Always consider includes from IMPORTED targets to be SYSTEM.

Introduce a target property to control this behavior variable
to set the default value for the target property.

This does not affect try_compile runs.

5 files changed, 95 insertions, 0 deletions

diff --git a/Tests/ExportImport/Export/CMakeLists.txt b/Tests/ExportImport/Export/CMakeLists.txt
index 1f23b2a..06238a4 100644
--- a/Tests/ExportImport/Export/CMakeLists.txt
+++ b/Tests/ExportImport/Export/CMakeLists.txt
@@ -298,6 +298,14 @@ set_property(TARGET cmp0022OLD APPEND PROPERTY LINK_INTERFACE_LIBRARIES testLib3
 
 add_library(noIncludesInterface empty.cpp)
 
+add_library(systemlib SHARED systemlib.cpp)
+install(FILES systemlib.h DESTINATION include/systemlib)
+target_include_directories(systemlib
+  INTERFACE
+    $<INSTALL_INTERFACE:include/systemlib>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+)
+
 install(TARGETS testLibRequired
         EXPORT RequiredExp DESTINATION lib
         INCLUDES DESTINATION
@@ -366,6 +374,7 @@ install(
   testLib6
   testLibCycleA testLibCycleB
   cmp0022NEW cmp0022OLD
+  systemlib
   EXPORT exp
   RUNTIME DESTINATION bin
   LIBRARY DESTINATION lib NAMELINK_SKIP
@@ -417,6 +426,7 @@ export(TARGETS testExe1 testLib1 testLib2 testLib3
   testSharedLibRequired testSharedLibRequiredUser testSharedLibRequiredUser2
   testSharedLibDepends renamed_on_export
   cmp0022NEW cmp0022OLD
+  systemlib
   NAMESPACE bld_
   FILE ExportBuildTree.cmake
   )
diff --git a/Tests/ExportImport/Export/systemlib.cpp b/Tests/ExportImport/Export/systemlib.cpp
new file mode 100644
index 0000000..ec45148
--- /dev/null
+++ b/Tests/ExportImport/Export/systemlib.cpp
@@ -0,0 +1,7 @@
+
+#include "systemlib.h"
+
+SystemStruct::SystemStruct()
+{
+
+}
diff --git a/Tests/ExportImport/Export/systemlib.h b/Tests/ExportImport/Export/systemlib.h
new file mode 100644
index 0000000..f7900c0
--- /dev/null
+++ b/Tests/ExportImport/Export/systemlib.h
@@ -0,0 +1,22 @@
+
+#ifndef SYSTEMLIB_H
+#define SYSTEMLIB_H
+
+#if defined(_WIN32) || defined(__CYGWIN__)
+# define systemlib_EXPORT __declspec(dllexport)
+#else
+# define systemlib_EXPORT
+#endif
+
+struct systemlib_EXPORT SystemStruct
+{
+  SystemStruct();
+
+  void someMethod()
+  {
+    int unused;
+    // unused warning not issued when this header is used as a system header.
+  }
+};
+
+#endif
diff --git a/Tests/ExportImport/Import/A/CMakeLists.txt b/Tests/ExportImport/Import/A/CMakeLists.txt
index 2627354..ebe4af2 100644
--- a/Tests/ExportImport/Import/A/CMakeLists.txt
+++ b/Tests/ExportImport/Import/A/CMakeLists.txt
@@ -265,3 +265,50 @@ foreach(_config ${_configs})
     )
 endforeach()
 unset(_configs)
+
+if (((CMAKE_C_COMPILER_ID STREQUAL GNU AND CMAKE_C_COMPILER_VERSION VERSION_GREATER 4.4)
+    OR CMAKE_C_COMPILER_ID STREQUAL Clang)
+    AND (CMAKE_GENERATOR STREQUAL "Unix Makefiles" OR CMAKE_GENERATOR STREQUAL "Ninja"))
+  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()
+  if (run_sys_includes_test)
+    add_executable(test_system_exp test_system.cpp)
+    target_link_libraries(test_system_exp exp_systemlib)
+    target_compile_options(test_system_exp PRIVATE -Wunused-variable -Werror=unused-variable)
+
+    unset(EXP_ERROR_VARIABLE CACHE)
+    try_compile(EXP_ERROR_VARIABLE
+      "${CMAKE_CURRENT_SOURCE_DIR}/test_system"
+      "${CMAKE_CURRENT_SOURCE_DIR}/test_system.cpp"
+      COMPILE_DEFINITIONS "-Wunused-variable -Werror=unused-variable"
+      LINK_LIBRARIES exp_systemlib
+      OUTPUT_VARIABLE OUTPUT
+      )
+    if(NOT EXP_ERROR_VARIABLE)
+      message(SEND_ERROR "EXP_ERROR_VARIABLE try_compile failed, but it was expected to succeed ${OUTPUT}.")
+    endif()
+
+    add_executable(test_system_bld test_system.cpp)
+    target_link_libraries(test_system_bld bld_systemlib)
+    target_compile_options(test_system_bld PRIVATE -Wunused-variable -Werror=unused-variable)
+
+    unset(BLD_ERROR_VARIABLE CACHE)
+    try_compile(BLD_ERROR_VARIABLE
+      "${CMAKE_CURRENT_SOURCE_DIR}/test_system"
+      "${CMAKE_CURRENT_SOURCE_DIR}/test_system.cpp"
+      COMPILE_DEFINITIONS "-Wunused-variable -Werror=unused-variable"
+      LINK_LIBRARIES bld_systemlib
+      OUTPUT_VARIABLE OUTPUT
+      )
+    if(NOT BLD_ERROR_VARIABLE)
+      message(SEND_ERROR "BLD_ERROR_VARIABLE try_compile failed, but it was expected to succeed.")
+    endif()
+  endif()
+endif()
diff --git a/Tests/ExportImport/Import/A/test_system.cpp b/Tests/ExportImport/Import/A/test_system.cpp
new file mode 100644
index 0000000..aae3583
--- /dev/null
+++ b/Tests/ExportImport/Import/A/test_system.cpp
@@ -0,0 +1,9 @@
+
+#include "systemlib.h"
+
+int main()
+{
+  SystemStruct s;
+  (void)s;
+  return 0;
+}