Re: [CMake] [MSVC] Setting warning level on target feels like long-time bug

[Brad King via CMake]

On 12/9/18 8:09 AM, Marc CHEVRIER wrote:
> The real question is how to manage cleanly target specific flags
> overriding global or directory defaults?

All the optimization and warning flags currently handled by
`CMAKE__FLAGS[_]` need to have abstractions
introduced (e.g. target properties or something) and the
defaults re-thought.  Transition can be handled via a policy.

-Brad
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Re: [CMake] [MSVC] Setting warning level on target feels like long-time bug

[Mateusz Loskot]

On Sun, 9 Dec 2018 at 14:09, Marc CHEVRIER  wrote:
>
> I think the discussion is shifting from the initial problem which was 
> unwanted warning « Command line warning D9025: overriding '/W3' with '/W4' ».

I disagree with your opinion.
Fixing just the warning would be a symptomatic treatment.

> Changing defaults is not a good idea from my point of view because relying on 
> defaults can be problematic if Microsoft decide to change the default 
> behaviour.

Although I think it is a long shot at something that is (highly)
unlikely to change, YAGNI consideration,
I understand CMake developers may be reluctant to change the long-time defaults.

> The real question is how to manage cleanly target specific flags overriding 
> global or directory defaults?

From end-user point of view (I have not checekd CMake implementation),
I'd either do not explicitly set -W defaults or strip any -W option
prior re-setting
with (possibly) new value passed to target_compile_options.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
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Re: [CMake] [MSVC] Setting warning level on target feels like long-time bug

[Marc CHEVRIER]

I think the discussion is shifting from the initial problem which was unwanted 
warning « Command line warning D9025: overriding '/W3' with '/W4' ».

Changing defaults is not a good idea from my point of view because relying on 
defaults can be problematic if Microsoft decide to change the default behaviour.

Moreover, removing ‘/W3’ from defaults will remove the warning for this flag 
but the problem remains for all other flags possibly overloaded.

The real question is how to manage cleanly target specific flags overriding 
global or directory defaults? And the frustrating thing is that cl.exe do not 
allow to disable D9025 warning! :(

Le 9 déc. 2018 à 13:32 +0100, Mateusz Loskot , a écrit :
> On Sun, 9 Dec 2018 at 12:14, Craig Scott  wrote:
> >
> > From what I understand from a very limited quick search just now,
> > it seems that /W3 is the default warning level for Visual Studio
>
> Yes, it is the default level indeed.
>
> > but CMake explicitly adds it as a default compiler flag in 
> > CMAKE__FLAGS_INIT.
> > This makes me wonder if it has always been the default, otherwise it isn't 
> > clear why it was deemed necessary to add it.
>
> Yes, I'd suspect it was added as 'just in case' too eagerly.
>
> > More to the point, unless there's a reason not to, perhaps we could 
> > consider removing it from the default flags CMake sets.
> > I think this would largely address the situation you're describing and 
> > shouldn't actually change the behavior of existing projects.
>
> Yes, it should be removed.
> Unless I'm missing an important reason behind the explicit -W3.
>
> No, "This has been the default since CMake began" [1], is not enough
> rationale to keep it.
>
> In the old times of manual editing of CMAKE_CXX_FLAGS, it was not a huge deal
> - in fact, fiddling with CMAKE_CXX_FLAGS was quite canonical way of
> doing things..
> But with the advent of target_compile_options, the string call
> requirement is just unacceptable.
>
> [1] https://gitlab.kitware.com/cmake/cmake/issues/18317
>
> > I've CC'ed the developer's list and suggest that follow-up discussion 
> > should occur there.
>
> FYI, I've just subscribed to the developer's list.
>
> Best regards,
> --
> Mateusz Loskot, http://mateusz.loskot.net
> --
>
> Powered by www.kitware.com
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> Please keep messages on-topic and check the CMake FAQ at: 
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Re: [CMake] [MSVC] Setting warning level on target feels like long-time bug

[Mateusz Loskot]

On Sun, 9 Dec 2018 at 12:14, Craig Scott  wrote:
>
> From what I understand from a very limited quick search just now,
> it seems that /W3 is the default warning level for Visual Studio

Yes, it is the default level indeed.

