⚠️ CMake 3.12 is required for the development branches

[drdanz]

According to YARP policies, we can now drop CMake 3.5 on the development branches.

As discussed in robotology/ycm-cmake-modules#261, we decided to make an exception for the next release cycle, and to require CMake 3.12. This will require some extra work for Debian 9 stretch (oldstable) and Ubuntu 18.04 bionic users who want to use the development branches, since on their main repositories a compatible version is not available.

Debian 9

[Note] I personally recommend to upgrade the system, or to keep working with the latest YCM/YARP release, since, according to our policies, it's really close to the end of support.

You can find CMake 3.13.2 in the stretch-backports repository.
Instructions to install from backports can be found here, this is just a summary that can be copied and pasted.

echo deb http://ftp.debian.org/debian stretch-backports main | sudo tee -a /etc/apt/sources.list.d/stretch-backports.list
sudo apt-get update
sudo apt-get -t stretch-backports install cmake

if you plan to use cmake-curses-gui and/or cmake-qt-gui, you should install these packages as well from the stretch-backports repository

Ubuntu 18.04

You can find the latest CMake release in the Kitware APT repository. You can find the full instructions for the installation on the website, this is just a summary that can be copied and pasted.

sudo apt-get update
sudo apt-get install apt-transport-https ca-certificates gnupg software-properties-common wget
wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | sudo apt-key add -
sudo apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main'
sudo apt-get update
sudo apt-get install kitware-archive-keyring
sudo apt-key --keyring /etc/apt/trusted.gpg del C1F34CDD40CD72DA
sudo apt-get install cmake

if you plan to use cmake-curses-gui and/or cmake-qt-gui, you should install these packages as well from the Kitware APT Repository repository

[drdanz]

Please note that it was reported that CMake 3.20 (released a couple of days ago) has a few regressions.
If you are still on Ubuntu 18.04 and you are using the Kitware APT repository and you experience issues, I suggest to downgrade CMake to 3.19.5 by running:

sudo apt-get install cmake=3.19.5-0kitware