cpp_cc_git_submodule helper requires newer version of CMake than documented

[olupton]

The BUILD and PACKAGE keyword arguments to cpp_cc_git_submodule are supposed to work as flags even when they are not passed values. i.e.

cpp_cc_git_submodule(foo)
cpp_cc_git_submodule(foo BUILD)
cpp_cc_git_submodule(foo BUILD bar)

are all supposed to do different things. This relies on the <prefix>_KEYWORDS_MISSING_VALUES output of cmake_parse_arguments, which was only added in CMake v3.15. Without this feature IIUC we cannot distinguish between the first two cases. The coding conventions' README states the minimum version is v3.10.

Either we should explicitly state that v3.15 is required, or cpp_cc_git_submodule should be modified for compatibility with older versions.

[olupton]

cc: @alkino @tristan0x

[alkino]

ubuntu 18.04 (LTS) install cmake 3.10.2. nmodl still needs cmake >= 3.8, coreneuron cmake >= 3.7.

[tristan0x]

Thank you for noticing this @olupton
cpp_cc_git_submodule CMake function should indeed be modified to work as expected with CMake 3.10.2 or higher.

[tristan0x]

ubuntu 18.04 (LTS) install cmake 3.10.2. nmodl still needs cmake >= 3.8, coreneuron cmake >= 3.7.

Are these CMake versions supported for a reason or could they be bumped to CMake 3.10.2?
Maybe @pramodk can answer this.

[olupton]

OK, if the minimum version is going to remain 3.10.2 then I fear we need to change the API to something like

cpp_cc_git_submodule(foo BUILD BUILD_ARGUMENTS bar)

for the third case above. Do you know if/were this is actually used?

[tristan0x]

OK, if the minimum version is going to remain 3.10.2 then I fear we need to change the API to something like

cpp_cc_git_submodule(foo BUILD BUILD_ARGUMENTS bar)

for the third case above. Do you know if/were this is actually used?

I thought it was used at least in CoreNeuron, but apparently not. API can be changed at will!