Which CMake version as the minimum?

Question

I want to define a minimum version to CMake with "cmake_minimum_required" facility. I have seen that some project set minimum version 2.8 some others set 3.0 or 3.2. I would like to learn your opinions and best practices about the topic.

Answer 1

The cmake_minimum_required() function is used to avoid any cryptic error messages due to the CMakeLists.txt assuming a later version of CMake than the one installed on the current host.

As an example, failing early, and with a clear message...

CMake 3.2 or higher is required. You are running version 2.8.12.2

...is to be preferred over something more cryptic (much) later on...

In file included from /home/foouser/src/testprj/string.cpp:1:0:
/home/foouser/src/testprj/string.hpp:94:29: error: ‘std::is_same’ has not been declared

...just because, in this example, the older CMake version does not support set( CMAKE_CXX_STANDARD 11 ). I am sure you'll agree.

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The ideal setting would be:

1. The oldest version with all the features your script needs.

Maximal compatibility with people running older versions, as well as with your script. But it requires testing which version exactly it was that first supported your constructs. So it usually boils down to:

2. The oldest version you have tested that has all the features your script needs.

That's probably good enough for most projects. And if you are the only one actually working on the project, and testing for CMake compatibility is really low on your list, you will probably end up with:

3. The version you are currently using.

This latter approach has a serious drawback once somebody else attempts to compile your project. Quite a few people are not using the latest version of everything. On Linux in particular, the default is to use whatever the package manager gives you. Ubuntu wily, for example, is currently at version 3.2.2 -- you may have a later version, but unless you need a later version, you shouldn't require it (as that means people won't be able to build your project without first installing a newer version of CMake, manually).

What you should not be doing is...

• Requiring a very old version, but not actually testing against that old version (NO!).

The reasons should be obvious -- building could fail, without the user getting any hint as to why things went wrong.