Add SYSTEM target property

If it is ON, treat INTERFACE_INCLUDE_DIRECTORIES as system include directories.

Issue: #18040

Signed-off-by: Da Quexian <daquexian566@gmail.com>

Help/manual/cmake-properties.7.rst

@@ -375,6 +375,7 @@ Properties on Targets
    /prop_tgt/Swift_LANGUAGE_VERSION
    /prop_tgt/Swift_MODULE_DIRECTORY
    /prop_tgt/Swift_MODULE_NAME
+   /prop_tgt/SYSTEM
    /prop_tgt/TYPE
    /prop_tgt/UNITY_BUILD
    /prop_tgt/UNITY_BUILD_BATCH_SIZE

Help/prop_tgt/IMPORTED_NO_SYSTEM.rst

@@ -7,7 +7,8 @@ Specifies that an :ref:`Imported Target <Imported Targets>` is not
 a ``SYSTEM`` library.  This has the following effects:
 
 * Entries of :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` are not treated
-  as ``SYSTEM`` include directories when compiling consumers, as they
+  as ``SYSTEM`` include directories when compiling consumers (regardless of
+  the value of the consumed target's :prop_tgt:`SYSTEM` property), as they
   would be by default.   Entries of
   :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` are not affected,
   and will always be treated as ``SYSTEM`` include directories.

Help/prop_tgt/SYSTEM.rst

@@ -0,0 +1,16 @@
+SYSTEM
+------
+
+.. versionadded:: 3.25
+
+Specifies that a target is a ``SYSTEM`` library.  This has the following effects:
+
+* Entries of :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` are treated as ``SYSTEM``
+  include directories when compiling consumers.
+  Entries of :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` are not affected,
+  and will always be treated as ``SYSTEM`` include directories.
+
+For imported targets, this property has a default value `ON`, which means that their
+`INTERFACE_INCLUDE_DIRECTORIES` are treated as ``SYSTEM`` by default. If their
+`SYSTEM` property is `OFF`, then their `INTERFACE_INCLUDE_DIRECTORIES` will not be
+treated as ``SYSTEM``, regardless of the value of `IMPORTED_NO_SYSTEM` property.

Help/release/dev/system.rst

@@ -0,0 +1,7 @@
+system
+------
+
+* The :prop_tgt:`SYSTEM` target property was added to specify
+  that a target should be treated as a system library (i.e.
+  its include directories are automatically ``SYSTEM`` when
+  compiling consumers).

Source/cmGeneratorTarget.cxx

@@ -807,12 +807,17 @@ void handleSystemIncludesDep(cmLocalGenerator* lg,
                                                  dagChecker, depTgt, language),
                  result);
   }
-  if (!depTgt->IsImported() || excludeImported) {
+  if (!depTgt->GetPropertyAsBool("SYSTEM")) {
+    return;
+  }
+  if (depTgt->IsImported()) {
+    if (excludeImported) {
       return;
     }
     if (depTgt->GetPropertyAsBool("IMPORTED_NO_SYSTEM")) {
       return;
     }
+  }
 
   if (cmValue dirs = depTgt->GetProperty("INTERFACE_INCLUDE_DIRECTORIES")) {
     cmExpandList(cmGeneratorExpression::Evaluate(*dirs, lg, config, headTarget,

Source/cmTarget.cxx

@@ -759,6 +759,10 @@ cmTarget::cmTarget(std::string const& name, cmStateEnums::TargetType type,
     }
   }
 
+  if (this->IsImported()) {
+    this->SetProperty("SYSTEM", "ON");
+  }
+
   for (auto const& prop : mf->GetState()->GetPropertyDefinitions().GetMap()) {
     if (prop.first.second == cmProperty::TARGET &&
         !prop.second.GetInitializeFromVariable().empty()) {

Tests/IncludeDirectories/CMakeLists.txt

@@ -121,12 +121,66 @@ add_library(ordertest ordertest.cpp)
 target_include_directories(ordertest SYSTEM PUBLIC SystemIncludeDirectories/systemlib)
 target_include_directories(ordertest PUBLIC SystemIncludeDirectories/userlib)
 
