DRAFT: FOR COMMENTS Support verbosity in cmake output

[coldav]

Overview

For message cmake commands replace with ca_message and support a verbosity level which can be changed using CA_CMAKE_VERBOSE_LEVEL(0 none, 1 summary, 2 detail). Including from LLVM will by default set to 0.

Reason for change

Including from LLVM was noisy

[hvdijk]

I think this should be a cached variable so that if CMake decides it needs to re-run itself, the previously set verbosity level gets picked up. It also means we only need a single variable because cache variables by default (if FORCE is not used) do not override user settings.

[coldav]

I did initially go that way, but it seemed to require the fetcher to set the variable, rather than doing it by default in "inside llvm".

[hvdijk]

We could just keep the default as always verbose, and override it from within DPC++.

[coldav]

I did think about that, I was worried that we end up adding loads and loads of cmake options before including it and maybe this was another way.

[hvdijk]

If DPC++ native CPU wants loads of things different from what we want as the default, there's probably a bigger problem that we should discuss. I would expect that a list of just those things where DPC++ wants something different to be relatively short, shorter than repeated OCK_IN_LLVM_TREE checks. Is that not the case?

[hvdijk]

STATUS already indicates the verbosity, and CMake has ways of automatically suppressing noise based on the requested verbosity level (CMAKE_MESSAGE_LOG_LEVEL). We could use that.

[coldav]

I thought about that, but it felt that we should output all warnings by default, and STATUS could have two levels i.e. summary information and detail information. The only one I felt has real meaning for me is the LLVM version when i run it. However I am open-minded we could just use STATUS etc as you suggest.

[hvdijk]

The ones that you mark as verbose here do have meaning for me, I check them almost every time I need to re-run CMake to make sure I didn't leave some extension off that I will be trying to test. But I wouldn't mind marking them as message(VERBOSE [...]) provided we continue to see them in our own CI, if it makes it easier for you to suppress what is just noise to you.

[coldav]

CMAKE_MESSAGE_LOG_LEVEL would be across LLVM too, whereas I think they want to only suppress OCK messages

[hvdijk]

CMake variables have directory scope. If set in a subdirectory, it should only affect that subdirectory without affecting the rest of LLVM.

[coldav]

I did try that, but I'll try again.

[hvdijk]

CMake's if command is weird and in most cases, variables should not be expanded explicitly, because if will already try to expand them and you run the risk of double expansion. if(CA_MESSAGE_VERBOSITY_LEVEL LESS_EQUAL OCK_CMAKE_VERBOSE_LEVEL) should work.