DeviceType

Enumeration for the different types of device.

Firefox Accounts and the broader Sync universe separates devices into broad categories for various purposes, such as distinguishing a desktop PC from a mobile phone. Upon signin, the application should inspect the device it is running on and select an appropriate `DeviceType` to include in its device registration record.

A special variant in this enum, `DeviceType::Unknown` is used to capture the string values we don't recognise. It also has a custom serde serializer and deserializer which implements the following semantics:

• deserializing a DeviceType which uses a string value we don't recognise or null will return DeviceType::Unknown rather than returning an error.

• serializing DeviceType::Unknown will serialize null.

This has a few important implications:

• In general, Option<DeviceType> should be avoided, and a plain DeviceType used instead, because in that case, None would be semantically identical to DeviceType::Unknown and as mentioned above, null already deserializes as DeviceType::Unknown.

• Any unknown device types can not be round-tripped via this enum - eg, if you deserialize a struct holding a DeviceType string value we don't recognize, then re-serialize it, the original string value is lost. We don't consider this a problem because in practice, we only upload records with this device's type, not the type of other devices, and it's reasonable to assume that this module knows about all valid device types for the device type it is deployed on.