Introduce CoerceShared lang item and trait, and basic Reborrow tests

compiler/rustc_hir/src/lang_items.rs

@@ -441,6 +441,7 @@ language_item_table! {
 
     // Reborrowing related lang-items
     Reborrow,                sym::reborrow,            reborrow,                   Target::Trait,          GenericRequirement::Exact(0);
+    CoerceShared,            sym::coerce_shared,       coerce_shared,              Target::Trait,          GenericRequirement::Exact(0);
 }
 
 /// The requirement imposed on the generics of a lang item

compiler/rustc_span/src/symbol.rs

@@ -679,6 +679,7 @@ symbols! {
         cmpxchg16b_target_feature,
         cmse_nonsecure_entry,
         coerce_pointee_validated,
+        coerce_shared,
         coerce_unsized,
         cold,
         cold_path,

library/core/src/marker.rs

@@ -1364,11 +1364,3 @@ pub macro CoercePointee($item:item) {
 pub trait CoercePointeeValidated {
     /* compiler built-in */
 }
-
-/// Allows value to be reborrowed as exclusive, creating a copy of the value
-/// that disables the source for reads and writes for the lifetime of the copy.
-#[lang = "reborrow"]
-#[unstable(feature = "reborrow", issue = "145612")]
-pub trait Reborrow {
-    // Empty.
-}

library/core/src/ops/mod.rs

@@ -149,6 +149,7 @@ mod function;
 mod index;
 mod index_range;
 mod range;
+mod reborrow;
 mod try_trait;
 mod unsize;
 
@@ -189,6 +190,8 @@ pub use self::range::{Bound, RangeBounds, RangeInclusive, RangeToInclusive};
 pub use self::range::{OneSidedRange, OneSidedRangeBound};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::range::{Range, RangeFrom, RangeFull, RangeTo};
+#[unstable(feature = "reborrow", issue = "145612")]
+pub use self::reborrow::{CoerceShared, Reborrow};
 #[unstable(feature = "try_trait_v2_residual", issue = "91285")]
 pub use self::try_trait::Residual;
 #[unstable(feature = "try_trait_v2_yeet", issue = "96374")]

library/core/src/ops/reborrow.rs

@@ -0,0 +1,16 @@
+/// Allows value to be reborrowed as exclusive, creating a copy of the value
+/// that disables the source for reads and writes for the lifetime of the copy.
+#[lang = "reborrow"]
+#[unstable(feature = "reborrow", issue = "145612")]
+pub trait Reborrow {
+    // Empty.
+}
+
+/// Allows reborrowable value to be reborrowed as shared, creating a copy
+/// that disables the source for writes for the lifetime of the copy.
+#[lang = "coerce_shared"]
+#[unstable(feature = "reborrow", issue = "145612")]
+pub trait CoerceShared: Reborrow {
+    /// The type of this value when reborrowed as shared.
+    type Target: Copy;
+}

tests/ui/feature-gates/feature-gate-reborrow-coerce-shared.rs

@@ -0,0 +1,3 @@
+use std::ops::CoerceShared; //~ ERROR  use of unstable library feature `reborrow`
+
+fn main() {}

tests/ui/feature-gates/feature-gate-reborrow-coerce-shared.stderr

@@ -0,0 +1,13 @@
+error[E0658]: use of unstable library feature `reborrow`
+  --> $DIR/feature-gate-reborrow-coerce-shared.rs:1:5
+   |
+LL | use std::ops::CoerceShared;
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #145612 <https://github.com/rust-lang/rust/issues/145612> for more information
+   = help: add `#![feature(reborrow)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/feature-gates/feature-gate-reborrow.rs

@@ -1,3 +1,3 @@
-use std::marker::Reborrow; //~ ERROR  use of unstable library feature `reborrow`
+use std::ops::Reborrow; //~ ERROR  use of unstable library feature `reborrow`
 
 fn main() {}

tests/ui/feature-gates/feature-gate-reborrow.stderr

@@ -1,8 +1,8 @@
 error[E0658]: use of unstable library feature `reborrow`
   --> $DIR/feature-gate-reborrow.rs:1:5
    |
-LL | use std::marker::Reborrow;
-   |     ^^^^^^^^^^^^^^^^^^^^^
+LL | use std::ops::Reborrow;
+   |     ^^^^^^^^^^^^^^^^^^
    |
    = note: see issue #145612 <https://github.com/rust-lang/rust/issues/145612> for more information
    = help: add `#![feature(reborrow)]` to the crate attributes to enable

