[petsc-dev] configureLibrary fails for c++11 projects

[Satish Balay]

-std=cxx11 for sure is a compile flag. But don't really know if its
also needed at pre-process stage and/or at link stage.

And for compile stage both CXXFLAGS and CXXPPFLAGS should get
used. [PETSc makefiles make sure this is the case]

And for link stage CXXFLAGS and LDFLAGS get used [but then sometimes
we have CLINKER, and FLINKER - and they certainly don't use CXXFLAGS -
so -std=cxx11 isn't really needed at link time?

So the previous default of CXXPPFLAGS=-std=cxx11 looks reasonable to me.

However if this project is not using PETSc makefiles - it should make sure all compile flags are grabbed.

# lib/petsc/conf/variables
PETSC_CXXCPPFLAGS       = ${PETSC_CC_INCLUDES} ${PETSCFLAGS} ${CXXPP_FLAGS} ${CXXPPFLAGS}
CXXCPPFLAGS             = ${PETSC_CXXCPPFLAGS}
PETSC_CXXCOMPILE_SINGLE = ${CXX} -o $*.o -c ${CXX_FLAGS} ${CXXFLAGS} ${CXXCPPFLAGS}

# lib/petsc/conf/rules
.cpp.o .cxx.o .cc.o .C.o:
        ${PETSC_CXXCOMPILE_SINGLE} `pwd`/$<

# gmakefile.test
PETSC_COMPILE.cxx = $(call quiet,CXX) -c $(CXX_FLAGS) $(CXXFLAGS) $(CXXCPPFLAGS) $(CXX_DEPFLAGS)

# lib/petsc/conf/test
LINK.cc = $(CXXLINKER) $(CXX_FLAGS) $(CXXFLAGS) $(CXXCPPFLAGS) $(LDFLAGS)

Satish


On Tue, 23 Mar 2021, Junchao Zhang wrote:

> I would rather directly change the project to use CXXFLAGS instead of
> CXXPPFLAGS.
> 
> --Junchao Zhang
> 
> 
> On Tue, Mar 23, 2021 at 10:01 AM Satish Balay via petsc-dev <
> petsc-dev at mcs.anl.gov> wrote:
> 
> > On Tue, 23 Mar 2021, Stefano Zampini wrote:
> >
> > > Just tried out of main, and and the include tests of a c++11 project fail
> > > Below my fix, if we agree on, I'll make a MR
> > >
> > > diff --git a/config/BuildSystem/config/compilers.py
> > > b/config/BuildSystem/config/compilers.py
> > > index c96967e..44e4657 100644
> > > --- a/config/BuildSystem/config/compilers.py
> > > +++ b/config/BuildSystem/config/compilers.py
> > > @@ -527,6 +527,8 @@ class Configure(config.base.Configure):
> > >          if self.setCompilers.checkCompilerFlag(flag, includes,
> > > body+body14):
> > >            newflag = getattr(self.setCompilers,LANG+'FLAGS') + ' ' +
> > flag #
> > > append flag to the old
> > >            setattr(self.setCompilers,LANG+'FLAGS',newflag)
> > > +          newflag = getattr(self.setCompilers,LANG+'PPFLAGS') + ' ' +
> > flag
> > > # append flag to the old
> > > +          setattr(self.setCompilers,LANG+'PPFLAGS',newflag)
> >
> >
> > https://gitlab.com/petsc/petsc/commit/ead1aa4045d7bca177e78933b9ca25145fc3c574
> >
> >           self.setCompilers.CXXPPFLAGS += ' ' + flag
> >           newflag = getattr(self.setCompilers,LANG+'FLAGS') + ' ' + flag #
> > append flag to the old
> >           setattr(self.setCompilers,LANG+'FLAGS',newflag)
> >
> > So the old code was setting 'PPFLAGS' - but this commit changed to
> > 'FLAGS'. Maybe this flag is needed at both compile time and link time?
> >
> > So this project is somehow using CXXPPFLAGS - but not CXXFLAGS?
> >
> > I'm fine with adding it to PPFLAGS - duplicate listing hopefully shouldn't
> > cause grief.
> >
> > Satish
> >
> > >            cxxdialect = 'C++14'
> > >            self.addDefine('HAVE_'+LANG+'_DIALECT_CXX14',1)
> > >            self.addDefine('HAVE_'+LANG+'_DIALECT_CXX11',1)
> > > @@ -546,6 +548,8 @@ class Configure(config.base.Configure):
> > >          if self.setCompilers.checkCompilerFlag(flag, includes, body):
> > >            newflag = getattr(self.setCompilers,LANG+'FLAGS') + ' ' +
> > flag #
> > > append flag to the old
> > >            setattr(self.setCompilers,LANG+'FLAGS',newflag)
> > > +          newflag = getattr(self.setCompilers,LANG+'PPFLAGS') + ' ' +
> > flag
> > > # append flag to the old
> > > +          setattr(self.setCompilers,LANG+'PPFLAGS',newflag)
> > >            cxxdialect = 'C++11'
> > >            self.addDefine('HAVE_'+LANG+'_DIALECT_CXX11',1)
> > >            break
> > >
> > >
> > >
> >
> >
>