[ros2] cv_bridge boost dependency

[jnoyola]

Problem
I'm trying to build the dashing branch but cv_bridge fails with the error:

cv_bridge\src\cv_bridge.cpp(39,10): error C1083: Cannot open include file: 'boost/endian/conversion.hpp'

I see that PR #212 intended to "remove boost dependence", removing Boost from the include_directories call, but cv_bridge\src\cv_bridge.cpp still contains the include (in fact the same PR updated that line).

Fix
If I add back the include to be include_directories(include ${Boost_INCLUDE_DIRS}), then it builds successfully.

Question
So my question is: am I doing something wrong or is it possible the ros2 branches haven't built in over a year?

I'm on Windows 10, but based on the evidence it shouldn't matter.

[mjcarroll]

You are correct, it needs to be there for Windows for the current build. I believe that the header gets found correctly on Linux because it's in the /usr/include or /usr/local/include based on the distribution.

I added a shim to rcpputils to remove the boost/endian dependency (https://github.com/ros2/rcpputils/blob/master/include/rcpputils/endian.hpp), we could potentially get that backported to dashing to completely remove boost dependency from C++, but there won't be any python until pybind11 lands.

[mjcarroll]

That was an oversight, I think that the cv_bridge package is blacklisted in the ROS2 CI on Windows, so I may have missed it.

[jnoyola]

I don't fully understand pybind11 work, but I believe it's working fine for me on Windows with boost::python, although I see how it can be more difficult to maintain.

So what's the best path forward here? I would love to see dashing in a buildable state, even if it still has the boost::python dependency in the interim.

[mjcarroll]

Let's add include_directories(include ${Boost_INCLUDE_DIRS}) back for now, it shouldn't have any impact.

[mjcarroll]

I don't fully understand pybind11 work, but I believe it's working fine for me on Windows with boost::python, although I see how it can be more difficult to maintain.

Generally, we're trying to avoid bringing in the Boost dependency in ROS2, if possible. C++11 and beyond add much of the functionality that ROS was using from Boost, and it keeps the dependency tree much smaller.

PyBind11 provides generally the same functionality as Boost::Python without the dependency.

[jnoyola]

If that's the case, should we reconsider #277? I don't have insight into the other changes to include OpenCV and export symbols. If that's overkill for now then we can just add the one line.

EDIT: I opened PR #290 with the one line change. Please take a look

[jnoyola]

Ping @mjcarroll, if you could please take a look at one of those 2 PRs

[jnoyola]

Resolved with #290