[http-client-java] make Accept header with constant @clientDefaultValue required

.chronus/changes/accept-constant-clientdefaultvalue-2026-03-27.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http-client-java"
+---
+
+Emitter support for constant optional Accept header with `@clientDefaultValue`. When an Accept header is optional with a constant type and has `@Legacy.clientDefaultValue`, the emitter now treats it as a required constant, ensuring the value is always sent and hidden from the public API.

packages/http-client-java/emitter/src/code-model-builder.ts

@@ -776,7 +776,7 @@ export class CodeModelBuilder {
         );
         const parentAccessorPublic = Boolean(
           subClient.clientInitialization.initializedBy & InitializedByFlags.Parent ||
-          subClient.clientInitialization.initializedBy === InitializedByFlags.Default,
+            subClient.clientInitialization.initializedBy === InitializedByFlags.Default,
         );
         codeModelClient.addSubClient(codeModelSubclient, buildMethodPublic, parentAccessorPublic);
       }
@@ -1522,12 +1522,22 @@ export class CodeModelBuilder {
       }
 
       const nullable = param.type.kind === "nullable";
+
+      // When Accept header is optional with constant type and has clientDefaultValue,
+      // treat as required constant — always sent, hidden from public API.
+      const isAcceptConstantWithDefault =
+        param.kind === "header" &&
+        param.serializedName.toLowerCase() === "accept" &&
+        param.optional &&
+        sdkType.kind === "constant" &&
+        param.clientDefaultValue !== undefined;
+
       const parameter = new Parameter(parameterName, param.doc ?? "", schema, {
         summary: param.summary,
         implementation: parameterOnClient
           ? ImplementationLocation.Client
           : ImplementationLocation.Method,
-        required: !param.optional,
+        required: isAcceptConstantWithDefault || !param.optional,
         nullable: nullable,
         protocol: {
           http: new HttpParameter(param.kind, {

packages/http-client-java/emitter/src/common/schemas/choice.ts

@@ -12,7 +12,8 @@ import { SchemaUsage } from "./usage.js";
 
 /** a schema that represents a choice of several values (ie, an 'enum') */
 export interface ChoiceSchema<ChoiceType extends PrimitiveSchema = StringSchema>
-  extends ValueSchema, SchemaUsage {
+  extends ValueSchema,
+    SchemaUsage {
   /** the schema type  */
   type: SchemaType.Choice;
   /** the primitive type for the choices */
@@ -39,7 +40,8 @@ export class ChoiceSchema<ChoiceType extends PrimitiveSchema = StringSchema>
 
 /** a schema that represents a choice of several values (ie, an 'enum') */
 export interface SealedChoiceSchema<ChoiceType extends PrimitiveSchema = StringSchema>
-  extends ValueSchema, SchemaUsage {
+  extends ValueSchema,
+    SchemaUsage {
   /** the schema type  */
   type: SchemaType.SealedChoice;
 

packages/http-client-java/generator/http-client-generator-test/src/main/java/tsptest/specialheaders/ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient.java

