C#: Operators are now allowed to be declared virtual.

Author: michaelnebel

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

@@ -184,7 +184,7 @@ private class TOverridable = @virtualizable or @callable_accessor;
 
 /**
  * A declaration that can be overridden or implemented. That is, a method,
- * a property, an indexer, an event, or an accessor.
+ * a property, an indexer, an event, an accessor, or an operator.
  *
  * Unlike `Virtualizable`, this class includes accessors.
  */
@@ -360,7 +360,7 @@ class Overridable extends Declaration, TOverridable {
 
 /**
  * A member where the `virtual` modifier is valid. That is, a method,
- * a property, an indexer, or an event.
+ * a property, an indexer, an event or an operator.
  *
  * Equivalently, these are the members that can be defined in an interface.
  *

csharp/ql/lib/semmlecode.csharp.dbscheme

@@ -670,7 +670,7 @@ compiler_generated(unique int id: @modifiable ref);
 
 @named_exprorstmt = @goto_stmt | @labeled_stmt | @expr;
 
-@virtualizable = @method | @property | @indexer | @event;
+@virtualizable = @method | @property | @indexer | @event | @operator;
 
 exprorstmt_name(
   unique int parent_id: @named_exprorstmt ref,