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[WinRT] Start exposing Windows Runtime headers to Swift #84669

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[WinRT] Start exposing Windows Runtime headers to Swift #84669

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7 changes: 7 additions & 0 deletions Runtimes/Overlay/Windows/clang/CMakeLists.txt
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Expand Up @@ -25,6 +25,12 @@ roots:
- name: module.modulemap
type: file
external-contents: "@CMAKE_CURRENT_SOURCE_DIR@/winsdk_shared.modulemap"
- name: "@WindowsSdkDir@/Include/@WindowsSDKVersion@/winrt"
type: directory
contents:
- name: module.modulemap
type: file
external-contents: "@CMAKE_CURRENT_SOURCE_DIR@/WinRT.modulemap"
- name: "@UniversalCRTSdkDir@/Include/@UCRTVersion@/ucrt"
type: directory
contents:
Expand Down Expand Up @@ -55,4 +61,5 @@ install(FILES
vcruntime.modulemap
winsdk_um.modulemap
winsdk_shared.modulemap
WinRT.modulemap
DESTINATION ${CMAKE_INSTALL_DATAROOTDIR})
1 change: 1 addition & 0 deletions Runtimes/Resync.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,7 @@ copy_files(public/Platform Overlay/Windows/clang
ucrt.modulemap
winsdk_um.modulemap
winsdk_shared.modulemap
WinRT.modulemap
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winsdk_winrt seems like a more consistent name? it would be ideal to import WinSDK.WinRT as opposed to import WinRT. the latter can cause lots of collisions with other WINMD based projection tools which will generate code in the WinRT module

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Is WinRT considered part of the Win32 SDK? I thought it was a separate parallel piece. The submodule support isn't sufficient to support that in Swift I think? So this will need to be a top-level module.

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there is just the "Windows SDK" . the distinction between Win32 and WinRT are the APIs used. but since the module is called WinSDK it seems appropriate to keep them all together? if WinSDK was named Win32 i would feel differently

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there are other submodules in WinSDK, so that should be fine?

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WinRT can't be a submodule of WinSDK mostly for build performance reasons. WinRT headers are huge, for instance for WinUI headers alone Clang produces a .pcm that is 300MB+ and takes over 10 minutes to precompile on my machine (with weak specs). Clang builds .pcms per top-level module, so all submodules are effectively merged into one. Similarly, Swift merges all submodules into a single module when importing them. That means that for a project that only uses Win32, clang would spend significant time prebuilding WinRT headers, and then Swift would spend time importing WinRT decls into Swift.

For this reason, I'm going to propose splitting WinRT headers into many top-level modules, e.g. having a top-level module WindowsXyz per windows.xyz.*.h. But that is out of scope of this PR ;)

the latter can cause lots of collisions with other WINMD based projection tools which will generate code in the WinRT module

Is WinRT a conventional name for some of the modules that are generated by other tools?

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For this reason, I'm going to propose splitting WinRT headers into many top-level modules, e.g. having a top-level module WindowsXyz per windows.xyz.*.h. But that is out of scope of this PR ;)

Does the fact that namespaces in WinRT can have cyclical dependencies affect this at all?

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Are you asking about namespaces that are redeclared across several different modules? Those aren't a problem, we run into the same situation with module std / module std_code / module std_config all redeclaring namespace std in libc++.

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@stevenbrix stevenbrix Oct 8, 2025 •
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No, i mean module Windows.xyz has a dependency on Windows.abc, but Windows.abc also has a dependency on Windows.xyz

namespace Windows.xyz {

   class XyzExample {
     void TakeAbc(Windows.abc abcClass);
   }
}

namespace Windows.abc {

  class AbcExample: XyzExample {
 
  }
}

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Oh, do you mean that they could have circular #includes? Then we'd have to make such headers a single module, yeah. Anyway, that would be an interesting question for future changes to the modulemap.

vcruntime.modulemap
vcruntime.apinotes)

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9 changes: 9 additions & 0 deletions lib/ClangImporter/ClangIncludePaths.cpp
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Expand Up @@ -506,6 +506,15 @@ void GetWindowsFileMappings(
if (!AuxiliaryFile.empty())
fileMapping.redirectedFiles.emplace_back(std::string(WinSDKInjection),
AuxiliaryFile);

llvm::sys::path::remove_filename(WinSDKInjection);
llvm::sys::path::remove_filename(WinSDKInjection);
llvm::sys::path::append(WinSDKInjection, "winrt", "module.modulemap");
AuxiliaryFile =
GetPlatformAuxiliaryFile("windows", "WinRT.modulemap", SearchPathOpts);
if (!AuxiliaryFile.empty())
fileMapping.redirectedFiles.emplace_back(std::string(WinSDKInjection),
AuxiliaryFile);
}

struct {
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6 changes: 6 additions & 0 deletions stdlib/cmake/WindowsVFS.yaml.in
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Expand Up @@ -15,6 +15,12 @@ roots:
- name: module.modulemap
type: file
external-contents: "@PROJECT_SOURCE_DIR@\\public\\Platform\\winsdk_shared.modulemap"
- name: "@UniversalCRTSdkDir@\\Include\\@UCRTVersion@\\winrt"
type: directory
contents:
- name: module.modulemap
type: file
external-contents: "@PROJECT_SOURCE_DIR@\\public\\Platform\\WinRT.modulemap"
- name: "@UniversalCRTSdkDir@\\Include\\@UCRTVersion@\\ucrt"
type: directory
contents:
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1 change: 1 addition & 0 deletions stdlib/public/Platform/CMakeLists.txt
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Expand Up @@ -469,6 +469,7 @@ if(WINDOWS IN_LIST SWIFT_SDKS)
vcruntime.modulemap
winsdk_um.modulemap
winsdk_shared.modulemap
WinRT.modulemap
DESTINATION "share"
COMPONENT sdk-overlay)
endif()
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31 changes: 31 additions & 0 deletions stdlib/public/Platform/WinRT.modulemap
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@@ -0,0 +1,31 @@
//===--- WinRT.modulemap --------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

module WinRT [system] {
link "WindowsApp.lib"
export *

module Base {
header "WinRTBase.h"
export *
}

module hstring {
header "hstring.h"
export *
}

module RoAPI {
header "roapi.h"
export *
}
}
8 changes: 8 additions & 0 deletions test/stdlib/WinRT_HSTRING.swift
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@@ -0,0 +1,8 @@
// RUN: %target-build-swift %s
// REQUIRES: OS=windows-msvc

// Make sure that importing WinRT brings in the HSTRING type.

import WinRT

public func usesHSTRING(_ x: HSTRING) {}