Optional Attributes Chapter 2

[siku2]

Optional attributes were implemented in #1537, but they require the use of a special syntax ?=. This was somewhat required for the first implementation because of the internal handling of attributes but the very same PR also changed that so it's no longer a requirement.

Initial discussion: #1537 (comment).

Required changes

1. Tag attributes which support the optional attribute syntax should instead accept values that implement Into<Option<_>>.
2. Optional component properties (i.e. props marked with #[prop_or*], not necessarily with value Option<_>) should also accept Into<Option<_>>. If the variant is None, the default value should remain. Hopefully this doesn't cause any type inference problems for the Transformer...
3. The documentation needs to be updated in a few places.

[jstarry]

@siku2 I agree will all the required changes, thanks for the write up. Also hoping we don't run into type inference problems 🤞

[ranile]

Should this issue be closed, now that the implementation is done?

[siku2]

Should this issue be closed, now that the implementation is done?

You're right!