cmd/vet: fix a crash in lostcancel check

Fixes issue 16143

Change-Id: Id9d257aee54d31fbf0d478cb07339729cd9712c0
Reviewed-on: https://go-review.googlesource.com/24325Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/lostcancel.go

@@ -276,7 +276,7 @@ func callName(info *types.Info, call *ast.CallExpr) string {
 			return obj.Name()
 		}
 	case *ast.SelectorExpr:
-		if sel, ok := info.Selections[fun]; ok {
+		if sel, ok := info.Selections[fun]; ok && sel.Kind() == types.MethodVal {
 			// method call, e.g. "(*testing.common).Fatal"
 			meth := sel.Obj()
 			return fmt.Sprintf("(%s).%s",

src/cmd/vet/testdata/lostcancel.go

@@ -135,3 +135,9 @@ func _() {
 
 var condition bool
 var someInt int
+
+// Regression test for Go issue 16143.
+func _() {
+	var x struct{ f func() }
+	x.f()
+}