Building Swift on Windows

This document describes how to build Swift for Windows natively. See the Windows doc for more about what is possible with Swift on Windows.

There are two supported ways to build Swift on Windows, they are

Using clang-cl
Using the Microsoft Visual C++ compiler (MSVC)

clang-cl is recommended over MSVC for building Swift on Windows.

Although it is possible to build the compiler and the standard library with MSVC and to use those built products to compile a Swift program, it won't be possible to run the binary without separately obtaining the Swift runtime. On the other hand, clang-cl is able to build the runtime, which makes it possible to build and run all the components required for Swift natively on Windows.

clang should be 7.0 or newer. Visual Studio 2017 is needed in all cases as it provides some of the needed headers and libraries.

`clang-cl`

1. Install dependencies

Latest version of Visual Studio

Make sure to include “Programming Languages|Visual C++” and “Windows and Web Development|Universal Windows App Development|Windows SDK” in your installation.

2. Clone the repositories

Create a folder to contain all the Swift repositories
Clone apple/swift-cmark into a folder named cmark
Clone apple/swift-clang into a folder named clang
Clone apple/swift-llvm into a folder named llvm
Clone apple/swift-compiler-rt into a folder named compiler-rt
Clone apple/swift into a folder named swift
Clone apple/swift-corelibs-libdispatch into a folder named swift-corelibs-libdispatch

Currently, other repositories in the Swift project have not been tested and may not be supported.

3. Acquire ICU

Download ICU from ICU Project for Windows x64 and extract the binaries.
Add the bin64 folder to your Path environment variable.

4. Get ready

From within a developer command prompt (not PowerShell nor cmd, but the Visual Studio Developer Command Prompt), execute the following command if you have an x64 PC.

VsDevCmd -arch=amd64

If instead you're compiling for a 32-bit Windows target, adapt the arch argument to x86 and run

VsDevCmd -arch=x86

Then adapt the following command and run it. Make sure to use forward slashes (/) instead of backslashes (\) as the path separators. clang breaks with backslashed paths.

set swift_source_dir=path-to-directory-containing-all-cloned-repositories

Decide whether you want to build a release or debug version of Swift on Windows and replace the CMAKE_BUILD_TYPE parameter in the build steps below with the correct value (Debug, RelWithDebInfoAssert or Release) to avoid conflicts between the debug and non-debug version of the MSCRT library.
Set up the ucrt, visualc, and WinSDK modules by copying ucrt.modulemap located at swift/stdlib/public/Platform/ucrt.modulemap into ${UniversalCRTSdkDir}/Include/${UCRTVersion}/ucrt as module.modulemap, copying visualc.modulemap located at swift/stdlib/public/Platform/visualc.modulemap into ${VCToolsInstallDir}/include as module.modulemap, and copying winsdk.modulemap located at swift/stdlib/public/Platform/winsdk.modulemap into ${UniversalCRTSdkDir}/Include/10.0.107663/um

5. Build CMark

This must be done from within a developer command prompt. CMark is a fairly small project and should only take a few minutes to build.

mkdir "%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"
pushd "%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"
cmake -G "Ninja" -DCMAKE_BUILD_TYPE=Debug "%swift_source_dir%/cmark"
popd
cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64/"

6. Build LLVM/Clang

This must be done from within a developer command prompt. LLVM and Clang are large projects, so building might take a few hours. Make sure that the build type (e.g. Debug, Release, RelWithDebInfoAssert) for LLVM/Clang matches the build type for Swift.

mkdir "%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"
pushd "%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"
cmake -G "Ninja"^
 -DLLVM_ENABLE_ASSERTIONS=TRUE^
 -DCMAKE_BUILD_TYPE=Debug^
 -DLLVM_ENABLE_PROJECTS=clang^
 -DLLVM_TARGETS_TO_BUILD=X86^
 -DLLVM_DEFAULT_TARGET_TRIPLE=x86_64-unknown-windows-msvc^
 "%swift_source_dir%/llvm"
popd
cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"

Store the LLVM bin directory in an environment variable so it can be used to build Swift. Assuming you followed the instructions exactly, the path below is correct, but it may be different based on your build variant and platform, so double check.

set llvm_bin_dir="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64/bin"

7. Build Swift

This must be done from within a developer command prompt and could take hours depending on your system.
You may need to adjust the SWIFT_WINDOWS_LIB_DIRECTORY parameter depending on your target platform or Windows SDK version.

