Tests/IncludeDirectories: support MSVC in system include tests

Tests/IncludeDirectories/CMakeLists.txt

@@ -3,17 +3,24 @@ project(IncludeDirectories)
 
 if (((CMAKE_C_COMPILER_ID STREQUAL GNU AND CMAKE_C_COMPILER_VERSION VERSION_GREATER 4.4)
     OR (CMAKE_C_COMPILER_ID STREQUAL Clang AND NOT "x${CMAKE_CXX_SIMULATE_ID}" STREQUAL "xMSVC")
-    OR CMAKE_C_COMPILER_ID STREQUAL AppleClang)
+    OR CMAKE_C_COMPILER_ID STREQUAL AppleClang
+    OR ("x${CMAKE_C_COMPILER_ID}" STREQUAL "xMSVC" AND
+       CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL "19.29.30036.3" AND
+       NOT CMAKE_GENERATOR MATCHES "Visual Studio")) # No support for VS generators yet.
     AND (CMAKE_GENERATOR STREQUAL "Unix Makefiles"
       OR CMAKE_GENERATOR STREQUAL "Ninja"
       OR (CMAKE_GENERATOR STREQUAL "Xcode" AND NOT XCODE_VERSION VERSION_LESS 6.0)))
-  include(CheckCXXCompilerFlag)
-  check_cxx_compiler_flag(-Wunused-variable run_sys_includes_test)
-  if(run_sys_includes_test)
-    # The Bullseye wrapper appears to break the -isystem effect.
-    execute_process(COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_VARIABLE out ERROR_VARIABLE out)
-    if("x${out}" MATCHES "Bullseye")
-      set(run_sys_includes_test 0)
+  if ("x${CMAKE_C_COMPILER_ID}" STREQUAL "xMSVC")
+    set(run_sys_includes_test 1)
+  else ()
+    include(CheckCXXCompilerFlag)
+    check_cxx_compiler_flag(-Wunused-variable run_sys_includes_test)
+    if(run_sys_includes_test)
+      # The Bullseye wrapper appears to break the -isystem effect.
+      execute_process(COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_VARIABLE out ERROR_VARIABLE out)
+      if("x${out}" MATCHES "Bullseye")
+        set(run_sys_includes_test 0)
+      endif()
     endif()
   endif()
   if (run_sys_includes_test)

Tests/IncludeDirectories/SystemIncludeDirectories/CMakeLists.txt

@@ -7,7 +7,11 @@ add_library(systemlib systemlib.cpp)
 target_include_directories(systemlib PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/systemlib")
 
 function (apply_error_flags target)
-  target_compile_options(${target} PRIVATE -Werror=unused-variable)
+  if (MSVC)
+    target_compile_options(${target} PRIVATE /we4101)
+  else ()
+    target_compile_options(${target} PRIVATE -Werror=unused-variable)
+  endif ()
 endfunction ()
 
 add_library(upstream upstream.cpp)
@@ -65,7 +69,11 @@ macro(do_try_compile error_option)
     LINK_LIBRARIES iface
   )
   if (${error_option} STREQUAL WITH_ERROR)
-    list(APPEND TC_ARGS COMPILE_DEFINITIONS -Werror=unused-variable)
+    if (MSVC)
+      list(APPEND TC_ARGS COMPILE_DEFINITIONS /we4101)
+    else ()
+      list(APPEND TC_ARGS COMPILE_DEFINITIONS -Werror=unused-variable)
+    endif ()
   endif()
   try_compile(${TC_ARGS})
 endmacro()

Tests/IncludeDirectories/SystemIncludeDirectoriesPerLang/CMakeLists.txt

@@ -7,14 +7,14 @@ set_target_properties(c_interface PROPERTIES
   INTERFACE_INCLUDE_DIRECTORIES "$<$<COMPILE_LANGUAGE:C>:${CMAKE_CURRENT_SOURCE_DIR}>"
   INTERFACE_SYSTEM_INCLUDE_DIRECTORIES "$<$<COMPILE_LANGUAGE:C>:${CMAKE_CURRENT_SOURCE_DIR}>"
 )
-target_compile_options(c_interface INTERFACE "$<$<COMPILE_LANG_AND_ID:C,GNU,Clang>:-Werror=unused-variable>")
+target_compile_options(c_interface INTERFACE "$<$<COMPILE_LANG_AND_ID:C,GNU,Clang>:-Werror=unused-variable>;$<$<COMPILE_LANG_AND_ID:C,MSVC>:/we4101>")
 
 add_library(cxx_interface INTERFACE)
 set_target_properties(cxx_interface PROPERTIES
   INTERFACE_INCLUDE_DIRECTORIES "$<$<COMPILE_LANGUAGE:CXX>:${CMAKE_CURRENT_SOURCE_DIR}/cxx_system_include>"
   INTERFACE_SYSTEM_INCLUDE_DIRECTORIES "$<$<COMPILE_LANGUAGE:CXX>:${CMAKE_CURRENT_SOURCE_DIR}/cxx_system_include>"
 )
-target_compile_options(cxx_interface INTERFACE "$<$<COMPILE_LANG_AND_ID:CXX,GNU,Clang>:-Werror=unused-variable>")
+target_compile_options(cxx_interface INTERFACE "$<$<COMPILE_LANG_AND_ID:CXX,GNU,Clang>:-Werror=unused-variable>;$<$<COMPILE_LANG_AND_ID:C,MSVC>:/we4101>")
 
 # The C header must come before the C++ header for this test to smoke out the
 # failure. The order of sources is how CMake determines the include cache