C#: Support generic extensions in non-generic extension types.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/CodeAnalysisExtensions/SymbolExtensions.cs

@@ -653,8 +653,7 @@ public static bool TryGetExtensionMethod(this IMethodSymbol method, out IMethodS
                     .FirstOrDefault(m => SymbolEqualityComparer.Default.Equals(m.AssociatedExtensionImplementation, method.ConstructedFrom));
 
                 var isFullyConstructed = method.IsBoundGenericMethod();
-                // TODO: We also need to handle generic methods in non-generic extension types.
-                if (isFullyConstructed && unboundDeclaration?.ContainingType is INamedTypeSymbol extensionType && extensionType.IsGenericType)
+                if (isFullyConstructed && unboundDeclaration?.ContainingType is INamedTypeSymbol extensionType)
                 {
                     try
                     {
@@ -663,7 +662,9 @@ public static bool TryGetExtensionMethod(this IMethodSymbol method, out IMethodS
                         var (extensionTypeArguments, extensionMethodArguments) = arguments.SplitAt(extensionType.TypeParameters.Length);
 
                         // Construct the extension type.
-                        var boundExtensionType = extensionType.Construct(extensionTypeArguments.ToArray());
+                        var boundExtensionType = extensionType.IsUnboundGenericType()
+                            ? extensionType.Construct(extensionTypeArguments.ToArray())
+                            : extensionType;
 
                         // Find the extension method declaration within the constructed extension type.
                         var extensionDeclaration = boundExtensionType.GetMembers()
@@ -690,10 +691,22 @@ public static bool TryGetExtensionMethod(this IMethodSymbol method, out IMethodS
             return declaration is not null;
         }
 
+        /// <summary>
+        /// Returns true if this method is an unbound generic method.
+        /// </summary>
         public static bool IsUnboundGenericMethod(this IMethodSymbol method) =>
             method.IsGenericMethod && SymbolEqualityComparer.Default.Equals(method.ConstructedFrom, method);
 
-        public static bool IsBoundGenericMethod(this IMethodSymbol method) => method.IsGenericMethod && !IsUnboundGenericMethod(method);
+        /// <summary>
+        /// Returns true if this method is a bound generic method.
+        /// </summary>
+        public static bool IsBoundGenericMethod(this IMethodSymbol method) => method.IsGenericMethod && !method.IsUnboundGenericMethod();
+
+        /// <summary>
+        /// Returns true if this type is an unbound generic type.
+        /// </summary>
+        public static bool IsUnboundGenericType(this INamedTypeSymbol type) =>
+            type.IsGenericType && SymbolEqualityComparer.Default.Equals(type.ConstructedFrom, type);
 
         /// <summary>
         /// Gets the base type of `symbol`. Unlike `symbol.BaseType`, this excludes effective base