New Go vet rule which detects overwrite of variable from the outer scope.

[guettli]

I wrote that code, and I did not understand why path was empty, although findDev() returns a non-empty path:

func getDeviceFromPath(path string) (*evdev.InputDevice, error) {
	if path == "" {
		path, err := findDev()   // "path" of outer block gets overwritten
		if err != nil {
			return nil, err
		}
		fmt.Printf("Using device %q\n", path)
	}
	sourceDev, err := evdev.Open(path)

I would like to see a warning in vet, when I overwrite a variable from the outer scope.

This is a common mistake for people new to Go, but even people with experience sometimes do that mistake.

@firelizzard18 had some ideas about that new analyzer: golang/vscode-go#3674 (comment)

[zigo101]

related: #377

[seankhliao]

see #22582 and #29260