Auto merge of #98910 - Dylan-DPC:rollup-9x82wdg, r=Dylan-DPC

Rollup of 6 pull requests

Successful merges:

 - #97300 (Implement `FusedIterator` for `std::net::[Into]Incoming`)
 - #98761 (more `need_type_info` improvements)
 - #98811 (Interpret: AllocRange Debug impl, and use it more consistently)
 - #98847 (fix interpreter validity check on Box)
 - #98854 (clean up the borrowing in rustc_hir_pretty)
 - #98873 (Suggest `#[derive(Default)]` to enums with `#[default]`)

Failed merges:

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

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -276,7 +276,7 @@ pub fn deallocate_ptr(
         kind: MemoryKind<M::MemoryKind>,
     ) -> InterpResult<'tcx> {
         let (alloc_id, offset, tag) = self.ptr_get_alloc_id(ptr)?;
-        trace!("deallocating: {}", alloc_id);
+        trace!("deallocating: {alloc_id:?}");
 
         if offset.bytes() != 0 {
             throw_ub_format!(
@@ -289,10 +289,10 @@ pub fn deallocate_ptr(
             // Deallocating global memory -- always an error
             return Err(match self.tcx.get_global_alloc(alloc_id) {
                 Some(GlobalAlloc::Function(..)) => {
-                    err_ub_format!("deallocating {}, which is a function", alloc_id)
+                    err_ub_format!("deallocating {alloc_id:?}, which is a function")
                 }
                 Some(GlobalAlloc::Static(..) | GlobalAlloc::Memory(..)) => {
-                    err_ub_format!("deallocating {}, which is static memory", alloc_id)
+                    err_ub_format!("deallocating {alloc_id:?}, which is static memory")
                 }
                 None => err_ub!(PointerUseAfterFree(alloc_id)),
             }
@@ -302,21 +302,17 @@ pub fn deallocate_ptr(
         debug!(?alloc);
 
         if alloc.mutability == Mutability::Not {
-            throw_ub_format!("deallocating immutable allocation {}", alloc_id);
+            throw_ub_format!("deallocating immutable allocation {alloc_id:?}");
         }
         if alloc_kind != kind {
             throw_ub_format!(
-                "deallocating {}, which is {} memory, using {} deallocation operation",
-                alloc_id,
-                alloc_kind,
-                kind
+                "deallocating {alloc_id:?}, which is {alloc_kind} memory, using {kind} deallocation operation"
             );
         }
         if let Some((size, align)) = old_size_and_align {
             if size != alloc.size() || align != alloc.align {
                 throw_ub_format!(
-                    "incorrect layout on deallocation: {} has size {} and alignment {}, but gave size {} and alignment {}",
-                    alloc_id,
+                    "incorrect layout on deallocation: {alloc_id:?} has size {} and alignment {}, but gave size {} and alignment {}",
                     alloc.size().bytes(),
                     alloc.align.bytes(),
                     size.bytes(),
@@ -815,7 +811,7 @@ fn write_allocation_track_relocs<'tcx, Tag: Provenance, Extra>(
                 continue;
             }
 
-            write!(fmt, "{}", id)?;
+            write!(fmt, "{id:?}")?;
             match self.ecx.memory.alloc_map.get(id) {
                 Some(&(kind, ref alloc)) => {
                     // normal alloc
@@ -859,25 +855,21 @@ fn write_allocation_track_relocs<'tcx, Tag: Provenance, Extra>(
 
 /// Reading and writing.
 impl<'tcx, 'a, Tag: Provenance, Extra> AllocRefMut<'a, 'tcx, Tag, Extra> {
+    /// `range` is relative to this allocation reference, not the base of the allocation.
     pub fn write_scalar(
         &mut self,
         range: AllocRange,
         val: ScalarMaybeUninit<Tag>,
     ) -> InterpResult<'tcx> {
         let range = self.range.subrange(range);
-        debug!(
-            "write_scalar in {} at {:#x}, size {}: {:?}",
-            self.alloc_id,
-            range.start.bytes(),
-            range.size.bytes(),
-            val
-        );
+        debug!("write_scalar at {:?}{range:?}: {val:?}", self.alloc_id);
         Ok(self
             .alloc
             .write_scalar(&self.tcx, range, val)
             .map_err(|e| e.to_interp_error(self.alloc_id))?)
     }
 
+    /// `offset` is relative to this allocation reference, not the base of the allocation.
     pub fn write_ptr_sized(
         &mut self,
         offset: Size,
@@ -896,6 +888,7 @@ pub fn write_uninit(&mut self) -> InterpResult<'tcx> {
 }
 
 impl<'tcx, 'a, Tag: Provenance, Extra> AllocRef<'a, 'tcx, Tag, Extra> {
+    /// `range` is relative to this allocation reference, not the base of the allocation.
     pub fn read_scalar(
         &self,
         range: AllocRange,
@@ -906,24 +899,16 @@ pub fn read_scalar(
             .alloc
             .read_scalar(&self.tcx, range, read_provenance)
             .map_err(|e| e.to_interp_error(self.alloc_id))?;
-        debug!(
-            "read_scalar in {} at {:#x}, size {}: {:?}",
-            self.alloc_id,
-            range.start.bytes(),
-            range.size.bytes(),
-            res
-        );
+        debug!("read_scalar at {:?}{range:?}: {res:?}", self.alloc_id);
         Ok(res)
     }
 
-    pub fn read_integer(
-        &self,
-        offset: Size,
-        size: Size,
-    ) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {
-        self.read_scalar(alloc_range(offset, size), /*read_provenance*/ false)
+    /// `range` is relative to this allocation reference, not the base of the allocation.
+    pub fn read_integer(&self, range: AllocRange) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {
+        self.read_scalar(range, /*read_provenance*/ false)
     }
 
+    /// `offset` is relative to this allocation reference, not the base of the allocation.
     pub fn read_pointer(&self, offset: Size) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {
         self.read_scalar(
             alloc_range(offset, self.tcx.data_layout().pointer_size),
@@ -931,6 +916,7 @@ pub fn read_pointer(&self, offset: Size) -> InterpResult<'tcx, ScalarMaybeUninit
         )
     }
 
+    /// `range` is relative to this allocation reference, not the base of the allocation.
     pub fn check_bytes(
         &self,
         range: AllocRange,

compiler/rustc_const_eval/src/interpret/traits.rs

@@ -1,6 +1,6 @@
 use std::convert::TryFrom;
 
-use rustc_middle::mir::interpret::{InterpResult, Pointer, PointerArithmetic};
+use rustc_middle::mir::interpret::{alloc_range, InterpResult, Pointer, PointerArithmetic};
 use rustc_middle::ty::{
     self, Ty, TyCtxt, COMMON_VTABLE_ENTRIES_ALIGN, COMMON_VTABLE_ENTRIES_DROPINPLACE,
     COMMON_VTABLE_ENTRIES_SIZE,
@@ -102,18 +102,18 @@ pub fn read_size_and_align_from_vtable(
             )?
             .expect("cannot be a ZST");
         let size = vtable
-            .read_integer(
+            .read_integer(alloc_range(
                 pointer_size * u64::try_from(COMMON_VTABLE_ENTRIES_SIZE).unwrap(),
                 pointer_size,
-            )?
+            ))?
             .check_init()?;
         let size = size.to_machine_usize(self)?;
         let size = Size::from_bytes(size);
         let align = vtable
-            .read_integer(
+            .read_integer(alloc_range(
                 pointer_size * u64::try_from(COMMON_VTABLE_ENTRIES_ALIGN).unwrap(),
                 pointer_size,
-            )?
+            ))?
             .check_init()?;
         let align = align.to_machine_usize(self)?;
         let align = Align::from_bytes(align).map_err(|e| err_ub!(InvalidVtableAlignment(e)))?;

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -593,16 +593,6 @@ fn try_visit_primitive(
                 self.check_safe_pointer(value, "reference")?;
                 Ok(true)
             }
-            ty::Adt(def, ..) if def.is_box() => {
-                let unique = self.ecx.operand_field(value, 0)?;
-                let nonnull = self.ecx.operand_field(&unique, 0)?;
-                let ptr = self.ecx.operand_field(&nonnull, 0)?;
-                self.check_safe_pointer(&ptr, "box")?;
-
-                // Check other fields of Box
-                self.walk_value(value)?;
-                Ok(true)
-            }
             ty::FnPtr(_sig) => {
                 let value = try_validation!(
                     self.ecx.read_scalar(value).and_then(|v| v.check_init()),
@@ -813,6 +803,12 @@ fn visit_union(
         Ok(())
     }
 
+    #[inline]
+    fn visit_box(&mut self, op: &OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx> {
+        self.check_safe_pointer(op, "box")?;
+        Ok(())
+    }
+
     #[inline]
     fn visit_value(&mut self, op: &OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx> {
         trace!("visit_value: {:?}, {:?}", *op, op.layout);
@@ -821,8 +817,6 @@ fn visit_value(&mut self, op: &OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx>
         if self.try_visit_primitive(op)? {
             return Ok(());
         }
-        // Sanity check: `builtin_deref` does not know any pointers that are not primitive.
-        assert!(op.layout.ty.builtin_deref(true).is_none());
 
         // Special check preventing `UnsafeCell` in the inner part of constants
         if let Some(def) = op.layout.ty.ty_adt_def() {

compiler/rustc_const_eval/src/interpret/visitor.rs

@@ -151,6 +151,14 @@ fn visit_union(&mut self, _v: &Self::V, _fields: NonZeroUsize) -> InterpResult<'
             {
                 Ok(())
             }
+            /// Visits the given value as the pointer of a `Box`. There is nothing to recurse into.
+            /// The type of `v` will be a raw pointer, but this is a field of `Box<T>` and the
+            /// pointee type is the actual `T`.
+            #[inline(always)]
+            fn visit_box(&mut self, _v: &Self::V) -> InterpResult<'tcx>
+            {
+                Ok(())
+            }
             /// Visits this value as an aggregate, you are getting an iterator yielding
             /// all the fields (still in an `InterpResult`, you have to do error handling yourself).
             /// Recurses into the fields.
@@ -221,6 +229,47 @@ fn walk_value(&mut self, v: &Self::V) -> InterpResult<'tcx>
                     // Slices do not need special handling here: they have `Array` field
                     // placement with length 0, so we enter the `Array` case below which
                     // indirectly uses the metadata to determine the actual length.
+
+                    // However, `Box`... let's talk about `Box`.
+                    ty::Adt(def, ..) if def.is_box() => {
+                        // `Box` is a hybrid primitive-library-defined type that one the one hand is
+                        // a dereferenceable pointer, on the other hand has *basically arbitrary
+                        // user-defined layout* since the user controls the 'allocator' field. So it
+                        // cannot be treated like a normal pointer, since it does not fit into an
+                        // `Immediate`. Yeah, it is quite terrible. But many visitors want to do
+                        // something with "all boxed pointers", so we handle this mess for them.
+                        //
+                        // When we hit a `Box`, we do not do the usual `visit_aggregate`; instead,
+                        // we (a) call `visit_box` on the pointer value, and (b) recurse on the
+                        // allocator field. We also assert tons of things to ensure we do not miss
+                        // any other fields.
+
+                        // `Box` has two fields: the pointer we care about, and the allocator.
+                        assert_eq!(v.layout().fields.count(), 2, "`Box` must have exactly 2 fields");
+                        let (unique_ptr, alloc) =
+                            (v.project_field(self.ecx(), 0)?, v.project_field(self.ecx(), 1)?);
+                        // Unfortunately there is some type junk in the way here: `unique_ptr` is a `Unique`...
+                        // (which means another 2 fields, the second of which is a `PhantomData`)
+                        assert_eq!(unique_ptr.layout().fields.count(), 2);
+                        let (nonnull_ptr, phantom) = (
+                            unique_ptr.project_field(self.ecx(), 0)?,
+                            unique_ptr.project_field(self.ecx(), 1)?,
+                        );
+                        assert!(
+                            phantom.layout().ty.ty_adt_def().is_some_and(|adt| adt.is_phantom_data()),
+                            "2nd field of `Unique` should be PhantomData but is {:?}",
+                            phantom.layout().ty,
+                        );
+                        // ... that contains a `NonNull`... (gladly, only a single field here)
+                        assert_eq!(nonnull_ptr.layout().fields.count(), 1);
+                        let raw_ptr = nonnull_ptr.project_field(self.ecx(), 0)?; // the actual raw ptr
+                        // ... whose only field finally is a raw ptr we can dereference.
+                        self.visit_box(&raw_ptr)?;
+
+                        // The second `Box` field is the allocator, which we recursively check for validity
+                        // like in regular structs.
+                        self.visit_field(v, 1, &alloc)?;
+                    }
                     _ => {},
                 };
 

