Add a PackageExtension module and library (analogous to PackageDescription). This contains the APIs that extensions can use.

Author: abertelrud

Package.swift

@@ -91,6 +91,12 @@ let package = Package(
             targets: ["PackageDescription"]
         ),
 
+        .library(
+            name: "PackageExtension",
+            type: .dynamic,
+            targets: ["PackageExtension"]
+        ),
+        
         .library(
             name: "PackageCollectionsModel",
             targets: ["PackageCollectionsModel"]
@@ -107,6 +113,9 @@ let package = Package(
             swiftSettings: [
                 .define("PACKAGE_DESCRIPTION_4_2"),
             ]),
+        
+        .target(
+            name: "PackageExtension"),
 
         // MARK: SwiftPM specific support libraries
 

Sources/CMakeLists.txt

@@ -14,6 +14,7 @@ add_subdirectory(PackageCollections)
 add_subdirectory(PackageCollectionsModel)
 add_subdirectory(PackageCollectionsSigning)
 add_subdirectory(PackageDescription)
+add_subdirectory(PackageExtension)
 add_subdirectory(PackageGraph)
 add_subdirectory(PackageLoading)
 add_subdirectory(PackageModel)

Sources/PackageExtension/CMakeLists.txt

@@ -0,0 +1,60 @@
+# This source file is part of the Swift.org open source project
+#
+# Copyright (c) 2021 Apple Inc. and the Swift project authors
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See http://swift.org/LICENSE.txt for license information
+# See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+
+add_library(PackageExtension
+    PackageExtension.swift)
+  
+if(CMAKE_HOST_SYSTEM_NAME STREQUAL Darwin)
+    set(SWIFT_INTERFACE_PATH ${CMAKE_BINARY_DIR}/pm/PackageExtension.swiftinterface)
+    target_compile_options(PackageExtension PUBLIC
+        $<$<COMPILE_LANGUAGE:Swift>:-enable-library-evolution>)
+    target_compile_options(PackageExtension PUBLIC
+        $<$<COMPILE_LANGUAGE:Swift>:-emit-module-interface-path$<SEMICOLON>${SWIFT_INTERFACE_PATH}>)
+    target_link_options(PackageExtension PRIVATE
+        "SHELL:-Xlinker -install_name -Xlinker @rpath/libPackageExtension.dylib")
+endif()
+
+set_target_properties(PackageExtension PROPERTIES
+    Swift_MODULE_NAME PackageExtension
+    Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/pm
+    INSTALL_NAME_DIR \\@rpath
+    OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/pm
+    OUTPUT_NAME PackageExtension
+    ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/pm
+    LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/pm
+    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/pm
+)
+
+if(NOT CMAKE_SYSTEM_NAME STREQUAL Darwin)
+    if(Foundation_FOUND)
+        target_link_libraries(PackageExtension PRIVATE
+            Foundation)
+    endif()
+    target_link_options(PackageExtension PRIVATE
+        "SHELL:-no-toolchain-stdlib-rpath")
+    set_target_properties(PackageExtension PROPERTIES
+        BUILD_WITH_INSTALL_RPATH TRUE
+        INSTALL_RPATH "$ORIGIN/../../$<LOWER_CASE:${CMAKE_SYSTEM_NAME}>")
+endif()
+
+if(CMAKE_HOST_SYSTEM_NAME STREQUAL Darwin)
+    install(FILES
+        ${CMAKE_BINARY_DIR}/pm/PackageExtension.swiftinterface
+        ${CMAKE_BINARY_DIR}/pm/PackageExtension.swiftdoc
+        DESTINATION lib/swift/pm
+    )
+else()
+    install(FILES
+        ${CMAKE_BINARY_DIR}/pm/PackageExtension.swiftmodule
+        ${CMAKE_BINARY_DIR}/pm/PackageExtension.swiftdoc
+        DESTINATION lib/swift/pm
+    )
+endif()
+
+install(TARGETS PackageExtension
+    DESTINATION lib/swift/pm)