Support inheriting enums

[vladfaust]

Extracted from #7629. Reopening doesn't work, but inheriting may do. I have a use-case described in the mentioned issue.

enum Foo
  Bar
end

enum Qux < Foo
  Baz
end

pp Qux.values # => [Qux::Bar, Qux::Baz]

Also:

def handle(foo : Foo)
end

def handle(qux : Qux)
  if qux.bar?
    handle(qux.as(Foo)) # Maybe another syntax, but you get the idea
  else
    # ...
  end
end

Also

#6653 (though I still don't have a usecase for this 😆):

abstract enum Foo
  Bar
end

enum Qux < Foo
end

pp Qux.values # => [Qux::Bar]

enum Quux < Foo
  Baz
end

pp Quux.values # => [Quux::Bar, Quux::Baz]

def handle(foo : Foo)
  if foo.bar?
  end
end

[j8r]

I've found this related comment https://github.com/crystal-lang/crystal/blob/master/src/compiler/crystal/types.cr#L2634
# enum Foo < Enum(Int32)

[straight-shoota]

I don't see how the concept of inheritance fits with enums. Is there any good use case for this?

I'd suggest to close this.

[j8r]

There is still this TODO, what's planned about it?

[asterite]

That's an implementation detail.