compiler/rustc_const_eval/src/lib.rs

@@ -21,6 +21,7 @@
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
+#![feature(is_some_with)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]
 

compiler/rustc_hir_pretty/src/lib.rs

@@ -59,7 +59,7 @@ fn nested(&self, state: &mut State<'_>, nested: Nested) {
             Nested::ImplItem(id) => state.print_impl_item(self.impl_item(id)),
             Nested::ForeignItem(id) => state.print_foreign_item(self.foreign_item(id)),
             Nested::Body(id) => state.print_expr(&self.body(id).value),
-            Nested::BodyParamPat(id, i) => state.print_pat(&self.body(id).params[i].pat),
+            Nested::BodyParamPat(id, i) => state.print_pat(self.body(id).params[i].pat),
         }
     }
 }
@@ -74,37 +74,37 @@ pub struct State<'a> {
 impl<'a> State<'a> {
     pub fn print_node(&mut self, node: Node<'_>) {
         match node {
-            Node::Param(a) => self.print_param(&a),
-            Node::Item(a) => self.print_item(&a),
-            Node::ForeignItem(a) => self.print_foreign_item(&a),
+            Node::Param(a) => self.print_param(a),
+            Node::Item(a) => self.print_item(a),
+            Node::ForeignItem(a) => self.print_foreign_item(a),
             Node::TraitItem(a) => self.print_trait_item(a),
             Node::ImplItem(a) => self.print_impl_item(a),
-            Node::Variant(a) => self.print_variant(&a),
-            Node::AnonConst(a) => self.print_anon_const(&a),
-            Node::Expr(a) => self.print_expr(&a),
-            Node::Stmt(a) => self.print_stmt(&a),
-            Node::PathSegment(a) => self.print_path_segment(&a),
-            Node::Ty(a) => self.print_type(&a),
-            Node::TypeBinding(a) => self.print_type_binding(&a),
-            Node::TraitRef(a) => self.print_trait_ref(&a),
-            Node::Pat(a) => self.print_pat(&a),
-            Node::Arm(a) => self.print_arm(&a),
+            Node::Variant(a) => self.print_variant(a),
+            Node::AnonConst(a) => self.print_anon_const(a),
+            Node::Expr(a) => self.print_expr(a),
+            Node::Stmt(a) => self.print_stmt(a),
+            Node::PathSegment(a) => self.print_path_segment(a),
+            Node::Ty(a) => self.print_type(a),
+            Node::TypeBinding(a) => self.print_type_binding(a),
+            Node::TraitRef(a) => self.print_trait_ref(a),
+            Node::Pat(a) => self.print_pat(a),
+            Node::Arm(a) => self.print_arm(a),
             Node::Infer(_) => self.word("_"),
             Node::Block(a) => {
                 // Containing cbox, will be closed by print-block at `}`.
                 self.cbox(INDENT_UNIT);
                 // Head-ibox, will be closed by print-block after `{`.
                 self.ibox(0);
-                self.print_block(&a)
+                self.print_block(a);
             }
-            Node::Lifetime(a) => self.print_lifetime(&a),
+            Node::Lifetime(a) => self.print_lifetime(a),
             Node::GenericParam(_) => panic!("cannot print Node::GenericParam"),
             Node::Field(_) => panic!("cannot print Node::Field"),
             // These cases do not carry enough information in the
             // `hir_map` to reconstruct their full structure for pretty
             // printing.
             Node::Ctor(..) => panic!("cannot print isolated Ctor"),
-            Node::Local(a) => self.print_local_decl(&a),
+            Node::Local(a) => self.print_local_decl(a),
             Node::Crate(..) => panic!("cannot print Crate"),
         }
     }
@@ -266,7 +266,7 @@ pub fn commasep_cmnt<T, F, G>(&mut self, b: Breaks, elts: &[T], mut op: F, mut g
     }
 
     pub fn commasep_exprs(&mut self, b: Breaks, exprs: &[hir::Expr<'_>]) {
-        self.commasep_cmnt(b, exprs, |s, e| s.print_expr(&e), |e| e.span)
+        self.commasep_cmnt(b, exprs, |s, e| s.print_expr(e), |e| e.span);
     }
 
     pub fn print_mod(&mut self, _mod: &hir::Mod<'_>, attrs: &[ast::Attribute]) {
@@ -287,9 +287,9 @@ pub fn print_type(&mut self, ty: &hir::Ty<'_>) {
         self.maybe_print_comment(ty.span.lo());
         self.ibox(0);
         match ty.kind {
-            hir::TyKind::Slice(ref ty) => {
+            hir::TyKind::Slice(ty) => {
                 self.word("[");
-                self.print_type(&ty);
+                self.print_type(ty);
                 self.word("]");
             }
             hir::TyKind::Ptr(ref mt) => {
@@ -304,23 +304,16 @@ pub fn print_type(&mut self, ty: &hir::Ty<'_>) {
             hir::TyKind::Never => {
                 self.word("!");
             }
-            hir::TyKind::Tup(ref elts) => {
+            hir::TyKind::Tup(elts) => {
                 self.popen();
-                self.commasep(Inconsistent, &elts, |s, ty| s.print_type(&ty));
+                self.commasep(Inconsistent, elts, |s, ty| s.print_type(ty));
                 if elts.len() == 1 {
                     self.word(",");
                 }
                 self.pclose();
             }
-            hir::TyKind::BareFn(ref f) => {
-                self.print_ty_fn(
-                    f.abi,
-                    f.unsafety,
-                    &f.decl,
-                    None,
-                    &f.generic_params,
-                    f.param_names,
-                );
+            hir::TyKind::BareFn(f) => {
+                self.print_ty_fn(f.abi, f.unsafety, f.decl, None, f.generic_params, f.param_names);
             }
             hir::TyKind::OpaqueDef(..) => self.word("/*impl Trait*/"),
             hir::TyKind::Path(ref qpath) => self.print_qpath(qpath, false),
@@ -344,9 +337,9 @@ pub fn print_type(&mut self, ty: &hir::Ty<'_>) {
                     self.print_lifetime(lifetime);
                 }
             }
-            hir::TyKind::Array(ref ty, ref length) => {
+            hir::TyKind::Array(ty, ref length) => {
                 self.word("[");
-                self.print_type(&ty);
+                self.print_type(ty);
                 self.word("; ");
                 self.print_array_length(length);
                 self.word("]");
@@ -373,7 +366,7 @@ pub fn print_foreign_item(&mut self, item: &hir::ForeignItem<'_>) {
         self.maybe_print_comment(item.span.lo());
         self.print_outer_attributes(self.attrs(item.hir_id()));
         match item.kind {
-            hir::ForeignItemKind::Fn(ref decl, ref arg_names, ref generics) => {
+            hir::ForeignItemKind::Fn(decl, arg_names, generics) => {
                 self.head("");
                 self.print_fn(
                     decl,
@@ -392,14 +385,14 @@ pub fn print_foreign_item(&mut self, item: &hir::ForeignItem<'_>) {
                 self.word(";");
                 self.end() // end the outer fn box
             }
-            hir::ForeignItemKind::Static(ref t, m) => {
+            hir::ForeignItemKind::Static(t, m) => {
                 self.head("static");
                 if m == hir::Mutability::Mut {
                     self.word_space("mut");
                 }
                 self.print_ident(item.ident);
                 self.word_space(":");
-                self.print_type(&t);
+                self.print_type(t);
                 self.word(";");
                 self.end(); // end the head-ibox
                 self.end() // end the outer cbox
@@ -442,7 +435,7 @@ fn print_associated_type(
     ) {
         self.word_space("type");
         self.print_ident(ident);
-        self.print_generic_params(&generics.params);
+        self.print_generic_params(generics.params);
         if let Some(bounds) = bounds {
             self.print_bounds(":", bounds);
         }
@@ -463,7 +456,7 @@ fn print_item_type(
     ) {
         self.head("type");
         self.print_ident(item.ident);
-        self.print_generic_params(&generics.params);
+        self.print_generic_params(generics.params);
         self.end(); // end the inner ibox
 
         self.print_where_clause(generics);
@@ -494,7 +487,7 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                 self.end(); // end inner head-block
                 self.end(); // end outer head-block
             }
-            hir::ItemKind::Use(ref path, kind) => {
+            hir::ItemKind::Use(path, kind) => {
                 self.head("use");
                 self.print_path(path, false);
 
@@ -513,14 +506,14 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                 self.end(); // end inner head-block
                 self.end(); // end outer head-block
             }
-            hir::ItemKind::Static(ref ty, m, expr) => {
+            hir::ItemKind::Static(ty, m, expr) => {
                 self.head("static");
                 if m == hir::Mutability::Mut {
                     self.word_space("mut");
                 }
                 self.print_ident(item.ident);
                 self.word_space(":");
-                self.print_type(&ty);
+                self.print_type(ty);
                 self.space();
                 self.end(); // end the head-ibox
 
@@ -529,11 +522,11 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                 self.word(";");
                 self.end(); // end the outer cbox
             }
-            hir::ItemKind::Const(ref ty, expr) => {
+            hir::ItemKind::Const(ty, expr) => {
                 self.head("const");
                 self.print_ident(item.ident);
                 self.word_space(":");
-                self.print_type(&ty);
+                self.print_type(ty);
                 self.space();
                 self.end(); // end the head-ibox
 
@@ -542,10 +535,10 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                 self.word(";");
                 self.end(); // end the outer cbox
             }
-            hir::ItemKind::Fn(ref sig, ref param_names, body) => {
+            hir::ItemKind::Fn(ref sig, param_names, body) => {
                 self.head("");
                 self.print_fn(
-                    &sig.decl,
+                    sig.decl,
                     sig.header,
                     Some(item.ident.name),
                     param_names,
@@ -578,22 +571,22 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                 }
                 self.bclose(item.span);
             }
-            hir::ItemKind::GlobalAsm(ref asm) => {
+            hir::ItemKind::GlobalAsm(asm) => {
                 self.head("global_asm!");
                 self.print_inline_asm(asm);
                 self.end()
             }
-            hir::ItemKind::TyAlias(ref ty, ref generics) => {
-                self.print_item_type(item, &generics, |state| {
+            hir::ItemKind::TyAlias(ty, generics) => {
+                self.print_item_type(item, generics, |state| {
                     state.word_space("=");
-                    state.print_type(&ty);
+                    state.print_type(ty);
                 });
             }
             hir::ItemKind::OpaqueTy(ref opaque_ty) => {
-                self.print_item_type(item, &opaque_ty.generics, |state| {
+                self.print_item_type(item, opaque_ty.generics, |state| {
                     let mut real_bounds = Vec::with_capacity(opaque_ty.bounds.len());
-                    for b in opaque_ty.bounds.iter() {
-                        if let GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = *b {
+                    for b in opaque_ty.bounds {
+                        if let GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = b {
                             state.space();
                             state.word_space("for ?");
                             state.print_trait_ref(&ptr.trait_ref);
@@ -604,39 +597,39 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                     state.print_bounds("= impl", real_bounds);
                 });
             }
-            hir::ItemKind::Enum(ref enum_definition, ref params) => {
+            hir::ItemKind::Enum(ref enum_definition, params) => {
                 self.print_enum_def(enum_definition, params, item.ident.name, item.span);
             }
-            hir::ItemKind::Struct(ref struct_def, ref generics) => {
+            hir::ItemKind::Struct(ref struct_def, generics) => {
                 self.head("struct");
                 self.print_struct(struct_def, generics, item.ident.name, item.span, true);
             }
-            hir::ItemKind::Union(ref struct_def, ref generics) => {
+            hir::ItemKind::Union(ref struct_def, generics) => {
                 self.head("union");
                 self.print_struct(struct_def, generics, item.ident.name, item.span, true);
             }
-            hir::ItemKind::Impl(hir::Impl {
+            hir::ItemKind::Impl(&hir::Impl {
                 unsafety,
                 polarity,
                 defaultness,
                 constness,
                 defaultness_span: _,
-                ref generics,
+                generics,
                 ref of_trait,
-                ref self_ty,
+                self_ty,
                 items,
             }) => {
                 self.head("");
-                self.print_defaultness(*defaultness);
-                self.print_unsafety(*unsafety);
+                self.print_defaultness(defaultness);
+                self.print_unsafety(unsafety);
                 self.word_nbsp("impl");
 
                 if !generics.params.is_empty() {
-                    self.print_generic_params(&generics.params);
+                    self.print_generic_params(generics.params);
                     self.space();
                 }
 
