Add an email member to Developer

[ShreckYe]

Similar to #4654. The email member is available in Maven, Gradle, and sbt. Shall we add it here too?

In sbt's official code, however, it's unclear to me why they pass the (GitHub) ID to the email member.

Compared to #4654, I don't think there is a way to make this change in a backward-compatible way with the default arguments though.

This is just a proposal so the changes are far from complete. Please let me know whether it's necessary.

[lefou]

Instead, we should encode an email with the mailto scheme into an url.

To be clear, we want to add the email, but once we have the email, the url need to become optional, but there is no elegant way to make email and url optional but enforce to have at least one.

[ShreckYe]

So by "elegant" do you mean all 3 cases (email only, url only, both email and url) should be supported, they shouldn't be encoded with an extra sum type or Either, and the constraint should happen at compile-time instead of runtime?

[lefou]

So by "elegant" do you mean all 3 cases (email only, url only, both email and url) should be supported, they shouldn't be encoded with an extra sum type or Either, and the constraint should happen at compile-time instead of runtime?

That's what I meant. But looking at https://maven.apache.org/pom.html#Developers, non of these fields are really required and it's up to the specific repository to accept or reject a pom.

In that case, we should also add all the other missing fields like roles, timezone and properties.

[ShreckYe]

Got it. Thanks. Feel free to close this PR.