Bazel windows_support module

⚠️ Warning: Repository under construction, some extensions APIs and their behavior may change without notice

Hermetic provider of Windows headers and libraries for native compilation in Bazel. Currently available:

• Microsoft Visual C++ (MSVC) runtime
• Microsoft Windows SDK

It allows to build native code targeting Windows MSVC, from Linux, macOS or Windows using Bazel.

Installation

bazel_dep(name = "windows_support", version = "0.0.1")

# Warning: using the generated `@msvc_runtime` repository requires the machine to have the right to use the MSVC runtime, see section below for more information.
msvc_runtime = use_extension("@windows_support//windows:extensions.bzl", "msvc_runtime")
msvc_runtime.configure(
  msvc_version = "14.50.35717",
)
use_repo(msvc_runtime, "msvc_runtime")

windows_sdk = use_extension("@windows_support//windows:extensions.bzl", "windows_sdk")
windows_sdk.configure(
    windows_sdk_version = "10.0.26100.7705",
)
use_repo(windows_sdk, "windows_sdk")

The generated repositories expose their resolved version information as public Starlark constants:

load(
    "@msvc_runtime//:versions.bzl",
    "MSVC_COMPATIBILITY_VERSION",
    "MSVC_TOOLSET_VERSION",
    "VC_REDIST_VERSION",
)
load(
    "@windows_sdk//:versions.bzl",
    "WINDOWS_SDK_INCLUDE_VERSION",
    "WINDOWS_SDK_VERSION",
)

MSVC_TOOLSET_VERSION is the selected Contents/VC/Tools/MSVC/<version> directory. MSVC_COMPATIBILITY_VERSION is the corresponding compiler version accepted by Clang's -fms-compatibility-version. VC_REDIST_VERSION is discovered independently because the redistributable payload may have a different build version. WINDOWS_SDK_VERSION is the selected NuGet package version, while WINDOWS_SDK_INCLUDE_VERSION is discovered from the extracted include tree.

About msvc_runtime license requirement

Using files from the generated @msvc_runtime repository requires the machine using the windows module to have the right to use the MSVC (Microsoft Visual Studio C+) runtime headers and libraries. This is guarded by the user-defined BAZEL_MSVC_RUNTIME_VISUAL_STUDIO_EULA environment variable.

To use @msvc_runtime targets:

1. ensure that your machine is legally allowed to use the MSVC runtime
2. set the environment variable BAZEL_MSVC_RUNTIME_VISUAL_STUDIO_EULA to 1, e.g. via --repo_env=BAZEL_MSVC_RUNTIME_VISUAL_STUDIO_EULA=1

See https://visualstudio.microsoft.com/license-terms for more information.

VC redistributable DLLs

@msvc_runtime also exposes the Visual C++ redistributable runtime DLLs (vcruntime140.dll, vcruntime140_1.dll, msvcp140*.dll, concrt140.dll, vcomp140.dll, vcamp140.dll, ...), which binaries built against the dynamic CRT (/MD) need at runtime:

• @msvc_runtime//:vc_redist — release redist DLLs for the target platform (selects between the targets below)
• @msvc_runtime//:vc_redist_x64 / @msvc_runtime//:vc_redist_arm64 — per-architecture release redist DLLs
• @msvc_runtime//:vc_redist_debug (and :vc_redist_debug_x64 / :vc_redist_debug_arm64) — debug CRT DLLs (vcruntime140d.dll, msvcp140d.dll, ...), needed to run binaries built against the debug CRT (/MDd). ⚠️ These are not redistributable per the Visual Studio license: use them for development and testing only, never ship them.

