Rollup of 7 pull requests

library/core/src/mem/maybe_uninit.rs

@@ -405,9 +405,11 @@ impl<T> MaybeUninit<T> {
     /// (Notice that the rules around references to uninitialized data are not finalized yet, but
     /// until they are, it is advisable to avoid them.)
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
+    #[rustc_const_unstable(feature = "const_maybe_uninit_as_ptr", issue = "75251")]
     #[inline(always)]
-    pub fn as_ptr(&self) -> *const T {
-        unsafe { &*self.value as *const T }
+    pub const fn as_ptr(&self) -> *const T {
+        // `MaybeUninit` and `ManuallyDrop` are both `repr(transparent)` so we can cast the pointer.
+        self as *const _ as *const T
     }
 
     /// Gets a mutable pointer to the contained value. Reading from this pointer or turning it
@@ -442,9 +444,11 @@ impl<T> MaybeUninit<T> {
     /// (Notice that the rules around references to uninitialized data are not finalized yet, but
     /// until they are, it is advisable to avoid them.)
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
+    #[rustc_const_unstable(feature = "const_maybe_uninit_as_ptr", issue = "75251")]
     #[inline(always)]
-    pub fn as_mut_ptr(&mut self) -> *mut T {
-        unsafe { &mut *self.value as *mut T }
+    pub const fn as_mut_ptr(&mut self) -> *mut T {
+        // `MaybeUninit` and `ManuallyDrop` are both `repr(transparent)` so we can cast the pointer.
+        self as *mut _ as *mut T
     }
 
     /// Extracts the value from the `MaybeUninit<T>` container. This is a great way

library/core/src/num/mod.rs

@@ -2346,17 +2346,12 @@ assert_eq!(
             #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
             // SAFETY: const sound because integers are plain old datatypes so we can always
             // transmute them to arrays of bytes
-            #[allow_internal_unstable(const_fn_union)]
+            #[allow_internal_unstable(const_fn_transmute)]
             #[inline]
             pub const fn to_ne_bytes(self) -> [u8; mem::size_of::<Self>()] {
-                #[repr(C)]
-                union Bytes {
-                    val: $SelfT,
-                    bytes: [u8; mem::size_of::<$SelfT>()],
-                }
                 // SAFETY: integers are plain old datatypes so we can always transmute them to
                 // arrays of bytes
-                unsafe { Bytes { val: self }.bytes }
+                unsafe { mem::transmute(self) }
             }
         }
 
@@ -2464,16 +2459,11 @@ fn read_ne_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
             #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
             // SAFETY: const sound because integers are plain old datatypes so we can always
             // transmute to them
-            #[allow_internal_unstable(const_fn_union)]
+            #[allow_internal_unstable(const_fn_transmute)]
             #[inline]
             pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
-                #[repr(C)]
-                union Bytes {
-                    val: $SelfT,
-                    bytes: [u8; mem::size_of::<$SelfT>()],
-                }
                 // SAFETY: integers are plain old datatypes so we can always transmute to them
-                unsafe { Bytes { bytes }.val }
+                unsafe { mem::transmute(bytes) }
             }
         }
 
@@ -4368,17 +4358,12 @@ assert_eq!(
             #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
             // SAFETY: const sound because integers are plain old datatypes so we can always
             // transmute them to arrays of bytes
-            #[allow_internal_unstable(const_fn_union)]
+            #[allow_internal_unstable(const_fn_transmute)]
             #[inline]
             pub const fn to_ne_bytes(self) -> [u8; mem::size_of::<Self>()] {
-                #[repr(C)]
-                union Bytes {
-                    val: $SelfT,
-                    bytes: [u8; mem::size_of::<$SelfT>()],
-                }
                 // SAFETY: integers are plain old datatypes so we can always transmute them to
                 // arrays of bytes
-                unsafe { Bytes { val: self }.bytes }
+                unsafe { mem::transmute(self) }
             }
         }
 
