Auto merge of #134628 - estebank:const-default, r=oli-obk

Make `Default` const and add some `const Default` impls

Full list of `impl const Default` types:

- ()
- bool
- char
- std::ascii::Char
- usize
- u8
- u16
- u32
- u64
- u128
- i8
- i16
- i32
- i64
- i128
- f16
- f32
- f64
- f128
- std::marker::PhantomData<T>
- Option<T>
- std::iter::Empty<T>
- std::ptr::Alignment
- &[T]
- &mut [T]
- &str
- &mut str
- String
- Vec<T>

28 files changed, 192 insertions, 160 deletions

diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 4290bb7a8a9..4ad65e678c3 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -107,8 +107,10 @@
 #![feature(char_max_len)]
 #![feature(clone_to_uninit)]
 #![feature(coerce_unsized)]
+#![feature(const_default)]
 #![feature(const_eval_select)]
 #![feature(const_heap)]
+#![feature(const_trait_impl)]
 #![feature(core_intrinsics)]
 #![feature(deprecated_suggestion)]
 #![feature(deref_pure_trait)]
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 187d1ca71d9..58baa07bc17 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -2611,7 +2611,8 @@ impl_eq! { Cow<'a, str>, &'b str }
 impl_eq! { Cow<'a, str>, String }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl Default for String {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl const Default for String {
     /// Creates an empty `String`.
     #[inline]
     fn default() -> String {
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index c8341750f4d..9dac58bac4f 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -3895,7 +3895,8 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Default for Vec<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T> const Default for Vec<T> {
     /// Creates an empty `Vec<T>`.
     ///
     /// The vector will not allocate until elements are pushed onto it.
diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index dfed8a00b7d..f7ea1f37a39 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -333,7 +333,8 @@ impl<T: Copy> Clone for Cell<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Default> Default for Cell<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T: ~const Default> const Default for Cell<T> {
     /// Creates a `Cell<T>`, with the `Default` value for T.
     #[inline]
     fn default() -> Cell<T> {
@@ -1323,7 +1324,8 @@ impl<T: Clone> Clone for RefCell<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Default> Default for RefCell<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T: ~const Default> const Default for RefCell<T> {
     /// Creates a `RefCell<T>`, with the `Default` value for T.
     #[inline]
     fn default() -> RefCell<T> {
@@ -2330,7 +2332,8 @@ impl<T: ?Sized> UnsafeCell<T> {
 }
 
 #[stable(feature = "unsafe_cell_default", since = "1.10.0")]
-impl<T: Default> Default for UnsafeCell<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T: ~const Default> const Default for UnsafeCell<T> {
     /// Creates an `UnsafeCell`, with the `Default` value for T.
     fn default() -> UnsafeCell<T> {
         UnsafeCell::new(Default::default())
@@ -2434,7 +2437,8 @@ impl<T: ?Sized> SyncUnsafeCell<T> {
 }
 
