Fix effective privateness of explicitly implemented members

Author: tamasvajk

csharp/ql/src/semmle/code/csharp/Member.qll

@@ -102,7 +102,8 @@ class Modifiable extends Declaration, @modifiable {
    */
   predicate isEffectivelyPrivate() {
     this.isPrivate() or
-    this.getDeclaringType+().isPrivate()
+    this.getDeclaringType+().isPrivate() or
+    this.(Virtualizable).getExplicitlyImplementedInterface().isEffectivelyPrivate()
   }
 
   /**
@@ -111,7 +112,8 @@ class Modifiable extends Declaration, @modifiable {
    */
   predicate isEffectivelyInternal() {
     this.isInternal() or
-    this.getDeclaringType+().isInternal()
+    this.getDeclaringType+().isInternal() or
+    this.(Virtualizable).getExplicitlyImplementedInterface().isInternal()
   }
 
   /**
@@ -159,6 +161,11 @@ class Virtualizable extends Member, @virtualizable {
     implementsExplicitInterface()
   }
 
+  override predicate isPrivate() {
+    Member.super.isPrivate() and
+    not implementsExplicitInterface()
+  }
+
   /**
    * Gets any interface this member explicitly implements; this only applies
    * to members that can be declared on an interface, i.e. methods, properties,

csharp/ql/test/library-tests/modifiers/Effectively.expected

@@ -26,3 +26,4 @@
 | Modifiers.cs:63:14:63:15 | M2 | public |
 | Modifiers.cs:68:14:68:15 | M1 | internal |
 | Modifiers.cs:71:18:71:19 | C2 | public |
+| Modifiers.cs:73:17:73:18 | M1 | internal |