Fix inability to create service clients when `default-features = false` (#2055)

* add: tests for config/client construction when default features are disabled
fix: enable users to create service clients when default features are disabled
update: missing HTTP connector panic messages

* Apply suggestions from code review
Co-authored-by: John DiSanti <jdisanti@amazon.com>

aws/rust-runtime/aws-config/src/connector.rs

@@ -13,7 +13,7 @@ use std::sync::Arc;
 // unused when all crate features are disabled
 /// Unwrap an [`Option<DynConnector>`](aws_smithy_client::erase::DynConnector), and panic with a helpful error message if it's `None`
 pub(crate) fn expect_connector(connector: Option<DynConnector>) -> DynConnector {
-    connector.expect("A connector was not available. Either set a custom connector or enable the `rustls` and `native-tls` crate features.")
+    connector.expect("No HTTP connector was available. Enable the `rustls` or `native-tls` crate feature or set a connector to fix this.")
 }
 
 #[cfg(any(feature = "rustls", feature = "native-tls"))]

aws/sdk-codegen/src/main/kotlin/software/amazon/smithy/rustsdk/AwsFluentClientDecorator.kt

@@ -158,13 +158,25 @@ private class AwsFluentClientExtensions(types: Types) {
             rustTemplate(
                 """
                 /// Creates a new client from an [SDK Config](#{aws_types}::sdk_config::SdkConfig).
-                ##[cfg(any(feature = "rustls", feature = "native-tls"))]
+                ///
+                /// ## Panics
+                ///
+                /// - This method will panic if the `sdk_config` is missing an async sleep implementation. If you experience this panic, set
+                ///     the `sleep_impl` on the Config passed into this function to fix it.
+                /// - This method will panic if the `sdk_config` is missing an HTTP connector. If you experience this panic, set the
+                ///     `http_connector` on the Config passed into this function to fix it.
                 pub fn new(sdk_config: &#{aws_types}::sdk_config::SdkConfig) -> Self {
                     Self::from_conf(sdk_config.into())
                 }
 
                 /// Creates a new client from the service [`Config`](crate::Config).
-                ##[cfg(any(feature = "rustls", feature = "native-tls"))]
+                ///
+                /// ## Panics
+                ///
+                /// - This method will panic if the `conf` is missing an async sleep implementation. If you experience this panic, set
+                ///     the `sleep_impl` on the Config passed into this function to fix it.
+                /// - This method will panic if the `conf` is missing an HTTP connector. If you experience this panic, set the
+                ///     `http_connector` on the Config passed into this function to fix it.
                 pub fn from_conf(conf: crate::Config) -> Self {
                     let retry_config = conf.retry_config().cloned().unwrap_or_else(#{RetryConfig}::disabled);
                     let timeout_config = conf.timeout_config().cloned().unwrap_or_else(#{TimeoutConfig}::disabled);
@@ -186,11 +198,21 @@ private class AwsFluentClientExtensions(types: Types) {
                     });
 
                     let builder = #{aws_smithy_client}::Builder::new();
+
                     let builder = match connector {
                         // Use provided connector
                         Some(c) => builder.connector(c),
+                        None =>{
+                            ##[cfg(any(feature = "rustls", feature = "native-tls"))]
+                            {
                                 // Use default connector based on enabled features
-                        None => builder.dyn_https_connector(#{ConnectorSettings}::from_timeout_config(&timeout_config)),
+                                builder.dyn_https_connector(#{ConnectorSettings}::from_timeout_config(&timeout_config))
+                            }
+                            ##[cfg(not(any(feature = "rustls", feature = "native-tls")))]
+                            {
+                                panic!("No HTTP connector was available. Enable the `rustls` or `native-tls` crate feature or set a connector to fix this.");
+                            }
+                        }
                     };
                     let mut builder = builder
                         .middleware(#{DynMiddleware}::new(#{Middleware}::new()))

aws/sdk/integration-tests/Cargo.toml

@@ -8,6 +8,7 @@ members = [
     "iam",
     "kms",
     "lambda",
+    "no-default-features",
     "polly",
     "qldbsession",
     "s3",

aws/sdk/integration-tests/no-default-features/Cargo.toml

+# This Cargo.toml is unused in generated code. It exists solely to enable these tests to compile in-situ
+[package]
+name = "no-default-features"
+version = "0.1.0"
+authors = ["Zelda Hessler <zhessler@amazon.com>"]
+description = """
+These tests ensure that things will fail (or not fail) as expected
+when default features are disabled for all SDK and runtime crates.
+"""
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dev-dependencies]
+aws-config = { path = "../../build/aws-sdk/sdk/aws-config", default-features = false }
+aws-sdk-s3 = { path = "../../build/aws-sdk/sdk/s3", default-features = false }
+futures = "0.3.25"
+tokio = { version = "1.8.4", features = ["full", "test-util"] }
+tracing-subscriber = { version = "0.3.15", features = ["env-filter"] }

aws/sdk/integration-tests/no-default-features/tests/client-construction.rs

+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// This will fail due to lack of a connector when constructing the SDK Config
+#[tokio::test]
+#[should_panic(
+    expected = "No HTTP connector was available. Enable the `rustls` or `native-tls` crate feature or set a connector to fix this."
+)]
+async fn test_clients_from_sdk_config() {
+    aws_config::load_from_env().await;
+}
+
+// This will fail due to lack of a connector when constructing the service client
+#[test]
+#[should_panic(
+    expected = "No HTTP connector was available. Enable the `rustls` or `native-tls` crate feature or set a connector to fix this."
+)]
+fn test_clients_from_service_config() {
+    let config = aws_sdk_s3::Config::builder().build();
+    // This will panic due to the lack of an HTTP connector
+    aws_sdk_s3::Client::from_conf(config);
+}