remove FP from js/regexpinjection where no regexp was constructed

javascript/ql/src/semmle/javascript/Regexp.qll

@@ -810,7 +810,8 @@ predicate isInterpretedAsRegExp(DataFlow::Node source) {
     // The argument of a call that coerces the argument to a regular expression.
     exists(MethodCallExpr mce, string methodName |
       mce.getReceiver().analyze().getAType() = TTString() and
-      mce.getMethodName() = methodName
+      mce.getMethodName() = methodName and
+      not exists(DataFlow::FunctionNode func | func = DataFlow::valueNode(mce.getCallee()).getAFunctionValue() | not func.getFunction().inExternsFile())
     |
       methodName = "match" and source.asExpr() = mce.getArgument(0) and mce.getNumArgument() = 1
       or

javascript/ql/test/query-tests/Security/CWE-730/RegExpInjection.js

@@ -50,4 +50,13 @@ app.get('/findKey', function(req, res) {
   URI(`${protocol}://${host}${path}`).search(input); // OK, but still flagged
   URI(`${protocol}://${host}${path}`).search(input).href(); // OK
   unknown.search(input).unknown; // OK
+
+});
+
+import * as Search from './search';
+
+app.get('/findKey', function(req, res) {
+  var key = req.param("key"), input = req.param("input");
+
+  Search.search(input); // OK!
 });

javascript/ql/test/query-tests/Security/CWE-730/search.js

@@ -0,0 +1,6 @@
+module.someOtherExport = true;
+
+
+export function search(query) {
+	// Do nothing!
+}