encoding/gob: type information missing from nested ignored interfaces

[siddharthab]

What version of Go are you using (go version)?

> println(runtime.Version())
go1.13.1

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

https://play.golang.org

What did you do?

I encoded a struct with multilevel nested interfaces, and then tried to ignore the encoded value when decoding.

https://play.golang.org/p/L0f2hXG46yx

What did you expect to see?

Decoding the stream to have been successful with type information from both nested interfaces received, while ignoring the first value.

What did you see instead?

gob: bad data: field numbers out of bounds

Also, the function ignoreInterface does not descend into its fields even if the concrete type name is registered. Without descending into the concrete type, it will not be able to get type information from any more interfaces nested inside the concrete type.

go/src/encoding/gob/decode.go

Line 692 in 50bd1c4

// ignoreInterface discards the data for an interface value with no destination.