Build and test Swift natively on a Windows host

.bazelci/presubmit.yml

@@ -39,12 +39,16 @@ x_defaults:
       - "-//test:output_file_map_default"
   windows_common: &windows_common
     platform: windows
-    build_flags:
-      # Override 'sandboxed' strategy set in .bazelrc because it's not
-      # available on Windows
-      - "--strategy=SwiftCompile="
     build_targets:
       - "//tools/..."
+      # Cross-platform Swift examples that exercise the Windows host toolchain:
+      # a `swift_binary` executable and a `linkshared` Windows DLL.
+      - "//examples/xplatform/hello_world"
+      - "//examples/xplatform/shared_library"
+    test_targets:
+      # Exercises XCTest discovery, the test runner, and `swift_test` execution
+      # on Windows.
+      - "//examples/xplatform/xctest"
 
 tasks:
   macos_latest:
@@ -97,11 +101,31 @@ tasks:
       - "curl https://download.swift.org/swift-${SWIFT_VERSION}-release/ubuntu2204/swift-${SWIFT_VERSION}-RELEASE/swift-${SWIFT_VERSION}-RELEASE-ubuntu22.04.tar.gz | tar xvz --strip-components=1 -C $SWIFT_HOME"
     <<: *linux_common
 
-  # TODO: re-enable when Windows in Bazel CI is properly configured for Swift.
-  # windows_last_green:
-  #   name: "Last Green Bazel"
-  #   bazel: last_green
-  #   <<: *windows_common
+  windows:
+    name: "Current LTS"
+    bazel: latest
+    # Expose the installed Swift toolchain and the MSVC/Windows SDK environment to
+    # the build. The swift.org installer (`batch_commands` below) records its
+    # Toolchains/Runtimes bin on the user's Path and sets SDKROOT, and a Visual
+    # Studio "developer prompt" (vcvars) would set INCLUDE/LIB for swiftc's clang
+    # to find the C headers (errno.h, ...) and for the linker — but none of that
+    # reaches the already-running CI process. Set it all here. BazelCI expands
+    # these with os.path.expandvars, so %VAR% resolves and earlier keys (listed
+    # first) are available to later ones. The VS/SDK versions are pinned to the
+    # Bazel CI Windows image; update them if `vcvars64.bat`'s output changes.
+    environment:
+      SWIFT_VERSION: "6.3.2"
+      VCToolsInstallDir: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2022\\BuildTools\\VC\\Tools\\MSVC\\14.39.33519"
+      WindowsSdkDir: "C:\\Program Files (x86)\\Windows Kits\\10"
+      WindowsSDKVersion: "10.0.26100.0"
+      Path: "%LOCALAPPDATA%\\Programs\\Swift\\Toolchains\\%SWIFT_VERSION%+Asserts\\usr\\bin;%LOCALAPPDATA%\\Programs\\Swift\\Runtimes\\%SWIFT_VERSION%\\usr\\bin;%LOCALAPPDATA%\\Programs\\Swift\\Tools\\%SWIFT_VERSION%;%VCToolsInstallDir%\\bin\\Hostx64\\x64;%WindowsSdkDir%\\bin\\%WindowsSDKVersion%\\x64;%PATH%"
+      SDKROOT: "%LOCALAPPDATA%\\Programs\\Swift\\Platforms\\%SWIFT_VERSION%\\Windows.platform\\Developer\\SDKs\\Windows.sdk"
+      INCLUDE: "%VCToolsInstallDir%\\include;%WindowsSdkDir%\\include\\%WindowsSDKVersion%\\ucrt;%WindowsSdkDir%\\include\\%WindowsSDKVersion%\\shared;%WindowsSdkDir%\\include\\%WindowsSDKVersion%\\um;%WindowsSdkDir%\\include\\%WindowsSDKVersion%\\winrt;%WindowsSdkDir%\\include\\%WindowsSDKVersion%\\cppwinrt"
+      LIB: "%VCToolsInstallDir%\\lib\\x64;%WindowsSdkDir%\\lib\\%WindowsSDKVersion%\\ucrt\\x64;%WindowsSdkDir%\\lib\\%WindowsSDKVersion%\\um\\x64"
+    batch_commands:
+      - "curl -sSL -o %TEMP%\\swift-installer.exe https://download.swift.org/swift-%SWIFT_VERSION%-release/windows10/swift-%SWIFT_VERSION%-RELEASE/swift-%SWIFT_VERSION%-RELEASE-windows10.exe"
+      - "%TEMP%\\swift-installer.exe -q"
+    <<: *windows_common
 
   doc_tests:
     name: "Doc tests"

