export: Propagate IMPORTED_NO_SYSTEM target property to consumers

Enabling `IMPORTED_NO_SYSTEM` on a target built within the project has
no effect on the build system, but it is still a useful way to set the
property on imported targets generated by `install(EXPORT)` and
`export()`.

Issue: #17364

Help/prop_tgt/IMPORTED_NO_SYSTEM.rst

@@ -8,7 +8,9 @@ a ``SYSTEM`` library.  This has the following effects:
   as ``SYSTEM`` include directories when compiling consumers, as they
   would be by default.
 
-Ignored for non-imported targets.
+This property can also be enabled on a non-imported target.  Doing so does
+not affect the build system, but does tell the :command:`install(EXPORT)` and
+:command:`export` commands to enable it on the imported targets they generate.
 
 See the :prop_tgt:`NO_SYSTEM_FROM_IMPORTED` target property to set this
 behavior on the target consuming the include directories rather than

Source/cmExportFileGenerator.cxx

@@ -1072,6 +1072,12 @@ void cmExportFileGenerator::GenerateImportTargetCode(
     os << "set_property(TARGET " << targetName << " PROPERTY DEPRECATION "
        << cmExportFileGeneratorEscape(target->GetDeprecation()) << ")\n";
   }
+
+  if (target->GetPropertyAsBool("IMPORTED_NO_SYSTEM")) {
+    os << "set_property(TARGET " << targetName
+       << " PROPERTY IMPORTED_NO_SYSTEM 1)\n";
+  }
+
   os << "\n";
 }
 

Tests/ExportImport/Export/CMakeLists.txt

@@ -145,6 +145,19 @@ set_property(TARGET testLibCycleA PROPERTY LINK_INTERFACE_MULTIPLICITY 3)
 add_library(testLibNoSONAME SHARED testLibNoSONAME.c)
 set_property(TARGET testLibNoSONAME PROPERTY NO_SONAME 1)
 
+add_library(testInterfaceIncludeUser INTERFACE)
+target_include_directories(testInterfaceIncludeUser
+  INTERFACE
+    "$<INSTALL_INTERFACE:include/testInterfaceIncludeUser>"
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/testInterfaceIncludeUser>"
+)
+set_property(TARGET testInterfaceIncludeUser PROPERTY IMPORTED_NO_SYSTEM 1)
+install(
+  FILES
+    "${CMAKE_CURRENT_SOURCE_DIR}/include/testInterfaceIncludeUser/testInterfaceInclude.h"
+  DESTINATION include/testInterfaceIncludeUser
+)
+
 cmake_policy(PUSH)
 cmake_policy(SET CMP0022 NEW)
 # Test exporting dependent libraries into different exports
@@ -531,6 +544,7 @@ install(
   cmp0022NEW cmp0022OLD
   TopDirLib SubDirLinkA
   systemlib
+  testInterfaceIncludeUser
   EXPORT exp
   RUNTIME DESTINATION $<1:bin>$<0:/wrong>
   LIBRARY DESTINATION $<1:lib>$<0:/wrong> NAMELINK_SKIP
@@ -590,6 +604,7 @@ export(TARGETS testExe1 testLib1 testLib2 testLib3
   cmp0022NEW cmp0022OLD
   TopDirLib SubDirLinkA
   systemlib
+  testInterfaceIncludeUser
   NAMESPACE bld_
   FILE ExportBuildTree.cmake
   )

Tests/ExportImport/Export/include/testInterfaceIncludeUser/testInterfaceInclude.h

@@ -0,0 +1 @@
+/* empty file */

Tests/ExportImport/Import/A/CMakeLists.txt

@@ -70,6 +70,10 @@ target_link_libraries(imp_testExe1
   exp_testLibPerConfigDest
   )
 
+add_library(imp_testInterfaceInclude1 STATIC imp_testInterfaceInclude1.c)
+target_include_directories(imp_testInterfaceInclude1 SYSTEM PRIVATE testInterfaceIncludeSystem)
+target_link_libraries(imp_testInterfaceInclude1 PRIVATE exp_testInterfaceIncludeUser)
+
 # Try building a plugin to an executable imported from the install tree.
 add_library(imp_mod1 MODULE imp_mod1.c)
 target_link_libraries(imp_mod1 exp_testExe2)
@@ -110,6 +114,10 @@ target_link_libraries(imp_testExe1b
   bld_testLibPerConfigDest
   )
 
+add_library(imp_testInterfaceInclude1b STATIC imp_testInterfaceInclude1.c)
+target_include_directories(imp_testInterfaceInclude1b SYSTEM PRIVATE testInterfaceIncludeSystem)
+target_link_libraries(imp_testInterfaceInclude1b PRIVATE bld_testInterfaceIncludeUser)
+
 add_custom_target(check_testLib1_genex ALL
   COMMAND ${CMAKE_COMMAND} -DtestLib1=$<TARGET_FILE:exp_testLib1>
                            -Dprefix=${CMAKE_INSTALL_PREFIX}

Tests/ExportImport/Import/A/imp_testInterfaceInclude1.c

@@ -0,0 +1,6 @@
+#include "testInterfaceInclude.h"
+
+int imp_testInterfaceInclude1(void)
+{
+  return 0;
+}

Tests/ExportImport/Import/A/testInterfaceIncludeSystem/testInterfaceInclude.h

@@ -0,0 +1 @@
+#error testInterfaceInclude.h included from testInterfaceIncludeSystem