Conflict with CMake's FindDart.cmake module when compiling a downstream project that depends on gazebo

[traversaro]

Some homebrew users of the https://github.com/robotology/robotology-superbuild on macOS (@DanielePucci) are reporting the impossibility of compiling a project that calls find_package(gazebo REQUIRED) when using the latest gazebo9 installed by homebrew.

I investigated a bit, and the problem is that:

• gazebo9 is now depending on Dart, that is installed by default
• The line find_package(DART ${GAZEBO_DART_MIN_REQUIRED_VERSION} REQUIRED) contained in the gazebo-config.cmake file does not work on macOs due to the conflict with the FindDart.cmake module distributed with CMake (see Use CONFIG mode to find DART in examples and tutorials dartsim/dart#889 for a related Dart PR).

The possibility of fixing this are (as far as I can think):

• either to patch the gazebo-config.cmake contained in the bottle to contain the line find_package(DART ${GAZEBO_DART_MIN_REQUIRED_VERSION} REQUIRED CONFIG)
• fix the problem in Gazebo upstream, and do a new release from which to generate a bottle.

[traversaro]

Upstream fix: https://bitbucket.org/osrf/gazebo/pull-requests/2919/fix-https-githubcom-osrf-homebrew/diff
Related Gazebo PR: https://bitbucket.org/osrf/gazebo/pull-requests/2862/use-config-with-find_package-dart-for/diff .

[scpeters]

I'm adding a patch to the gazebo9 formula in #386

[traversaro]

Thanks!