Use-cases for Swift interop in .NET 10

[kotlarmilos]

Overview

This issue presents use-cases we want to support. They are required to define and limit the scope of Swift interop effort in .NET 10. While it's difficult to clearly specify the exact Swift language features that will be supported in the next release, we can establish our definition of done.

Milestone 1 – StoreKit2 purchase MVP

Implement basic purchase functionality without UI components. Below is an example of Swift pseudo code.

func requestProducts() async {
    do {
        let storeProducts = try await Product.products(for: productIdentifiers)
        products = storeProducts
    } catch {
        print("Error fetching products: \(error)")
    }
}

func purchase(_ product: Product) async throws -> Transaction? {
    let result = try await product.purchase()
    return result
}

Objectives

• Establish projection tooling skeleton: parsers->marshalers->emitters
• Project structs and it's members
• Project Swift runtime features: metadata, value witness table, and async
• Project optional types
• Project Swift errors/exceptions in C#
• Project StoreKit2 types with its members needed for the basic purchase functionality. Specifically:
  • struct Product : Swift.Identifiable {}

Deliverables

• [Swift runtime features] Implement Swift metadata runtimelab#2838
• [Swift runtime features] Implement Swift value witness tables support runtimelab#2840
• [Swift language features] Implement Swift structs in C# runtimelab#2822
• [Swift language features] Implement Swift.Optional in C# runtimelab#2929
• [Swift language features] Implement Swift async runtimelab#2837
• [Swift language features] Implement Swift.Array in C# runtimelab#2833
• [Swift language features] Implement generic methods runtimelab#2940
• [Projection tooling] Implement type database runtimelab#2842
• [Swift language features] Implement Swift.Set in C# runtimelab#2834
• [Swift language features] Implement Swift.String in C# runtimelab#2831
• [Swift language features] Bind property getters runtimelab#2986
• [Swift language features] Implement Foundation.Data in C# runtimelab#2992

Risks

• Work items are too broad, which may affect group focus
• Significant fundamental work on the projection tooling in a single iteration

Milestone 2 – Subscriptions and list purchased products

Implement advanced purchase experience with subscriptions and list of already purchased products. Below is an example of Swift pseudo code.

func updateProductStatus() async {
    var purchasedProducts: [Product] = []

    for await result in Transaction.currentEntitlements {
        do {
            switch transaction.productType {
            case .nonConsumable:
                //
            case .nonRenewable:
                // 
            case .autoRenewable:
                // 
            default:
                break
            }
        } catch {
            print("Transaction failed verification: \(error)")
        }
    }
}

Objectives

• Project enums and it's members
• Project StoreKit2 types needed for subscriptions purchase functionality. Specifically:
  • struct Transaction : Swift.Identifiable {}
  • struct Product.Subscription* : Swift.Identifiable {}

Deliverables

• [Swift language features] Implement Swift generics support for structs runtimelab#2930
• [Swift language features] Implement Swift generics support for enums runtimelab#2931
• [Swift language feature] Support async generics methods & special-case Array/Set bound generics methods runtimelab#3001

Risks

• Limited functionality due to dependencies on other frameworks

Milestone 3 – Pack StoreKit2 bindings in the experimental NuGet

Pack and distribute StoreKit2 bindings for supported scenarios.

Objectives

• Implement in-app purchase using StoreKit bindings NuGet
• Make the projection tooling extensible and ensure it outputs only supported types
• Implement simple KPI metrics

Deliverables

• [Projection tooling] Add symbols from dynamic library to type database runtimelab#2918
• [Swift ABI compatibility] Implement correct memory handling in C# bindings runtimelab#2851
• [Swift shipping] Implement testing framework runtimelab#2850

Risks

• Limited functionality due to dependencies on other frameworks
• Incomplete / non-functional bindings
• Poor UX

Note

This effort is experimental and not officially supported.

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Issue Details

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Description

This issue tracks the top-level scenarios for end-users regarding .NET Swift interop. The goal is to demonstrate the practical application of .NET Swift interop within Maui scenarios. One possible approach is to select an existing Maui sample from https://github.com/dotnet/maui-samples and improve it by incorporating native libraries and widgets, such as UIKit or SwiftUI. There are some other ideas, which may be desirable but not required, and will be added later.

Below is a list of tasks that needs to be implemented. Please note that the breakdown of the issues does not impose hard deadlines. If some of the functionality does not get upstreamed for a particular preview version, this issue will be updated accordingly.

Tasks

.NET9 Preview 1

• Compile a list of libraries and features to support in .NET 9
• Select Maui applications to showcase the .NET Swift interop
• Propose design for VSCode extension

.NET9 Preview 2

• Update Maui applications to utilize the .NET Swift interop
• Implement and deploy the VSCode extension

.NET9 Preview 3

• Implement telemetry for BTfS usage
• Write a blog post that showcases the usage of .NET Swift interop

.NET9 Preview 4

TBD

Author:	kotlarmilos
Assignees:	kotlarmilos
Labels:	area-Meta, User Story
Milestone:	9.0.0