@@ -0,0 +1,75 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+// Code generated by Microsoft (R) TypeSpec Code Generator.
+
+package tsptest.specialheaders;
+
+import com.azure.core.annotation.Generated;
+import com.azure.core.annotation.ReturnType;
+import com.azure.core.annotation.ServiceClient;
+import com.azure.core.annotation.ServiceMethod;
+import com.azure.core.exception.ClientAuthenticationException;
+import com.azure.core.exception.HttpResponseException;
+import com.azure.core.exception.ResourceModifiedException;
+import com.azure.core.exception.ResourceNotFoundException;
+import com.azure.core.http.rest.RequestOptions;
+import com.azure.core.http.rest.Response;
+import com.azure.core.util.FluxUtil;
+import reactor.core.publisher.Mono;
+import tsptest.specialheaders.implementation.ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl;
+
+/**
+ * Initializes a new instance of the asynchronous SpecialHeadersClient type.
+ */
+@ServiceClient(builder = SpecialHeadersClientBuilder.class, isAsync = true)
+public final class ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient {
+    @Generated
+    private final ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl serviceClient;
+
+    /**
+     * Initializes an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient class.
+     * 
+     * @param serviceClient the service client implementation.
+     */
+    @Generated
+    ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient(
+        ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl serviceClient) {
+        this.serviceClient = serviceClient;
+    }
+
+    /**
+     * Accept header with constant type and default value should be marked as required, before we support
+     * clientDefaultValue. Issue: https://github.com/microsoft/typespec/issues/10178.
+     * 
+     * @param requestOptions The options to configure the HTTP request before HTTP client sends it.
+     * @throws HttpResponseException thrown if the request is rejected by server.
+     * @throws ClientAuthenticationException thrown if the request is rejected by server on status code 401.
+     * @throws ResourceNotFoundException thrown if the request is rejected by server on status code 404.
+     * @throws ResourceModifiedException thrown if the request is rejected by server on status code 409.
+     * @return the {@link Response} on successful completion of {@link Mono}.
+     */
+    @Generated
+    @ServiceMethod(returns = ReturnType.SINGLE)
+    public Mono<Response<Void>> retrieveWithResponse(RequestOptions requestOptions) {
+        return this.serviceClient.retrieveWithResponseAsync(requestOptions);
+    }
+
+    /**
+     * Accept header with constant type and default value should be marked as required, before we support
+     * clientDefaultValue. Issue: https://github.com/microsoft/typespec/issues/10178.
+     * 
+     * @throws HttpResponseException thrown if the request is rejected by server.
+     * @throws ClientAuthenticationException thrown if the request is rejected by server on status code 401.
+     * @throws ResourceNotFoundException thrown if the request is rejected by server on status code 404.
+     * @throws ResourceModifiedException thrown if the request is rejected by server on status code 409.
+     * @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent.
+     * @return A {@link Mono} that completes when a successful response is received.
+     */
+    @Generated
+    @ServiceMethod(returns = ReturnType.SINGLE)
+    public Mono<Void> retrieve() {
+        // Generated convenience method for retrieveWithResponse
+        RequestOptions requestOptions = new RequestOptions();
+        return retrieveWithResponse(requestOptions).flatMap(FluxUtil::toMono);
+    }
+}

packages/http-client-java/generator/http-client-generator-test/src/main/java/tsptest/specialheaders/ConstantAcceptHeaderWithDefaultValueAsRequiredClient.java

@@ -0,0 +1,72 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+// Code generated by Microsoft (R) TypeSpec Code Generator.
+
+package tsptest.specialheaders;
+
+import com.azure.core.annotation.Generated;
+import com.azure.core.annotation.ReturnType;
+import com.azure.core.annotation.ServiceClient;
+import com.azure.core.annotation.ServiceMethod;
+import com.azure.core.exception.ClientAuthenticationException;
+import com.azure.core.exception.HttpResponseException;
+import com.azure.core.exception.ResourceModifiedException;
+import com.azure.core.exception.ResourceNotFoundException;
+import com.azure.core.http.rest.RequestOptions;
+import com.azure.core.http.rest.Response;
+import tsptest.specialheaders.implementation.ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl;
+
+/**
+ * Initializes a new instance of the synchronous SpecialHeadersClient type.
+ */
+@ServiceClient(builder = SpecialHeadersClientBuilder.class)
+public final class ConstantAcceptHeaderWithDefaultValueAsRequiredClient {
+    @Generated
+    private final ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl serviceClient;
+
+    /**
+     * Initializes an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredClient class.
+     * 
+     * @param serviceClient the service client implementation.
+     */
+    @Generated
+    ConstantAcceptHeaderWithDefaultValueAsRequiredClient(
+        ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl serviceClient) {
+        this.serviceClient = serviceClient;
+    }
+
+    /**
+     * Accept header with constant type and default value should be marked as required, before we support
+     * clientDefaultValue. Issue: https://github.com/microsoft/typespec/issues/10178.
+     * 
+     * @param requestOptions The options to configure the HTTP request before HTTP client sends it.
+     * @throws HttpResponseException thrown if the request is rejected by server.
+     * @throws ClientAuthenticationException thrown if the request is rejected by server on status code 401.
+     * @throws ResourceNotFoundException thrown if the request is rejected by server on status code 404.
+     * @throws ResourceModifiedException thrown if the request is rejected by server on status code 409.
+     * @return the {@link Response}.
+     */
+    @Generated
+    @ServiceMethod(returns = ReturnType.SINGLE)
+    public Response<Void> retrieveWithResponse(RequestOptions requestOptions) {
+        return this.serviceClient.retrieveWithResponse(requestOptions);
+    }
+
+    /**
+     * Accept header with constant type and default value should be marked as required, before we support
+     * clientDefaultValue. Issue: https://github.com/microsoft/typespec/issues/10178.
+     * 
+     * @throws HttpResponseException thrown if the request is rejected by server.
+     * @throws ClientAuthenticationException thrown if the request is rejected by server on status code 401.
+     * @throws ResourceNotFoundException thrown if the request is rejected by server on status code 404.
+     * @throws ResourceModifiedException thrown if the request is rejected by server on status code 409.
+     * @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent.
+     */
+    @Generated
+    @ServiceMethod(returns = ReturnType.SINGLE)
+    public void retrieve() {
+        // Generated convenience method for retrieveWithResponse
+        RequestOptions requestOptions = new RequestOptions();
+        retrieveWithResponse(requestOptions).getValue();
+    }
+}

packages/http-client-java/generator/http-client-generator-test/src/main/java/tsptest/specialheaders/SpecialHeadersClientBuilder.java

