Few more improvements

crates/bindings-csharp/BSATN.Codegen/Type.cs

@@ -15,10 +15,17 @@ public MemberDeclaration(ISymbol member, ITypeSymbol type, DiagReporter diag)
         {
             TypeInfo = GetTypeInfo(type);
         }
+        catch (UnresolvedTypeException)
+        {
+            // If it's an unresolved type, this error will have been already highlighted by .NET itself, no need to add noise.
+            // Just add some dummy type to avoid further errors.
+            // Note that we just use `object` here because emitting the unresolved type's name again would produce more of said noise.
+            TypeInfo = "SpacetimeDB.BSATN.Unsupported<object>";
+        }
         catch (Exception e)
         {
             diag.Report(ErrorDescriptor.UnsupportedType, (member, type, e));
-            // dummy type; can't instantiate an interface, but at least it will produce fewer noisy errors
+            // dummy BSATN implementation to produce fewer noisy errors
             TypeInfo = $"SpacetimeDB.BSATN.Unsupported<{Type}>";
         }
     }

crates/bindings-csharp/BSATN.Codegen/Utils.cs

@@ -72,6 +72,9 @@ IncrementalGeneratorInitializationContext context
 
     public static string MakeRwTypeParam(string typeParam) => typeParam + "RW";
 
+    public class UnresolvedTypeException(INamedTypeSymbol type)
+        : InvalidOperationException($"Could not resolve type {type}") { }
+
     public static string GetTypeInfo(ITypeSymbol type)
     {
         // We need to distinguish handle nullable reference types specially:
@@ -120,7 +123,7 @@ static string GetTypeInfoForNamedType(INamedTypeSymbol type)
         {
             if (type.TypeKind == Microsoft.CodeAnalysis.TypeKind.Error)
             {
-                throw new InvalidOperationException($"Could not resolve type {type}");
+                throw new UnresolvedTypeException(type);
             }
             if (type.TypeKind == Microsoft.CodeAnalysis.TypeKind.Enum)
             {

crates/bindings-csharp/Codegen.Tests/fixtures/diag/snapshots/ExtraCompilationErrors.verified.txt

@@ -44,28 +44,5 @@
         NotConfigurable
       ]
     }
-  },
-  {/*
-internal static readonly SpacetimeDB.BSATN.Unsupported<System.Exception> UnsupportedSystemType = new();
-internal static readonly SpacetimeDB.BSATN.Unsupported<UnresolvedType> UnresolvedType = new();
-                                                       ^^^^^^^^^^^^^^
-internal static readonly SpacetimeDB.BSATN.Unsupported<LocalEnum> UnsupportedEnum = new();
-*/
-    Message: The type or namespace name 'UnresolvedType' could not be found (are you missing a using directive or an assembly reference?),
-    Severity: Error,
-    Descriptor: {
-      Id: CS0246,
-      Title: ,
-      HelpLink: https://msdn.microsoft.com/query/roslyn.query?appId=roslyn&k=k(CS0246),
-      MessageFormat: The type or namespace name '{0}' could not be found (are you missing a using directive or an assembly reference?),
-      Category: Compiler,
-      DefaultSeverity: Error,
-      IsEnabledByDefault: true,
-      CustomTags: [
-        Compiler,
-        Telemetry,
-        NotConfigurable
-      ]
-    }
   }
 ]

crates/bindings-csharp/Codegen.Tests/fixtures/diag/snapshots/Type.verified.txt

@@ -86,23 +86,6 @@
       }
     },
     {/*
-    public Exception UnsupportedSystemType;
-    public UnresolvedType UnresolvedType;
-                          ^^^^^^^^^^^^^^
-    public LocalEnum UnsupportedEnum;
-*/
-      Message: BSATN implementation for UnresolvedType is not found: Could not resolve type UnresolvedType,
-      Severity: Error,
-      Descriptor: {
-        Id: BSATN0001,
-        Title: Unsupported type,
-        MessageFormat: BSATN implementation for {0} is not found: {1},
-        Category: SpacetimeDB.BSATN,
-        DefaultSeverity: Error,
-        IsEnabledByDefault: true
-      }
-    },
-    {/*
     public UnresolvedType UnresolvedType;
     public LocalEnum UnsupportedEnum;
                      ^^^^^^^^^^^^^^^