0 is reserved for errors.
Order is weird for historical reasons.
Enum
Fixed32
Fixed64
Float
Group
Tag-delimited aggregate.
Group type is deprecated and not supported in proto3. However, Proto3
implementations should still be able to parse the group wire format and
treat group fields as unknown fields.
Int32
Not ZigZag encoded. Negative numbers take 10 bytes. Use TYPE_SINT32 if
negative values are likely.
Int64
Not ZigZag encoded. Negative numbers take 10 bytes. Use TYPE_SINT64 if
negative values are likely.