cmd/vet: internal error: no range for "n"

[dvyukov]

go version devel +ce06f5a222 Tue Jul 31 18:11:29 2018 +0000 linux/amd64
Checkout google/syzkaller@8ef497b

$ pkg/tool/linux_amd64/vet --shadow  $GOPATH/src/github.com/google/syzkaller/pkg/compiler
src/github.com/google/syzkaller/pkg/compiler/check.go:90: internal error: no range for "n"

[ianlancetaylor]

Also happens with 1.10 so not a regression; setting milestone to 1.12.

[ianlancetaylor]

Simpler reproduction case:

package p

func F(x interface{}) int {
	switch v := x.(type) {
	case int, int32:
		if v, ok := x.(int); ok {
			return v
		}
	case int64:
		return int(v)
	}
	return 0
}

[ianlancetaylor]

The error has happened since 1.5, when vet was added to the Go release.

[ianlancetaylor]

I think the bug is that for a variable defined in a type switch statement the go/types package returns it with a nil entry in Defs. In vet that turns into passing nil as the obj argument to growSpan, which seems meaningless. Oddly, though, looking up the identifier in the parent scope returns a non-nil types.Object, an Object that is not found elsewhere in Defs or Uses.

CC @griesemer

[griesemer]

@ianlancetaylor That object is introduced implicitly for each type switch case clause; it is found in the Implicits map.

[gopherbot]

Change https://golang.org/cl/135117 mentions this issue: cmd/vet: avoid internal error for implicitly declared type switch vars

[griesemer]

This was fixed by https://golang.org/cl/135117, but the respective commit message contained a typo in the "Fixes ..." line and thus didn't auto-close this issue. Closing now.