feat: Add full-featured code generator #1016

jbelkins · 2026-01-19T21:41:28Z

Description of changes

This PR merges to the schema-based serialization epic branch epic/sbs.

This PR includes the entire native-Swift code generator. It generates error- and warning-free code for all AWS services when used in conjunction with its companion aws-sdk-swift PR awslabs/aws-sdk-swift#2094.

Specific changes:

Adds a native-Swift code generator that will be used to generate schema-based serialization code.
Generates schemas for model shapes to a Swift generated source file. This replaces the schema generation that was previously implemented in Kotlin.

Also:

Refactors and renames some code in the Kotlin code generator related to sdkId and client naming.
Adds several model transforms that duplicate those in the Kotlin code generator, so that the Swift code generator works from a model equivalent to the one in Kotlin.

Scope

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

jbelkins · 2026-01-19T21:45:10Z

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/SwiftSettings.kt

            val gitRepo = config.expectStringMember(GIT_REPO).value
            val swiftVersion = config.expectStringMember(SWIFT_VERSION).value
-            val sdkId = sanitizeSdkId(config.getStringMemberOrDefault(SDK_ID, serviceId.name))
+            val sdkId = config.getStringMemberOrDefault(SDK_ID, service?.sdkId ?: serviceId.name)


What we currently call sdkId here is actually the service's sdkId with some transformations applied to it. To avoid confusion, this settings field is now the sdkId taken directly from the service.

jbelkins · 2026-01-19T21:47:03Z

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/SwiftSettings.kt

+
+    val clientBaseName: String
+        get() = sdkIdStrippingService.clientName()
 }


The 4 methods above, extended onto SwiftSettings, provide names of Swift symbols that are needed throughout the codebase, but provide them with more meaningful descriptions than they have right now.

jbelkins · 2026-01-19T21:49:07Z

...hy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/SwiftSymbolProvider.kt


    override fun serviceShape(shape: ServiceShape): Symbol {
-        val name = sdkId.clientName()
+        val name = swiftSettings.clientBaseName


Currently, clientName isn't actually the client name - it's the client name minus the word Client attached to the end.

The new name makes it more clear that it is the base for the client name.

jbelkins · 2026-01-19T21:50:05Z

Sources/Smithy/Document/Implementations/BigIntegerDocument.swift

+    let value: Int64

-    public init(value: Int) {
+    public init(value: Int64) {


This type was incorrect in our Smithy document implementation.

This is a @spi() interface so no harm in changing it.

jbelkins · 2026-01-19T21:50:38Z

Sources/Smithy/Schema/Prelude.swift


    public static var documentSchema: Schema {
-        Schema(id: .init("smithy.api", "PrimitiveDocument"), type: .document)
+        Schema(id: .init("smithy.api", "Document"), type: .document)


This name was incorrect, fixed.

jbelkins · 2026-01-19T21:51:13Z

Sources/Smithy/Schema/Schema.swift

 /// Typically, the Schema contains only modeled info & properties that are relevant to
 /// serialization, transport bindings, and other functions performed by the SDK.
-public final class Schema: Sendable {
+public struct Schema: Sendable {


Changed this to a struct. There is no advantage to typing it as class.

jbelkins · 2026-01-19T21:54:51Z

Sources/Smithy/Schema/Schema.swift

-        id.member
+    /// Only access this property on a schema of type `.map`.
+    public var value: Schema {
+        members[1] // `value` will be the second / last member in a map schema, after `key`


Added some convenience accessors to Schema above.

jbelkins · 2026-01-19T21:55:54Z

Sources/Smithy/Trait/Trait.swift

+// SPDX-License-Identifier: Apache-2.0
+//
+
+public protocol Trait {


This is a protocol for type-safe traits. See TraitCollection below for how it's used.

jbelkins · 2026-01-19T21:58:26Z

Sources/Smithy/Trait/TraitCollection.swift

+// SPDX-License-Identifier: Apache-2.0
+//
+
+public struct TraitCollection: Sendable, Hashable {


