Smithy IDL 1.0 to 2.0 Migration Guide#

This guide describes how to migrate your models from Smithy IDL version 1.0 to version 2.0 without breaking your models or customers.

Update the model file version#

For each model file you are upgrading, change the version from 1 or 1.0 to 2.0. In the IDL this is controlled with the version statement, and in the AST it is controlled with the smithy top level property. For example, the following model:

$version: "1.0"
namespace smithy.example

string Foo

Should be updated to:

$version: "2"
namespace smithy.example

string Foo

An IDL model file may not have a version control statement at the top. In this case, it uses version 1.0 by default. For example:

namespace smithy.example

string Foo

Also needs to be updated to:

$version: "2"
namespace smithy.example

string Foo

Smithy's tooling is able to load both 1.0 model files and 2.0 model files into a single combined model. Therefore when migrating, it may be wise to migrate one file at a time.

Replace the box trait#

The box trait is removed in 2.0. Any shape marked with the box trait needs to be updated.

Boxed root-level shapes#

For non-member, root level shapes, simply remove the box trait. Root level shapes in Smithy 2.0 have no default values unless you explicitly assign them one.

This 1.0 model:

$version: "1.0"
namespace smithy.example

@box // < remove this
boolean MyBoolean

Becomes this 2.0 model:

$version: "2"
namespace smithy.example

boolean MyBoolean

Converting primitive root-level shapes from 1.0#

Some shapes in Smithy 1.0 had default zero values: boolean, byte, short, integer, long, float, and double. If you defined any of these shapes and did not mark them with the @box trait, add the @default trait to them set to false for booleans and 0 for numbers. Any member that targets them also need to repeat this default value on the member.

This 1.0 model:

$version: "1.0"
namespace smithy.example

boolean MyPrimitiveBoolean

boolean MyPrimitiveInteger

structure Foo {
    myBoolean: MyPrimitiveBoolean,
    myInteger: MyPrimitiveInteger
}

Becomes this 2.0 model:

$version: "2"
namespace smithy.example

@default(false)
boolean MyPrimitiveBoolean

@default(0)
boolean MyPrimitiveInteger

structure Foo {
    myBoolean: MyPrimitiveBoolean = false
    myInteger: MyPrimitiveInteger = 0
}

Boxed members#

If a member is marked with the box trait, replace the trait with a @default(null) trait to have the same effect of overriding the default value of the target shape.

This 1.0 model:

$version: "1.0"
namespace smithy.example

structure MyStructure {
    @box // change this to = null below
    foo: PrimitiveBoolean
}

Becomes this 2.0 model:

$version: "2"
namespace smithy.example

structure MyStructure {
    foo: PrimitiveBoolean = null
}

Convert set shapes to list shapes#

The set shape was deprecated for IDL 2.0. Each set shape must be replaced by a list shape with the uniqueItems trait.

For example, the following set:

$version: "1.0"
namespace smithy.example

set StringSet {
    member: String
}

Needs to be updated to:

$version: "2"
namespace smithy.example

@uniqueItems
list StringSet {
    member: String
}

Add the default trait to streaming blobs#

Members that target a blob shape with the streaming trait have always had an implicit default empty value. In IDL 2.0, that will become explicit. Any such members that are not already marked with the required trait will now need to be marked with the default trait.

For example, the following model:

$version: "1.0"
namespace smithy.example

structure OptionalStream {
    // This needs to be updated since it doesn't have the required or
    // default trait already.
    payload: StreamingBlob
}

structure RequiredStream {
    // This doesn't need to be updated because it already has the required
    // trait.
    @required
    payload: StreamingBlob
}

@streaming
blob StreamingBlob

Needs to be updated to:

$version: "2"
namespace smithy.example

structure OptionalStream {
    payload: StreamingBlob = ""
}

structure RequiredStream {
    @required
    payload: StreamingBlob
}

@streaming
blob StreamingBlob

Optional migration steps#

The following steps are not required to update a model to be fully compatible with 2.0, but instead are refactoring steps that can be taken to simplify a your model.

