Check is_callable parent methods before invoke

src/View/ViewableData.php

@@ -7,6 +7,7 @@
 use InvalidArgumentException;
 use IteratorAggregate;
 use LogicException;
+use ReflectionObject;
 use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Config\Configurable;
@@ -155,13 +156,22 @@ public function __get($property)
     public function __set($property, $value)
     {
         $this->objCacheClear();
-        if ($this->hasMethod($method = "set$property")) {
+        $method = "set$property";
+
+        if ($this->hasMethod($method) && !$this->isPrivate($this, $method)) {
             $this->$method($value);
         } else {
             $this->setField($property, $value);
         }
     }
 
+    private function isPrivate(object $class, string $method): bool
+    {
+        $class = new ReflectionObject($class);
+
+        return $class->getMethod($method)->isPrivate();
+    }
+
     /**
      * Set a failover object to attempt to get data from if it is not present on this object.
      *

tests/php/View/ViewableDataTest.php

@@ -2,11 +2,13 @@
 
 namespace SilverStripe\View\Tests;
 
+use ReflectionMethod;
 use SilverStripe\ORM\FieldType\DBField;
 use SilverStripe\Dev\SapphireTest;
 use SilverStripe\View\ArrayData;
 use SilverStripe\View\SSViewer;
 use SilverStripe\View\ViewableData;
+use SilverStripe\View\Tests\ViewableDataTestObject;
 
 /**
  * See {@link SSViewerTest->testCastingHelpers()} for more tests related to casting and ViewableData behaviour,
@@ -205,4 +207,17 @@ public function testSetFailover()
         $this->assertSame($failover, $container->getFailover(), 'getFailover() returned a different object');
         $this->assertFalse($container->hasMethod('testMethod'), 'testMethod() incorrectly reported as existing');
     }
+
+    public function testIsPrivate()
+    {
+        $reflectionMethod = new ReflectionMethod(ViewableData::class, 'isPrivate');
+        $reflectionMethod->setAccessible(true);
+        $object = new ViewableDataTestObject();
+
+        $output = $reflectionMethod->invokeArgs($object, [$object, 'privateMethod']);
+        $this->assertTrue($output, 'Method is not private');
+
+        $output = $reflectionMethod->invokeArgs($object, [$object, 'publicMethod']);
+        $this->assertFalse($output, 'Method is private');
+    }
 }

tests/php/View/ViewableDataTestObject.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace SilverStripe\View\Tests;
+
+use SilverStripe\Dev\TestOnly;
+use SilverStripe\ORM\DataObject;
+
+class ViewableDataTestObject extends DataObject implements TestOnly
+{
+    private function privateMethod(): string
+    {
+        return 'Private function';
+    }
+
+    public function publicMethod(): string
+    {
+        return 'Public function';
+    }
+}