Merge pull request #9876 from smowton/smowton/feature/interface-forwarding

Kotlin: implement default interface forwarding

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

@@ -67,6 +67,8 @@ class Element extends @element, Top {
       i = 9 and result = "Forwarder for a @JvmOverloads-annotated function"
       or
       i = 10 and result = "Forwarder for Kotlin calls that need default arguments filling in"
+      or
+      i = 11 and result = "Forwarder for a Kotlin class inheriting an interface default method"
     )
   }
 }
@@ -77,7 +79,18 @@ class Element extends @element, Top {
 private predicate hasChildElement(Element parent, Element e) {
   cupackage(e, parent)
   or
-  enclInReftype(e, parent)
+  enclInReftype(e, parent) and
+  not e instanceof LocalClassOrInterface
+  or
+  // Reasoning: any specialised instance of a local class is supposed to belong to the general
+  // case of its enclosing method because we don't instantiate specialised variants of either generic
+  // functions or function bodies, and therefore the local class cannot be specialised with respect
+  // to its enclosing reftypes.
+  e.(LocalClassOrInterface)
+      .getSourceDeclaration()
+      .(LocalClassOrInterface)
+      .getLocalTypeDeclStmt()
+      .getEnclosingCallable() = parent
   or
   not enclInReftype(e, _) and
   e.(Class).getCompilationUnit() = parent

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

@@ -471,7 +471,12 @@ class Method extends Callable, @method {
   }
 
   override predicate isAbstract() {
-    Callable.super.isAbstract()
+    // The combination `abstract default` isn't legal in Java,
+    // but it occurs when the Kotlin extractor records a default
+    // body, but the output class file in fact uses an abstract
+    // method and an associated static helper, which we don't
+    // extract as an implementation detail.
+    Callable.super.isAbstract() and not this.isDefault()
     or
     // JLS 9.4: An interface method lacking a `private`, `default`, or `static` modifier
     // is implicitly abstract.