BUG: Change link type in via a GridField edit form.

src/Models/EmailLink.php

@@ -3,6 +3,7 @@
 namespace SilverStripe\LinkField\Models;
 
 use SilverStripe\Forms\EmailField;
+use SilverStripe\Forms\FieldList;
 
 /**
  * A link to an Email address.
@@ -24,7 +25,7 @@ public function generateLinkDescription(array $data): string
         return isset($data['Email']) ? $data['Email'] : '';
     }
 
-    public function getCMSFields()
+    public function getCMSFields(): FieldList
     {
         $fields = parent::getCMSFields();
 

src/Models/Link.php

@@ -3,8 +3,14 @@
 namespace SilverStripe\LinkField\Models;
 
 use InvalidArgumentException;
+use ReflectionException;
+use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Injector\Injector;
+use SilverStripe\Forms\CompositeValidator;
+use SilverStripe\Forms\DropdownField;
 use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\RequiredFields;
 use SilverStripe\LinkField\JsonData;
 use SilverStripe\LinkField\Type\Registry;
 use SilverStripe\LinkField\Type\Type;
@@ -28,6 +34,15 @@ class Link extends DataObject implements JsonData, Type
         'OpenInNew' => 'Boolean'
     ];
 
+    /**
+     * In-memory only property used to change link type
+     * This case is relevant for CMS edit form which doesn't use React driven UI
+     * This is a workaround as changing the ClassName directly is not fully supported in the GridField admin
+     *
+     * @var string
+     */
+    private $linkType;
+
 
     public function defineLinkTypeRequirements()
     {
@@ -51,11 +66,80 @@ public function LinkTypeTile(): string
         return $this->i18n_singular_name();
     }
 
+    /**
+     * @param array $data
+     * @return FieldList
+     * @throws ReflectionException
+     */
     public function scaffoldLinkFields(array $data): FieldList
     {
         return $this->getCMSFields();
     }
 
+    /**
+     * @return FieldList
+     * @throws ReflectionException
+     */
+    public function getCMSFields(): FieldList
+    {
+        $fields = parent::getCMSFields();
+        $linkTypes = $this->getLinkTypes();
+
+        if (static::class === self::class) {
+            // Add a link type selection field for generic links
+            $fields->addFieldsToTab(
+                'Root.Main',
+                [
+                    $linkTypeField = DropdownField::create('LinkType', 'Link Type', $linkTypes),
+                ],
+                'Title'
+            );
+
+            $linkTypeField->setEmptyString('-- select type --');
+        }
+
+        return $fields;
+    }
+
+    /**
+     * @return CompositeValidator
+     */
+    public function getCMSCompositeValidator(): CompositeValidator
+    {
+        $validator = parent::getCMSCompositeValidator();
+
+        if (static::class === self::class) {
+            // Make Link type mandatory for generic links
+            $validator->addValidator(RequiredFields::create([
+                'LinkType',
+            ]));
+        }
+
+        return $validator;
+    }
+
+    /**
+     * Form hook defined in @see Form::saveInto()
+     * We use this to work with an in-memory only field
+     *
+     * @param $value
+     */
+    public function saveLinkType($value)
+    {
+        $this->linkType = $value;
+    }
+
+    public function onBeforeWrite(): void
+    {
+        // Detect link type change and update the class accordingly
+        if ($this->linkType && DataObject::singleton($this->linkType) instanceof Link) {
+            $this->setClassName($this->linkType);
+            $this->populateDefaults();
+            $this->forceChange();
+        }
+
+        parent::onBeforeWrite();
+    }
 
     function setData($data): JsonData
     {
@@ -142,4 +226,26 @@ public function forTemplate()
     {
         return $this->renderWith([self::class]);
     }
+
+    /**
+     * Get all link types except the generic one
+     *
+     * @return array
+     * @throws ReflectionException
+     */
+    private function getLinkTypes(): array
+    {
+        $classes = ClassInfo::subclassesFor(self::class);
+        $types = [];
+
+        foreach ($classes as $class) {
+            if ($class === self::class) {
+                continue;
+            }
+
+            $types[$class] = ClassInfo::shortName($class);
+        }
+
+        return $types;
+    }
 }

src/Models/SiteTreeLink.php

@@ -4,6 +4,7 @@
 
 use SilverStripe\CMS\Forms\AnchorSelectorField;
 use SilverStripe\CMS\Model\SiteTree;
+use SilverStripe\Forms\FieldList;
 use SilverStripe\Forms\TreeDropdownField;
 
 /**
@@ -38,7 +39,7 @@ public function generateLinkDescription(array $data): string
         return $page ? $page->URLSegment : '';
     }
 
-    public function getCMSFields()
+    public function getCMSFields(): FieldList
     {
         $fields = parent::getCMSFields();
 

tests/php/Models/LinkTest.php

@@ -2,10 +2,15 @@
 
 namespace SilverStripe\LinkField\Tests\Models;
 
+use ReflectionException;
 use SilverStripe\CMS\Model\SiteTree;
 use SilverStripe\Dev\SapphireTest;
+use SilverStripe\LinkField\Models\EmailLink;
+use SilverStripe\LinkField\Models\ExternalLink;
+use SilverStripe\LinkField\Models\FileLink;
 use SilverStripe\LinkField\Models\Link;
 use SilverStripe\LinkField\Models\SiteTreeLink;
+use SilverStripe\ORM\DataObject;
 use SilverStripe\ORM\ValidationException;
 
 class LinkTest extends SapphireTest
@@ -47,4 +52,32 @@ public function testSiteTreeLinkTitleFallback(): void
 
         $this->assertEquals($customTitle, $model->Title, 'We expect to get the custom title not page title');
     }
+
+    /**
+     * @param string $class
+     * @param bool $expected
+     * @throws ReflectionException
+     * @dataProvider linkTypeProvider
+     */
+    public function testLinkType(string $class, bool $expected): void
+    {
+        /** @var Link $model */
+        $model = DataObject::singleton($class);
+        $fields = $model->getCMSFields();
+        $linkTypeField = $fields->fieldByName('Root.Main.LinkType');
+        $expected
+            ? $this->assertNotNull($linkTypeField, 'We expect to a find link type field')
+            : $this->assertNull($linkTypeField, 'We do not expect to a find link type field');
+    }
+
+    public function linkTypeProvider(): array
+    {
+        return [
+            [EmailLink::class, false],
+            [ExternalLink::class, false],
+            [FileLink::class, false],
+            [SiteTreeLink::class, false],
+            [Link::class, true],
+        ];
+    }
 }