Include empty statements in allowlist

Author: owen-mc

go/ql/src/RedundantCode/UnreachableStatement.ql

@@ -87,6 +87,8 @@ predicate isAllowedReturnValue(Expr retval) {
  * Matches if `s` is an allowed unreachable statement.
  */
 predicate allowlist(Stmt s) {
+  s instanceof EmptyStmt
+  or
   // `panic("unreachable")` and similar
   exists(CallExpr ce | ce = s.(ExprStmt).getExpr() or ce = s.(ReturnStmt).getExpr() |
     ce.getTarget().mustPanic() or ce.getCalleeName().toLowerCase() = "error"
@@ -100,7 +102,7 @@ predicate allowlist(Stmt s) {
 
 /** Holds if `s` is part of a non-reportable prefix of a run of unreachable statements. */
 predicate isInNonReportableUnreachablePrefix(Stmt s) {
-  (allowlist(s) or s instanceof EmptyStmt) and
+  allowlist(s) and
   (
     firstUnreachableStmt(s)
     or
@@ -111,7 +113,6 @@ predicate isInNonReportableUnreachablePrefix(Stmt s) {
 /** Holds if `s` is the first non-allowlisted statement in a run of unreachable statements. */
 predicate firstNonAllowlistedUnreachableStmt(Stmt s) {
   not isReachable(s) and
-  not s instanceof EmptyStmt and
   not allowlist(s) and
   (
     firstUnreachableStmt(s)