Add a SpacetimeDBException to C# SDK to aid in debugging (#3386)

# Description of Changes

This implements a fix to an issue with debugging using the C# SDK, by
adding new exception types:
* `SpacetimeDBException`, 
* `SpacetimeDBArgumentException`,
* `SpacetimeDBEmptyReducerNameException`

Additional, regenerating bindings will now allow clients to report an
`SpacetimeDBEmptyReducerNameException` rather than an
`ArgumentOutOfRangeException` when the client receives an empty reducer
name from the server.

An example of the generated code currently, that results in the
exception:
https://github.com/clockworklabs/SpacetimeDB/blob/544e2edc2d1f7d1dd118832a815b6dbd7a6c1d82/sdks/csharp/examples~/quickstart-chat/client/module_bindings/SpacetimeDBClient.g.cs#L475

Note: Normally this is not an issue for a client, because the
`SpacetimeDBEmptyReducerNameException` would be caught by the
[Try/Catch](https://github.com/clockworklabs/SpacetimeDB/blob/9f59118e24449cdd2d3e182bd44fdb26078e921b/sdks/csharp/src/SpacetimeDBClient.cs#L421C25-L421C42)
statement, but a debugger will still catch the exception and halt
operation. This can be annoying to a developer when debugging.

By separating out the exception into a custom `Exception` type, we allow
a developer to flag the new exception type as something it can ignore,
without ignoring other relevant exceptions.

# API and ABI breaking changes

Not a breaking change.
Clients will need to regenerate bindings to get the new exceptions

# Expected complexity level and risk

1

# Testing

- [X] Tested regenerating bindings and confirmed intended output.
- [X] Tested debugging and receiving
`SpacetimeDBEmptyReducerNameException` when expected.

---------

Co-authored-by: Zeke Foppa <bfops@users.noreply.github.com>

Author: rekhoff

crates/codegen/src/csharp.rs

@@ -789,6 +789,10 @@ impl Lang for Csharp<'_> {
                             "\"{reducer_str_name}\" => BSATNHelpers.Decode<Reducer.{reducer_name}>(encodedArgs),"
                         );
                     }
+                    writeln!(
+                        output,
+                        r#""" => throw new SpacetimeDBEmptyReducerNameException("Reducer name is empty"),"#
+                    );
                     writeln!(
                         output,
                         r#"var reducer => throw new ArgumentOutOfRangeException("Reducer", $"Unknown reducer {{reducer}}")"#

crates/codegen/tests/snapshots/codegen__codegen_csharp.snap

@@ -1,5 +1,6 @@
 ---
 source: crates/codegen/tests/codegen.rs
+assertion_line: 37
 expression: outfiles
 ---
 "Reducers/Add.g.cs" = '''
@@ -1463,6 +1464,7 @@ namespace SpacetimeDB
                 "say_hello" => BSATNHelpers.Decode<Reducer.SayHello>(encodedArgs),
                 "test" => BSATNHelpers.Decode<Reducer.Test>(encodedArgs),
                 "test_btree_index_args" => BSATNHelpers.Decode<Reducer.TestBtreeIndexArgs>(encodedArgs),
+                "" => throw new SpacetimeDBEmptyReducerNameException("Reducer name is empty"),
                 var reducer => throw new ArgumentOutOfRangeException("Reducer", $"Unknown reducer {reducer}")
             };
         }

demo/Blackholio/client-unity/Assets/Scripts/autogen/SpacetimeDBClient.g.cs

@@ -8,7 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="SpacetimeDB.ClientSDK" Version="1.5.0" />
+    <ProjectReference Include="../../../../SpacetimeDB.ClientSDK.csproj" />
   </ItemGroup>
 
 </Project>

sdks/csharp/examples~/quickstart-chat/client/module_bindings/SpacetimeDBClient.g.cs

