Could our long nightmare with finding netcdf with cmake be nearly over???

[jgfouca]

I'm trying to build scorpio on a generic linux machine (ubuntu). I have installed the various netcdf packages with apt-get. My package manager did install a file that would allow a CMake user to do find_package(netCDF ...):

/usr/lib/x86_64-linux-gnu/cmake/netCDF/netCDFConfig.cmake

I tested this with a simple program and it seems to work:

find_package(netCDF REQUIRED C)

# Add an executable target
add_executable(my_netcdf_app main.c)

# Link the NetCDF library to the executable
# The netCDF::netcdf target is an imported target defined by find_package(netCDF)
target_link_libraries(my_netcdf_app PRIVATE netCDF::netcdf)

The version of netcdf that I have is 4.8.1. I don't know when proper CMake support was finally added. AI is telling me this support was added in 4.3, which is older than our minimum required version, so perhaps this is a feature we can rely on? If not, it might be worth bumping the minimum netcdf to something newer just to avoid dealing with the current hellscape of netcdf integration with our cmake projects.

As I understand it, most of E3SM is currently relying on scorpio to find the netcdf cmake package. Due to historical lack of a reliable find module for netcdf, scorpio supplies its own module scorpio/cmake/FindNetCDF.cmake. We have used various homegrown modules over the years, all of which use "old-school" cmake style the predates object-oriented targets.

I will note that I currently cannot build eamxx/scorpio on my generic linux machine due to the scorpio FindNetCDF not finding netcdf. I can't even force it to use the module that my package manager gave me due to the capitalization being different NetCDF vs. netCDF (we also have NETCDF in many places as well, so three different ways to capitalize "netcdf", what fun!).

CMake Error at /home/jfoucar/E3SM/externals/scorpio/src/clib/CMakeLists.txt:245 (message):
  Could not find PnetCDF and NetCDF libraries.  SCORPIO requires PnetCDF
  and/or NetCDF C libraries

I think it would be great for the project to finally move past the era of home-rolled find modules for netcdf, so I have marked this as "high priority". Feel free to overrule me.

[jayeshkrishna]

I am ok with moving to the CMake provided modules for finding NetCDF. But we first need to test it on all the machines that we care about and then make the change. We would also need to check if these modules have enough information about the NetCDF features supported in the build (e.g. is NCZarr supported etc).

A related feature is the transition to using find_library(SCORPIO) for CIME builds and I will work on that feature.

(I would not categorize this feature as "high priority" though)

[bartgol]

It would be really nice to simply rely on TPLs to provide the correct cmake modules without having to ship user-provided ones. If this is indeed working out of the box with reasonable netcdf versions, then it would be a nice improvement.

I agree that it is not a "high" priority. But for those who maintain e3sm build system it may be ground for a celebratory beer... :)