pluginlib-macOS-10.14.md

ROS 2 Foxy pluginlib build on macOS < 10.15

Note: This only applies to the pluginlib foxy version. In the galactic, the problematic filesystem impl. header file was replaced in favor of rcpputils's filesystem_helper.hpp and filesystem_helper.cpp, which do not do any feature detection (that's the thing that was broken in foxy) and instead always emulate std::filesystem.

Problem

ROS Foxy's pluginlib package tries to use std::filesystem or std::experimental::filesystem.

However, when building pluginlib on macOS < 10.15 (e.g. macOS 10.14 Mojave), clang compiler evaluates this line with __has_include(<experimental/filesystem>) as true so the #include <experimental/filesystem> with std::experimental::filesystem is used.

And when the build targets macOS < 10.15, the implementation of std::experimental::filesystem is not included and the build fails with multiple errors ... is unavailable: introduced in macOS 10.15. We could solve this with the compilation flag -mmacosx-version-min=10.15 but then the resulting executable could not run on macOS < 10.15 (and that's not what we want).

Solution

The correct solution is to let the filesystem_helper.hpp use its emulated version of std::filesystem.

You can use the following command to apply the patch to the filesystem_helper.hpp:

patch /path/to/ros/foxy/include/pluginlib/impl/filesystem_helper.hpp patches/pluginlib-macOS-10.14.patch

Explanation of the patch file

We need to alter this line so the std::experimental::filesystem is not used on macOS < 10.15:

# elif __has_include(<experimental/filesystem>) && (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500)

In order to be able to use __MAC_OS_X_VERSION_MIN_REQUIRED we need to add a conditional include at the top of the file:

#ifdef __APPLE__ || __OSX__
# include <Availability.h>
#endif

Related info

• ros/pluginlib#215
• ros-perception/image_common#139

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Just for reference: macOS 10.14.6 with XCode 11.3.1 (11C504) clang -v prints:

Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bi