-                if *constness == hir::Constness::Const {
+                if constness == hir::Constness::Const {
                     self.word_nbsp("const");
                 }
 
@@ -644,33 +637,33 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                     self.word("!");
                 }
 
-                if let Some(ref t) = of_trait {
+                if let Some(t) = of_trait {
                     self.print_trait_ref(t);
                     self.space();
                     self.word_space("for");
                 }
 
-                self.print_type(&self_ty);
+                self.print_type(self_ty);
                 self.print_where_clause(generics);
 
                 self.space();
                 self.bopen();
                 self.print_inner_attributes(attrs);
-                for impl_item in *items {
+                for impl_item in items {
                     self.ann.nested(self, Nested::ImplItem(impl_item.id));
                 }
                 self.bclose(item.span);
             }
-            hir::ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, trait_items) => {
+            hir::ItemKind::Trait(is_auto, unsafety, generics, bounds, trait_items) => {
                 self.head("");
                 self.print_is_auto(is_auto);
                 self.print_unsafety(unsafety);
                 self.word_nbsp("trait");
                 self.print_ident(item.ident);
-                self.print_generic_params(&generics.params);
+                self.print_generic_params(generics.params);
                 let mut real_bounds = Vec::with_capacity(bounds.len());
-                for b in bounds.iter() {
-                    if let GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = *b {
+                for b in bounds {
+                    if let GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = b {
                         self.space();
                         self.word_space("for ?");
                         self.print_trait_ref(&ptr.trait_ref);
@@ -687,14 +680,14 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
                 }
                 self.bclose(item.span);
             }
-            hir::ItemKind::TraitAlias(ref generics, ref bounds) => {
+            hir::ItemKind::TraitAlias(generics, bounds) => {
                 self.head("trait");
                 self.print_ident(item.ident);
-                self.print_generic_params(&generics.params);
+                self.print_generic_params(generics.params);
                 let mut real_bounds = Vec::with_capacity(bounds.len());
                 // FIXME(durka) this seems to be some quite outdated syntax
-                for b in bounds.iter() {
-                    if let GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = *b {
+                for b in bounds {
+                    if let GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = b {
                         self.space();
                         self.word_space("for ?");
                         self.print_trait_ref(&ptr.trait_ref);
@@ -714,7 +707,7 @@ pub fn print_item(&mut self, item: &hir::Item<'_>) {
     }
 
     pub fn print_trait_ref(&mut self, t: &hir::TraitRef<'_>) {
-        self.print_path(&t.path, false)
+        self.print_path(t.path, false);
     }
 
     fn print_formal_generic_params(&mut self, generic_params: &[hir::GenericParam<'_>]) {
@@ -726,8 +719,8 @@ fn print_formal_generic_params(&mut self, generic_params: &[hir::GenericParam<'_
     }
 
     fn print_poly_trait_ref(&mut self, t: &hir::PolyTraitRef<'_>) {
-        self.print_formal_generic_params(&t.bound_generic_params);
-        self.print_trait_ref(&t.trait_ref)
+        self.print_formal_generic_params(t.bound_generic_params);
+        self.print_trait_ref(&t.trait_ref);
     }
 
     pub fn print_enum_def(
@@ -739,10 +732,10 @@ pub fn print_enum_def(
     ) {
         self.head("enum");
         self.print_name(name);
-        self.print_generic_params(&generics.params);
+        self.print_generic_params(generics.params);
         self.print_where_clause(generics);
         self.space();
-        self.print_variants(&enum_definition.variants, span)
+        self.print_variants(enum_definition.variants, span);
     }
 
     pub fn print_variants(&mut self, variants: &[hir::Variant<'_>], span: rustc_span::Span) {
@@ -776,7 +769,7 @@ pub fn print_struct(
         print_finalizer: bool,
     ) {
         self.print_name(name);
-        self.print_generic_params(&generics.params);
+        self.print_generic_params(generics.params);
         match struct_def {
             hir::VariantData::Tuple(..) | hir::VariantData::Unit(..) => {
                 if let hir::VariantData::Tuple(..) = struct_def {
@@ -784,7 +777,7 @@ pub fn print_struct(
                     self.commasep(Inconsistent, struct_def.fields(), |s, field| {
                         s.maybe_print_comment(field.span.lo());
                         s.print_outer_attributes(s.attrs(field.hir_id));
-                        s.print_type(&field.ty)
+                        s.print_type(field.ty);
                     });
                     self.pclose();
                 }
@@ -807,7 +800,7 @@ pub fn print_struct(
                     self.print_outer_attributes(self.attrs(field.hir_id));
                     self.print_ident(field.ident);
                     self.word_nbsp(":");
-                    self.print_type(&field.ty);
+                    self.print_type(field.ty);
                     self.word(",");
                 }
 
@@ -819,7 +812,7 @@ pub fn print_struct(
     pub fn print_variant(&mut self, v: &hir::Variant<'_>) {
         self.head("");
         let generics = hir::Generics::empty();
-        self.print_struct(&v.data, &generics, v.ident.name, v.span, false);
+        self.print_struct(&v.data, generics, v.ident.name, v.span, false);
         if let Some(ref d) = v.disr_expr {
             self.space();
             self.word_space("=");
@@ -834,7 +827,7 @@ pub fn print_method_sig(
         arg_names: &[Ident],
         body_id: Option<hir::BodyId>,
     ) {
-        self.print_fn(&m.decl, m.header, Some(ident.name), generics, arg_names, body_id)
+        self.print_fn(m.decl, m.header, Some(ident.name), generics, arg_names, body_id);
     }
 
     pub fn print_trait_item(&mut self, ti: &hir::TraitItem<'_>) {
@@ -843,28 +836,23 @@ pub fn print_trait_item(&mut self, ti: &hir::TraitItem<'_>) {
         self.maybe_print_comment(ti.span.lo());
         self.print_outer_attributes(self.attrs(ti.hir_id()));
         match ti.kind {
-            hir::TraitItemKind::Const(ref ty, default) => {
-                self.print_associated_const(ti.ident, &ty, default);
+            hir::TraitItemKind::Const(ty, default) => {
+                self.print_associated_const(ti.ident, ty, default);
             }
-            hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(ref arg_names)) => {
-                self.print_method_sig(ti.ident, sig, &ti.generics, arg_names, None);
+            hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(arg_names)) => {
+                self.print_method_sig(ti.ident, sig, ti.generics, arg_names, None);
                 self.word(";");
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Provided(body)) => {
                 self.head("");
-                self.print_method_sig(ti.ident, sig, &ti.generics, &[], Some(body));
+                self.print_method_sig(ti.ident, sig, ti.generics, &[], Some(body));
                 self.nbsp();
                 self.end(); // need to close a box
                 self.end(); // need to close a box
                 self.ann.nested(self, Nested::Body(body));
             }
-            hir::TraitItemKind::Type(ref bounds, ref default) => {
-                self.print_associated_type(
-                    ti.ident,
-                    &ti.generics,
-                    Some(bounds),
-                    default.as_ref().map(|ty| &**ty),
-                );
+            hir::TraitItemKind::Type(bounds, default) => {
+                self.print_associated_type(ti.ident, ti.generics, Some(bounds), default);
             }
         }
         self.ann.post(self, AnnNode::SubItem(ti.hir_id()))
@@ -877,19 +865,19 @@ pub fn print_impl_item(&mut self, ii: &hir::ImplItem<'_>) {
         self.print_outer_attributes(self.attrs(ii.hir_id()));
 
         match ii.kind {
-            hir::ImplItemKind::Const(ref ty, expr) => {
-                self.print_associated_const(ii.ident, &ty, Some(expr));
+            hir::ImplItemKind::Const(ty, expr) => {
+                self.print_associated_const(ii.ident, ty, Some(expr));
             }
             hir::ImplItemKind::Fn(ref sig, body) => {
                 self.head("");
-                self.print_method_sig(ii.ident, sig, &ii.generics, &[], Some(body));
+                self.print_method_sig(ii.ident, sig, ii.generics, &[], Some(body));
                 self.nbsp();
                 self.end(); // need to close a box
                 self.end(); // need to close a box
                 self.ann.nested(self, Nested::Body(body));
             }
-            hir::ImplItemKind::TyAlias(ref ty) => {
-                self.print_associated_type(ii.ident, &ii.generics, None, Some(ty));
+            hir::ImplItemKind::TyAlias(ty) => {
+                self.print_associated_type(ii.ident, ii.generics, None, Some(ty));
             }
         }
         self.ann.post(self, AnnNode::SubItem(ii.hir_id()))
@@ -904,10 +892,10 @@ pub fn print_local(&mut self, init: Option<&hir::Expr<'_>>, decl: impl Fn(&mut S
         decl(self);
         self.end();
 
