Cannot redefine existing variables inside an if statement when ":=" is required

[MarkGaskinRR]

What version of Go are you using (go version)?

Reproducible in go.dev/play with Go 1.19

$ go version
1.19

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

Just using go.dev/play here

What did you do?

https://go.dev/play/p/VF4NlYvP7ce

func generateNumberAndError() (int, error) {
	return 1, errors.New("Test")
}

func main() {
	var err error
	if true {
		i, err := generateNumberAndError()
		fmt.Println(i)
		fmt.Println(err)
	}

	fmt.Println(err) // Expecting "Test", but receiving nil
}

What did you expect to see?

"Test"

What did you see instead?

nil

Workarounds

func generateNumberAndError() (int, error) {
	return 1, errors.New("Test")
}

func main() {
	var err error
	var i int
	if true {
		i, err = generateNumberAndError()
		fmt.Println(i)
		fmt.Println(err)
	}

	fmt.Println(err) // Works
}

But this is not feasible for situations where multiple return values are needed. It would unnecessarily bloat the code.

[seankhliao]

Working as intended for the spec.

[MarkGaskinRR]

Can you link where in the spec I would find this @seankhliao ?

[randall77]

https://go.dev/ref/spec#Declarations_and_scope and https://go.dev/ref/spec#Short_variable_declarations

[MarkGaskinRR]

Thanks @randall77 and @seankhliao.

I'll just note for me, this is unintuitive behaviour worth reconsidering.

[ianlancetaylor]

@MarkGaskinRR Lots of discussion in #377.

It's unlikely that we can change any of this behavior now.