 #[unstable(feature = "sync_unsafe_cell", issue = "95439")]
-impl<T: Default> Default for SyncUnsafeCell<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T: ~const Default> const Default for SyncUnsafeCell<T> {
     /// Creates an `SyncUnsafeCell`, with the `Default` value for T.
     fn default() -> SyncUnsafeCell<T> {
         SyncUnsafeCell::new(Default::default())
diff --git a/library/core/src/default.rs b/library/core/src/default.rs
index 0a15cedfb55..4d108b0c18e 100644
--- a/library/core/src/default.rs
+++ b/library/core/src/default.rs
@@ -103,6 +103,8 @@ use crate::ascii::Char as AsciiChar;
 /// ```
 #[rustc_diagnostic_item = "Default"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///
@@ -149,7 +151,8 @@ pub macro Default($item:item) {
 macro_rules! default_impl {
     ($t:ty, $v:expr, $doc:tt) => {
         #[stable(feature = "rust1", since = "1.0.0")]
-        impl Default for $t {
+        #[rustc_const_unstable(feature = "const_default", issue = "67792")]
+        impl const Default for $t {
             #[inline(always)]
             #[doc = $doc]
             fn default() -> $t {
diff --git a/library/core/src/iter/sources/empty.rs b/library/core/src/iter/sources/empty.rs
index 3c3acceded8..309962ab70c 100644
--- a/library/core/src/iter/sources/empty.rs
+++ b/library/core/src/iter/sources/empty.rs
@@ -81,7 +81,8 @@ impl<T> Clone for Empty<T> {
 // not #[derive] because that adds a Default bound on T,
 // which isn't necessary.
 #[stable(feature = "iter_empty", since = "1.2.0")]
-impl<T> Default for Empty<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T> const Default for Empty<T> {
     fn default() -> Empty<T> {
         Empty(marker::PhantomData)
     }
diff --git a/library/core/src/marker.rs b/library/core/src/marker.rs
index ccbd2b00cfd..2aeb0b0c31e 100644
--- a/library/core/src/marker.rs
+++ b/library/core/src/marker.rs
@@ -858,7 +858,8 @@ impl<T: PointeeSized> Clone for PhantomData<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PointeeSized> Default for PhantomData<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T: PointeeSized> const Default for PhantomData<T> {
     fn default() -> Self {
         Self
     }
diff --git a/library/core/src/option.rs b/library/core/src/option.rs
index f2a1e901188..38eb2662b34 100644
--- a/library/core/src/option.rs
+++ b/library/core/src/option.rs
@@ -2111,7 +2111,8 @@ where
 impl<T> crate::clone::UseCloned for Option<T> where T: crate::clone::UseCloned {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Default for Option<T> {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T> const Default for Option<T> {
     /// Returns [`None`][Option::None].
     ///
     /// # Examples
diff --git a/library/core/src/ptr/alignment.rs b/library/core/src/ptr/alignment.rs
index 3e66e271f03..304cde05af9 100644
--- a/library/core/src/ptr/alignment.rs
+++ b/library/core/src/ptr/alignment.rs
@@ -230,7 +230,8 @@ impl hash::Hash for Alignment {
 
 /// Returns [`Alignment::MIN`], which is valid for any type.
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
-impl Default for Alignment {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl const Default for Alignment {
     fn default() -> Alignment {
         Alignment::MIN
     }
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index dc09ba8d788..479fe0f1554 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -5158,7 +5158,8 @@ where
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Default for &[T] {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T> const Default for &[T] {
     /// Creates an empty slice.
     fn default() -> Self {
         &[]
@@ -5166,7 +5167,8 @@ impl<T> Default for &[T] {
 }
 
 #[stable(feature = "mut_slice_default", since = "1.5.0")]
-impl<T> Default for &mut [T] {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl<T> const Default for &mut [T] {
     /// Creates a mutable empty slice.
     fn default() -> Self {
         &mut []
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index fe64132ff22..32a22988175 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -3072,7 +3072,8 @@ impl AsRef<[u8]> for str {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl Default for &str {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl const Default for &str {
     /// Creates an empty str
     #[inline]
     fn default() -> Self {
@@ -3081,7 +3082,8 @@ impl Default for &str {
 }
 
 #[stable(feature = "default_mut_str", since = "1.28.0")]
-impl Default for &mut str {
+#[rustc_const_unstable(feature = "const_default", issue = "67792")]
+impl const Default for &mut str {
     /// Creates an empty mutable str
     #[inline]
     fn default() -> Self {
diff --git a/src/tools/clippy/clippy_utils/src/visitors.rs b/src/tools/clippy/clippy_utils/src/visitors.rs
index fc6e30a9804..615a0910dfd 100644
--- a/src/tools/clippy/clippy_utils/src/visitors.rs
+++ b/src/tools/clippy/clippy_utils/src/visitors.rs
@@ -1,5 +1,7 @@
+use crate::msrvs::Msrv;
 use crate::ty::needs_ordered_drop;
 use crate::{get_enclosing_block, path_to_local_id};
+use crate::qualify_min_const_fn::is_stable_const_fn;
 use core::ops::ControlFlow;
 use rustc_ast::visit::{VisitorResult, try_visit};
 use rustc_hir::def::{CtorKind, DefKind, Res};
@@ -343,13 +345,13 @@ pub fn is_const_evaluatable<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) ->
                     .cx
                     .qpath_res(p, hir_id)
                     .opt_def_id()
-                    .is_some_and(|id| self.cx.tcx.is_const_fn(id)) => {},
+                    .is_some_and(|id| is_stable_const_fn(self.cx, id, Msrv::default())) => {},
                 ExprKind::MethodCall(..)
                     if self
                         .cx
                         .typeck_results()
                         .type_dependent_def_id(e.hir_id)
-                        .is_some_and(|id| self.cx.tcx.is_const_fn(id)) => {},
+                        .is_some_and(|id| is_stable_const_fn(self.cx, id, Msrv::default())) => {},
                 ExprKind::Binary(_, lhs, rhs)
                     if self.cx.typeck_results().expr_ty(lhs).peel_refs().is_primitive_ty()
                         && self.cx.typeck_results().expr_ty(rhs).peel_refs().is_primitive_ty() => {},
diff --git a/tests/ui/consts/rustc-impl-const-stability.rs b/tests/ui/consts/rustc-impl-const-stability.rs
index 0df8482bec1..93a5e8e4f45 100644
--- a/tests/ui/consts/rustc-impl-const-stability.rs
+++ b/tests/ui/consts/rustc-impl-const-stability.rs
@@ -2,7 +2,7 @@
 //@ known-bug: #110395
 