-        if let Some(ref init) = init {
+        if let Some(init) = init {
             self.nbsp();
             self.word_space("=");
-            self.print_expr(&init);
+            self.print_expr(init);
         }
         self.end()
     }
@@ -915,17 +903,17 @@ pub fn print_local(&mut self, init: Option<&hir::Expr<'_>>, decl: impl Fn(&mut S
     pub fn print_stmt(&mut self, st: &hir::Stmt<'_>) {
         self.maybe_print_comment(st.span.lo());
         match st.kind {
-            hir::StmtKind::Local(ref loc) => {
-                self.print_local(loc.init, |this| this.print_local_decl(&loc));
+            hir::StmtKind::Local(loc) => {
+                self.print_local(loc.init, |this| this.print_local_decl(loc));
             }
             hir::StmtKind::Item(item) => self.ann.nested(self, Nested::Item(item)),
-            hir::StmtKind::Expr(ref expr) => {
+            hir::StmtKind::Expr(expr) => {
                 self.space_if_not_bol();
-                self.print_expr(&expr);
+                self.print_expr(expr);
             }
-            hir::StmtKind::Semi(ref expr) => {
+            hir::StmtKind::Semi(expr) => {
                 self.space_if_not_bol();
-                self.print_expr(&expr);
+                self.print_expr(expr);
                 self.word(";");
             }
         }
@@ -966,9 +954,9 @@ pub fn print_block_maybe_unclosed(
         for st in blk.stmts {
             self.print_stmt(st);
         }
-        if let Some(ref expr) = blk.expr {
+        if let Some(expr) = blk.expr {
             self.space_if_not_bol();
-            self.print_expr(&expr);
+            self.print_expr(expr);
             self.maybe_print_trailing_comment(expr.span, Some(blk.span.hi()));
         }
         self.bclose_maybe_open(blk.span, close_box);
@@ -979,21 +967,21 @@ fn print_else(&mut self, els: Option<&hir::Expr<'_>>) {
         if let Some(els_inner) = els {
             match els_inner.kind {
                 // Another `else if` block.
-                hir::ExprKind::If(ref i, ref then, ref e) => {
+                hir::ExprKind::If(i, then, e) => {
                     self.cbox(INDENT_UNIT - 1);
                     self.ibox(0);
                     self.word(" else if ");
-                    self.print_expr_as_cond(&i);
+                    self.print_expr_as_cond(i);
                     self.space();
-                    self.print_expr(&then);
-                    self.print_else(e.as_ref().map(|e| &**e))
+                    self.print_expr(then);
+                    self.print_else(e);
                 }
                 // Final `else` block.
-                hir::ExprKind::Block(ref b, _) => {
+                hir::ExprKind::Block(b, _) => {
                     self.cbox(INDENT_UNIT - 1);
                     self.ibox(0);
                     self.word(" else ");
-                    self.print_block(&b)
+                    self.print_block(b);
                 }
                 // Constraints would be great here!
                 _ => {
@@ -1048,7 +1036,7 @@ fn print_expr_cond_paren(&mut self, expr: &hir::Expr<'_>, needs_par: bool) {
         if needs_par {
             self.popen();
         }
-        if let hir::ExprKind::DropTemps(ref actual_expr) = expr.kind {
+        if let hir::ExprKind::DropTemps(actual_expr) = expr.kind {
             self.print_expr(actual_expr);
         } else {
             self.print_expr(expr);
@@ -1114,7 +1102,7 @@ fn print_expr_struct(
         &mut self,
         qpath: &hir::QPath<'_>,
         fields: &[hir::ExprField<'_>],
-        wth: &Option<&hir::Expr<'_>>,
+        wth: Option<&hir::Expr<'_>>,
     ) {
         self.print_qpath(qpath, true);
         self.word("{");
@@ -1127,28 +1115,24 @@ fn print_expr_struct(
                     s.print_ident(field.ident);
                     s.word_space(":");
                 }
-                s.print_expr(&field.expr);
+                s.print_expr(field.expr);
                 s.end()
             },
             |f| f.span,
         );
-        match *wth {
-            Some(ref expr) => {
-                self.ibox(INDENT_UNIT);
-                if !fields.is_empty() {
-                    self.word(",");
-                    self.space();
-                }
-                self.word("..");
-                self.print_expr(&expr);
-                self.end();
-            }
-            _ => {
-                if !fields.is_empty() {
-                    self.word(",")
-                }
+        if let Some(expr) = wth {
+            self.ibox(INDENT_UNIT);
+            if !fields.is_empty() {
+                self.word(",");
+                self.space();
             }
+            self.word("..");
+            self.print_expr(expr);
+            self.end();
+        } else if !fields.is_empty() {
+            self.word(",");
         }
+
         self.word("}");
     }
 
@@ -1249,18 +1233,17 @@ enum AsmArg<'a> {
             Options(ast::InlineAsmOptions),
         }
 
-        let mut args =
-            vec![AsmArg::Template(ast::InlineAsmTemplatePiece::to_string(&asm.template))];
+        let mut args = vec![AsmArg::Template(ast::InlineAsmTemplatePiece::to_string(asm.template))];
         args.extend(asm.operands.iter().map(|(o, _)| AsmArg::Operand(o)));
         if !asm.options.is_empty() {
             args.push(AsmArg::Options(asm.options));
         }
 
         self.popen();
-        self.commasep(Consistent, &args, |s, arg| match arg {
-            AsmArg::Template(template) => s.print_string(&template, ast::StrStyle::Cooked),
-            AsmArg::Operand(op) => match op {
-                hir::InlineAsmOperand::In { reg, expr } => {
+        self.commasep(Consistent, &args, |s, arg| match *arg {
+            AsmArg::Template(ref template) => s.print_string(template, ast::StrStyle::Cooked),
+            AsmArg::Operand(op) => match *op {
+                hir::InlineAsmOperand::In { reg, ref expr } => {
                     s.word("in");
                     s.popen();
                     s.word(format!("{}", reg));
@@ -1268,8 +1251,8 @@ enum AsmArg<'a> {
                     s.space();
                     s.print_expr(expr);
                 }
-                hir::InlineAsmOperand::Out { reg, late, expr } => {
-                    s.word(if *late { "lateout" } else { "out" });
+                hir::InlineAsmOperand::Out { reg, late, ref expr } => {
+                    s.word(if late { "lateout" } else { "out" });
                     s.popen();
                     s.word(format!("{}", reg));
                     s.pclose();
@@ -1279,16 +1262,16 @@ enum AsmArg<'a> {
                         None => s.word("_"),
                     }
                 }
-                hir::InlineAsmOperand::InOut { reg, late, expr } => {
-                    s.word(if *late { "inlateout" } else { "inout" });
+                hir::InlineAsmOperand::InOut { reg, late, ref expr } => {
+                    s.word(if late { "inlateout" } else { "inout" });
                     s.popen();
                     s.word(format!("{}", reg));
                     s.pclose();
                     s.space();
                     s.print_expr(expr);
                 }
-                hir::InlineAsmOperand::SplitInOut { reg, late, in_expr, out_expr } => {
-                    s.word(if *late { "inlateout" } else { "inout" });
+                hir::InlineAsmOperand::SplitInOut { reg, late, ref in_expr, ref out_expr } => {
+                    s.word(if late { "inlateout" } else { "inout" });
                     s.popen();
                     s.word(format!("{}", reg));
                     s.pclose();
@@ -1301,17 +1284,17 @@ enum AsmArg<'a> {
                         None => s.word("_"),
                     }
                 }
-                hir::InlineAsmOperand::Const { anon_const } => {
+                hir::InlineAsmOperand::Const { ref anon_const } => {
                     s.word("const");
                     s.space();
                     s.print_anon_const(anon_const);
                 }
-                hir::InlineAsmOperand::SymFn { anon_const } => {
+                hir::InlineAsmOperand::SymFn { ref anon_const } => {
                     s.word("sym_fn");
                     s.space();
                     s.print_anon_const(anon_const);
                 }
-                hir::InlineAsmOperand::SymStatic { path, def_id: _ } => {
+                hir::InlineAsmOperand::SymStatic { ref path, def_id: _ } => {
                     s.word("sym_static");
                     s.space();
                     s.print_qpath(path, true);
@@ -1363,57 +1346,57 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
         self.ibox(INDENT_UNIT);
         self.ann.pre(self, AnnNode::Expr(expr));
         match expr.kind {
-            hir::ExprKind::Box(ref expr) => {
+            hir::ExprKind::Box(expr) => {
                 self.word_space("box");
                 self.print_expr_maybe_paren(expr, parser::PREC_PREFIX);
             }
-            hir::ExprKind::Array(ref exprs) => {
+            hir::ExprKind::Array(exprs) => {
                 self.print_expr_vec(exprs);
             }
             hir::ExprKind::ConstBlock(ref anon_const) => {
                 self.print_expr_anon_const(anon_const);
             }
-            hir::ExprKind::Repeat(ref element, ref count) => {
-                self.print_expr_repeat(&element, count);
+            hir::ExprKind::Repeat(element, ref count) => {
+                self.print_expr_repeat(element, count);
             }
-            hir::ExprKind::Struct(ref qpath, fields, ref wth) => {
+            hir::ExprKind::Struct(qpath, fields, wth) => {
                 self.print_expr_struct(qpath, fields, wth);
             }
-            hir::ExprKind::Tup(ref exprs) => {
+            hir::ExprKind::Tup(exprs) => {
                 self.print_expr_tup(exprs);
             }
-            hir::ExprKind::Call(ref func, ref args) => {
-                self.print_expr_call(&func, args);
+            hir::ExprKind::Call(func, args) => {
+                self.print_expr_call(func, args);
             }
-            hir::ExprKind::MethodCall(ref segment, ref args, _) => {
+            hir::ExprKind::MethodCall(segment, args, _) => {
                 self.print_expr_method_call(segment, args);
             }
-            hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
-                self.print_expr_binary(op, &lhs, &rhs);
+            hir::ExprKind::Binary(op, lhs, rhs) => {
+                self.print_expr_binary(op, lhs, rhs);
             }
-            hir::ExprKind::Unary(op, ref expr) => {
-                self.print_expr_unary(op, &expr);
+            hir::ExprKind::Unary(op, expr) => {
+                self.print_expr_unary(op, expr);
             }
-            hir::ExprKind::AddrOf(k, m, ref expr) => {
-                self.print_expr_addr_of(k, m, &expr);
+            hir::ExprKind::AddrOf(k, m, expr) => {
+                self.print_expr_addr_of(k, m, expr);
             }
             hir::ExprKind::Lit(ref lit) => {
-                self.print_literal(&lit);
+                self.print_literal(lit);
             }
-            hir::ExprKind::Cast(ref expr, ref ty) => {
+            hir::ExprKind::Cast(expr, ty) => {
                 let prec = AssocOp::As.precedence() as i8;
-                self.print_expr_maybe_paren(&expr, prec);
+                self.print_expr_maybe_paren(expr, prec);
                 self.space();
                 self.word_space("as");
-                self.print_type(&ty);
+                self.print_type(ty);
             }
-            hir::ExprKind::Type(ref expr, ref ty) => {
+            hir::ExprKind::Type(expr, ty) => {
                 let prec = AssocOp::Colon.precedence() as i8;
-                self.print_expr_maybe_paren(&expr, prec);
+                self.print_expr_maybe_paren(expr, prec);
                 self.word_space(":");
-                self.print_type(&ty);
+                self.print_type(ty);
             }
-            hir::ExprKind::DropTemps(ref init) => {
+            hir::ExprKind::DropTemps(init) => {
                 // Print `{`:
                 self.cbox(INDENT_UNIT);
                 self.ibox(0);
@@ -1431,25 +1414,25 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
                 // Print `}`:
                 self.bclose_maybe_open(expr.span, true);
             }
-            hir::ExprKind::Let(hir::Let { pat, ty, init, .. }) => {
-                self.print_let(pat, *ty, init);
+            hir::ExprKind::Let(&hir::Let { pat, ty, init, .. }) => {
+                self.print_let(pat, ty, init);
             }
-            hir::ExprKind::If(ref test, ref blk, ref elseopt) => {
-                self.print_if(&test, &blk, elseopt.as_ref().map(|e| &**e));
+            hir::ExprKind::If(test, blk, elseopt) => {
+                self.print_if(test, blk, elseopt);
             }
-            hir::ExprKind::Loop(ref blk, opt_label, _, _) => {
+            hir::ExprKind::Loop(blk, opt_label, _, _) => {
                 if let Some(label) = opt_label {
                     self.print_ident(label.ident);
                     self.word_space(":");
                 }
                 self.head("loop");
-                self.print_block(&blk);
+                self.print_block(blk);
             }
-            hir::ExprKind::Match(ref expr, arms, _) => {
+            hir::ExprKind::Match(expr, arms, _) => {
                 self.cbox(INDENT_UNIT);
                 self.ibox(INDENT_UNIT);
                 self.word_nbsp("match");
-                self.print_expr_as_cond(&expr);
+                self.print_expr_as_cond(expr);
                 self.space();
                 self.bopen();
                 for arm in arms {
@@ -1460,7 +1443,7 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
             hir::ExprKind::Closure {
                 capture_clause,
                 bound_generic_params,
-                ref fn_decl,
+                fn_decl,
                 body,
                 fn_decl_span: _,
                 movability: _,
@@ -1468,7 +1451,7 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
                 self.print_formal_generic_params(bound_generic_params);
                 self.print_capture_clause(capture_clause);
 
