Rfc30/feature gate for generated crates

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/rustlang/CargoDependency.kt

@@ -16,6 +16,7 @@ import java.nio.file.Path
 sealed class DependencyScope {
     object Dev : DependencyScope()
     object Compile : DependencyScope()
+    object CfgUnstable : DependencyScope()
 }
 
 sealed class DependencyLocation
@@ -245,5 +246,8 @@ data class CargoDependency(
         fun smithyQuery(runtimeConfig: RuntimeConfig) = runtimeConfig.smithyRuntimeCrate("smithy-query")
         fun smithyTypes(runtimeConfig: RuntimeConfig) = runtimeConfig.smithyRuntimeCrate("smithy-types")
         fun smithyXml(runtimeConfig: RuntimeConfig) = runtimeConfig.smithyRuntimeCrate("smithy-xml")
+
+        // behind feature-gate
+        val Serde = CargoDependency("serde", CratesIo("1.0"), features = setOf("derive"), scope = DependencyScope.CfgUnstable)
     }
 }

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

@@ -239,6 +239,10 @@ data class RuntimeType(val path: String, val dependency: RustDependency? = null)
         val ConstrainedTrait = RuntimeType("crate::constrained::Constrained", InlineDependency.constrained())
         val MaybeConstrained = RuntimeType("crate::constrained::MaybeConstrained", InlineDependency.constrained())
 
+        // serde types. They will be behind feature gates
+        val SerdeSerialize = CargoDependency.Serde.toType().resolve("Serialize")
+        val SerdeDeserialize = CargoDependency.Serde.toType().resolve("Deserialize")
+
         // smithy runtime types
         fun smithyAsync(runtimeConfig: RuntimeConfig) = CargoDependency.smithyAsync(runtimeConfig).toType()
         fun smithyChecksums(runtimeConfig: RuntimeConfig) = CargoDependency.smithyChecksums(runtimeConfig).toType()

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

@@ -54,6 +54,9 @@ class CargoTomlGenerator(
         if (features.isNotEmpty()) {
             cargoFeatures.add("default" to features.filter { it.default }.map { it.name })
         }
+        // add serde related features
+        cargoFeatures.add("serialize" to listOf("aws-smithy-types/serialize"))
+        cargoFeatures.add("deserialize" to listOf("aws-smithy-types/deserialize"))
 
         val cargoToml = mapOf(
             "package" to listOfNotNull(
@@ -74,6 +77,8 @@ class CargoTomlGenerator(
                 .associate { it.name to it.toMap() },
             "dev-dependencies" to dependencies.filter { it.scope == DependencyScope.Dev }
                 .associate { it.name to it.toMap() },
+            "target.'cfg(aws_sdk_unstable)'" to dependencies.filter { it.scope == DependencyScope.CfgUnstable }
+                .associate { it.name to it.toMap() },
             "features" to cargoFeatures.toMap(),
         ).deepMergeWith(manifestCustomizations)