TraitCollection allows for access to traits by trait types which provide safe, easy access to traits. Internally, TraitCollection still stores traits by Shape ID & Node, but Trait-conforming structures are passed in & out of this type.

jbelkins · 2026-01-19T22:00:01Z

Sources/Smithy/TraitLibrary/AddedDefaultTrait.swift

+//
+// SPDX-License-Identifier: Apache-2.0
+//
+


This is a very simple trait. It has an ID, and its node value is not used or important (Smithy uses empty object as placeholder for this type of trait.)

jbelkins · 2026-01-19T22:01:29Z

Sources/Smithy/TraitLibrary/AllSupportedTraits.swift

+///
+/// This list can be expanded as features are added to Smithy/SDK that use them.
+public let allSupportedTraits = Set([
+


This list of traits is the only ones that will be copied into a schema; other traits will be used at codegen time only but since they don't appear in a schema, can't be used at runtime.

jbelkins · 2026-01-19T22:03:19Z

Sources/Smithy/TraitLibrary/AWSQueryErrorTrait.swift

+//
+// SPDX-License-Identifier: Apache-2.0
+//
+


This is an example of a trait that has content in its node.

Code is provided to safely unwrap the data in the node and provide it to callers in simple properties.

jbelkins · 2026-01-19T22:05:37Z

Sources/Smithy/TraitLibrary/TargetsUnitTrait.swift

+//
+// SPDX-License-Identifier: Apache-2.0
+//
+


This is a "synthetic trait" (i.e. it doesn't exist in the Smithy spec, only in smithy-swift.)

It is used to signify inputs & outputs that were synthesized because either no shape or the Unit shape was targeted by an operation input/output.

jbelkins · 2026-01-19T22:07:07Z

Sources/Smithy/ShapeID.swift

        self.name = id.name
        self.member = member
    }



Below, clarified names around string conversions of Shape ID.

jbelkins · 2026-01-19T22:09:23Z

Sources/SmithyCodegenCLI/SmithyCodegenCLI.swift

@@ -12,34 +12,44 @@ import struct SmithyCodegenCore.CodeGenerator
 @main
 struct SmithyCodegenCLI: AsyncParsableCommand {



In this type below, added a service param for the Shape ID of the service to be generated, and got rid of a lot of logging we don't need.

Only thing that is now logged by the codegen CLI is what model was generated and the elapsed time.

jbelkins · 2026-01-19T22:10:24Z

Sources/SmithyCodegenCore/Model/Model+AST.swift


        // Initialize the properties of self
        self.init(version: astModel.smithy, metadata: astModel.metadata, shapes: shapes)
-


The functions below are moved elsewhere.

jbelkins · 2026-01-19T22:11:18Z

Sources/SmithyCodegenCore/Model/Model+AST.swift

@@ -56,14 +51,30 @@ extension Model {
            baseMembers["value"] = value
        }



The conversion below is needed because several AWS services still use the @enum trait to define enums, even though it is deprecated in Smithy 2.0.

jbelkins · 2026-01-19T22:12:20Z

Sources/SmithyCodegenCore/Model/Model+AST.swift

+                resourceIDs: try astShape.resources?.map { try $0.id } ?? [],
                errorIDs: try astShape.errors?.map { try $0.id } ?? []
            )
            return (shapeID, shape)


Below, resource shape is now added.

jbelkins · 2026-01-19T22:15:31Z

Sources/SmithyCodegenCore/Model/Model.swift

    init(version: String, metadata: Node?, shapes: [ShapeID: Shape]) {
        self.version = version
        self.metadata = metadata
        self.shapes = shapes


Shapes need a reference back to the model that contains them so that they can resolve their relations to other shapes.

Because of this relation, Shape must have a mutable property, and therefore can't be Sendable.

