[!298] [cmake] Give a meaningful error message if not cloned recursively

Merge branch 'feature/check-for-submodule-existence' into 'master'

See merge request [extensions/dune-codegen!298]

  [extensions/dune-codegen!298]: Noneextensions/dune-codegen/merge_requests/298

cmake/modules/CMakeLists.txt

 install(FILES deplist.py
               dune-codegen_sourcepath.py
               DuneCodegenMacros.cmake
+              DuneSubmoduleChecker.cmake
               GeneratedSystemtest.cmake
         DESTINATION ${DUNE_INSTALL_MODULEDIR})

cmake/modules/DuneCodegenMacros.cmake

@@ -160,3 +160,4 @@ function(add_generated_executable)
 endfunction()
 
 include(GeneratedSystemtests)
+include(DuneSubmoduleChecker)

cmake/modules/DuneSubmoduleChecker.cmake

+# A CMake module to check for the existence of submodules!
+#
+# .. cmake_function:: dune_check_submodule
+#
+#    .. cmake_param:: PATH
+#       :required:
+#
+#       The relative path to the submodule directory
+#
+#    .. cmake_param:: INDICATOR
+#       :required:
+#
+#       A filename (like setup.py) that indicates a correctly cloned submodule
+#
+
+
+function(dune_check_submodule)
+  # Parse Arguments
+  include(CMakeParseArguments)
+  cmake_parse_arguments(SUBMODULE "" "PATH;INDICATOR" "" ${ARGN})
+
+  if(SUBMODULE_UNPARSED_ARGUMENTS)
+    message(WARNING "Unparsed arguments in dune_check_submodule: This often indicates typos!")
+  endif()
+
+  if(NOT SUBMODULE_PATH)
+    message(FATAL_ERROR "PATH argument not given to dune_check_submodule!")
+  endif()
+  if(NOT SUBMODULE_INDICATOR)
+    message(FATAL_ERROR "INDICATOR argument not given to dune_check_submodule!")
+  endif()
+
+  if(NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${SUBMODULE_PATH}/${SUBMODULE_INDICATOR})
+    message(FATAL_ERROR "No git submodule found at location ${CMAKE_CURRENT_SOURCE_DIR}/${SUBMODULE_PATH}. You should clone this repository with the --recursive flag! It is described in the README!")
+  endif()
+endfunction()

python/CMakeLists.txt

+# Check that the submodules have been checked out!
+dune_check_submodule(PATH pytools INDICATOR setup.py)
+dune_check_submodule(PATH cgen INDICATOR setup.py)
+dune_check_submodule(PATH pymbolic INDICATOR setup.py)
+dune_check_submodule(PATH loopy INDICATOR setup.py)
+dune_check_submodule(PATH ufl INDICATOR setup.py)
+
 # Install all the external packages that we have as submodules
 dune_python_install_package(PATH pytools)
 dune_python_install_package(PATH cgen)