[tcgc] one client multiple services

.chronus/changes/tcgc-multiServiceOneClient-2025-9-30-17-39-36.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+Add support to define one client from multiple services. Api versions for services will rest on the subclient

packages/typespec-client-generator-core/lib/decorators.tsp

@@ -126,6 +126,11 @@ model ClientOptions {
    * The name of the client. If not specified, the default name will be `<Name of the target>Client`.
    */
   name?: string;
+
+  /**
+   * The parent client of this client. If specified, this client will be generated as a sub client of the parent client.
+   */
+  parent?: Namespace | Interface;
 }
 
 /**

packages/typespec-client-generator-core/src/cache.ts

@@ -111,6 +111,22 @@ export function prepareClientAndOperationCache(context: TCGCContext): void {
       // operations directly under the group
       const operations = [...group.type.operations.values()];
 
+      // For interfaces that extend other interfaces, also collect operations from the source interfaces
+      // TypeSpec doesn't always automatically copy operations from extended interfaces,
+      // especially in versioning scenarios, so we need to manually collect them
+      if (group.type.kind === "Interface" && group.type.sourceInterfaces.length > 0) {
+        const operationsByName = new Map(operations.map((op) => [op.name, op]));
+        for (const sourceIface of group.type.sourceInterfaces) {
+          for (const [name, op] of sourceIface.operations) {
+            // Only add if not already present (prefer operations from derived interface)
+            if (!operationsByName.has(name)) {
+              operations.push(op);
+              operationsByName.set(name, op);
+            }
+          }
+        }
+      }
+
       // when there is explicitly `@operationGroup` or `@client`
       // operations under namespace or interface that are not decorated with `@operationGroup` or `@client`
       // should be placed in the first accessor client or operation group

packages/typespec-client-generator-core/src/clients.ts

@@ -1,6 +1,13 @@
-import { createDiagnosticCollector, Diagnostic, getDoc, getSummary } from "@typespec/compiler";
+import {
+  createDiagnosticCollector,
+  Diagnostic,
+  getDoc,
+  getSummary,
+  listServices,
+} from "@typespec/compiler";
 import { $ } from "@typespec/compiler/typekit";
 import { getServers, HttpServer } from "@typespec/http";
+import { getVersionDependencies } from "@typespec/versioning";
 import {
   getClientInitializationOptions,
   getClientNameOverride,
@@ -17,6 +24,7 @@ import {
   SdkEndpointParameter,
   SdkEndpointType,
   SdkHttpOperation,
+  SdkMethodParameter,
   SdkOperationGroup,
   SdkPathParameter,
   SdkServiceOperation,
@@ -190,6 +198,14 @@ export function createSdkClientType<TServiceOperation extends SdkServiceOperatio
       name = override;
     }
   }
+  if (!parent && client.kind === "SdkClient" && client.parent) {
+    const parentRaw = context.__rawClientsOperationGroupsCache?.get(client.parent) as
+      | SdkClient
+      | undefined;
+    parent = context.__clientTypesCache?.find((c) => c.__raw === parentRaw) as
+      | SdkClientType<TServiceOperation>
+      | undefined;
+  }
   const sdkClientType: SdkClientType<TServiceOperation> = {
     __raw: client,
     kind: "client",
@@ -213,7 +229,8 @@ export function createSdkClientType<TServiceOperation extends SdkServiceOperatio
   );
   addDefaultClientParameters(context, sdkClientType);
   // update initialization model properties
-
+  context.__clientTypesCache = context.__clientTypesCache || [];
+  context.__clientTypesCache.push(sdkClientType);
   return diagnostics.wrap(sdkClientType);
 }
 
@@ -239,6 +256,48 @@ function addDefaultClientParameters<
       if (apiVersionParam) break;
     }
   }
+
+  // Check for multi-service scenario with @useDependency
+  if (!apiVersionParam && client.__raw.kind === "SdkClient") {
+    const services = listServices(context.program);
+    if (services.length > 1 && client.__raw.type?.kind === "Namespace") {
+      // Check if this is a multi-service client with @useDependency
+      const versionDependencies = getVersionDependencies(context.program, client.__raw.type);
+      if (versionDependencies && versionDependencies.size > 0) {
+        // Create an API version parameter for multi-service clients with @useDependency
+        const stringType = context.program.checker.getStdType("string");
+
+        // Create a SdkMethodParameter for the API version
+        const apiVersionMethodParam: SdkMethodParameter = {
+          __raw: undefined,
+          kind: "method",
+          name: "apiVersion",
+          isGeneratedName: false,
+          doc: "The API version to use for the operation",
+          type: getSdkBuiltInType(context, stringType),
+          optional: false,
+          isApiVersionParam: true,
+          onClient: true,
+          apiVersions: context.getApiVersionsForType(client.__raw.type ?? client.__raw.service),
+          clientDefaultValue: undefined,
+          decorators: [],
+          crossLanguageDefinitionId: `${client.crossLanguageDefinitionId}.apiVersion`,
+          access: "public",
+          flatten: false,
+        };
+
+        // Add to cache
+        let clientParams = context.__clientParametersCache.get(client.__raw);
+        if (!clientParams) {
+          clientParams = [];
+          context.__clientParametersCache.set(client.__raw, clientParams);
+        }
+        clientParams.push(apiVersionMethodParam);
+        apiVersionParam = apiVersionMethodParam;
+      }
+    }
+  }
+
   if (apiVersionParam) {
     defaultClientParamters.push(apiVersionParam);
   }