Show that attrs auto_detect does not work

This test demonstrates that addition of dunder methods in attrs classes
isn't quite complete.

While the existing test demonstrates that it was working for classes
defined with `init=False`, the `__attrs_init__` method wasn't generated
in the same way when `__init__` was defined with `auto_detect=True`
enabled (either explicitly, or by default).

This auto-generated `__attrs_init__` has been enabled in Attrs as of
version 21.1.0.

Related to: python#10328
Ref: python-attrs/attrs#793
Ref: https://www.attrs.org/en/stable/changelog.html

Author: meshy

test-data/unit/check-plugin-attrs.test

@@ -1656,6 +1656,42 @@ reveal_type(A.__attrs_init__)  # N: Revealed type is "def (self: __main__.A, b:
 
 [builtins fixtures/plugin_attrs.pyi]
 
+[case testAttrsInitMethodGeneratedWhenAutoDetectTrue]
+from typing import Tuple
+import attr
+
+@attr.define(auto_detect=True)
+class A:
+    b: int
+    c: str
+    def __init__(self, bc: Tuple[int, str]) -> None:
+        b, c = bc
+        self.__attrs_init__(b, c)
+
+reveal_type(A)  # N: Revealed type is "def (bc: Tuple[builtins.int, builtins.str]) -> __main__.A"
+reveal_type(A.__init__)  # N: Revealed type is "def (self: __main__.A, bc: Tuple[builtins.int, builtins.str])"
+reveal_type(A.__attrs_init__)  # N: Revealed type is "def (self: __main__.A, b: builtins.int, c: builtins.str)"
+
+[builtins fixtures/plugin_attrs.pyi]
+
+[case testAttrsInitMethodGeneratedWhenAutoDetectTrueDefault]
+from typing import Tuple
+import attr
+
+@attr.define
+class A:
+    b: int
+    c: str
+    def __init__(self, bc: Tuple[int, str]) -> None:
+        b, c = bc
+        self.__attrs_init__(b, c)
+
+reveal_type(A)  # N: Revealed type is "def (bc: Tuple[builtins.int, builtins.str]) -> __main__.A"
+reveal_type(A.__init__)  # N: Revealed type is "def (self: __main__.A, bc: Tuple[builtins.int, builtins.str])"
+reveal_type(A.__attrs_init__)  # N: Revealed type is "def (self: __main__.A, b: builtins.int, c: builtins.str)"
+
+[builtins fixtures/plugin_attrs.pyi]
+
 [case testAttrsClassWithSlots]
 import attr