Added implementation on set_permissions_nofollow for all primary platforms

[asder8215]

View all comments

For context, this PR is related to the tracking issue for std::fs::set_permissions_nofollow. This PR does a few different things:

• Windows support is provided for std::fs::set_permissions_nofollow. On Windows, it uses OpenOptions::open with the custom flag FILE_FLAG_OPEN_REPARSE_POINT enabled and then sets the permissions on the reparse point directly. All other platforms (hermit, motor, solid, uefi, etc.) defer to what fs::set_permissions does since symlinks aren't supported on those platforms, so they effectively do the same thing.
• The implementation for Unix was modified to use fchmodat instead of doing two separate calls (open and then fchmod via OpenOptions).
• Because the previous implementations actually used fchmod instead of chmod underneath the hood (as that's what File::set_permissions, which is not to be confused with fs::set_permissions as that does use chmod, does underneath the hood), it actually had some incorrect documentation about the error returned by fchmod on symlinks. Instead of io::ErrorKind::FilesystemLoop, it returns io::ErrorKind::InvalidInput. You can read the documentation for fchmod. fchmodat does effectively the same thing as the open + fchmod combo, but it does return a different error, io::ErrorKind::Unsupported, that makes more sense. Regardless, I corrected the documentation for std::fs::set_permissions_nofollow and added a lot more clarifying information.
• A test case has been added to verify if set_permissions_nofollow is operating correctly.

cc @ChrisDenton and @lolbinarycat

[rustbot]

r? @clarfonthey

rustbot has assigned @clarfonthey.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @ChrisDenton, libs
• @ChrisDenton, libs expanded to 12 candidates
• Random selection from Darksonn, Mark-Simulacrum, clarfonthey, jhpratt

[clarfonthey]

Similar to UEFI, I would swap the method bodies here, so that set_perm defers to set_perm_nofollow plus a comment that says symlinks aren't supported.

View changes since the review

[clarfonthey]

@rustbot author

CI failure appears to be a simple typo but I also left some feedback on other stuff to fix. Otherwise, implementation looks good, although I would add an extra comment on the tracking issue once this is merged to have some Windows folks double-check that opening all reparse points in this method doesn't do anything we don't want, since that technically includes more than just symlinks. It should work in pretty much all normal use cases, just want to double-check the edge cases before stabilisation.

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] gimli test:false 8.340
[RUSTC-TIMING] object test:false 11.694
warning: dropping unsupported crate type `dylib` for target `wasm32-wasip1`

error[E0425]: cannot find function `fchmodat` in crate `libc`
    --> library/std/src/sys/fs/unix.rs:1998:23
     |
1998 |                 libc::fchmodat(libc::AT_FDCWD, p.as_ptr(), perm.mode, libc::AT_SYMLINK_NOFOLLOW)
     |                       ^^^^^^^^
     |
    ::: /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.185/src/wasi/mod.rs:1027:5
     |
1027 |     pub fn fchmod(fd: c_int, mode: mode_t) -> c_int;
     |     ------------------------------------------------ similarly named function `fchmod` defined here
     |
help: a function with a similar name exists
     |
1998 -                 libc::fchmodat(libc::AT_FDCWD, p.as_ptr(), perm.mode, libc::AT_SYMLINK_NOFOLLOW)
1998 +                 libc::fchmod(libc::AT_FDCWD, p.as_ptr(), perm.mode, libc::AT_SYMLINK_NOFOLLOW)
     |

For more information about this error, try `rustc --explain E0425`.
[RUSTC-TIMING] std test:false 4.508
warning: `std` (lib) generated 1 warning