C#: Guard against AssociatedSymbol not being an IEventSymbol

Apply same logic as for property/indexer accessors to account for cases where
the associated event cannot be determined. I have not been able to reproduce
such cases locally, though we have seen reports of it happening.

Author: hvitved

csharp/extractor/Semmle.Extraction.CSharp/Entities/Accessor.cs

@@ -6,11 +6,15 @@ namespace Semmle.Extraction.CSharp.Entities
 {
     internal class Accessor : Method
     {
-        protected Accessor(Context cx, IMethodSymbol init)
-            : base(cx, init) { }
+        private readonly IPropertySymbol property;
+        protected Accessor(Context cx, IMethodSymbol init, IPropertySymbol property)
+            : base(cx, init)
+        {
+            this.property = property;
+        }
 
         /// <summary>
-        /// Gets the property symbol associated accessor `symbol`, or `null`
+        /// Gets the property symbol associated with accessor `symbol`, or `null`
         /// if there is no associated symbol.
         /// </summary>
         public static IPropertySymbol? GetPropertySymbol(IMethodSymbol symbol)
@@ -26,39 +30,26 @@ protected Accessor(Context cx, IMethodSymbol init)
             return props.SingleOrDefault();
         }
 
-        /// <summary>
-        /// Gets the property symbol associated with this accessor.
-        /// </summary>
-        private IPropertySymbol? PropertySymbol => GetPropertySymbol(Symbol);
-
-        public new Accessor OriginalDefinition => Create(Context, Symbol.OriginalDefinition);
-
         public override void Populate(TextWriter trapFile)
         {
             PopulateMethod(trapFile);
             PopulateModifiers(trapFile);
             ContainingType!.PopulateGenerics();
 
-            var prop = PropertySymbol;
-            if (prop is null)
-            {
-                var type = Symbol.AssociatedSymbol?.GetType().ToString() ?? "null";
-                Context.ModelError(Symbol, $"Unhandled accessor associated symbol of type {type}");
-                return;
-            }
-
-            var parent = Property.Create(Context, prop);
+            var parent = Property.Create(Context, property);
             int kind;
             Accessor unboundAccessor;
-            if (SymbolEqualityComparer.Default.Equals(Symbol, prop.GetMethod))
+            if (SymbolEqualityComparer.Default.Equals(Symbol, property.GetMethod))
             {
                 kind = 1;
-                unboundAccessor = Create(Context, prop.OriginalDefinition.GetMethod!);
+                var orig = property.OriginalDefinition;
+                unboundAccessor = Create(Context, orig.GetMethod!, orig);
             }
-            else if (SymbolEqualityComparer.Default.Equals(Symbol, prop.SetMethod))
+            else if (SymbolEqualityComparer.Default.Equals(Symbol, property.SetMethod))
             {
                 kind = 2;
-                unboundAccessor = Create(Context, prop.OriginalDefinition.SetMethod!);
+                var orig = property.OriginalDefinition;
+                unboundAccessor = Create(Context, orig.SetMethod!, orig);
             }
             else
             {
@@ -84,14 +75,14 @@ public override void Populate(TextWriter trapFile)
             }
         }
 
-        public static new Accessor Create(Context cx, IMethodSymbol symbol) =>
-            AccessorFactory.Instance.CreateEntityFromSymbol(cx, symbol);
+        public static Accessor Create(Context cx, IMethodSymbol symbol, IPropertySymbol prop) =>
+            AccessorFactory.Instance.CreateEntity(cx, symbol, (symbol, prop));
 
-        private class AccessorFactory : CachedEntityFactory<IMethodSymbol, Accessor>
+        private class AccessorFactory : CachedEntityFactory<(IMethodSymbol, IPropertySymbol), Accessor>
         {
             public static AccessorFactory Instance { get; } = new AccessorFactory();
 
-            public override Accessor Create(Context cx, IMethodSymbol init) => new Accessor(cx, init);
+            public override Accessor Create(Context cx, (IMethodSymbol, IPropertySymbol) init) => new(cx, init.Item1, init.Item2);
         }
     }
 }

csharp/extractor/Semmle.Extraction.CSharp/Entities/EventAccessor.cs

@@ -3,45 +3,46 @@
 
 namespace Semmle.Extraction.CSharp.Entities
 {
-    internal class EventAccessor : Accessor
+    internal class EventAccessor : Method
     {
-        private EventAccessor(Context cx, IMethodSymbol init)
-            : base(cx, init) { }
+        private readonly IEventSymbol @event;
+
+        private EventAccessor(Context cx, IMethodSymbol init, IEventSymbol @event)
+            : base(cx, init)
+        {
+            this.@event = @event;
+        }
 
