Merge pull request #20873 from github/shared-xml-discard

Share XML discard predicates

javascript/ql/lib/semmle/javascript/internal/Overlay.qll

@@ -1,4 +1,5 @@
 private import javascript
+private import OverlayXml
 
 /** Holds if the database is an overlay. */
 overlay[local]
@@ -12,8 +13,6 @@ private string getFileFromEntity(@locatable node) {
     json_locations(node, loc)
     or
     yaml_locations(node, loc)
-    or
-    xmllocations(node, loc)
   |
     result = getFileFromLocation(loc)
   )

javascript/ql/lib/semmle/javascript/internal/OverlayXml.qll

@@ -0,0 +1,46 @@
+overlay[local]
+module;
+
+/**
+ * A local predicate that always holds for the overlay variant and never holds for the base variant.
+ * This is used to define local predicates that behave differently for the base and overlay variant.
+ */
+private predicate isOverlay() { databaseMetadata("isOverlay", "true") }
+
+private string getXmlFile(@xmllocatable locatable) {
+  exists(@location_default location, @file file | xmllocations(locatable, location) |
+    locations_default(location, file, _, _, _, _) and
+    files(file, result)
+  )
+}
+
+private string getXmlFileInBase(@xmllocatable locatable) {
+  not isOverlay() and
+  result = getXmlFile(locatable)
+}
+
+/**
+ * Holds if the given `file` was extracted as part of the overlay and was extracted by the HTML/XML
+ * extractor.
+ */
+private predicate overlayXmlExtracted(string file) {
+  isOverlay() and
+  exists(@xmllocatable locatable |
+    not files(locatable, _) and not xmlNs(locatable, _, _, _) and file = getXmlFile(locatable)
+  )
+}
+
+/**
+ * Holds if the given XML `locatable` should be discarded, because it is part of the overlay base
+ * and is in a file that was also extracted as part of the overlay database.
+ */
+overlay[discard_entity]
+private predicate discardXmlLocatable(@xmllocatable locatable) {
+  exists(string file | file = getXmlFileInBase(locatable) |
+    overlayChangedFiles(file)
+    or
+    // The HTML/XML extractor is currently not incremental and may extract more files than those
+    // included in overlayChangedFiles.
+    overlayXmlExtracted(file)
+  )
+}