Handle no-target case through a user information. (#408)

Config.cmake.in

@@ -108,7 +108,7 @@ IF(COMMAND ADD_REQUIRED_DEPENDENCY)
   ENDFOREACH()
 ENDIF(COMMAND ADD_REQUIRED_DEPENDENCY)
 
-include("${CMAKE_CURRENT_LIST_DIR}/@[email protected]")
+@INCLUDE_TARGETS_FILE@
 
 foreach(component ${@PROJECT_NAME@_FIND_COMPONENTS})
   set(comp_file "${CMAKE_CURRENT_LIST_DIR}/${component}Config.cmake")

base.cmake

@@ -76,6 +76,13 @@
 #     This tells jrl-cmakemodules that you are using export functionalities so it will
 #     hook the installation of your configuration files. Defaults to false
 #
+#   .. variable:: PROJECT_EXPORT_NO_TARGET
+#
+#     This tells jrl-cmakemodules that there is no targets in the project.
+#     However the export functionalities are still provided to detect the
+#     project properties. Not setting this variable when no target is present
+#     will result in an error.
+#
 #   Macros
 #   ------
 #

package-config.cmake

@@ -154,6 +154,13 @@ if(_PKG_CONFIG_REQUIRES)
   endforeach()
   list(REMOVE_DUPLICATES _PKG_CONFIG_REQUIRES_LIST)
 endif(_PKG_CONFIG_REQUIRES)
+
+if(NOT PROJECT_EXPORT_NO_TARGET)
+  set(INCLUDE_TARGETS_FILE "include(\"\${CMAKE_CURRENT_LIST_DIR}/${TARGETS_EXPORT_NAME}.cmake\")")  
+else()
+  set(INCLUDE_TARGETS_FILE "# Package with no targets")
+endif()
+
 configure_package_config_file(
     "cmake/Config.cmake.in"
     "${PROJECT_CONFIG}"
@@ -170,11 +177,14 @@ install(
 
 # Config
 #   * <prefix>/lib/cmake/Foo/FooTargets.cmake
-install(
+if(NOT PROJECT_EXPORT_NO_TARGET)
+  install(
     EXPORT "${TARGETS_EXPORT_NAME}"
     NAMESPACE "${namespace}"
     DESTINATION "${CONFIG_INSTALL_DIR}"
-)
+    )
+endif()
+
 ENDMACRO(SETUP_PROJECT_PACKAGE_FINALIZE)
 
 #.rst: