JS: Add: taint step for Map.groupBy function

javascript/ql/lib/semmle/javascript/Collections.qll

@@ -151,4 +151,17 @@ private module CollectionDataFlow {
       )
     }
   }
+
+  /**
+   * A step for a call to `groupBy` on an iterable object.
+   */
+  private class GroupByTaintStep extends TaintTracking::SharedTaintStep {
+    override predicate heapStep(DataFlow::Node pred, DataFlow::Node succ) {
+      exists(DataFlow::MethodCallNode call |
+        call = DataFlow::globalVarRef("Map").getAMemberCall("groupBy") and
+        pred = call.getArgument(0) and
+        succ = call
+      )
+    }
+  }
 }

javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected

@@ -244,6 +244,7 @@ typeInferenceMismatch
 | tst.js:2:13:2:20 | source() | tst.js:66:10:66:16 | xSorted |
 | tst.js:2:13:2:20 | source() | tst.js:68:10:68:23 | x.toReversed() |
 | tst.js:2:13:2:20 | source() | tst.js:70:10:70:18 | xReversed |
+| tst.js:2:13:2:20 | source() | tst.js:72:10:72:31 | Map.gro ... z => z) |
 | xml.js:5:18:5:25 | source() | xml.js:8:14:8:17 | text |
 | xml.js:12:17:12:24 | source() | xml.js:13:14:13:19 | result |
 | xml.js:23:18:23:25 | source() | xml.js:20:14:20:17 | attr |

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

@@ -69,6 +69,6 @@ function test() {
     const xReversed = x.toReversed();
     sink(xReversed) // NOT OK
 
-    sink(Map.groupBy(x, z => z)); // NOT OK -- This should be marked via taint step, but it is not.
+    sink(Map.groupBy(x, z => z)); // NOT OK
     sink(Custom.groupBy(x, z => z)); // OK
 }