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

[Mate Nagy-Egri via cmake-developers]

 I was just about to write a mail with similar content than this one, so allow 
me to add my 5 cents.
Fear of reyling on defaults in case Microsoft decides to change them?
1) Defaults don't change often. BTW, don't we rely on defaults for GCC and 
Clang anyway?2) Defaults change to benefit users. If the default changes from 
/W3 to /W4 per say, it would be because windows.h headers and the STL would be 
cleaned up for the warnings in /W4 and MS felt that it would be better if users 
relied on all the warning they packed there. (Currently it is not the case)
As for having to call string() on CMAKE_CXX_FLAGS to up my warning level for a 
single compiler... these sort of idiosincrecies are the ones that drive people 
away from CMake to Meson and other, more modern build systems. Not being able 
to clean up decades worth of sediments in script style will result in CMake's 
demise.

if (MSVC)  string(REGEX REPLACE "/W[0-9]""" CMAKE_CXX_FLAGS 
${CMAKE_CXX_FLAGS})endif (MSVC) add_executable(${PROJECT_NAME}main.cpp) 
target_compile_options(${PROJECT_NAME}PRIVATE$<$,$>:-Wall-Wextra
 -pedantic>  
$<$:/W4>) 
Instead of
 add_executable(${PROJECT_NAME}main.cpp) 
target_compile_options(${PROJECT_NAME}PRIVATE$<$,$>:-Wall-Wextra
 -pedantic>  
$<$:/W4>)
Or even
add_executable(${PROJECT_NAME}main.cpp)
set_target_properties(${PROJECT_NAME}PROPERTIES WARNING_LEVEL HIGH)
is nonsense. There should be direct support for a few pre-defined, commonly 
accepted warning levels. If not this, having to explain to C++ freshmen why 
we're running regexes over lists default args to clean them up BEFORE even 
stating our bussiness...


Please, remove this default because it hurts CMake as a whole.
Cheers,Máté

-Original Message-
From: Mateusz Loskot 
To: marc.chevrier 
Cc: cmake-developers ; cmake 
Sent: Sun, Dec 9, 2018 2:55 pm
Subject: Re: [cmake-developers] [CMake] [MSVC] Setting warning level on target 
feels like long-time bug

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

[Brad King via cmake-developers]

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

[Ray Donnelly]

Cmake is already full of do much hardcoded logic / flags and does new
releases so frequently (maybe there's some correlation between these two)
that adding this would hardly impact upon its quality or maintainability.

So to that end, hardcoding the default per msvc version so that it's not
added unnecessarily, triggering this warning would seem appropriate to me.
Either that or disabling this warning with more hard coded flags would also
be appropriate.

The current status in not ideal.

On Sun, Dec 9, 2018, 7:55 AM 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
> --
>
> 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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>
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Re: [cmake-developers] [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-developers] [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-developers] [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:
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-- 
Craig Scott
Melbourne, Australia
https://crascit.com

New book released: Professional CMake: A Practical Guide

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