Don't create incomplete __init__ signatures for deferred dataclasses (#7382)

Author: ilevkivskyi

mypy/plugins/dataclasses.py

@@ -2,7 +2,7 @@
 
 from collections import OrderedDict
 
-from typing import Dict, List, Set, Tuple
+from typing import Dict, List, Set, Tuple, Optional
 from typing_extensions import Final
 
 from mypy.nodes import (
@@ -79,7 +79,9 @@ def transform(self) -> None:
         ctx = self._ctx
         info = self._ctx.cls.info
         attributes = self.collect_attributes()
-        # Check if attribute types are ready.
+        if attributes is None:
+            # Some definitions are not ready, defer() should be already called.
+            return
         for attr in attributes:
             if info[attr.name].type is None:
                 ctx.api.defer()
@@ -95,7 +97,9 @@ def transform(self) -> None:
         # processed them yet. In order to work around this, we can simply skip generating
         # __init__ if there are no attributes, because if the user truly did not define any,
         # then the object default __init__ with an empty signature will be present anyway.
-        if decorator_arguments['init'] and '__init__' not in info.names and attributes:
+        if (decorator_arguments['init'] and
+                ('__init__' not in info.names or info.names['__init__'].plugin_generated) and
+                attributes):
             add_method(
                 ctx,
                 '__init__',
@@ -189,7 +193,7 @@ def reset_init_only_vars(self, info: TypeInfo, attributes: List[DataclassAttribu
                             # recreate a symbol node for this attribute.
                             lvalue.node = None
 
-    def collect_attributes(self) -> List[DataclassAttribute]:
+    def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
         """Collect all attributes declared in the dataclass and its parents.
 
         All assignments of the form
@@ -225,7 +229,7 @@ def collect_attributes(self) -> List[DataclassAttribute]:
             node = sym.node
             if isinstance(node, PlaceholderNode):
                 # This node is not ready yet.
-                continue
+                return None
             assert isinstance(node, Var)
 
             # x: ClassVar[int] is ignored by dataclasses.

test-data/unit/check-dataclasses.test

@@ -698,3 +698,35 @@ C('no')  # E: Argument 1 to "C" has incompatible type "str"; expected "int"
 [file other.py]
 import lib
 [builtins fixtures/bool.pyi]
+
+[case testDeferredDataclassInitSignature]
+from dataclasses import dataclass
+from typing import Optional, Type
+
+@dataclass
+class C:
+    x: Optional[int] = None
+    y: Type[Deferred] = Deferred
+
+    @classmethod
+    def default(cls) -> C:
+        return cls(x=None, y=None)
+
+class Deferred: pass
+[builtins fixtures/classmethod.pyi]
+
+[case testDeferredDataclassInitSignatureSubclass]
+# flags: --strict-optional
+from dataclasses import dataclass
+from typing import Optional
+
+@dataclass
+class B:
+    x: Optional[C]
+
+@dataclass
+class C(B):
+    y: str
+
+a = C(None, 'abc')
+[builtins fixtures/bool.pyi]