Set up a client-side C library to talk with C APIs exposed from the compiler

CMakeLists.txt

@@ -10,7 +10,7 @@ cmake_minimum_required(VERSION 3.15.1)
 
 list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules)
 
-project(SwiftDriver LANGUAGES Swift)
+project(SwiftDriver LANGUAGES Swift C)
 
 set(SWIFT_VERSION 5)
 set(CMAKE_Swift_LANGUAGE_VERSION ${SWIFT_VERSION})
@@ -19,6 +19,9 @@ if(CMAKE_VERSION VERSION_LESS 3.16)
     set(CMAKE_LINK_LIBRARY_FLAG "-l")
 endif()
 
+# ensure Swift compiler can find _CSwiftDriver
+add_compile_options($<$<COMPILE_LANGUAGE:Swift>:-I$<SEMICOLON>${CMAKE_CURRENT_SOURCE_DIR}/Sources/_CSwiftDriver/include>)
+
 set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/swift)
 
 if(CMAKE_VERSION VERSION_LESS 3.16 AND CMAKE_SYSTEM_NAME STREQUAL Windows)

Package.swift

@@ -36,10 +36,12 @@ let package = Package(
       targets: ["SwiftDriverExecution"]),
   ],
   targets: [
+    .target(name: "_CSwiftDriver"),
+
     /// The driver library.
     .target(
       name: "SwiftDriver",
-      dependencies: ["SwiftOptions", "SwiftToolsSupport-auto", "Yams"]),
+      dependencies: ["SwiftOptions", "SwiftToolsSupport-auto", "Yams", "_CSwiftDriver"]),
 
     /// The execution library.
     .target(

Sources/CMakeLists.txt

@@ -6,6 +6,7 @@
 # See http://swift.org/LICENSE.txt for license information
 # See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
+add_subdirectory(_CSwiftDriver)
 add_subdirectory(SwiftOptions)
 add_subdirectory(SwiftDriver)
 add_subdirectory(SwiftDriverExecution)

Sources/SwiftDriver/CMakeLists.txt

@@ -99,7 +99,8 @@ target_link_libraries(SwiftDriver PUBLIC
   SwiftOptions)
 target_link_libraries(SwiftDriver PRIVATE
   CYaml
-  Yams)
+  Yams
+  CSwiftDriver)
 
 set_property(GLOBAL APPEND PROPERTY SWIFTDRIVER_EXPORTS SwiftDriver)
 

Sources/SwiftDriver/Driver/Driver.swift

@@ -13,6 +13,7 @@ import TSCBasic
 import TSCUtility
 import Foundation
 import SwiftOptions
+@_implementationOnly import _CSwiftDriver
 
 /// The Swift driver.
 public struct Driver {

Sources/_CSwiftDriver/CMakeLists.txt

@@ -0,0 +1,10 @@
+# This source file is part of the Swift.org open source project
+#
+# Copyright (c) 2014 - 2020 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(CSwiftDriver STATIC
+  _CSwiftDriverImpl.c)

Sources/_CSwiftDriver/_CSwiftDriverImpl.c

@@ -0,0 +1 @@
+// This file is here to prevent the package manager from warning about a target with no sources.

Sources/_CSwiftDriver/include/_CSwiftDriver.h

@@ -0,0 +1,9 @@
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 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
+
+void dummyfunction();

Sources/_CSwiftDriver/include/module.modulemap

@@ -0,0 +1,4 @@
+module _CSwiftDriver {
+    umbrella "."
+    export *
+}