Auto merge of #111671 - Dylan-DPC:rollup-1jy5r16, r=Dylan-DPC

Rollup of 6 pull requests

Successful merges:

 - #110145 (Share slice of bytes)
 - #111043 (Stabilize feature `cstr_is_empty`)
 - #111648 (Remove `LangItems::require`)
 - #111649 (Add derive for `core::marker::ConstParamTy`)
 - #111654 (Add a conversion from `&mut T` to `&mut UnsafeCell<T>`)
 - #111661 (Erase regions of type in `offset_of!`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -27,3 +27,26 @@ pub fn expand_deriving_copy(
 
     trait_def.expand(cx, mitem, item, push);
 }
+
+pub fn expand_deriving_const_param_ty(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    mitem: &MetaItem,
+    item: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+    is_const: bool,
+) {
+    let trait_def = TraitDef {
+        span,
+        path: path_std!(marker::ConstParamTy),
+        skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: false,
+        additional_bounds: Vec::new(),
+        supports_unions: false,
+        methods: Vec::new(),
+        associated_types: Vec::new(),
+        is_const,
+    };
+
+    trait_def.expand(cx, mitem, item, push);
+}

compiler/rustc_builtin_macros/src/lib.rs

@@ -115,6 +115,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
     register_derive! {
         Clone: clone::expand_deriving_clone,
         Copy: bounds::expand_deriving_copy,
+        ConstParamTy: bounds::expand_deriving_const_param_ty,
         Debug: debug::expand_deriving_debug,
         Default: default::expand_deriving_default,
         Eq: eq::expand_deriving_eq,

compiler/rustc_codegen_cranelift/src/base.rs

@@ -966,11 +966,7 @@ fn codegen_panic_inner<'tcx>(
     args: &[Value],
     span: Span,
 ) {
-    let def_id = fx
+    let def_id = fx.tcx.require_lang_item(lang_item, Some(span));
-        .tcx
-        .lang_items()
-        .require(lang_item)
-        .unwrap_or_else(|e| fx.tcx.sess.span_fatal(span, e.to_string()));
 
     let instance = Instance::mono(fx.tcx, def_id).polymorphize(fx.tcx);
     let symbol_name = fx.tcx.symbol_name(instance).name;

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -14,8 +14,7 @@ use snap::write::FrameEncoder;
 
 use object::elf::NT_GNU_PROPERTY_TYPE_0;
 use rustc_data_structures::memmap::Mmap;
-use rustc_data_structures::owned_slice::try_slice_owned;
+use rustc_data_structures::owned_slice::{try_slice_owned, OwnedSlice};
-use rustc_data_structures::sync::MetadataRef;
 use rustc_metadata::fs::METADATA_FILENAME;
 use rustc_metadata::EncodedMetadata;
 use rustc_session::cstore::MetadataLoader;
@@ -39,7 +38,7 @@ pub struct DefaultMetadataLoader;
 fn load_metadata_with(
     path: &Path,
     f: impl for<'a> FnOnce(&'a [u8]) -> Result<&'a [u8], String>,
-) -> Result<MetadataRef, String> {
+) -> Result<OwnedSlice, String> {
     let file =
         File::open(path).map_err(|e| format!("failed to open file '{}': {}", path.display(), e))?;
 
@@ -49,7 +48,7 @@ fn load_metadata_with(
 }
 
 impl MetadataLoader for DefaultMetadataLoader {
-    fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
+    fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<OwnedSlice, String> {
         load_metadata_with(path, |data| {
             let archive = object::read::archive::ArchiveFile::parse(&*data)
                 .map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?;
@@ -69,7 +68,7 @@ impl MetadataLoader for DefaultMetadataLoader {
         })
     }
 
-    fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
+    fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<OwnedSlice, String> {
         load_metadata_with(path, |data| search_for_section(path, data, ".rustc"))
     }
 }

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -1,3 +1,5 @@
+use std::any::Any;
+
 use super::write::WriteBackendMethods;
 use super::CodegenObject;
 use crate::back::write::TargetMachineFactoryFn;
@@ -5,6 +7,7 @@ use crate::{CodegenResults, ModuleCodegen};
 
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::{DynSend, DynSync};
 use rustc_errors::ErrorGuaranteed;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
@@ -20,11 +23,6 @@ use rustc_span::symbol::Symbol;
 use rustc_target::abi::call::FnAbi;
 use rustc_target::spec::Target;
 
