Deprecate GetModelIsPrivate, replace with extender (#2587)

src/Extend/ModelPrivate.php

@@ -0,0 +1,82 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Extension\Extension;
+use Flarum\Foundation\ContainerUtil;
+use Illuminate\Contracts\Container\Container;
+
+/**
+ * Some models, in particular Discussion and Post, are intended to
+ * support a "private" mode, wherein they aren't visible unless some
+ * criteria is met. This can be used to implement anything from
+ * private discussions to post approvals.
+ *
+ * When a model is saved, any "privacy checkers" registered for it will
+ * be run. If any privacy checkers return `true`, the `is_private` field
+ * of that model instance will be set to `true`. Otherwise, it will be set to
+ * `false`. Accordingly, this is only available for models with an `is_private`
+ * field.
+ *
+ * In Flarum core, the Discussion and Post models come with private support.
+ * Core also contains visibility scopers that hide instances of these models
+ * with `is_private = true` from queries. Extensions can register custom scopers
+ * for these classes with the `viewPrivate` ability to grant access to view some
+ * private instances under some conditions.
+ */
+class ModelPrivate implements ExtenderInterface
+{
+    private $modelClass;
+    private $checkers = [];
+
+    /**
+     * @param string $modelClass The ::class attribute of the model you are applying scopers to.
+     *                           This model must have a `is_private` field.
+     */
+    public function __construct(string $modelClass)
+    {
+        $this->modelClass = $modelClass;
+    }
+
+    /**
+     * Add a model privacy checker.
+     *
+     * @param callable|string $callback
+     *
+     * The callback can be a closure or invokable class, and should accept:
+     * - \Flarum\User\User $actor
+     * - \Illuminate\Database\Eloquent\Builder $query
+     *
+     * It should return `true` if the model instance should be made private.
+     *
+     * @return self
+     */
+    public function checker($callback)
+    {
+        $this->checkers[] = $callback;
+
+        return $this;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        if (! class_exists($this->modelClass)) {
+            return;
+        }
+
+        $container->extend('flarum.database.model_private_checkers', function ($originalCheckers) use ($container) {
+            foreach ($this->checkers as $checker) {
+                $originalCheckers[$this->modelClass][] = ContainerUtil::wrapCallback($checker, $container);
+            }
+
+            return $originalCheckers;
+        });
+    }
+}