 #![crate_type = "lib"]
-#![feature(staged_api, const_trait_impl)]
+#![feature(staged_api, const_trait_impl, const_default)]
 #![stable(feature = "foo", since = "1.0.0")]
 
 #[stable(feature = "potato", since = "1.27.0")]
@@ -12,8 +12,8 @@ pub struct Data {
 
 #[stable(feature = "potato", since = "1.27.0")]
 #[rustc_const_unstable(feature = "data_foo", issue = "none")]
-impl const Default for Data {
-    fn default() -> Data {
-        Data { _data: 42 }
+impl const std::fmt::Debug for Data {
+    fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
+        Ok(())
     }
 }
diff --git a/tests/ui/consts/rustc-impl-const-stability.stderr b/tests/ui/consts/rustc-impl-const-stability.stderr
index 19c6bb5907f..a3ef4031a13 100644
--- a/tests/ui/consts/rustc-impl-const-stability.stderr
+++ b/tests/ui/consts/rustc-impl-const-stability.stderr
@@ -1,8 +1,8 @@
-error: const `impl` for trait `Default` which is not marked with `#[const_trait]`
+error: const `impl` for trait `Debug` which is not marked with `#[const_trait]`
   --> $DIR/rustc-impl-const-stability.rs:15:12
    |
-LL | impl const Default for Data {
-   |            ^^^^^^^ this trait is not `const`
+LL | impl const std::fmt::Debug for Data {
+   |            ^^^^^^^^^^^^^^^ this trait is not `const`
    |
    = 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
diff --git a/tests/ui/lint/dead-code/unused-struct-derive-default.rs b/tests/ui/lint/dead-code/unused-struct-derive-default.rs
index f20b7cb66ee..bfbdf57b0dc 100644
--- a/tests/ui/lint/dead-code/unused-struct-derive-default.rs
+++ b/tests/ui/lint/dead-code/unused-struct-derive-default.rs
@@ -1,4 +1,4 @@
-#![deny(dead_code)]
+#![deny(dead_code)] //~ NOTE the lint level is defined here
 
 #[derive(Default)]
 struct T; //~ ERROR struct `T` is never constructed
@@ -7,7 +7,7 @@ struct T; //~ ERROR struct `T` is never constructed
 struct Used;
 
 #[derive(Default)]
-enum E {
+enum E { //~ NOTE variant in this enum
     #[default]
     A,
     B, //~ ERROR variant `B` is never constructed
diff --git a/tests/ui/specialization/const_trait_impl.rs b/tests/ui/specialization/const_trait_impl.rs
index 2df92dfad3b..e917263d193 100644
--- a/tests/ui/specialization/const_trait_impl.rs
+++ b/tests/ui/specialization/const_trait_impl.rs
@@ -2,6 +2,8 @@
 
 #![feature(const_trait_impl, min_specialization, rustc_attrs)]
 
+use std::fmt::Debug;
+
 #[rustc_specialization_trait]
 #[const_trait]
 pub unsafe trait Sup {
@@ -31,19 +33,19 @@ pub trait A {
     fn a() -> u32;
 }
 
-impl<T: [const] Default> const A for T {
+impl<T: [const] Debug> const A for T {
     default fn a() -> u32 {
         2
     }
 }
 
-impl<T: [const] Default + [const] Sup> const A for T {
+impl<T: [const] Debug + [const] Sup> const A for T {
     default fn a() -> u32 {
         3
     }
 }
 