-pub use rustc_data_structures::sync::MetadataRef;
-
-use rustc_data_structures::sync::{DynSend, DynSync};
-use std::any::Any;
-
 pub trait BackendTypes {
     type Value: CodegenObject;
     type Function: CodegenObject;

compiler/rustc_data_structures/src/owned_slice.rs

@@ -1,5 +1,6 @@
 use std::{borrow::Borrow, ops::Deref};
 
+use crate::sync::Lrc;
 // Use our fake Send/Sync traits when on not parallel compiler,
 // so that `OwnedSlice` only implements/requires Send/Sync
 // for parallel compiler builds.
@@ -7,7 +8,7 @@ use crate::sync::{Send, Sync};
 
 /// An owned slice.
 ///
-/// This is similar to `Box<[u8]>` but allows slicing and using anything as the
+/// This is similar to `Lrc<[u8]>` but allows slicing and using anything as the
 /// backing buffer.
 ///
 /// See [`slice_owned`] for `OwnedSlice` construction and examples.
@@ -16,6 +17,7 @@ use crate::sync::{Send, Sync};
 ///
 /// This is essentially a replacement for `owning_ref` which is a lot simpler
 /// and even sound! 🌸
+#[derive(Clone)]
 pub struct OwnedSlice {
     /// This is conceptually a `&'self.owner [u8]`.
     bytes: *const [u8],
@@ -31,7 +33,7 @@ pub struct OwnedSlice {
     //       \/
     //      ⊂(´･◡･⊂ )∘˚˳° (I am the phantom remnant of #97770)
     #[expect(dead_code)]
-    owner: Box<dyn Send + Sync>,
+    owner: Lrc<dyn Send + Sync>,
 }
 
 /// Makes an [`OwnedSlice`] out of an `owner` and a `slicer` function.
@@ -72,10 +74,10 @@ where
     O: Send + Sync + 'static,
     F: FnOnce(&O) -> Result<&[u8], E>,
 {
-    // We box the owner of the bytes, so it doesn't move.
+    // We wrap the owner of the bytes in, so it doesn't move.
     //
     // Since the owner does not move and we don't access it in any way
-    // before drop, there is nothing that can invalidate the bytes pointer.
+    // before dropping, there is nothing that can invalidate the bytes pointer.
     //
     // Thus, "extending" the lifetime of the reference returned from `F` is fine.
     // We pretend that we pass it a reference that lives as long as the returned slice.
@@ -83,12 +85,39 @@ where
     // N.B. the HRTB on the `slicer` is important — without it the caller could provide
     // a short lived slice, unrelated to the owner.
 
-    let owner = Box::new(owner);
+    let owner = Lrc::new(owner);
     let bytes = slicer(&*owner)?;
 
     Ok(OwnedSlice { bytes, owner })
 }
 
+impl OwnedSlice {
+    /// Slice this slice by `slicer`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use rustc_data_structures::owned_slice::{OwnedSlice, slice_owned};
+    /// let vec = vec![1, 2, 3, 4];
+    ///
+    /// // Identical to slicing via `&v[1..3]` but produces an owned slice
+    /// let slice: OwnedSlice = slice_owned(vec, |v| &v[..]);
+    /// assert_eq!(&*slice, [1, 2, 3, 4]);
+    ///
+    /// let slice = slice.slice(|slice| &slice[1..][..2]);
+    /// assert_eq!(&*slice, [2, 3]);
+    /// ```
+    ///
+    pub fn slice(self, slicer: impl FnOnce(&[u8]) -> &[u8]) -> OwnedSlice {
+        // This is basically identical to `try_slice_owned`,
+        // `slicer` can only return slices of its argument or some static data,
+        // both of which are valid while `owner` is alive.
+
+        let bytes = slicer(&self);
+        OwnedSlice { bytes, ..self }
+    }
+}
+
 impl Deref for OwnedSlice {
     type Target = [u8];
 
@@ -108,11 +137,11 @@ impl Borrow<[u8]> for OwnedSlice {
     }
 }
 
-// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Box<dyn Send + Sync>)`, which is `Send`
+// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Arc<dyn Send + Sync>)`, which is `Send`
 #[cfg(parallel_compiler)]
 unsafe impl Send for OwnedSlice {}
 
-// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Box<dyn Send + Sync>)`, which is `Sync`
+// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Arc<dyn Send + Sync>)`, which is `Sync`
 #[cfg(parallel_compiler)]
 unsafe impl Sync for OwnedSlice {}
 

compiler/rustc_data_structures/src/owned_slice/tests.rs

@@ -26,7 +26,7 @@ fn static_storage() {
 }
 
 #[test]
-fn slice_the_slice() {
+fn slice_owned_the_slice() {
     let slice = slice_owned(vec![1, 2, 3, 4, 5, 6], Vec::as_slice);
     let slice = slice_owned(slice, |s| &s[1..][..4]);
     let slice = slice_owned(slice, |s| s);
@@ -35,6 +35,16 @@ fn slice_the_slice() {
     assert_eq!(&*slice, &[1, 2, 3, 4, 5, 6][1..][..4][1..]);
 }
 
+#[test]
+fn slice_the_slice() {
+    let slice = slice_owned(vec![1, 2, 3, 4, 5, 6], Vec::as_slice)
+        .slice(|s| &s[1..][..4])
+        .slice(|s| s)
+        .slice(|s| &s[1..]);
+
+    assert_eq!(&*slice, &[1, 2, 3, 4, 5, 6][1..][..4][1..]);
+}
+
 #[test]
 fn try_and_fail() {
     let res = try_slice_owned(vec![0], |v| v.get(12..).ok_or(()));

compiler/rustc_data_structures/src/sync.rs

@@ -40,7 +40,6 @@
 //! [^2] `MTLockRef` is a typedef.
 
 pub use crate::marker::*;
-use crate::owned_slice::OwnedSlice;
 use std::collections::HashMap;
 use std::hash::{BuildHasher, Hash};
 use std::ops::{Deref, DerefMut};
@@ -92,6 +91,7 @@ mod mode {
 }
 
 pub use mode::{is_dyn_thread_safe, set_dyn_thread_safe_mode};
+
 cfg_if! {
     if #[cfg(not(parallel_compiler))] {
         pub unsafe auto trait Send {}
@@ -244,8 +244,6 @@ cfg_if! {
             r
         }
 
-        pub type MetadataRef = OwnedSlice;
-
         pub use std::rc::Rc as Lrc;
         pub use std::rc::Weak as Weak;
         pub use std::cell::Ref as ReadGuard;
@@ -517,8 +515,6 @@ cfg_if! {
             }
         }
 
-        pub type MetadataRef = OwnedSlice;
-
         /// This makes locks panic if they are already held.
         /// It is only useful when you are running in a single thread
         const ERROR_CHECKING: bool = false;

compiler/rustc_hir/src/errors.rs

@@ -1,10 +0,0 @@
-use crate::LangItem;
-
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Encodable, Decodable)]
-pub struct LangItemError(pub LangItem);
-
-impl ToString for LangItemError {
-    fn to_string(&self) -> String {
-        format!("requires `{}` lang_item", self.0.name())
-    }
-}

compiler/rustc_hir/src/lang_items.rs

@@ -8,7 +8,6 @@
 //! * Functions called by the compiler itself.
 
 use crate::def_id::DefId;
-use crate::errors::LangItemError;
 use crate::{MethodKind, Target};
 
 use rustc_ast as ast;
@@ -42,13 +41,6 @@ impl LanguageItems {
         self.items[item as usize] = Some(def_id);
     }
 
-    /// Requires that a given `LangItem` was bound and returns the corresponding `DefId`.
-    /// If it wasn't bound, e.g. due to a missing `#[lang = "<it.name()>"]`,
-    /// returns an error encapsulating the `LangItem`.
-    pub fn require(&self, it: LangItem) -> Result<DefId, LangItemError> {
-        self.get(it).ok_or_else(|| LangItemError(it))
-    }
-
     pub fn iter(&self) -> impl Iterator<Item = (LangItem, DefId)> + '_ {
         self.items
             .iter()

compiler/rustc_hir/src/lib.rs

@@ -30,7 +30,6 @@ pub mod def;
 pub mod def_path_hash_map;
 pub mod definitions;
 pub mod diagnostic_items;
-pub mod errors;
 pub use rustc_span::def_id;
 mod hir;
 pub mod hir_id;

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -298,9 +298,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
 
     let coerce_unsized_trait = tcx.require_lang_item(LangItem::CoerceUnsized, Some(span));
 