         /// <summary>
-        /// Gets the event symbol associated with this accessor.
+        /// Gets the event symbol associated with accessor `symbol`, or `null`
+        /// if there is no associated symbol.
         /// </summary>
-        private IEventSymbol? EventSymbol => Symbol.AssociatedSymbol as IEventSymbol;
+        public static IEventSymbol? GetEventSymbol(IMethodSymbol symbol) =>
+            symbol.AssociatedSymbol as IEventSymbol;
 
         public override void Populate(TextWriter trapFile)
         {
             PopulateMethod(trapFile);
             ContainingType!.PopulateGenerics();
 
-            var @event = EventSymbol;
-            if (@event is null)
-            {
-                var type = Symbol.AssociatedSymbol?.GetType().ToString() ?? "null";
-                Context.ModelError(Symbol, $"Unhandled event accessor associated symbol of type {type}");
-                return;
-            }
-
             var parent = Event.Create(Context, @event);
             int kind;
             EventAccessor unboundAccessor;
             if (SymbolEqualityComparer.Default.Equals(Symbol, @event.AddMethod))
             {
                 kind = 1;
-                unboundAccessor = Create(Context, @event.OriginalDefinition.AddMethod!);
+                var orig = @event.OriginalDefinition;
+                unboundAccessor = Create(Context, orig.AddMethod!, orig);
             }
             else if (SymbolEqualityComparer.Default.Equals(Symbol, @event.RemoveMethod))
             {
                 kind = 2;
-                unboundAccessor = Create(Context, @event.OriginalDefinition.RemoveMethod!);
+                var orig = @event.OriginalDefinition;
+                unboundAccessor = Create(Context, orig.RemoveMethod!, orig);
             }
             else
             {
-                Context.ModelError(Symbol, "Undhandled event accessor kind");
+                Context.ModelError(Symbol, $"Undhandled event accessor kind {Symbol.ToDisplayString()}");
                 return;
             }
 
@@ -53,14 +54,14 @@ public override void Populate(TextWriter trapFile)
             Overrides(trapFile);
         }
 
-        public static new EventAccessor Create(Context cx, IMethodSymbol symbol) =>
-            EventAccessorFactory.Instance.CreateEntityFromSymbol(cx, symbol);
+        public static EventAccessor Create(Context cx, IMethodSymbol symbol, IEventSymbol @event) =>
+            EventAccessorFactory.Instance.CreateEntity(cx, symbol, (symbol, @event));
 
-        private class EventAccessorFactory : CachedEntityFactory<IMethodSymbol, EventAccessor>
+        private class EventAccessorFactory : CachedEntityFactory<(IMethodSymbol, IEventSymbol), EventAccessor>
         {
             public static EventAccessorFactory Instance { get; } = new EventAccessorFactory();
 
-            public override EventAccessor Create(Context cx, IMethodSymbol init) => new EventAccessor(cx, init);
+            public override EventAccessor Create(Context cx, (IMethodSymbol, IEventSymbol) init) => new EventAccessor(cx, init.Item1, init.Item2);
         }
     }
 }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs

@@ -262,10 +262,10 @@ public static void AddExplicitInterfaceQualifierToId(Context cx, EscapingTextWri
                     return Destructor.Create(cx, methodDecl);
                 case MethodKind.PropertyGet:
                 case MethodKind.PropertySet:
-                    return Accessor.GetPropertySymbol(methodDecl) is null ? OrdinaryMethod.Create(cx, methodDecl) : (Method)Accessor.Create(cx, methodDecl);
+                    return Accessor.GetPropertySymbol(methodDecl) is IPropertySymbol prop ? Accessor.Create(cx, methodDecl, prop) : OrdinaryMethod.Create(cx, methodDecl);
                 case MethodKind.EventAdd:
                 case MethodKind.EventRemove:
-                    return EventAccessor.Create(cx, methodDecl);
+                    return EventAccessor.GetEventSymbol(methodDecl) is IEventSymbol @event ? EventAccessor.Create(cx, methodDecl, @event) : OrdinaryMethod.Create(cx, methodDecl);
                 case MethodKind.UserDefinedOperator:
                 case MethodKind.BuiltinOperator:
                     return UserOperator.Create(cx, methodDecl);