fix: custom validation error is cleared when calling setRule() twice

Author: kenjis

system/Validation/Validation.php

@@ -399,7 +399,7 @@ public function setRule(string $field, ?string $label, $rules, array $errors = [
             $ruleSet[$field]['errors'] = $errors;
         }
 
-        $this->setRules($ruleSet + $this->getRules());
+        $this->setRules($ruleSet + $this->getRules(), $this->customErrors);
 
         return $this;
     }

tests/system/Validation/StrictRules/ValidationTest.php

@@ -221,6 +221,33 @@ public function testRunWithCustomErrors(): void
         $this->assertSame('No. Not a number.', $this->validation->getError('bar'));
     }
 
+    /**
+     * @see https://github.com/codeigniter4/CodeIgniter4/issues/6239
+     */
+    public function testSetRuleWithCustomErrors(): void
+    {
+        $data = [
+            'foo' => 'notanumber',
+            'bar' => 'notanumber',
+        ];
+        $this->validation->setRule(
+            'foo',
+            'Foo',
+            ['foo'        => 'is_numeric'],
+            ['is_numeric' => 'Nope. Not a number.']
+        );
+        $this->validation->setRule(
+            'bar',
+            'Bar',
+            ['bar'        => 'is_numeric'],
+            ['is_numeric' => 'Nope. Not a number.']
+        );
+        $this->validation->run($data);
+
+        $this->assertSame('Nope. Not a number.', $this->validation->getError('foo'));
+        $this->assertSame('Nope. Not a number.', $this->validation->getError('bar'));
+    }
+
     public function testCheck(): void
     {
         $this->assertFalse($this->validation->check('notanumber', 'is_numeric'));

tests/system/Validation/ValidationTest.php

@@ -324,6 +324,33 @@ public function testRunWithCustomErrors(): void
         $this->assertSame('No. Not a number.', $this->validation->getError('bar'));
     }
 
+    /**
+     * @see https://github.com/codeigniter4/CodeIgniter4/issues/6239
+     */
+    public function testSetRuleWithCustomErrors(): void
+    {
+        $data = [
+            'foo' => 'notanumber',
+            'bar' => 'notanumber',
+        ];
+        $this->validation->setRule(
+            'foo',
+            'Foo',
+            ['foo'        => 'is_numeric'],
+            ['is_numeric' => 'Nope. Not a number.']
+        );
+        $this->validation->setRule(
+            'bar',
+            'Bar',
+            ['bar'        => 'is_numeric'],
+            ['is_numeric' => 'Nope. Not a number.']
+        );
+        $this->validation->run($data);
+
+        $this->assertSame('Nope. Not a number.', $this->validation->getError('foo'));
+        $this->assertSame('Nope. Not a number.', $this->validation->getError('bar'));
+    }
+
     public function testCheck(): void
     {
         $this->assertFalse($this->validation->check('notanumber', 'is_numeric'));