assign from shift

[mvertes]

The following program sample.go triggers a panic:

package main

type H struct {
    bits uint
}

func main() {
    h := &H{8}
    var x uint = (1 << h.bits) >> 6

    println(x)
}

Expected result:

$ go run ./sample.go
4

Got:

$ yaegi ./sample.go
run: ./sample.go:9:15: CFG post-order panic: reflect: call of reflect.Value.Interface on zero Value
goroutine 1 [running]:
runtime/debug.Stack(0x1, 0xc0002e0600, 0x40)
        /usr/lib/go/src/runtime/debug/stack.go:24 +0x9f
github.com/traefik/yaegi/interp.(*Interpreter).eval.func1(0xc0001e3c70)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:480 +0xc5
panic(0xeab440, 0xc000209020)
        /usr/lib/go/src/runtime/panic.go:969 +0x175
github.com/traefik/yaegi/interp.(*Interpreter).cfg.func2.1(0xc000463b00)
        /home/marc/go/src/github.com/traefik/yaegi/interp/cfg.go:424 +0xb3
panic(0xe01b20, 0xc000208fe0)
        /usr/lib/go/src/runtime/panic.go:969 +0x175
reflect.valueInterface(0x0, 0x0, 0x0, 0x10a1601, 0xdccd60, 0x1)
        /usr/lib/go/src/reflect/value.go:1020 +0x1ad
reflect.Value.Interface(...)
        /usr/lib/go/src/reflect/value.go:1015
github.com/traefik/yaegi/interp.typecheck.shift(0xc000463b00, 0x7fafa5972280, 0x0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/typecheck.go:152 +0x552
github.com/traefik/yaegi/interp.typecheck.binaryExpr(0xc000463b00, 0xc00030a960, 0xef901c)
        /home/marc/go/src/github.com/traefik/yaegi/interp/typecheck.go:223 +0x547
github.com/traefik/yaegi/interp.(*Interpreter).cfg.func2(0xc000463b00)
        /home/marc/go/src/github.com/traefik/yaegi/interp/cfg.go:633 +0x8ffd
github.com/traefik/yaegi/interp.(*node).Walk(0xc000463b00, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:220 +0xa5
github.com/traefik/yaegi/interp.(*node).Walk(0xc000463800, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:217 +0x66
github.com/traefik/yaegi/interp.(*node).Walk(0xc000463700, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:217 +0x66
github.com/traefik/yaegi/interp.(*node).Walk(0xc000463600, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:217 +0x66
github.com/traefik/yaegi/interp.(*node).Walk(0xc000462f00, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:217 +0x66
github.com/traefik/yaegi/interp.(*node).Walk(0xc000462a00, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:217 +0x66
github.com/traefik/yaegi/interp.(*node).Walk(0xc000462000, 0xc0001e3af0, 0xc0001e3ac0)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:217 +0x66
github.com/traefik/yaegi/interp.(*Interpreter).cfg(0xc00035e000, 0xc000462000, 0xc0002178e8, 0x4, 0xc0002178e8, 0x4, 0x0, 0x0, 0xc000462000)
        /home/marc/go/src/github.com/traefik/yaegi/interp/cfg.go:63 +0x20f
github.com/traefik/yaegi/interp.(*Interpreter).eval(0xc00035e000, 0xc0002babd0, 0x87, 0x7ffc443d9498, 0x19, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:507 +0x2f3
github.com/traefik/yaegi/interp.(*Interpreter).EvalPath(0xc00035e000, 0x7ffc443d9498, 0x19, 0xc0002bab00, 0x87, 0x0, 0x0, 0xc000212c30)
        /home/marc/go/src/github.com/traefik/yaegi/interp/interp.go:394 +0xfa
main.runFile(0xc00035e000, 0x7ffc443d9498, 0x19, 0xc000200180, 0x1)
        /home/marc/go/src/github.com/traefik/yaegi/cmd/yaegi/run.go:123 +0xae
main.run(0xc000128030, 0x1, 0x1, 0x13, 0x13)
        /home/marc/go/src/github.com/traefik/yaegi/cmd/yaegi/run.go:89 +0x7e5
main.main()
        /home/marc/go/src/github.com/traefik/yaegi/cmd/yaegi/yaegi.go:144 +0x415