Xcode: Control emission of EFFECTIVE_PLATFORM_NAME

When building with multiple SDKs within one project Xcode requires
the usage of ${EFFECTIVE_PLATFORM_NAME} to put temporary and build
outout into separate directories. For example an iOS device and
simulator build use two different SDKs (iphoneos and iphonesimulator).

In the past cmake tries to detect embedded toolchains that could
possibly use simulators and emitted EFFECTIVE_PLATFORM_NAME (EPN)
at the proper locations. In #16253 Mark noticed that if he
uses macosx and iphoneos in combination the necessary EPN is not
emitted. This is because CMake by default assumes macosx SDK which
does not trigger EPN emission.

The fist naive approach - enabling EPN unconditionally revealed that
then the EPN leaks into generator expressions like $<TARGET_FILE:xxx>
which might be a regression and thus is unacceptable.

The next approach was to add an CMake property to enable EPN emission
unconditionally. This solved the reported problem.

But the EPN leakage also happened for the embedded toolchains already
without anyone noticing. So the control property was turned into a
tri-state one:

 * No definition: EPN is activated for embedded toolchains like before
 * ON: EPN is always emitted
 * OFF: EPN is never emitted

That approach gives the user the chance to disable EPN for embedded
toolchains and restores generator expression functionality for those.

Closes: #16253

2 files changed, 35 insertions, 0 deletions

diff --git a/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake b/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake
index 60912c2..f51a107 100644
--- a/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake
+++ b/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake
@@ -166,3 +166,24 @@ if(NOT XCODE_VERSION VERSION_LESS 6)
   unset(RunCMake_TEST_NO_CLEAN)
   unset(RunCMake_TEST_OPTIONS)
 endif()
+
+if(NOT XCODE_VERSION VERSION_LESS 5)
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/XcodeMultiplatform-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+
+  run_cmake(XcodeMultiplatform)
+
+  # build ios before macos
+  run_cmake_command(XcodeMultiplatform-iphonesimulator-build ${CMAKE_COMMAND} --build . -- -sdk iphonesimulator)
+  run_cmake_command(XcodeMultiplatform-iphonesimulator-install ${CMAKE_COMMAND} --build . --target install -- -sdk iphonesimulator DESTDIR=${RunCMake_TEST_BINARY_DIR}/_install_iphonesimulator)
+
+  run_cmake_command(XcodeMultiplatform-macosx-build ${CMAKE_COMMAND} --build . -- -sdk macosx)
+  run_cmake_command(XcodeMultiplatform-macosx-install ${CMAKE_COMMAND} --build . --target install -- -sdk macosx DESTDIR=${RunCMake_TEST_BINARY_DIR}/_install_macosx)
+
+  unset(RunCMake_TEST_BINARY_DIR)
+  unset(RunCMake_TEST_NO_CLEAN)
+  unset(RunCMake_TEST_OPTIONS)
+endif()
diff --git a/Tests/RunCMake/XcodeProject/XcodeMultiplatform.cmake b/Tests/RunCMake/XcodeProject/XcodeMultiplatform.cmake
new file mode 100644
index 0000000..a1064f4
--- /dev/null
+++ b/Tests/RunCMake/XcodeProject/XcodeMultiplatform.cmake
@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.3)
+enable_language(CXX)
+
+set_property(GLOBAL PROPERTY XCODE_EMIT_EFFECTIVE_PLATFORM_NAME ON)
+
+set(CMAKE_XCODE_ATTRIBUTE_SUPPORTED_PLATFORMS "macosx iphonesimulator")
+set(CMAKE_MACOSX_BUNDLE true)
+
+add_library(library STATIC foo.cpp)
+
+add_executable(main main.cpp)
+target_link_libraries(main library)
+
+install(TARGETS library ARCHIVE DESTINATION lib)