-                self.print_closure_params(&fn_decl, body);
+                self.print_closure_params(fn_decl, body);
                 self.space();
 
                 // This is a bare expression.
@@ -1480,7 +1463,7 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
                 // empty box to satisfy the close.
                 self.ibox(0);
             }
-            hir::ExprKind::Block(ref blk, opt_label) => {
+            hir::ExprKind::Block(blk, opt_label) => {
                 if let Some(label) = opt_label {
                     self.print_ident(label.ident);
                     self.word_space(":");
@@ -1489,42 +1472,42 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
                 self.cbox(INDENT_UNIT);
                 // head-box, will be closed by print-block after `{`
                 self.ibox(0);
-                self.print_block(&blk);
+                self.print_block(blk);
             }
-            hir::ExprKind::Assign(ref lhs, ref rhs, _) => {
+            hir::ExprKind::Assign(lhs, rhs, _) => {
                 let prec = AssocOp::Assign.precedence() as i8;
-                self.print_expr_maybe_paren(&lhs, prec + 1);
+                self.print_expr_maybe_paren(lhs, prec + 1);
                 self.space();
                 self.word_space("=");
-                self.print_expr_maybe_paren(&rhs, prec);
+                self.print_expr_maybe_paren(rhs, prec);
             }
-            hir::ExprKind::AssignOp(op, ref lhs, ref rhs) => {
+            hir::ExprKind::AssignOp(op, lhs, rhs) => {
                 let prec = AssocOp::Assign.precedence() as i8;
-                self.print_expr_maybe_paren(&lhs, prec + 1);
+                self.print_expr_maybe_paren(lhs, prec + 1);
                 self.space();
                 self.word(op.node.as_str());
                 self.word_space("=");
-                self.print_expr_maybe_paren(&rhs, prec);
+                self.print_expr_maybe_paren(rhs, prec);
             }
-            hir::ExprKind::Field(ref expr, ident) => {
+            hir::ExprKind::Field(expr, ident) => {
                 self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX);
                 self.word(".");
                 self.print_ident(ident);
             }
-            hir::ExprKind::Index(ref expr, ref index) => {
-                self.print_expr_maybe_paren(&expr, parser::PREC_POSTFIX);
+            hir::ExprKind::Index(expr, index) => {
+                self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX);
                 self.word("[");
-                self.print_expr(&index);
+                self.print_expr(index);
                 self.word("]");
             }
             hir::ExprKind::Path(ref qpath) => self.print_qpath(qpath, true),
-            hir::ExprKind::Break(destination, ref opt_expr) => {
+            hir::ExprKind::Break(destination, opt_expr) => {
                 self.word("break");
                 if let Some(label) = destination.label {
                     self.space();
                     self.print_ident(label.ident);
                 }
-                if let Some(ref expr) = *opt_expr {
+                if let Some(expr) = opt_expr {
                     self.space();
                     self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
                 }
@@ -1536,20 +1519,20 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
                     self.print_ident(label.ident);
                 }
             }
-            hir::ExprKind::Ret(ref result) => {
+            hir::ExprKind::Ret(result) => {
                 self.word("return");
-                if let Some(ref expr) = *result {
+                if let Some(expr) = result {
                     self.word(" ");
-                    self.print_expr_maybe_paren(&expr, parser::PREC_JUMP);
+                    self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
                 }
             }
-            hir::ExprKind::InlineAsm(ref asm) => {
+            hir::ExprKind::InlineAsm(asm) => {
                 self.word("asm!");
                 self.print_inline_asm(asm);
             }
-            hir::ExprKind::Yield(ref expr, _) => {
+            hir::ExprKind::Yield(expr, _) => {
                 self.word_space("yield");
-                self.print_expr_maybe_paren(&expr, parser::PREC_JUMP);
+                self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
             }
             hir::ExprKind::Err => {
                 self.popen();
@@ -1562,10 +1545,10 @@ pub fn print_expr(&mut self, expr: &hir::Expr<'_>) {
     }
 
     pub fn print_local_decl(&mut self, loc: &hir::Local<'_>) {
-        self.print_pat(&loc.pat);
-        if let Some(ref ty) = loc.ty {
+        self.print_pat(loc.pat);
+        if let Some(ty) = loc.ty {
             self.word_space(":");
-            self.print_type(&ty);
+            self.print_type(ty);
         }
     }
 
@@ -1596,8 +1579,8 @@ pub fn print_path_segment(&mut self, segment: &hir::PathSegment<'_>) {
 
     pub fn print_qpath(&mut self, qpath: &hir::QPath<'_>, colons_before_params: bool) {
         match *qpath {
-            hir::QPath::Resolved(None, ref path) => self.print_path(path, colons_before_params),
-            hir::QPath::Resolved(Some(ref qself), ref path) => {
+            hir::QPath::Resolved(None, path) => self.print_path(path, colons_before_params),
+            hir::QPath::Resolved(Some(qself), path) => {
                 self.word("<");
                 self.print_type(qself);
                 self.space();
@@ -1627,11 +1610,11 @@ pub fn print_qpath(&mut self, qpath: &hir::QPath<'_>, colons_before_params: bool
                     colons_before_params,
                 )
             }
-            hir::QPath::TypeRelative(ref qself, ref item_segment) => {
+            hir::QPath::TypeRelative(qself, item_segment) => {
                 // If we've got a compound-qualified-path, let's push an additional pair of angle
                 // brackets, so that we pretty-print `<<A::B>::C>` as `<A::B>::C`, instead of just
                 // `A::B::C` (since the latter could be ambiguous to the user)
-                if let hir::TyKind::Path(hir::QPath::Resolved(None, _)) = &qself.kind {
+                if let hir::TyKind::Path(hir::QPath::Resolved(None, _)) = qself.kind {
                     self.print_type(qself);
                 } else {
                     self.word("<");
@@ -1663,7 +1646,7 @@ fn print_generic_args(
     ) {
         if generic_args.parenthesized {
             self.word("(");
-            self.commasep(Inconsistent, generic_args.inputs(), |s, ty| s.print_type(&ty));
+            self.commasep(Inconsistent, generic_args.inputs(), |s, ty| s.print_type(ty));
             self.word(")");
 
             self.space_if_not_bol();
@@ -1694,7 +1677,7 @@ fn print_generic_args(
                 start_or_comma(self);
                 self.commasep(
                     Inconsistent,
-                    &generic_args.args,
+                    generic_args.args,
                     |s, generic_arg| match generic_arg {
                         GenericArg::Lifetime(lt) if !elide_lifetimes => s.print_lifetime(lt),
                         GenericArg::Lifetime(_) => {}
@@ -1712,7 +1695,7 @@ fn print_generic_args(
                 self.word("..");
             }
 
-            for binding in generic_args.bindings.iter() {
+            for binding in generic_args.bindings {
                 start_or_comma(self);
                 self.print_type_binding(binding);
             }
@@ -1731,7 +1714,7 @@ pub fn print_type_binding(&mut self, binding: &hir::TypeBinding<'_>) {
             hir::TypeBindingKind::Equality { ref term } => {
                 self.word_space("=");
                 match term {
-                    Term::Ty(ref ty) => self.print_type(ty),
+                    Term::Ty(ty) => self.print_type(ty),
                     Term::Const(ref c) => self.print_anon_const(c),
                 }
             }
@@ -1748,7 +1731,7 @@ pub fn print_pat(&mut self, pat: &hir::Pat<'_>) {
         // is that it doesn't matter
         match pat.kind {
             PatKind::Wild => self.word("_"),
-            PatKind::Binding(binding_mode, _, ident, ref sub) => {
+            PatKind::Binding(binding_mode, _, ident, sub) => {
                 match binding_mode {
                     hir::BindingAnnotation::Ref => {
                         self.word_nbsp("ref");
@@ -1764,33 +1747,33 @@ pub fn print_pat(&mut self, pat: &hir::Pat<'_>) {
                     }
                 }
                 self.print_ident(ident);
-                if let Some(ref p) = *sub {
+                if let Some(p) = sub {
                     self.word("@");
-                    self.print_pat(&p);
+                    self.print_pat(p);
                 }
             }
-            PatKind::TupleStruct(ref qpath, ref elts, ddpos) => {
+            PatKind::TupleStruct(ref qpath, elts, ddpos) => {
                 self.print_qpath(qpath, true);
                 self.popen();
                 if let Some(ddpos) = ddpos {
-                    self.commasep(Inconsistent, &elts[..ddpos], |s, p| s.print_pat(&p));
+                    self.commasep(Inconsistent, &elts[..ddpos], |s, p| s.print_pat(p));
                     if ddpos != 0 {
                         self.word_space(",");
                     }
                     self.word("..");
                     if ddpos != elts.len() {
                         self.word(",");
-                        self.commasep(Inconsistent, &elts[ddpos..], |s, p| s.print_pat(&p));
+                        self.commasep(Inconsistent, &elts[ddpos..], |s, p| s.print_pat(p));
                     }
                 } else {
-                    self.commasep(Inconsistent, &elts, |s, p| s.print_pat(&p));
+                    self.commasep(Inconsistent, elts, |s, p| s.print_pat(p));
                 }
                 self.pclose();
             }
             PatKind::Path(ref qpath) => {
                 self.print_qpath(qpath, true);
             }
-            PatKind::Struct(ref qpath, ref fields, etc) => {
+            PatKind::Struct(ref qpath, fields, etc) => {
                 self.print_qpath(qpath, true);
                 self.nbsp();
                 self.word("{");
@@ -1800,14 +1783,14 @@ pub fn print_pat(&mut self, pat: &hir::Pat<'_>) {
                 }
                 self.commasep_cmnt(
                     Consistent,
-                    &fields,
+                    fields,
                     |s, f| {
                         s.cbox(INDENT_UNIT);
                         if !f.is_shorthand {
                             s.print_ident(f.ident);
                             s.word_nbsp(":");
                         }
-                        s.print_pat(&f.pat);
+                        s.print_pat(f.pat);
                         s.end()
                     },
                     |f| f.pat.span,
@@ -1823,58 +1806,58 @@ pub fn print_pat(&mut self, pat: &hir::Pat<'_>) {
                 }
                 self.word("}");
             }
-            PatKind::Or(ref pats) => {
-                self.strsep("|", true, Inconsistent, &pats, |s, p| s.print_pat(&p));
+            PatKind::Or(pats) => {
+                self.strsep("|", true, Inconsistent, pats, |s, p| s.print_pat(p));
             }
-            PatKind::Tuple(ref elts, ddpos) => {
+            PatKind::Tuple(elts, ddpos) => {
                 self.popen();
                 if let Some(ddpos) = ddpos {
-                    self.commasep(Inconsistent, &elts[..ddpos], |s, p| s.print_pat(&p));
+                    self.commasep(Inconsistent, &elts[..ddpos], |s, p| s.print_pat(p));
                     if ddpos != 0 {
                         self.word_space(",");
                     }
                     self.word("..");
                     if ddpos != elts.len() {
                         self.word(",");
-                        self.commasep(Inconsistent, &elts[ddpos..], |s, p| s.print_pat(&p));
+                        self.commasep(Inconsistent, &elts[ddpos..], |s, p| s.print_pat(p));
                     }
                 } else {
-                    self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(&p));
+                    self.commasep(Inconsistent, elts, |s, p| s.print_pat(p));
                     if elts.len() == 1 {
                         self.word(",");
                     }
                 }
                 self.pclose();
             }
-            PatKind::Box(ref inner) => {
+            PatKind::Box(inner) => {
                 let is_range_inner = matches!(inner.kind, PatKind::Range(..));
                 self.word("box ");
                 if is_range_inner {
                     self.popen();
                 }
-                self.print_pat(&inner);
+                self.print_pat(inner);
                 if is_range_inner {
                     self.pclose();
                 }
             }
-            PatKind::Ref(ref inner, mutbl) => {
+            PatKind::Ref(inner, mutbl) => {
                 let is_range_inner = matches!(inner.kind, PatKind::Range(..));
                 self.word("&");
                 self.word(mutbl.prefix_str());
                 if is_range_inner {
                     self.popen();
                 }
-                self.print_pat(&inner);
+                self.print_pat(inner);
                 if is_range_inner {
                     self.pclose();
                 }
             }
-            PatKind::Lit(ref e) => self.print_expr(&e),
-            PatKind::Range(ref begin, ref end, ref end_kind) => {
+            PatKind::Lit(e) => self.print_expr(e),
+            PatKind::Range(begin, end, end_kind) => {
                 if let Some(expr) = begin {
                     self.print_expr(expr);
                 }
-                match *end_kind {
+                match end_kind {
                     RangeEnd::Included => self.word("..."),
                     RangeEnd::Excluded => self.word(".."),
                 }
@@ -1882,24 +1865,24 @@ pub fn print_pat(&mut self, pat: &hir::Pat<'_>) {
                     self.print_expr(expr);
                 }
             }
-            PatKind::Slice(ref before, ref slice, ref after) => {
+            PatKind::Slice(before, slice, after) => {
                 self.word("[");
-                self.commasep(Inconsistent, &before, |s, p| s.print_pat(&p));
-                if let Some(ref p) = *slice {
+                self.commasep(Inconsistent, before, |s, p| s.print_pat(p));
+                if let Some(p) = slice {
                     if !before.is_empty() {
                         self.word_space(",");
                     }
                     if let PatKind::Wild = p.kind {
                         // Print nothing.
                     } else {
-                        self.print_pat(&p);
+                        self.print_pat(p);
                     }
                     self.word("..");
                     if !after.is_empty() {
                         self.word_space(",");
                     }
                 }
-                self.commasep(Inconsistent, &after, |s, p| s.print_pat(&p));
+                self.commasep(Inconsistent, after, |s, p| s.print_pat(p));
                 self.word("]");
             }
         }
@@ -1908,7 +1891,7 @@ pub fn print_pat(&mut self, pat: &hir::Pat<'_>) {
 
