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Yechan Bae 2021-09-28 13:46:13 -04:00
parent 6458630e1a
commit a81a5ad1a8
1 changed files with 19 additions and 16 deletions
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35
clippy_lints/src/non_send_field_in_send_ty.rs
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@ -12,31 +12,34 @@ declare_clippy_lint! {
/// Warns about a field in a `Send` struct that is neither `Send` nor `Copy`.
///
/// ### Why is this bad?
/// Sending the struct to another thread and drops it there will also drop
/// the field in the new thread. This effectively changes the ownership of
/// the field type to the new thread and creates a soundness issue by
/// breaking the non-`Send` invariant.
/// Sending the struct to another thread will transfer the ownership to
/// the new thread by dropping in the current thread during the transfer.
/// This causes soundness issues for non-`Send` fields, as they are also
/// dropped and might not be set up to handle this.
///
/// See:
/// * [*The Rustonomicon* about *Send and Sync*](https://doc.rust-lang.org/nomicon/send-and-sync.html)
/// * [The documentation of `Send`](https://doc.rust-lang.org/std/marker/trait.Send.html)
///
/// ### Known Problems
/// Data structures that contain raw pointers may cause false positives.
/// They are sometimes safe to be sent across threads but do not implement
/// the `Send` trait. This lint has a heuristic to filter out basic cases
/// such as `Vec<*const T>`, but it's not perfect.
/// such as `Vec<*const T>`, but it's not perfect. Feel free to create an
/// issue if you have a suggestion on how this heuristic can be improved.
///
/// ### Example
/// ```rust
/// use std::sync::Arc;
///
/// // There is no `RC: Send` bound here
/// unsafe impl<RC, T: Send> Send for ArcGuard<RC, T> {}
///
/// #[derive(Debug, Clone)]
/// pub struct ArcGuard<RC, T> {
/// inner: T,
/// // Possibly drops `Arc<RC>` (and in turn `RC`) on a wrong thread
/// head: Arc<RC>
/// ```rust,ignore
/// struct ExampleStruct<T> {
/// rc_is_not_send: Rc<String>,
/// unbounded_generic_field: T,
/// }
///
/// // This impl is unsound because it allows sending `!Send` types through `ExampleStruct`
/// unsafe impl<T> Send for ExampleStruct<T> {}
/// ```
/// Use thread-safe types like [`std::sync::Arc`](https://doc.rust-lang.org/std/sync/struct.Arc.html)
/// and specify correct bounds on generic type parameters (`T: Send`).
pub NON_SEND_FIELD_IN_SEND_TY,
nursery,
"there is field that does not implement `Send` in a `Send` struct"