feat: better support 3rd party extensions setting canonical urls (#4244)

Author: imorland

framework/core/src/Forum/Content/Discussion.php

@@ -100,7 +100,12 @@ public function __invoke(Document $document, Request $request)
         $document->content = $this->view->make('flarum.forum::frontend.content.discussion', compact('apiDocument', 'page', 'hasPrevPage', 'hasNextPage', 'getResource', 'posts', 'url'));
         $document->payload['apiDocument'] = $apiDocument;
 
-        $document->canonicalUrl = $url([]);
+        // Only apply the canonical URL if it's empty. It could have been set by another extension already,
+        // if so, we'll leave it alone.
+        if (empty($document->canonicalUrl)) {
+            $document->canonicalUrl = $url([]);
+        }
+
         $document->page = $page;
         $document->hasNextPage = $hasNextPage;
 

framework/core/src/Forum/Content/Index.php

@@ -89,7 +89,12 @@ public function __invoke(Document $document, Request $request)
         $document->content = $this->view->make('flarum.forum::frontend.content.index', compact('apiDocument', 'page'));
         $document->payload['apiDocument'] = $apiDocument;
 
-        $document->canonicalUrl = $this->url->to('forum')->base().($defaultRoute === '/all' ? '' : $request->getUri()->getPath());
+        // Only apply the canonical URL if it's empty. It could have been set by another extension already,
+        // if so, we'll leave it alone.
+        if (empty($document->canonicalUrl)) {
+            $document->canonicalUrl = $this->url->to('forum')->base().($defaultRoute === '/all' ? '' : $request->getUri()->getPath());
+        }
+
         $document->page = $page;
         $document->hasNextPage = isset($apiDocument->links->next);
 

framework/core/src/Forum/Content/User.php

@@ -47,7 +47,13 @@ public function __invoke(Document $document, Request $request)
         $user = $apiDocument->data->attributes;
 
         $document->title = $user->displayName;
-        $document->canonicalUrl = $this->url->to('forum')->route('user', ['username' => $user->slug]);
+
+        // Only apply the canonical URL if it's empty. It could have been set by another extension already,
+        // if so, we'll leave it alone.
+        if (empty($document->canonicalUrl)) {
+            $document->canonicalUrl = $this->url->to('forum')->route('user', ['username' => $user->slug]);
+        }
+
         $document->payload['apiDocument'] = $apiDocument;
 
         return $document;