Check for macro collisions with system headers during header testing.

Related to NVIDIA/thrust#1244.

cmake/CubHeaderTesting.cmake

@@ -4,6 +4,9 @@
 # .inl files are not globbed for, because they are not supposed to be used as public
 # entrypoints.
 
+# Meta target for all configs' header builds:
+add_custom_target(cub.all.headers)
+
 file(GLOB_RECURSE headers
   RELATIVE "${CUB_SOURCE_DIR}/cub"
   CONFIGURE_DEPENDS
@@ -25,5 +28,6 @@ foreach(cub_target IN LISTS CUB_TARGETS)
   target_link_libraries(${headertest_target} PUBLIC ${cub_target})
   cub_clone_target_properties(${headertest_target} ${cub_target})
 
+  add_dependencies(cub.all.headers ${headertest_target})
   add_dependencies(${config_prefix}.all ${headertest_target})
 endforeach()

cmake/header_test.in

@@ -1 +1,46 @@
+// This source file checks that:
+// 1) Header <cub/${header}> compiles without error.
+// 2) Common macro collisions with platform/system headers are avoided.
+
+// Define CUB_MACRO_CHECK(macro, header), which emits a diagnostic indicating
+// a potential macro collision and halts.
+//
+// Use raw platform checks instead of the CUB_HOST_COMPILER macros since we
+// don't want to #include any headers other than the one being tested.
+//
+// This is only implemented for MSVC/GCC/Clang.
+#if defined(_MSC_VER) // MSVC
+
+// Fake up an error for MSVC
+#define CUB_MACRO_CHECK_IMPL(msg)                                              \
+  /* Print message that looks like an error: */                                \
+  __pragma(message(__FILE__ ":" CUB_MACRO_CHECK_IMPL0(__LINE__)                \
+                   ": error: " #msg))                                          \
+  /* abort compilation due to static_assert or syntax error: */                \
+  static_assert(false, #msg);
+#define CUB_MACRO_CHECK_IMPL0(x) CUB_MACRO_CHECK_IMPL1(x)
+#define CUB_MACRO_CHECK_IMPL1(x) #x
+
+#elif defined(__clang__) || defined(__GNUC__)
+
+// GCC/clang are easy:
+#define CUB_MACRO_CHECK_IMPL(msg) CUB_MACRO_CHECK_IMPL0(GCC error #msg)
+#define CUB_MACRO_CHECK_IMPL0(expr) _Pragma(#expr)
+
+#endif
+
+// Hacky way to build a string, but it works on all tested platforms.
+#define CUB_MACRO_CHECK(MACRO, HEADER)                                         \
+  CUB_MACRO_CHECK_IMPL(Identifier MACRO should not be used from Thrust         \
+                            headers due to conflicts with HEADER.)
+
+// complex.h conflicts
+#define I CUB_MACRO_CHECK('I', complex.h)
+
+// windows.h conflicts
+// Disabling for now; we use min/max in many places, but since most
+// projects build with NOMINMAX this doesn't seem to be high priority to fix.
+//#define min(...) CUB_MACRO_CHECK('min', windows.h)
+//#define max(...) CUB_MACRO_CHECK('max', windows.h)
+
 #include <cub/${header}>