tests/ui/reborrow/custom_mut.rs

@@ -0,0 +1,13 @@
+#![feature(reborrow)]
+use std::ops::Reborrow;
+
+struct CustomMut<'a, T>(&'a mut T);
+impl<'a, T> Reborrow for CustomMut<'a, T> {}
+
+fn method(a: CustomMut<'_, ()>) {}
+
+fn main() {
+    let a = CustomMut(&mut ());
+    let _ = method(a);
+    let _ = method(a); //~ERROR use of moved value: `a`
+}

tests/ui/reborrow/custom_mut.stderr

@@ -0,0 +1,29 @@
+error[E0382]: use of moved value: `a`
+  --> $DIR/custom_mut.rs:12:20
+   |
+LL |     let a = CustomMut(&mut ());
+   |         - move occurs because `a` has type `CustomMut<'_, ()>`, which does not implement the `Copy` trait
+LL |     let _ = method(a);
+   |                    - value moved here
+LL |     let _ = method(a);
+   |                    ^ value used here after move
+   |
+note: consider changing this parameter type in function `method` to borrow instead if owning the value isn't necessary
+  --> $DIR/custom_mut.rs:7:14
+   |
+LL | fn method(a: CustomMut<'_, ()>) {}
+   |    ------    ^^^^^^^^^^^^^^^^^ this parameter takes ownership of the value
+   |    |
+   |    in this function
+note: if `CustomMut<'_, ()>` implemented `Clone`, you could clone the value
+  --> $DIR/custom_mut.rs:4:1
+   |
+LL | struct CustomMut<'a, T>(&'a mut T);
+   | ^^^^^^^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
+...
+LL |     let _ = method(a);
+   |                    - you could clone this value
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.

tests/ui/reborrow/custom_mut_coerce_shared.rs

@@ -0,0 +1,28 @@
+#![feature(reborrow)]
+use std::ops::{CoerceShared, Reborrow};
+
+struct CustomMut<'a, T>(&'a mut T);
+impl<'a, T> Reborrow for CustomMut<'a, T> {}
+impl<'a, T> CoerceShared for CustomMut<'a, T> {
+    type Target = CustomRef<'a, T>;
+}
+
+struct CustomRef<'a, T>(&'a T);
+
+impl<'a, T> Clone for CustomRef<'a, T> {
+    fn clone(&self) -> Self {
+        Self(self.0)
+    }
+}
+impl<'a, T> Copy for CustomRef<'a, T> {}
+
+fn method(a: CustomRef<'_, ()>) {}  //~NOTE function defined here
+
+fn main() {
+    let a = CustomMut(&mut ());
+    method(a);
+    //~^ ERROR mismatched types
+    //~| NOTE expected `CustomRef<'_, ()>`, found `CustomMut<'_, ()>`
+    //~| NOTE arguments to this function are incorrect
+    //~| NOTE expected struct `CustomRef<'_, ()>`
+}

tests/ui/reborrow/custom_mut_coerce_shared.stderr

@@ -0,0 +1,19 @@
+error[E0308]: mismatched types
+  --> $DIR/custom_mut_coerce_shared.rs:23:12
+   |
+LL |     method(a);
+   |     ------ ^ expected `CustomRef<'_, ()>`, found `CustomMut<'_, ()>`
+   |     |
+   |     arguments to this function are incorrect
+   |
+   = note: expected struct `CustomRef<'_, ()>`
+              found struct `CustomMut<'_, ()>`
+note: function defined here
+  --> $DIR/custom_mut_coerce_shared.rs:19:4
+   |
+LL | fn method(a: CustomRef<'_, ()>) {}
+   |    ^^^^^^ --------------------
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/reborrow/option_mut.rs

