[cmake-developers] A policy for Policies

[Bill Hoffman]

On 6/10/2015 4:57 PM, Alexander Neundorf wrote:
> If the conclusion would be a policy is removed after 5 years, it's deadline
> could even be part of the error/warning message right from the point when it
> is introduced ("you are relying on CMP1234 OLD behaviour. This will be removed
> June 2020.").
>
> Then I could (at work) ignore this maybe until 2017 or 2018, and then it would
> slowly rise in my priority, and at some point I would fix it in some spare
> time.
I guess what we want to do is to come up with a system where the "fix" 
is not to just add OLD.   We want to be able to build old releases of 
projects and not break them.  However, if we change something that 
requires changes in the CMakeLists.txt we don't want the developers to 
just set to OLD, we want them to fix it.  If someone goes to the trouble 
of editing the CMakeLists.txt, they should just do the fix not set to 
OLD to shut up the warning.

There is also a whole bunch of users of CMake that have never written a 
single line of CMake code.  They just build software and follow 
instructions.  We want to try real hard to make things work for them and 
not to have a version of CMake nightmare for them.

So, erroring on OLD earlier might work, but still supporting the OLD 
stuff with a warning if no one tried explicitly to set things to use 
OLD, they just had a working build system.

-Bill