Kotlin: do not report on unused object extension parameters

Author: tamasvajk

java/ql/lib/semmle/code/java/deadcode/DeadCode.qll

@@ -281,7 +281,12 @@ class RootdefCallable extends Callable {
   Parameter unusedParameter() {
     exists(int i | result = this.getParameter(i) |
       not exists(result.getAnAccess()) and
-      not overrideAccess(this, i)
+      not overrideAccess(this, i) and
+      // Do not report unused parameters on extension parameters that are (companion) objects.
+      not (
+        result.isExtensionParameter() and
+        (result.getType() instanceof CompanionObject or result.getType() instanceof ClassObject)
+      )
     )
   }
 

java/ql/test/kotlin/query-tests/UselessParameter/UselessParameter.expected

@@ -1,4 +1,2 @@
 | Test.kt:11:8:11:18 | a | The parameter 'a' is never used. |
 | Test.kt:19:5:19:5 | <this> | The parameter '<this>' is never used. |
-| Test.kt:20:5:20:15 | <this> | The parameter '<this>' is never used. |
-| Test.kt:21:5:21:5 | <this> | The parameter '<this>' is never used. |