Re: [cmake-developers] Automatically set policies for shipped modules

[Brad King]

On 09/17/2018 09:14 AM, Craig Scott wrote:
> We may also need to be careful about CMP0011

The policy scope added for our own modules can be marked as a "weak"
scope.  This means that specific policies can be set when the scope
is first opened in C++ code, but policy settings inside the scope will
leak out to the parent scope.  This inner "weak" scope can be added
to apply CMP0057 and such whether or not the main inclusion has its
own strong scope.

-Brad
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Re: [cmake-developers] Automatically set policies for shipped modules

[Craig Scott]

On Mon, Sep 17, 2018 at 9:07 PM Brad King  wrote:

> On 09/17/2018 04:01 AM, Rolf Eike Beer wrote:
> > I suggest that every module included from the CMake installation is
> > considered clean for whatever we do and automatically gets a policy
> > scope push/pop right from the C++ level.
>
> That's fine with me for policies like CMP0057 that affect the
> CMake language features.  We can't do that for every policy
> because some policies affect the way modules behave for the
> calling project.
>
> When include() or find_package() establishes the policy scope
> for the included module we can inject a few settings.
>

We may also need to be careful about CMP0011 (Included scripts do automatic
cmake_policy PUSH and POP), since that has come up before with regard to
why some modules needed explicit policy push-pop even though include()
would normally do that for us automatically.


-- 
Craig Scott
Melbourne, Australia
https://crascit.com

New book released: Professional CMake: A Practical Guide

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Re: [cmake-developers] Automatically set policies for shipped modules

[Brad King]

On 09/17/2018 04:01 AM, Rolf Eike Beer wrote:
> I suggest that every module included from the CMake installation is 
> considered clean for whatever we do and automatically gets a policy 
> scope push/pop right from the C++ level.

That's fine with me for policies like CMP0057 that affect the
CMake language features.  We can't do that for every policy
because some policies affect the way modules behave for the
calling project.

When include() or find_package() establishes the policy scope
for the included module we can inject a few settings.

Thanks,
-Brad
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[cmake-developers] Automatically set policies for shipped modules

[Rolf Eike Beer]

I have seen multiple commits basically wrapping Modules/* in 
cmake_policy(PUSH|POP). I neither find that appealing nor do I think 
that this will scale for maintenance.


I suggest that every module included from the CMake installation is 
considered clean for whatever we do and automatically gets a policy 
scope push/pop right from the C++ level. The policies are all set to 
new. This has several advantages:


-we can just use whatever things CMake offers in them
-adding new policies during development would more likely cause things 
to "break" earlier, i.e. if a module is not clean for a new policy we 
may notice this earlier
-processing of the modules themselves should be slightly faster as the 
whole compat code paths are not taken into account right from the start


If a module needs to offer e.g. a function with a specific "old" 
behavior it can still explicitely set this policy to whatever value it 
needs. It does not need to push/pop as that will be done by the C++ code 
anyway.


Opinions?

Eike
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