enforce event to topic map if the endpoint specifies

src/AcceptanceTests/When_loading_from_options.cs

@@ -45,7 +45,8 @@ await Scenario.Define<Context>()
                         {
                             QueueNameToSubscriptionNameMap = { { Conventions.EndpointNamingConvention(typeof(Publisher)), TopicName } },
                             PublishedEventToTopicsMap = { { typeof(Event).FullName, TopicName } },
-                            SubscribedEventToTopicsMap = { { typeof(Event).FullName, [TopicName] } }
+                            SubscribedEventToTopicsMap = { { typeof(Event).FullName, [TopicName] } },
+                            ThrowIfUnmappedEventTypes = true
                         }, TopologyOptionsSerializationContext.Default.TopologyOptions);
                         var options = JsonSerializer.Deserialize(serializedOptions, TopologyOptionsSerializationContext.Default.TopologyOptions);
                         transport.Topology = TopicTopology.FromOptions(options);
@@ -72,7 +73,7 @@ await Scenario.Define<Context>()
                             SubscribedEventToRuleNameMap = { { typeof(Event).FullName, typeof(Event).FullName.Shorten() } },
                             TopicToPublishTo = TopicName,
                             TopicToSubscribeOn = TopicName,
-                            EventsToMigrateMap = [typeof(Event).FullName]
+                            EventsToMigrateMap = [typeof(Event).FullName],
                         }, TopologyOptionsSerializationContext.Default.TopologyOptions);
 
                         var options = JsonSerializer.Deserialize(serializedOptions, TopologyOptionsSerializationContext.Default.TopologyOptions);

src/Tests/ApprovalFiles/APIApprovals.Approve.approved.txt

@@ -142,6 +142,7 @@ namespace NServiceBus.Transport.AzureServiceBus
         public System.Collections.Generic.HashSet<string> EventsToMigrateMap { get; init; }
         [NServiceBus.Transport.AzureServiceBus.AzureServiceBusRules]
         public System.Collections.Generic.Dictionary<string, string> SubscribedEventToRuleNameMap { get; init; }
+        public new bool ThrowIfUnmappedEventTypes { get; }
         [NServiceBus.Transport.AzureServiceBus.AzureServiceBusTopics]
         [System.ComponentModel.DataAnnotations.Required]
         public required string? TopicToPublishTo { get; init; }
@@ -185,6 +186,7 @@ namespace NServiceBus.Transport.AzureServiceBus
         [NServiceBus.Transport.AzureServiceBus.AzureServiceBusTopics]
         [System.Text.Json.Serialization.JsonConverter(typeof(NServiceBus.Transport.AzureServiceBus.SubscribedEventToTopicsMapConverter))]
         public System.Collections.Generic.Dictionary<string, System.Collections.Generic.HashSet<string>> SubscribedEventToTopicsMap { get; init; }
+        public bool ThrowIfUnmappedEventTypes { get; set; }
     }
     public sealed class TopologyOptionsDisableValidationValidator : Microsoft.Extensions.Options.IValidateOptions<NServiceBus.Transport.AzureServiceBus.TopologyOptions>
     {
@@ -198,6 +200,7 @@ namespace NServiceBus.Transport.AzureServiceBus
     {
         public TopologyOptionsSerializationContext() { }
         public TopologyOptionsSerializationContext(System.Text.Json.JsonSerializerOptions options) { }
+        public System.Text.Json.Serialization.Metadata.JsonTypeInfo<bool> Boolean { get; }
         public System.Text.Json.Serialization.Metadata.JsonTypeInfo<System.Collections.Generic.Dictionary<string, System.Collections.Generic.HashSet<string>>> DictionaryStringHashSetString { get; }
         public System.Text.Json.Serialization.Metadata.JsonTypeInfo<System.Collections.Generic.Dictionary<string, string>> DictionaryStringString { get; }
         protected override System.Text.Json.JsonSerializerOptions? GeneratedSerializerOptions { get; }

src/Tests/EventRouting/TopicPerEventTopologyTests.cs

@@ -1,5 +1,6 @@
 namespace NServiceBus.Transport.AzureServiceBus.Tests;
 
+using System;
 using System.ComponentModel.DataAnnotations;
 using NUnit.Framework;
 using Particular.Approvals;
@@ -25,6 +26,31 @@ public void PublishDestination_Should_return_mapped_topic_when_event_is_mapped()
         Assert.That(result, Is.EqualTo("MyTopic"));
     }
 
+    [Test]
+    public void PublishDestination_Should_default_topic_to_event_name()
+    {
+        var topologyOptions = new TopologyOptions();
+
+        var topology = TopicTopology.FromOptions(topologyOptions);
+
+        var result = topology.GetPublishDestination(typeof(MyEvent));
+
+        Assert.That(result, Is.EqualTo(typeof(MyEvent).FullName));
+    }
+
+    [Test]
+    public void PublishDestination_Should_throw_when_instructed_to_and_type_unmapped()
+    {
+        var topologyOptions = new TopologyOptions
+        {
+            ThrowIfUnmappedEventTypes = true
+        };
+
+        var topology = TopicTopology.FromOptions(topologyOptions);
+
+        Assert.Throws<Exception>(() => topology.GetPublishDestination(typeof(MyEvent)));
+    }
+
     [Test]
     public void Should_self_validate()
     {

src/Transport/EventRouting/EntityValidator.cs

@@ -19,6 +19,7 @@ static partial class EntityValidator
             : ValidationResult.Success;
     }
 