-impl<T: [const] Default + [const] Sub> const A for T {
+impl<T: [const] Debug + [const] Sub> const A for T {
     fn a() -> u32 {
         T::foo()
     }
diff --git a/tests/ui/specialization/const_trait_impl.stderr b/tests/ui/specialization/const_trait_impl.stderr
index ea3ec16ac1e..b9c768812c8 100644
--- a/tests/ui/specialization/const_trait_impl.stderr
+++ b/tests/ui/specialization/const_trait_impl.stderr
@@ -1,58 +1,58 @@
 error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/const_trait_impl.rs:34:9
+  --> $DIR/const_trait_impl.rs:36:9
    |
-LL | impl<T: [const] Default> const A for T {
-   |         ^^^^^^^ can't be applied to `Default`
+LL | impl<T: [const] Debug> const A for T {
+   |         ^^^^^^^ can't be applied to `Debug`
    |
-note: `Default` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/default.rs:LL:COL
+note: `Debug` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
 
 error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/const_trait_impl.rs:40:9
+  --> $DIR/const_trait_impl.rs:42:9
    |
-LL | impl<T: [const] Default + [const] Sup> const A for T {
-   |         ^^^^^^^ can't be applied to `Default`
+LL | impl<T: [const] Debug + [const] Sup> const A for T {
+   |         ^^^^^^^ can't be applied to `Debug`
    |
-note: `Default` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/default.rs:LL:COL
+note: `Debug` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
 
 error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/const_trait_impl.rs:46:9
+  --> $DIR/const_trait_impl.rs:48:9
    |
-LL | impl<T: [const] Default + [const] Sub> const A for T {
-   |         ^^^^^^^ can't be applied to `Default`
+LL | impl<T: [const] Debug + [const] Sub> const A for T {
+   |         ^^^^^^^ can't be applied to `Debug`
    |
-note: `Default` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/default.rs:LL:COL
+note: `Debug` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
 
