JSON and MsgPack don't handle OptionalAttributes correctly

[paddycarver]

terraform-plugin-go version

v0.3.1

Expected Behavior

Complex types that have object elements or attributes that contain optional attributes (a map of objects with optional attributes, an object with an object attribute that has optional attributes, etc.) should be surfaced as a value without optional attributes when surfaced from msgpack or JSON.

Actual Behavior

The values retain their type constraints as types, instead of the actual type. Meaning they'd still have optional attributes as part of their type, instead of their concrete type.

References

• tftypes: Enhance Type Comparisons Functionality #94 discovered this problem but for DynamicPseudoType, which is the other place type constraints come up

[paddycarver]

Upon investigation, it looks like the only real problem here is that if we have an Object with OptionalAttributes, the msgpackUnmarshal code for null/unknown values will preserve the OptionalAttributes. DynamicPseudoType seems to be handled correctly. Objects that have values besides unknown/null have their OptionalAttributes stripped appropriately.