[tcgc] allow models-only packages (#2179)

fixes #1755

---------

Co-authored-by: iscai-msft <[email protected]>

Author: iscai-msft

.chronus/changes/tcgc-modelsOnly-2025-1-6-13-47-10.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+add support for models-only packages

cspell.yaml

@@ -39,6 +39,7 @@ words:
   - Donezo
   - dynatrace
   - espt
+  - fhir
   - foos
   - français
   - horiz

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

@@ -25,6 +25,7 @@ import {
   getEncode,
   getKnownValues,
   getLifecycleVisibilityEnum,
+  getLocationContext,
   getSummary,
   getVisibilityForClass,
   ignoreDiagnostics,
@@ -1867,8 +1868,11 @@ export function handleAllTypes(context: TCGCContext): [void, readonly Diagnostic
     }
   }
   // update for orphan models/enums/unions
-  for (const client of listClients(context)) {
-    const namespaces = [client.service];
+  const allNamespaces = [...context.program.getGlobalNamespaceType().namespaces.values()].filter(
+    (x) => getLocationContext(context.program, x).type === "project",
+  );
+  for (const currNamespace of allNamespaces) {
+    const namespaces = [currNamespace];
     while (namespaces.length) {
       const namespace = namespaces.pop()!;
       // orphan models

packages/typespec-client-generator-core/test/package.test.ts

@@ -1260,6 +1260,79 @@ describe("typespec-client-generator-core: package", () => {
       strictEqual(sdkPackage.enums.length, 2);
     });
   });
+  it("models only package", async () => {
+    await runner.compile(`
+      @usage(Usage.input | Usage.output)
+      namespace EventGridClient {
+        model CloudEvent {
+          id: string;
+        }
+      }
+    `);
+    const sdkPackage = runner.context.sdkPackage;
+    strictEqual(sdkPackage.models.length, 1);
+    strictEqual(sdkPackage.models[0].name, "CloudEvent");
+    strictEqual(sdkPackage.clients.length, 0);
+  });
+
+  it("models only package with azure and versioning decorators", async () => {
+    const runnerWithCore = await createSdkTestRunner({
+      librariesToAdd: [AzureCoreTestLibrary],
+      autoUsings: ["Azure.Core"],
+      emitterName: "@azure-tools/typespec-java",
+    });
+    await runnerWithCore.compile(`
+      @usage(Usage.input | Usage.output)
+      @versioned(ServiceApiVersions)
+      namespace EventGridClient {
+        enum ServiceApiVersions {
+          @useDependency(Versions.v1_0_Preview_2)
+          v2018_01_01: "2018-01-01",
+          @useDependency(Versions.v1_0_Preview_2)
+          v2024_01_01: "2024-01-01",
+        }
+        /**
+         * CloudEvent comments
+         */
+        model CloudEvent {
+          /**
+           * id comments
+           */
+          id: string;
+        }
+
+        /**
+         * Healthcare comments
+         */
+        model HealthcareFhirResourceCreatedEventData {
+          /**
+           * resourceVersionId comments
+           */
+          @added(ServiceApiVersions.v2024_01_01)
+          resourceVersionId: int64;
+        }
+      }
+    `);
+    const sdkPackage = runnerWithCore.context.sdkPackage;
+    strictEqual(sdkPackage.models.length, 2);
+    const cloudEventModel = sdkPackage.models.find((x) => x.name === "CloudEvent");
+    ok(cloudEventModel);
+    strictEqual(cloudEventModel.properties.length, 1);
+    const idProperty = cloudEventModel.properties[0];
+    strictEqual(idProperty.name, "id");
+    strictEqual(idProperty.kind, "property");
+    deepStrictEqual(idProperty.apiVersions, ["2018-01-01", "2024-01-01"]);
+
+    const healthcareEventDataModel = sdkPackage.models.find(
+      (x) => x.name === "HealthcareFhirResourceCreatedEventData",
+    );
+    ok(healthcareEventDataModel);
+    strictEqual(healthcareEventDataModel.properties.length, 1);
+    const resourceVersionIdProperty = healthcareEventDataModel.properties[0];
+    strictEqual(resourceVersionIdProperty.name, "resourceVersionId");
+    strictEqual(resourceVersionIdProperty.kind, "property");
+    deepStrictEqual(resourceVersionIdProperty.apiVersions, ["2024-01-01"]);
+  });
 });
 
 function getServiceMethodOfClient(