> but CMake explicitly adds it as a default compiler flag in 
> CMAKE__FLAGS_INIT.
> This makes me wonder if it has always been the default, otherwise it isn't 
> clear why it was deemed necessary to add it.

Yes, I'd suspect it was added as 'just in case'  too eagerly.

> More to the point, unless there's a reason not to, perhaps we could consider 
> removing it from the default flags CMake sets.
> I think this would largely address the situation you're describing and 
> shouldn't actually change the behavior of existing projects.

Yes, it should be removed.
Unless I'm missing an important reason behind the explicit -W3.

No, "This has been the default since CMake began" [1], is not enough
rationale to keep it.

In the old times of manual editing of CMAKE_CXX_FLAGS, it was not a huge deal
- in fact, fiddling with CMAKE_CXX_FLAGS was quite canonical way of
doing things..
But with the advent of target_compile_options, the string call
requirement is just unacceptable.

[1] https://gitlab.kitware.com/cmake/cmake/issues/18317

> I've CC'ed the developer's list and suggest that follow-up discussion should 
> occur there.

FYI, I've just subscribed to the developer's list.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
-- 

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Re: [CMake] [MSVC] Setting warning level on target feels like long-time bug

[Craig Scott]

>From what I understand from a very limited quick search just now, it seems
that /W3 is the default warning level for Visual Studio (according to
the Microsoft
docs
),
but CMake explicitly adds it

as a default compiler flag in CMAKE__FLAGS_INIT. This makes me wonder
if it has always been the default, otherwise it isn't clear why it was
deemed necessary to add it. More to the point, unless there's a reason not
to, perhaps we could consider removing it from the default flags CMake
sets. I think this would largely address the situation you're describing
and shouldn't actually change the behavior of existing projects. I've CC'ed
the developer's list and suggest that follow-up discussion should occur
there.


On Sun, Dec 9, 2018 at 8:07 AM Mateusz Loskot  wrote:

> Hi,
>
> I define a target for a library, and set warning level for MSVC compiler:
>
> target_compile_options(mylib PRIVATE $<$:-W4>)
>
> Although this works well, the compiler throws this warning:
>
> cl : Command line warning D9025: overriding '/W3' with '/W4'
>
> I want to get rid of this warning, so I fix it this way
>
> if(MSVC)
>   string(REGEX REPLACE "/W3" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
>   string(REGEX REPLACE "-W3" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
> endif()
>
> target_compile_options(mylib PRIVATE $<$:-W4>)
>
> This works like charm, but leaves me with sour feeling that
> something is not right here.The REGEX REPLACE clean-up
> has become such a habit, it's almost canonical thing I do in
> all my CMake-based projects.
>
> Shouldn't CMake drop the default when target_compile_options is called?
> Is this behaviour by design, for MSVC?
> Could anyone help me to understand if this is actually a bug
> or am I misunderstanding anything?
>
> Best regards,
> --
> Mateusz Loskot, http://mateusz.loskot.net
> --
>
> Powered by www.kitware.com
>
> Please keep messages on-topic and check the CMake FAQ at:
> http://www.cmake.org/Wiki/CMake_FAQ
>
> Kitware offers various services to support the CMake community. For more
> information on each offering, please visit:
>
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-- 
Craig Scott
Melbourne, Australia
https://crascit.com

New book released: Professional CMake: A Practical Guide

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[CMake] [MSVC] Setting warning level on target feels like long-time bug

[Mateusz Loskot]

Hi,

I define a target for a library, and set warning level for MSVC compiler:

target_compile_options(mylib PRIVATE $<$:-W4>)

Although this works well, the compiler throws this warning:

cl : Command line warning D9025: overriding '/W3' with '/W4'

I want to get rid of this warning, so I fix it this way

if(MSVC)
  string(REGEX REPLACE "/W3" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
  string(REGEX REPLACE "-W3" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
endif()

target_compile_options(mylib PRIVATE $<$:-W4>)

This works like charm, but leaves me with sour feeling that
something is not right here.The REGEX REPLACE clean-up
has become such a habit, it's almost canonical thing I do in
all my CMake-based projects.

Shouldn't CMake drop the default when target_compile_options is called?
Is this behaviour by design, for MSVC?
Could anyone help me to understand if this is actually a bug
or am I misunderstanding anything?

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
-- 

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