+# Test "IMPORTED_NO_SYSTEM" property and its interaction with "SYSTEM"
 add_library(ordertest2 ordertest.cpp)
 target_include_directories(ordertest2 SYSTEM PRIVATE SystemIncludeDirectories/systemlib)
 target_link_libraries(ordertest2 PRIVATE ordertest2_userlib)
 add_library(ordertest2_userlib INTERFACE IMPORTED)
 target_include_directories(ordertest2_userlib INTERFACE SystemIncludeDirectories/userlib)
 set_property(TARGET ordertest2_userlib PROPERTY IMPORTED_NO_SYSTEM 1)
+get_property(system_prop_value TARGET ordertest2_userlib PROPERTY SYSTEM)
+if (NOT system_prop_value)
+  message(SEND_ERROR "ordertest2_userlib SYSTEM property should be ON.")
+endif()
+
+# Test "SYSTEM" property of non-imported libraries
+add_library(ordertest3_systemlib INTERFACE)
+target_include_directories(ordertest3_systemlib INTERFACE SystemIncludeDirectories/systemlib)
+set_property(TARGET ordertest3_systemlib PROPERTY SYSTEM 1)
+add_library(ordertest3_userlib INTERFACE)
+target_include_directories(ordertest3_userlib INTERFACE SystemIncludeDirectories/userlib)
+add_library(ordertest3 ordertest.cpp)
+target_link_libraries(ordertest3 PRIVATE ordertest3_systemlib ordertest3_userlib)
+
+# Test "SYSTEM" property of imported libraries and its interaction with "IMPORTED_NO_SYSTEM"
+add_library(ordertest4 ordertest.cpp)
+target_include_directories(ordertest4 SYSTEM PRIVATE SystemIncludeDirectories/systemlib)
+target_link_libraries(ordertest4 PRIVATE ordertest4_userlib)
+add_library(ordertest4_userlib INTERFACE IMPORTED)
+target_include_directories(ordertest4_userlib INTERFACE SystemIncludeDirectories/userlib)
+set_property(TARGET ordertest4_userlib PROPERTY SYSTEM 0)
+get_property(imported_no_system_prop_value TARGET ordertest4_userlib PROPERTY IMPORTED_NO_SYSTEM)
+if (imported_no_system_prop_value)
+  message(SEND_ERROR "ordertest4_userlib IMPORTED_NO_SYSTEM property should be OFF.")
+endif()
+
+# Test the interaction between "SYSTEM" and "INTERFACE_SYSTEM_INCLUDE_DIRECTORIES"
+add_library(ordertest5_systemlib INTERFACE)
+target_include_directories(ordertest5_systemlib SYSTEM INTERFACE SystemIncludeDirectories/systemlib)
+# The default value of `SYSTEM` is already `OFF`. Here we explicitly set it again.
+set_property(TARGET ordertest5_systemlib PROPERTY SYSTEM 0)
+add_library(ordertest5_userlib INTERFACE)
+target_include_directories(ordertest5_userlib INTERFACE SystemIncludeDirectories/userlib)
+add_library(ordertest5 ordertest.cpp)
+target_link_libraries(ordertest5 PRIVATE ordertest5_systemlib ordertest5_userlib)
+
+# Test that the include of imported executable is treated as system by default.
+add_executable(ordertest6_systemexe IMPORTED)
+target_include_directories(ordertest6_systemexe INTERFACE SystemIncludeDirectories/systemlib)
+set_property(TARGET ordertest6_systemexe PROPERTY ENABLE_EXPORTS 1)
+add_library(ordertest6_userlib INTERFACE)
+target_include_directories(ordertest6_userlib INTERFACE SystemIncludeDirectories/userlib)
+add_library(ordertest6 ordertest.cpp)
+target_link_libraries(ordertest6 PRIVATE ordertest6_systemexe ordertest6_userlib)
+
+# Test that the include of imported executable is not treated as system if "SYSTEM" property is OFF.
+add_library(ordertest7 ordertest.cpp)
+target_include_directories(ordertest7 SYSTEM PRIVATE SystemIncludeDirectories/systemlib)
+target_link_libraries(ordertest7 PRIVATE ordertest7_userexe)
+add_library(ordertest7_userexe INTERFACE IMPORTED)
+target_include_directories(ordertest7_userexe INTERFACE SystemIncludeDirectories/userlib)
+set_property(TARGET ordertest7_userexe PROPERTY ENABLE_EXPORTS 1)
+set_property(TARGET ordertest7_userexe PROPERTY SYSTEM 0)
 
 add_subdirectory(StandardIncludeDirectories)
 add_subdirectory(TargetIncludeDirectories)