@@ -4486,16 +4471,11 @@ fn read_ne_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
             #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
             // SAFETY: const sound because integers are plain old datatypes so we can always
             // transmute to them
-            #[allow_internal_unstable(const_fn_union)]
+            #[allow_internal_unstable(const_fn_transmute)]
             #[inline]
             pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
-                #[repr(C)]
-                union Bytes {
-                    val: $SelfT,
-                    bytes: [u8; mem::size_of::<$SelfT>()],
-                }
                 // SAFETY: integers are plain old datatypes so we can always transmute to them
-                unsafe { Bytes { bytes }.val }
+                unsafe { mem::transmute(bytes) }
             }
         }
 

library/test/src/helpers/concurrency.rs

@@ -4,7 +4,7 @@ use std::env;
 
 #[allow(deprecated)]
 pub fn get_concurrency() -> usize {
-    return match env::var("RUST_TEST_THREADS") {
+    match env::var("RUST_TEST_THREADS") {
         Ok(s) => {
             let opt_n: Option<usize> = s.parse().ok();
             match opt_n {
@@ -13,7 +13,7 @@ pub fn get_concurrency() -> usize {
             }
         }
         Err(..) => num_cpus(),
-    };
+    }
 }
 
 cfg_if::cfg_if! {

src/librustc_ast/ast.rs

@@ -378,7 +378,7 @@ impl Default for Generics {
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct WhereClause {
     /// `true` if we ate a `where` token: this can happen
-    /// if we parsed no predicates (e.g. `struct Foo where {}
+    /// if we parsed no predicates (e.g. `struct Foo where {}`).
     /// This allows us to accurately pretty-print
     /// in `nt_to_tokenstream`
     pub has_where_token: bool,

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -960,15 +960,15 @@ fn pointer_type_metadata(
 fn param_type_metadata(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll DIType {
     debug!("param_type_metadata: {:?}", t);
     let name = format!("{:?}", t);
-    return unsafe {
+    unsafe {
         llvm::LLVMRustDIBuilderCreateBasicType(
             DIB(cx),
             name.as_ptr().cast(),
             name.len(),
             Size::ZERO.bits(),
             DW_ATE_unsigned,
         )
-    };
+    }
 }
 
 pub fn compile_unit_metadata(

src/librustc_codegen_ssa/back/write.rs

@@ -490,7 +490,7 @@ fn copy_all_cgu_workproducts_to_incr_comp_cache_dir(
     let _timer = sess.timer("copy_all_cgu_workproducts_to_incr_comp_cache_dir");
 
     for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) {
-        let path = module.object.as_ref().map(|path| path.clone());
+        let path = module.object.as_ref().cloned();
 
         if let Some((id, product)) =
             copy_cgu_workproduct_to_incr_comp_cache_dir(sess, &module.name, &path)

src/librustc_infer/infer/error_reporting/nice_region_error/named_anon_conflict.rs

@@ -85,11 +85,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 
                 debug!("try_report_named_anon_conflict: ret ty {:?}", ty);
                 if sub == &ty::ReStatic
-                    && v.0
-                        .into_iter()
-                        .filter(|t| t.span.desugaring_kind().is_none())
-                        .next()
-                        .is_some()
+                    && v.0.into_iter().find(|t| t.span.desugaring_kind().is_none()).is_some()
                 {
                     // If the failure is due to a `'static` requirement coming from a `dyn` or
                     // `impl` Trait that *isn't* caused by `async fn` desugaring, handle this case

src/librustc_infer/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -257,7 +257,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                             param.param_ty.to_string(),
                             Applicability::MaybeIncorrect,
                         );
-                    } else if let Some(_) = opaque
+                    } else if opaque
                         .bounds
                         .iter()
                         .filter_map(|arg| match arg {
@@ -269,6 +269,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                             _ => None,
                         })
                         .next()
+                        .is_some()
                     {
                     } else {
                         err.span_suggestion_verbose(

