[CMake] FindIce module and C++11

[rleigh at codelibre.net]

On 2017-08-10 10:28, rleigh at codelibre.net wrote:
> On 2017-08-10 09:50, Jones J.W. wrote:
>> I'm building my code on Linux using the g++ flags "-std=c++11". This
>> means that I must link with the libIce++11 libraries instead of
>> libIce.
>> 
>> The FindIce module, however as no provision for choosing these
>> libraries thus resulting in unresolved symbols at link time.
>> 
>> I tried getting around the problem by simply listing Ice++11 as a
>> COMPONENT which works in Linux but the same CMakeLists.txt file in
>> Windows won't work as there is no Ice++11. Currently I have resolved
>> this by having two calls to the FindIce module inside an IF( MSVC )
>> conditional.

Looking at the NuGet packages, I can see Ice++11 on Windows; it's named 
Ice37++11[d].lib.  Helpfully not following the existing conventions on 
the other platforms and previous Ice releases, but I think I've worked 
around this now.

>> Would it be possible to add a flag to tell the FindIce module whether
>> C++11 is being used or not?
> 
> FindIce certainly needs an update for Ice 3.7.
> 
> Regarding C++11, their approach here is certainly a bit unorthodox as
> well as being inconsistent between platforms, and FindIce will need to
> deal with that unfortunate situation.  Since the old and new APIs are
> incompatible, and you have to explicitly opt-in to using the new one,
> I don't think that using "-std=c++11" on its own is sufficient reason
> to select the C++11 library?  Can you use the old API with a C++11
> compiler?  It might be best to have a set of C++11 component names,
> and map these to the appropriate library names on Linux (separate
> libs) and Windows (not separate), if that would make the intent of the
> user clear and unambiguous.
> 
> I will try to look at this, but I'm a little busy with other things at
> the moment, and so it's not at top of my list.  If you wanted to
> propose a change an/or open a merge request that would certainly be
> welcome.

I have done some preliminary work here:

   https://gitlab.kitware.com/rleigh/cmake/commits/ice-3.7.0

It's working on Linux, but not yet finding the libraries on Windows when 
using the NuGet distribution of the libraries.  This is likely some 
minor bug which I need to identify; it's using all the correct paths and 
suffixes that I can see.

If you would like to give this a go and help fix the detection on 
Windows, that would be really helpful.  I've left some extra debugging 
messages in to trace how find_library is working.  If you set 
CMAKE_PREFIX_PATH to the location where the NuGet packages live, it 
should automatically detect the package name.  Do we have any existing 
conventions within CMake for finding libraries within such packages?  
Should the package be listed specifically on CMAKE_PREFIX_PATH, or is 
finding the package itself on the path acceptable?  Or should both be 
supported?


Regards,
Roger