Move operation inputs and outputs inline#

The structures that define operation inputs and outputs very often use boilerplate names and for readability are usually placed close to their parent operation shapes to improve readability of the model. Smithy 2.0 introduced inline input and output, which allows you to define those shapes as part of the definition of the operation rather than separately. This improves readability and reduces the amount of boilerplate needed to model an operation. For example, the following model:

$version: "1.0"
namespace smithy.example

operation PutUser {
    input: PutUserInput,
    output: PutUserOutput
}

@input
structure PutUserInput {
    email: String,
    id: String,
    username: String,
    description: String
}

@output
structure PutUserOutput {}

can be updated to:

$version: "2"
namespace smithy.example

operation PutUser {
    input := {
        email: String
        id: String
        username: String
        description: String
    },
    output := {}
}

See also

the inline input / output section of the spec for more details.

Abstract shared shape configuration with mixins#

Models often have several shapes that refer to the same sets of members, or which share a set of trait configurations. For example, resource instance operations all require that the resource's identifiers be present in input. With Mixins, it is easy to simply share these member definitions without having to copy and paste them. The following model:

$version: "1.0"
namespace smithy.example

operation GetUser {
    input: GetUserInput,
    output: GetUserOutput
}

@input
structure GetUserInput {
    @required
    email: String,

    @required
    id: String,
}

@output
structure GetUserOutput {
    @required
    email: String,

    @required
    id: String,

    description: String
}

Can be updated to:

$version: "2"
namespace smithy.example

@mixin
structure UserIdentifiers {
    @required
    email: String

    @required
    id: String
}

operation GetUser {
    input := with [UserIdentifiers] {}
    output := with [UserIdentifiers] {
        description: String
    }
}

Similarly, Mixins can be useful if you have a shared set of traits that otherwise have to be copied and pasted.

See also

the mixins section of the spec for more details on how they work.

Use the target elision syntax sugar to reduce boilerplate#

Resource shapes contain a set of identifiers, but when writing structures that contain those identifiers you have to duplicate those definitions entirely. In IDL 2.0, you can use the target elision syntax with a structure bound to a resource. For example:

$version: "2"
namespace smithy.example

resource User {
    identifiers: {
        id: String
        email: String
    }
}

// The `for` syntax here determines which resource should be checked.
structure UserDetails for User {
    // With this syntax, the target is automatically inferred from the
    // resource.
    $id

    // Uncomment this to include an email member. Unlike with mixins, you
    // must opt in to the members that you want to include. This allows you
    // to have partial views of a resource, such as in a create operation
    // that does not bind all of the identifiers.
    // $email

    address: String
}

This syntax can also be used with mixins to more succinctly add additional traits to included members.

$version: "2"
namespace smithy.example

@mixin
structure UserIdentifiers {
    id: String
    email: String
}

structure UserDetails with [UserIdentifiers] {
    @required
    $id

    @required
    $email
}

Remove unsightly commas#

Smithy IDL 2.0 removed the need to include commas when defining, lists, maps, and shape properties. For example, the following model:

$version: "1.0"
namespace smithy.example

operation GetUser {
    input: GetUserInput,
    output: GetUserOutput,
    errors: [
        NotFoundError,
        AccessDeniedError,
    ],
}

can be updated to:

$version: "2"
namespace smithy.example

operation GetUser {
    input: GetUserInput
    output: GetUserOutput
    errors: [
        NotFoundError
        AccessDeniedError
    ]
}

Migrate trait-based string enums to enum shapes#

Smithy IDL 2.0 introduced two new shape types: enum and intEnum. While the latter is entirely new, the use case for the former was previously handled by applying the enum trait to a string shape. A major advantage of using the enum shapes is that each enum value is now a Member shapes. This means they can be individually targeted by traits, without having to have special handling inside of Smithy itself. Their definitions in the IDL are now also much more concise and readable. For example, the following model:

$version: "1.0"
namespace smithy.example

@enum([
    {
        name: "DIAMOND",
        value: "diamond"
    },
    {
        name: "CLUB",
        value: "club"
    },
    {
        name: "HEART",
        value: "heart"
    },
    {
        name: "SPADE",
        value: "spade"
    }
])
string Suit

can be updated to:

$version: "2"
namespace smithy.example

enum Suit {
    DIAMOND = "diamond"
    CLUB = "club"
    HEART = "heart"
    SPADE = "spade"
}