[mypyc] Handle non extention classes with attribute annotations for forward defined classes

mypyc/irbuild/classdef.py

@@ -645,7 +645,16 @@ def add_non_ext_class_attr_ann(
     if get_type_info is not None:
         type_info = get_type_info(stmt)
         if type_info:
-            typ = load_type(builder, type_info, stmt.line)
+            # NOTE: Using string type information is similar to using
+            # `from __future__ import annotations` in standard python.
+            # NOTE: For string types we need to use the fullname since it
+            # includes the module. If string type doesn't have the module,
+            # @dataclass will try to get the current module and fail since the
+            # current module is not in sys.modules.
+            if builder.current_module == type_info.module_name and stmt.line < type_info.line:
+                typ = builder.load_str(type_info.fullname)
+            else:
+                typ = load_type(builder, type_info, stmt.line)
 
     if typ is None:
         # FIXME: if get_type_info is not provided, don't fall back to stmt.type?

mypyc/test-data/run-classes.test

@@ -2719,3 +2719,32 @@ print(native.A(ints=[1, -17]).ints)
 
 [out]
 \[1, -17]
+
+[case testDataclassClassReference]
+from __future__ import annotations
+from dataclasses import dataclass
+
+class BackwardDefinedClass:
+    pass
+
+@dataclass
+class Data:
+    bitem: BackwardDefinedClass
+    bitems: 'BackwardDefinedClass'
+    fitem: ForwardDefinedClass
+    fitems: 'ForwardDefinedClass'
+
+class ForwardDefinedClass:
+    pass
+
+def test_function():
+    d = Data(
+        bitem=BackwardDefinedClass(),
+        bitems=BackwardDefinedClass(),
+        fitem=ForwardDefinedClass(),
+        fitems=ForwardDefinedClass(),
+    )
+    assert(isinstance(d.bitem, BackwardDefinedClass))
+    assert(isinstance(d.bitems, BackwardDefinedClass))
+    assert(isinstance(d.fitem, ForwardDefinedClass))
+    assert(isinstance(d.fitems, ForwardDefinedClass))