Add literal typing.Unpack syntax (issue #802)

coconut/compiler/compiler.py

@@ -1004,6 +1004,7 @@ def bind(cls):
         cls.base_match_for_stmt <<= attach(cls.base_match_for_stmt_ref, cls.method("base_match_for_stmt_handle"))
         cls.async_with_for_stmt <<= attach(cls.async_with_for_stmt_ref, cls.method("async_with_for_stmt_handle"))
         cls.unsafe_typedef_tuple <<= attach(cls.unsafe_typedef_tuple_ref, cls.method("unsafe_typedef_tuple_handle"))
+        cls.unpack_typedef <<= attach(cls.unpack_typedef_ref, cls.method("unpack_typedef_handle"))
         cls.impl_call <<= attach(cls.impl_call_ref, cls.method("impl_call_handle"))
         cls.protocol_intersect_expr <<= attach(cls.protocol_intersect_expr_ref, cls.method("protocol_intersect_expr_handle"))
 
@@ -5229,6 +5230,11 @@ def unsafe_typedef_tuple_handle(self, original, loc, tokens):
         tuple_items = self.testlist_star_expr_handle(original, loc, tokens)
         return "_coconut.typing.Tuple[" + tuple_items + "]"
 
+    def unpack_typedef_handle(self, tokens):
+        """Handle **Type -> Unpack[Type] in type annotations."""
+        typedef, = tokens
+        return "_coconut.typing.Unpack[" + typedef + "]"
+
     def term_handle(self, tokens):
         """Handle terms seperated by mul-like operators."""
         out = [tokens[0]]

coconut/compiler/grammar.py

@@ -1055,6 +1055,7 @@ class Grammar(object):
         typedef_tuple = Forward()
         typedef_ellipsis = Forward()
         typedef_op_item = Forward()
+        unpack_typedef = Forward()
 
         expr_lambdef = Forward()
         stmt_lambdef = Forward()
@@ -1198,9 +1199,10 @@ class Grammar(object):
         # we include (var)arg_comma to ensure the pattern matches the whole arg
         arg_comma = comma | fixto(FollowedBy(rparen), "")
         setarg_comma = arg_comma | fixto(FollowedBy(colon), "")
-        typedef_ref = setname + colon.suppress() + typedef_test + arg_comma
+        unpack_typedef_ref = dubstar.suppress() + typedef_test
+        typedef_ref = setname + colon.suppress() + (unpack_typedef | typedef_test) + arg_comma
         default = condense(equals + test)
-        unsafe_typedef_default_ref = setname + colon.suppress() + typedef_test + Optional(default)
+        unsafe_typedef_default_ref = setname + colon.suppress() + (unpack_typedef | typedef_test) + Optional(default)
         typedef_default_ref = unsafe_typedef_default_ref + arg_comma
         tfpdef = condense(setname + arg_comma) | typedef
         tfpdef_default = condense(setname + Optional(default) + arg_comma) | typedef_default

coconut/tests/src/extras.coco

@@ -354,6 +354,16 @@ cannot reassign type variable 'T' (use explicit '\T' syntax if intended) (line 1
     assert_raises(-> parse_with_state("final x = 1\nmatch y:\n    case x: pass"), CoconutSyntaxError, err_has="final")
     assert_raises(-> parse_with_state("final x = 1\nfinal x = 2"), CoconutSyntaxError, err_has="final")
 
+    # typing.Unpack syntax: **Type -> _coconut.typing.Unpack[Type]
+    assert "_coconut.typing.Unpack[int]" in parse_with_state("def f(**kwargs: **int): pass", "block")
+    assert "_coconut.typing.Unpack[MyDict]" in parse_with_state("def f(**kwargs: **MyDict): pass", "block")
+    assert "_coconut.typing.Unpack[MyDict]" in parse_with_state("def f(x: **MyDict): pass", "block")
+    assert "_coconut.typing.Unpack[dict[str, int]]" in parse_with_state("def f(**kwargs: **dict[str, int]): pass", "block")
+    assert "_coconut.typing.Unpack[" in parse_with_state("def f(a: int, **kwargs: **MyDict): pass", "block")
+    # ensure normal type annotations are not affected
+    assert "Unpack" not in parse_with_state("def f(**kwargs: str): pass", "block")
+    assert "Unpack" not in parse_with_state("def f(x: int): pass", "block")
+
     return True