-    let unsize_trait = tcx.lang_items().require(LangItem::Unsize).unwrap_or_else(|err| {
+    let unsize_trait = tcx.require_lang_item(LangItem::Unsize, Some(span));
-        tcx.sess.fatal(format!("`CoerceUnsized` implementation {}", err.to_string()));
-    });
 
     let source = tcx.type_of(impl_did).subst_identity();
     let trait_ref = tcx.impl_trait_ref(impl_did).unwrap().subst_identity();

compiler/rustc_metadata/src/locator.rs

@@ -220,7 +220,6 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::owned_slice::slice_owned;
 use rustc_data_structures::svh::Svh;
-use rustc_data_structures::sync::MetadataRef;
 use rustc_errors::{DiagnosticArgValue, FatalError, IntoDiagnosticArg};
 use rustc_fs_util::try_canonicalize;
 use rustc_session::config::{self, CrateType};
@@ -782,7 +781,7 @@ fn get_metadata_section<'p>(
     if !filename.exists() {
         return Err(MetadataError::NotPresent(filename));
     }
-    let raw_bytes: MetadataRef = match flavor {
+    let raw_bytes = match flavor {
         CrateFlavor::Rlib => {
             loader.get_rlib_metadata(target, filename).map_err(MetadataError::LoadFailure)?
         }
@@ -843,7 +842,7 @@ fn get_metadata_section<'p>(
             slice_owned(mmap, Deref::deref)
         }
     };
-    let blob = MetadataBlob::new(raw_bytes);
+    let blob = MetadataBlob(raw_bytes);
     if blob.is_compatible() {
         Ok(blob)
     } else {

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -7,6 +7,7 @@ use crate::rmeta::*;
 use rustc_ast as ast;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::owned_slice::OwnedSlice;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{AppendOnlyVec, Lock, Lrc, OnceCell};
 use rustc_data_structures::unhash::UnhashMap;
@@ -50,7 +51,7 @@ mod cstore_impl;
 /// A `MetadataBlob` internally is just a reference counted pointer to
 /// the actual data, so cloning it is cheap.
 #[derive(Clone)]
-pub(crate) struct MetadataBlob(Lrc<MetadataRef>);
+pub(crate) struct MetadataBlob(pub(crate) OwnedSlice);
 
 impl std::ops::Deref for MetadataBlob {
     type Target = [u8];
@@ -660,10 +661,6 @@ impl<'a, 'tcx, I: Idx, T> Decodable<DecodeContext<'a, 'tcx>> for LazyTable<I, T>
 implement_ty_decoder!(DecodeContext<'a, 'tcx>);
 
 impl MetadataBlob {
-    pub(crate) fn new(metadata_ref: MetadataRef) -> MetadataBlob {
-        MetadataBlob(Lrc::new(metadata_ref))
-    }
-
     pub(crate) fn is_compatible(&self) -> bool {
         self.blob().starts_with(METADATA_HEADER)
     }

compiler/rustc_metadata/src/rmeta/def_path_hash_map.rs

@@ -1,6 +1,5 @@
 use crate::rmeta::DecodeContext;
 use crate::rmeta::EncodeContext;
-use rustc_data_structures::owned_slice::slice_owned;
 use rustc_data_structures::owned_slice::OwnedSlice;
 use rustc_hir::def_path_hash_map::{Config as HashMapConfig, DefPathHashMap};
 use rustc_middle::parameterized_over_tcx;
@@ -47,7 +46,7 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for DefPathHashMapRef<'static>
     fn decode(d: &mut DecodeContext<'a, 'tcx>) -> DefPathHashMapRef<'static> {
         let len = d.read_usize();
         let pos = d.position();
-        let o = slice_owned(d.blob().clone(), |blob| &blob[pos..pos + len]);
+        let o = d.blob().clone().0.slice(|blob| &blob[pos..pos + len]);
 
         // Although we already have the data we need via the `OwnedSlice`, we still need
         // to advance the `DecodeContext`'s position so it's in a valid state after

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -7,7 +7,6 @@ use table::TableBuilder;
 use rustc_ast as ast;
 use rustc_attr as attr;
 use rustc_data_structures::svh::Svh;
-use rustc_data_structures::sync::MetadataRef;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap};
 use rustc_hir::def_id::{CrateNum, DefId, DefIndex, DefPathHash, StableCrateId};

compiler/rustc_middle/messages.ftl

@@ -39,5 +39,7 @@ middle_strict_coherence_needs_negative_coherence =
     to use `strict_coherence` on this trait, the `with_negative_coherence` feature must be enabled
     .label = due to this attribute
 
