Add CMake build support

CMakeLists.txt

@@ -0,0 +1,64 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift Service Context open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift Service Context project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of Swift Service Context project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+cmake_minimum_required(VERSION 3.29)
+project(SwiftServiceContext LANGUAGES C Swift)
+
+# Match the DLL runtime used by the Windows Swift SDK, including Debug builds.
+if(WIN32 AND NOT DEFINED CMAKE_MSVC_RUNTIME_LIBRARY)
+  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
+endif()
+
+if(CMAKE_Swift_COMPILER_VERSION VERSION_LESS 6.2)
+  message(FATAL_ERROR "Swift 6.2 or newer is required")
+endif()
+if(WIN32 AND BUILD_SHARED_LIBS AND CMAKE_C_COMPILER_FRONTEND_VARIANT STREQUAL "MSVC")
+  message(FATAL_ERROR
+    "Swift shared-library builds require Clang's GNU-style driver on Windows. Configure with -DCMAKE_C_COMPILER=clang.")
+endif()
+set(CMAKE_Swift_LANGUAGE_VERSION 6)
+include(GNUInstallDirs)
+include(CMakePackageConfigHelpers)
+include(cmake/SwiftLibrary.cmake)
+
+add_library(ServiceContextModule
+  Sources/ServiceContextModule/ServiceContext.swift
+  Sources/ServiceContextModule/ServiceContextKey.swift
+)
+add_library(SwiftServiceContext::ServiceContextModule ALIAS ServiceContextModule)
+_swift_service_context_library(ServiceContextModule)
+
+# This compatibility module has no runtime symbols, so Windows cannot create
+# a DLL import library for it. Preserve the module in a static archive instead.
+set(compatibility_library_type)
+if(WIN32)
+  set(compatibility_library_type STATIC)
+endif()
+add_library(InstrumentationBaggage ${compatibility_library_type}
+  Sources/InstrumentationBaggage/CompatibilityShims.swift
+)
+add_library(SwiftServiceContext::InstrumentationBaggage ALIAS InstrumentationBaggage)
+_swift_service_context_library(InstrumentationBaggage)
+target_link_libraries(InstrumentationBaggage PUBLIC ServiceContextModule)
+
+set(package_directory "${CMAKE_INSTALL_LIBDIR}/cmake/SwiftServiceContext")
+configure_package_config_file(cmake/SwiftServiceContextConfig.cmake.in
+  "${CMAKE_CURRENT_BINARY_DIR}/SwiftServiceContextConfig.cmake"
+  INSTALL_DESTINATION "${package_directory}")
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/SwiftServiceContextConfig.cmake"
+  DESTINATION "${package_directory}")
+install(EXPORT SwiftServiceContextTargets NAMESPACE SwiftServiceContext::
+  DESTINATION "${package_directory}")
+export(EXPORT SwiftServiceContextTargets NAMESPACE SwiftServiceContext::
+  FILE "${CMAKE_CURRENT_BINARY_DIR}/SwiftServiceContextTargets.cmake")

