Rollup merge of #130827 - fmease:library-mv-obj-save-dyn-compat, r=ibraheemdev

Library: Rename "object safe" to "dyn compatible"

Completed T-lang FCP: https://github.com/rust-lang/lang-team/issues/286#issuecomment-2338905118.
Tracking issue: https://github.com/rust-lang/rust/issues/130852

Regarding https://github.com/rust-lang/rust/labels/relnotes, I guess I will manually open a https://github.com/rust-lang/rust/labels/relnotes-tracking-issue since this change affects everything (compiler, library, tools, docs, books, everyday language).

r? ghost

library/core/src/cell.rs

@@ -666,7 +666,7 @@ impl<T: Default> Cell<T> {
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
 
 // Allow types that wrap `Cell` to also implement `DispatchFromDyn`
-// and become object safe method receivers.
+// and become dyn-compatible method receivers.
 // Note that currently `Cell` itself cannot be a method receiver
 // because it does not implement Deref.
 // In other words:
@@ -2247,7 +2247,7 @@ impl<T> From<T> for UnsafeCell<T> {
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 
 // Allow types that wrap `UnsafeCell` to also implement `DispatchFromDyn`
-// and become object safe method receivers.
+// and become dyn-compatible method receivers.
 // Note that currently `UnsafeCell` itself cannot be a method receiver
 // because it does not implement Deref.
 // In other words:
@@ -2349,7 +2349,7 @@ impl<T> From<T> for SyncUnsafeCell<T> {
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
 
 // Allow types that wrap `SyncUnsafeCell` to also implement `DispatchFromDyn`
-// and become object safe method receivers.
+// and become dyn-compatible method receivers.
 // Note that currently `SyncUnsafeCell` itself cannot be a method receiver
 // because it does not implement Deref.
 // In other words:

library/core/src/error.rs

@@ -335,16 +335,17 @@ impl dyn Error {
     #[unstable(feature = "error_iter", issue = "58520")]
     #[inline]
     pub fn sources(&self) -> Source<'_> {
-        // You may think this method would be better in the Error trait, and you'd be right.
-        // Unfortunately that doesn't work, not because of the object safety rules but because we
-        // save a reference to self in Sources below as a trait object. If this method was
-        // declared in Error, then self would have the type &T where T is some concrete type which
-        // implements Error. We would need to coerce self to have type &dyn Error, but that requires
-        // that Self has a known size (i.e., Self: Sized). We can't put that bound on Error
-        // since that would forbid Error trait objects, and we can't put that bound on the method
-        // because that means the method can't be called on trait objects (we'd also need the
-        // 'static bound, but that isn't allowed because methods with bounds on Self other than
-        // Sized are not object-safe). Requiring an Unsize bound is not backwards compatible.
+        // You may think this method would be better in the `Error` trait, and you'd be right.
+        // Unfortunately that doesn't work, not because of the dyn-incompatibility rules but
+        // because we save a reference to `self` in `Source`s below as a trait object.
+        // If this method was declared in `Error`, then `self` would have the type `&T` where
+        // `T` is some concrete type which implements `Error`. We would need to coerce `self`
+        // to have type `&dyn Error`, but that requires that `Self` has a known size
+        // (i.e., `Self: Sized`). We can't put that bound on `Error` since that would forbid
+        // `Error` trait objects, and we can't put that bound on the method because that means
+        // the method can't be called on trait objects (we'd also need the `'static` bound,
+        // but that isn't allowed because methods with bounds on `Self` other than `Sized` are
+        // dyn-incompatible). Requiring an `Unsize` bound is not backwards compatible.
 
