CMake: Install _TestingInternals in static library builds

When building the Testing library as a static library
(BUILD_SHARED_LIBS=FALSE), `_TestingInternals` was not being installed
alongside the main library. This caused the missing symbol error when
linking against the Testing library statically.

Author: kateinoigakukun

CMakeLists.txt

@@ -38,4 +38,5 @@ if(NOT SWIFT_SYSTEM_NAME)
   endif()
 endif()
 
+include(SwiftModuleInstallation)
 add_subdirectory(Sources)

Sources/Testing/CMakeLists.txt

@@ -94,11 +94,16 @@ add_library(Testing
   Traits/Trait.swift)
 target_link_libraries(Testing PRIVATE
   _TestingInternals)
+if(NOT BUILD_SHARED_LIBS)
+  # When building a static library, tell clients to autolink the internal
+  # library.
+  target_compile_options(Testing PRIVATE
+    "SHELL:-Xfrontend -public-autolink-library -Xfrontend _TestingInternals")
+endif()
 add_dependencies(Testing
   TestingMacros)
 target_compile_options(Testing PRIVATE
   -enable-library-evolution
   -emit-module-interface -emit-module-interface-path $<TARGET_PROPERTY:Testing,Swift_MODULE_DIRECTORY>/Testing.swiftinterface)
 
-include(SwiftModuleInstallation)
 _swift_testing_install_target(Testing)

Sources/_TestingInternals/CMakeLists.txt

@@ -17,3 +17,12 @@ target_include_directories(_TestingInternals PUBLIC
   ${CMAKE_CURRENT_SOURCE_DIR}/include)
 target_compile_options(_TestingInternals PRIVATE
   -fno-exceptions)
+
+if(NOT BUILD_SHARED_LIBS)
+  # When building a static library, install the internal library archive
+  # alongside the main library. In shared library builds, the internal library
+  # is linked into the main library and does not need to be installed separately.
+  get_swift_install_lib_dir(STATIC_LIBRARY lib_destination_dir)
+  install(TARGETS _TestingInternals
+    ARCHIVE DESTINATION ${lib_destination_dir})
+endif()

cmake/modules/SwiftModuleInstallation.cmake

@@ -18,28 +18,44 @@ function(get_swift_host_os result_var_name)
   set(${result_var_name} ${SWIFT_SYSTEM_NAME} PARENT_SCOPE)
 endfunction()
 
-function(_swift_testing_install_target module)
+# Returns the path to the Swift Testing library installation directory
+#
+# Usage:
+#   get_swift_testing_install_lib_dir(type result_var_name)
+#
+# Arguments:
+#   type: The type of the library (STATIC_LIBRARY, SHARED_LIBRARY, or EXECUTABLE).
+#         Typically, the value of the TYPE target property.
+#   result_var_name: The name of the variable to set
+function(get_swift_testing_install_lib_dir type result_var_name)
   get_swift_host_os(swift_os)
-  get_target_property(type ${module} TYPE)
-
   if(type STREQUAL STATIC_LIBRARY)
     set(swift swift_static)
   else()
     set(swift swift)
   endif()
 
+  if(APPLE)
+    set(${result_var_name} "lib/${swift}/${swift_os}/testing" PARENT_SCOPE)
+  else()
+    set(${result_var_name} "lib/${swift}/${swift_os}" PARENT_SCOPE)
+  endif()
+endfunction()
+
+function(_swift_testing_install_target module)
   target_compile_options(Testing PRIVATE "-no-toolchain-stdlib-rpath")
 
-  if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
-    set(lib_destination_dir "lib/${swift}/${swift_os}/testing")
+  if(APPLE)
     set_property(TARGET ${module} PROPERTY
       INSTALL_RPATH "@loader_path/..")
   else()
-    set(lib_destination_dir "lib/${swift}/${swift_os}")
     set_property(TARGET ${module} PROPERTY
       INSTALL_RPATH "$ORIGIN")
   endif()
 
+  get_target_property(type ${module} TYPE)
+  get_swift_testing_install_lib_dir(${type} lib_destination_dir)
+
   install(TARGETS ${module}
     ARCHIVE DESTINATION "${lib_destination_dir}"
     LIBRARY DESTINATION "${lib_destination_dir}"
@@ -71,7 +87,7 @@ function(_swift_testing_install_target module)
   install(FILES $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftmodule
     DESTINATION "${module_dir}"
     RENAME ${SwiftTesting_MODULE_TRIPLE}.swiftmodule)
-  if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+  if(APPLE)
     # Only Darwin has stable ABI. 
     install(FILES $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftinterface
       DESTINATION "${module_dir}"