spec: prevent variable aliasing in *any* way

[kodawah]

the following code

func OpenLogFile(lo LogOptions) (io.WriteCloser, error) {
    var logw io.WriteCloser
    switch lo.LogPath {
    case "stderr":
        logw = os.Stderr
    default:
        logw, err := openLogFileInternal(lo)
        if err != nil {
            return logw, err
        }
    }
    log.SetOutput(logw)
    return logw, nil
}

will alias the logw variable: since logw is declared outside, and in the default switch case another logw is created with :=, every default case will return a nil. Fun ensues.

Go should either prevent this behaviour with a panic/error/warning or should note that the variable is initialized in an external block and properly initialize it rather than creating a new one.

[adg]

Can't change this now. https://golang.org/doc/go1compat

We will certainly revisit variable declarations and scoping rules in Go 2.

[minux]

Declare err at the outer scope and use = instead of :=.

This proposal is an incompatible language change, so
it's not going to happen, at least not for Go 1.

[dwbuiten]

Declare err at the outer scope and use = instead of :=.

The problem is that it's very easy to typo = and :=.

This proposal is an incompatible language change, so it's not going to happen, at least not for Go 1.

Yep!

[kodawah]

It's fine if this waits until Go 2, just don't forget about it when it is time :)

[minux]

Even for Go 2, I think a better way is to have golint or govet detect such cases rather than make a language change.

[kodawah]

sure, as long as it automated and the developer is notified of this in some way