     pub fn print_param(&mut self, arg: &hir::Param<'_>) {
         self.print_outer_attributes(self.attrs(arg.hir_id));
-        self.print_pat(&arg.pat);
+        self.print_pat(arg.pat);
     }
 
     pub fn print_arm(&mut self, arm: &hir::Arm<'_>) {
@@ -1920,32 +1903,32 @@ pub fn print_arm(&mut self, arm: &hir::Arm<'_>) {
         self.cbox(INDENT_UNIT);
         self.ann.pre(self, AnnNode::Arm(arm));
         self.ibox(0);
-        self.print_outer_attributes(&self.attrs(arm.hir_id));
-        self.print_pat(&arm.pat);
+        self.print_outer_attributes(self.attrs(arm.hir_id));
+        self.print_pat(arm.pat);
         self.space();
         if let Some(ref g) = arm.guard {
-            match g {
+            match *g {
                 hir::Guard::If(e) => {
                     self.word_space("if");
-                    self.print_expr(&e);
+                    self.print_expr(e);
                     self.space();
                 }
-                hir::Guard::IfLet(hir::Let { pat, ty, init, .. }) => {
+                hir::Guard::IfLet(&hir::Let { pat, ty, init, .. }) => {
                     self.word_nbsp("if");
-                    self.print_let(pat, *ty, init);
+                    self.print_let(pat, ty, init);
                 }
             }
         }
         self.word_space("=>");
 
         match arm.body.kind {
-            hir::ExprKind::Block(ref blk, opt_label) => {
+            hir::ExprKind::Block(blk, opt_label) => {
                 if let Some(label) = opt_label {
                     self.print_ident(label.ident);
                     self.word_space(":");
                 }
                 // the block will close the pattern's ibox
-                self.print_block_unclosed(&blk);
+                self.print_block_unclosed(blk);
 
                 // If it is a user-provided unsafe block, print a comma after it
                 if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = blk.rules
@@ -1955,7 +1938,7 @@ pub fn print_arm(&mut self, arm: &hir::Arm<'_>) {
             }
             _ => {
                 self.end(); // close the ibox for the pattern
-                self.print_expr(&arm.body);
+                self.print_expr(arm.body);
                 self.word(",");
             }
         }
@@ -1978,13 +1961,13 @@ pub fn print_fn(
             self.nbsp();
             self.print_name(name);
         }
-        self.print_generic_params(&generics.params);
+        self.print_generic_params(generics.params);
 
         self.popen();
         let mut i = 0;
         // Make sure we aren't supplied *both* `arg_names` and `body_id`.
         assert!(arg_names.is_empty() || body_id.is_none());
-        self.commasep(Inconsistent, &decl.inputs, |s, ty| {
+        self.commasep(Inconsistent, decl.inputs, |s, ty| {
             s.ibox(INDENT_UNIT);
             if let Some(arg_name) = arg_names.get(i) {
                 s.word(arg_name.to_string());
@@ -2011,7 +1994,7 @@ pub fn print_fn(
     fn print_closure_params(&mut self, decl: &hir::FnDecl<'_>, body_id: hir::BodyId) {
         self.word("|");
         let mut i = 0;
-        self.commasep(Inconsistent, &decl.inputs, |s, ty| {
+        self.commasep(Inconsistent, decl.inputs, |s, ty| {
             s.ibox(INDENT_UNIT);
 
             s.ann.nested(s, Nested::BodyParamPat(body_id, i));
@@ -2035,8 +2018,8 @@ fn print_closure_params(&mut self, decl: &hir::FnDecl<'_>, body_id: hir::BodyId)
         self.space_if_not_bol();
         self.word_space("->");
         match decl.output {
-            hir::FnRetTy::Return(ref ty) => {
-                self.print_type(&ty);
+            hir::FnRetTy::Return(ty) => {
+                self.print_type(ty);
                 self.maybe_print_comment(ty.span.lo());
             }
             hir::FnRetTy::DefaultReturn(..) => unreachable!(),
@@ -2107,20 +2090,20 @@ pub fn print_generic_param(&mut self, param: &GenericParam<'_>) {
 
         match param.kind {
             GenericParamKind::Lifetime { .. } => {}
-            GenericParamKind::Type { ref default, .. } => {
+            GenericParamKind::Type { default, .. } => {
                 if let Some(default) = default {
                     self.space();
                     self.word_space("=");
-                    self.print_type(&default)
+                    self.print_type(default);
                 }
             }
-            GenericParamKind::Const { ref ty, ref default } => {
+            GenericParamKind::Const { ty, ref default } => {
                 self.word_space(":");
                 self.print_type(ty);
-                if let Some(ref default) = default {
+                if let Some(default) = default {
                     self.space();
                     self.word_space("=");
-                    self.print_anon_const(&default)
+                    self.print_anon_const(default);
                 }
             }
         }
@@ -2143,7 +2126,7 @@ pub fn print_where_clause(&mut self, generics: &hir::Generics<'_>) {
                 self.word_space(",");
             }
 
-            match predicate {
+            match *predicate {
                 hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
                     bound_generic_params,
                     bounded_ty,
@@ -2151,11 +2134,11 @@ pub fn print_where_clause(&mut self, generics: &hir::Generics<'_>) {
                     ..
                 }) => {
                     self.print_formal_generic_params(bound_generic_params);
-                    self.print_type(&bounded_ty);
-                    self.print_bounds(":", *bounds);
+                    self.print_type(bounded_ty);
+                    self.print_bounds(":", bounds);
                 }
                 hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
-                    lifetime,
+                    ref lifetime,
                     bounds,
                     ..
                 }) => {
@@ -2200,7 +2183,7 @@ pub fn print_mutability(&mut self, mutbl: hir::Mutability, print_const: bool) {
 
     pub fn print_mt(&mut self, mt: &hir::MutTy<'_>, print_const: bool) {
         self.print_mutability(mt.mutbl, print_const);
-        self.print_type(&mt.ty)
+        self.print_type(mt.ty);
     }
 
     pub fn print_fn_output(&mut self, decl: &hir::FnDecl<'_>) {
@@ -2213,11 +2196,11 @@ pub fn print_fn_output(&mut self, decl: &hir::FnDecl<'_>) {
         self.word_space("->");
         match decl.output {
             hir::FnRetTy::DefaultReturn(..) => unreachable!(),
-            hir::FnRetTy::Return(ref ty) => self.print_type(&ty),
+            hir::FnRetTy::Return(ty) => self.print_type(ty),
         }
         self.end();
 
-        if let hir::FnRetTy::Return(ref output) = decl.output {
+        if let hir::FnRetTy::Return(output) = decl.output {
             self.maybe_print_comment(output.span.lo());
         }
     }
@@ -2243,7 +2226,7 @@ pub fn print_ty_fn(
                 asyncness: hir::IsAsync::NotAsync,
             },
             name,
-            &generics,
+            generics,
             arg_names,
             None,
         );
@@ -2312,7 +2295,7 @@ fn stmt_ends_with_semi(stmt: &hir::StmtKind<'_>) -> bool {
     match *stmt {
         hir::StmtKind::Local(_) => true,
         hir::StmtKind::Item(_) => false,
-        hir::StmtKind::Expr(ref e) => expr_requires_semi_to_be_stmt(&e),
+        hir::StmtKind::Expr(e) => expr_requires_semi_to_be_stmt(e),
         hir::StmtKind::Semi(..) => false,
     }
 }
@@ -2351,22 +2334,22 @@ fn contains_exterior_struct_lit(value: &hir::Expr<'_>) -> bool {
     match value.kind {
         hir::ExprKind::Struct(..) => true,
 
-        hir::ExprKind::Assign(ref lhs, ref rhs, _)
-        | hir::ExprKind::AssignOp(_, ref lhs, ref rhs)
-        | hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
+        hir::ExprKind::Assign(lhs, rhs, _)
+        | hir::ExprKind::AssignOp(_, lhs, rhs)
+        | hir::ExprKind::Binary(_, lhs, rhs) => {
             // `X { y: 1 } + X { y: 2 }`
-            contains_exterior_struct_lit(&lhs) || contains_exterior_struct_lit(&rhs)
+            contains_exterior_struct_lit(lhs) || contains_exterior_struct_lit(rhs)
         }
-        hir::ExprKind::Unary(_, ref x)
-        | hir::ExprKind::Cast(ref x, _)
-        | hir::ExprKind::Type(ref x, _)
-        | hir::ExprKind::Field(ref x, _)
-        | hir::ExprKind::Index(ref x, _) => {
+        hir::ExprKind::Unary(_, x)
+        | hir::ExprKind::Cast(x, _)
+        | hir::ExprKind::Type(x, _)
+        | hir::ExprKind::Field(x, _)
+        | hir::ExprKind::Index(x, _) => {
             // `&X { y: 1 }, X { y: 1 }.y`
-            contains_exterior_struct_lit(&x)
+            contains_exterior_struct_lit(x)
         }
 
-        hir::ExprKind::MethodCall(.., ref exprs, _) => {
+        hir::ExprKind::MethodCall(.., exprs, _) => {
             // `X { y: 1 }.bar(...)`
             contains_exterior_struct_lit(&exprs[0])
         }

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -315,8 +315,6 @@ pub fn emit_inference_failure_err(
         body_id: Option<hir::BodyId>,
         failure_span: Span,
         arg: GenericArg<'tcx>,
-        // FIXME(#94483): Either use this or remove it.
-        _impl_candidates: Vec<ty::TraitRef<'tcx>>,
         error_code: TypeAnnotationNeeded,
         should_label_span: bool,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
@@ -534,6 +532,23 @@ enum InferSourceKind<'tcx> {
     },
 }
 
