garble build main.go
exec ./main
cmp stderr main.stderr

-- main.go --
package main

import (
	"encoding/json"
	"go/ast"
)

var V interface{}

type T struct {
	ast.Node
	*ast.Ident
}

type EncodingT struct {
	Foo int
}

func main() {
	switch V := V.(type) {
	case int:
		var _ int = V
	case nil:
		println("nil case")
	}

	enc, _ := json.Marshal(EncodingT{Foo: 3})
	println(string(enc))
}
-- main.stderr --
nil case
{"Foo":3}