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.

3 files changed, 39 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