allow ptr in inline structs

[larrycinnabar]

BSON encoder doesn't allow to use pointers to struct in inline mode.

There was an issue on the same topic on old repo:
https://github.com/go-mgo/mgo/issues/346

Such structure:

type MStruct struct {
	M int `bson:"m,omitempty"`
}
type inlinePtrStruct struct {
	A int
	*MStruct `bson:",inline"`
}

is assumed to become {"a":0, "m":0} (without mstruct structure) - the same way as json encoder does it

without fix we get: "reflect: indirection through nil pointer to embedded struct"

[domodwyer]

Hi @larrycinnabar

Thanks for the PR - we'll take a proper look but seems like a great change!

Dom

[szank]

Looks good!

[tadukurow]

this change will silently skip encoding errors, where they used to panic before.
Not very familiar with the bson encoder anymore, @domodwyer thoughts?

[larrycinnabar]

Encoder has a structInfo object, based only on type, not on value.
As we allow pointers to structs here, we can have chain of inline indices (info.Inline) and e.g. element behind a n-1 index might be nil, so trying to get element by index n will panic because of reflect: indirection through nil pointer to embedded struct

[domodwyer]

I think this is probably fine either way - relying on the encoder to panic because the input was invalid is a bit of a stretch in terms of backwards-compatibility.

[domodwyer]

Hi @larrycinnabar

Would you pull the latest development into this branch and we'll get it merged!

Thanks for taking the time to open a PR - it's really appreciated.

Dom

[larrycinnabar]

Branch is updated. Also a commit with some extra comments is added

[domodwyer]

Hi @larrycinnabar

Thanks for taking the time to contribute 👍

Dom

[bojangavrovski]

This only works when transforming data to bson to be written into mongo. When reading (populating the struct with) a record I still get the "reflect: indirection through nil pointer to embedded struct" error.

[larrycinnabar]

@bojangavrovski hm. Ok, I'm looking into it