+impl<'tcx> InferSource<'tcx> {
+    fn from_expansion(&self) -> bool {
+        let source_from_expansion = match self.kind {
+            InferSourceKind::LetBinding { insert_span, .. }
+            | InferSourceKind::ClosureArg { insert_span, .. }
+            | InferSourceKind::GenericArg { insert_span, .. } => insert_span.from_expansion(),
+            InferSourceKind::FullyQualifiedMethodCall { receiver, .. } => {
+                receiver.span.from_expansion()
+            }
+            InferSourceKind::ClosureReturn { data, should_wrap_expr, .. } => {
+                data.span().from_expansion() || should_wrap_expr.map_or(false, Span::from_expansion)
+            }
+        };
+        source_from_expansion || self.span.from_expansion()
+    }
+}
+
 impl<'tcx> InferSourceKind<'tcx> {
     fn ty_msg(&self, infcx: &InferCtxt<'_, 'tcx>) -> String {
         match *self {
@@ -604,43 +619,65 @@ fn new(
     /// Sources with a small cost are prefer and should result
     /// in a clearer and idiomatic suggestion.
     fn source_cost(&self, source: &InferSource<'tcx>) -> usize {
-        let tcx = self.infcx.tcx;
-
-        fn arg_cost<'tcx>(arg: GenericArg<'tcx>) -> usize {
-            match arg.unpack() {
-                GenericArgKind::Lifetime(_) => 0, // erased
-                GenericArgKind::Type(ty) => ty_cost(ty),
-                GenericArgKind::Const(_) => 3, // some non-zero value
-            }
+        #[derive(Clone, Copy)]
+        struct CostCtxt<'tcx> {
+            tcx: TyCtxt<'tcx>,
         }
-        fn ty_cost<'tcx>(ty: Ty<'tcx>) -> usize {
-            match ty.kind() {
-                ty::Closure(..) => 100,
-                ty::FnDef(..) => 20,
-                ty::FnPtr(..) => 10,
-                ty::Infer(..) => 0,
-                _ => 1,
+        impl<'tcx> CostCtxt<'tcx> {
+            fn arg_cost(self, arg: GenericArg<'tcx>) -> usize {
+                match arg.unpack() {
+                    GenericArgKind::Lifetime(_) => 0, // erased
+                    GenericArgKind::Type(ty) => self.ty_cost(ty),
+                    GenericArgKind::Const(_) => 3, // some non-zero value
+                }
+            }
+            fn ty_cost(self, ty: Ty<'tcx>) -> usize {
+                match *ty.kind() {
+                    ty::Closure(..) => 1000,
+                    ty::FnDef(..) => 150,
+                    ty::FnPtr(..) => 30,
+                    ty::Adt(def, substs) => {
+                        5 + self
+                            .tcx
+                            .generics_of(def.did())
+                            .own_substs_no_defaults(self.tcx, substs)
+                            .iter()
+                            .map(|&arg| self.arg_cost(arg))
+                            .sum::<usize>()
+                    }
+                    ty::Tuple(args) => 5 + args.iter().map(|arg| self.ty_cost(arg)).sum::<usize>(),
+                    ty::Ref(_, ty, _) => 2 + self.ty_cost(ty),
+                    ty::Infer(..) => 0,
+                    _ => 1,
+                }
             }
         }
 
         // The sources are listed in order of preference here.
-        match source.kind {
-            InferSourceKind::LetBinding { ty, .. } => ty_cost(ty),
-            InferSourceKind::ClosureArg { ty, .. } => 5 + ty_cost(ty),
+        let tcx = self.infcx.tcx;
+        let ctx = CostCtxt { tcx };
+        let base_cost = match source.kind {
+            InferSourceKind::LetBinding { ty, .. } => ctx.ty_cost(ty),
+            InferSourceKind::ClosureArg { ty, .. } => ctx.ty_cost(ty),
             InferSourceKind::GenericArg { def_id, generic_args, .. } => {
                 let variant_cost = match tcx.def_kind(def_id) {
-                    DefKind::Variant | DefKind::Ctor(CtorOf::Variant, _) => 15, // `None::<u32>` and friends are ugly.
-                    _ => 12,
+                    // `None::<u32>` and friends are ugly.
+                    DefKind::Variant | DefKind::Ctor(CtorOf::Variant, _) => 15,
+                    _ => 10,
                 };
-                variant_cost + generic_args.iter().map(|&arg| arg_cost(arg)).sum::<usize>()
+                variant_cost + generic_args.iter().map(|&arg| ctx.arg_cost(arg)).sum::<usize>()
             }
             InferSourceKind::FullyQualifiedMethodCall { substs, .. } => {
-                20 + substs.iter().map(|arg| arg_cost(arg)).sum::<usize>()
+                20 + substs.iter().map(|arg| ctx.arg_cost(arg)).sum::<usize>()
             }
             InferSourceKind::ClosureReturn { ty, should_wrap_expr, .. } => {
-                30 + ty_cost(ty) + if should_wrap_expr.is_some() { 10 } else { 0 }
+                30 + ctx.ty_cost(ty) + if should_wrap_expr.is_some() { 10 } else { 0 }
             }
-        }
+        };
+
+        let suggestion_may_apply = if source.from_expansion() { 10000 } else { 0 };
+
+        base_cost + suggestion_may_apply
     }
 
     /// Uses `fn source_cost` to determine whether this inference source is preferable to
@@ -648,6 +685,7 @@ fn ty_cost<'tcx>(ty: Ty<'tcx>) -> usize {
     #[instrument(level = "debug", skip(self))]
     fn update_infer_source(&mut self, new_source: InferSource<'tcx>) {
         let cost = self.source_cost(&new_source) + self.attempt;
+        debug!(?cost);
         self.attempt += 1;
         if cost < self.infer_source_cost {
             self.infer_source_cost = cost;
@@ -655,6 +693,11 @@ fn update_infer_source(&mut self, new_source: InferSource<'tcx>) {
         }
     }
 
+    fn node_substs_opt(&self, hir_id: HirId) -> Option<SubstsRef<'tcx>> {
+        let substs = self.typeck_results.node_substs_opt(hir_id);
+        self.infcx.resolve_vars_if_possible(substs)
+    }
+
     fn opt_node_type(&self, hir_id: HirId) -> Option<Ty<'tcx>> {
         let ty = self.typeck_results.node_type_opt(hir_id);
         self.infcx.resolve_vars_if_possible(ty)
@@ -737,7 +780,7 @@ fn expr_inferred_subst_iter(
         let tcx = self.infcx.tcx;
         match expr.kind {
             hir::ExprKind::Path(ref path) => {
-                if let Some(substs) = self.typeck_results.node_substs_opt(expr.hir_id) {
+                if let Some(substs) = self.node_substs_opt(expr.hir_id) {
                     return self.path_inferred_subst_iter(expr.hir_id, substs, path);
                 }
             }
@@ -765,7 +808,7 @@ fn expr_inferred_subst_iter(
                         if generics.has_impl_trait() {
                             None?
                         }
-                        let substs = self.typeck_results.node_substs_opt(expr.hir_id)?;
+                        let substs = self.node_substs_opt(expr.hir_id)?;
                         let span = tcx.hir().span(segment.hir_id?);
                         let insert_span = segment.ident.span.shrink_to_hi().with_hi(span.hi());
                         InsertableGenericArgs {
@@ -980,8 +1023,10 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
             debug!(?args);
             let InsertableGenericArgs { insert_span, substs, generics_def_id, def_id } = args;
             let generics = tcx.generics_of(generics_def_id);
-            if let Some(argument_index) =
-                generics.own_substs(substs).iter().position(|&arg| self.generic_arg_is_target(arg))
+            if let Some(argument_index) = generics
+                .own_substs(substs)
+                .iter()
+                .position(|&arg| self.generic_arg_contains_target(arg))
             {
                 let substs = self.infcx.resolve_vars_if_possible(substs);
                 let generic_args = &generics.own_substs_no_defaults(tcx, substs)
@@ -1037,7 +1082,7 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
             .any(|generics| generics.has_impl_trait())
         };
         if let ExprKind::MethodCall(path, args, span) = expr.kind
-            && let Some(substs) = self.typeck_results.node_substs_opt(expr.hir_id)
+            && let Some(substs) = self.node_substs_opt(expr.hir_id)
             && substs.iter().any(|arg| self.generic_arg_contains_target(arg))
             && let Some(def_id) = self.typeck_results.type_dependent_def_id(expr.hir_id)
             && self.infcx.tcx.trait_of_item(def_id).is_some()

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -160,12 +160,18 @@ pub fn to_interp_error<'tcx>(self, alloc_id: AllocId) -> InterpError<'tcx> {
 }
 
 /// The information that makes up a memory access: offset and size.
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone)]
 pub struct AllocRange {
     pub start: Size,
     pub size: Size,
 }
 
+impl fmt::Debug for AllocRange {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "[{:#x}..{:#x}]", self.start.bytes(), self.end().bytes())
+    }
+}
+
 /// Free-starting constructor for less syntactic overhead.
 #[inline(always)]
 pub fn alloc_range(start: Size, size: Size) -> AllocRange {

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -334,36 +334,30 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                 p,
             ),
             PointerUseAfterFree(a) => {
-                write!(f, "pointer to {} was dereferenced after this allocation got freed", a)
+                write!(f, "pointer to {a:?} was dereferenced after this allocation got freed")
             }
             PointerOutOfBounds { alloc_id, alloc_size, ptr_offset, ptr_size: Size::ZERO, msg } => {
                 write!(
                     f,
-                    "{}{alloc_id} has size {alloc_size}, so pointer at offset {ptr_offset} is out-of-bounds",
-                    msg,
-                    alloc_id = alloc_id,
+                    "{msg}{alloc_id:?} has size {alloc_size}, so pointer at offset {ptr_offset} is out-of-bounds",
                     alloc_size = alloc_size.bytes(),
-                    ptr_offset = ptr_offset,
                 )
             }
             PointerOutOfBounds { alloc_id, alloc_size, ptr_offset, ptr_size, msg } => write!(
                 f,
-                "{}{alloc_id} has size {alloc_size}, so pointer to {ptr_size} byte{ptr_size_p} starting at offset {ptr_offset} is out-of-bounds",
-                msg,
-                alloc_id = alloc_id,
+                "{msg}{alloc_id:?} has size {alloc_size}, so pointer to {ptr_size} byte{ptr_size_p} starting at offset {ptr_offset} is out-of-bounds",
                 alloc_size = alloc_size.bytes(),
                 ptr_size = ptr_size.bytes(),
                 ptr_size_p = pluralize!(ptr_size.bytes()),
-                ptr_offset = ptr_offset,
             ),
             DanglingIntPointer(0, CheckInAllocMsg::InboundsTest) => {
                 write!(f, "null pointer is not a valid pointer for this operation")
             }
             DanglingIntPointer(0, msg) => {
-                write!(f, "{}null pointer is not a valid pointer", msg)
+                write!(f, "{msg}null pointer is not a valid pointer")
             }
             DanglingIntPointer(i, msg) => {
-                write!(f, "{}0x{:x} is not a valid pointer", msg, i)
+                write!(f, "{msg}{i:#x} is not a valid pointer")
             }
             AlignmentCheckFailed { required, has } => write!(
                 f,
@@ -371,8 +365,8 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                 has.bytes(),
                 required.bytes()
             ),
-            WriteToReadOnly(a) => write!(f, "writing to {} which is read-only", a),
-            DerefFunctionPointer(a) => write!(f, "accessing {} which contains a function", a),
+            WriteToReadOnly(a) => write!(f, "writing to {a:?} which is read-only"),
+            DerefFunctionPointer(a) => write!(f, "accessing {a:?} which contains a function"),
             ValidationFailure { path: None, msg } => {
                 write!(f, "constructing invalid value: {}", msg)
             }

compiler/rustc_middle/src/mir/interpret/mod.rs

@@ -190,11 +190,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     }
 }
 
-impl fmt::Display for AllocId {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(self, f)
-    }
-}
+// No "Display" since AllocIds are not usually user-visible.
 