mkdir "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"
pushd "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"
cmake -G "Ninja"^
 -DCMAKE_BUILD_TYPE=Debug^
 -DCMAKE_C_COMPILER="%llvm_bin_dir%/clang-cl.exe"^
 -DCMAKE_CXX_COMPILER="%llvm_bin_dir%/clang-cl.exe"^
 -DSWIFT_PATH_TO_CMARK_SOURCE="%swift_source_dir%/cmark"^
 -DCMAKE_CXX_FLAGS="-Wno-c++98-compat -Wno-c++98-compat-pedantic"^
 -DCMAKE_EXE_LINKER_FLAGS:STRING="/INCREMENTAL:NO"^
 -DCMAKE_SHARED_LINKER_FLAGS="/INCREMENTAL:NO"^
 -DSWIFT_INCLUDE_DOCS=NO^
 -DSWIFT_PATH_TO_LLVM_SOURCE="%swift_source_dir%/llvm"^
 -DSWIFT_PATH_TO_CLANG_SOURCE="%swift_source_dir%/clang"^
 -DSWIFT_PATH_TO_LIBDISPATCH_SOURCE="%swift_source_dir%/swift-corelibs-libdispatch"^
 -DSWIFT_PATH_TO_LLVM_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"^
 -DSWIFT_PATH_TO_CLANG_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"^
 -DSWIFT_PATH_TO_CMARK_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"^
 -DSWIFT_WINDOWS_x86_64_ICU_UC_INCLUDE="%swift_source_dir%/icu/include"^
 -DSWIFT_WINDOWS_x86_64_ICU_UC="%swift_source_dir%/icu/lib64/icuuc.lib"^
 -DSWIFT_WINDOWS_x86_64_ICU_I18N_INCLUDE="%swift_source_dir%/icu/include"^
 -DSWIFT_WINDOWS_x86_64_ICU_I18N="%swift_source_dir%/icu/lib64/icuin.lib"^
 -DCMAKE_INSTALL_PREFIX="C:/Program Files (x86)/Swift"^
 "%swift_source_dir%/swift"
popd
cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"

To create a Visual Studio project, you'll need to change the generator and, if you have a 64 bit processor, specify the generator platform. Note that you may get multiple build errors compiling the swift project due to an MSBuild limitation that file paths cannot exceed 260 characters. These can be ignored, as they occur after the build when writing the last build status to a file.

cmake -G "Visual Studio 2017" "%swift_source_dir%/swift"^
 -DCMAKE_GENERATOR_PLATFORM="x64"^
 ...

8. Build lldb

This must be done from within a developer command prompt and could take hours depending on your system.

mkdir "%swift_source_dir%/build/Ninja-DebugAssert/lldb-windows-amd64"
pushd "%swift_source_dir%/build/Ninja-DebugAssert/lldb-windows-amd64"
cmake -G "Ninja" "%swift_source_dir%/lldb"^
  -DCMAKE_BUILD_TYPE=Debug^
  -DLLDB_PATH_TO_CMARK_SOURCE="%swift_source_dir%/cmark"^
  -DLLDB_PATH_TO_LLVM_SOURCE="%swift_source_dir%/llvm"^
  -DLLDB_PATH_TO_CLANG_SOURCE="%swift_source_dir%/clang"^
  -DLLDB_PATH_TO_SWIFT_SOURCE="%swift_source_dir%/swift"^
  -DLLDB_PATH_TO_CMARK_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"^
  -DLLDB_PATH_TO_CLANG_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"^
  -DLLDB_PATH_TO_LLVM_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"^
  -DLLDB_PATH_TO_SWIFT_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"^
  -DLLVM_ENABLE_ASSERTIONS=YES
popd
cmake --build "%swift_source_dir%/build/Ninja-RelWithDebInfoAssert/lldb-windows-amd64"

9. Install Swift on Windows

Run ninja install:

pushd "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"
ninja install
popd

Add the Swift on Windows binaries path (C:\Program Files (x86)\Swift\bin) to the Path environment variable.
Add the Swift on Windows library path (C:\Program Files (x86)\Swift\lib\swift\windows) to the Path environment variable.

MSVC

Follow instructions 1-6 for clang-cl, but run the following instead to build Swift

mkdir "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"
pushd "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"
cmake -G "Ninja"^
 -DCMAKE_BUILD_TYPE=Debug^
 -DSWIFT_PATH_TO_CMARK_SOURCE="%swift_source_dir%/cmark"^
 -DSWIFT_PATH_TO_CMARK_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"^
 -DSWIFT_CMARK_LIBRARY_DIR="%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64/src"^
 -DSWIFT_PATH_TO_LLVM_SOURCE="%swift_source_dir%/llvm"^
 -DSWIFT_PATH_TO_LLVM_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"^
 -DSWIFT_PATH_TO_CLANG_SOURCE="%swift_source_dir%/llvm/tools/clang"^
 -DSWIFT_PATH_TO_CLANG_BUILD="%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"^
 -DICU_WINDOWS_x86_64_UC_INCLUDE="%swift_source_dir%/icu/include"^
 -DICU_WINDOWS_x86_64_UC_LIBRARY="%swift_source_dir%/icu/lib64/icuuc.lib"^
 -DICU_WINDOWS_x86_64_I18N_INCLUDE="%swift_source_dir%/icu/include"^
 -DICU_WINDOWS_x86_64_I18N_LIBRARY="%swift_source_dir%/icu/lib64/icuin.lib"^
 -DSWIFT_INCLUDE_DOCS=FALSE^
 -DSWIFT_INCLUDE_TESTS=FALSE^
 -DSWIFT_BUILD_DYNAMIC_SDK_OVERLAY=FALSE^
 -DSWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER=FALSE^
  "%swift_source_dir%/swift"
popd
cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64"