@@ -46,10 +46,12 @@
         EtagHeadersClient.class,
         EtagHeadersOptionalBodyClient.class,
         SkipSpecialHeadersClient.class,
+        ConstantAcceptHeaderWithDefaultValueAsRequiredClient.class,
         RepeatabilityHeadersAsyncClient.class,
         EtagHeadersAsyncClient.class,
         EtagHeadersOptionalBodyAsyncClient.class,
-        SkipSpecialHeadersAsyncClient.class })
+        SkipSpecialHeadersAsyncClient.class,
+        ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient.class })
 public final class SpecialHeadersClientBuilder implements HttpTrait<SpecialHeadersClientBuilder>,
     ConfigurationTrait<SpecialHeadersClientBuilder>, EndpointTrait<SpecialHeadersClientBuilder> {
     @Generated
@@ -332,6 +334,18 @@ public SkipSpecialHeadersAsyncClient buildSkipSpecialHeadersAsyncClient() {
         return new SkipSpecialHeadersAsyncClient(buildInnerClient().getSkipSpecialHeaders());
     }
 
+    /**
+     * Builds an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient class.
+     * 
+     * @return an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient.
+     */
+    @Generated
+    public ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient
+        buildConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient() {
+        return new ConstantAcceptHeaderWithDefaultValueAsRequiredAsyncClient(
+            buildInnerClient().getConstantAcceptHeaderWithDefaultValueAsRequireds());
+    }
+
     /**
      * Builds an instance of RepeatabilityHeadersClient class.
      * 
@@ -372,5 +386,17 @@ public SkipSpecialHeadersClient buildSkipSpecialHeadersClient() {
         return new SkipSpecialHeadersClient(buildInnerClient().getSkipSpecialHeaders());
     }
 
+    /**
+     * Builds an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredClient class.
+     * 
+     * @return an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredClient.
+     */
+    @Generated
+    public ConstantAcceptHeaderWithDefaultValueAsRequiredClient
+        buildConstantAcceptHeaderWithDefaultValueAsRequiredClient() {
+        return new ConstantAcceptHeaderWithDefaultValueAsRequiredClient(
+            buildInnerClient().getConstantAcceptHeaderWithDefaultValueAsRequireds());
+    }
+
     private static final ClientLogger LOGGER = new ClientLogger(SpecialHeadersClientBuilder.class);
 }

packages/http-client-java/generator/http-client-generator-test/src/main/java/tsptest/specialheaders/implementation/ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl.java

