MarshalYAML interface with and without pointers

[vanbroup]

MarshalYAML doesn't seem to have the same behaviour as MarshalJSON, for example when the interface is implemented on an interface:

In encoding/json the MarshalJSON interface implemented as (d *Data) MarshalJSON() triggers on pointers and non-pointers:
https://play.golang.org/p/LFoqw1VHz8l

Doing the same with (d *Data) MarshalYAML(), doesn't work:
https://play.golang.org/p/hFnuiLpKq73

But when removing the pointer to (d Data) MarshalYAML() or by changing the data to pointers, it works fine:
https://play.golang.org/p/FyngGj0lATf

[cyberbeast]

Any comments on this? This is a very subtle departure from MarshalJSON() but one with high impact. I've encountered this behavior in a project recently and it was hard to reconcile findings because it doesn't work the same way as MarshalJSON(), and there is no explicit documentation regarding the usage of the Marshaler interface to document this either.

[aathan]

#979