Rollup merge of #45095 - bluss:discriminant-send-sync, r=alexcrichton
Ensure std::mem::Discriminant is Send + Sync `PhantomData<*const T>` has the implication of Send / Syncness following the *const T type, but the discriminant should always be Send and Sync. Use `PhantomData<fn() -> T>` which has the same variance in T, but is Send + Sync
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2 changed files with 17 additions and 1 deletions
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@ -836,7 +836,7 @@ pub unsafe fn transmute_copy<T, U>(src: &T) -> U {
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///
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/// See the `discriminant` function in this module for more information.
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#[stable(feature = "discriminant_value", since = "1.21.0")]
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pub struct Discriminant<T>(u64, PhantomData<*const T>);
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pub struct Discriminant<T>(u64, PhantomData<fn() -> T>);
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// N.B. These trait implementations cannot be derived because we don't want any bounds on T.
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@ -121,3 +121,19 @@ fn test_transmute() {
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}
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}
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#[test]
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#[allow(dead_code)]
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fn test_discriminant_send_sync() {
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enum Regular {
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A,
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B(i32)
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}
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enum NotSendSync {
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A(*const i32)
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}
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fn is_send_sync<T: Send + Sync>() { }
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is_send_sync::<Discriminant<Regular>>();
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is_send_sync::<Discriminant<NotSendSync>>();
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}
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