Upcoming new libxml2 dependency for iDynTree

[traversaro]

In the next days, a new shiny URDF parser with much better diagnostic errors will land on iDynTree devel branch, contributed by @francesco-romano at DeepMind.

The new parser is based on the MIT-licensed libxml2 library: as a consequence, libxml2 will become a new required dependency of iDynTree, so if you are using the devel branch of iDynTree, you will need to have libxml2 installed in your system. Check the following for the detailed instructions on the recommended way of installing it.

Debian/Ubuntu

sudo apt install libxml2-dev 

macOS

libxml2 is already part of the library distributed with the developement tools on macOS.

Windows

If you are using vcpkg to manage your dependencies, you can install libxml2 via vcpkg :

./vcpkg install --triplet x64-windows libxml2 

where x64-windows should be changed to x86-windows if you are targeting 32-bit binaries.

If you typically install your dependencies using the YARP and ICUB dependencies installers, we recommend you to use the new robotology-additional-dependencies, that is a new installer of dependencies generated by vcpkg that contains libxml2. This installer is automatically accounting for environment variables, similarly to how the YARP and ICUB dependencies installers do.

Please report any issue or problem regarding to this, thanks!

[francesco-romano]

@traversaro note that macOS already ships with libxml2.
If brew is used, it should be specified in some way to CMake, otherwise I think by default the system one get picked.

[traversaro]

@francesco-romano so do you think it make sense not to install libxml2 using homebrew to avoid confusion?

[francesco-romano]

It is a good question.

From my investigations I found the following: (macOS 10.13.6):

• version: 2.9.4
• library is in /usr/lib/libxml2
• headers in /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/usr/include/libxml2 but it might be that I did not symlinked the standard libraries in /usr (it is something you do with Xcode. Anyway, this implies that you need Xcode, but I think this requirement should be verified in all cases).

The question is: what version of libxml2 is shipped in previous OS versions?
I do not know the frequency of updates of the libraries in macOS - note that 2.9.4 is 2 years old (https://gitlab.gnome.org/GNOME/libxml2/tags)

So we might want to setup some instructions to use brew, just to stay on the safe side.

[traversaro]

I checked and libxml2 is present in most recent versions of Developer SDKs on macOS . I assume CMake has no trouble in finding it, right? For this reason, I updated the instructions relatively to macOS .

By the way, the parser have been merged in the devel branch, see robotology/idyntree#460 .

[traversaro]

The parser will be part of the upcoming iDynTree 0.11 .

[francesco-romano]

Sounds good to me. Let's keep it in this way. If in the future we realise we need a more recent version, we can switch to the one provided by homebrew