fix: narrow ARM metadata filter to only strip exclusively read-only properties

packages/typespec-ts/src/modular/emitModels.ts

@@ -747,12 +747,15 @@ function buildModelInterface(
         if (!hasInputUsage && p.__raw && isMetadata(context.program, p.__raw)) {
           return false;
         }
-        // Skip required metadata properties with Read visibility for ARM as they are not intended to be in the model
+        // Skip required metadata properties with Read-only visibility for ARM as they are not intended to be in the model
         // These properties are not be generated no matter they are in input or output models in most cases in HLC
+        // Only skip properties that have exclusively Read visibility to avoid stripping @path properties
+        // on parameter bag models that also carry other visibility flags (e.g. Create/Update)
         if (
           context.arm &&
           p.__raw &&
           isMetadata(context.program, p.__raw) &&
+          p.visibility?.length === 1 &&
           p.visibility?.includes(Visibility.Read)
         ) {
           return false;

packages/typespec-ts/test/modularUnit/scenarios/models/arm/armMetadataFilter.md

@@ -0,0 +1,274 @@
+# ARM metadata filter should not strip @path properties from parameter bag models with no ARM base class
+
+In ARM mode, the metadata filter should only strip properties that have exclusively
+`Lifecycle.Read` visibility (i.e. truly read-only ARM properties like `id`, `name`, `type`).
+It must NOT strip `@path`-decorated properties on plain parameter bag models that have no ARM
+base class, because those properties carry multiple visibility flags (Read + Create + Update…)
+and must remain accessible in the generated interface so users can set them.
+
+## TypeSpec
+
+```tsp
+import "@typespec/http";
+import "@typespec/rest";
+import "@typespec/versioning";
+import "@azure-tools/typespec-azure-core";
+import "@azure-tools/typespec-azure-resource-manager";
+import "@azure-tools/typespec-client-generator-core";
+
+using TypeSpec.Http;
+using TypeSpec.Rest;
+using TypeSpec.Versioning;
+using Azure.Core;
+using Azure.ResourceManager;
+using Azure.ClientGenerator.Core;
+
+@armProviderNamespace
+@service(#{
+  title: "Test ARM Service",
+})
+@versioned(Versions)
+namespace Microsoft.Test;
+
+enum Versions {
+  @armCommonTypesVersion(Azure.ResourceManager.CommonTypes.Versions.v5)
+  v2021_10_01: "2021-10-01",
+}
+
+/** Parameters for the private link resource. */
+model PrivateLinkParameters {
+  /** The name of the private link resource. */
+  @path
+  privateLinkName: string;
+}
+
+#suppress "@azure-tools/typespec-azure-resource-manager/arm-resource-operation" "test"
+#suppress "@azure-tools/typespec-azure-core/documentation-required" "test"
+op getPrivateLink(
+  ...ApiVersionParameter,
+  ...SubscriptionIdParameter,
+  ...ResourceGroupParameter,
+  params?: PrivateLinkParameters,
+): ArmResponse<{}> | ErrorResponse;
+```
+
+```yaml
+needTCGC: true
+withRawContent: true
+mustEmptyDiagnostic: false
+```
+
+## Models interface PrivateLinkParameters
+
+```ts models interface PrivateLinkParameters
+/**
+ * This file contains only generated model types and their (de)serializers.
+ * Disable the following rules for internal models with '_' prefix and deserializers which require 'any' for raw JSON input.
+ */
+/* eslint-disable @typescript-eslint/naming-convention */
+/* eslint-disable @typescript-eslint/explicit-module-boundary-types */
+/** Parameters for the private link resource. */
+export interface PrivateLinkParameters {
+  /** The name of the private link resource. */
+  privateLinkName: string;
+}
+```
+
+# ARM metadata filter should preserve @path property with Read & Create visibility
+
+In ARM mode, a `@path` property that carries both `Lifecycle.Read` AND `Lifecycle.Create`
+visibility flags must NOT be stripped by the metadata filter, because the filter only removes
+properties that are *exclusively* read-only (i.e. `visibility.length === 1 && Read`).
+
+## TypeSpec
+
+```tsp
+import "@typespec/http";
+import "@typespec/rest";
+import "@typespec/versioning";
+import "@azure-tools/typespec-azure-core";
+import "@azure-tools/typespec-azure-resource-manager";
+import "@azure-tools/typespec-client-generator-core";
+
+using TypeSpec.Http;
+using TypeSpec.Rest;
+using TypeSpec.Versioning;
+using Azure.Core;
+using Azure.ResourceManager;
+using Azure.ClientGenerator.Core;
+
+@armProviderNamespace
+@service(#{
+  title: "Test ARM Service",
+})
+@versioned(Versions)
+namespace Microsoft.Test;
+
+enum Versions {
+  @armCommonTypesVersion(Azure.ResourceManager.CommonTypes.Versions.v5)
+  v2021_10_01: "2021-10-01",
+}
+
+model ParamBagReadCreate {
+  @path
+  @visibility(Lifecycle.Read, Lifecycle.Create)
+  resourceName: string;
+}
+
+#suppress "@azure-tools/typespec-azure-resource-manager/arm-resource-operation" "test"
