feat: add closure validation rule

Author: kenjis

system/Validation/Validation.php

@@ -11,6 +11,7 @@
 
 namespace CodeIgniter\Validation;
 
+use Closure;
 use CodeIgniter\HTTP\IncomingRequest;
 use CodeIgniter\HTTP\RequestInterface;
 use CodeIgniter\Validation\Exceptions\ValidationException;
@@ -195,7 +196,7 @@ public function check($value, string $rule, array $errors = []): bool
      *
      * @param array|string $value
      * @param array|null   $rules
-     * @param array        $data          The array of data to validate, with `DBGroup`.
+     * @param array|null   $data          The array of data to validate, with `DBGroup`.
      * @param string|null  $originalField The original asterisk field name like "foo.*.bar".
      */
     protected function processRules(
@@ -277,7 +278,7 @@ protected function processRules(
             $rules = array_diff($rules, ['permit_empty']);
         }
 
-        foreach ($rules as $rule) {
+        foreach ($rules as $i => $rule) {
             $isCallable = is_callable($rule);
 
             $passed = false;
@@ -333,7 +334,7 @@ protected function processRules(
 
                 // @phpstan-ignore-next-line $error may be set by rule methods.
                 $this->errors[$field] = $error ?? $this->getErrorMessage(
-                    $rule,
+                    $this->isClosure($rule) ? $i : $rule,
                     $field,
                     $label,
                     $param,
@@ -348,6 +349,14 @@ protected function processRules(
         return true;
     }
 
+    /**
+     * @param Closure|string $rule
+     */
+    private function isClosure($rule): bool
+    {
+        return $rule instanceof Closure;
+    }
+
     /**
      * Is the array a string list `list<string>`?
      */

tests/system/Validation/ValidationTest.php

@@ -204,6 +204,31 @@ public function testRunDoesTheBasics(): void
         $this->assertFalse($this->validation->run($data));
     }
 
+    public function testClosureRule(): void
+    {
+        $this->validation->setRules(
+            [
+                'foo' => ['required', static fn ($value) => $value === 'abc'],
+            ],
+            [
+                // Errors
+                'foo' => [
+                    // Specify the array key for the closure rule.
+                    1 => 'The value is not "abc"',
+                ],
+            ],
+        );
+
+        $data   = ['foo' => 'xyz'];
+        $return = $this->validation->run($data);
+
+        $this->assertFalse($return);
+        $this->assertSame(
+            ['foo' => 'The value is not "abc"'],
+            $this->validation->getErrors()
+        );
+    }
+
     /**
      * @see https://github.com/codeigniter4/CodeIgniter4/issues/5368
      *