This is not a problem because the code generator is not asynchronous.

jbelkins · 2026-01-19T22:16:12Z

Sources/SmithyCodegenCore/Model/Model.swift

        }
        return shape
    }
+


Below are several convenience accessors for getting shapes of a certain type by ID.

jbelkins · 2026-01-19T22:19:29Z

Sources/SmithyCodegenCore/ModelTransformer/Model+Box.swift

+import struct Smithy.ShapeID
+
+extension Model {
+


This model transform is needed to generate code with the same optionality as the existing code generator.

It reproduces the logic in BoxServices.kt.

jbelkins · 2026-01-20T00:40:22Z

Plugins/SmithyCodeGeneratorPlugin/SmithyCodeGeneratorPlugin.swift

@@ -43,31 +43,40 @@ struct SmithyCodeGeneratorPlugin: BuildToolPlugin {

        let currentWorkingDirectoryFileURL = URL(fileURLWithPath: FileManager.default.currentDirectoryPath)



This file adds a service param, to specify the service in the model that should be built.

jbelkins · 2026-01-20T00:41:38Z

Sources/SmithyCodegenCore/ModelTransformer/Model+Deprecated.swift

+
+import Foundation
+
+extension Model {


This extension removes shapes that were deprecated prior to GA.

It duplicates logic in AWSDeprecatedShapeRemover.kt.

jbelkins · 2026-01-20T00:44:04Z

Sources/SmithyCodegenCore/ModelTransformer/Model+InputOutput.swift

+import struct Smithy.TargetsUnitTrait
+import struct Smithy.TraitCollection
+
+extension Model {


This model transformer:

adds empty structures to the model wherever an operation has no input/output, or the input/output targets Unit.

adds the UsedAsInputTrait & UsedAsInputTrait to inputs/outputs so codegen can reliably tell which shapes are inputs/outputs.

jbelkins · 2026-01-20T00:47:52Z

Sources/SmithyCodegenCore/ModelTransformer/Model+PruneToService.swift

+
+import struct Smithy.ShapeID
+
+extension Model {


This model transform deletes all shapes from the model that are not referenced directly or indirectly by the service being built.

jbelkins · 2026-01-20T00:49:36Z

Sources/SmithyCodegenCore/ModelTransformer/Model+Union.swift

+import enum Smithy.Prelude
+import struct Smithy.ShapeID
+
+extension Model {


This transform creates an associated empty structure for union cases that target Unit. (Our current codegen creates an empty structure for these cases, so we reproduce that behavior here.)

jbelkins · 2026-01-20T00:59:17Z

Sources/SmithyCodegenCore/Resources/DefaultSwiftHeader.txt

+// SPDX-License-Identifier: Apache-2.0
+//
+
+// Code generated by SmithyCodegenCLI. DO NOT EDIT!


The contents above are the header that gets put at the top of every Swift source file.

jbelkins · 2026-01-20T01:08:39Z

Sources/SmithyCodegenCore/Schemas/SchemasCodegen.swift

+import struct Smithy.ShapeID
+import enum Smithy.ShapeType
+
+package struct SchemasCodegen {


This type generates the schemas for the service.

Schemas are generated for:

the service

all operations

any model shape referenced by an operation's input, output, and errors.

Note that both shapes that generate to a custom Swift type (like Smithy structures, unions & enums) and shapes that don't (i.e. a map/list of some shape type, or a String, Integer, etc. with traits applied to it) will get schemas.

jbelkins · 2026-01-20T01:13:08Z

Sources/SmithyCodegenCore/Schemas/Shape+Schema.swift

+
+import struct Smithy.ShapeID
+
+extension Shape {


This extension provides the variable name for a schema.

