Add `WritablePath.copy_from()`

[barneygale]

To support metadata transfers, we need to add a method to WritablePath that allows receivers to copy metadata from some ReadablePath source. Currently we have _copy_from(), but it's got an underscore prefix.

This will affect pathlib.Path

Perhaps the method should return an iterator that emits progress reports? If so can someone come up with a better name than iter_copy_from()? :)

See also python/cpython#131636

[barneygale]

Alternatively:

• Add PathInfo.mode(), access_time() and modify_time() methods.
• Add keyword-only info arguments to __open_writer__(), mkdir() and symlink_to(). If not None, methods are expected to copy metadata from the PathInfo object when creating files/directories/symlinks.
• Implementations of these methods for (local filesystem) Path would apply the equivalent of the 'data' filter for tar files: https://docs.python.org/3/library/tarfile.html#tarfile.data_filter
  • __open_writer__() - access/modify times and limited permissions info
  • mkdir() - access/modify times only
  • symlink_to() - access/modify times only
• Implementation of ReadablePath.copy() should call these methods rather than target._copy_from().
• Implementation of Path.copy() should detect a local filesystem target and apply additional metadata with chmod() etc
  • xattrs
  • bsd flags
  • full permissions