Handle serialization exceptions in ToDiagnosticString method and add unit test to validate error handling logic

Author: machibuse

Source/Porticle.Grpc.TypeMapper/ClassVisitor.cs

@@ -37,7 +37,8 @@ public class ClassVisitor(TaskLoggingHelper log, bool wrapAllNonNullableStrings,
         var isMessageClass = node.BaseList?.Types.Any(t => t.ToString().Contains("IMessage")) ?? false;
         if (isMessageClass)
         {
-            node = node.AddMembers(MethodFromSource("public string ToDiagnosticString() { return System.Text.Json.JsonSerializer.Serialize(this); }"));
+            node = node.AddMembers(MethodFromSource(
+                "public string ToDiagnosticString() { try { return System.Text.Json.JsonSerializer.Serialize(this); } catch(Exception ex) { return \"Message Invalid - \" + ex.Message; } }"));
         }
 
         return node;

Source/Porticle.Grpc.UnitTests/Tests.cs

@@ -45,6 +45,18 @@ public void TestToString()
         Assert.AreEqual(customDiagnosticMessage.ToString(), customDiagnosticMessage.ToDiagnosticString());
     }
 
+    [TestMethod]
+    public void TestToStringError()
+    {
+        var message = new TestMessageMapped();
+
+        // Should crash when deserializing, because "SingleGuid" backend field ist an empty string and cannot be converted to a Guid
+        var equatable = message.ToString();
+
+        // Expect Exception
+        Assert.AreEqual(equatable.Split('-').First().Trim(), "Message Invalid");
+    }
+
     [TestMethod]
     public void TestWithoutNull()
     {