cc2

[tarrinneal]

wip

fixes flutter/flutter#147454
fixes flutter/flutter#147127
fixes flutter/flutter#147587
fixes flutter/flutter#148065

[stuartmorgan]

WriteValue(EncodableValue(static_cast<int>(std::any_cast<${customType.name}>(*custom_value))), stream);

(Not doing as a GitHub code suggestion since I'm not sure which of my email addresses committing it would use, and I don't want to blow up the CLA check.)

[stuartmorgan]

The bad variant access error is coming from this pattern: if the arg's value is null, then encodable_an_enum_arg isn't a CustomEncodableValue at all, it's a monotype (i.e., IsNull() is true). So you need to check IsNull() before doing a std::get instead of after, or you need to use a get_if<CustomEncodableValue>(&encodable_an_enum_arg) and then if that's null, pass null, and if it's not not, do the any-cast. (The thing that tripped me up in my first attempt to write a fix for this is that you can't any_cast a CustomEncodableValue* because of how implicit conversions work, so you'll need to do some gymnastics with a value variable like before I think.)

[stuartmorgan]

This is kind of clunky, but the only way I can find to do it in a single statement involves a pointer to a reference that I can't prove to myself has a lifetime beyond that statement, and I'd rather the code be longer than have undefined behavior...

AnEnum an_enum_arg_value;
const AnEnum* an_enum_arg = nullptr;
if (!encodable_an_enum_arg.IsNull()) {
  an_enum_arg_value = std::any_cast<AnEnum>(std::get<CustomEncodableValue>(encodable_an_enum_arg));
  an_enum_arg = &an_enum_arg_value;
}
...EchoNullableEnum(an_enum_arg);