With 4.2.0 and yaml-cpp 0.6.2, it was possible to build mongoDB using yaml-cpp as a system package.

yaml-cpp 0.6.3 was released (at least on Arch) 13 days ago.  Upgrading the system package requires recompiling mongodb, which causes cpp_unit_test:options_parser_test to fail.

The entire test failure is attached.

Looks like the issue is math::pi being

3.1415926500000002

vs

3.14159265

I see https://github.com/jbeder/yaml-cpp/pull/649 which fixes a yaml-cpp round trip decimal error, which I assume is the change in the new version causing this test failure.

I also saw https://github.com/jbeder/yaml-cpp/issues/761 where a user was having a similar problem of an expected value of "123.456" printed as "123.456001".  The developer said to now specify precision when using an emitter, i.e.:

emitter << YAML::Precision(3) << node;

I haven't looked to see if 0.6.2 and previous has YAML::Precision(), so whether mongo's code could be fixed and still run on previous errors, or if this is a true breaking change.

I wanted to report this issue, reported to me by Arch user mrohnstock, but in the meantime will be removing yaml-cpp to be used as a system library by mongo on Arch, and let it pull it in itself.