Allow accessing __init__ on final classes and when __init__ is final (#19035)

Fixes #19033.

Author: sterliakov

mypy/checkmember.py

@@ -308,18 +308,21 @@ def report_missing_attribute(
 def analyze_instance_member_access(
     name: str, typ: Instance, mx: MemberContext, override_info: TypeInfo | None
 ) -> Type:
-    if name == "__init__" and not mx.is_super:
-        # Accessing __init__ in statically typed code would compromise
-        # type safety unless used via super().
-        mx.fail(message_registry.CANNOT_ACCESS_INIT)
-        return AnyType(TypeOfAny.from_error)
-
-    # The base object has an instance type.
-
     info = typ.type
     if override_info:
         info = override_info
 
+    method = info.get_method(name)
+
+    if name == "__init__" and not mx.is_super and not info.is_final:
+        if not method or not method.is_final:
+            # Accessing __init__ in statically typed code would compromise
+            # type safety unless used via super() or the method/class is final.
+            mx.fail(message_registry.CANNOT_ACCESS_INIT)
+            return AnyType(TypeOfAny.from_error)
+
+    # The base object has an instance type.
+
     if (
         state.find_occurrences
         and info.name == state.find_occurrences[0]
@@ -329,7 +332,6 @@ def analyze_instance_member_access(
         mx.msg.note("Occurrence of '{}.{}'".format(*state.find_occurrences), mx.context)
 
     # Look up the member. First look up the method dictionary.
-    method = info.get_method(name)
     if method and not isinstance(method, Decorator):
         if mx.is_super and not mx.suppress_errors:
             validate_super_call(method, mx)

test-data/unit/check-final.test

@@ -1229,3 +1229,24 @@ reveal_type(B() and 42)  # N: Revealed type is "Literal[42]?"
 reveal_type(C() and 42)  # N: Revealed type is "__main__.C"
 
 [builtins fixtures/bool.pyi]
+
+[case testCanAccessFinalClassInit]
+from typing import final
+
+@final
+class FinalClass:
+    pass
+
+def check_final_class() -> None:
+    new_instance = FinalClass()
+    new_instance.__init__()
+
+class FinalInit:
+    @final
+    def __init__(self) -> None:
+        pass
+
+def check_final_init() -> None:
+    new_instance = FinalInit()
+    new_instance.__init__()
+[builtins fixtures/tuple.pyi]