Overlay: Add discarding of base XML locatables for Java

Author: kaspersv

java/ql/lib/semmle/code/java/Overlay.qll

@@ -99,3 +99,23 @@ private predicate discardBaseConfigLocatable(@configLocatable el) {
   // should be discarded.
   baseConfigLocatable(el) and overlayHasConfigLocatables()
 }
+
+overlay[local]
+private predicate baseXmlLocatable(@xmllocatable l) {
+  not isOverlay() and not files(l, _) and not xmlNs(l, _, _, _)
+}
+
+overlay[local]
+private predicate overlayHasXmlLocatable() {
+  isOverlay() and
+  exists(@xmllocatable l | not files(l, _) and not xmlNs(l, _, _, _))
+}
+
+overlay[discard_entity]
+private predicate discardBaseXmlLocatable(@xmllocatable el) {
+  // The XML extractor is currently not incremental, so if
+  // the overlay contains any XML locatables, the overlay should
+  // contain a full extraction and all XML locatables from base
+  // should be discarded.
+  baseXmlLocatable(el) and overlayHasXmlLocatable()
+}