@@ -0,0 +1,123 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+// Code generated by Microsoft (R) TypeSpec Code Generator.
+
+package tsptest.specialheaders.implementation;
+
+import com.azure.core.annotation.ExpectedResponses;
+import com.azure.core.annotation.Get;
+import com.azure.core.annotation.HeaderParam;
+import com.azure.core.annotation.Host;
+import com.azure.core.annotation.HostParam;
+import com.azure.core.annotation.ReturnType;
+import com.azure.core.annotation.ServiceInterface;
+import com.azure.core.annotation.ServiceMethod;
+import com.azure.core.annotation.UnexpectedResponseExceptionType;
+import com.azure.core.exception.ClientAuthenticationException;
+import com.azure.core.exception.HttpResponseException;
+import com.azure.core.exception.ResourceModifiedException;
+import com.azure.core.exception.ResourceNotFoundException;
+import com.azure.core.http.rest.RequestOptions;
+import com.azure.core.http.rest.Response;
+import com.azure.core.http.rest.RestProxy;
+import com.azure.core.util.Context;
+import com.azure.core.util.FluxUtil;
+import reactor.core.publisher.Mono;
+import tsptest.specialheaders.SpecialHeadersServiceVersion;
+
+/**
+ * An instance of this class provides access to all the operations defined in
+ * ConstantAcceptHeaderWithDefaultValueAsRequireds.
+ */
+public final class ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl {
+    /**
+     * The proxy service used to perform REST calls.
+     */
+    private final ConstantAcceptHeaderWithDefaultValueAsRequiredsService service;
+
+    /**
+     * The service client containing this operation class.
+     */
+    private final SpecialHeadersClientImpl client;
+
+    /**
+     * Initializes an instance of ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl.
+     * 
+     * @param client the instance of the service client containing this operation class.
+     */
+    ConstantAcceptHeaderWithDefaultValueAsRequiredsImpl(SpecialHeadersClientImpl client) {
+        this.service = RestProxy.create(ConstantAcceptHeaderWithDefaultValueAsRequiredsService.class,
+            client.getHttpPipeline(), client.getSerializerAdapter());
+        this.client = client;
+    }
+
+    /**
+     * Gets Service version.
+     * 
+     * @return the serviceVersion value.
+     */
+    public SpecialHeadersServiceVersion getServiceVersion() {
+        return client.getServiceVersion();
+    }
+
+    /**
+     * The interface defining all the services for SpecialHeadersClientConstantAcceptHeaderWithDefaultValueAsRequireds
+     * to be used by the proxy service to perform REST calls.
+     */
+    @Host("{endpoint}")
+    @ServiceInterface(name = "SpecialHeadersClientConstantAcceptHeaderWithDefaultValueAsRequireds")
+    public interface ConstantAcceptHeaderWithDefaultValueAsRequiredsService {
+        @Get("/constant-optional-accept-header-with-default-value")
+        @ExpectedResponses({ 200 })
+        @UnexpectedResponseExceptionType(value = ClientAuthenticationException.class, code = { 401 })
+        @UnexpectedResponseExceptionType(value = ResourceNotFoundException.class, code = { 404 })
+        @UnexpectedResponseExceptionType(value = ResourceModifiedException.class, code = { 409 })
+        @UnexpectedResponseExceptionType(HttpResponseException.class)
+        Mono<Response<Void>> retrieve(@HostParam("endpoint") String endpoint, @HeaderParam("accept") String accept,
+            RequestOptions requestOptions, Context context);
+
+        @Get("/constant-optional-accept-header-with-default-value")
+        @ExpectedResponses({ 200 })
+        @UnexpectedResponseExceptionType(value = ClientAuthenticationException.class, code = { 401 })
+        @UnexpectedResponseExceptionType(value = ResourceNotFoundException.class, code = { 404 })
+        @UnexpectedResponseExceptionType(value = ResourceModifiedException.class, code = { 409 })
+        @UnexpectedResponseExceptionType(HttpResponseException.class)
+        Response<Void> retrieveSync(@HostParam("endpoint") String endpoint, @HeaderParam("accept") String accept,
+            RequestOptions requestOptions, Context context);
+    }
+
+    /**
+     * Accept header with constant type and default value should be marked as required, before we support
+     * clientDefaultValue. Issue: https://github.com/microsoft/typespec/issues/10178.
+     * 
+     * @param requestOptions The options to configure the HTTP request before HTTP client sends it.
+     * @throws HttpResponseException thrown if the request is rejected by server.
+     * @throws ClientAuthenticationException thrown if the request is rejected by server on status code 401.
+     * @throws ResourceNotFoundException thrown if the request is rejected by server on status code 404.
+     * @throws ResourceModifiedException thrown if the request is rejected by server on status code 409.
+     * @return the {@link Response} on successful completion of {@link Mono}.
+     */
+    @ServiceMethod(returns = ReturnType.SINGLE)
+    public Mono<Response<Void>> retrieveWithResponseAsync(RequestOptions requestOptions) {
+        final String accept = "application/json;odata.metadata=minimal";
+        return FluxUtil
+            .withContext(context -> service.retrieve(this.client.getEndpoint(), accept, requestOptions, context));
+    }
+
+    /**
+     * Accept header with constant type and default value should be marked as required, before we support
+     * clientDefaultValue. Issue: https://github.com/microsoft/typespec/issues/10178.
+     * 
+     * @param requestOptions The options to configure the HTTP request before HTTP client sends it.
+     * @throws HttpResponseException thrown if the request is rejected by server.
+     * @throws ClientAuthenticationException thrown if the request is rejected by server on status code 401.
+     * @throws ResourceNotFoundException thrown if the request is rejected by server on status code 404.
+     * @throws ResourceModifiedException thrown if the request is rejected by server on status code 409.
+     * @return the {@link Response}.
+     */
+    @ServiceMethod(returns = ReturnType.SINGLE)
+    public Response<Void> retrieveWithResponse(RequestOptions requestOptions) {
+        final String accept = "application/json;odata.metadata=minimal";
+        return service.retrieveSync(this.client.getEndpoint(), accept, requestOptions, Context.NONE);
+    }
+}