copy_file doesn't work for directories

[alexeagle]

There should be a way to copy directories, just like we copy files.

It would use ctx.actions.declare_directory so that Bazel tracks the result as a TreeArtifact.

We need this in rules_nodejs for example, because third-party packages are always on disk as directories, and globbing them as a bunch of files runs into filename restrictions (spaces in names) and is very non-performant (thousands of files to symlink into execroot/runfiles trees).

Another reasoning for this: RBE doesn't allow InputArtifacts that are directories (see @ulfjack's note on bazelbuild/bazel@c64421b) so it's necessary to copy them as TreeArtifacts to use them in remote-compatible actions.

[bsilver8192]

I ran across this, it looks like it's been implemented with copy_directory.

[tetromino]

Thanks for the reminder! This was fixed by #366 - but we forgot to close the issue.