Bug 321684 – [CMake] Mac build fails to resolve the WebCore_Private module when ENABLE_BACK_FORWARD_LIST_SWIFT is off

• Status: RESOLVED
• Resolution: FIXED
• Component: New Bugs

[Basuke Suzuki]

The CMake macOS build fails when configured with --no-swift-back-forward-list (ENABLE_BACK_FORWARD_LIST_SWIFT=OFF):

    Source/WebKit/SwiftPrewarmMac.swift:27:8: error: unable to resolve module dependency: 'WebCore_Private'
    import WebCore_Private
           ^
    note: a dependency of main module 'SwiftPrewarmMac'

319083@main added unconditional imports of the WebKit stack's own modules to Source/WebKit/SwiftPrewarmMac.swift, including 'import WebCore_Private'. But staging the in-tree WebCore_Private module map into WebCore.framework/Versions/A/Modules/module.private.modulemap -- where the Swift Clang importer finds it via -F -- is gated on ENABLE_BACK_FORWARD_LIST_SWIFT in Source/WebCore/PlatformCocoa.cmake. With the feature off, WebCore.framework/Modules is left empty and the module cannot be resolved.

The prewarm target itself is not gated on that feature: on Cocoa SWIFT_REQUIRED is unconditionally ON (Source/cmake/OptionsCocoa.cmake), and Source/WebKit/CMakeLists.txt adds the prewarm target for 'SWIFT_REQUIRED AND WEBKIT_SDK_IS_MACOS'. So every macOS build with ENABLE_BACK_FORWARD_LIST_SWIFT=OFF is broken.

Steps to reproduce:

1. export BUILD_WEBKIT_ARGS=--no-swift-back-forward-list
2. Tools/Scripts/build-webkit --cmake --release

Fix: gate the module map staging on SWIFT_REQUIRED instead of ENABLE_BACK_FORWARD_LIST_SWIFT. The block already lives inside 'if (WEBKIT_SDK_IS_MACOS)', and the iOS path in the same file stages the map unconditionally, so this makes macOS match iOS.

[Basuke Suzuki]

rdar://184829371

[Basuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/71551

[EWS]

Committed 319166@main (ba82b6ab43ce): <https://commits.webkit.org/319166@main>

Reviewed commits have been landed. Closing PR #71551 and removing active labels.