From 8533d278f0f44a84b9540428bdc68dc12ee1cd34 Mon Sep 17 00:00:00 2001
From: Mojmir Fendek <mfendek@silverstripe.com>
Date: Tue, 20 Jun 2023 14:33:11 +1200
Subject: [PATCH] BUG: Allow CMS fields customisations via extension to be
 executed after the default setup.

---
 src/Models/EmailLink.php    |  8 +++----
 src/Models/Link.php         | 33 +++++++++++++++--------------
 src/Models/SiteTreeLink.php | 42 +++++++++++++++++++++----------------
 3 files changed, 45 insertions(+), 38 deletions(-)

diff --git a/src/Models/EmailLink.php b/src/Models/EmailLink.php
index de01aaa1..3e9aadea 100644
--- a/src/Models/EmailLink.php
+++ b/src/Models/EmailLink.php
@@ -25,11 +25,11 @@ public function generateLinkDescription(array $data): string
 
     public function getCMSFields(): FieldList
     {
-        $fields = parent::getCMSFields();
+        $this->beforeUpdateCMSFields(static function (FieldList $fields) {
+            $fields->replaceField('Email', EmailField::create('Email'));
+        });
 
-        $fields->replaceField('Email', EmailField::create('Email'));
-
-        return $fields;
+        return parent::getCMSFields();
     }
 
     public function getURL()
diff --git a/src/Models/Link.php b/src/Models/Link.php
index 84a7dc17..cc58cea4 100644
--- a/src/Models/Link.php
+++ b/src/Models/Link.php
@@ -80,23 +80,24 @@ public function scaffoldLinkFields(array $data): FieldList
      */
     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 --');
-        }
+        $this->beforeUpdateCMSFields(function (FieldList $fields) {
+            $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 parent::getCMSFields();
     }
 
     /**
diff --git a/src/Models/SiteTreeLink.php b/src/Models/SiteTreeLink.php
index acbcbe40..a6c374b4 100644
--- a/src/Models/SiteTreeLink.php
+++ b/src/Models/SiteTreeLink.php
@@ -40,25 +40,31 @@ public function generateLinkDescription(array $data): string
 
     public function getCMSFields(): FieldList
     {
-        $fields = parent::getCMSFields();
-
-        $fields->insertAfter(
-            'Title',
-            TreeDropdownField::create(
+        $this->beforeUpdateCMSFields(static function (FieldList $fields) {
+            // Remove scaffolded fields to we don't have field name conflicts which would prevent field customisation
+            $fields->removeByName([
+                'PageID',
+                'Anchor',
+            ]);
+
+            $fields->insertAfter(
+                'Title',
+                TreeDropdownField::create(
+                    'PageID',
+                    'Page',
+                    SiteTree::class,
+                    'ID',
+                    'TreeTitle'
+                )
+            );
+
+            $fields->insertAfter(
                 'PageID',
-                'Page',
-                SiteTree::class,
-                'ID',
-                'TreeTitle'
-            )
-        );
-
-        $fields->insertAfter(
-            'PageID',
-            AnchorSelectorField::create('Anchor')
-        );
-
-        return $fields;
+                AnchorSelectorField::create('Anchor')
+            );
+        });
+
+        return parent::getCMSFields();
     }
 
     public function getURL(): ?string