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### 2681. `filesystem::copy()` cannot copy symlinks

Section: 29.12.13.4 [fs.op.copy] Status: C++17 Submitter: Jonathan Wakely Opened: 2016-04-19 Last modified: 2017-07-30

Priority: 2

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Discussion:

29.12.13.4 [fs.op.copy] paragraph 3 bullet (3.4) says that if `is_symlink(f)` and `copy_options` is set in options then it should copy a symlink, but that case cannot be reached.

`is_symlink(f)` can only be true if f was set using `symlink_status(from)`, but that doesn't happen unless one of `create_symlinks` or `skip_symlinks` is set in options. It should depend on `copy_symlinks` too.

I'm not sure what the correct behaviour is, but I don't think we want to simply add a check for `copy_symlinks` in bullet (3.1) because that would mean that `t = symlink_status(to)`, and I don't think we want that. Consider `'touch file; mkdir dir; ln -s dir link;'` and then `filesystem::copy("file", "link", filesystem::copy_options::copy_symlinks)`. If `t = symlink_status(to)` then `is_directory(t) == false`, and we don't use bullet (3.5.4) but go to (3.5.5) instead and fail. So when `copy_symlinks` is set we still need to use `t = status(to)` as specified today.

[2016-05 Issues Telecon]

This is related to 2682; and should be considered together.

[2016-08 Chicago]

Wed AM: Move to Tentatively Ready

Proposed resolution:

Modify paragraph 3 of 29.12.13.4 [fs.op.copy] as shown:

> Effects: Before the first use of `f` and `t`:
> — If `(options & copy_options::create_symlinks) != copy_options::none || (options & copy_options::skip_symlinks) != copy_options::none` then `auto f = symlink_status(from)` and if needed `auto t = symlink_status(to)`.
> — Otherwise, if `(options & copy_options::copy_symlinks) != copy_options::none` then `auto f = symlink_status(from)` and if needed `auto t = status(to)`.
> — Otherwise, `auto f = status(from)` and if needed `auto t = status(to)`.