interp: fix type assertion issues

[ssbeatty]

closes #1514

hi!
I had the same problem as #1514 and I wanted to fix it, I found
When asserting *crypto/rsa.PublicKey, using the typ attribute of node to get an nil rtype, resulting in the assertion result being nok

This code contains the same problem

package main

import (
	"log"
	"crypto/rsa"
)

func main() {

    var pKey interface{} = &rsa.PublicKey{}

    if _, ok := pKey.(*rsa.PublicKey); ok {
        log.Println("ok")
    } else {
        log.Println("nok")
    }
}

So I submitted this Pull Request, hope it will be merged

[CLAassistant]

All committers have signed the CLA.

[mvertes]

Nice catch! Thank you for this excellent first submission.

Can you also add your test sample as _test/assert3.go so we have a good non regression test for this ?

I changed it to avoid using log.Println which displays a different date at each run, not suitable for reproduction and added expected output comment so it can be checked by the test suite.

Thanks again

package main

import "crypto/rsa"

func main() {
    var pKey interface{} = &rsa.PublicKey{}

    if _, ok := pKey.(*rsa.PublicKey); ok {
        println("ok")
    } else {
        println("nok")
    }
}

// Output:
// ok

[ssbeatty]

Thank you very much for your reply, I added new test file for this use case