[mypyc] Add basic support for class-based named tuples

Not all possible variants are tested, but at least simple things work.

Fixes mypyc/mypyc#719.

Author: JukkaL

mypyc/irbuild/classdef.py

@@ -213,11 +213,16 @@ def populate_non_ext_bases(builder: IRBuilder, cdef: ClassDef) -> Value:
 
     The tuple is passed to the metaclass constructor.
     """
+    is_named_tuple = cdef.info.is_named_tuple
     ir = builder.mapper.type_to_ir[cdef.info]
     bases = []
     for cls in cdef.info.mro[1:]:
         if cls.fullname == 'builtins.object':
             continue
+        if is_named_tuple and cls.fullname in ('typing.Sequence', 'typing.Iterable'):
+            # HAX: Synthesized base classes added by mypy don't exist at runtime, so skip them.
+            #      This could break if they were added explicitly, though...
+            continue
         # Add the current class to the base classes list of concrete subclasses
         if cls in builder.mapper.type_to_ir:
             base_ir = builder.mapper.type_to_ir[cls]
@@ -237,6 +242,8 @@ def populate_non_ext_bases(builder: IRBuilder, cdef: ClassDef) -> Value:
                 # In Python 3.9 TypedDict is not a real type.
                 name = '_TypedDict'
             base = builder.get_module_attr(module, name, cdef.line)
+        elif is_named_tuple and cls.fullname == 'builtins.tuple':
+            base = builder.get_module_attr('typing', 'NamedTuple', cdef.line)
         else:
             base = builder.load_global_str(cls.name, cdef.line)
         bases.append(base)
@@ -455,7 +462,7 @@ def cache_class_attrs(builder: IRBuilder,
                       attrs_to_cache: List[Tuple[Lvalue, RType]],
                       cdef: ClassDef) -> None:
     """Add class attributes to be cached to the global cache."""
-    typ = builder.load_native_type_object(cdef.fullname)
+    typ = builder.load_native_type_object(cdef.info.fullname)
     for lval, rtype in attrs_to_cache:
         assert isinstance(lval, NameExpr)
         rval = builder.py_get_attr(typ, lval.name, cdef.line)

mypyc/irbuild/util.py

@@ -84,6 +84,8 @@ def is_extension_class(cdef: ClassDef) -> bool:
         return False
     if cdef.info.typeddict_type:
         return False
+    if cdef.info.is_named_tuple:
+        return False
     if (cdef.info.metaclass_type and cdef.info.metaclass_type.type.fullname not in (
             'abc.ABCMeta', 'typing.TypingMeta', 'typing.GenericMeta')):
         return False

mypyc/test-data/run-misc.test

@@ -775,6 +775,19 @@ def test_non_total_typed_dict() -> None:
     assert d3['c'] == 3
     assert d4['d'] == 4
 
+[case testClassBasedNamedTuple]
+from typing import NamedTuple
+
+class NT(NamedTuple):
+    a: int
+
+def test_named_tuple() -> None:
+    t = NT(a=1)
+    assert t.a == 1
+    assert type(t) is NT
+    assert isinstance(t, tuple)
+    assert not isinstance(tuple([1]), NT)
+
 [case testUnion]
 from typing import Union