Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 4e646d190c3faf19195be9e2532318526865044b
https://github.com/WebKit/WebKit/commit/4e646d190c3faf19195be9e2532318526865044b
Author: Ian Grunert <[email protected]>
Date: 2026-08-26 (Wed, 26 Aug 2026)
Changed paths:
M Source/WTF/Scripts/generate-platform-args
M Source/WebKit/CMakeLists.txt
M Source/WebKit/PlatformWin.cmake
A Source/WebKit/Scripts/generate-msvc-stl-modulemap.py
M Source/cmake/WebKitMacros.cmake
Log Message:
-----------
Fix the Swift clang importer on Windows: MSVC STL module visibility and more
https://bugs.webkit.org/show_bug.cgi?id=322271
Reviewed by Ian Grunert and Elliott Williams.
The Windows Swift build failed in the clang importer for several stacked
reasons:
1. The Swift SDK's vcruntime.modulemap wraps the MSVC STL in a clang
module whose yvals_core.h lives in an explicit submodule, so the
__cpp_lib_* feature-test macros never become visible to headers that
reach <version> through a module import. WTF/simdutf then mix
pre-C++20 and C++23 preprocessor paths. Seed the macros through the
platform-swift-args.resp response file (generate-platform-args
--stl-feature-macros); they must not go on the command line, which
already sits near the 32767-char CreateProcess limit that ninja hits
before swiftc-wrapper can expand its own response file.
2. The same modulemap names only two of the STL's __msvc_*.hpp internal
headers, leaving e.g. std::views::transform (__msvc_ranges_to.hpp)
invisible at use sites. Generate an amended modulemap listing all of
them and mount it over the MSVC include dir with a VFS overlay.
Alternatives considered:
1. Generate the amened modulemap directly in cmake rather than python.
This was more concise but was unusually complex cmake code.
2. Do not _generate_ an amended modulemap; instead ship a static one.
However, the SDK-provided VC modulemap is currently 796 lines which
would be troublesome to maintain if we forked. A live amendment
to insert the extra files seems less bad. (Licensing might also
have made this awkward.)
3. Instead of execute_process, use a add_custom_command such that the
python script runs in parallel with other build steps instead of
at each configure time. Architecturally nicer, but the extra
dependency edges, plus the need to respect CONFIGURE_DEPENDS
would have made this even more verbose (and it's only one of
hundreds of existing python invocations during cmake configure.)
4. List the headers which need to be added, instead of globbing.
Everyone knows globbing is fragile and bad. However, the list
of headers may also be fragile, and hopefully the use of
CONFIGURE_DEPENDS reduces the globbing risk by prompting
regeneration if the VC runtime header file set changes.
The reference for the limitations of the shipping modulemap is
rdar://185507163.
Co-Authored-By: Adrian Taylor <[email protected]>
Canonical link: https://commits.webkit.org/319854@main
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