 error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/const_trait_impl.rs:40:9
+  --> $DIR/const_trait_impl.rs:42:9
    |
-LL | impl<T: [const] Default + [const] Sup> const A for T {
-   |         ^^^^^^^ can't be applied to `Default`
+LL | impl<T: [const] Debug + [const] Sup> const A for T {
+   |         ^^^^^^^ can't be applied to `Debug`
    |
-note: `Default` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/default.rs:LL:COL
+note: `Debug` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/const_trait_impl.rs:34:9
+  --> $DIR/const_trait_impl.rs:36:9
    |
-LL | impl<T: [const] Default> const A for T {
-   |         ^^^^^^^ can't be applied to `Default`
+LL | impl<T: [const] Debug> const A for T {
+   |         ^^^^^^^ can't be applied to `Debug`
    |
-note: `Default` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/default.rs:LL:COL
+note: `Debug` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/const_trait_impl.rs:46:9
+  --> $DIR/const_trait_impl.rs:48:9
    |
-LL | impl<T: [const] Default + [const] Sub> const A for T {
-   |         ^^^^^^^ can't be applied to `Default`
+LL | impl<T: [const] Debug + [const] Sub> const A for T {
+   |         ^^^^^^^ can't be applied to `Debug`
    |
-note: `Default` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/default.rs:LL:COL
+note: `Debug` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors
diff --git a/tests/ui/traits/const-traits/const-traits-alloc.rs b/tests/ui/traits/const-traits/const-traits-alloc.rs
new file mode 100644
index 00000000000..07725ef02f1
--- /dev/null
+++ b/tests/ui/traits/const-traits/const-traits-alloc.rs
@@ -0,0 +1,9 @@
+//@ run-pass
+#![feature(const_trait_impl, const_default)]
+#![allow(dead_code)]
+// alloc::string
+const STRING: String = Default::default();
+// alloc::vec
+const VEC: Vec<()> = Default::default();
+
+fn main() {}
diff --git a/tests/ui/traits/const-traits/const-traits-core.rs b/tests/ui/traits/const-traits/const-traits-core.rs
new file mode 100644
index 00000000000..6df53daae13
--- /dev/null
+++ b/tests/ui/traits/const-traits/const-traits-core.rs
@@ -0,0 +1,46 @@
+//@ run-pass
+#![feature(
+    const_trait_impl, const_default, ptr_alignment_type, ascii_char, f16, f128, sync_unsafe_cell,
+)]
+#![allow(dead_code)]
+// core::default
+const UNIT: () = Default::default();
+const BOOL: bool = Default::default();
+const CHAR: char = Default::default();
+const ASCII_CHAR: std::ascii::Char = Default::default();
+const USIZE: usize = Default::default();
+const U8: u8 = Default::default();
+const U16: u16 = Default::default();
+const U32: u32 = Default::default();
+const U64: u64 = Default::default();
+const U128: u128 = Default::default();
+const I8: i8 = Default::default();
+const I16: i16 = Default::default();
+const I32: i32 = Default::default();
+const I64: i64 = Default::default();
+const I128: i128 = Default::default();
+const F16: f16 = Default::default();
+const F32: f32 = Default::default();
+const F64: f64 = Default::default();
+const F128: f128 = Default::default();
+// core::marker
+const PHANTOM: std::marker::PhantomData<()> = Default::default();
+// core::option
+const OPT: Option<i32> = Default::default();
+// core::iter::sources::empty
+const EMPTY: std::iter::Empty<()> = Default::default();
+// core::ptr::alignment
+const ALIGNMENT: std::ptr::Alignment = Default::default();
+// core::slice
+const SLICE: &[()] = Default::default();
+const MUT_SLICE: &mut [()] = Default::default();
+// core::str
+const STR: &str = Default::default();
+const MUT_STR: &mut str = Default::default();
+// core::cell
+const CELL: std::cell::Cell<()> = Default::default();
+const REF_CELL: std::cell::RefCell<()> = Default::default();
+const UNSAFE_CELL: std::cell::UnsafeCell<()> = Default::default();
+const SYNC_UNSAFE_CELL: std::cell::SyncUnsafeCell<()> = Default::default();
+
+fn main() {}
diff --git a/tests/ui/traits/const-traits/const_derives/derive-const-gate.rs b/tests/ui/traits/const-traits/const_derives/derive-const-gate.rs
index a772d69c9e2..04fea1189ae 100644
--- a/tests/ui/traits/const-traits/const_derives/derive-const-gate.rs
+++ b/tests/ui/traits/const-traits/const_derives/derive-const-gate.rs
@@ -1,5 +1,6 @@
-#[derive_const(Default)] //~ ERROR use of unstable library feature
-//~^ ERROR const `impl` for trait `Default` which is not marked with `#[const_trait]`
+#[derive_const(Debug)] //~ ERROR use of unstable library feature
+//~^ ERROR const `impl` for trait `Debug` which is not marked with `#[const_trait]`
+//~| ERROR cannot call non-const method
 pub struct S;
 
 fn main() {}
diff --git a/tests/ui/traits/const-traits/const_derives/derive-const-gate.stderr b/tests/ui/traits/const-traits/const_derives/derive-const-gate.stderr
index 202210a2e65..5bde358001c 100644
--- a/tests/ui/traits/const-traits/const_derives/derive-const-gate.stderr
+++ b/tests/ui/traits/const-traits/const_derives/derive-const-gate.stderr
@@ -1,21 +1,30 @@
 error[E0658]: use of unstable library feature `derive_const`
   --> $DIR/derive-const-gate.rs:1:3
    |
-LL | #[derive_const(Default)]
+LL | #[derive_const(Debug)]
    |   ^^^^^^^^^^^^
    |
    = help: add `#![feature(derive_const)]` 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: const `impl` for trait `Default` which is not marked with `#[const_trait]`
+error: const `impl` for trait `Debug` which is not marked with `#[const_trait]`
   --> $DIR/derive-const-gate.rs:1:16
    |
-LL | #[derive_const(Default)]
-   |                ^^^^^^^ this trait is not `const`
+LL | #[derive_const(Debug)]
+   |                ^^^^^ this trait is not `const`
    |
    = 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: aborting due to 2 previous errors
+error[E0015]: cannot call non-const method `Formatter::<'_>::write_str` in constant functions
+  --> $DIR/derive-const-gate.rs:1:16
+   |
+LL | #[derive_const(Debug)]
+   |                ^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0658`.
+Some errors have detailed explanations: E0015, E0658.
+For more information about an error, try `rustc --explain E0015`.
diff --git a/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.rs b/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.rs
index 7bda7117a47..0bc25ce5f65 100644
--- a/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.rs
+++ b/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.rs
@@ -3,11 +3,13 @@
 
 pub struct A;
 
