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cmd/compile: add error if unsigned tested for negativity #22844

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SMerrony opened this issue Nov 22, 2017 · 2 comments
Closed

cmd/compile: add error if unsigned tested for negativity #22844

SMerrony opened this issue Nov 22, 2017 · 2 comments
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@SMerrony
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What version of Go are you using (go version)?

1.9,2

Does this issue reproduce with the latest release?

Yes

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

amd64/windows and also amd64/linux

What did you do?

Compiled this...

import "fmt"
import "time"
func main() {
	var uns uint32
	uns = uint32(time.Now().Weekday())
	if uns < 0 {
		fmt.Printf("Negative uns: %d\n", uns)
	}
}

What did you expect to see?

Error when unsigned is tested for negative.

What did you see instead?

Nothing

I believe it would be very useful if this error could be trapped at compile time.
@ALTree
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ALTree commented Nov 22, 2017 •
edited

This has been proposed (and rejected) in the past.

Ref: #8601.

Initially, the proposal said

the compiler should refuse to compile this statement.

but the commenters agreed that a vet check might be more appropriate (see the discussion on the linked issue for more details).

Someone sent a change to add a vet check, but it wasn't merged. Apparently, it didn't satisfy the 3 vet requirements (correctness, precision, frequency).

Anyway, that was about vet. It seems like everyone agreed not to make this a compile error.

@ianlancetaylor
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Closing as dup.

@golang golang locked and limited conversation to collaborators Nov 22, 2018
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@ianlancetaylor @ALTree @gopherbot @SMerrony