Fix generic inheritance for attrs init methods (#9383)

Fixes #5744

Updates the attrs plugin. Instead of directly copying attribute type along the MRO, this first resolves typevar in the context of the subtype.

mypy/plugins/attrs.py

@@ -15,14 +15,16 @@
     SymbolTableNode, MDEF, JsonDict, OverloadedFuncDef, ARG_NAMED_OPT, ARG_NAMED,
     TypeVarExpr, PlaceholderNode
 )
+from mypy.plugin import SemanticAnalyzerPluginInterface
 from mypy.plugins.common import (
-    _get_argument, _get_bool_argument, _get_decorator_bool_argument, add_method
+    _get_argument, _get_bool_argument, _get_decorator_bool_argument, add_method,
+    deserialize_and_fixup_type
 )
 from mypy.types import (
     Type, AnyType, TypeOfAny, CallableType, NoneType, TypeVarDef, TypeVarType,
     Overloaded, UnionType, FunctionLike, get_proper_type
 )
-from mypy.typeops import make_simplified_union
+from mypy.typeops import make_simplified_union, map_type_from_supertype
 from mypy.typevars import fill_typevars
 from mypy.util import unmangle
 from mypy.server.trigger import make_wildcard_trigger
@@ -70,19 +72,22 @@ class Attribute:
 
     def __init__(self, name: str, info: TypeInfo,
                  has_default: bool, init: bool, kw_only: bool, converter: Converter,
-                 context: Context) -> None:
+                 context: Context,
+                 init_type: Optional[Type]) -> None:
         self.name = name
         self.info = info
         self.has_default = has_default
         self.init = init
         self.kw_only = kw_only
         self.converter = converter
         self.context = context
+        self.init_type = init_type
 
     def argument(self, ctx: 'mypy.plugin.ClassDefContext') -> Argument:
         """Return this attribute as an argument to __init__."""
         assert self.init
-        init_type = self.info[self.name].type
+
+        init_type = self.init_type or self.info[self.name].type
 
         if self.converter.name:
             # When a converter is set the init_type is overridden by the first argument
@@ -168,20 +173,33 @@ def serialize(self) -> JsonDict:
             'converter_is_attr_converters_optional': self.converter.is_attr_converters_optional,
             'context_line': self.context.line,
             'context_column': self.context.column,
+            'init_type': self.init_type.serialize() if self.init_type else None,
         }
 
     @classmethod
-    def deserialize(cls, info: TypeInfo, data: JsonDict) -> 'Attribute':
+    def deserialize(cls, info: TypeInfo,
+                    data: JsonDict,
+                    api: SemanticAnalyzerPluginInterface) -> 'Attribute':
         """Return the Attribute that was serialized."""
-        return Attribute(
-            data['name'],
+        raw_init_type = data['init_type']
+        init_type = deserialize_and_fixup_type(raw_init_type, api) if raw_init_type else None
+
+        return Attribute(data['name'],
             info,
             data['has_default'],
             data['init'],
             data['kw_only'],
             Converter(data['converter_name'], data['converter_is_attr_converters_optional']),
-            Context(line=data['context_line'], column=data['context_column'])
-        )
+            Context(line=data['context_line'], column=data['context_column']),
+            init_type)
+
+    def expand_typevar_from_subtype(self, sub_type: TypeInfo) -> None:
+        """Expands type vars in the context of a subtype when an attribute is inherited
+        from a generic super type."""
+        if not isinstance(self.init_type, TypeVarType):
+            return
+
+        self.init_type = map_type_from_supertype(self.init_type, sub_type, self.info)
 
 
 def _determine_eq_order(ctx: 'mypy.plugin.ClassDefContext') -> bool:
@@ -363,7 +381,8 @@ def _analyze_class(ctx: 'mypy.plugin.ClassDefContext',
                 # Only add an attribute if it hasn't been defined before.  This
                 # allows for overwriting attribute definitions by subclassing.
                 if data['name'] not in taken_attr_names:
-                    a = Attribute.deserialize(super_info, data)
+                    a = Attribute.deserialize(super_info, data, ctx.api)
+                    a.expand_typevar_from_subtype(ctx.cls.info)
                     super_attrs.append(a)
                     taken_attr_names.add(a.name)
     attributes = super_attrs + list(own_attrs.values())
@@ -491,7 +510,9 @@ def _attribute_from_auto_attrib(ctx: 'mypy.plugin.ClassDefContext',
     name = unmangle(lhs.name)
     # `x: int` (without equal sign) assigns rvalue to TempNode(AnyType())
     has_rhs = not isinstance(rvalue, TempNode)
-    return Attribute(name, ctx.cls.info, has_rhs, True, kw_only, Converter(), stmt)
+    sym = ctx.cls.info.names.get(name)
+    init_type = sym.type if sym else None
+    return Attribute(name, ctx.cls.info, has_rhs, True, kw_only, Converter(), stmt, init_type)
 
