[piercifani]

Stack 23/23 · base: jni/22-export-control · previous: #26

Problem

Data, Date and URL reach Java as Swift-backed wrapper classes generated into every module's Java package. In a multi-module app, a URL returned by one module's API is a different Java type from the URL another module's API accepts, so the value can't be passed along. Optional URL? parameters weren't supported either. Skip bridges these as java.net.URI, java.util.Date and ByteArray.

Changes

This ports upstream swiftlang#952. With "foundationTypesAsJavaTypes": true:

Swift	Java / Kotlin
URL	java.net.URI
Date	java.util.Date
Data	byte[] / ByteArray
Locale	java.util.Locale
TimeZone	java.util.TimeZone

CGFloat is a double either way. The values conform to JavaValue in SwiftJavaRuntimeSupport, and no wrapper classes are generated.

On top of swiftlang#952, for features that only exist in this stack:

• Escaping closures (JNI: escaping closures taking jextracted types; @Sendable/@MainActor closure types #2) pass these values to Java as they are: jextract prints their @JavaInterface itself, and the values are JavaValues.
• Closures returned to Java (JNI: closures returned to Java, and optional closure parameters #21), such as a closure property's getter, box them with a new JavaObjectValueBridge.
• Protocols implemented in Java still skip them. wrap-java maps java.net.URI and the other types on its own terms.
• optionalsAsNullable (JNI: optionalsAsNullable passes optionals as nullable Java types #19) now also applies to an optional parameter whose Java type has a package, such as Optional<java.net.URI>. Before, the dots made that one-name spelling parse as a package plus a class named URI>, so the parameter stayed an Optional, and Kotlin saw a read-only property for a URL? var.

Kotlin in this PR

FoundationValuesTest.kt with Bookmarks.swift:

val bookmark = Bookmark.init(URI.create("https://swift.org/docs"), null, Date(1_700_000_000_123),
    byteArrayOf(1, 2, -1), Locale.forLanguageTag("pt-BR"), TimeZone.getTimeZone("Europe/Rome"), 1.5)
bookmark.icon = URI.create("https://swift.org/favicon.ico")      // var icon: URL?
bookmark.onOpen = { url: URI -> opened += url }                   // var onOpen: ((URL) -> Void)?
bookmark.observeVisits { url, date -> visit = url to date }       // @escaping (URL, Date) -> Void
bookmark.refreshed().get().time                                   // async -> Date

Why Skip needs it

Skip bridges these types by value, to the same Java types. On a production Skip Fuse app (9 Skip modules) run through this stack in annotated mode, with the app's bridging annotations as @JavaExport markers:

• skipped declarations went from 994 to 930, and none of the remaining ones are an optional URL parameter;
• javac errors in the generated Java went from 667 to 96. Most of that drop is the missing wrapper classes, plus the fix in JNI: choose what jextract exports with @JavaExport(false) and exportMode #26 for members that use unexported types.

Testing

• Kotlin sample: ./gradlew :Samples:SwiftJavaExtractJNIKotlinSampleApp:test passes (54 tests, including 3 in FoundationValuesTest).
• From jextract: Foundation values as standard Java types swiftlang/swift-java#952: JNIFoundationJavaTypesTests (3 tests) and FoundationJavaValueTests (5 tests on a real JVM).
• swift test passes.

🤖 Generated with Claude Code