                ['foo' => []],
+                true,
+            ],
+            [
+                ['foo' => 'field_exists'],
+                [],
+                false,
+            ],
+        ];
+    }
 }