Constify Drop and Destruct

library/core/src/marker.rs

@@ -957,6 +957,7 @@ marker_impls! {
 #[lang = "destruct"]
 #[rustc_on_unimplemented(message = "can't drop `{Self}`", append_const_msg)]
 #[rustc_deny_explicit_impl(implement_via_object = false)]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Destruct {}
 
 /// A marker for tuple types.

library/core/src/ops/drop.rs

@@ -203,7 +203,7 @@
 /// [nomicon]: ../../nomicon/phantom-data.html#an-exception-the-special-case-of-the-standard-library-and-its-unstable-may_dangle
 #[lang = "drop"]
 #[stable(feature = "rust1", since = "1.0.0")]
-// FIXME(const_trait_impl) #[const_trait]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Drop {
     /// Executes the destructor for this type.
     ///

tests/ui/consts/const-block-const-bound.stderr

@@ -1,25 +1,9 @@
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/const-block-const-bound.rs:8:15
+error[E0277]: the trait bound `UnconstDrop: const Destruct` is not satisfied
+  --> $DIR/const-block-const-bound.rs:18:9
    |
-LL | const fn f<T: ~const Destruct>(x: T) {}
-   |               ^^^^^^
+LL |         f(UnconstDrop);
+   |         ^^^^^^^^^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/const-block-const-bound.rs:8:15
-   |
-LL | const fn f<T: ~const Destruct>(x: T) {}
-   |               ^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error[E0493]: destructor of `T` cannot be evaluated at compile-time
-  --> $DIR/const-block-const-bound.rs:8:32
-   |
-LL | const fn f<T: ~const Destruct>(x: T) {}
-   |                                ^      - value is dropped here
-   |                                |
-   |                                the destructor for this type cannot be evaluated in constant functions
-
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0493`.
+For more information about this error, try `rustc --explain E0277`.

tests/ui/consts/fn_trait_refs.stderr

@@ -16,12 +16,6 @@ error: `~const` can only be applied to `#[const_trait]` traits
 LL |     T: ~const Fn<()> + ~const Destruct,
    |        ^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:14:24
-   |
-LL |     T: ~const Fn<()> + ~const Destruct,
-   |                        ^^^^^^
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:14:8
    |
@@ -38,26 +32,12 @@ LL |     T: ~const Fn<()> + ~const Destruct,
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:14:24
-   |
-LL |     T: ~const Fn<()> + ~const Destruct,
-   |                        ^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:21:8
    |
 LL |     T: ~const FnMut<()> + ~const Destruct,
    |        ^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:21:27
-   |
-LL |     T: ~const FnMut<()> + ~const Destruct,
-   |                           ^^^^^^
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:21:8
    |
@@ -74,14 +54,6 @@ LL |     T: ~const FnMut<()> + ~const Destruct,
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:21:27
-   |
-LL |     T: ~const FnMut<()> + ~const Destruct,
-   |                           ^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:28:8
    |
@@ -110,12 +82,6 @@ error: `~const` can only be applied to `#[const_trait]` traits
 LL |     T: ~const Fn<()> + ~const Destruct,
    |        ^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:35:24
-   |
-LL |     T: ~const Fn<()> + ~const Destruct,
-   |                        ^^^^^^
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:35:8
    |
@@ -132,26 +98,12 @@ LL |     T: ~const Fn<()> + ~const Destruct,
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:35:24
-   |
-LL |     T: ~const Fn<()> + ~const Destruct,
-   |                        ^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:49:8
    |
 LL |     T: ~const FnMut<()> + ~const Destruct,
    |        ^^^^^^
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:49:27
-   |
-LL |     T: ~const FnMut<()> + ~const Destruct,
-   |                           ^^^^^^
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/fn_trait_refs.rs:49:8
    |
@@ -168,29 +120,35 @@ LL |     T: ~const FnMut<()> + ~const Destruct,
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: `~const` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:49:27
-   |
-LL |     T: ~const FnMut<()> + ~const Destruct,
-   |                           ^^^^^^
+error[E0277]: the trait bound `fn() -> i32 {one}: const Destruct` is not satisfied
+  --> $DIR/fn_trait_refs.rs:70:24
    |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+LL |         let test_one = test_fn(one);
+   |                        ^^^^^^^^^^^^
 
-error[E0015]: cannot call non-const operator in constants
-  --> $DIR/fn_trait_refs.rs:71:17
+error[E0277]: the trait bound `fn() -> i32 {two}: const Destruct` is not satisfied
+  --> $DIR/fn_trait_refs.rs:73:24
    |
-LL |         assert!(test_one == (1, 1, 1));
-   |                 ^^^^^^^^^^^^^^^^^^^^^
+LL |         let test_two = test_fn_mut(two);
+   |                        ^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `&T: ~const Destruct` is not satisfied
+  --> $DIR/fn_trait_refs.rs:39:9
    |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+LL |         tester_fn(&f),
+   |         ^^^^^^^^^^^^^
 
