BridgeJS: Swift -> JS Optionals support

[krodak]

Introduction

This PR adds support for Swift Optionals when exporting Swift funcionality to JS / TS using BridgeJS plugin.

Overview

• Swift Optionals are represented by T | null union, as null explicitly represents intentional absent of value, which aligns with Swift's nil.
• for each parameter additional "isSome" flag is used to represent optionality.
• new shared extension Optionals were added to BridgeJSIntrinsics to keep generated Swift glue code sparse and reuse existing patterns. This required new protocols for case and associated enum value types, which
• for support of return values, new bjs module methods were added for JS lowering _swift_js_return_optional_<type>
• support for different Optional syntax was added (including typealiasing), so all of the below should work identically:

@JS func test(name: String?) -> String?
@JS func test(name: Optional<String>) -> Optional<String>
@JS func test(name: Swift.Optional<String>) -> Swift.Optional<String>
@JS func test(name: Swift.Optional<  String >) -> Swift.Optional< String. >
typealias OptionalName = String?
@JS func test(name: OptionalName) -> OptionalName

Examples

@JS class UserService {
    var userId: Int? 
    func findUser(id: Int) -> User?
    func process(data: String?) -> String
}

Generated TypeScript:

export interface UserService extends SwiftHeapObject {
    userId: number | null;
    findUser(id: number | null): User | null;
    process(data: string | null): string;
}

Testing

Added tests for different scenarios for all supported optional data types, including parameters, properties and return value usage.

Documentation

Extended current documentation with new Exporting-Swift-Optional.md

[Copilot]

Pull Request Overview

This PR adds comprehensive support for Swift Optional types when exporting Swift functionality to JavaScript/TypeScript using the BridgeJS plugin. Swift optionals are mapped to T | null union types in TypeScript, using null to represent the absence of a value which aligns with Swift's nil semantics.

Key changes include:

• Support for all optional syntax forms: T?, Optional<T>, Swift.Optional<T>, and type aliases
• Bidirectional optional handling for parameters, return values, and class properties
• New intrinsic functions for optional type bridging and lowering operations

Reviewed Changes

Copilot reviewed 57 out of 65 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
Sources/JavaScriptKit/BridgeJSInstrincics.swift	Adds extensive optional bridging support with new protocols and extension methods
Sources/JavaScriptKit/Documentation.docc/Articles/BridgeJS/Exporting-Swift/Exporting-Swift-Optional.md	Comprehensive documentation for optional types usage
Tests/BridgeJSRuntimeTests/ExportAPITests.swift	Test functions for all optional type scenarios
Plugins/BridgeJS/Sources/BridgeJSSkeleton/BridgeJSSkeleton.swift	Updates type system to include optional case
Plugins/BridgeJS/Sources/BridgeJSCore/ExportSwift.swift	Core optional type resolution and code generation logic

Comments suppressed due to low confidence (1)

Sources/JavaScriptKit/BridgeJSInstrincics.swift:1

• The function should be marked as consuming like other similar functions in this file to match the pattern used elsewhere for bridge lowering functions.

/// BridgeJS Intrinsics

---

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[Copilot]

There's a typo with an extra period before the closing angle bracket: String. > should be String >.

Suggested change

	@JS func test(name: Swift.Optional< String >) -> Swift.Optional< String. > { return name }
	@JS func test(name: Swift.Optional< String >) -> Swift.Optional< String > { return name }

[Copilot]

Wrong variable assignment: should assign to tmpRetString for object return storage, but this should likely be a different variable for optional object returns.

[kateinoigakukun]

Great job 👏