feat: move Expectations API out of external plugin

src/Concerns/Extendable.php

@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Concerns;
+
+use Closure;
+use Pest\HigherOrderExpectation;
+
+/**
+ * @internal
+ */
+trait Extendable
+{
+    /**
+     * @var array<string, Closure>
+     */
+    private static $extends = [];
+
+    /**
+     * Register a custom extend.
+     */
+    public static function extend(string $name, Closure $extend): void
+    {
+        static::$extends[$name] = $extend;
+    }
+
+    /**
+     * Checks if extend is registered.
+     */
+    public static function hasExtend(string $name): bool
+    {
+        return array_key_exists($name, static::$extends);
+    }
+
+    /**
+     * Dynamically handle calls to the class.
+     *
+     * @param array<int, mixed> $parameters
+     *
+     * @return mixed
+     */
+    public function __call(string $method, array $parameters)
+    {
+        if (!static::hasExtend($method)) {
+            return new HigherOrderExpectation($this, $method, $parameters);
+        }
+
+        /** @var Closure $extend */
+        $extend = static::$extends[$method]->bindTo($this, static::class);
+
+        return $extend(...$parameters);
+    }
+}