For example, to package the redist DLLs next to a binary:

load("@rules_pkg//pkg:zip.bzl", "pkg_zip")

pkg_zip(
    name = "my_app_dist",
    srcs = [
        ":my_app",
        "@msvc_runtime//:vc_redist",
    ],
)

Notes:

• the redist DLLs only exist for the x64, x86 and arm64 architectures (no VC redistributable exists for arm or arm64ec, the latter uses the x64/arm64 redists)
• only the desktop flavor of the redist is exposed, the onecore flavor is not kept

Limitations

Sadly, that module is not perfect, there are several major limitations:

• Case-sensitive systems are poorly supported by the inefficient transformations attribute, we plan to support vfsoverlay configuration in the future see #3
• The specified MSVC runtime version must be present in the Visual Studio installer manifest specified or resolved from the Visual Studio channel, it cannot be any version
• Declaring multiple repositories for multiple versions of the MSVC runtime to coexist is unsupported
• Declaring multiple repositories for multiple versions of the Windows SDK to coexist is unsupported

Reproducibility

Visual Studio installer manifest URL is resolved from the channel URL specified by visual_studio_channel_url (defaulting to https://aka.ms/vs/stable/channel). That URL resolution is cached in your MODULE.bazel.lock to ensure reproducibility.

However, alternatively you could set the Visual Studio installer manifest URL and integrity manually to avoid channel resolution:

bazel_dep(name = "windows_support", version = "0.0.1")

msvc_runtime = use_extension("@windows_support//windows:extensions.bzl", "msvc_runtime")
msvc_runtime.configure(
  msvc_version = "14.50.35717",
  visual_studio_installer_manifest_url = "https://download.visualstudio.microsoft.com/download/pr/fdc37f6e-59f6-4054-838a-b476eeaa6ec3/1d82370739911457e0a2f6be15d8b5f569531b352b2eabb961429eea1e99e356/VisualStudio.vsman",
  visual_studio_installer_manifest_integrity = "sha256-qOhU+p8/uurCfXME4pfxZg1xN0ATid61fPeYPzPBb+8=",
)
use_repo(msvc_runtime, "msvc_runtime")

windows_sdk = use_extension("@windows_support//windows:extensions.bzl", "windows_sdk")
windows_sdk.configure(
    windows_sdk_version = "10.0.26100.7705",
    windows_sdk_integrity = {
      "Microsoft.Windows.SDK.CPP": "sha256-/0VWYL7gcadEcVqWZWZvopwHaBV509gVlZqe7FpVZCQ=",
      "Microsoft.Windows.SDK.CPP.x64": "sha256-rWzpD/lAEGmdKVSLPCseUsieuBFD4hmRVdmlw4ABtSs=",
      "Microsoft.Windows.SDK.CPP.arm64": "sha256-A7wMA9Q5zvhQdLvNQl+dXTptO0Z5Z6zSHaO6bf7q+mc="
    },
)
use_repo(windows_sdk, "windows_sdk")

Case-sensitive filesystem support

This is an example on how case-sensitive filesystems can be supported. This example does two things:

• naively lowercases (while keeping originals) headers and libraries files, either by symlinking (if supported) or copying them
• transforms (while keeping originals) to some cased variant observed in some C sources in the wild, either by symlinking (if supported) or copying them

windows_sdk = use_extension("@windows_support//windows:extensions.bzl", "windows_sdk")
windows_sdk.configure(
    windows_sdk_version = "10.0.26100.7705",
    transformations = {
        "base/c/Include/10.0.26100.0/shared/driverspecs.h": "base/c/Include/10.0.26100.0/shared/DriverSpecs.h",
        "base/c/Include/10.0.26100.0/shared/specstrings.h": "base/c/Include/10.0.26100.0/shared/SpecStrings.h",
        "base/c/Include/10.0.26100.0/um/ole2.h": "base/c/Include/10.0.26100.0/um/Ole2.h",
        "base/c/Include/10.0.26100.0/um/olectl.h": "base/c/Include/10.0.26100.0/um/OleCtl.h",
        "**/*.h": "lowercase",
        "**/*.lib": "lowercase",
        "**/*.Lib": "lowercase",
    },
)
use_repo(windows_sdk, "windows_sdk")

Acknowledgements

• The resolution logic is heavily inspired by lorenz/winsysroot, thank you Lorenz!