JS: Model 'merge-descriptors' as a shallow extender and accept test changes.

Author: MathiasVP

javascript/ql/lib/semmle/javascript/Extend.qll

@@ -146,6 +146,19 @@ private class ExtendCallShallow extends ExtendCall {
   override predicate isDeep() { none() }
 }
 
+/** A shallow extend call of form `mergeDescriptors(dst, src)`. */
+private class MergeDescriptorsCall extends ExtendCall {
+  MergeDescriptorsCall() {
+    this = DataFlow::moduleImport("merge-descriptors").getACall()
+  }
+
+  override DataFlow::Node getASourceOperand() { result = this.getArgument(1) }
+
+  override DataFlow::Node getDestinationOperand() { result = this.getArgument(0) }
+
+  override predicate isDeep() { none() }
+}
+
 /**
  * A shallow extend call of form `extend(src1, src2, ...)`.
  */

javascript/ql/test/library-tests/Extend/ExtendCalls.expected

@@ -29,7 +29,7 @@
 | tst.js:64:1:64:48 | checkSh ... arg())) | OK |
 | tst.js:65:1:65:54 | checkSh ... arg())) | OK |
 | tst.js:66:1:66:45 | checkSh ... arg())) | OK |
-| tst.js:67:1:67:57 | checkSh ... arg())) | Not an extend call |
+| tst.js:67:1:67:57 | checkSh ... arg())) | OK |
 | tst.js:68:1:68:52 | checkSh ... arg())) | OK |
 | tst.js:69:1:69:53 | checkSh ... arg())) | OK |
 | tst.js:70:1:70:53 | checkSh ... arg())) | OK |