C#: Improve the type ID construction and display name for extension types.

Author: michaelnebel

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

@@ -277,14 +277,18 @@ private static void BuildFunctionPointerTypeId(this IFunctionPointerTypeSymbol f
         public static IEnumerable<IFieldSymbol?> GetTupleElementsMaybeNull(this INamedTypeSymbol type) =>
             type.TupleElements;
 
-        private static string GetExtensionTypeName(this INamedTypeSymbol named, Context cx)
+        private static void BuildExtensionTypeId(this INamedTypeSymbol named, Context cx, EscapingTextWriter trapFile)
         {
-            var type = named.ExtensionParameter?.Type.Name;
-            if (type is null)
+            trapFile.Write("extension(");
+            if (named.ExtensionMarkerName is not null)
             {
-                cx.ModelError(named, "Failed to get extension method type.");
+                trapFile.Write(named.ExtensionMarkerName);
             }
-            return $"extension({type ?? "unknown"})";
+            else
+            {
+                trapFile.Write("unknown");
+            }
+            trapFile.Write(")");
         }
 
         private static void BuildQualifierAndName(INamedTypeSymbol named, Context cx, EscapingTextWriter trapFile, ISymbol symbolBeingDefined)
@@ -307,8 +311,7 @@ private static void BuildQualifierAndName(INamedTypeSymbol named, Context cx, Es
             }
             else if (named.IsExtension)
             {
-                var name = GetExtensionTypeName(named, cx);
-                trapFile.Write(name);
+                named.BuildExtensionTypeId(cx, trapFile);
             }
             else
             {
@@ -489,6 +492,20 @@ public static void BuildFunctionPointerSignature(IFunctionPointerTypeSymbol funp
         private static void BuildFunctionPointerTypeDisplayName(this IFunctionPointerTypeSymbol funptr, Context cx, TextWriter trapFile) =>
             BuildFunctionPointerSignature(funptr, trapFile, s => s.BuildDisplayName(cx, trapFile));
 
+        private static void BuildExtensionTypeDisplayName(this INamedTypeSymbol named, Context cx, TextWriter trapFile)
+        {
+            trapFile.Write("extension(");
+            if (named.ExtensionParameter?.Type is ITypeSymbol type)
+            {
+                type.BuildDisplayName(cx, trapFile);
+            }
+            else
+            {
+                trapFile.Write("unknown");
+            }
+            trapFile.Write(")");
+        }
+
         private static void BuildNamedTypeDisplayName(this INamedTypeSymbol namedType, Context cx, TextWriter trapFile, bool constructUnderlyingTupleType)
         {
             if (!constructUnderlyingTupleType && namedType.IsTupleType)
@@ -510,8 +527,7 @@ private static void BuildNamedTypeDisplayName(this INamedTypeSymbol namedType, C
 
             if (namedType.IsExtension)
             {
-                var name = GetExtensionTypeName(namedType, cx);
-                trapFile.Write(name);
+                namedType.BuildExtensionTypeDisplayName(cx, trapFile);
                 return;
             }