Prevent nrnivmodl running on every build (#496)

* Prevent nrnivmodl running on every build.
    Also run cmake-format for the sake of the CI.
* Fix standalone build of CoreNEURON.
* Declare {build}/share/modfile/*.mod dependencies.
    This means that modifying
     {source}/coreneuron/mechanism/mech/modfile/{foo}.mod and running cmake
     --build will update {build}/share/modfile/{foo}.mod.

Author: olupton

coreneuron/CMakeLists.txt

@@ -53,9 +53,29 @@ set(KINDERIV_HEADER_FILE "${CMAKE_CURRENT_BINARY_DIR}/_kinderiv.h")
 
 set(NMODL_UNITS_FILE "${CMAKE_BINARY_DIR}/share/mod2c/nrnunits.lib")
 
-# copy inbuilt mod files to share
-file(COPY ${CORENEURON_PROJECT_SOURCE_DIR}/coreneuron/mechanism/mech/modfile
-     DESTINATION ${CMAKE_BINARY_DIR}/share)
+# copy inbuilt mod files {source}/coreneuron/mechanism/mech/modfile/*.mod to
+# {build_dir}/share/modfile/
+file(GLOB builtin_modfiles
+     "${CORENEURON_PROJECT_SOURCE_DIR}/coreneuron/mechanism/mech/modfile/*.mod")
+# get the corresponding list of paths to the modfiles in the build directory
+set(builtin_modfile_in_build_dir)
+foreach(builtin_modfile ${builtin_modfiles})
+  get_filename_component(builtin_modfile_name "${builtin_modfile}" NAME)
+  list(APPEND builtin_modfile_in_build_dir
+       "${CMAKE_BINARY_DIR}/share/modfile/${builtin_modfile_name}")
+endforeach()
+file(MAKE_DIRECTORY "${CMAKE_BINARY_DIR}/share/modfile")
+# set up a build rule that ensures the modfiles in the build directory are updated if their
+# counterparts in the source directory are touched
+add_custom_command(
+  OUTPUT ${builtin_modfile_in_build_dir}
+  DEPENDS ${builtin_modfiles}
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different ${builtin_modfiles}
+          "${CMAKE_BINARY_DIR}/share/modfile")
+add_custom_target(copy-builtin-modfiles ALL DEPENDS ${builtin_modfile_in_build_dir})
+set(CORENEURON_BUILTIN_MODFILES
+    "${builtin_modfile_in_build_dir}"
+    CACHE STRING "List of builtin modfiles that nrnivmodl-core implicitly depends on" FORCE)
 
 # =============================================================================
 # coreneuron GPU library
@@ -155,14 +175,18 @@ set_target_properties(
 # =============================================================================
 # create special-core with halfgap.mod for tests
 # =============================================================================
-add_custom_target(
-  nrniv-core ALL
+set(modfile_directory "${CORENEURON_PROJECT_SOURCE_DIR}/tests/integration/ring_gap/mod")
+file(GLOB modfiles "${modfile_directory}/*.mod")
+set(output_binaries "${CMAKE_BINARY_DIR}/bin/${CMAKE_SYSTEM_PROCESSOR}/special-core"
+                    "${CMAKE_BINARY_DIR}/bin/${CMAKE_SYSTEM_PROCESSOR}/libcorenrnmech.a")
+add_custom_command(
+  OUTPUT ${output_binaries}
+  DEPENDS scopmath coreneuron ${NMODL_TARGET_TO_DEPEND} ${modfiles} ${CORENEURON_BUILTIN_MODFILES}
   COMMAND ${CMAKE_BINARY_DIR}/bin/nrnivmodl-core -b STATIC -m ${CORENRN_MOD2CPP_BINARY} -p 1
-          ${CORENEURON_PROJECT_SOURCE_DIR}/tests/integration/ring_gap/mod
+          "${modfile_directory}"
   WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/bin
-  BYPRODUCTS ${CMAKE_BINARY_DIR}/bin/${CMAKE_SYSTEM_PROCESSOR}/special-core
   COMMENT "Running nrnivmodl-core with halfgap.mod")
-add_dependencies(nrniv-core scopmath coreneuron ${NMODL_TARGET_TO_DEPEND})
+add_custom_target(nrniv-core ALL DEPENDS ${output_binaries})
 
 include_directories(${CORENEURON_PROJECT_SOURCE_DIR})