 
 def _attribute_from_attrib_maker(ctx: 'mypy.plugin.ClassDefContext',
@@ -557,7 +578,8 @@ def _attribute_from_attrib_maker(ctx: 'mypy.plugin.ClassDefContext',
     converter_info = _parse_converter(ctx, converter)
 
     name = unmangle(lhs.name)
-    return Attribute(name, ctx.cls.info, attr_has_default, init, kw_only, converter_info, stmt)
+    return Attribute(name, ctx.cls.info, attr_has_default, init,
+                     kw_only, converter_info, stmt, init_type)
 
 
 def _parse_converter(ctx: 'mypy.plugin.ClassDefContext',

test-data/unit/check-attr.test

@@ -454,6 +454,109 @@ A([1], '2')  # E: Cannot infer type argument 1 of "A"
 
 [builtins fixtures/list.pyi]
 
+
+[case testAttrsUntypedGenericInheritance]
+from typing import Generic, TypeVar
+import attr
+
+T = TypeVar("T")
+
+@attr.s(auto_attribs=True)
+class Base(Generic[T]):
+    attr: T
+
+@attr.s(auto_attribs=True)
+class Sub(Base):
+    pass
+
+sub = Sub(attr=1)
+reveal_type(sub)  # N: Revealed type is '__main__.Sub'
+reveal_type(sub.attr)  # N: Revealed type is 'Any'
+
+[builtins fixtures/bool.pyi]
+
+
+[case testAttrsGenericInheritance]
+from typing import Generic, TypeVar
+import attr
+
+S = TypeVar("S")
+T = TypeVar("T")
+
+@attr.s(auto_attribs=True)
+class Base(Generic[T]):
+    attr: T
+
+@attr.s(auto_attribs=True)
+class Sub(Base[S]):
+    pass
+
+sub_int = Sub[int](attr=1)
+reveal_type(sub_int)  # N: Revealed type is '__main__.Sub[builtins.int*]'
+reveal_type(sub_int.attr)  # N: Revealed type is 'builtins.int*'
+
+sub_str = Sub[str](attr='ok')
+reveal_type(sub_str)  # N: Revealed type is '__main__.Sub[builtins.str*]'
+reveal_type(sub_str.attr)  # N: Revealed type is 'builtins.str*'
+
+[builtins fixtures/bool.pyi]
+
+
+[case testAttrsGenericInheritance]
+from typing import Generic, TypeVar
+import attr
+
+T1 = TypeVar("T1")
+T2 = TypeVar("T2")
+T3 = TypeVar("T3")
+
+@attr.s(auto_attribs=True)
+class Base(Generic[T1, T2, T3]):
+    one: T1
+    two: T2
+    three: T3
+
+@attr.s(auto_attribs=True)
+class Sub(Base[int, str, float]):
+    pass
+
+sub = Sub(one=1, two='ok', three=3.14)
+reveal_type(sub)  # N: Revealed type is '__main__.Sub'
+reveal_type(sub.one)  # N: Revealed type is 'builtins.int*'
+reveal_type(sub.two)  # N: Revealed type is 'builtins.str*'
+reveal_type(sub.three)  # N: Revealed type is 'builtins.float*'
+
+[builtins fixtures/bool.pyi]
+
+
+[case testAttrsMultiGenericInheritance]
+from typing import Generic, TypeVar
+import attr
+
+T = TypeVar("T")
+
+@attr.s(auto_attribs=True, eq=False)
+class Base(Generic[T]):
+    base_attr: T
+
+S = TypeVar("S")
+
+@attr.s(auto_attribs=True, eq=False)
+class Middle(Base[int], Generic[S]):
+    middle_attr: S
+
+@attr.s(auto_attribs=True, eq=False)
+class Sub(Middle[str]):
+    pass
+
+sub = Sub(base_attr=1, middle_attr='ok')
+reveal_type(sub)  # N: Revealed type is '__main__.Sub'
+reveal_type(sub.base_attr)  # N: Revealed type is 'builtins.int*'
+reveal_type(sub.middle_attr)  # N: Revealed type is 'builtins.str*'
+
+[builtins fixtures/bool.pyi]
+
+
 [case testAttrsGenericClassmethod]
 from typing import TypeVar, Generic, Optional
 import attr