Add metaclass support, support PEP 3115 and PEP 487

NEWS.rst

@@ -19,6 +19,8 @@ Other Breaking Changes
 New Features
 ------------------------------
 * Added `mangle` and `unmangle` as core functions
+* `defclass` in Python 3 now supports specifying metaclasses and other
+  keyword arguments
 
 Bug Fixes
 ------------------------------

hy/compiler.py

@@ -2057,11 +2057,12 @@ class HyASTCompiler(object):
 
         bases_expr = []
         bases = Result()
+        keywords = []
         if expressions:
             base_list = expressions.pop(0)
             if not isinstance(base_list, HyList):
                 raise HyTypeError(base_list, "Base classes must be a list.")
-            bases_expr, bases, _ = self._compile_collect(base_list)
+            bases_expr, bases, keywords = self._compile_collect(base_list, with_kwargs=PY3)
 
         body = Result()
 
@@ -2092,7 +2093,7 @@ class HyASTCompiler(object):
             expressions,
             decorator_list=[],
             name=ast_str(class_name),
-            keywords=[],
+            keywords=keywords,
             starargs=None,
             kwargs=None,
             bases=bases_expr,

tests/compilers/test_ast.py

@@ -214,6 +214,13 @@ def test_ast_good_defclass():
     can_compile("(defclass a [])")
 
 
+@pytest.mark.skipif(not PY3, reason="Python 3 supports class keywords")
+def test_ast_good_defclass_with_metaclass():
+    "Make sure AST can compile valid defclass with keywords"
+    can_compile("(defclass a [:metaclass b])")
+    can_compile("(defclass a [:b c])")
+
+
 def test_ast_bad_defclass():
     "Make sure AST can't compile invalid defclass"
     cant_compile("(defclass)")

tests/native_tests/py36_only_tests.hy

@@ -37,3 +37,11 @@
         (setv x (+ x a))
         (else (setv x (+ x 50))))
       (assert (= x 53)))))
+
+(defn test-pep-487 []
+  (defclass QuestBase []
+    [--init-subclass-- (fn [cls swallow &kwargs kwargs]
+                         (setv cls.swallow swallow))])
+
+  (defclass Quest [QuestBase :swallow "african"])
+  (assert (= (. (Quest) swallow) "african")))

tests/native_tests/py3_only_tests.hy

@@ -84,3 +84,26 @@
        (assert (= (foo :b 20 :a 10 :c 30)
                   (, 10 20 30)))))
 
+(defn test-pep-3115 []
+  (defclass member-table [dict]
+    [--init-- (fn [self] (setv self.member-names []))
+
+     --setitem-- (fn [self key value]
+                   (if (not-in key self)
+                       (.append self.member-names key))
+                   (dict.--setitem-- self key value))])
+
+  (defclass OrderedClass [type]
+    [--prepare-- (classmethod (fn [metacls name bases] (member-table)))
+
+     --new-- (fn [cls name bases classdict]
+               (setv result (type.--new-- cls name bases (dict classdict)))
+               (setv result.member-names classdict.member-names)
+               result)])
+
+  (defclass MyClass [:metaclass OrderedClass]
+    [method1 (fn [self] (pass))
+     method2 (fn [self] (pass))])
+
+  (assert (= (. (MyClass) member-names)
+             ["__module__" "__qualname__" "method1" "method2"])))