Prefer using symlinks on Windows

[ChrisDenton]

Problem you are trying to solve

On Windows rustup currently uses junction points exclusively.

rustup/src/utils/raw.rs

Lines 136 to 141 in d55d41c

	fn symlink_dir_inner(src: &Path, dest: &Path) -> io::Result<()> {
	// std's symlink uses Windows's symlink function, which requires
	// admin. We can create directory junctions the hard way without
	// though.
	symlink_junction_inner(src, dest)
	}

(note: that comment is wrong, user symlinks can be enabled by granting a single permission or more recently by enabling developer mode)

Junction points are always absolute which makes moving rustup (e.g. when setting up a dev drive) a more fraught process than it needs to be.

Solution you'd like

Use symlink_dir and only fallback to juncture points if that fails.

Notes

No response

[djc]

Would you be able to contribute some code in this direction? I don't have any Windows systems available to me to test.

[ChrisDenton]

For sure! I just wanted to make sure there were no objections.