-impl Default for A {
-    fn default() -> A { A }
+impl std::fmt::Debug for A {
+    fn fmt(&self, _: &mut std::fmt::Formatter<'_>)  -> Result<(), std::fmt::Error> {
+        panic!()
+    }
 }
 
-#[derive_const(Default)]
+#[derive_const(Debug)]
 pub struct S(A);
 
 fn main() {}
diff --git a/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.stderr b/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.stderr
index 27f4bcf46ef..c0bd360ebe5 100644
--- a/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.stderr
+++ b/tests/ui/traits/const-traits/const_derives/derive-const-non-const-type.stderr
@@ -1,19 +1,17 @@
-error: const `impl` for trait `Default` which is not marked with `#[const_trait]`
-  --> $DIR/derive-const-non-const-type.rs:10:16
+error: const `impl` for trait `Debug` which is not marked with `#[const_trait]`
+  --> $DIR/derive-const-non-const-type.rs:12:16
    |
-LL | #[derive_const(Default)]
-   |                ^^^^^^^ this trait is not `const`
+LL | #[derive_const(Debug)]
+   |                ^^^^^ this trait is not `const`
    |
    = 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[E0015]: cannot call non-const associated function `<A as Default>::default` in constant functions
-  --> $DIR/derive-const-non-const-type.rs:11:14
+error[E0015]: cannot call non-const method `Formatter::<'_>::debug_tuple_field1_finish` in constant functions
+  --> $DIR/derive-const-non-const-type.rs:12:16
    |
-LL | #[derive_const(Default)]
-   |                ------- in this derive macro expansion
-LL | pub struct S(A);
-   |              ^
+LL | #[derive_const(Debug)]
+   |                ^^^^^
    |
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 
diff --git a/tests/ui/traits/const-traits/const_derives/derive-const-use.rs b/tests/ui/traits/const-traits/const_derives/derive-const-use.rs
index 1e447147213..1a3012de06f 100644
--- a/tests/ui/traits/const-traits/const_derives/derive-const-use.rs
+++ b/tests/ui/traits/const-traits/const_derives/derive-const-use.rs
@@ -1,6 +1,6 @@
 //@ known-bug: #110395
 
-#![feature(const_trait_impl, const_cmp, const_default_impls, derive_const)]
+#![feature(const_trait_impl, const_default, const_cmp, derive_const)]
 
 pub struct A;
 
diff --git a/tests/ui/traits/const-traits/const_derives/derive-const-use.stderr b/tests/ui/traits/const-traits/const_derives/derive-const-use.stderr
index ce61eb9a1ab..4ea11a0c7ed 100644
--- a/tests/ui/traits/const-traits/const_derives/derive-const-use.stderr
+++ b/tests/ui/traits/const-traits/const_derives/derive-const-use.stderr
@@ -1,27 +1,3 @@
-error[E0635]: unknown feature `const_default_impls`
-  --> $DIR/derive-const-use.rs:3:41
-   |
-LL | #![feature(const_trait_impl, const_cmp, const_default_impls, derive_const)]
-   |                                         ^^^^^^^^^^^^^^^^^^^
-
-error: const `impl` for trait `Default` which is not marked with `#[const_trait]`
-  --> $DIR/derive-const-use.rs:7:12
-   |
-LL | impl const Default for A {
-   |            ^^^^^^^ this trait is not `const`
-   |
-   = 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: const `impl` for trait `Default` which is not marked with `#[const_trait]`
-  --> $DIR/derive-const-use.rs:15:16
-   |
-LL | #[derive_const(Default, PartialEq)]
-   |                ^^^^^^^ this trait is not `const`
-   |
-   = 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[E0277]: the trait bound `(): [const] PartialEq` is not satisfied
   --> $DIR/derive-const-use.rs:16:14
    |
@@ -30,35 +6,6 @@ LL | #[derive_const(Default, PartialEq)]
 LL | pub struct S((), A);
    |              ^^
 
