Cannot compile with sync features

[HalfPhoton]

Hi all, newbie here trying to install tokio for the first time.

After doing some searching I've narrowed down the issue to specifically: I'm unable to compile tokio when the "sync" feature is enabled.

On a new cargo init, cargo add tokio and cargo build will pull tokio v1.21.0 and compile. However, if I cargo add tokio --features sync and then cargo build I get the following compilation errors. I've tried looking around on google / SO but I'm not getting any hits. I've had a look at the docs but I can't see any additional dependencies that I need. Can anyone help?

test-tok | cargo build
   Compiling tokio v1.21.0
error[E0432]: unresolved import `crate::sync::rwlock::owned_read_guard::OwnedRwLockReadGuard`
 --> path/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.0/src/sync/rwlock/owned_write_guard.rs:1:5
  |
1 | use crate::sync::rwlock::owned_read_guard::OwnedRwLockReadGuard;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `OwnedRwLockReadGuard` in `sync::rwlock::owned_read_guard`

error[E0432]: unresolved import `owned_read_guard::OwnedRwLockReadGuard`
  --> path/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.0/src/sync/rwlock.rs:17:16
   |
17 | pub(crate) use owned_read_guard::OwnedRwLockReadGuard;
   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `OwnedRwLockReadGuard` in `sync::rwlock::owned_read_guard`

error[E0432]: unresolved import `rwlock::owned_read_guard::OwnedRwLockReadGuard`
   --> path/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.0/src/sync/mod.rs:459:13
    |
459 |     pub use rwlock::owned_read_guard::OwnedRwLockReadGuard;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `OwnedRwLockReadGuard` in `sync::rwlock::owned_read_guard`

error[E0321]: cross-crate traits with a default impl, like `Send`, can only be implemented for a struct/enum type, not `[type error]`
   --> path/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.0/src/sync/rwlock.rs:160:1
    |
160 | / unsafe impl<T, U> Send for OwnedRwLockReadGuard<T, U>
161 | | where
162 | |     T: ?Sized + Send + Sync,
163 | |     U: ?Sized + Sync,
164 | | {
165 | | }
    | |_^ can't implement cross-crate trait with a default impl for non-struct/enum type

error[E0321]: cross-crate traits with a default impl, like `Sync`, can only be implemented for a struct/enum type, not `[type error]`
   --> path/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.0/src/sync/rwlock.rs:166:1
    |
166 | / unsafe impl<T, U> Sync for OwnedRwLockReadGuard<T, U>
167 | | where
168 | |     T: ?Sized + Send + Sync,
169 | |     U: ?Sized + Send + Sync,
170 | | {
171 | | }
    | |_^ can't implement cross-crate trait with a default impl for non-struct/enum type

Some errors have detailed explanations: E0321, E0432.
For more information about an error, try `rustc --explain E0321`.
error: could not compile `tokio` due to 5 previous errors

[Darksonn]

I'm guessing that you've modified the files in the cargo registry cache in some way that caused this error. I would delete the registry and try again.

[HalfPhoton]

Hi @Darksonn, thank you for this tip!
I had to delete all the registry directories with rm -rf .cargo/registry/* but this worked and everything runs smoothly!

Thank you very much for your speedy and accurate response! Very much appreciated!