C++ code fails to find libc++ headers using the WebAssembly Swift SDK

[jakepetroules]

Is it reproducible with SwiftPM command-line tools: swift build, swift test, swift package etc?

• Confirmed reproduction steps with SwiftPM CLI. The description text must include reproduction steps with either of command-line SwiftPM commands, swift build, swift test, swift package etc.

Description

Builds will fail to find standard C++ headers when using a WebAssembly Swift SDK.

This is due to the following code in SwiftPM passing a hardcoded sysroot (using --sysroot) for WASM triples:

/// Returns a default Swift SDK of a given target environment.
public static func defaultSwiftSDK(
    for targetTriple: Triple,
    hostSDK: SwiftSDK,
    environment: Environment = .current
) -> SwiftSDK? {
    if targetTriple.isWASI() {
        let wasiSysroot = hostSDK.toolset.rootPaths.first?
            .parentDirectory // usr
            .appending(components: "share", "wasi-sysroot")
        return SwiftSDK(
            targetTriple: targetTriple,
            toolset: hostSDK.toolset,
            pathsConfiguration: .init(sdkRootPath: wasiSysroot)
        )
    }

On my system, that expands to:

$HOME/Library/Developer/Toolchains/swift-6.1-RELEASE.xctoolchain/usr/share/wasi-sysroot

which does not exist. The actual path should be:

$HOME/Library/org.swift.swiftpm/swift-sdks/swift-wasm-6.1-RELEASE-wasm32-unknown-wasi.artifactbundle/6.1-RELEASE-wasm32-unknown-wasi/wasm32-unknown-wasi

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

• git clone https://github.com/swiftlang/swift-build
• cd swift-build
• swift build --triple wasm32-unknown-wasi --swift-sdk swift-wasm-6.1-RELEASE-wasm32-unknown-wasi

Swift Package Manager version/commit hash

6.1-RELEASE

Swift & OS version (output of swift --version ; uname -a)

Apple Swift version 6.1 (swift-6.1-RELEASE)
Target: arm64-apple-macosx15.0

[jakepetroules]

It looks like this "defaultSwiftSDK" function is actually behaving as a sort of override. Should the WASI branch in there simply be removed? @MaxDesiatov, I'm assuming you have the most knowledge in this area.

[MaxDesiatov]

cc @kateinoigakukun

[kateinoigakukun]

So I think this issue can be split into two issues:

1. --swift-sdk option is ignored when --triple is specified per --swift-sdk option cannot uniquely select a Swift SDK #7973
2. Since we dropped support for Wasm "toolchain" (not Swift SDK for Wasm), the targetTriple.isWASI() branch no longer makes sense.