add an option to deep-copy symlinks

[yasushi-saito]

Can we have an option to copy symlinks? I'm imagining something like:

Opts struct {
  // Called if a symlink is found. If this function returns false, 
  // Copy copies the symlink itself. Else, Copy() follows the link.
  // If FollowSymlink=nil, Copy never follows symlinks.
  FollowSymlink func(path string) bool
}

func Copy(src, dest string, opt... Opts) error;

I can create a pull request if it looks good.

[otiai10]

Can you please list up expected usecases of this option first?

[otiai10]

From my perspective, there are 3 usecases when it comes to symlink:

1. Hard copy
2. Soft copy (create a link to the same resource)
3. Ignore

What do you think?

[yasushi-saito]

Yes, the only feature I need now is deep-copies (i.e., follow all symlinks). So we can just have

type Opt struct { FollowSymlink bool }

I can't think a use case to ignore symlinks.

[otiai10]

OK, then

1. Hard copy ← is this what you want?
2. Soft copy (create symlink) (follow) what you want
3. Others (Skip?)

Is it right?

[otiai10]

hmm, confusing... I'm still not sure what you want since your test cases are not descriptive enough and even failing.