rust-lang · matthiaskrgr · Jul 7, 2025 · Jul 7, 2025 · Dec 21, 2024 · Jul 7, 2025
diff --git a/compiler/rustc_attr_parsing/src/attributes/mod.rs b/compiler/rustc_attr_parsing/src/attributes/mod.rs
@@ -217,7 +217,14 @@ impl<S: Stage> OnDuplicate<S> {
 // them will be merged in another PR
 #[allow(unused)]
 pub(crate) enum AttributeOrder {
-    /// Duplicates after the first attribute will be an error.
+    /// Duplicates after the first attribute will be an error. I.e. only keep the lowest attribute.
+    ///
+    /// Attributes are processed from bottom to top, so this raises an error on all the attributes
+    /// further above the lowest one:
+    /// ```
+    /// #[stable(since="1.0")] //~ WARNING duplicated attribute
+    /// #[stable(since="2.0")]
+    /// ```
     ///
     /// This should be used where duplicates would be ignored, but carry extra
     /// meaning that could cause confusion. For example, `#[stable(since="1.0")]
@@ -227,6 +234,13 @@ pub(crate) enum AttributeOrder {
     /// Duplicates preceding the last instance of the attribute will be a
     /// warning, with a note that this will be an error in the future.
     ///
+    /// Attributes are processed from bottom to top, so this raises a warning on all the attributes
+    /// below the higher one:
+    /// ```
+    /// #[path="foo.rs"]
+    /// #[path="bar.rs"] //~ WARNING duplicated attribute
+    /// ```
+    ///
     /// This is the same as `FutureWarnFollowing`, except the last attribute is
     /// the one that is "used". Ideally these can eventually migrate to
     /// `ErrorPreceding`.

diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -1933,7 +1933,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     StringPart::highlighted("multiple different versions".to_string()),
                     StringPart::normal(" of crate `".to_string()),
                     StringPart::highlighted(format!("{crate_name}")),
-                    StringPart::normal("` in the dependency graph\n".to_string()),
+                    StringPart::normal("` in the dependency graph".to_string()),
                 ],
             );
             if points_at_type {

diff --git 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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -5158,15 +5158,17 @@ 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 {
         &[]
     }
 }
 
 #[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
@@ -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/doc/rustc/src/SUMMARY.md b/src/doc/rustc/src/SUMMARY.md
@@ -83,6 +83,7 @@
     - [m68k-unknown-linux-gnu](platform-support/m68k-unknown-linux-gnu.md)
     - [m68k-unknown-none-elf](platform-support/m68k-unknown-none-elf.md)
     - [mips64-openwrt-linux-musl](platform-support/mips64-openwrt-linux-musl.md)
+    - [mips64-unknown-linux-muslabi64](platform-support/mips64-unknown-linux-muslabi64.md)
     - [mipsel-sony-psx](platform-support/mipsel-sony-psx.md)
     - [mipsel-unknown-linux-gnu](platform-support/mipsel-unknown-linux-gnu.md)
     - [mips\*-mti-none-elf](platform-support/mips-mti-none-elf.md)

diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
@@ -333,7 +333,7 @@ target | std | host | notes
 `mips-unknown-linux-uclibc` | ✓ |  | MIPS Linux with uClibc
 [`mips64-openwrt-linux-musl`](platform-support/mips64-openwrt-linux-musl.md) | ? |  | MIPS64 for OpenWrt Linux musl 1.2.3
 `mips64-unknown-linux-gnuabi64` | ✓ | ✓ | MIPS64 Linux, N64 ABI (kernel 4.4, glibc 2.23)
-`mips64-unknown-linux-muslabi64` | ✓ |  | MIPS64 Linux, N64 ABI, musl 1.2.3
+[`mips64-unknown-linux-muslabi64`](platform-support/mips64-unknown-linux-muslabi64.md) | ✓ | ✓ | MIPS64 Linux, N64 ABI, musl 1.2.3
 `mips64el-unknown-linux-gnuabi64` | ✓ | ✓ | MIPS64 (little endian) Linux, N64 ABI (kernel 4.4, glibc 2.23)
 `mips64el-unknown-linux-muslabi64` | ✓ |  | MIPS64 (little endian) Linux, N64 ABI, musl 1.2.3
 `mipsel-sony-psp` | * |  | MIPS (LE) Sony PlayStation Portable (PSP)

diff --git a/src/doc/rustc/src/platform-support/mips64-unknown-linux-muslabi64.md b/src/doc/rustc/src/platform-support/mips64-unknown-linux-muslabi64.md
@@ -0,0 +1,49 @@
+# mips64-unknown-linux-muslabi64
+
+**Tier: 3**
+
+Target for 64-bit big endian MIPS Linux programs using musl libc and the N64 ABI.
+
+## Target maintainers
+
+[@Gelbpunkt](https://github.com/Gelbpunkt)
+
+## Requirements
+
+Building the target itself requires a 64-bit big endian MIPS compiler that is
+supported by `cc-rs`.
+
+## Building the target
+
+The target can be built by enabling it for a `rustc` build.
+
+```toml
+[build]
+target = ["mips64-unknown-linux-muslabi64"]
+```
+
+Make sure your C compiler is included in `$PATH`, then add it to the
+`bootstrap.toml`:
+
+```toml
+[target.mips64-unknown-linux-muslabi64]
+cc = "mips64-linux-musl-gcc"
+cxx = "mips64-linux-musl-g++"
+ar = "mips64-linux-musl-ar"
+linker = "mips64-linux-musl-gcc"
+```
+
+## Building Rust programs
+
+Rust does not yet ship pre-compiled artifacts for this target. To compile for
+this target, you will first need to build Rust with the target enabled (see
+"Building the target" above).
+
+## Cross-compilation
+
+This target can be cross-compiled from any host.
+
+## Testing
+
+This target can be tested as normal with `x.py` on a 64-bit big endian MIPS
+host or via QEMU emulation.
diff --git a/src/doc/rustc/src/platform-support/wasm32-wasip1.md b/src/doc/rustc/src/platform-support/wasm32-wasip1.md
@@ -4,37 +4,35 @@
 
