Unify cmake_minimum_required to 3.14.2

[jkotas]

• Set cmake_minimum_required in top level projects to 3.14.2 (the lowest version used by the CI currently)
• Delete cmake_minimum_required from child projects
• Leave the cmake_minimum_required alone in vendored projects (zlib)

Fixed #1311

[danmoseley]

Does CMake allow the cmake_minimum_required to be in a shared imported file?

[danmoseley]

Should we upgrade the CI machines?

[jkotas]

Should we upgrade the CI machines?

I do not see a good reason to. We have more important things to do. Note that forcing newer version of the tools is creating a lot of busy work for everybody. I think it should be done with very low frequency (e.g. once a year at most).

[jkotas]

Does CMake allow the cmake_minimum_required to be in a shared imported file?

Probably yes. There is a lot of other stuff that the top-level cmake files can share.

[am11]

the lowest version used by the CI currently

Typically the cmake_minimum_required version is the lowest version which supports all features used by the project. The lower this version is the less pain it is to build the project to older platforms, so folks normally tend to push back a little and rev min version sparingly. For example, the version of cmake provided by yum on CentOS 6.10 i386 (rel. JUL 2018) is v2.8.8 (rel MAY 2013). In such platforms, the only option is to compile newer cmake from source by ourselves.

[jkotas]

The lower this version is the less pain it is to build the project to older platforms, so folks normally tend to push back a little and rev min version sparingly.

Yes, I agree. For better or worse, we officially require 3.15.5 now and I hope that we won't bump this for a while.

[danmoseley]

Yes, I agree. For better or worse, we officially require 3.15.5 now and I hope that we won't bump this for a while.

If we're not updating the CI machines, it sounds like it's 3.14.2 isn't it? (And docs should match)

As I understand it, we have periodically required a newer CMake in order to create project files that open clean in the latest VS, and many folks on the team stay up to date with previews, etc. Perhaps the way forward is to require 3.14.2 as long as possible, but allow newer versions, adding "policy" directives as needed to ensure we get the same result from both.

[jkotas]

it sounds like it's 3.14.2 isn't it?

I believe that we need 3.15.x on Windows, but can get away with a bit lower version on Unix.

[jkotas]

we have periodically required a newer CMake in order to create project files that open clean in the latest VS

Yes, we required newer CMake on Windows to keep up with latest VS. The minimum required version on non-Windows was quite a bit lower. The thing that forced us to 3.14+ on non-Windows was taking advantage of the new CMake features.

adding "policy" directives as needed to ensure we get the same result from both.

I do not follow. You will get the same results as long as you specify the target version.

[danmoseley]

I do not follow. You will get the same results as long as you specify the target version.

You're right - you already explained that cmake_minimum_required also sets the "compat mode" to that version.

[danmoseley]

OK to indicate 3.14.2 in https://github.com/dotnet/runtime/blob/master/docs/workflow/requirements/linux-requirements.md ? It currently does not specify. They'll find out as soon as they hit build, but it is nice to know when you set up.

[jkotas]

OK to indicate 3.14.2 in https://github.com/dotnet/runtime/blob/master/docs/workflow/requirements/linux-requirements.md ?

Done.

[jkotas]

@danmosemsft @jkoritzinsky Could you please take a look and sign-off if the change looks good?