The schema variable is constructed from the shape's ID, i.e. the schema var for com.amazonaws.ec2#AmazonEC2 would be:

schema__com_amazonaws_ec2__AmazonEC2

These schema vars are internal only, and are only referenced by generated code.

jbelkins · 2026-01-20T01:26:42Z

Sources/SmithyCodegenCore/Shape/ServiceShape.swift

+            try errorIDs.compactMap { try model.expectStructureShape(id: $0) }
+        }
+    }
+


Below,, there are methods for generating service-related names that closely follow those that are now used in Kotlin codegen.

jbelkins · 2026-01-20T01:27:58Z

Sources/SmithyCodegenCore/Shape/EnumShape.swift

+    }
+
+    override func immediateDescendants(includeInput: Bool, includeOutput: Bool) throws -> Set<Shape> {
+        try Set(members)


Each shape also gets an immediateDescendants method that is used to access the shapes referenced by a shape.

jbelkins · 2026-01-20T01:31:51Z

Sources/SmithyCodegenCore/Shape/Shape.swift

        new.model = model
        return new
    }



Below, public Shape properties descendants, inputDescendants, and outputDescendants are used to get a set of the shapes referenced by this shape.

These properties use the immediateDescendants() method on every shape subclass to get the exact shapes referenced by a particular shape.

jbelkins · 2026-01-20T01:50:37Z

Sources/SmithyCodegenCore/Shape/Shape.swift

+    /// - Parameters:
+    ///   - includeInput: Whether to include shapes that are associated with input
+    ///   - includeOutput: Whether to include shapes that are associated with input
+    /// - Returns: A set of shapes that this shape refers to.


Shape subclasses customize the method below to return their referenced shapes. This is used to build a set of shapes that are used in a services' inputs, outputs, or both.

jbelkins · 2026-01-20T01:52:14Z

Sources/SmithyCodegenCore/SwiftRendering/Node+Rendered.swift

+
+import enum Smithy.Node
+
+extension Node {


Renders a Node into generated Swift. The node is generated onto a single line, i.e. it's not "pretty printed".

jbelkins · 2026-01-20T01:53:31Z

Sources/SmithyCodegenCore/SwiftRendering/SwiftWriter.swift

+import struct Foundation.Data
+import struct Foundation.URL
+
+class SwiftWriter {


This type reproduces some of the functionality of the Kotlin codegen's SwiftWriter to write structured Swift code.

jbelkins · 2026-01-20T01:56:09Z

Sources/SmithyCodegenCore/TraitLibrary/DeprecatedTrait.swift

+//
+// SPDX-License-Identifier: Apache-2.0
+//
+


This trait is used by the model transformer above to remove deprecated shapes prior to codegen.

This trait is not used at runtime, so it does not appear in schemas.

jbelkins · 2026-01-20T01:57:37Z

Sources/SmithyCodegenCore/TraitLibrary/EnumTrait.swift

+import struct Smithy.ShapeID
+import protocol Smithy.Trait
+import struct Smithy.TraitError
+


This trait is the now-deprecated method of defining a Smithy enum.

This trait is converted to an enum with members when the model is loaded, so it is not referenced at runtime & doesn't appear in schemas.

jbelkins · 2026-01-20T01:59:35Z

Sources/SmithyCodegenCore/CodeGenerator.swift

 import struct Foundation.URL
+import struct Smithy.ShapeID

 public struct CodeGenerator {


The CodeGenerator now takes a service as a param, and actually generates schemas to be compiled.

jbelkins · 2026-01-20T02:00:35Z

Sources/SmithyCodegenCore/GenerationContext.swift

-        self.model = model
-        self.symbolProvider = SymbolProvider(service: service, model: model)
+    init(serviceID: ShapeID, model: Model) throws {
+


Below, several transforms (code is up above) are applied to the model after it is loaded, and before the model is used to generate code.

jbelkins · 2026-01-20T02:02:14Z

Sources/SmithyCodegenCore/HasShapeID.swift

+    var id: ShapeID { get }
+}
+
+extension Array where Element: HasShapeID {


This extension implements sorting with an algorithm equivalent to what is used by Kotlin, to ensure that sorted lists in this code generator match sorted lists in the Kotlin code generator.

jbelkins · 2026-01-20T02:03:42Z

Sources/SmithyCodegenCore/HasShapeID.swift

+//
+
+import struct Smithy.ShapeID
+


The purpose of the HasShapeID protocol is to extend collections with a custom sorting algorithm. (See the Array extension immediately below.)

jbelkins · 2026-01-20T02:06:50Z

Tests/SmithyCodegenCoreTests/SmithyCodegenCoreTests.swift

+import Smithy
+@testable import SmithyCodegenCore
+
+class SmithyCodegenCoreTests: XCTestCase {


When the code generator runs as part of the build process, the debugger does not attach to it, which makes it hard to debug code generator failures.

