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

$ go version
go version devel +1b08acee45 Thu Jun 25 23:22:18 2020 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes, as of commit 1b08ace

What did you do?

$ go tool go2go run err.go2 
# command-line-arguments
./err.go2:8: undefined: embedPair
./err.go2:8: type a is not an expression
./err.go2:8: type b is not an expression

where err.go2 is:

package main

type a struct{}
type b struct{}
type c struct{}

type embedPair(type T, U) struct {
        T
        U
}

func main() {
        _ = embedPair(embedPair(a, b), c){}
}

It gives a different error in the playground: https://go2goplay.golang.org/p/2h7HWFVkvW2

(a couple days ago it crashed, so this is better than it was)

What did you expect to see?

I expected it to construct a type like:

type x struct {
  a
  b
}

type y struct {
  x
  c
}

Only x will be unnamed, so I'm not sure how this is supposed to work, which is why I was trying it.

What did you see instead?

It gives confusing error messages.