Re: [RESEND PATCH 05/12] golang/xenlight: use struct pointers in keyed union fields

[George Dunlap <George.Dunlap@citrix.com>]

> On May 24, 2021, at 9:36 PM, Nick Rosbrook <rosbrookn@gmail.com> wrote:
> 
> Currently, when marshalig Go types with keyed union fields, we assign the
> value of the struct (e.g. DomainBuildInfoTypeUnionHvm) which implements the
> interface of the keyed union field (e.g. DomainBuildInfoTypeUnion).
> As-is, this means that if a populated DomainBuildInfo is marshaled to
> e.g. JSON, unmarshaling back to DomainBuildInfo will fail.
> 
> When the encoding/json is unmarshaling data into a Go type, and
> encounters a JSON object, it basically can either marshal the data into
> an empty interface, a map, or a struct. It cannot, however, marshal data
> into an interface with at least one method defined on it (e.g.
> DomainBuildInfoTypeUnion). Before this check is done, however, the
> decoder will check if the Go type is a pointer, and dereference it if
> so. It will then use the type of this value as the "target" type.
> 
> This means that if the TypeUnion field is populated with a
> DomainBuildInfoTypeUnion, the decoder will see a non-empty interface and
> fail. If the TypeUnion field is populated with a
> *DomainBuildInfoTypeUnionHvm, it dereferences the pointer and sees a
> struct instead, allowing decoding to continue normally.
> 
> Since there does not appear to be a strict need for NOT using pointers
> in these fields, update code generation to set keyed union fields to
> pointers of their implementing structs.
> 
> Signed-off-by: Nick Rosbrook <rosbrookn@ainfosec.com>

Reviewed-by: George Dunlap <george.dunlap@citrix.com>