         Source { current: Some(self) }
     }

library/core/src/iter/traits/iterator.rs

@@ -9,7 +9,7 @@ use crate::cmp::{self, Ordering};
 use crate::num::NonZero;
 use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try};
 
-fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
+fn _assert_is_dyn_compatible(_: &dyn Iterator<Item = ()>) {}
 
 /// A trait for dealing with iterators.
 ///

library/core/src/marker.rs

@@ -158,7 +158,7 @@ pub trait Sized {
 /// - Arrays `[T; N]` implement `Unsize<[T]>`.
 /// - A type implements `Unsize<dyn Trait + 'a>` if all of these conditions are met:
 ///   - The type implements `Trait`.
-///   - `Trait` is object safe.
+///   - `Trait` is dyn-compatible[^1].
 ///   - The type is sized.
 ///   - The type outlives `'a`.
 /// - Structs `Foo<..., T1, ..., Tn, ...>` implement `Unsize<Foo<..., U1, ..., Un, ...>>`
@@ -178,6 +178,7 @@ pub trait Sized {
 /// [`Rc`]: ../../std/rc/struct.Rc.html
 /// [RFC982]: https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md
 /// [nomicon-coerce]: ../../nomicon/coercions.html
+/// [^1]: Formerly known as *object safe*.
 #[unstable(feature = "unsize", issue = "18598")]
 #[lang = "unsize"]
 #[rustc_deny_explicit_impl(implement_via_object = false)]

library/core/src/ops/unsize.rs

@@ -68,8 +68,8 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *mut T {}
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
 
-/// `DispatchFromDyn` is used in the implementation of object safety checks (specifically allowing
-/// arbitrary self types), to guarantee that a method's receiver type can be dispatched on.
+/// `DispatchFromDyn` is used in the implementation of dyn-compatibility[^1] checks (specifically
+/// allowing arbitrary self types), to guarantee that a method's receiver type can be dispatched on.
 ///
 /// Note: `DispatchFromDyn` was briefly named `CoerceSized` (and had a slightly different
 /// interpretation).
@@ -80,7 +80,7 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
 /// type). The compiler must generate an implicit conversion from the trait object/wide pointer to
 /// the concrete reference/narrow pointer. Implementing `DispatchFromDyn` indicates that that
 /// conversion is allowed and thus that the type implementing `DispatchFromDyn` is safe to use as
-/// the self type in an object-safe method. (in the above example, the compiler will require
+/// the self type in an dyn-compatible method. (in the above example, the compiler will require
 /// `DispatchFromDyn` is implemented for `&'a U`).
 ///
 /// `DispatchFromDyn` does not specify the conversion from wide pointer to narrow pointer; the
@@ -112,6 +112,8 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
 ///     T: Unsize<U>,
 /// {}
 /// ```
+///
+/// [^1]: Formerly known as *object safety*.
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
 #[lang = "dispatch_from_dyn"]
 pub trait DispatchFromDyn<T> {

library/core/tests/hash/mod.rs

@@ -164,7 +164,7 @@ fn test_indirect_hasher() {
 }
 
 #[test]
-fn test_build_hasher_object_safe() {
+fn test_build_hasher_dyn_compatible() {
     use std::hash::{DefaultHasher, RandomState};
 
     let _: &dyn BuildHasher<Hasher = DefaultHasher> = &RandomState::new();

library/std/src/keyword_docs.rs

@@ -2349,12 +2349,13 @@ mod async_keyword {}
 /// [`async`]: ../std/keyword.async.html
 mod await_keyword {}
 
+// FIXME(dyn_compat_renaming): Update URL and link text.
 #[doc(keyword = "dyn")]
 //
 /// `dyn` is a prefix of a [trait object]'s type.
 ///
 /// The `dyn` keyword is used to highlight that calls to methods on the associated `Trait`
-/// are [dynamically dispatched]. To use the trait this way, it must be 'object safe'.
+/// are [dynamically dispatched]. To use the trait this way, it must be 'dyn-compatible'[^1].
 ///
 /// Unlike generic parameters or `impl Trait`, the compiler does not know the concrete type that
 /// is being passed. That is, the type has been [erased].
@@ -2382,6 +2383,7 @@ mod await_keyword {}
 /// [ref-trait-obj]: ../reference/types/trait-object.html
 /// [ref-obj-safety]: ../reference/items/traits.html#object-safety
 /// [erased]: https://en.wikipedia.org/wiki/Type_erasure
+/// [^1]: Formerly known as 'object safe'.
 mod dyn_keyword {}
 
 #[doc(keyword = "union")]