Can't test macros on Xcode 15.1+

Development Macros
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1

Hi! I try to use new macros on Xcode 15.1+. I created a default template from Apple (File -> New -> Package -> Macro...) and tried to start tests on Simulator (iOS 17.0.1) and tests throws error about "Test skipped - macros are only supported when running tests for the host platform"

Any ideas what's the problem?

But how I noticed on Xcode 15.0.1 all good.

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2

Because macros run during compilation, they are executed on your Mac. You thus need to select your Mac as the run destination when testing macros.

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3

You might want to check out swift-macro-testing by PointFree: GitHub - pointfreeco/swift-macro-testing: Magical testing tools for Swift macros.

4

I was able to solve this by creating a bridge module that expose the implementation as macro while the implementation itself is linked as normal target so it can be seen from unit tests.

targets: [
    .target(
        name: "TestSwiftMacros",
        dependencies: [
            "TestSwiftMacrosBridge"
        ]
    ),
    .macro( // Exposes the implementation as macros
        name: "TestSwiftMacrosBridge",
        dependencies: [
            "TestSwiftMacrosImplementation",
            .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
            .product(name: "SwiftCompilerPlugin", package: "swift-syntax")
        ]
    ),
    .target( // The key is here, that the implementation is built as normal target
        name: "TestSwiftMacrosImplementation",
        dependencies: [
            .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
            .product(name: "SwiftCompilerPlugin", package: "swift-syntax")
        ]
    ),
    .testTarget(
        name: "TestSwiftMacrosTests",
        dependencies: [
            "TestSwiftMacrosImplementation",
            .product(name: "SwiftSyntaxMacrosTestSupport", package: "swift-syntax"),
        ]
    ),
]

Then in the bridge module, you will need to add a wrapper over the implementation

import TestSwiftMacrosImplementation
import SwiftCompilerPlugin
import SwiftSyntax
import SwiftSyntaxMacros

public struct TestSwiftMacroBridge: PeerMacro {
    public static func expansion(of node: AttributeSyntax,
                                 providingPeersOf declaration: some DeclSyntaxProtocol,
                                 in context: some MacroExpansionContext) throws -> [DeclSyntax] {
        try TestSwiftMacro.expansion(of: node, providingPeersOf: declaration, in: context)
    }
}

finally, update the main declaration to read the new bridge

@attached(member, names: arbitrary)
public macro TestSwift() = #externalMacro(module: "TestSwiftMacrosBridge", type: "TestSwiftMacroBridge")
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