Review Request 113805: Do not change the build types available with cmake

David Faure faure at kde.org
Sun Nov 24 12:22:00 UTC 2013 


> On Nov. 12, 2013, 7:24 p.m., Alexander Neundorf wrote:
> > IMO the patch as it is is not good.
> > 
> > Several things:
> > 1) This file, is not mandatory at all with KDE frameworks.
> > You can build applications using KDE frameworks libraries without it. You (the developer of the application) simply has to not-load the file KDECompilerSettings.
> > If the developer has decided to load this file, it is not surprising that he gets modified compiler flags, because this is what he decided to do.
> > 
> > 2) You removed e.g. the flags for the build types COVERAGE and PROFILE. CMake doesn't provide these build types or flags itself, so the patch removes support for these buildtypes. I don't see the need to remove support for profile or coverage builds. CMake itself comes with "debug", "minsizerel", "release" and "relwithdebinfo".
> > 
> > 3) You remove the flags for Linux and/or gcc. Why didn't you remove them for other compilers/operating systems ?
> > 
> > 
> > I know that what we are doing in this file is not the cmake-recommended way.
> > From cmake, the variables for the flags are cache variables which are set to some default. The idea is that the person who compiles some package can adjust them to his liking. This is from my experience not what we expect from the average KDE contributor. He should get a working set up, with known compiler flags so it is easy to fix buid bugs (or avoid them in the first place).
> > By simply setting the normal (non-cache) variables, the person building the package can set the cache variables to whatever he wants, it will be overridden to what is set in KDECompilerSettings.cmake.
> > Maybe the way this is done could be improved by doing something like
> > if(NOT DEFINED SOME_CXX_FLAGS_ALREADY_PRESET)
> >    set(SOME_CXX_FLAGS_ALREADY_PRESET TRUE CACHE BOOL "docs..." )
> >    set(SOME_CXX_FLAGS "--some-flag --another-flag" CACHE STRING "docs..." FORCE)
> > endif()
> > 
> > This way it would be only on the initial cmake run forced into the cache, and afterwards the user should be able to change them as he wants.
> > 
> > 
> >
> 
> Sune Vuorela wrote:
>     1) THis file is used by all kde frameworks, so it should not put in surprises for the developers there. ONe shouldn't be 100% familiar with all the internals to hack on stuff.
>     
>     2) IF we want to add such things, it should be in a "ECMAddProfileBuildType" or similar.
>     
>     3) For the other compilers, the build types aren't touched.
>     
>     ANd note that this doesn't modify the flags that covers everything. That I'm saving for another patch.
>     
>     And let us do thhings the cmake way, one step at a time.
> 
> Alexander Neundorf wrote:
>     1) I don't really understand. You say "no surprises" and at the same time you say that developers shouldn't have to be familiar with all internals to hack on stuff. If you want "no surprises", remove the line include(KDECompilerSettings) from the project. That's why it has been separated out, to make it optional for users who don't want it. Then you get plain cmake, and can/have to take care of the compiler settings yourself. Add that line, and you get "no need to care about internals".
>     
>     Is your plan also to remove the added defintions, linker flags, etc. ?
>     I'm fine if you post a patch which removes the file completely. I just doubt that the KDE community will be happy with this.
>     
>     This is the state as it was May 2006:
>     http://quickgit.kde.org/?p=kdelibs.git&a=blob&hb=5713bc5ddd7f11ef73e63cf67c4a0ba69180ef3a&f=cmake%2Fmodules%2FFindKDE4Internal.cmake
>     
>     You'll see that it was quite different from what we have today. It is much less than today. Back then I also started with a minimal set of flags to get KDE built at all. But between then and now, all those changes have gone in for a reason, each single one of them.
>     
>     
>     P.S. I am not objecting, just giving comments.
>
> 
> Sune Vuorela wrote:
>     1) By no surprises I mean by 3rd party users, skilled in Qt and cmake, of a KDE framework  - like if I end up using one at work and some of my colleagues need to fix a bug or add a feature, then this would be a unpleasant surprise when dealing with a standalone framework.
>     
>     My plan isn't - yet - to remove the file completely, but first to slice it down to a size where one can see what happens and what side effects it has. I have at least concrete plans for two or three more chunks to remove, but I prefer slice it down chunks at a time.
> 
> Alexander Neundorf wrote:
>     1) Let's assume karchive. You have currently at least the following options
>     
>     find_package(KArchive REQUIRED NO_MODULE)
>     
>     This finds the library, KDECompilerSettings.cmake is not involved at all.
>     
>     
>     OR
>     
>     find_package(KF5 REQUIRED NO_MODULE COMPONENTS KArchive)
>     
>     This finds the library, via tier1/kf5umbrella/, KDECompilerSettings.cmake is not involved at all.
>     
>     OR
>     
>     (when ECM still had FindKF5.cmake)
>     find_package(KF5 REQUIRED NO_MODULE COMPONENTS Compiler KArchive)
>     
>     This will find the library via FindKF5.cmake, and load the compiler flags, because this was requested.
>     
>     
>     
>     You were aware of that, right ?
>     
>     
>     P.S. the last option has SAFAIK been changed to the following:
>     
>     find_package(ECM REQUIRED NO_MODULE)
>     include(KDECompilerSettings)
>     find_package(KArchive REQUIRED NO_MODULE)
>     
>     As above, this finds the library and loads the compiler settings, since this was requested.
>     
>     
>     OR
>     
>     AFAIK today:
>     find_package(ECM REQUIRED NO_MODULE)
>     include(KDECompilerSettings)
>     find_package(KF5 REQUIRED NO_MODULE COMPONENTS KArchive)
>     
>     As above, this finds the library via tier1/kf5umbrealla/ and loads the compiler settings, since this was requested. Using kf5umbrella brings some conveniences when using multiple KF5 libs.
>
> 
> Sune Vuorela wrote:
>     I'm not talking about the simple using, but we all know that there will be bugs in our libraries and we all hope that we can get library users to help fix them. For that, we need to make it possible to see what's going on.
> 
> Alexander Neundorf wrote:
>     I don't see clearly in which way this is related to this patch. Can you elaborate ?
>
> 
> Nicolás Alvarez wrote:
>     "Outside" people would want to contribute to KDE Frameworks or other parts of KDE, and having 'Debug' mean something different than in any other CMake-based build system is yet another 'surprise' for a new contributor.
> 
> Alexander Neundorf wrote:
>     I think you are making up problems.
>     I don't think that it is an obstacle in any way to a contributor that the Debug buildtype uses somewhat different flags than the default ones coming from cmake.
>     
>     I'm not even sure how many projects are using the default flags as they are coming with cmake. E.g. at work we defined our own very specific set of compiler flags for the build types.
>     
>     As I said before, what I personally would like, would be an extension of the file so that the value end up in the cache, and so the user can modify them, and the same switch might by used to skip the file at all.
>     With that, the compiler flags could be set as in any other cmake buildsystem by the user via the cache.
>     
>     But as I said, these are just comments, I'm not maintaining this.
>
> 
> Alexander Neundorf wrote:
>     I just checked what the default flags are with gcc:
>     default, no build type set:
>     /usr/bin/c++ -o CMakeFiles/hello.dir/hello.cpp.o -c hello.cpp
>     debug:
>     /usr/bin/c++ -g -o CMakeFiles/hello.dir/hello.cpp.o -c hello.cpp
>     release:
>     /usr/bin/c++ -O3 -DNDEBUG -o CMakeFiles/hello.dir/hello.cpp.o -c hello.cpp
>     relwithdebinfo:
>     /usr/bin/c++ -O2 -g -DNDEBUG -o CMakeFiles/hello.dir/hello.cpp.o -c hello.cpp
>     minsizerel:
>     /usr/bin/c++ -Os -DNDEBUG -o CMakeFiles/hello.dir/hello.cpp.o -c hello.cpp
>     
>     I regularly miss at least -Wall from this.
>     So IMO "it is different from default cmake" is not a strong argument here.
>

