NEW Add ClassInfo method to get all classes with a given extension applied

src/Core/ClassInfo.php

@@ -560,4 +560,40 @@ class ClassInfo
         static::$_cache_parse[$classSpec] = $result;
         return $result;
     }
+
+    /**
+     * Returns a list of classes with a particular extension applied
+     *
+     * This reflects all extensions added (or removed) both via the configuration API as well as dynamically
+     * using Extensible::add_extension() and Extensible::remove_extension().
+     *
+     * @param string $extensionClass        Extension class name
+     * @param string $baseClassOrObject     Class or object to find subclasses of with the extension applied
+     * @param bool $includeBaseClass        Include the base class itself if it has the extension applied?
+     * @return string[] Class names with the extension applied
+     * @throws \ReflectionException
+     */
+    public static function classesWithExtension(
+        string $extensionClass,
+        string $baseClassOrObject = DataObject::class,
+        bool $includeBaseClass = false
+    ): array {
+        // get class names
+        $baseClass = self::class_name($baseClassOrObject);
+
+        // get a list of all subclasses for a given class
+        $classes = ClassInfo::subclassesFor($baseClass, $includeBaseClass);
+
+        // include the base class if required
+        if ($includeBaseClass) {
+            $classes = array_merge([strtolower($baseClass) => $baseClass], $classes);
+        }
+
+        // only keep classes with the Extension applied
+        $classes = array_filter($classes, function ($class) use ($extensionClass) {
+            return Extensible::has_extension($class, $extensionClass);
+        });
+
+        return $classes;
+    }
 }

tests/php/Core/ClassInfoTest.php

@@ -6,7 +6,13 @@ use ReflectionException;
 use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Tests\ClassInfoTest\BaseClass;
 use SilverStripe\Core\Tests\ClassInfoTest\BaseDataClass;
+use SilverStripe\Core\Tests\ClassInfoTest\BaseObject;
 use SilverStripe\Core\Tests\ClassInfoTest\ChildClass;
+use SilverStripe\Core\Tests\ClassInfoTest\ExtendTest;
+use SilverStripe\Core\Tests\ClassInfoTest\ExtendTest2;
+use SilverStripe\Core\Tests\ClassInfoTest\ExtendTest3;
+use SilverStripe\Core\Tests\ClassInfoTest\ExtensionTest1;
+use SilverStripe\Core\Tests\ClassInfoTest\ExtensionTest2;
 use SilverStripe\Core\Tests\ClassInfoTest\GrandChildClass;
 use SilverStripe\Core\Tests\ClassInfoTest\HasFields;
 use SilverStripe\Core\Tests\ClassInfoTest\NoFields;
@@ -28,6 +34,10 @@ class ClassInfoTest extends SapphireTest
         NoFields::class,
         WithCustomTable::class,
         WithRelation::class,
+        BaseObject::class,
+        ExtendTest::class,
+        ExtendTest2::class,
+        ExtendTest3::class,
     );
 
