RFC30: add Serde Decorator to RustClientCodegenPlugin

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/RustClientCodegenPlugin.kt

@@ -18,6 +18,7 @@ import software.amazon.smithy.rust.codegen.client.smithy.customizations.Sensitiv
 import software.amazon.smithy.rust.codegen.client.smithy.customize.ClientCodegenDecorator
 import software.amazon.smithy.rust.codegen.client.smithy.customize.CombinedClientCodegenDecorator
 import software.amazon.smithy.rust.codegen.client.smithy.customize.RequiredCustomizations
+import software.amazon.smithy.rust.codegen.client.smithy.customize.SerdeDecorator
 import software.amazon.smithy.rust.codegen.client.smithy.endpoint.EndpointParamsDecorator
 import software.amazon.smithy.rust.codegen.client.smithy.endpoint.EndpointsDecorator
 import software.amazon.smithy.rust.codegen.client.smithy.generators.client.FluentClientDecorator
@@ -59,6 +60,7 @@ class RustClientCodegenPlugin : ClientDecoratableBuildPlugin() {
         val codegenDecorator =
             CombinedClientCodegenDecorator.fromClasspath(
                 context,
+                SerdeDecorator(),
                 ClientCustomizations(),
                 RequiredCustomizations(),
                 FluentClientDecorator(),

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/customize/SerdeDecorator.kt

@@ -0,0 +1,81 @@
+/*
+* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+* SPDX-License-Identifier: Apache-2.0
+*/
+
+package software.amazon.smithy.rust.codegen.client.smithy.customize
+
+import software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenContext
+import software.amazon.smithy.rust.codegen.core.rustlang.Feature
+import software.amazon.smithy.rust.codegen.core.rustlang.Writable
+import software.amazon.smithy.rust.codegen.core.rustlang.containerDocs
+import software.amazon.smithy.rust.codegen.core.rustlang.writable
+import software.amazon.smithy.rust.codegen.core.smithy.RustCrate
+import software.amazon.smithy.rust.codegen.core.smithy.generators.LibRsCustomization
+import software.amazon.smithy.rust.codegen.core.smithy.generators.LibRsSection
+import software.amazon.smithy.rust.codegen.core.smithy.generators.ModuleDocSection
+
+/**
+ * Decorator that adds the `serde-serialize` and `serde-deserialize` features.
+ */
+class SerdeDecorator : ClientCodegenDecorator {
+    override val name: String = "SerdeDecorator"
+    override val order: Byte = 5
+
+    override fun extras(codegenContext: ClientCodegenContext, rustCrate: RustCrate) {
+        fun feature(featureName: String): Feature {
+            return Feature(featureName, false, listOf("aws-smithy-types/$featureName"))
+        }
+        rustCrate.mergeFeature(feature("serde-serialize"))
+        rustCrate.mergeFeature(feature("serde-deserialize"))
+    }
+
+    override fun libRsCustomizations(
+        codegenContext: ClientCodegenContext,
+        baseCustomizations: List<LibRsCustomization>,
+    ): List<LibRsCustomization> {
+        return baseCustomizations + SerdeDocGenerator(codegenContext)
+    }
+}
+
+class SerdeDocGenerator(private val codegenContext: ClientCodegenContext) : LibRsCustomization() {
+    override fun section(section: LibRsSection): Writable {
+        return when (section) {
+            is LibRsSection.ModuleDoc ->
+                if (section.subsection is ModuleDocSection.AWSSdkUnstable) {
+                    serdeInfoText()
+                } else {
+                    emptySection
+                }
+
+            else -> emptySection
+        }
+    }
+
+    private fun serdeInfoText(): Writable {
+        return writable {
+            containerDocs(
+                """
+                ## How to enable `Serialize` and `Deserialize`
+
+                This data type implements `Serialize` and `Deserialize` traits from the popular serde crate, but those traits are behind feature gate.
+
+                As they increase it's compile time dramatically, you should not turn them on unless it's necessary.
+                Implementation of `serde` traits in AWS SDK for Rust is still unstable, and implementation may change anytime in future.
+
+                To enable traits, you must pass `aws_sdk_unstable` to RUSTFLAGS and enable `serde-serialize` or `serde-deserialize` feature.
+
+                e.g.
+                ```bash,no_run
+                export RUSTFLAGS="--cfg aws_sdk_unstable"
+                cargo build --features serde-serialize serde-deserialize
+                ```
+
+                If you enable `serde-serialize` and/or `serde-deserialize` without `RUSTFLAGS="--cfg aws_sdk_unstable"`,
+                compilation will fail with warning.
+
+                """.trimIndent(),
+            )
+        }
+    }
+}

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/LibRsGenerator.kt

@@ -25,6 +25,7 @@ sealed class ModuleDocSection {
     object CrateOrganization : ModuleDocSection()
 
     object Examples : ModuleDocSection()
+    object AWSSdkUnstable : ModuleDocSection()
 }
 
 sealed class LibRsSection(name: String) : Section(name) {
@@ -78,6 +79,15 @@ class LibRsGenerator(
                 }
             }
 
+            docSection(ModuleDocSection.AWSSdkUnstable).also { docs ->
+                if (docs.isNotEmpty()) {
+                    containerDocs("\n## Enabling Unstable Features")
+                    docs.forEach { writeTo ->
+                        writeTo(this)
+                    }
+                }
+            }
+
             // Examples
             docSection(ModuleDocSection.Examples).also { docs ->
                 if (docs.isNotEmpty() || settings.examplesUri != null) {