Cannot build `SwiftKitSampleApp` with Swift 6.2 snapshot

[madsodgaard]

When trying to build the SwiftKitSampleApp with ./gradlew Samples:SwiftKitSampleApp:run using the latest 6.2 development snapshot (2025-05-15), the build fails:

[289/291] Linking JExtractSwiftTool-tool
[290/291] Applying JExtractSwiftTool-tool
error: a prebuild command cannot use executables built from source, including executable target 'JExtractSwiftTool-tool'
error: build planning stopped due to build-tool plugin failures

> Task :Samples:SwiftKitSampleApp:jextract FAILED

It builds fine in Swift 6.1.0.

Environment

swift --version
Apple Swift version 6.2-dev (LLVM 74f18b3ab32b72c, Swift 245514cab31b823)
Target: arm64-apple-macosx15.0
Build config: +assertions

java --version
openjdk 22 2024-03-19
OpenJDK Runtime Environment (build 22+36-2370)
OpenJDK 64-Bit Server VM (build 22+36-2370, mixed mode, sharing)

[ktoso]

Confirmed, I'll chat with swiftpm folks to see what the solution is supposed to be.

[ktoso]

The exact way we use this is

swift-java/Plugins/JExtractSwiftPlugin/JExtractSwiftPlugin.swift

Line 25 in 7a9ecb8

let toolURL = try context.tool(named: "JExtractSwiftTool").url

So we get the tool URL and use it in a prebuild command:

swift-java/Plugins/JExtractSwiftPlugin/JExtractSwiftPlugin.swift

Lines 68 to 77 in 7a9ecb8

	return [
	.prebuildCommand(
	displayName: "Generate Java wrappers for Swift types",
	executable: toolURL,
	arguments: arguments,
	// inputFiles: [ configFile ] + swiftFiles,
	// outputFiles: outputJavaFiles
	outputFilesDirectory: outputDirectorySwift
	)
	]

And this used to work on 6.0

[ktoso]

This seems to be intended behavior here's the test https://github.com/swiftlang/swift-package-manager/blame/e75b4d20bacef12cd5560bf34ca3708cccf84f01/Tests/BuildTests/PluginInvocationTests.swift#L983

if anything it seems the 6.0 was somehow letting it through by accident huh... We'll have to figure out how to solve this in 6.2 then, and what else we can do.

[ktoso]

It's likely that we need to abandon the prebuild command, I'm looking into it.