@@ -0,0 +1,138 @@
+using System;
+using System.Runtime.Serialization;
+
+namespace SpacetimeDB
+{
+    /// <summary>
+    /// The base class for all SpacetimeDB SDK exceptions.
+    /// This allows users to catch all SpacetimeDB-specific exceptions in one catch block
+    /// or configure their debugger to ignore them.
+    /// </summary>
+    [Serializable]
+    public class SpacetimeDBException : Exception
+    {
+        // Base HRESULT for SpacetimeDB exceptions (0x8A000000 is in the user-defined range)
+        private const int SPACETIMEDB_HRESULT_BASE = unchecked((int)0x8A000000);
+
+        // Specific HRESULTs for different exception types
+        public const int SPACETIMEDB_EMPTY_REDUCER_NAME = SPACETIMEDB_HRESULT_BASE + 1;
+
+        public SpacetimeDBException()
+            : base()
+        {
+            HResult = SPACETIMEDB_HRESULT_BASE;
+        }
+
+        public SpacetimeDBException(string? message)
+            : base(message)
+        {
+            HResult = SPACETIMEDB_HRESULT_BASE;
+        }
+
+        public SpacetimeDBException(string? message, Exception? innerException)
+            : base(message, innerException)
+        {
+            HResult = SPACETIMEDB_HRESULT_BASE;
+        }
+
+        protected SpacetimeDBException(SerializationInfo info, StreamingContext context)
+            : base(info, context) { }
+    }
+
+    /// <summary>
+    /// The exception that is thrown when one of the arguments provided to a method is not valid.
+    /// This is the base class for all SpacetimeDB argument exceptions.
+    /// </summary>
+    [Serializable]
+    public class SpacetimeDBArgumentException : SpacetimeDBException
+    {
+        private readonly string? _paramName;
+
+        public SpacetimeDBArgumentException()
+            : base("Value does not fall within the expected range.") { }
+
+        public SpacetimeDBArgumentException(string? message)
+            : base(message) { }
+
+        public SpacetimeDBArgumentException(string? message, Exception? innerException)
+            : base(message, innerException) { }
+
+        public SpacetimeDBArgumentException(
+            string? message,
+            string? paramName,
+            Exception? innerException
+        )
+            : base(message, innerException)
+        {
+            _paramName = paramName;
+        }
+
+        public SpacetimeDBArgumentException(string? message, string? paramName)
+            : base(message)
+        {
+            _paramName = paramName;
+        }
+
+        protected SpacetimeDBArgumentException(SerializationInfo info, StreamingContext context)
+            : base(info, context)
+        {
+            _paramName = info.GetString("ParamName");
+        }
+
+        public override void GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            base.GetObjectData(info, context);
+            info.AddValue("ParamName", _paramName, typeof(string));
+        }
+
+        public virtual string? ParamName => _paramName;
+    }
+
+    /// <summary>
+    /// The exception that is thrown when an empty reducer name is received from the server.
+    /// This is a known condition that is handled internally by the SpacetimeDB client.
+    /// </summary>
+    [Serializable]
+    public class SpacetimeDBEmptyReducerNameException : SpacetimeDBArgumentException
+    {
+        public SpacetimeDBEmptyReducerNameException()
+            : base("Empty reducer name received from server", (string?)null)
+        {
+            HResult = SPACETIMEDB_EMPTY_REDUCER_NAME;
+        }
+
+        public SpacetimeDBEmptyReducerNameException(string? paramName)
+            : base("Empty reducer name received from server", paramName)
+        {
+            HResult = SPACETIMEDB_EMPTY_REDUCER_NAME;
+        }
+
+        public SpacetimeDBEmptyReducerNameException(string? message, string? paramName)
+            : base(message, paramName)
+        {
+            HResult = SPACETIMEDB_EMPTY_REDUCER_NAME;
+        }
+
+        public SpacetimeDBEmptyReducerNameException(string? message, Exception? innerException)
+            : base(message, null, innerException)
+        {
+            HResult = SPACETIMEDB_EMPTY_REDUCER_NAME;
+        }
+
+        public SpacetimeDBEmptyReducerNameException(
+            string? message,
+            string? paramName,
+            Exception? innerException
+        )
+            : base(message, paramName, innerException)
+        {
+            HResult = SPACETIMEDB_EMPTY_REDUCER_NAME;
+        }
+
+        protected SpacetimeDBEmptyReducerNameException(
+            SerializationInfo info,
+            StreamingContext context
+        )
+            : base(info, context) { }
+    }
+}