Restore the CoreFoundation Swift overlay on non-Darwin

CMakeLists.txt

@@ -36,6 +36,8 @@ endif()
 project(Foundation
     LANGUAGES C Swift)
 
+include(CTest)
+
 option(FOUNDATION_SWIFTPM_DEPS "build Windows SwiftPM dependencies via CMake" NO)
 if(FOUNDATION_SWIFTPM_DEPS)
     include(WindowsSwiftPMDependencies)
@@ -249,4 +251,7 @@ include(GNUInstallDirs)
 include(FoundationSwiftSupport)
 
 add_subdirectory(Sources)
+if(BUILD_TESTING)
+    add_subdirectory(Tests)
+endif()
 add_subdirectory(cmake/modules)

Package.swift

@@ -231,7 +231,11 @@ let package = Package(
             path: "Sources/CoreFoundation",
             exclude: [
                 "BlockRuntime",
-                "CMakeLists.txt"
+                "CMakeLists.txt",
+                // SwiftPM does not support mixed C and Swift targets. The
+                // CoreFoundation Swift overlay is built by CMake as part of
+                // the toolchain build.
+                "CoreFoundation.swift"
             ],
             cSettings: coreFoundationBuildSettings,
             linkerSettings: [.linkedLibrary("log", .when(platforms: [.android]))]
@@ -339,6 +343,12 @@ let package = Package(
                 "Testing",
                 .target(name: "xdgTestHelper", condition: .when(platforms: [.linux, .android, .windows]))
             ],
+            exclude: [
+                "CMakeLists.txt",
+                // The CoreFoundation Swift overlay is built and tested by
+                // CMake because SwiftPM cannot build mixed C/Swift targets.
+                "CoreFoundation"
+            ],
             resources: [
                 .copy("Foundation/Resources")
             ],

Sources/CoreFoundation/CMakeLists.txt

@@ -120,6 +120,32 @@ target_link_libraries(CoreFoundation
         _FoundationICU
         dispatch)
 
+if(NOT CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+    add_library(CoreFoundationOverlay OBJECT
+        CoreFoundation.swift)
+    # The Clang importer looks specifically for the compiler-known protocol
+    # CoreFoundation._CFObject. The CMake target may have a distinct name, but
+    # the emitted Swift module must remain CoreFoundation for imported CF
+    # reference types to receive their synthesized conformance.
+    set_target_properties(CoreFoundationOverlay PROPERTIES
+        Swift_MODULE_NAME CoreFoundation)
+    target_include_directories(CoreFoundationOverlay INTERFACE
+        include)
+    target_compile_options(CoreFoundationOverlay
+        PRIVATE
+            "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-swift-version 6>"
+            "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -module-link-name -Xfrontend Foundation>"
+            "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xcc -fmodule-map-file=${CMAKE_CURRENT_SOURCE_DIR}/include/module.modulemap>"
+        INTERFACE
+            "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xcc -fmodule-map-file=${CMAKE_CURRENT_SOURCE_DIR}/include/module.modulemap>")
+    set_property(GLOBAL APPEND PROPERTY Foundation_EXPORTS
+        CoreFoundationOverlay)
+    if(NOT BUILD_SHARED_LIBS)
+        target_compile_options(CoreFoundationOverlay PRIVATE
+            "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -public-autolink-library -Xfrontend CoreFoundation>")
+    endif()
+endif()
+
 if(CMAKE_SYSTEM_NAME STREQUAL "WASI")
     # On WASI, we use vendored BlocksRuntime instead of the one from libdispatch
     add_subdirectory(BlockRuntime)
@@ -146,6 +172,21 @@ install(DIRECTORY
         DESTINATION
             lib/${swift}/CoreFoundation)
 
