8000 [WIP] DO NOT MERGE - [core] Remove `@unchecked Sendable` from Lambda Runtime (depends on PR#508) by sebsto · Pull Request #526 · swift-server/swift-aws-lambda-runtime · GitHub
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[WIP] DO NOT MERGE - [core] Remove @unchecked Sendable from Lambda Runtime (depends on PR#508) #526

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[WIP] DO NOT MERGE - [core] Remove @unchecked Sendable from Lambda Runtime (depends on PR#508) #526

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@sebsto sebsto commented Jul 2, 2025 •
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This PR depends on #508

When removing the NIOLockedBox, we wanted to remove the last @unchecked Sendable in the code.

Motivation:

There is no good reason to bypass compiler verifications with @unchecked Sendable in this scenario. We would like to bring the extra verifications' benefit to the user of the library.

Modifications:

Lambda handlers and all depending structs and functions are tagged @sendable

Result:

This adds a requirement on user defined handlers (the public API of this library).
Code like

let handler:
    (Event, LambdaContext) async throws -> Response = {
        (request: Event, context: LambdaContext) in
    ...
    return Response() 
}
let runtime = LambdaRuntime(body: handler) 
try await runtime().run()

is no longer accepted. The handler must marked @Sendable

let handler:
    @Sendable (Event, LambdaContext) async throws -> Response = {
        (request: Event, context: LambdaContext) in
    ...
    return Response() 
}

Fortunately, thanks to the compiler type inference, this does not affect handlers passed as a closure, such as

let runtime = LambdaRuntime {
    (event: HelloRequest, context: LambdaContext) in

    HelloResponse(
        greetings: "Hello \(event.name). You look \(event.age > 30 ? "younger" : "older") than your age."
    )
}

As we expect this is the preferred way to write a handler, we think the change in the public API is acceptable. Only more advanced users will have to explicitly add the @Sendable conformance to their standalone handler functions.

@sebsto sebsto changed the title [WIP] DO NOT MERGE - Remove @unchecked Sendable from Lambda Runtime [WIP] DO NOT MERGE - Remove @unchecked Sendable from Lambda Runtime (depends on PR#508) Jul 2, 2025
@sebsto sebsto self-assigned this Jul 2, 2025
@sebsto sebsto added the ⚠️ semver/major Breaks existing public API. label Jul 2, 2025
@sebsto sebsto changed the title [WIP] DO NOT MERGE - Remove @unchecked Sendable from Lambda Runtime (depends on PR#508) [WIP] DO NOT MERGE - [core] Remove @unchecked Sendable from Lambda Runtime (depends on PR#508) Jul 2, 2025
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sebsto commented Jul 3, 2025

We decided to not force Sendable on Handler. This commit should allow that
7b50167

@sebsto sebsto closed this Jul 3, 2025
@sebsto sebsto deleted the sebsto/handler+sendable branch July 4, 2025 05:50
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