create_directories returns true if the path is empty

[fujitatomoya]

fix #94, and address #96

[fujitatomoya]

@wjwwood @christophebedard

I've added minor fix based on #95.

confirmed rosbag2 test does not detects any failures.

[christophebedard]

thank you @fujitatomoya!

[clalancette]

The problem I have with this change is that this makes us act different than std::filesystem (which we eventually want to switch to). As far as I can tell, if you call:

std::filesystem::create_directories("");

It throws an exception:

terminate called after throwing an instance of 'std::filesystem::__cxx11::filesystem_error'
  what():  filesystem error: cannot create directories: Invalid argument []

Also, from a pure semantic point-of-view, the documentation says that it returns true if the directory is created, and false otherwise. Since it could not create the directory on an empty string, returning true seems wrong here.

My suggestion is that we actually fix the test in rosbag2 that is trying to call this API with an empty string. Once that is done, we can reapply #95 as it was, and then things shouldn't break on the farm.

[christophebedard]

That makes sense. I can do the rosbag2 changes (@fujitatomoya let me know if you've started working on it).

[christophebedard]

My suggestion is that we actually fix the test in rosbag2 that is trying to call this API with an empty string. Once that is done, we can reapply #95 as it was, and then things shouldn't break on the farm.

I opened ros2/rosbag2#526

[fujitatomoya]

@christophebedard @clalancette

i will close this PR, you can revert #96 after ros2/rosbag2#526.