This test case runs the code generator in the context of an XCTest so that it may be debugged. The CBOR protocol test model is included here but any model may be copied into this test bundle's Resources and the test below may be modified to build its service.

jbelkins · 2026-01-20T20:20:38Z

Sources/Smithy/Schema/Schema.swift

+
+    /// Target schema is passed as an autoclosure so that schemas with self-referencing targets will not cause
+    /// an infinite loop when accessed.
+    private let _target: @Sendable () -> Schema?


The Schema target property, which references another Schema, has been changed to a closure because some models are self-referencing, and this can cause an infinite loop when creating or accessing schemas.

The Swift @autoclosure feature is used on the initializer to simplify generated code.

sichanyoo

Just one comment on module name for the plugin

sichanyoo · 2026-01-28T19:59:56Z

Package.swift

I know this isn't part of this PR but I think better name for this might be something like SmithyCodegenPlugin since it's just a build tool plugin that uses CLI.

An informal survey of plugins shows that about 50% use Plugin as part of their name:
https://github.com/BarredEwe/awesome-swift-plugins

If you want to add Plugin to the name of ours, I'll add it. (I'd prefer to do it in a separate PR though, for the purpose of managing size/conflicts in this one)

Add full-featured code generator

ed8cc78

jbelkins commented Jan 19, 2026

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jbelkins commented Jan 20, 2026

View reviewed changes

jbelkins added 3 commits January 19, 2026 20:09

Fix tests, remove unneeded code

52adbb5

Fix Swift 6 build

1483b46

Restore SmithyCBOR dependencies

e796292

jbelkins changed the title ~~Add full-featured code generator~~ feat: Add full-featured code generator Jan 20, 2026

jbelkins mentioned this pull request Jan 20, 2026

feat: Add full-featured code generator awslabs/aws-sdk-swift#2094

Merged

jbelkins commented Jan 20, 2026

View reviewed changes

jbelkins added 2 commits January 23, 2026 16:15

Comments and code cleanup

676d306

Fix swiftlint

a8e69ec

jbelkins marked this pull request as ready for review January 26, 2026 20:13

jbelkins requested review from dayaffe and sichanyoo January 26, 2026 20:14

sichanyoo reviewed Jan 29, 2026

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sichanyoo self-requested a review February 2, 2026 17:21

sichanyoo approved these changes Feb 2, 2026

View reviewed changes

Merge branch 'epic/sbs' into jbe/codegen_core

34e8709

aws-sdk-swift-automation merged commit a38fa1f into epic/sbs Feb 2, 2026
0 of 30 checks passed

aws-sdk-swift-automation deleted the jbe/codegen_core branch February 2, 2026 21:00

		@@ -12,34 +12,44 @@ import struct SmithyCodegenCore.CodeGenerator
		@main
		struct SmithyCodegenCLI: AsyncParsableCommand {


		// Initialize the properties of self
		self.init(version: astModel.smithy, metadata: astModel.metadata, shapes: shapes)

		@@ -56,14 +51,30 @@ extension Model {
		baseMembers["value"] = value
		}

		@@ -43,31 +43,40 @@ struct SmithyCodeGeneratorPlugin: BuildToolPlugin {

		let currentWorkingDirectoryFileURL = URL(fileURLWithPath: FileManager.default.currentDirectoryPath)

feat: Add full-featured code generator #1016

feat: Add full-featured code generator #1016

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jbelkins commented Jan 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Description of changes

Scope

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jbelkins commented Jan 19, 2026 •

edited

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sichanyoo Jan 28, 2026 •

edited

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