+middle_requires_lang_item = requires `{$name}` lang_item
+
 middle_const_not_used_in_type_alias =
     const parameter `{$ct}` is part of concrete type but not used in parameter list for the `impl Trait` type alias

compiler/rustc_middle/src/error.rs

@@ -1,5 +1,5 @@
 use rustc_macros::Diagnostic;
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 
 use crate::ty::Ty;
 
@@ -73,6 +73,14 @@ pub(crate) struct StrictCoherenceNeedsNegativeCoherence {
     pub attr_span: Option<Span>,
 }
 
+#[derive(Diagnostic)]
+#[diag(middle_requires_lang_item)]
+pub(crate) struct RequiresLangItem {
+    #[primary_span]
+    pub span: Option<Span>,
+    pub name: Symbol,
+}
+
 #[derive(Diagnostic)]
 #[diag(middle_const_not_used_in_type_alias)]
 pub(super) struct ConstNotUsedTraitAlias {

compiler/rustc_middle/src/middle/lang_items.rs

@@ -18,12 +18,8 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Returns the `DefId` for a given `LangItem`.
     /// If not found, fatally aborts compilation.
     pub fn require_lang_item(self, lang_item: LangItem, span: Option<Span>) -> DefId {
-        self.lang_items().require(lang_item).unwrap_or_else(|err| {
+        self.lang_items().get(lang_item).unwrap_or_else(|| {
-            if let Some(span) = span {
+            self.sess.emit_fatal(crate::error::RequiresLangItem { span, name: lang_item.name() });
-                self.sess.span_fatal(span, err.to_string())
-            } else {
-                self.sess.fatal(err.to_string())
-            }
         })
     }
 

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -481,9 +481,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 }))))
             }
 
-            ExprKind::OffsetOf { container, fields } => {
+            ExprKind::OffsetOf { container, fields } => block.and(Rvalue::NullaryOp(
-                block.and(Rvalue::NullaryOp(NullOp::OffsetOf(fields), container))
+                NullOp::OffsetOf(fields),
-            }
+                this.tcx.erase_regions(container),
+            )),
 
             ExprKind::Literal { .. }
             | ExprKind::NamedConst { .. }

compiler/rustc_session/src/cstore.rs

@@ -6,7 +6,8 @@ use crate::search_paths::PathKind;
 use crate::utils::NativeLibKind;
 use crate::Session;
 use rustc_ast as ast;
-use rustc_data_structures::sync::{self, AppendOnlyIndexVec, MetadataRef, RwLock};
+use rustc_data_structures::owned_slice::OwnedSlice;
+use rustc_data_structures::sync::{self, AppendOnlyIndexVec, RwLock};
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, StableCrateId, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash, Definitions};
 use rustc_span::hygiene::{ExpnHash, ExpnId};
@@ -203,8 +204,8 @@ pub enum ExternCrateSource {
 /// metadata in library -- this trait just serves to decouple rustc_metadata from
 /// the archive reader, which depends on LLVM.
 pub trait MetadataLoader: std::fmt::Debug {
-    fn get_rlib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String>;
+    fn get_rlib_metadata(&self, target: &Target, filename: &Path) -> Result<OwnedSlice, String>;
-    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String>;
+    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<OwnedSlice, String>;
 }
 
 pub type MetadataLoaderDyn = dyn MetadataLoader + Send + Sync + sync::DynSend + sync::DynSync;

compiler/rustc_span/src/symbol.rs

@@ -164,6 +164,7 @@ symbols! {
         Capture,
         Center,
         Clone,
+        ConstParamTy,
         Context,
         Continue,
         Copy,
@@ -1583,6 +1584,7 @@ symbols! {
         unrestricted_attribute_tokens,
         unsafe_block_in_unsafe_fn,
         unsafe_cell,
+        unsafe_cell_from_mut,
         unsafe_no_drop_flag,
         unsafe_pin_internals,
         unsize,

