feat: provide client config property for region provider

codegen/smithy-aws-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/aws/customization/RegionSupport.kt

@@ -43,6 +43,19 @@ class RegionSupport : KotlinIntegration {
                 The region to sign with and make requests to.
             """.trimIndent()
         }
+
+        val RegionProviderProp: ConfigProperty = ConfigProperty {
+            name = "regionProvider"
+            symbol = RuntimeTypes.SmithyClient.Region.RegionProvider.asNullable()
+            documentation = """
+              An optional region provider that determines the AWS region for client operations. When specified, this provider
+              takes precedence over the default region provider chain, unless a static region is explicitly configured.
+              The region resolution order is:
+              1. Static region (if specified)
+              2. Custom region provider (if configured)
+              3. Default region provider chain
+            """.trimIndent()
+        }
     }
 
     // Allow other integrations to customize the service config props, later integrations take precedence.
@@ -57,8 +70,10 @@ class RegionSupport : KotlinIntegration {
         return supportsSigv4 || hasRegionBuiltin || isAwsSdk
     }
 
-    override fun additionalServiceConfigProps(ctx: CodegenContext): List<ConfigProperty> = listOf(RegionProp)
-
+    override fun additionalServiceConfigProps(ctx: CodegenContext): List<ConfigProperty> = buildList {
+        add(RegionProp)
+        add(RegionProviderProp)
+    }
     override fun customizeEndpointResolution(ctx: ProtocolGenerator.GenerationContext): EndpointCustomization =
         object : EndpointCustomization {
             override fun renderBindEndpointBuiltins(

codegen/smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/core/RuntimeTypes.kt

@@ -247,6 +247,10 @@ object RuntimeTypes {
                 val Url = symbol("Url")
             }
         }
+
+        object Region : RuntimeTypePackage(KotlinDependency.SMITHY_CLIENT, "region") {
+            val RegionProvider = symbol("RegionProvider")
+        }
     }
 
     object Serde : RuntimeTypePackage(KotlinDependency.SERDE) {
@@ -409,6 +413,7 @@ object RuntimeTypes {
 
         val CompletableDeferred = "kotlinx.coroutines.CompletableDeferred".toSymbol()
         val job = "kotlinx.coroutines.job".toSymbol()
+        val runBlocking = "kotlinx.coroutines.runBlocking".toSymbol()
 
         object Flow {
             // NOTE: smithy-kotlin core has an API dependency on this already

runtime/smithy-client/api/smithy-client.api

@@ -325,3 +325,7 @@ public final class aws/smithy/kotlin/runtime/client/endpoints/functions/Url {
 	public fun toString ()Ljava/lang/String;
 }
 
+public abstract interface class aws/smithy/kotlin/runtime/client/region/RegionProvider {
+	public abstract fun getRegion (Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+}
+

runtime/smithy-client/common/src/aws/smithy/kotlin/runtime/client/region/RegionProvider.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package aws.smithy.kotlin.runtime.client.region
+
+/**
+ * Interface for providing AWS region information. Implementations are free to use any strategy for
+ * providing region information
+ */
+public interface RegionProvider {
+    /**
+     * Return the region name to use. If region information is not available, implementations should return null
+     */
+    public suspend fun getRegion(): String?
+}