Better message when mdbook clean is run on clean workspace

[amanjeev]

Currently, if you run mdbook clean twice, you get the following error:

$ mdbook clean
2019-10-02 20:18:03 [ERROR] (mdbook::utils): Error: Unable to remove the build directory
2019-10-02 20:18:03 [ERROR] (mdbook::utils):    Caused By: No such file or directory (os error 2)

Would it make sense to show a better message to the user when running mdbook clean on an already clean workspace?

If you think this proposal makes sense, I could perhaps do this but I would need suggestions from you. If you think I am missing something and this is not a good idea, please close this issue.

Thank you.

[rnitta]

How about replacing fs::remove_dir_all with fs::remove_dir_content like here or here?

If it is done, the error due to nonexistence of the build directory will not occur, because it will not be removed once created.
So the error message will make more sense.

[amanjeev]

@rnitta Thank you. I would like to know if it is ok to not remove the build directory? If you see, as an example, cargo clean which removes the target directory. What do you think?

[ehuss]

I think it would be good if it didn't print anything if the output directory doesn't exist, and exited 0. Also, unless you see a reason, I think it would be fine to just delete the directory, too, I don't see a reason to keep an empty directory around. That is, just wrap the fs::remove_dir_all with a check if the path exists.

[amanjeev]

@ehuss I think that is also consistent with cargo clean. Will do!