gopherjs: Interface implementation errors are not descriptive.

Running this program on play.golang.org produces:

/tmp/sandbox161431897/main.go:14: cannot convert T literal (type T) to type FooBar:
    T does not implement FooBar (missing Bar method)

It tells us that Bar is the missing method (i.e. what the error actually is).

But running the same program via gopherjs.org/play produces a error that is very hard to understand:

prog.go:14:13: cannot convert (T literal) (value of type T) to FooBar 

I actually have code that uses some very large composite interfaces – and it’s hard to track down exactly what I’ve done wrong (it’s code that cannot be run via the standard Go compiler itself, only by gopherjs).

Any ideas on a potential workaround or improvement to this situation?