0 "numeric errors" will be == to any error created with errors.New

[thehowl]

package main

import (
	"errors"
	"strconv"
)

type Error int64

func (e Error) Error() string {
	return "error: " + strconv.Itoa(int(e))
}

var errCmp = errors.New("XXXX")

func main() {
	if Error(0) == errCmp {
		println("what the firetruck?")
	}
}

// Output: what the firetruck?

Discovered while fixing out bugs for #1290.

If the error is Error(1), it works normally.

A workaround is that of making Error a struct [ n int64 }, and its Error method a pointer receiver. Weirdly enough, without the pointer receiver it doesn't work still!

[thehowl]

The root cause is probably different, related to how we pass around errors as values; but I'm leaving that as a // TODO for the undertaker

[ltzmaxwell]

Briefly it's because the incorrect type. the vm erroneously treat Error(0) and errCmp with same type of int64, which is the underlying type of Error, thus the value evaluated as int64 are both 0. that is also why Error(1) works. I opened an issue to discuss this #1424 .