README.md

@@ -75,3 +75,7 @@ targets: [
     // ...
 ]
 ```
+
+## Building with CMake
+
+See [the CMake build instructions](cmake/README.md) for library builds and consumer validation.

Tests/CMake/CMakeLists.txt

@@ -0,0 +1,30 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift Service Context open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift Service Context project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of Swift Service Context project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+cmake_minimum_required(VERSION 3.29)
+project(CMakeConsumer LANGUAGES C Swift)
+
+# Match the DLL runtime used by the Windows Swift SDK, including Debug builds.
+if(WIN32 AND NOT DEFINED CMAKE_MSVC_RUNTIME_LIBRARY)
+  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
+endif()
+find_package(SwiftServiceContext CONFIG REQUIRED)
+add_executable(CMakeConsumer main.swift)
+target_link_libraries(CMakeConsumer PRIVATE SwiftServiceContext::ServiceContextModule SwiftServiceContext::InstrumentationBaggage)
+enable_testing()
+add_test(NAME CMakeConsumer COMMAND CMakeConsumer)
+if(WIN32)
+  set_tests_properties(CMakeConsumer PROPERTIES ENVIRONMENT_MODIFICATION
+    "PATH=path_list_prepend:$<TARGET_FILE_DIR:SwiftServiceContext::InstrumentationBaggage>;PATH=path_list_prepend:$<TARGET_FILE_DIR:SwiftServiceContext::ServiceContextModule>")
+endif()

Tests/CMake/main.swift

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Service Context open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift Service Context project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift Service Context project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import InstrumentationBaggage
+import ServiceContextModule
+
+enum MessageKey: ServiceContextKey {
+    typealias Value = String
+}
+var context = ServiceContext.topLevel
+context[MessageKey.self] = "CMake"
+precondition(context[MessageKey.self] == "CMake")

cmake/README.md

@@ -0,0 +1,37 @@
+# Building with CMake
+
+CMake 3.29 or newer, Ninja, and Swift 6.2 or newer are required. Ninja Multi-Config
+requires CMake 4.0 or newer. SwiftPM remains the test runner for the Swift unit tests.
+
+On Windows, run CMake from a Visual Studio developer command prompt so the MSVC
+linker and Windows SDK are available. Add `-DCMAKE_C_COMPILER=clang` to each configure
+command to use the Clang driver supplied with Swift. Shared builds require this
+GNU-style driver because CMake's MSVC C driver initializes linker flags that Swift
+cannot consume directly. Use the same build configuration for libraries and their
+consumer. The default Windows runtime is `MultiThreadedDLL` to match Swift's SDK;
+set `-DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreadedDLL` in independent consumers too.
+
+Configure, build, and install the libraries:
+
+```sh
+cmake -S . -B build -G Ninja -DCMAKE_INSTALL_PREFIX=/path/to/install
+cmake --build build
+cmake --install build
+```
+
+Pass `-DBUILD_SHARED_LIBS=ON` to build shared libraries. On Windows, the
+`InstrumentationBaggage` compatibility module remains static because its
+re-exports and type aliases have no runtime symbols for a DLL import library.
+An enclosing CMake project can also use `add_subdirectory` and link the namespaced targets. The build directory
+and install prefix both provide a `SwiftServiceContext` package configuration.
+
+The independent consumer verifies that public modules can be imported and linked:
+
+```sh
+cmake -S Tests/CMake -B consumer -G Ninja -DCMAKE_PREFIX_PATH=/path/to/install
+cmake --build consumer
+ctest --test-dir consumer --output-on-failure
+```
+
+Test relocated installations by moving the installation prefix before configuring the consumer.
+For Ninja Multi-Config, pass `--config Debug` to build/install and `-C Debug` to CTest.

cmake/SwiftLibrary.cmake

@@ -0,0 +1,45 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift Service Context open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift Service Context project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of Swift Service Context project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+function(_swift_service_context_library target)
+  set(module_directory "${CMAKE_CURRENT_BINARY_DIR}/swift")
+  if(CMAKE_CONFIGURATION_TYPES)
+    foreach(configuration IN LISTS CMAKE_CONFIGURATION_TYPES)
+      file(MAKE_DIRECTORY "${module_directory}/${configuration}")
+    endforeach()
+    set(module_directory "${module_directory}/$<CONFIG>")
+    if(CMAKE_VERSION VERSION_LESS 4.0)
+      message(FATAL_ERROR "Swift multi-configuration builds require CMake 4.0 or newer")
+    endif()
+  endif()
+  set_target_properties(${target} PROPERTIES
+    Swift_MODULE_DIRECTORY "${module_directory}"
+    POSITION_INDEPENDENT_CODE YES)
+  get_target_property(library_type ${target} TYPE)
+  if(WIN32 AND library_type STREQUAL "STATIC_LIBRARY")
+    # Swift autolinks lib-prefixed static archives, but unprefixed DLL import libraries.
+    set_target_properties(${target} PROPERTIES PREFIX "lib")
+  endif()
+  target_compile_options(${target} PRIVATE
+    "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-package-name swift_service_context>"
+    "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature StrictConcurrency=complete>")
+  target_include_directories(${target} PUBLIC
+    "$<BUILD_INTERFACE:${module_directory}>"
+    "$<INSTALL_INTERFACE:${CMAKE_INSTALL_LIBDIR}/swift>")
+  install(TARGETS ${target} EXPORT SwiftServiceContextTargets)
+  install(FILES
+    "${module_directory}/${target}.swiftmodule"
+    "${module_directory}/${target}.swiftdoc"
+    DESTINATION "${CMAKE_INSTALL_LIBDIR}/swift")
+endfunction()

cmake/SwiftServiceContextConfig.cmake.in

@@ -0,0 +1,18 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift Service Context open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift Service Context project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of Swift Service Context project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/SwiftServiceContextTargets.cmake")
+check_required_components(SwiftServiceContext)