@@ -0,0 +1,7 @@
+fn method(a: Option<&mut ()>) {}
+
+fn main() {
+    let a = Some(&mut ());
+    let _ = method(a);
+    let _ = method(a); //~ERROR use of moved value: `a`
+}

tests/ui/reborrow/option_mut.stderr

@@ -0,0 +1,21 @@
+error[E0382]: use of moved value: `a`
+  --> $DIR/option_mut.rs:6:20
+   |
+LL |     let a = Some(&mut ());
+   |         - move occurs because `a` has type `Option<&mut ()>`, which does not implement the `Copy` trait
+LL |     let _ = method(a);
+   |                    - value moved here
+LL |     let _ = method(a);
+   |                    ^ value used here after move
+   |
+note: consider changing this parameter type in function `method` to borrow instead if owning the value isn't necessary
+  --> $DIR/option_mut.rs:1:14
+   |
+LL | fn method(a: Option<&mut ()>) {}
+   |    ------    ^^^^^^^^^^^^^^^ this parameter takes ownership of the value
+   |    |
+   |    in this function
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.

tests/ui/reborrow/option_mut_coerce_shared.rs

@@ -0,0 +1,11 @@
+fn method(a: Option<&()>) {}  //~NOTE function defined here
+
+fn main() {
+    let a = Some(&mut ());
+    method(a);
+    //~^ ERROR mismatched types
+    //~| NOTE arguments to this function are incorrect
+    //~| NOTE types differ in mutability
+    //~| NOTE expected enum `Option<&()>`
+    //~| NOTE    found enum `Option<&mut ()>`
+}

tests/ui/reborrow/option_mut_coerce_shared.stderr

@@ -0,0 +1,23 @@
+error[E0308]: mismatched types
+  --> $DIR/option_mut_coerce_shared.rs:5:12
+   |
+LL |     method(a);
+   |     ------ ^ types differ in mutability
+   |     |
+   |     arguments to this function are incorrect
+   |
+   = note: expected enum `Option<&()>`
+              found enum `Option<&mut ()>`
+note: function defined here
+  --> $DIR/option_mut_coerce_shared.rs:1:4
+   |
+LL | fn method(a: Option<&()>) {}
+   |    ^^^^^^ --------------
+help: try using `.as_deref()` to convert `Option<&mut ()>` to `Option<&()>`
+   |
+LL |     method(a.as_deref());
+   |             +++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/reborrow/pin_mut.rs

@@ -0,0 +1,10 @@
+use std::pin::Pin;
+
+fn method(a: Pin<&mut ()>) {}
+
+fn main() {
+    let a = &mut ();
+    let a = Pin::new(a);
+    let _ = method(a);
+    let _ = method(a); //~ERROR use of moved value: `a`
+}

tests/ui/reborrow/pin_mut.stderr

@@ -0,0 +1,21 @@
+error[E0382]: use of moved value: `a`
+  --> $DIR/pin_mut.rs:9:20
+   |
+LL |     let a = Pin::new(a);
+   |         - move occurs because `a` has type `Pin<&mut ()>`, which does not implement the `Copy` trait
+LL |     let _ = method(a);
+   |                    - value moved here
+LL |     let _ = method(a);
+   |                    ^ value used here after move
+   |
+note: consider changing this parameter type in function `method` to borrow instead if owning the value isn't necessary
+  --> $DIR/pin_mut.rs:3:14
+   |
+LL | fn method(a: Pin<&mut ()>) {}
+   |    ------    ^^^^^^^^^^^^ this parameter takes ownership of the value
+   |    |
+   |    in this function
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.

tests/ui/reborrow/pin_mut_coerce_shared.rs

@@ -0,0 +1,13 @@
+use std::pin::Pin;
+
+fn method(a: Pin<&()>) {}  //~NOTE function defined here
+
+fn main() {
+    let a = &mut ();
+    let a = Pin::new(a);
+    method(a);
+    //~^ ERROR mismatched types
+    //~| NOTE arguments to this function are incorrect
+    //~| NOTE types differ in mutability
+    //~| NOTE expected struct `Pin<&()>`
+}

tests/ui/reborrow/pin_mut_coerce_shared.stderr

@@ -0,0 +1,19 @@
+error[E0308]: mismatched types
+  --> $DIR/pin_mut_coerce_shared.rs:8:12
+   |
+LL |     method(a);
+   |     ------ ^ types differ in mutability
+   |     |
+   |     arguments to this function are incorrect
+   |
+   = note: expected struct `Pin<&()>`
+              found struct `Pin<&mut ()>`
+note: function defined here
+  --> $DIR/pin_mut_coerce_shared.rs:3:4
+   |
+LL | fn method(a: Pin<&()>) {}
+   |    ^^^^^^ -----------
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.