cmd/vet: vet should warn on possible mis-shaddows caused by short variable declarations.

[go101]

Many new gophers give up using Go when they ever fall into the famous trap in Go.

func f() int {
	var a = 1
	if a != 0 {
		a, b := 2, 3 // vet should consider here the "a" might be mis-shaddowed.
		if b == 2 {
			return a
		}
	}
	return a
}

Go vet should make a warning for such cases to get better user experience.

[cznic]

This example cannot be vetted.

[go101]

@cznic
why?

[cznic]

Legitimate code.

[go101]

Yes, it is. But legitimate code can't be vetted?

[cznic]

What should vet say about it? 'Warning: legitimate code detected'?

[bontibon]

Many new gophers give up using Go ...

That seems hyperbolic.

[go101]

What should vet say about it? 'Warning: legitimate code detected'?

"possible mis-shaddow of a" is better.

[go101]

That seems hyperbolic.

Not at all. I read many anti-Go articles, this trap is a must-have in them.
And personally, I agree with them on this specific point.
(BTW, I really wanted to give up Go when I first encountered this trap.
It is more a problem than lacking of general generic for me.
Even if I am aware of this trap, I still often fall into it again and again.)

[dominikh]

This is already implemented and guarded by the -shadow flag:

$ go vet -shadow foo.go
foo.go:6: declaration of "a" shadows declaration at foo.go:4
exit status 1

This check cannot be enabled by default because it is noisy and produces false positives – not all shadowing is buggy, and a lot of shadowing is intentional.

[go101]

Great! Glad to know it is supported.