fix(universal-method): 修复扩展方法链式调用的返回类型推断

- 在内置方法查找后添加扩展方法的返回类型检查
- 重构 findExtensionMethod 调用逻辑以支持链式调用场景
- 使用函数定义的返回类型而非默认的 TYPE_VAR
- 移除冗余的命名空间函数查找逻辑

src/Php/UniversalMethodCall.php

@@ -340,10 +340,19 @@ trait UniversalMethodCall
                 if ($def !== null) {
                     return $def['return_type'];
                 }
+                $ext = $this->findExtensionMethod($searchType, $method);
+                if ($ext !== null) {
+                    return $ext['return_type'];
+                }
             }
             return null;
         }
-        return static::UNIVERSAL_METHODS[$type][$method]['return_type'] ?? null;
+        $builtin = static::UNIVERSAL_METHODS[$type][$method]['return_type'] ?? null;
+        if ($builtin !== null) {
+            return $builtin;
+        }
+        $ext = $this->findExtensionMethod($type, $method);
+        return $ext ? $ext['return_type'] : null;
     }
 
     private const array TYPE_EXTENSION_PREFIX = [
@@ -407,11 +416,13 @@ trait UniversalMethodCall
             return null;
         }
 
+        $funcDef = $this->getFunction($funcName);
+
         return [
             'handler'      => 'php_fn',
             'fn'           => $funcName,
             'receiver_pos' => 1,
-            'return_type'  => self::TYPE_VAR,
+            'return_type'  => $funcDef->returnType,
             'min_args'     => 0,
             'max_args'     => -1,
         ];
@@ -422,12 +433,6 @@ trait UniversalMethodCall
         if ($this->hasFunction($funcName)) {
             return $funcName;
         }
-        if ($this->namespace) {
-            $nsFunc = $this->namespace . '\\' . $funcName;
-            if ($this->hasFunction($nsFunc)) {
-                return $nsFunc;
-            }
-        }
         return null;
     }
 

tests/aot/universal_method_extension_chain.phpt

@@ -0,0 +1,55 @@
+--TEST--
+Universal method: extension function chaining with typed return
+--FILE--
+<?php
+
+use native_types;
+
+function int_to_words(int $int): string
+{
+    $map = [1 => 'one', 2 => 'two', 3 => 'three'];
+    return $map[$int] ?? 'unknown';
+}
+
+function str_double(string $str): string
+{
+    return $str . $str;
+}
+
+function str_get_length(string $str): int
+{
+    return strlen($str);
+}
+
+function str_to_array(string $str, string $delimiter): array
+{
+    return $str->split($delimiter);
+}
+
+function array_last(array $arr): mixed {
+    if ($arr->count() === 0) {
+        return null;
+    }
+    return $arr[$arr->count() - 1];
+}
+
+function main()
+{
+    $num = 2;
+    var_dump($num->toWords()->upper());
+    var_dump($num->toWords()->double()->upper());
+
+    $str = "hello";
+    var_dump($str->getLength()->add(100));
+    var_dump($str->double()->length());
+
+    $str2 = "hello world";
+    var_dump($str2->split(" ")->last());
+}
+?>
+--EXPECT--
+string(3) "TWO"
+string(6) "TWOTWO"
+int(105)
+int(10)
+string(5) "world"