+    // Enforces naming according to the specification https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-name-rules#microsoftservicebus
     [GeneratedRegex(@"^(?=.{1,260}$)(?=^[A-Za-z0-9])(?!.*[\\?#])(?:[A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9./_-]*[A-Za-z0-9])$")]
     private static partial Regex TopicNameRegex();
 
@@ -34,6 +35,7 @@ static partial class EntityValidator
             : ValidationResult.Success;
     }
 
+    // Enforces naming according to the specification https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-name-rules#microsoftservicebus
     // Note the queue pattern is the same as the topic pattern. Deliberately kept separate for future extensibility.
     [GeneratedRegex(@"^(?=.{1,260}$)(?=^[A-Za-z0-9])(?!.*[\\?#])(?:[A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9./_-]*[A-Za-z0-9])$")]
     private static partial Regex QueueNameRegex();
@@ -50,6 +52,7 @@ static partial class EntityValidator
             : ValidationResult.Success;
     }
 
+    // Enforces naming according to the specification https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-name-rules#microsoftservicebus
     [GeneratedRegex(@"^(?!\$)(?=.{1,50}$)(?=^[A-Za-z0-9])(?!.*[\/\\?#])[A-Za-z0-9](?:[A-Za-z0-9._-]*[A-Za-z0-9])?$")]
     private static partial Regex RuleNameRegex();
 
@@ -66,6 +69,7 @@ static partial class EntityValidator
             : ValidationResult.Success;
     }
 
+    //enforces naming according to the specification https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-name-rules#microsoftservicebus
     // Note the subscription pattern is the same as the rule pattern. Deliberately kept separate for future extensibility.
     [GeneratedRegex(@"^(?!\$)(?=.{1,50}$)(?=^[A-Za-z0-9])(?!.*[\/\\?#])[A-Za-z0-9](?:[A-Za-z0-9._-]*[A-Za-z0-9])?$")]
     private static partial Regex SubscriptionNameRegex();

src/Transport/EventRouting/MigrationTopologyOptions.cs

@@ -3,6 +3,7 @@ namespace NServiceBus.Transport.AzureServiceBus;
 using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.Text.Json.Serialization;
 using Particular.Obsoletes;
 
 /// <summary>
@@ -45,4 +46,9 @@ public Dictionary<string, string> SubscribedEventToRuleNameMap
         get;
         init => field = value ?? [];
     } = [];
+
+    // NOTE: explicitly set to true always and ignored from JSON, since MigrationTopology is already obsolete and we don't want to have a fallback naming strategy
+    /// <inheritdoc cref="TopologyOptions.ThrowIfUnmappedEventTypes" />
+    [JsonIgnore]
+    public new bool ThrowIfUnmappedEventTypes => true;
 }

src/Transport/EventRouting/TopicPerEventTopology.cs

@@ -1,7 +1,6 @@
 namespace NServiceBus.Transport.AzureServiceBus;
 
 using System;
-using System.Collections.Generic;
 
 /// <summary>
 /// A topology that uses separate topic for each event.
@@ -105,7 +104,13 @@ public void OverrideSubscriptionNameFor(string queueName, string subscriptionNam
 
     /// <inheritdoc />
     protected override string GetPublishDestinationCore(string eventTypeFullName)
-        => Options.PublishedEventToTopicsMap.GetValueOrDefault(eventTypeFullName, eventTypeFullName);
+    {
+        if (!Options.PublishedEventToTopicsMap.TryGetValue(eventTypeFullName, out string? topic) && Options.ThrowIfUnmappedEventTypes)
+        {
+            throw new Exception($"Unmapped event type '{eventTypeFullName}'. All events must be mapped in `{nameof(TopologyOptions.PublishedEventToTopicsMap)}` when `{nameof(TopologyOptions.ThrowIfUnmappedEventTypes)}` is set");
+        }
+        return topic ?? eventTypeFullName;
+    }
 
     internal override SubscriptionManager CreateSubscriptionManager(
         SubscriptionManagerCreationOptions creationOptions) =>

src/Transport/EventRouting/TopologyOptions.cs

@@ -43,4 +43,9 @@ public Dictionary<string, string> QueueNameToSubscriptionNameMap
         get;
         init => field = value ?? [];
     } = [];
+
+    /// <summary>
+    /// Determines if an exception should be thrown when attempting to publish an event not mapped in PublishedEventToTopicsMap
+    /// </summary>
+    public bool ThrowIfUnmappedEventTypes { get; set; } = false;
 }