-error[E0015]: cannot call non-const operator in constants
-  --> $DIR/fn_trait_refs.rs:74:17
+error[E0277]: the trait bound `&T: ~const Destruct` is not satisfied
+  --> $DIR/fn_trait_refs.rs:41:9
    |
-LL |         assert!(test_two == (2, 2));
-   |                 ^^^^^^^^^^^^^^^^^^
+LL |         tester_fn_mut(&f),
+   |         ^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `&mut T: ~const Destruct` is not satisfied
+  --> $DIR/fn_trait_refs.rs:53:9
    |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+LL |         tester_fn_mut(&mut f),
+   |         ^^^^^^^^^^^^^^^^^^^^^
 
 error[E0015]: cannot call non-const closure in constant functions
   --> $DIR/fn_trait_refs.rs:16:5
@@ -204,15 +162,6 @@ help: consider further restricting this bound
 LL |     T: ~const Fn<()> + ~const Destruct + ~const Fn(),
    |                                        +++++++++++++
 
-error[E0493]: destructor of `T` cannot be evaluated at compile-time
-  --> $DIR/fn_trait_refs.rs:12:23
-   |
-LL | const fn tester_fn<T>(f: T) -> T::Output
-   |                       ^ the destructor for this type cannot be evaluated in constant functions
-...
-LL | }
-   | - value is dropped here
-
 error[E0015]: cannot call non-const closure in constant functions
   --> $DIR/fn_trait_refs.rs:23:5
    |
@@ -225,15 +174,6 @@ help: consider further restricting this bound
 LL |     T: ~const FnMut<()> + ~const Destruct + ~const FnMut(),
    |                                           ++++++++++++++++
 
-error[E0493]: destructor of `T` cannot be evaluated at compile-time
-  --> $DIR/fn_trait_refs.rs:19:27
-   |
-LL | const fn tester_fn_mut<T>(mut f: T) -> T::Output
-   |                           ^^^^^ the destructor for this type cannot be evaluated in constant functions
-...
-LL | }
-   | - value is dropped here
-
 error[E0015]: cannot call non-const closure in constant functions
   --> $DIR/fn_trait_refs.rs:30:5
    |
@@ -246,25 +186,7 @@ help: consider further restricting this bound
 LL |     T: ~const FnOnce<()> + ~const FnOnce(),
    |                          +++++++++++++++++
 
-error[E0493]: destructor of `T` cannot be evaluated at compile-time
-  --> $DIR/fn_trait_refs.rs:33:21
-   |
-LL | const fn test_fn<T>(mut f: T) -> (T::Output, T::Output, T::Output)
-   |                     ^^^^^ the destructor for this type cannot be evaluated in constant functions
-...
-LL | }
-   | - value is dropped here
-
-error[E0493]: destructor of `T` cannot be evaluated at compile-time
-  --> $DIR/fn_trait_refs.rs:47:25
-   |
-LL | const fn test_fn_mut<T>(mut f: T) -> (T::Output, T::Output)
-   |                         ^^^^^ the destructor for this type cannot be evaluated in constant functions
-...
-LL | }
-   | - value is dropped here
-
-error: aborting due to 34 previous errors
+error: aborting due to 25 previous errors
 
-Some errors have detailed explanations: E0015, E0493, E0635.
+Some errors have detailed explanations: E0015, E0277, E0635.
 For more information about an error, try `rustc --explain E0015`.

tests/ui/consts/promoted-const-drop.rs

@@ -3,7 +3,6 @@
 struct A();
 
 impl const Drop for A {
-    //~^ ERROR const `impl` for trait `Drop` which is not marked with `#[const_trait]`
     fn drop(&mut self) {}
 }
 

tests/ui/consts/promoted-const-drop.stderr

@@ -1,14 +1,5 @@
-error: const `impl` for trait `Drop` which is not marked with `#[const_trait]`
-  --> $DIR/promoted-const-drop.rs:5:12
-   |
-LL | impl const Drop for A {
-   |            ^^^^
-   |
-   = note: marking a trait with `#[const_trait]` ensures all default method bodies are `const`
-   = note: adding a non-const method body in the future would be a breaking change
-
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promoted-const-drop.rs:13:26
+  --> $DIR/promoted-const-drop.rs:12:26
    |
 LL |     let _: &'static A = &A();
    |            ----------    ^^^ creates a temporary value which is freed while still in use
@@ -19,7 +10,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promoted-const-drop.rs:14:28
+  --> $DIR/promoted-const-drop.rs:13:28
    |
 LL |     let _: &'static [A] = &[C];
    |            ------------    ^^^ creates a temporary value which is freed while still in use
@@ -28,6 +19,6 @@ LL |     let _: &'static [A] = &[C];
 LL | }
    | - temporary value is freed at the end of this statement
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0716`.

tests/ui/consts/promoted_const_call.stderr

@@ -1,12 +1,3 @@
-error: const `impl` for trait `Drop` which is not marked with `#[const_trait]`
-  --> $DIR/promoted_const_call.rs:6:12
-   |
-LL | impl const Drop for Panic { fn drop(&mut self) { panic!(); } }
-   |            ^^^^
-   |
-   = note: marking a trait with `#[const_trait]` ensures all default method bodies are `const`
-   = note: adding a non-const method body in the future would be a breaking change
-
 error[E0493]: destructor of `Panic` cannot be evaluated at compile-time
   --> $DIR/promoted_const_call.rs:10:30
    |
@@ -57,7 +48,7 @@ LL |     let _: &'static _ = &&(Panic, 0).1;
 LL | }
    | - temporary value is freed at the end of this statement
 
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0493, E0716.
 For more information about an error, try `rustc --explain E0493`.