+#suppress "@azure-tools/typespec-azure-core/documentation-required" "test"
+op getResource(params?: ParamBagReadCreate): ArmResponse<{}> | ErrorResponse;
+```
+
+```yaml
+needTCGC: true
+withRawContent: true
+mustEmptyDiagnostic: false
+```
+
+## Models interface ParamBagReadCreate
+
+```ts models interface ParamBagReadCreate
+/**
+ * This file contains only generated model types and their (de)serializers.
+ * Disable the following rules for internal models with '_' prefix and deserializers which require 'any' for raw JSON input.
+ */
+/* eslint-disable @typescript-eslint/naming-convention */
+/* eslint-disable @typescript-eslint/explicit-module-boundary-types */
+/** model interface ParamBagReadCreate */
+export interface ParamBagReadCreate {
+  resourceName: string;
+}
+```
+
+# ARM metadata filter should strip @path property with exclusively Read visibility
+
+In ARM mode, a `@path` property that has *only* `Lifecycle.Read` visibility should be
+stripped by the metadata filter. Such a property is purely decorative/read-only metadata
+(e.g. an ARM resource system-assigned `id`) and must not appear in the model interface.
+
+## TypeSpec
+
+```tsp
+import "@typespec/http";
+import "@typespec/rest";
+import "@typespec/versioning";
+import "@azure-tools/typespec-azure-core";
+import "@azure-tools/typespec-azure-resource-manager";
+import "@azure-tools/typespec-client-generator-core";
+
+using TypeSpec.Http;
+using TypeSpec.Rest;
+using TypeSpec.Versioning;
+using Azure.Core;
+using Azure.ResourceManager;
+using Azure.ClientGenerator.Core;
+
+@armProviderNamespace
+@service(#{
+  title: "Test ARM Service",
+})
+@versioned(Versions)
+namespace Microsoft.Test;
+
+enum Versions {
+  @armCommonTypesVersion(Azure.ResourceManager.CommonTypes.Versions.v5)
+  v2021_10_01: "2021-10-01",
+}
+
+model ParamBagReadOnly {
+  @path
+  @visibility(Lifecycle.Read)
+  resourceName: string;
+}
+
+#suppress "@azure-tools/typespec-azure-resource-manager/arm-resource-operation" "test"
+#suppress "@azure-tools/typespec-azure-core/documentation-required" "test"
+op getResource(params?: ParamBagReadOnly): ArmResponse<{}> | ErrorResponse;
+```
+
+```yaml
+needTCGC: true
+withRawContent: true
+mustEmptyDiagnostic: false
+```
+
+## Models interface ParamBagReadOnly
+
+```ts models interface ParamBagReadOnly
+/**
+ * This file contains only generated model types and their (de)serializers.
+ * Disable the following rules for internal models with '_' prefix and deserializers which require 'any' for raw JSON input.
+ */
+/* eslint-disable @typescript-eslint/naming-convention */
+/* eslint-disable @typescript-eslint/explicit-module-boundary-types */
+/** model interface ParamBagReadOnly */
+export interface ParamBagReadOnly {}
+```
+
+# ARM metadata filter should preserve @path property with Read & Update & Create visibility
+
+In ARM mode, a `@path` property that carries `Lifecycle.Read`, `Lifecycle.Update`, AND
+`Lifecycle.Create` visibility flags must NOT be stripped. Only properties that are
+*exclusively* read-only (`visibility.length === 1 && Read`) are filtered out.
+
+## TypeSpec
+
+```tsp
+import "@typespec/http";
+import "@typespec/rest";
+import "@typespec/versioning";
+import "@azure-tools/typespec-azure-core";
+import "@azure-tools/typespec-azure-resource-manager";
+import "@azure-tools/typespec-client-generator-core";
+
+using TypeSpec.Http;
+using TypeSpec.Rest;
+using TypeSpec.Versioning;
+using Azure.Core;
+using Azure.ResourceManager;
+using Azure.ClientGenerator.Core;
+
+@armProviderNamespace
+@service(#{
+  title: "Test ARM Service",
+})
+@versioned(Versions)
+namespace Microsoft.Test;
+
+enum Versions {
+  @armCommonTypesVersion(Azure.ResourceManager.CommonTypes.Versions.v5)
+  v2021_10_01: "2021-10-01",
+}
+
+model ParamBagReadUpdateCreate {
+  @path
+  @visibility(Lifecycle.Read, Lifecycle.Update, Lifecycle.Create)
+  resourceName: string;
+}
+
+#suppress "@azure-tools/typespec-azure-resource-manager/arm-resource-operation" "test"
+#suppress "@azure-tools/typespec-azure-core/documentation-required" "test"
+op getResource(params?: ParamBagReadUpdateCreate): ArmResponse<{}> | ErrorResponse;
+```
+
+```yaml
+needTCGC: true
+withRawContent: true
+mustEmptyDiagnostic: false
+```
+
+## Models interface ParamBagReadUpdateCreate
+
+```ts models interface ParamBagReadUpdateCreate
+/**
+ * This file contains only generated model types and their (de)serializers.
+ * Disable the following rules for internal models with '_' prefix and deserializers which require 'any' for raw JSON input.
+ */
+/* eslint-disable @typescript-eslint/naming-convention */
+/* eslint-disable @typescript-eslint/explicit-module-boundary-types */
+/** model interface ParamBagReadUpdateCreate */
+export interface ParamBagReadUpdateCreate {
+  resourceName: string;
+}
+```