Xcode 26 / Unable to Find Module Dependency

[ianthetechie]

It looks like we have some update work to do for Xcode 26 builds. Helpfully, GitHub Actions run nondeterministically on different versions 😂

It looks like Xcode 26 may have changed something with implicit dependencies and/or the way modules get built. We may also need to update SwifSyntax.

Current Workaround

1. Set defaults write com.apple.dt.Xcode IDEPackageEnablePrebuilts NO
2. Clean, quit xcode, and nuke derived data

[ianthetechie]

Updating this with a bit more information. @scottrhoyt was able to find a workaround for this in #111.

But reports are mixed on whether it builds for various devs easily. I believe @scottrhoyt said it's working fine for him on macOS 26, but @Archdoog, also on macOS 26, hits the same issue as I reported + you can see in the old CI logs.

At present, we both get a compilation error along these lines. I am still on Sequoia 15.6.1, but am running Xcode 26.0.1. The warnings remain even after nuking derived data, pointing to the prebuilts being from an incompatible Swift SDK.

/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/StyleExpressionMacro.swift:96:15: warning: CanImport() evaluated to false due to invalid swiftmodule: /Users/ianthetechie/Library/Developer/Xcode/DerivedData/swiftui-dsl-etvkqzrkswffbucabclckawkattg/SourcePackages/prebuilts/swift-syntax/602.0.0/swiftlang-6.2.0.19.9-MacroSupport-macos_aarch64/Modules/SwiftSyntax601.swiftmodule
#if canImport(SwiftSyntax601)
              ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
warning: Module file '/Users/ianthetechie/Library/Developer/Xcode/DerivedData/swiftui-dsl-etvkqzrkswffbucabclckawkattg/SourcePackages/prebuilts/swift-syntax/602.0.0/swiftlang-6.2.0.19.9-MacroSupport-macos_aarch64/Modules/SwiftSyntaxBuilder.swiftmodule' is incompatible with this Swift compiler: SDK does not match (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
warning: Module file '/Users/ianthetechie/Library/Developer/Xcode/DerivedData/swiftui-dsl-etvkqzrkswffbucabclckawkattg/SourcePackages/prebuilts/swift-syntax/602.0.0/swiftlang-6.2.0.19.9-MacroSupport-macos_aarch64/Modules/SwiftCompilerPlugin.swiftmodule' is incompatible with this Swift compiler: SDK does not match (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
warning: Module file '/Users/ianthetechie/Library/Developer/Xcode/DerivedData/swiftui-dsl-etvkqzrkswffbucabclckawkattg/SourcePackages/prebuilts/swift-syntax/602.0.0/swiftlang-6.2.0.19.9-MacroSupport-macos_aarch64/Modules/SwiftSyntaxMacros.swiftmodule' is incompatible with this Swift compiler: SDK does not match (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
warning: Module file '/Users/ianthetechie/Library/Developer/Xcode/DerivedData/swiftui-dsl-etvkqzrkswffbucabclckawkattg/SourcePackages/prebuilts/swift-syntax/602.0.0/swiftlang-6.2.0.19.9-MacroSupport-macos_aarch64/Modules/SwiftSyntax.swiftmodule' is incompatible with this Swift compiler: SDK does not match (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/MapLibreSwiftMacrosPlugin.swift:1:8: error: Unable to find module dependency: 'SwiftCompilerPlugin'
import SwiftCompilerPlugin
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/MapLibreSwiftMacrosPlugin.swift:1:8: note: A dependency of main module 'MapLibreSwiftMacrosImpl'
import SwiftCompilerPlugin
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/MapLibreSwiftMacrosPlugin.swift:2:8: error: Unable to find module dependency: 'SwiftSyntaxMacros'
import SwiftSyntaxMacros
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/MapLibreSwiftMacrosPlugin.swift:2:8: note: A dependency of main module 'MapLibreSwiftMacrosImpl'
import SwiftSyntaxMacros
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/StyleExpressionMacro.swift:4:8: note: Also imported here
import SwiftSyntaxMacros
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/StyleExpressionMacro.swift:2:8: error: Unable to find module dependency: 'SwiftSyntax'
import SwiftSyntax
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/StyleExpressionMacro.swift:2:8: note: A dependency of main module 'MapLibreSwiftMacrosImpl'
import SwiftSyntax
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/StyleExpressionMacro.swift:3:8: error: Unable to find module dependency: 'SwiftSyntaxBuilder'
import SwiftSyntaxBuilder
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')
/Users/ianthetechie/swiftui-dsl/Sources/MapLibreSwiftMacrosImpl/StyleExpressionMacro.swift:3:8: note: A dependency of main module 'MapLibreSwiftMacrosImpl'
import SwiftSyntaxBuilder
       ^ (in target 'MapLibreSwiftMacrosImpl' from project 'MapLibreSwiftUI')

I wonder if this is a consequence of supporting both Swift 5 and 6?

At any rate, the workaround that Scott pushed in the PR does seem to work to unblock local development:

1. Execute defaults write com.apple.dt.Xcode IDEPackageEnablePrebuilts NO in a terminal.
2. Clean your project and nuke derived data.
3. Restart Xcode

[ianthetechie]

This issue from the Swift forums seems similar, but nobody mentions prebuilts: https://forums.swift.org/t/xcode-26-unable-to-find-module-dependency/80516/24

[scottrhoyt]

The issue here is a limitation of SPM prebuilts--which is now enabled by default in Xcode 26 and swift 6.2.

The failure happens in Xcode if you have a macro or a macro test that depends on a library that depends on swift-syntax.

Apparently there is some problem currently with mixing build environments between prebuilts and building from source when this happens. The case here--and with others in that thread--is due to depending on the swift-macro-testing library for tests which depends on and extends swift-syntax. This currently needs a full source build, which is why disabling prebuilts works. The main/non-testing targets compile fine against the prebuilts so consumers of this library willl still get that benefit. The error above is when building the whole package scheme which builds the tests as well.

I have the same problem as well on my local machine. My earlier reports of success were just building the non-test targets, which I'm assuming works for you as well?