.bazelrc

@@ -35,6 +35,12 @@ common:linux --repo_env=CC=clang
 build:linux --cxxopt='-std=c++17' --host_cxxopt='-std=c++17'
 common:linux --//test:apple_build_tests=False
 
+# Worker sandboxing copies the worker into a sandbox exec root and cleans it
+# between invocations. On Windows a running/recently-run executable cannot be
+# deleted, so that cleanup fails with "Permission denied". Run Swift workers
+# unsandboxed on Windows.
+build:windows --noworker_sandboxing
+
 # This C2K warning causes zlib to fail to compile.
 # There is an open issue about it on the zlib repository here:
 # https://github.com/madler/zlib/issues/633

swift/internal/compiling.bzl

@@ -1667,7 +1667,9 @@ def _declare_per_source_output_file(actions, extension, target_name, src):
         The declared `File`.
     """
     objs_dir = "{}_objs".format(target_name)
-    owner_rel_path = owner_relative_path(src)
+
+    # Spaces in object file paths break response-file parsing on Windows
+    owner_rel_path = owner_relative_path(src).replace(" ", "_")
     basename = paths.basename(owner_rel_path)
     dirname = paths.join(objs_dir, paths.dirname(owner_rel_path))
 

swift/internal/swift_autoconfiguration.bzl

@@ -179,6 +179,22 @@ def _normalized_linux_cpu(cpu):
         return "x86_64"
     return cpu
 
+def _normalized_windows_cpu(cpu):
+    """Normalizes a host CPU name to the value Swift uses on Windows.
+
+    The returned value is used both as the toolchain's `arch` and as the
+    architecture component of the Swift SDK's library layout (for example
+    `usr/lib/swift/windows/x86_64`) and the target triple.
+    """
+    cpu = cpu.lower()
+    if cpu in ("amd64", "x86_64", "x64"):
+        return "x86_64"
+    if cpu in ("arm64", "aarch64"):
+        return "aarch64"
+    if cpu in ("x86", "i686"):
+        return "i686"
+    return cpu
+
 def _resolve_toolchain_root(repository_ctx, swiftc_path):
     """Returns the Swift toolchain root directory for `swiftc_path`.
 
@@ -269,15 +285,28 @@ xcode_swift_toolchain(
         ]),
     )
 
+def _python_executable_works(repository_ctx, python_bin):
+    """Returns True if `python_bin` is a real, runnable Python 3 interpreter.
+
+    On Windows, `python3.exe`/`python.exe` found on `PATH` are frequently the
+    Microsoft Store "App execution alias" stubs rather than real interpreters:
+    when run non-interactively they print a message pointing at the Store and
+    exit nonzero. Probe the candidate so those stubs are skipped in favor of a
+    working interpreter later on `PATH`. We also confirm it is Python 3, since
+    the caller needs the Python 3 `plistlib` API.
+    """
+    result = repository_ctx.execute(
+        [python_bin, "-c", "import sys; print('ok' if sys.version_info[0] == 3 else 'no')"],
+    )
+    return result.return_code == 0 and result.stdout.strip() == "ok"
+
 def _get_python_bin(repository_ctx):
     if "PYTHON_BIN_PATH" in repository_ctx.os.environ:
         return repository_ctx.os.environ.get("PYTHON_BIN_PATH").strip()
-    out = repository_ctx.which("python3.exe")
-    if out:
-        return out
-    out = repository_ctx.which("python.exe")
-    if out:
-        return out
+    for name in ("python3.exe", "python3", "python.exe", "python"):
+        candidate = repository_ctx.which(name)
+        if candidate and _python_executable_works(repository_ctx, candidate):
+            return candidate
     return None
 
 def _create_windows_toolchain(*, repository_ctx):
@@ -294,6 +323,7 @@ Swift toolchain.
 """
 
     root = path_to_swiftc.dirname.dirname
+    arch = _normalized_windows_cpu(repository_ctx.os.arch)
     enabled_features = [
         SWIFT_FEATURE_CODEVIEW_DEBUG_INFO,
         SWIFT_FEATURE_DECLARE_SWIFTSOURCEINFO,
@@ -305,22 +335,34 @@ Swift toolchain.
     disabled_features = []
 
