Notice that the types/methods will compile, the error only occurs when they are used. The following code from the draft spec compiles: https://go2goplay.golang.org/p/xPQmnRMC2kV

Downloaded go2go and examined the generated source. It appears that embedded generic types are left alone during instantiation, but post instantiation the generic "T" type is no longer defined. Generated incorrect code:

//line main.go2:7
type instantiate୦୦Lockable୦string struct {
//line main.go2:11
 T
        mu sync.Mutex
}

Correct code (I think) with T replaced with the instantiated type:

//line main.go2:7
type instantiate୦୦Lockable୦string struct {
//line main.go2:11
 T string
        mu sync.Mutex
}

Change https://golang.org/cl/238621 mentions this issue: [dev.go2go] go/go2go: instantiate embedded type parameters

Thanks, this should be fixed now.