     protected function setUp()
@@ -189,4 +199,70 @@ class ClassInfoTest extends SapphireTest
         ClassInfo::reset_db_cache();
         $this->assertEquals($expect, ClassInfo::dataClassesFor(strtolower($classes[2])));
     }
+
+    /**
+     * @covers \SilverStripe\Core\ClassInfo::classesWithExtension()
+     */
+    public function testClassesWithExtensionUsingConfiguredExtensions()
+    {
+        $expect = [
+            'silverstripe\\core\\tests\\classinfotest\\extendtest' => ExtendTest::class,
+            'silverstripe\\core\\tests\\classinfotest\\extendtest2' => ExtendTest2::class,
+            'silverstripe\\core\\tests\\classinfotest\\extendtest3' => ExtendTest3::class,
+        ];
+        $this->assertEquals(
+            $expect,
+            ClassInfo::classesWithExtension(ExtensionTest1::class, BaseObject::class),
+            'ClassInfo::testClassesWithExtension() returns class with extensions applied via class config'
+        );
+
+        $expect = [
+            'silverstripe\\core\\tests\\classinfotest\\extendtest' => ExtendTest::class,
+            'silverstripe\\core\\tests\\classinfotest\\extendtest2' => ExtendTest2::class,
+            'silverstripe\\core\\tests\\classinfotest\\extendtest3' => ExtendTest3::class,
+        ];
+        $this->assertEquals(
+            $expect,
+            ClassInfo::classesWithExtension(ExtensionTest1::class, ExtendTest::class, true),
+            'ClassInfo::testClassesWithExtension() returns class with extensions applied via class config, including the base class'
+        );
+    }
+
+    /**
+     * @covers \SilverStripe\Core\ClassInfo::classesWithExtension()
+     */
+    public function testClassesWithExtensionUsingDynamicallyAddedExtensions()
+    {
+        $this->assertEquals(
+            [],
+            ClassInfo::classesWithExtension(ExtensionTest2::class, BaseObject::class),
+            'ClassInfo::testClassesWithExtension() returns no classes for extension that hasn\'t been applied yet.'
+        );
+
+        ExtendTest::add_extension(ExtensionTest2::class);
+
+        $expect = [
+            'silverstripe\\core\\tests\\classinfotest\\extendtest2' => ExtendTest2::class,
+            'silverstripe\\core\\tests\\classinfotest\\extendtest3' => ExtendTest3::class,
+        ];
+        $this->assertEquals(
+            $expect,
+            ClassInfo::classesWithExtension(ExtensionTest2::class, ExtendTest::class),
+            'ClassInfo::testClassesWithExtension() returns class with extra extension dynamically added'
+        );
+    }
+
+    /**
+     * @covers \SilverStripe\Core\ClassInfo::classesWithExtension()
+     */
+    public function testClassesWithExtensionWithDynamicallyRemovedExtensions()
+    {
+        ExtendTest::remove_extension(ExtensionTest1::class);
+
+        $this->assertEquals(
+            [],
+            ClassInfo::classesWithExtension(ExtensionTest1::class, BaseObject::class),
+            'ClassInfo::testClassesWithExtension() returns no classes after an extension being removed'
+        );
+    }
 }

tests/php/Core/ClassInfoTest/BaseObject.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace SilverStripe\Core\Tests\ClassInfoTest;
+
+use SilverStripe\Core\Config\Configurable;
+use SilverStripe\Core\Extensible;
+use SilverStripe\Dev\TestOnly;
+
+class BaseObject implements TestOnly
+{
+    use Configurable;
+    use Extensible;
+}

tests/php/Core/ClassInfoTest/ExtendTest.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace SilverStripe\Core\Tests\ClassInfoTest;
+
+class ExtendTest extends BaseObject
+{
+    private static $extensions = [
+        ExtensionTest1::class,
+    ];
+}

tests/php/Core/ClassInfoTest/ExtendTest2.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace SilverStripe\Core\Tests\ClassInfoTest;
+
+class ExtendTest2 extends ExtendTest
+{
+}

tests/php/Core/ClassInfoTest/ExtendTest3.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace SilverStripe\Core\Tests\ClassInfoTest;
+
+class ExtendTest3 extends ExtendTest2
+{
+}

tests/php/Core/ClassInfoTest/ExtensionTest1.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace SilverStripe\Core\Tests\ClassInfoTest;
+
+use SilverStripe\Core\Extension;
+use SilverStripe\Dev\TestOnly;
+
+class ExtensionTest1 extends Extension implements TestOnly
+{
+}

tests/php/Core/ClassInfoTest/ExtensionTest2.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace SilverStripe\Core\Tests\ClassInfoTest;
+
+use SilverStripe\Core\Extension;
+use SilverStripe\Dev\TestOnly;
+
+class ExtensionTest2 extends Extension implements TestOnly
+{
+}