[App Service] az webapp create: Add error message that clearly lists all valid options and tells them how to discover available runtimes (#33252)

Author: Shi1810

src/azure-cli/azure/cli/command_modules/appservice/custom.py

@@ -269,17 +269,25 @@ def create_webapp(cmd, resource_group_name, name, plan, runtime=None, startup_fi
         if not validate_container_app_create_options(runtime, container_image_name,
                                                      multicontainer_config_type, multicontainer_config_file,
                                                      sitecontainers_app):
+            if not any([runtime, container_image_name, multicontainer_config_type,
+                        multicontainer_config_file, deployment_container_image_name, sitecontainers_app]):
+                raise ArgumentUsageError('Creating a Linux webapp requires one of the following: '
+                                         '--runtime, --container-image-name, '
+                                         'or --sitecontainers-app. '
+                                         "Run 'az webapp list-runtimes --os-type linux' for supported runtimes. "
+                                         "For custom containers, see 'az webapp sitecontainers create --help': "
+                                         "https://learn.microsoft.com/cli/azure/webapp/sitecontainers")
             if deployment_container_image_name:
                 raise ArgumentUsageError('Please specify both --multicontainer-config-type TYPE '
                                          'and --multicontainer-config-file FILE, '
                                          'and only specify one out of --runtime, '
                                          '--deployment-container-image-name, --multicontainer-config-type '
-                                         'or --sitecontainers_app')
+                                         'or --sitecontainers-app')
             raise ArgumentUsageError('Please specify both --multicontainer-config-type TYPE '
                                      'and --multicontainer-config-file FILE, '
                                      'and only specify one out of --runtime, '
                                      '--container-image-name, --multicontainer-config-type '
-                                     'or --sitecontainers_app')
+                                     'or --sitecontainers-app')
         if startup_file:
             site_config.app_command_line = startup_file
         if sitecontainers_app:

src/azure-cli/azure/cli/command_modules/appservice/tests/latest/test_webapp_commands_thru_mock.py

@@ -12,7 +12,8 @@
 from knack.util import CLIError
 from azure.cli.core.azclierror import (InvalidArgumentValueError,
                                        MutuallyExclusiveArgumentError,
-                                       AzureResponseError)
+                                       AzureResponseError,
+                                       ArgumentUsageError)
 from azure.cli.command_modules.appservice.custom import (set_deployment_user,
                                                          update_git_token, add_hostname,
                                                          update_site_configs,
@@ -33,7 +34,8 @@
                                                          add_github_actions,
                                                          update_app_settings,
                                                          update_application_settings_polling,
-                                                         update_webapp)
+                                                         update_webapp,
+                                                         create_webapp)
 
 # pylint: disable=line-too-long
 from azure.cli.core.profiles import ResourceType
@@ -436,6 +438,36 @@ def test_valid_linux_create_options(self):
         self.assertFalse(validate_container_app_create_options(None, None, test_multi_container_config, None))
         self.assertFalse(validate_container_app_create_options(None, None, None, None))
 
+    @mock.patch('azure.cli.command_modules.appservice.custom.web_client_factory', autospec=True)
+    @mock.patch('azure.cli.command_modules.appservice.custom._StackRuntimeHelper', autospec=True)
+    @mock.patch('azure.cli.command_modules.appservice.custom.get_site_availability', autospec=True)
+    def test_linux_webapp_create_no_runtime_raises_error(self, get_site_avail_mock,
+                                                         stack_helper_mock, web_client_mock):
+        cmd_mock = _get_test_cmd()
+        SiteConfig, SkuDescription, NameValuePair = cmd_mock.get_models(
+            'SiteConfig', 'SkuDescription', 'NameValuePair')
+        cmd_mock.get_models = mock.MagicMock(return_value=(SiteConfig, SkuDescription, NameValuePair))
+
+        # Mock a Linux plan (reserved=True)
+        plan_info = mock.MagicMock()
+        plan_info.reserved = True
+        plan_info.location = 'eastus'
+        plan_info.id = '/subscriptions/sub/resourceGroups/rg/providers/Microsoft.Web/serverfarms/plan'
+        plan_info.sku = SkuDescription(name='F1')
+        web_client_mock.return_value.app_service_plans.get.return_value = plan_info
+
+        # Mock site availability (new app name)
+        name_validation = mock.MagicMock()
+        name_validation.name_available = True
+        get_site_avail_mock.return_value = name_validation
+
+        with self.assertRaises(ArgumentUsageError) as context:
+            create_webapp(cmd_mock, 'test-rg', 'test-app', 'test-plan')
+
+        self.assertIn('Creating a Linux webapp requires one of the following', str(context.exception))
+        self.assertIn('--runtime', str(context.exception))
+        self.assertIn('--os-type linux', str(context.exception))
+
     @mock.patch('azure.cli.command_modules.appservice.custom._verify_hostname_binding', autospec=True)
     @mock.patch('azure.cli.command_modules.appservice.custom.web_client_factory', autospec=True)
     @mock.patch('azure.cli.command_modules.appservice.custom._generic_site_operation', autospec=True)