C#: Exclude interfaces and abstract classes from cs/call-to-object-tostring

csharp/ql/src/Useless code/DefaultToString.ql

@@ -54,7 +54,9 @@ predicate alwaysDefaultToString(ValueOrRefType t) {
   not exists(RefType overriding |
     overriding.getAMethod() instanceof ToStringMethod and
     overriding.getABaseType+() = t
-  )
+  ) and
+  not t.isAbstract() and
+  not t instanceof Interface
 }
 
 newtype TDefaultToStringType = TDefaultToStringType0(ValueOrRefType t) { alwaysDefaultToString(t) }

csharp/ql/test/query-tests/Useless Code/DefaultToString/DefaultToString.cs

@@ -29,6 +29,9 @@ class DefaultToString
 
         var sb = new StringBuilder();
         sb.Append(new char[] { 'a', 'b', 'c' }, 0, 3); // GOOD
+
+        IInterface f = null;
+        Console.WriteLine(f);  // GOOD
     }
 
     class A
@@ -48,6 +51,10 @@ class DefaultToString
     {
         override public string ToString() { return "D"; }
     }
+    
+    interface IInterface
+    {
+    }
 }
 
 // semmle-extractor-options: /r:System.Runtime.Extensions.dll