 The `wasm32-wasip1` target is a WebAssembly compilation target which
 assumes that the [WASIp1] (aka "WASI preview1") set of "syscalls" are available
-for use in the standard library. Historically this target in the Rust compiler
-was one of the first for WebAssembly where Rust and C code are explicitly
-intended to interoperate as well.
-
-There's a bit of history to the target and current development which is also
-worth explaining before going much further. Historically this target was
-originally called `wasm32-wasi` in both rustc and Clang. This was first added
-to Rust in 2019. In the intervening years leading up to 2024 the WASI standard
-continued to be developed and was eventually "rebased" on top of the [Component
-Model]. This was a large change to the WASI specification and was released as
-0.2.0 ("WASIp2" colloquially) in January 2024. The previous target's name in
-rustc, `wasm32-wasi`, was then renamed to `wasm32-wasip1`, to avoid
-confusion with this new target to be added to rustc as `wasm32-wasip2`.
-Some more context can be found in these MCPs:
-
-* [Rename wasm32-wasi target to wasm32-wasip1](https://github.com/rust-lang/compiler-team/issues/607)
-* [Smooth the renaming transition of wasm32-wasi](https://github.com/rust-lang/compiler-team/issues/695)
-
-At this point the `wasm32-wasip1` target is intended for historical
-compatibility with the first version of the WASI standard. As of now (January
-2024) the 0.2.0 target of WASI ("WASIp2") is relatively new. The state of
-WASI will likely change in few years after which point this documentation will
-probably receive another update.
-
-[WASI Preview1]: https://github.com/WebAssembly/WASI/tree/main/legacy/preview1
+for use in the standard library. This target explicitly supports interop with
+non-Rust code such as C and C++.
+
+The [WASIp1] set of syscalls is standard insofar as it was written down once by
+a set of folks and has not changed since then. Additionally the [WASIp1]
+syscalls have been adapted and adopted into a number of runtimes and embeddings.
+It is not standard in the sense that there are no formal semantics for each
+syscall and APIs are no longer receiving any maintenance (e.g. no new APIs, no
+new documentation, etc). After [WASIp1] was originally developed in 2019 the
+WASI standard effort has since been "rebased" on top of the [Component Model].
+This was a large change to the WASI specification and was released as 0.2.0
+("WASIp2" colloquially) in January 2024. Current standardization efforts are
+focused on the Component Model-based definition of WASI. At this point the
+`wasm32-wasip1` Rust target is intended for historical compatibility with
+[WASIp1] set of syscalls.
+
+[WASIp1]: https://github.com/WebAssembly/WASI/tree/main/legacy/preview1
 [Component Model]: https://github.com/webassembly/component-model
 
 Today the `wasm32-wasip1` target will generate core WebAssembly modules
 which will import functions from the `wasi_snapshot_preview1` module for
 OS-related functionality (e.g. printing).
 
+> **Note**: Prior to March 2024 this target was known as `wasm32-wasi` with some
+> historical context found in old MCPs:
+>
+> * [Rename wasm32-wasi target to wasm32-wasip1](https://github.com/rust-lang/compiler-team/issues/607)
+> * [Smooth the renaming transition of wasm32-wasi](https://github.com/rust-lang/compiler-team/issues/695)
+
 ## Target maintainers
 
 When this target was added to the compiler platform-specific documentation here

diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
@@ -7,6 +7,7 @@ use rustc_ast::ast;
 use rustc_attr_data_structures::{self as attrs, DeprecatedSince};
 use rustc_hir::def::CtorKind;
 use rustc_hir::def_id::DefId;
+use rustc_hir::{HeaderSafety, Safety};
 use rustc_metadata::rendered_const;
 use rustc_middle::{bug, ty};
 use rustc_span::{Pos, kw, sym};
@@ -381,10 +382,22 @@ impl FromClean<clean::Union> for Union {
 
 impl FromClean<rustc_hir::FnHeader> for FunctionHeader {
     fn from_clean(header: &rustc_hir::FnHeader, renderer: &JsonRenderer<'_>) -> Self {
+        let is_unsafe = match header.safety {
+            HeaderSafety::SafeTargetFeatures => {
+                // The type system's internal implementation details consider
+                // safe functions with the `#[target_feature]` attribute to be analogous
+                // to unsafe functions: `header.is_unsafe()` returns `true` for them.
+                // For rustdoc, this isn't the right decision, so we explicitly return `false`.
+                // Context: https://github.com/rust-lang/rust/issues/142655
+                false
+            }
+            HeaderSafety::Normal(Safety::Safe) => false,
+            HeaderSafety::Normal(Safety::Unsafe) => true,
+        };
         FunctionHeader {
             is_async: header.is_async(),
             is_const: header.is_const(),
-            is_unsafe: header.is_unsafe(),
+            is_unsafe,
             abi: header.abi.into_json(renderer),
         }
     }

diff --git 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() => {},