Python .pyi stubs not defining optional boolean fields correctly.

[cobusc]

What version of protobuf and what language are you using?
Version: protobuf==5.29.3
Language: Python

What operating system (Linux, Windows, ...) and version?
Linux 6.11.0-14-generic #15-Ubuntu SMP PREEMPT_DYNAMIC x86_64 GNU/Linux

What runtime / compiler are you using (e.g., python version or gcc version)
Multiple Python versions

What did you do?
I compiled .proto files, and the generated .pyi stubs was not correct. Examples:

Example 1 (syntax proto2):

syntax = "proto2";

message Test2 {
  optional uint32 an_integer = 1;
  optional bool a_boolean = 2;
}

generated the following .pyi file:

from google.protobuf import descriptor as _descriptor
from google.protobuf import message as _message
from typing import ClassVar as _ClassVar, Optional as _Optional

DESCRIPTOR: _descriptor.FileDescriptor

class Test2(_message.Message):
    __slots__ = ("an_integer", "a_boolean")
    AN_INTEGER_FIELD_NUMBER: _ClassVar[int]
    A_BOOLEAN_FIELD_NUMBER: _ClassVar[int]
    an_integer: int
    a_boolean: bool
    def __init__(self, an_integer: _Optional[int] = ..., a_boolean: bool = ...) -> None: ...

Note that a_boolean does not have the _Optional[] definition in __init__().

Example 2 (syntax proto3):

syntax = "proto3";

message Test3 {
  optional uint32 an_integer = 1;
  optional bool a_boolean = 2;
}

generated the following .pyi file:

from google.protobuf import descriptor as _descriptor
from google.protobuf import message as _message
from typing import ClassVar as _ClassVar, Optional as _Optional

DESCRIPTOR: _descriptor.FileDescriptor

class Test3(_message.Message):
    __slots__ = ("an_integer", "a_boolean")
    AN_INTEGER_FIELD_NUMBER: _ClassVar[int]
    A_BOOLEAN_FIELD_NUMBER: _ClassVar[int]
    an_integer: int
    a_boolean: bool
    def __init__(self, an_integer: _Optional[int] = ..., a_boolean: bool = ...) -> None: ...

Note that a_boolean does not have the _Optional[] definition in __init__().

What did you expect to see
In both cases above I expected the _Optional[] annotation for a_boolean.

What did you see instead?
Type annotation issues, like these, when checking my code:

Argument "a_boolean" to "Test2" has incompatible type "Optional[bool]"; expected "bool"  [arg-type]

It looks like the _Optional[] definition is explicitly not done for booleans, and this does not seem right.
Here is where it is excluded:
opening
closing

Someone else reported it to the grpc project, but it never made its way here:
grpc/grpc#33181