JS: Ignore obvious Array.prototype.concat calls

Author: asgerf

javascript/ql/src/semmle/javascript/StringConcatenation.qll

@@ -55,6 +55,13 @@ module StringConcatenation {
     exists(DataFlow::MethodCallNode call |
       node = call and
       call.getMethodName() = "concat" and
+      not (
+        exists(DataFlow::ArrayCreationNode array |
+          array.flowsTo(call.getAnArgument()) or array.flowsTo(call.getReceiver())
+        )
+        or
+        DataFlow::reflectiveCallNode(_) = call
+      ) and
       (
         n = 0 and
         result = call.getReceiver()

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

@@ -95,3 +95,7 @@ function concatCall() {
   x = x.concat('two', 'three');
   return x;
 }
+
+function arrayConcat(a, b) {
+  return [].concat(a, b);
+}