[cmake-developers] different behavior of cmake_minimum_required(3.0) and 3.1

[Rolf Eike Beer]

Am 2019-03-18 14:45, schrieb Brad King:
> On 3/15/19 6:10 PM, Rolf Eike Beer wrote:
>> I suspected it was a policy thing, so I tried this:
>> 
>> foreach(_p RANGE 21 54)
>>        cmake_policy(SET CMP00${_p} OLD)
>> endforeach()
> 
> Only policies 51-54 were added between 3.0 and 3.1.

The starting point was 2.8.11, I have not bothered to change the loop 
afterwards.

>  I suggest
> testing with
> 
>     cmake_minimum_required(VERSION 3.0)
>     cmake_policy(SET CMP0051 NEW)
>     cmake_policy(SET CMP0052 NEW)
>     cmake_policy(SET CMP0053 NEW)
>     cmake_policy(SET CMP0054 NEW)
> 
> and then trying different combinations.  My guess is CMP0054.

Good idea.

> -------------------------------------------------------------
> 
> While looking at the source of that project, I noticed that
> both `CMakeLists.txt` and `smtk-import/CMakeLists.txt` call
> the `project()` command before `cmake_minimum_required()`.
> The other order is preferred:
> 
>     cmake_minimum_required(VERSION 2.8.11)
>     project(Subsurface)
> 
> because there are policies that affect project()'s behavior.
> This order preference is documented by both commands.

This is not the case, I have changed that and it did not help.

> I also noticed this code:
> 
> ```
> # don't process generated files - this is new in 3.10
> if (POLICY CMP0071)
>         cmake_policy(SET CMP0071 OLD)
> endif()
> ```
> 
> The cmake-policies(7) manual states that a policy should only
> be set to OLD to silence warnings in frozen code bases or in
> short-term circumstances.
> 
> The proper way to deal with CMP0071 is to set it to NEW
> and set the `SKIP_AUTO*` properties on the sources that should
> not be processed.

I'll look into this. The problem here is that this IIRC breaks with new
CMake and old Qt version where this would process generated files twice.

Eike