     version_file, parsed_version = _write_swift_version(repository_ctx, path_to_swiftc)
+
+    # Normalize SDKROOT to forward slashes with no trailing separator: the raw
+    # environment value typically ends in a backslash, which is both invalid at
+    # the end of a Python raw-string literal (used below) and produces doubled
+    # separators when joined.
+    sdkroot = repository_ctx.os.environ["SDKROOT"].replace("\\", "/").rstrip("/")
+
+    info_plist = sdkroot + "/../../../Info.plist"
+    python_bin = _get_python_bin(repository_ctx)
+    if not python_bin:
+        fail("Could not find a working Python 3 interpreter on PATH; it is " +
+             "required to read the XCTest version from the Swift SDK's Info.plist.")
     xctest_version = repository_ctx.execute([
-        _get_python_bin(repository_ctx),
+        python_bin,
         "-c",
-        "import os, plistlib; " +
-        "print(plistlib.loads(open(os.path.join(r'{}', '..', '..', '..', 'Info.plist'), 'rb').read(), fmt=plistlib.FMT_XML)['DefaultProperties']['XCTEST_VERSION'])".format(repository_ctx.os.environ["SDKROOT"]),
+        "import plistlib; " +
+        "print(plistlib.load(open(r'{}', 'rb'))['DefaultProperties']['XCTEST_VERSION'])".format(info_plist),
     ])
 
     env = {
         "Path": repository_ctx.os.environ["Path"] if "Path" in repository_ctx.os.environ else repository_ctx.os.environ["PATH"],
-        "ProgramData": repository_ctx.os.environ["ProgramData"],
+        "ProgramData": repository_ctx.os.environ.get("ProgramData", "C:\\ProgramData"),
     }
 
     return """\
 swift_toolchain(
   name = "windows-toolchain",
-  arch = "x86_64",
+  arch = "{arch}",
   features = [{features}],
   os = "windows",
   root = "{root}",
@@ -332,11 +374,12 @@ swift_toolchain(
   xctest_version = "{xctest_version}",
 )
 """.format(
+        arch = arch,
         features = ", ".join(['"{}"'.format(feature) for feature in enabled_features] + ['"-{}"'.format(feature) for feature in disabled_features]),
         root = root,
         env = env,
         parsed_version = parsed_version,
-        sdkroot = repository_ctx.os.environ["SDKROOT"].replace("\\", "/"),
+        sdkroot = sdkroot,
         xctest_version = xctest_version.stdout.rstrip(),
         version_file = version_file,
     )

swift/swift_test.bzl

@@ -94,6 +94,7 @@ def _generate_test_discovery_srcs(
         *,
         actions,
         deps,
+        env = {},
         name,
         objc_test_discovery,
         owner_module_name,
@@ -109,6 +110,9 @@ def _generate_test_discovery_srcs(
     Args:
         actions: The context's actions object.
         deps: The list of direct dependencies of the test target.
+        env: Environment variables to set when running the discovery tool. On
+            Windows this must include a `Path` that contains the Swift runtime
+            DLLs, otherwise the (Swift) discovery executable fails to launch.
         name: The name of the target being built, which will be used to derive
             the basename of the directory containing the generated files.
         objc_test_discovery: If `True`, the runner should use Objective-C-based
@@ -197,6 +201,7 @@ def _generate_test_discovery_srcs(
 
     actions.run(
         arguments = [args],
+        env = env,
         executable = test_discoverer,
         exec_group = _DISCOVER_TESTS_EXEC_GROUP,
         inputs = inputs,
@@ -411,6 +416,7 @@ def _swift_test_impl(ctx):
         discovery_srcs = _generate_test_discovery_srcs(
             actions = ctx.actions,
             deps = ctx.attr.deps,
+            env = toolchains.swift.test_configuration.env,
             name = ctx.label.name,
             objc_test_discovery = objc_test_discovery,
             owner_module_name = module_name,

swift/toolchains/BUILD

@@ -138,6 +138,21 @@ toolchain(
     visibility = ["//visibility:public"],
 )
 
+toolchain(
+    name = "windows-swift-toolchain-aarch64",
+    exec_compatible_with = [
+        "@platforms//os:windows",
+        "@platforms//cpu:aarch64",
+    ],
+    target_compatible_with = [
+        "@platforms//os:windows",
+        "@platforms//cpu:aarch64",
+    ],
+    toolchain = "@rules_swift_local_config//:windows-toolchain",
+    toolchain_type = "//toolchains:toolchain_type",
+    visibility = ["//visibility:public"],
+)
+
 # Consumed by Bazel integration tests.
 filegroup(
     name = "for_bazel_tests",