library/core/src/cell.rs

@@ -2030,6 +2030,27 @@ impl<T> UnsafeCell<T> {
 }
 
 impl<T: ?Sized> UnsafeCell<T> {
+    /// Converts from `&mut T` to `&mut UnsafeCell<T>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![feature(unsafe_cell_from_mut)]
+    /// use std::cell::UnsafeCell;
+    ///
+    /// let mut val = 42;
+    /// let uc = UnsafeCell::from_mut(&mut val);
+    ///
+    /// *uc.get_mut() -= 1;
+    /// assert_eq!(*uc.get_mut(), 41);
+    /// ```
+    #[inline(always)]
+    #[unstable(feature = "unsafe_cell_from_mut", issue = "111645")]
+    pub const fn from_mut(value: &mut T) -> &mut UnsafeCell<T> {
+        // SAFETY: `UnsafeCell<T>` has the same memory layout as `T` due to #[repr(transparent)].
+        unsafe { &mut *(value as *mut T as *mut UnsafeCell<T>) }
+    }
+
     /// Gets a mutable pointer to the wrapped value.
     ///
     /// This can be cast to a pointer of any kind.

library/core/src/ffi/c_str.rs

@@ -517,8 +517,6 @@ impl CStr {
     /// # Examples
     ///
     /// ```
-    /// #![feature(cstr_is_empty)]
-    ///
     /// use std::ffi::CStr;
     /// # use std::ffi::FromBytesWithNulError;
     ///
@@ -533,7 +531,8 @@ impl CStr {
     /// # }
     /// ```
     #[inline]
-    #[unstable(feature = "cstr_is_empty", issue = "102444")]
+    #[stable(feature = "cstr_is_empty", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "cstr_is_empty", since = "CURRENT_RUSTC_VERSION")]
     pub const fn is_empty(&self) -> bool {
         // SAFETY: We know there is at least one byte; for empty strings it
         // is the NUL terminator.

library/core/src/marker.rs

@@ -986,6 +986,14 @@ pub trait PointerLike {}
 #[rustc_on_unimplemented(message = "`{Self}` can't be used as a const parameter type")]
 pub trait ConstParamTy: StructuralEq {}
 
+/// Derive macro generating an impl of the trait `Copy`.
+#[rustc_builtin_macro]
+#[unstable(feature = "adt_const_params", issue = "95174")]
+#[cfg(not(bootstrap))]
+pub macro ConstParamTy($item:item) {
+    /* compiler built-in */
+}
+
 // FIXME(generic_const_parameter_types): handle `ty::FnDef`/`ty::Closure`
 // FIXME(generic_const_parameter_types): handle `ty::Tuple`
 marker_impls! {

src/tools/clippy/clippy_lints/src/matches/redundant_pattern_match.rs

@@ -289,10 +289,11 @@ fn is_pat_variant(cx: &LateContext<'_>, pat: &Pat<'_>, path: &QPath<'_>, expecte
     let Some(id) = cx.typeck_results().qpath_res(path, pat.hir_id).opt_def_id() else { return false };
 
     match expected_item {
-        Item::Lang(expected_lang_item) => {
+        Item::Lang(expected_lang_item) => cx
-            let expected_id = cx.tcx.lang_items().require(expected_lang_item).unwrap();
+            .tcx
-            cx.tcx.parent(id) == expected_id
+            .lang_items()
-        },
+            .get(expected_lang_item)
+            .map_or(false, |expected_id| cx.tcx.parent(id) == expected_id),
         Item::Diag(expected_ty, expected_variant) => {
             let ty = cx.typeck_results().pat_ty(pat);
 

tests/ui/const-generics/adt_const_params/const_param_ty_good.rs

@@ -11,6 +11,13 @@ struct S<T> {
 
 impl<T: ConstParamTy> ConstParamTy for S<T> {}
 
+#[derive(PartialEq, Eq, ConstParamTy)]
+struct D<T> {
+    field: u8,
+    gen: T,
+}
+
+
 fn check<T: ConstParamTy + ?Sized>() {}
 
 fn main() {
@@ -39,5 +46,8 @@ fn main() {
     check::<S<u8>>();
     check::<S<[&[bool]; 8]>>();
 
+    check::<D<u8>>();
+    check::<D<[&[bool]; 8]>>();
+
     // FIXME: test tuples
 }

tests/ui/const-generics/adt_const_params/const_param_ty_impl_bad_field.rs

@@ -10,4 +10,8 @@ struct CantParam(NotParam);
 impl std::marker::ConstParamTy for CantParam {}
 //~^ error: the trait `ConstParamTy` cannot be implemented for this type
 