src/librustc_infer/infer/glb.rs

@@ -50,7 +50,7 @@ impl TypeRelation<'tcx> for Glb<'combine, 'infcx, 'tcx> {
             ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
             ty::Covariant => self.relate(a, b),
             // FIXME(#41044) -- not correct, need test
-            ty::Bivariant => Ok(a.clone()),
+            ty::Bivariant => Ok(a),
             ty::Contravariant => self.fields.lub(self.a_is_expected).relate(a, b),
         }
     }
@@ -97,7 +97,7 @@ impl TypeRelation<'tcx> for Glb<'combine, 'infcx, 'tcx> {
         // very challenging, switch to invariance. This is obviously
         // overly conservative but works ok in practice.
         self.relate_with_variance(ty::Variance::Invariant, a, b)?;
-        Ok(a.clone())
+        Ok(a)
     }
 }
 

src/librustc_infer/infer/nll_relate/mod.rs

@@ -719,7 +719,7 @@ where
             self.a_scopes.pop().unwrap();
         }
 
-        Ok(a.clone())
+        Ok(a)
     }
 }
 

src/librustc_infer/infer/region_constraints/leak_check.rs

@@ -288,9 +288,9 @@ impl<'me, 'tcx> LeakCheck<'me, 'tcx> {
     ) -> TypeError<'tcx> {
         debug!("error: placeholder={:?}, other_region={:?}", placeholder, other_region);
         if self.overly_polymorphic {
-            return TypeError::RegionsOverlyPolymorphic(placeholder.name, other_region);
+            TypeError::RegionsOverlyPolymorphic(placeholder.name, other_region)
         } else {
-            return TypeError::RegionsInsufficientlyPolymorphic(placeholder.name, other_region);
+            TypeError::RegionsInsufficientlyPolymorphic(placeholder.name, other_region)
         }
     }
 }

src/librustc_infer/infer/sub.rs

@@ -68,7 +68,7 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
         match variance {
             ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
             ty::Covariant => self.relate(a, b),
-            ty::Bivariant => Ok(a.clone()),
+            ty::Bivariant => Ok(a),
             ty::Contravariant => self.with_expected_switched(|this| this.relate(b, a)),
         }
     }

src/librustc_lint/types.rs

@@ -1074,7 +1074,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
             }
             // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
             // argument, which after substitution, is `()`, then this branch can be hit.
-            FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => return,
+            FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
             FfiResult::FfiUnsafe { ty, reason, help } => {
                 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
             }

src/librustc_metadata/rmeta/encoder.rs

@@ -162,7 +162,7 @@ impl<'a, 'tcx> SpecializedEncoder<ExpnId> for EncodeContext<'a, 'tcx> {
     fn specialized_encode(&mut self, expn: &ExpnId) -> Result<(), Self::Error> {
         rustc_span::hygiene::raw_encode_expn_id(
             *expn,
-            &mut self.hygiene_ctxt,
+            &self.hygiene_ctxt,
             ExpnDataEncodeMode::Metadata,
             self,
         )

src/librustc_middle/traits/query.rs

@@ -128,7 +128,7 @@ pub struct DropckOutlivesResult<'tcx> {
 
 impl<'tcx> DropckOutlivesResult<'tcx> {
     pub fn report_overflows(&self, tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
-        if let Some(overflow_ty) = self.overflows.iter().next() {
+        if let Some(overflow_ty) = self.overflows.get(0) {
             let mut err = struct_span_err!(
                 tcx.sess,
                 span,

src/librustc_mir/borrow_check/diagnostics/mod.rs

@@ -868,7 +868,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
             }
         }
-        return normal_ret;
+        normal_ret
     }
 
     /// Finds the span of arguments of a closure (within `maybe_closure_span`)

src/librustc_mir/transform/simplify_try.rs

@@ -361,7 +361,7 @@ fn optimization_applies<'tcx>(
     }
 
     trace!("SUCCESS: optimization applies!");
-    return true;
+    true
 }
 
 impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {

src/librustc_mir/transform/validate.rs

@@ -115,7 +115,7 @@ pub fn equal_up_to_regions(
             T: Relate<'tcx>,
         {
             self.relate(a.skip_binder(), b.skip_binder())?;
-            Ok(a.clone())
+            Ok(a)
         }
     }
 

