ACP: `std::os::windows::fs::junction_point`

[ChrisDenton]

Proposal

Problem statement

On Windows creating symlinks is (be default) a privileged operation. However, many types of applications may want to create links. Junction points can be used by less privileged users to create directory links.

Motivation, use-cases

For example, bootstrap uses junction points as an alternative to symlinks on Windows: https://github.com/rust-lang/rust/blob/90a9f69c80812c8694959c1f2d5c336e3300d1e2/src/bootstrap/util.rs#L134-L135

Solution sketches

// std::os::windows::fs

/// Create a junction point.
///
/// The `link` path will be a directory junction pointing to the original path.
/// If `link` is a relative path then it will be made absolute prior to creating the junction point.
/// The `original` path must be a directory or a link to a directory, otherwise the junction point will be broken.
///
/// If either path is not a local file path then this will fail.
fn junction_point<P: AsRef<Path>, Q: AsRef<Path>>(
    original: P,
    link: Q
) -> Result<()>;

Links and related work

• Windows only std::os::windows::fssymlink_dir function for creating directory symlinks (which is likely to fail for most users due to lack of privileges).
• The standard library already has a function for creating junction points but it's only used in tests. See symlink_junction

What happens now?

This issue is part of the libs-api team API change proposal process. Once this issue is filed the libs-api team will review open proposals in its weekly meeting. You should receive feedback within a week or two.