+#[derive(std::marker::ConstParamTy, Eq, PartialEq)]
+//~^ error: the trait `ConstParamTy` cannot be implemented for this type
+struct CantParamDerive(NotParam);
+
 fn main() {}

tests/ui/const-generics/adt_const_params/const_param_ty_impl_bad_field.stderr

@@ -7,6 +7,17 @@ LL |
 LL | impl std::marker::ConstParamTy for CantParam {}
    |                                    ^^^^^^^^^
 
-error: aborting due to previous error
+error[E0204]: the trait `ConstParamTy` cannot be implemented for this type
+  --> $DIR/const_param_ty_impl_bad_field.rs:13:10
+   |
+LL | #[derive(std::marker::ConstParamTy, Eq, PartialEq)]
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | struct CantParamDerive(NotParam);
+   |                        -------- this field does not implement `ConstParamTy`
+   |
+   = note: this error originates in the derive macro `std::marker::ConstParamTy` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0204`.

tests/ui/const-generics/adt_const_params/const_param_ty_impl_no_structural_eq.rs

@@ -10,6 +10,10 @@ struct CantParam(ImplementsConstParamTy);
 impl std::marker::ConstParamTy for CantParam {}
 //~^ error: the type `CantParam` does not `#[derive(Eq)]`
 
+#[derive(std::marker::ConstParamTy)]
+//~^ error: the type `CantParamDerive` does not `#[derive(Eq)]`
+struct CantParamDerive(ImplementsConstParamTy);
+
 fn check<T: std::marker::ConstParamTy>() {}
 
 fn main() {

tests/ui/const-generics/adt_const_params/const_param_ty_impl_no_structural_eq.stderr

@@ -7,6 +7,16 @@ LL | impl std::marker::ConstParamTy for CantParam {}
 note: required by a bound in `ConstParamTy`
   --> $SRC_DIR/core/src/marker.rs:LL:COL
 
-error: aborting due to previous error
+error[E0277]: the type `CantParamDerive` does not `#[derive(Eq)]`
+  --> $DIR/const_param_ty_impl_no_structural_eq.rs:13:10
+   |
+LL | #[derive(std::marker::ConstParamTy)]
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `StructuralEq` is not implemented for `CantParamDerive`
+   |
+note: required by a bound in `ConstParamTy`
+  --> $SRC_DIR/core/src/marker.rs:LL:COL
+   = note: this error originates in the derive macro `std::marker::ConstParamTy` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/const-generics/adt_const_params/const_param_ty_impl_union.rs

@@ -0,0 +1,33 @@
+#![allow(incomplete_features)]
+#![feature(adt_const_params, structural_match)]
+
+union Union {
+    a: u8,
+}
+
+impl PartialEq for Union {
+    fn eq(&self, other: &Union) -> bool {
+        true
+    }
+}
+impl Eq for Union {}
+impl std::marker::StructuralEq for Union {}
+
+impl std::marker::ConstParamTy for Union {}
+
+#[derive(std::marker::ConstParamTy)]
+//~^ ERROR this trait cannot be derived for unions
+union UnionDerive {
+    a: u8,
+}
+
+impl PartialEq for UnionDerive {
+    fn eq(&self, other: &UnionDerive) -> bool {
+        true
+    }
+}
+impl Eq for UnionDerive {}
+impl std::marker::StructuralEq for UnionDerive {}
+
+
+fn main() {}

tests/ui/const-generics/adt_const_params/const_param_ty_impl_union.stderr

@@ -0,0 +1,8 @@
+error: this trait cannot be derived for unions
+  --> $DIR/const_param_ty_impl_union.rs:18:10
+   |
+LL | #[derive(std::marker::ConstParamTy)]
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

tests/ui/offset-of/offset-of-arg-count.rs

@@ -12,6 +12,11 @@ fn main() {
     offset_of!(S, f.,); //~ ERROR expected identifier
     offset_of!(S, f..); //~ ERROR no rules expected the token
     offset_of!(S, f..,); //~ ERROR no rules expected the token
+    offset_of!(Lt<'static>, bar); // issue #111657
+
 }
 
 struct S { f: u8, }
+struct Lt<'a> {
+    bar: &'a (),
+}