JS: make LocalObjects::isEscape aware of yield

javascript/ql/src/semmle/javascript/dataflow/LocalObjects.qll

@@ -12,6 +12,8 @@ private predicate isEscape(DataFlow::Node escape, string cause) {
   or
   escape = any(DataFlow::FunctionNode fun).getAReturn() and cause = "return"
   or
+  escape = any(YieldExpr yield).getOperand().flow() and cause = "yield"
+  or
   escape = any(ThrowStmt t).getExpr().flow() and cause = "throw"
   or
   escape = any(GlobalVariable v).getAnAssignedExpr().flow() and cause = "global"

javascript/ql/test/library-tests/LocalObjects/tst.js

@@ -89,3 +89,9 @@
 	let bound = {};
 	bound::unknown();
 });
+
+(async function* f() {
+  yield* {
+    get p() { }
+  };
+});

javascript/ql/test/query-tests/Declarations/UnusedProperty/tst-yield.js

@@ -0,0 +1,5 @@
+async function* f() {
+  yield* {
+    get p() { }
+  };
+}