cmake: Overhaul downstream config to properly export version and dependencies

CMakeLists.txt

@@ -20,13 +20,26 @@ CMAKE_MINIMUM_REQUIRED(VERSION 3.15)
 
 project(k4FWCore)
 
+set(${PROJECT_NAME}_VERSION_MAJOR 1)
+set(${PROJECT_NAME}_VERSION_MINOR 1)
+set(${PROJECT_NAME}_VERSION_PATCH 0)
+
+set( ${PROJECT_NAME}_VERSION  "${${PROJECT_NAME}_VERSION_MAJOR}.${${PROJECT_NAME}_VERSION_MINOR}.${${PROJECT_NAME}_VERSION_PATCH}" )
+
 find_package(ROOT COMPONENTS RIO Tree REQUIRED)
 find_package(Gaudi REQUIRED)
-  find_package(podio 0.16.3)  # this will not find 1.0 and newer
-  if(NOT podio_FOUND)
-    # we try to find a newer version now
-    find_package(podio 1.0 REQUIRED)
-  endif()
+find_package(podio 0.16.3 QUIET)  # this will not find 1.0 and newer
+if(NOT podio_FOUND)
+  # we try to find a newer version now
+  find_package(podio 1.0 REQUIRED)
+else()
+  message(WARNING "Found podio < 1.0. This should still work, but consider moving to a newer version")
+endif()
+
+if(NOT podio_FOUND)
+  message(FATAL_ERROR "Could not find a suitable version of podio")
+endif()
+
 find_package(EDM4HEP REQUIRED)
 
 include(cmake/Key4hepConfig.cmake)
@@ -52,12 +65,4 @@ if(ENABLE_CPACK)
   include(cmake/${PROJECT_NAME}CPack.cmake)
 endif()
 
-
-install(EXPORT ${PROJECT_NAME}Targets
-  NAMESPACE ${PROJECT_NAME}::
-  FILE "${PROJECT_NAME}Targets.cmake"
-  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}/"
-  )
-
-gaudi_install(CMAKE cmake/${PROJECT_NAME}Config.cmake)
-
+include(cmake/k4FWCoreCreateConfig.cmake)

cmake/k4FWCoreConfig.cmake.in

@@ -0,0 +1,34 @@
+###############################################################################
+# k4FWCore CMake Config
+#
+# Exported Targets
+#  - k4FWCore::k4FWCore         The core library containing the PodioDataSvc
+#                               and the KeepDropSwitch
+#  - k4FWCore::k4FWCorePlugins  The plugin library for the core plugins
+#                               provided by k4FWCore. Includes all major
+#                               services for I/O and as well as some utility
+#                               algorithms
+#  - k4FWCore::k4Interface      The (header-only) target containing all
+#                               interface definitions
+#
+###############################################################################
+@PACKAGE_INIT@
+
+set_and_check(k4FWCore_INCLUDE_DIR "@PACKAGE_CMAKE_INSTALL_INCLUDEDIR@")
+set_and_check(k4FWCore_LIBRARY_DIR "@PACKAGE_CMAKE_INSTALL_LIBDIR@")
+
+include(CMakeFindDependencyMacro)
+find_dependency(podio @podio_VERSION@)
+find_dependency(Gaudi @Gaudi_VERSION@)
+find_dependency(EDM4HEP @EDM4HEP_VERSION@)
+find_dependency(ROOT @ROOT_VERSION@ COMPONENTS RIO Tree)
+
+if(NOT TARGET k4FWCore::k4FWCore)
+  include("${CMAKE_CURRENT_LIST_DIR}/k4FWCoreTargets.cmake")
+endif()
+
+check_required_components(k4FWCore)
+
+include(FindPackageHandleStandardArgs)
+get_property(TEST_K4FWCORE_LIBRARY TARGET k4FWCore::k4FWCore PROPERTY LOCATION)
+find_package_handle_standard_args(k4FWCore DEFAULT_MSG CMAKE_CURRENT_LIST_FILE TEST_K4FWCORE_LIBRARY)

cmake/k4FWCoreCreateConfig.cmake

@@ -0,0 +1,22 @@
+include(CMakePackageConfigHelpers)
+
+# Version file is same wherever we are
+write_basic_package_version_file(${PROJECT_BINARY_DIR}/k4FWCoreConfigVersion.cmake
+                                 VERSION ${k4FWCore_VERSION}
+                                 COMPATIBILITY SameMajorVersion)
+
+
+configure_package_config_file(${PROJECT_SOURCE_DIR}/cmake/k4FWCoreConfig.cmake.in
+                              ${PROJECT_BINARY_DIR}/k4FWCoreConfig.cmake
+                              INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/k4FWCore
+                              PATH_VARS CMAKE_INSTALL_INCLUDEDIR CMAKE_INSTALL_LIBDIR)
+
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/k4FWCoreConfig.cmake
+              ${CMAKE_CURRENT_BINARY_DIR}/k4FWCoreConfigVersion.cmake
+              DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME} )
+
+install(EXPORT ${PROJECT_NAME}Targets
+  NAMESPACE ${PROJECT_NAME}::
+  FILE "${PROJECT_NAME}Targets.cmake"
+  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}/"
+)

test/downstream-project-cmake-test/CMakeLists.txt

@@ -23,5 +23,13 @@ project(DownstreamProjectUsingk4FWCore)
 
 find_package(k4FWCore)
 
+if (NOT DEFINED ${k4FWCore_VERSION})
+  message(FATAL_ERROR "CAnnot find k4FWCore version information")
+endif()
+
+if (NOT ${k4FWCore_VERSION} MATCHES "^[0-9]+\\.[0-9+](\\.[0-9]+)?$")
+  message(FATEL_ERROR "Exported k4FWCore version cannot be used as a version: " ${k4FWCore_VERSION})
+endif()
+
 add_executable(appUsingk4FWCore main.cxx)
 target_link_libraries(appUsingk4FWCore k4FWCore::k4FWCore)