-error[E0015]: cannot call non-const associated function `<S as Default>::default` in constants
-  --> $DIR/derive-const-use.rs:18:35
-   |
-LL | const _: () = assert!(S((), A) == S::default());
-   |                                   ^^^^^^^^^^^^
-   |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
-
-error[E0015]: cannot call non-const associated function `<() as Default>::default` in constant functions
-  --> $DIR/derive-const-use.rs:16:14
-   |
-LL | #[derive_const(Default, PartialEq)]
-   |                ------- in this derive macro expansion
-LL | pub struct S((), A);
-   |              ^^
-   |
-   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-
-error[E0015]: cannot call non-const associated function `<A as Default>::default` in constant functions
-  --> $DIR/derive-const-use.rs:16:18
-   |
-LL | #[derive_const(Default, PartialEq)]
-   |                ------- in this derive macro expansion
-LL | pub struct S((), A);
-   |                  ^
-   |
-   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-
-error: aborting due to 7 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0015, E0277, E0635.
-For more information about an error, try `rustc --explain E0015`.
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/traits/const-traits/std-impl-gate.gated.stderr b/tests/ui/traits/const-traits/std-impl-gate.gated.stderr
deleted file mode 100644
index a78cf8ce61e..00000000000
--- a/tests/ui/traits/const-traits/std-impl-gate.gated.stderr
+++ /dev/null
@@ -1,18 +0,0 @@
-error[E0635]: unknown feature `const_default_impls`
-  --> $DIR/std-impl-gate.rs:6:46
-   |
-LL | #![cfg_attr(gated, feature(const_trait_impl, const_default_impls))]
-   |                                              ^^^^^^^^^^^^^^^^^^^
-
-error[E0015]: cannot call non-const associated function `<Vec<usize> as Default>::default` in constant functions
-  --> $DIR/std-impl-gate.rs:13:5
-   |
-LL |     Default::default()
-   |     ^^^^^^^^^^^^^^^^^^
-   |
-   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-
-error: aborting due to 2 previous errors
-
-Some errors have detailed explanations: E0015, E0635.
-For more information about an error, try `rustc --explain E0015`.
diff --git a/tests/ui/traits/const-traits/std-impl-gate.rs b/tests/ui/traits/const-traits/std-impl-gate.rs
index 84091931997..d29bccf17c9 100644
--- a/tests/ui/traits/const-traits/std-impl-gate.rs
+++ b/tests/ui/traits/const-traits/std-impl-gate.rs
@@ -1,9 +1,9 @@
 // This tests feature gates for const impls in the standard library.
 
 //@ revisions: stock gated
-//@[gated] known-bug: #110395
+//@[gated] run-pass
 
-#![cfg_attr(gated, feature(const_trait_impl, const_default_impls))]
+#![cfg_attr(gated, feature(const_trait_impl, const_default))]
 
 fn non_const_context() -> Vec<usize> {
     Default::default()
@@ -11,7 +11,8 @@ fn non_const_context() -> Vec<usize> {
 
 const fn const_context() -> Vec<usize> {
     Default::default()
-    //[stock]~^ ERROR cannot call non-const associated function
+    //[stock]~^ ERROR cannot call conditionally-const associated function
+    //[stock]~| ERROR `Default` is not yet stable as a const trait
 }
 
 fn main() {
diff --git a/tests/ui/traits/const-traits/std-impl-gate.stock.stderr b/tests/ui/traits/const-traits/std-impl-gate.stock.stderr
index 8728f652ef9..1fa71e41a98 100644
--- a/tests/ui/traits/const-traits/std-impl-gate.stock.stderr
+++ b/tests/ui/traits/const-traits/std-impl-gate.stock.stderr
@@ -1,11 +1,25 @@
-error[E0015]: cannot call non-const associated function `<Vec<usize> as Default>::default` in constant functions
+error[E0658]: cannot call conditionally-const associated function `<Vec<usize> as Default>::default` in constant functions
   --> $DIR/std-impl-gate.rs:13:5
    |
 LL |     Default::default()
    |     ^^^^^^^^^^^^^^^^^^
    |
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+   = note: see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information
+   = help: add `#![feature(const_trait_impl)]` 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
+error: `Default` is not yet stable as a const trait
+  --> $DIR/std-impl-gate.rs:13:5
+   |
+LL |     Default::default()
+   |     ^^^^^^^^^^^^^^^^^^
+   |
+help: add `#![feature(const_default)]` to the crate attributes to enable
+   |
+LL + #![feature(const_default)]
+   |
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0015`.
+For more information about this error, try `rustc --explain E0658`.