swiftlang · slavapestov · Jan 11, 2017 · Nov 21, 2016
diff --git a/docs/Windows.md b/docs/Windows.md
@@ -38,7 +38,114 @@ Additionally, the ICU headers and libraries need to be provided for the build.
 ```
 
 ## MSVC
-To be filled in.
+- Windows doesn't currently have a build script. You'll need to run commands manually to build Swift on Windows.
+- Release/RelWithDebInfo modes have not been tested and may not be supported.
+- Windows support for Swift is very much a WIP, and may not work on your system.
+
+### 1. Install dependencies
+- Make sure to add Python, CMake and Ninja to your `Path` environment variable
+1. Latest version (2.7.12 tested) of [Python 2](https://www.python.org/downloads/)
+2. Latest version (3.7.0-rc3 tested) of [CMake](https://cmake.org/download/)
+3. Latest version (1.7.1 tested) of [Ninja](https://github.com/ninja-build/ninja/releases/latest)
+4. Latest version (2015 Update 3 tested) of [Visual Studio](https://www.visualstudio.com/downloads/)
+- Make sure to include `Programming Languages|Visual C++`, and `Windows and Web Development|Universal Windows App Development|Windows SDK` in your installation.
+- Windows SDK 10.0.10240 was tested. Some later versions (e.g. 10.0.14393) are known not to work, as they are not supported by `compiler-rt`.
+
+### 2. Clone the repositories
+1. Create a folder to contain all the Swift repositories
+2. `apple/swift-cmark` into a folder named `cmark`
+3. `apple/swift-clang` into a folder named `clang`
+5. `apple/swift-llvm` into a folder named `llvm`
+5. `apple/swift` into a folder named `swift`
+- Currently, other repositories in the Swift project have not been tested, and may not be supported.
+
+### 3. Build ICU
+1. Download and extract the [ICU source code](http://site.icu-project.org/download) to a folder named `icu` in the same directory as the other Swift project repositories.
+2. Open `src/win32/allinone.sln` in Visual Studio.
+3. Make sure to select the correct architecture from the drop-down in Visual Studio.
+4. Right click on the solution in the Solution Explorer window and select `Build Solution`.
+5. When this is done, add the `<icu-source>/bin` folder to your `Path` environment variable.
+
+### 4. Get ready
+- From within a **developer** command prompt, execute the following command if you have an x64 PC.
+```
+"C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/vcvarsall.bat" amd64
+```
+- Then adapt the following command, and run it.
+```
+set swift_source_dir=path-to-directory-containing-all-cloned-repositories
+```
+
+### 5. Build CMark
+- This must be done from within a developer command prompt, and could take up to 10 minutes.
+```
+mkdir "%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"
+pushd "%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64"
+cmake -G "Ninja" "%swift_source_dir%/cmark"
+popd
+cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/cmark-windows-amd64/"
+```
+
+### 6. Build LLVM/Clang/Compiler-RT
+- This must be done from within a developer command prompt, and could take up to 5 hours.
+```
+mklink /J "%swift_source_dir%/llvm/tools/clang" "%swift_source_dir%my-swift/clang"
+mklink /J "%swift_source_dir%/llvm/tools/compiler-rt" "%swift_source_dir%/compiler-rt"
+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_TOOL_SWIFT_BUILD=NO^
+ -DLLVM_INCLUDE_DOCS=TRUE^
+ -DLLVM_TOOL_COMPILER_RT_BUILD=TRUE^
+ -DLLVM_BUILD_EXTERNAL_COMPILER_RT=TRUE^
+ -DLLVM_LIT_ARGS=-sv^
+ "%swift_source_dir%/llvm"
+popd
+cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"
+```
+
+### 7. Build Swift
+- This must be done from within a developer command prompt, and could take up to 2 hours.
+- 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/ninja"
+pushd "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64/ninja"
+cmake -G "Ninja" "%swift_source_dir%/swift"^
+ -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_UC_INCLUDE_DIRS="%swift_source_dir%/icu/include"^
+ -DICU_UC_LIBRARY_DIRS="%swift_source_dir%/icu/lib64"^
+ -DICU_I18N_INCLUDE_DIRS="%swift_source_dir%/icu/include"^
+ -DICU_I18N_LIBRARY_DIRS="%swift_source_dir%/icu/lib64"^
+ -DICU_UC_LIB_NAME="icuuc"^
+ -DICU_I18N_LIB_NAME="icuin"^
+ -DSWIFT_INCLUDE_DOCS=FALSE^
+ -DSWIFT_INCLUDE_TESTS=FALSE^
+ -DSWIFT_BUILD_SDK_OVERLAY=FALSE^
+ -DSWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER=FALSE^
+ -DPYTHON_EXECUTABLE="python"
+popd
+cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/swift-windows-amd64/ninja"
+```
+
+## Clang-cl
+
+Follow the instructions for MSVC, but add the following lines to each CMake configuration command. We need to use LLVM's `lld-link.exe` linker, as MSVC's `link.exe` crashes due to corrupt PDB files using `clang-cl`. `Clang-cl` 3.9.0 has been tested.
+
+```
+ -DCMAKE_C_COMPILER="<path-to-llvm-bin>/clang-cl.exe"^
+ -DCMAKE_CXX_COMPILER="<path-to-llvm-bin>/bin/clang-cl.exe"^
+ -DCMAKE_LINKER="<path-to-llvm-bin>/lld-link.exe"^
+```
+
 
 ## Windows Subsystem for Linux (WSL)
 - Note that all compiled Swift binaries are only executable within Bash on Windows and are Ubuntu, not Windows, executables.