fix: remove hardcoded cmake install path

[khangtpham25]

Hi @ThomasDuvinage,

This fix the installation path of mc_rtc_tutorials.

The error happen when CMAKE_INSTALL_PREFIX is usr/ (since mc_rtc is installed through apt), CMAKE_INSTALL_LIBDIR is set to lib/x86_64-linux-gnu/ instead of just lib/. More details can be found here

[arntanguy]

This most likely will break things for Nix builds, I'll double check.

ref: #495 where indeed I never tried mixing installation from packages with cmake builds.

[arntanguy]

My apologies for taking so long to get to it. My latest changes should fix it for both Nix and ubuntu packages.

For a bit of background on the complexities behind this:

• Historically we were always installing runtime dependencies (controlllers, plugins, etc) in mc_rtc's install prefix.
• This was done to simplify setup, as then mc_rtc would know at compile time where to load runtime dependencies from: paths relative to its own install prefix (e.g <mc_rtc_prefix>/lib/mc_controllers, etc)
• src/mc_rtcMacros.cmake provides macros to simplify installing runtime dependencies from user projects. In particular this defines MC_RTC_LIBDIR (resp BINDIR, DOCDIR)
• This introduces two issues:
  • We are modifying the global install tree. This means that when mc_rtc is installed in a global system path (/usr/local/lib, ...), the user needs to install as sudo as runtime dependencies are installed there too
  • Modifying mc_rtc's install tree is dirty, and is in fact impossible in Nix, as outputs from a derivation are immutable in the Nix store (mc-rtc's path in the nix store is a hash of all inputs that were used to generate it, installing in it would break immutability).

Thus we introduced MC_RTC_HONOR_INSTALL_PREFIX boolean option. When a user project is built with it ON, it modifies mc_rtcMacros behaviour to install runtime dependencies in their own user-provided install prefix (through -DCMAKE_INSTALL_PREFIX). This allows for instance in Nix to have all runtime dependencies in their own install path in the nix store (thus in Nix, MC_RTC_HONOR_INSTALL_PREFIX=ON by default). Note that on other systems such as ubuntu this also allows to have mc_rtc installed system-wide (e.g through apt), but still install your controllers in a custom user install prefix.

But now to add a bit of additional complexity:

• for FSM states, we still need to know where mc_rtc's default states are for controllers to use them. Actually I'm not sure why this wasn't handled at compile-time, we should probably change this in the future.
• for reasons I did not fully understand, when building in the Nix sandbox, paths generated by GNUInstallDir are always absolute, that is CMAKE_INSTALL_LIBDIR = CMAKE_INSTALL_FULL_LIBDIR. On other systems, CMAKE_INSTALL_LIBDIR is relative while CMAKE_INSTALL_FULL_LIBDIR is absolute.

@khangtpham25 I have only tested for Nix, could you please confirm that the issue is resolved on your build against ubuntu packages?