cmd/go2go: compiler error after translation #39692
Description
What version of Go are you using (go version)?
go2go playground
What did you do?
https://go2goplay.golang.org/p/LDEr36y6IUr
Source
package main
type Func(type A, B) interface {
Run(A) B
}
//////
type Pair(type A, B) struct {
L A
R B
}
//////
type Compose(type A, B, C) struct {
L Func(A, B)
R Func(B, C)
}
func (p Compose(A, B, C)) Run(in A) C {
return p.R.Run(p.L.Run(in))
}
//////
type Dup(type A) struct{}
func (d Dup(A)) Run(in A) Pair(A, A) {
return Pair(A, A){
L: in,
R: in,
}
}
//////
func main() {
_ = Compose(
int,
Pair(int, int),
Pair(Pair(int, int), Pair(int, int)),
){
L: Dup(int){},
R: Dup(Pair(int, int)){},
}
}
What did you expect to see?
No compiler error and no output
What did you see instead?
A large error message
# play
./prog.go2:45: cannot use instantiate୦୦Dup୦main୮aPair୮8int୮3୮0int୮9 literal (type instantiate୦୦Dup୦main୮aPair୮8int୮3୮0int୮9) as type instantiate୦୦Func୦main୮aPair୮8int୮3୮0int୮9୦main୮aPair୮8main୮aPair୮8int୮3୮0int୮9୮3୮0main୮aPair୮8int୮3୮0int୮9୮9 in field value:
instantiate୦୦Dup୦main୮aPair୮8int୮3୮0int୮9 does not implement instantiate୦୦Func୦main୮aPair୮8int୮3୮0int୮9୦main୮aPair୮8main୮aPair୮8int୮3୮0int୮9୮3୮0main୮aPair୮8int୮3୮0int୮9୮9 (wrong type for Run method)
have Run(instantiate୦୦Pair୦int୦int) instantiate୦୦Pair୦main୮aPair୮8int୮3୮0int୮9୦main୮aPair୮8int୮3୮0int୮9
want Run(instantiate୦୦Pair୦int୦int) instantiate୦୦Pair୦struct୮4L୮0int୮2୮0R୮0int୮5୦struct୮4L୮0int୮2୮0R୮0int୮5
This seemed more important because it happens after translation, which possibly indicates a soundness hole in the type checker? Though, I do believe the program is well typed, so maybe just a bug in the translation.