+if(NOT CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+    install(FILES
+                $<TARGET_PROPERTY:CoreFoundationOverlay,Swift_MODULE_DIRECTORY>/CoreFoundation.swiftdoc
+            DESTINATION
+                lib/${swift}/${SWIFT_SYSTEM_NAME}/CoreFoundation.swiftmodule
+            RENAME
+                ${SwiftFoundation_MODULE_TRIPLE}.swiftdoc)
+    install(FILES
+                $<TARGET_PROPERTY:CoreFoundationOverlay,Swift_MODULE_DIRECTORY>/CoreFoundation.swiftmodule
+            DESTINATION
+                lib/${swift}/${SWIFT_SYSTEM_NAME}/CoreFoundation.swiftmodule
+            RENAME
+                ${SwiftFoundation_MODULE_TRIPLE}.swiftmodule)
+endif()
+
 if(NOT BUILD_SHARED_LIBS)
     install(TARGETS CoreFoundation
         ARCHIVE DESTINATION lib/swift_static/${SWIFT_SYSTEM_NAME}

Sources/CoreFoundation/CoreFoundation.swift

@@ -0,0 +1,29 @@
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+@_exported import CoreFoundation
+
+// The Clang importer synthesizes conformance to the compiler-known
+// CoreFoundation._CFObject protocol for declarations it recognizes as Core
+// Foundation reference types. Both the module and protocol names are required;
+// the default witnesses below then satisfy Hashable for those imported types.
+public protocol _CFObject: AnyObject, Hashable {}
+
+extension _CFObject {
+    public var hashValue: Int {
+        Int(bitPattern: CFHash(self))
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(hashValue)
+    }
+
+    public static func == (lhs: Self, rhs: Self) -> Bool {
+        CFEqual(lhs, rhs)
+    }
+}

Sources/Foundation/CMakeLists.txt

@@ -155,6 +155,11 @@ target_link_libraries(Foundation
         FoundationEssentials
         FoundationInternationalization)
 
+if(TARGET CoreFoundationOverlay)
+    target_link_libraries(Foundation PRIVATE
+        CoreFoundationOverlay)
+endif()
+
 if(NOT BUILD_SHARED_LIBS)
     target_compile_options(Foundation PRIVATE
         "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -public-autolink-library -Xfrontend CoreFoundation>")

Tests/CMakeLists.txt

@@ -0,0 +1,33 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.md for the list of Swift project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    add_executable(CoreFoundationHashableTests
+        CoreFoundation/TestCFObjectHashable.swift)
+
+    target_compile_options(CoreFoundationHashableTests PRIVATE
+        "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-parse-as-library -swift-version 6>"
+        "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xcc -fmodule-map-file=${CMAKE_SOURCE_DIR}/Sources/CoreFoundation/include/module.modulemap>")
+    target_include_directories(CoreFoundationHashableTests PRIVATE
+        ${CMAKE_SOURCE_DIR}/Sources/CoreFoundation/include)
+
+    target_link_libraries(CoreFoundationHashableTests PRIVATE
+        Foundation)
+
+    add_test(NAME CoreFoundation.Hashable
+        COMMAND CoreFoundationHashableTests)
+    set_property(TEST CoreFoundation.Hashable PROPERTY
+        ENVIRONMENT_MODIFICATION
+            "LD_LIBRARY_PATH=path_list_prepend:$<TARGET_FILE_DIR:Foundation>")
+endif()

Tests/CoreFoundation/TestCFObjectHashable.swift

@@ -0,0 +1,33 @@
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+import CoreFoundation
+
+private func requireHashable<T: Hashable>(_: T.Type) {}
+
+@main
+struct TestCFObjectHashable {
+    static func main() {
+        requireHashable(CFDictionary.self)
+        requireHashable(CFMutableDictionary.self)
+        requireHashable(CFArray.self)
+        requireHashable(CFMutableArray.self)
+        requireHashable(CFSet.self)
+        requireHashable(CFMutableSet.self)
+        requireHashable(CFString.self)
+        requireHashable(CFMutableString.self)
+        requireHashable(CFData.self)
+        requireHashable(CFMutableData.self)
+
+        let lhs = CFDictionaryCreate(nil, nil, nil, 0, nil, nil)!
+        let rhs = CFDictionaryCreate(nil, nil, nil, 0, nil, nil)!
+
+        precondition(lhs == rhs)
+        precondition(Set([lhs, rhs]).count == 1)
+    }
+}