src/librustc_parse/parser/mod.rs

@@ -103,6 +103,8 @@ pub struct Parser<'a> {
     /// error.
     pub(super) unclosed_delims: Vec<UnmatchedBrace>,
     last_unexpected_token_span: Option<Span>,
+    /// Span pointing at the `:` for the last type ascription the parser has seen, and whether it
+    /// looked like it could have been a mistyped path or literal `Option:Some(42)`).
     pub last_type_ascription: Option<(Span, bool /* likely path typo */)>,
     /// If present, this `Parser` is not parsing Rust code but rather a macro call.
     subparser_name: Option<&'static str>,

src/librustc_parse_format/lib.rs

@@ -820,7 +820,7 @@ fn find_skips_from_snippet(
     }
 
     let r_start = str_style.map(|r| r + 1).unwrap_or(0);
-    let r_end = str_style.map(|r| r).unwrap_or(0);
+    let r_end = str_style.unwrap_or(0);
     let s = &snippet[r_start + 1..snippet.len() - r_end - 1];
     (find_skips(s, str_style.is_some()), true)
 }

src/librustc_resolve/late.rs

@@ -226,7 +226,7 @@ impl<'a> PathSource<'a> {
                 ValueNS => "method or associated constant",
                 MacroNS => bug!("associated macro"),
             },
-            PathSource::Expr(parent) => match &parent.as_ref().map(|p| &p.kind) {
+            PathSource::Expr(parent) => match parent.as_ref().map(|p| &p.kind) {
                 // "function" here means "anything callable" rather than `DefKind::Fn`,
                 // this is not precise but usually more helpful than just "value".
                 Some(ExprKind::Call(call_expr, _)) => match &call_expr.kind {

src/librustc_save_analysis/lib.rs

@@ -702,7 +702,7 @@ impl<'tcx> SaveContext<'tcx> {
             Res::Def(HirDefKind::ConstParam, def_id) => {
                 Some(Ref { kind: RefKind::Variable, span, ref_id: id_from_def_id(def_id) })
             }
-            Res::Def(HirDefKind::Ctor(_, ..), def_id) => {
+            Res::Def(HirDefKind::Ctor(..), def_id) => {
                 // This is a reference to a tuple struct or an enum variant where the def_id points
                 // to an invisible constructor function. That is not a very useful
                 // def, so adjust to point to the tuple struct or enum variant itself.

src/librustc_session/filesearch.rs

@@ -98,7 +98,7 @@ impl<'a> FileSearch<'a> {
         p.push(RUST_LIB_DIR);
         p.push(&self.triple);
         p.push("bin");
-        if self_contained { vec![p.clone(), p.join("self-contained")] } else { vec![p.clone()] }
+        if self_contained { vec![p.clone(), p.join("self-contained")] } else { vec![p] }
     }
 }
 

src/librustc_span/hygiene.rs

@@ -1030,7 +1030,7 @@ pub fn decode_expn_id<
         drop(expns);
         expn_id
     });
-    return Ok(expn_id);
+    Ok(expn_id)
 }
 
 // Decodes `SyntaxContext`, using the provided `HygieneDecodeContext`
@@ -1103,7 +1103,7 @@ pub fn decode_syntax_context<
         assert_eq!(dummy.dollar_crate_name, kw::Invalid);
     });
 
-    return Ok(new_ctxt);
+    Ok(new_ctxt)
 }
 
 pub fn num_syntax_ctxts() -> usize {

src/librustc_trait_selection/autoderef.rs

@@ -187,7 +187,7 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
     }
 
     pub fn span(&self) -> Span {
-        self.span.clone()
+        self.span
     }
 
     pub fn reached_recursion_limit(&self) -> bool {

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -495,7 +495,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(span) {
                         // Don't care about `&mut` because `DerefMut` is used less
                         // often and user will not expect autoderef happens.
-                        if src.starts_with("&") && !src.starts_with("&mut ") {
+                        if src.starts_with('&') && !src.starts_with("&mut ") {
                             let derefs = "*".repeat(steps);
                             err.span_suggestion(
                                 span,