Do not generate the operation registry when there are no operations

codegen-server-test/build.gradle.kts

@@ -33,6 +33,7 @@ dependencies {
 }
 
 val allCodegenTests = listOf(
+    CodegenTest("com.aws.example#EmptyService", "empty"),
     CodegenTest("com.amazonaws.simple#SimpleService", "simple"),
     CodegenTest("aws.protocoltests.restjson#RestJson", "rest_json"),
     CodegenTest("aws.protocoltests.restjson.validation#RestJsonValidation", "rest_json_validation"),

codegen-server-test/model/empty.smithy

@@ -0,0 +1,10 @@
+$version: "1.0"
+
+namespace com.aws.example
+
+use aws.protocols#restJson1
+
+@restJson1
+service EmptyService {
+    version: "2022-05-06",
+}

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerOperationHandlerGenerator.kt

@@ -50,6 +50,8 @@ class ServerOperationHandlerGenerator(
     )
 
     fun render(writer: RustWriter) {
+        check(operations.isNotEmpty())
+
         renderHandlerImplementations(writer, false)
         renderHandlerImplementations(writer, true)
     }

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerOperationRegistryGenerator.kt

@@ -52,6 +52,8 @@ class ServerOperationRegistryGenerator(
     private val operationRegistryBuilderNameWithArguments = "$operationRegistryBuilderName<$genericArguments>"
 
     fun render(writer: RustWriter) {
+        check(operations.isNotEmpty())
+
         renderOperationRegistryStruct(writer)
         renderOperationRegistryBuilderStruct(writer)
         renderOperationRegistryBuilderError(writer)

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerServiceGenerator.kt

@@ -13,6 +13,7 @@ import software.amazon.smithy.rust.codegen.smithy.RustCrate
 import software.amazon.smithy.rust.codegen.smithy.generators.protocol.ProtocolGenerator
 import software.amazon.smithy.rust.codegen.smithy.generators.protocol.ProtocolSupport
 import software.amazon.smithy.rust.codegen.smithy.protocols.HttpBindingResolver
+import java.util.logging.Logger
 
 /**
  * ServerServiceGenerator
@@ -28,6 +29,7 @@ class ServerServiceGenerator(
     private val context: CodegenContext,
 ) {
     private val index = TopDownIndex.of(context.model)
+    private val logger = Logger.getLogger(javaClass.name)
 
     /**
      * Render Service Specific code. Code will end up in different files via [useShapeWriter]. See `SymbolVisitor.kt`
@@ -52,13 +54,17 @@ class ServerServiceGenerator(
                 }
             }
         }
-        rustCrate.withModule(RustModule.public("operation_handler", "Operation handlers definition and implementation.")) { writer ->
-            ServerOperationHandlerGenerator(context, operations)
-                .render(writer)
-        }
-        rustCrate.withModule(RustModule.public("operation_registry", "A registry of your service's operations.")) { writer ->
-            ServerOperationRegistryGenerator(context, httpBindingResolver, operations)
-                .render(writer)
+        if (operations.isNotEmpty()) {
+            rustCrate.withModule(RustModule.public("operation_handler", "Operation handlers definition and implementation.")) { writer ->
+                ServerOperationHandlerGenerator(context, operations)
+                    .render(writer)
+            }
+            rustCrate.withModule(RustModule.public("operation_registry", "A registry of your service's operations.")) { writer ->
+                ServerOperationRegistryGenerator(context, httpBindingResolver, operations)
+                    .render(writer)
+            }
+        } else {
+            logger.warning("[rust-server-codegen] There are no operations in the service closure")
         }
     }
 }