[neteler]

WIP

With Fedora 45 the autoconf based PDAL test fails (both in G85 and main).

Fedora 45 ships:

• PDAL-libs-2.10.1-2.fc45.x86_64
• PDAL-devel-2.10.1-2.fc45.x86_64

This PR correctly retrieves the PDAL-related CPP flags and uses them for the configure test.

Note that there are still undeclared definitions, see:

configure:10554: checking whether to use PDAL
configure:10573: result: yes
configure:10603: g++ -std=gnu++11 -o conftest -g -Wall  -O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -march=x86-64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -mtls-dialect=gnu2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -Wl,--no-undefined -Wl,-z,now -Wl,--export-dynamic conftest.cpp  -L/usr/lib -lpdalcpp >&5
In file included from /usr/include/pdal/pdal_types.hpp:49,
                 from /usr/include/pdal/pdal_internal.hpp:42,
                 from /usr/include/pdal/SpatialReference.hpp:37,
                 from /usr/include/pdal/PointTable.hpp:41,
                 from conftest.cpp:59:
/usr/include/pdal/util/Utils.hpp:979:31: error: 'std::enable_if_t' has not been declared
  979 |     template<typename T, std::enable_if_t<!std::is_integral<T>::value>* = nullptr>
      |                               ^~~~~~~~~~~
/usr/include/pdal/util/Utils.hpp:979:31: note: 'std::enable_if_t' is only available from C++14 onwards
/usr/include/pdal/util/Utils.hpp:979:42: error: expected '>' before '<' token
  979 |     template<typename T, std::enable_if_t<!std::is_integral<T>::value>* = nullptr>

[...]

Might the reason be -std=gnu++11?

Edits of this PR are welcome.

[neteler]

Update:

The PDAL test compiles with CXX="g++ -std=gnu++17":

GRASS is now configured for:  x86_64-pc-linux-gnu
  Source directory:           /data
  Build directory:            /data
  Installation directory:     ${prefix}/grass85
  Startup script in directory:${exec_prefix}/bin
  C compiler:                 gcc -g -O2 
  C++ compiler:               g++ -std=gnu++17 -g -O2
[...]

How to inject it apart from using CXX="g++ -std=gnu++17" ?

[nilason]

PDAL is C++17, so why not pass CXXFLAGS="-std=c++17", actually officially we are too.

[nilason]

... I don't think the configure.ac needs modifications, CXXFLAGS="-std=c++17" should be enough.

[nilason]

I believe, package distribution systems usually have a common way to handle what standard a software needs to be built with.