So I got curious and I looked at the compiler source code, and it does a depth-first search.
The fascinating bit to me is that there is a consolidateMultiples function in go/src/go/types/lookup.go (lines 286-304) that detects when multiple embedded types at the same depth provide the same field name. I wonder why they don’t do this for all levels. How deep could this even be in practice for it to matter? You could just have a hashmap with them all.
> I wonder why they don’t do this for all levels. How deep could this even be in practice for it to matter? You could just have a hashmap with them all.
While it may seem questionable for fields; it applies to methods too and is potentially more useful as a way to override them when doing struct embedding but wanting to preserve an interface.
To protect against changes in structs coming from external libraries. Or, better phrased, external structs should not dictate what names you're allowed to use in your own structs (so they have priority).
It performs a breadth-first search, not a depth-first search.