swift/toolchains/swift_toolchain.bzl

@@ -267,6 +267,7 @@ def _all_action_configs(os, arch, target_triple, sdkroot, xctest_version, additi
                     actions = all_compile_action_names() + [
                         SWIFT_ACTION_DUMP_AST,
                         SWIFT_ACTION_PRECOMPILE_C_MODULE,
+                        SWIFT_ACTION_SYMBOL_GRAPH_EXTRACT,
                     ],
                     configurators = [
                         add_arg(
@@ -294,6 +295,7 @@ def _all_action_configs(os, arch, target_triple, sdkroot, xctest_version, additi
                         actions = all_compile_action_names() + [
                             SWIFT_ACTION_DUMP_AST,
                             SWIFT_ACTION_PRECOMPILE_C_MODULE,
+                            SWIFT_ACTION_SYMBOL_GRAPH_EXTRACT,
                         ],
                         configurators = [
                             add_arg(
@@ -364,6 +366,13 @@ def _swift_windows_linkopts_cc_info(
         "-LIBPATH:{}".format(platform_lib_dir),
         "-LIBPATH:{}".format(paths.join(sdkroot, "..", "..", "Library", "XCTest-{}".format(xctest_version), "usr", "lib", "swift", "windows", arch)),
         runtime_object_path,
+        # Swift marks references to symbols in other modules (for example the
+        # type metadata accessors a generated test runner references via
+        # `@testable import`) as `dllimport`. Bazel links everything statically,
+        # so those symbols resolve locally and `link.exe` emits LNK4217. The
+        # warning is benign for static linking; suppress it so it is not fatal
+        # under `/WX` (treat-warnings-as-errors).
+        "-IGNORE:4217",
     ]
 
     return CcInfo(
@@ -480,6 +489,17 @@ def _entry_point_linkopts_provider(*, entry_point_name):
         linkopts = ["-Wl,--defsym,main={}".format(entry_point_name)],
     )
 
+def _windows_entry_point_linkopts_provider(*, entry_point_name):
+    """Returns linkopts to customize the entry point of a binary on Windows.
+
+    MSVC `link.exe` does not understand the GNU `ld` `--defsym` alias used on
+    other platforms; `/ALTERNATENAME` is the equivalent, resolving the
+    CRT-referenced `main` symbol to the renamed Swift entry point.
+    """
+    return struct(
+        linkopts = ["/ALTERNATENAME:main={}".format(entry_point_name)],
+    )
+
 def _parse_target_system_name(*, arch, os, target_system_name):
     """Returns the target system name set by the CC toolchain or attempts to create one based on the OS and arch."""
 
@@ -488,6 +508,10 @@ def _parse_target_system_name(*, arch, os, target_system_name):
 
     if os == "linux":
         return "%s-unknown-linux-gnu" % arch
+    elif os == "windows":
+        # The MSVC cc toolchain reports a `target_gnu_system_name` of "local",
+        # so synthesize the triple.
+        return "%s-unknown-windows-msvc" % arch
     else:
         return "%s-unknown-%s" % (arch, os)
 
@@ -520,7 +544,7 @@ def _swift_toolchain_impl(ctx):
         target_triples.parse(ctx.var.get("CC_TARGET_TRIPLE") or target_system_name),
     )
 
-    if "clang" not in cc_toolchain.compiler and "llvm" not in cc_toolchain.compiler:
+    if ctx.attr.os != "windows" and "clang" not in cc_toolchain.compiler and "llvm" not in cc_toolchain.compiler:
         fail("Swift requires the configured CC toolchain use clang. " +
              "Either use the locally installed LLVM by setting `CC=clang` in your environment " +
              "before invoking Bazel, or configure a Bazel LLVM CC toolchain. " +
@@ -646,7 +670,7 @@ def _swift_toolchain_impl(ctx):
             bindir = "bin64"
         elif ctx.attr.arch == "i686":
             bindir = "bin32"
-        elif ctx.attr.arch == "arm64":
+        elif ctx.attr.arch in ("aarch64", "arm64"):
             bindir = "bin64a"
         else:
             fail("unsupported arch `{}`".format(ctx.attr.arch))
@@ -672,7 +696,9 @@ def _swift_toolchain_impl(ctx):
         cross_import_overlays = collect_cross_import_overlays(ctx.attr.cross_import_overlays),
         debug_outputs_provider = None,
         developer_dirs = [],
-        entry_point_linkopts_provider = _entry_point_linkopts_provider,
+        entry_point_linkopts_provider = (
+            _windows_entry_point_linkopts_provider if ctx.attr.os == "windows" else _entry_point_linkopts_provider
+        ),
         feature_allowlists = [
             target[SwiftFeatureAllowlistInfo]
             for target in ctx.attr.feature_allowlists

tools/test_observer/BUILD

@@ -10,11 +10,11 @@ swift_library(
         "BazelXMLTestObserver.swift",
         "Concurrency.swift",
         "JSON.swift",
-        "LinuxXCTestRunner.swift",
         "Locked.swift",
         "ObjectiveCXCTestRunner.swift",
         "ShardingFilteringTestCollector.swift",
         "StringInterpolation+XMLEscaping.swift",
+        "SwiftCorelibsXCTestRunner.swift",
         "SwiftTestingRunner.swift",
         "XUnitTestRecorder.swift",
     ],