Merge pull request github#10992 from tamasvajk/kotlin-unused-extension

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/Test.kt

@@ -9,3 +9,13 @@ class B : A<B, Int> {
 }
 
 fun fn(a: Int = 10) {}
+
+class C {
+    companion object {}
+}
+
+object O {}
+
+fun C.fn() {}
+fun C.Companion.fn() {}
+fun O.fn() {}

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

@@ -1 +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. |