Ah, this is a good point.
Here's what I would like to see:

* ECM provides a ECMStricterFlags.cmake
* It does not *undo* things done on purpose by cmake, e.g. Debug means "no optimization" (and therefore debugfull can be removed).
* But it improves things by adding the useful set of warnings that prevent writing buggy code (e.g. -Wall, -Werror=return-type, etc.). I definitely want this set of flags to be on by default for all KDE developers, rather than just "making it possible for people to add their own flags".
* It also improves Debug by adding -g3.

This combines "no surprises by undoing what cmake does", with "having useful warnings".

Stricter compilation flags is not KDE specific, we want developers to use them outside KDE too, for better code quality everywhere. These would be "the compiler flags as deemed useful by the ECM community" :-)


- David


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On Nov. 11, 2013, 10:16 p.m., Sune Vuorela wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/113805/
> -----------------------------------------------------------
> 
> (Updated Nov. 11, 2013, 10:16 p.m.)
> 
> 
> Review request for Build System and KDE Frameworks.
> 
> 
> Repository: extra-cmake-modules
> 
> 
> Description
> -------
> 
> Do not change the build types available with cmake.
> 
> 
> Diffs
> -----
> 
>   kde-modules/KDECompilerSettings.cmake b034751a5be8073f9628971b552faa079c64e8b6 
> 
> Diff: http://git.reviewboard.kde.org/r/113805/diff/
> 
> 
> Testing
> -------
> 
> Built kdelibs on linux with gcc.
> 
> 
> Thanks,
> 
> Sune Vuorela
> 
>

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