Allow returning errors when marshaling scalars

[pkosiec]

I have a case when marshaling a scalar can return an error.

Currently we have the following Marshaler and Unmarshaler interfaces:

type Marshaler interface {
	MarshalGQL(w io.Writer)
}

type Unmarshaler interface {
	UnmarshalGQL(v interface{}) error
}

It'd be great to allow return errors for Marshaler, similarly to Unmarshaler.

versions

• gqlgen version 0.9.0

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[pkosiec]

This issue is still valid.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[pkosiec]

Still valid. @vektah if you agree, I can create a PR with this change during my spare time. It would be a breaking change, but I can try to avoid this. Waiting for your feedback. Cheers!

[adrianduke]

Implementing this would make resolving issue #1195 simpler.

[duckbrain]

Linking #1645 because it also deals with changing the scalar interface.

[duckbrain]

This can probably be closed. #1652; using the context interface allows returning an error.