Strict enum support

[jmattheis]

It would be cool if goverter could strictly convert named types / enums.

// goverter:converter
type Converter interface {
    Convert(InputColor) OutputColor
}

type InputColor int
const (
    InputGreen InputColor = iota
    InputBlue
    InputRed
)

type OutputColor string
const (
    OutputGreen OutputColor = "green"
    OutputBlue  OutputColor = "blue"
    OutputRed   OutputColor = "red"
)

Goverter should fail if the target enum is missing options from the source type.

Currently, goverter just converts the underlying value for named types. So a named string type will be converted to another named string type, without checking if the value is valid.

Unknowns:

• How to know if a named type is an enum. We could use the definition from here https://pkg.go.dev/github.com/nishanths/exhaustive#hdr-Definition_of_enum, but we still need to somehow override this in case it's wrong
• How to support value mappings, should we overload goverter:map to map between enum keys that are differently named. See https://mapstruct.org/documentation/stable/reference/html/#_mapping_enum_to_enum_types
• Do we need special handling for MappingConstants.ANY_REMAINING like it's done in mapstruct?

Please :+1: this issue if you like this functionality

[jmattheis]

Fixed with v1.4.0. See Guide: Enum.