JS: Enhance void context propagation

javascript/ql/lib/Expressions/ExprHasNoEffect.qll

@@ -22,6 +22,9 @@ predicate inVoidContext(Expr e) {
     )
   )
   or
+  // propagate void context through parenthesized expressions
+  inVoidContext(e.getParent().(ParExpr))
+  or
   exists(SeqExpr seq, int i, int n |
     e = seq.getOperand(i) and
     n = seq.getNumOperands()

javascript/ql/test/query-tests/Expressions/ExprHasNoEffect/ExprHasNoEffect.expected

@@ -11,4 +11,6 @@
 | tst.js:49:3:49:49 | new Syn ... o me?") | This expression has no effect. |
 | tst.js:50:3:50:36 | new Err ... age(e)) | This expression has no effect. |
 | tst.js:61:2:61:20 | o.trivialNonGetter1 | This expression has no effect. |
+| tst.js:75:3:75:3 | o | This expression has no effect. |
 | tst.js:77:24:77:24 | o | This expression has no effect. |
+| uselessfn.js:1:2:1:26 | functio ... d.");\\n} | This expression has no effect. |

javascript/ql/test/query-tests/Expressions/ExprHasNoEffect/tst.js

@@ -72,7 +72,7 @@ function g() {
 	Object.defineProperty(o, "nonTrivialGetter2", unknownGetterDef());
 	o.nonTrivialGetter2;
 	
-	(o: empty);
+	(o: empty); // $SPURIOUS:Alert
 
 	testSomeCondition() ? o : // $ Alert
 		doSomethingDangerous();

javascript/ql/test/query-tests/Expressions/ExprHasNoEffect/uselessfn.js

@@ -1,3 +1,3 @@
-(function f() { // $MISSING: Alert
+(function f() { // $ Alert
   console.log("I'm never called.");
 })