 #[derive(TyDecodable, TyEncodable)]
 enum AllocDiscriminant {
@@ -470,7 +466,7 @@ fn reserve_and_set_dedup(self, alloc: GlobalAlloc<'tcx>) -> AllocId {
             return alloc_id;
         }
         let id = alloc_map.reserve();
-        debug!("creating alloc {:?} with id {}", alloc, id);
+        debug!("creating alloc {alloc:?} with id {id:?}");
         alloc_map.alloc_map.insert(id, alloc.clone());
         alloc_map.dedup.insert(alloc, id);
         id
@@ -538,7 +534,7 @@ pub fn get_global_alloc(self, id: AllocId) -> Option<GlobalAlloc<'tcx>> {
     pub fn global_alloc(self, id: AllocId) -> GlobalAlloc<'tcx> {
         match self.get_global_alloc(id) {
             Some(alloc) => alloc,
-            None => bug!("could not find allocation for {}", id),
+            None => bug!("could not find allocation for {id:?}"),
         }
     }
 
@@ -546,7 +542,7 @@ pub fn global_alloc(self, id: AllocId) -> GlobalAlloc<'tcx> {
     /// call this function twice, even with the same `Allocation` will ICE the compiler.
     pub fn set_alloc_id_memory(self, id: AllocId, mem: ConstAllocation<'tcx>) {
         if let Some(old) = self.alloc_map.lock().alloc_map.insert(id, GlobalAlloc::Memory(mem)) {
-            bug!("tried to set allocation ID {}, but it was already existing as {:#?}", id, old);
+            bug!("tried to set allocation ID {id:?}, but it was already existing as {old:#?}");
         }
     }
 

compiler/rustc_middle/src/mir/interpret/pointer.rs

@@ -144,7 +144,7 @@ fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         }
         // Print offset only if it is non-zero.
         if ptr.offset.bytes() > 0 {
-            write!(f, "+0x{:x}", ptr.offset.bytes())?;
+            write!(f, "+{:#x}", ptr.offset.bytes())?;
         }
         Ok(())
     }
@@ -181,7 +181,7 @@ impl<Tag: Provenance> fmt::Debug for Pointer<Option<Tag>> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.provenance {
             Some(tag) => Provenance::fmt(&Pointer::new(tag, self.offset), f),
-            None => write!(f, "0x{:x}", self.offset.bytes()),
+            None => write!(f, "{:#x}", self.offset.bytes()),
         }
     }
 }

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -167,7 +167,7 @@ impl<Tag: Provenance> fmt::LowerHex for Scalar<Tag> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Scalar::Ptr(ptr, _size) => write!(f, "pointer to {:?}", ptr),
-            Scalar::Int(int) => write!(f, "0x{:x}", int),
+            Scalar::Int(int) => write!(f, "{:#x}", int),
         }
     }
 }

compiler/rustc_middle/src/mir/pretty.rs

@@ -716,12 +716,12 @@ fn visit_constant(&mut self, c: &Constant<'tcx>, loc: Location) {
                 }
                 write!(w, "{}", display_allocation(tcx, alloc.inner()))
             };
-        write!(w, "\n{}", id)?;
+        write!(w, "\n{id:?}")?;
         match tcx.get_global_alloc(id) {
             // This can't really happen unless there are bugs, but it doesn't cost us anything to
             // gracefully handle it and allow buggy rustc to be debugged via allocation printing.
             None => write!(w, " (deallocated)")?,
-            Some(GlobalAlloc::Function(inst)) => write!(w, " (fn: {})", inst)?,
+            Some(GlobalAlloc::Function(inst)) => write!(w, " (fn: {inst})")?,
             Some(GlobalAlloc::Static(did)) if !tcx.is_foreign_item(did) => {
                 match tcx.eval_static_initializer(did) {
                     Ok(alloc) => {

compiler/rustc_middle/src/ty/consts/int.rs

@@ -452,6 +452,10 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 impl fmt::LowerHex for ScalarInt {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.check_data();
+        if f.alternate() {
+            // Like regular ints, alternate flag adds leading `0x`.
+            write!(f, "0x")?;
+        }
         // Format as hex number wide enough to fit any value of the given `size`.
         // So data=20, size=1 will be "0x14", but with size=4 it'll be "0x00000014".
         // Using a block `{self.data}` here to force a copy instead of using `self.data`

compiler/rustc_resolve/src/diagnostics.rs

@@ -1495,6 +1495,15 @@ pub(crate) fn unresolved_macro_suggestions(
             err.help("have you added the `#[macro_use]` on the module/import?");
             return;
         }
+        if ident.name == kw::Default
+            && let ModuleKind::Def(DefKind::Enum, def_id, _) = parent_scope.module.kind
+            && let Some(span) = self.opt_span(def_id)
+        {
+            err.span_help(
+                self.session.source_map().guess_head_span(span),
+                "consider adding `#[derive(Default)]` to this enum",
+            );
+        }
         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
             if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
                 ident,

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1980,7 +1980,6 @@ fn maybe_report_ambiguity(
                             body_id,
                             span,
                             trait_ref.self_ty().skip_binder().into(),
-                            vec![],
                             ErrorCode::E0282,
                             false,
                         )
@@ -2005,19 +2004,7 @@ fn maybe_report_ambiguity(
                 let subst = data.trait_ref.substs.iter().find(|s| s.has_infer_types_or_consts());
 
                 let mut err = if let Some(subst) = subst {
-                    let impl_candidates = self
-                        .find_similar_impl_candidates(trait_ref)
-                        .into_iter()
-                        .map(|candidate| candidate.trait_ref)
-                        .collect();
-                    self.emit_inference_failure_err(
-                        body_id,
-                        span,
-                        subst,
-                        impl_candidates,
-                        ErrorCode::E0283,
-                        true,
-                    )
+                    self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
                 } else {
                     struct_span_err!(
                         self.tcx.sess,
@@ -2117,7 +2104,7 @@ fn maybe_report_ambiguity(
                     return;
                 }
 
-                self.emit_inference_failure_err(body_id, span, arg, vec![], ErrorCode::E0282, false)
+                self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
             }
 
             ty::PredicateKind::Subtype(data) => {
@@ -2131,14 +2118,7 @@ fn maybe_report_ambiguity(
                 let SubtypePredicate { a_is_expected: _, a, b } = data;
                 // both must be type variables, or the other would've been instantiated
                 assert!(a.is_ty_var() && b.is_ty_var());
-                self.emit_inference_failure_err(
-                    body_id,
-                    span,
-                    a.into(),
-                    vec![],
-                    ErrorCode::E0282,
-                    true,
-                )
+                self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
             }
             ty::PredicateKind::Projection(data) => {
                 if predicate.references_error() || self.is_tainted_by_errors() {
@@ -2155,7 +2135,6 @@ fn maybe_report_ambiguity(
                         body_id,
                         span,
                         subst,
-                        vec![],
                         ErrorCode::E0284,
                         true,
                     );

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -1538,15 +1538,8 @@ pub fn structurally_resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
             ty
         } else {
             if !self.is_tainted_by_errors() {
-                self.emit_inference_failure_err(
-                    (**self).body_id,
-                    sp,
-                    ty.into(),
-                    vec![],
-                    E0282,
-                    true,
-                )
-                .emit();
+                self.emit_inference_failure_err((**self).body_id, sp, ty.into(), E0282, true)
+                    .emit();
             }
             let err = self.tcx.ty_error();
             self.demand_suptype(sp, err, ty);

compiler/rustc_typeck/src/check/writeback.rs

@@ -692,7 +692,6 @@ fn report_type_error(&self, t: Ty<'tcx>) {
                     Some(self.body.id()),
                     self.span.to_span(self.tcx),
                     t.into(),
-                    vec![],
                     E0282,
                     false,
                 )
@@ -707,7 +706,6 @@ fn report_const_error(&self, c: ty::Const<'tcx>) {
                     Some(self.body.id()),
                     self.span.to_span(self.tcx),
                     c.into(),
-                    vec![],
                     E0282,
                     false,
                 )

library/std/src/net/tcp.rs

@@ -7,6 +7,7 @@
 
 use crate::fmt;
 use crate::io::{self, IoSlice, IoSliceMut};
+use crate::iter::FusedIterator;
 use crate::net::{Shutdown, SocketAddr, ToSocketAddrs};
 use crate::sys_common::net as net_imp;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
@@ -1009,6 +1010,9 @@ fn next(&mut self) -> Option<io::Result<TcpStream>> {
     }
 }
 
+#[stable(feature = "tcp_listener_incoming_fused_iterator", since = "1.64.0")]
+impl FusedIterator for Incoming<'_> {}
+
 #[unstable(feature = "tcplistener_into_incoming", issue = "88339")]
 impl Iterator for IntoIncoming {
     type Item = io::Result<TcpStream>;
@@ -1017,6 +1021,9 @@ fn next(&mut self) -> Option<io::Result<TcpStream>> {
     }
 }
 
+#[unstable(feature = "tcplistener_into_incoming", issue = "88339")]
+impl FusedIterator for IntoIncoming {}
+
 impl AsInner<net_imp::TcpListener> for TcpListener {
     fn as_inner(&self) -> &net_imp::TcpListener {
         &self.0

src/test/ui/enum/suggest-default-attribute.rs

@@ -0,0 +1,8 @@
+pub enum Test { //~ HELP consider adding `#[derive(Default)]` to this enum
+    #[default]
+    //~^ ERROR cannot find attribute `default` in this scope
+    First,
+    Second,
+}
+
+fn main() {}

src/test/ui/enum/suggest-default-attribute.stderr

@@ -0,0 +1,14 @@
+error: cannot find attribute `default` in this scope
+  --> $DIR/suggest-default-attribute.rs:2:7
+   |
+LL |     #[default]
+   |       ^^^^^^^
+   |
+help: consider adding `#[derive(Default)]` to this enum
+  --> $DIR/suggest-default-attribute.rs:1:1
+   |
+LL | pub enum Test {
+   | ^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/inference/ambiguous_type_parameter.stderr

@@ -2,7 +2,12 @@ error[E0282]: type annotations needed
   --> $DIR/ambiguous_type_parameter.rs:16:19
    |
 LL |     InMemoryStore.get_raw(&String::default());
-   |                   ^^^^^^^ cannot infer type for type parameter `K`
+   |                   ^^^^^^^
+   |
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     <InMemoryStore as Store<String, HashMap<K, String>>>::get_raw(&InMemoryStore, &String::default());
+   |     +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++             ~
 
 error: aborting due to previous error
 

src/test/ui/inference/cannot-infer-partial-try-return.rs

@@ -16,8 +16,8 @@ fn infallible() -> Result<(), std::convert::Infallible> {
 
 fn main() {
     let x = || -> Result<_, QualifiedError<_>> {
-        //~^ ERROR type annotations needed for `Result<(), QualifiedError<_>>`
         infallible()?;
         Ok(())
+        //~^ ERROR type annotations needed
     };
 }

src/test/ui/inference/cannot-infer-partial-try-return.stderr

@@ -1,16 +1,15 @@
-error[E0282]: type annotations needed for `Result<(), QualifiedError<_>>`
-  --> $DIR/cannot-infer-partial-try-return.rs:18:13
+error[E0282]: type annotations needed
+  --> $DIR/cannot-infer-partial-try-return.rs:20:9
    |
-LL |     let x = || -> Result<_, QualifiedError<_>> {
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-LL |
 LL |         infallible()?;
    |         ------------- type must be known at this point
+LL |         Ok(())
+   |         ^^ cannot infer type of the type parameter `E` declared on the enum `Result`
    |
-help: try giving this closure an explicit return type
+help: consider specifying the generic arguments
    |
-LL |     let x = || -> Result<(), QualifiedError<_>> {
-   |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+LL |         Ok::<(), QualifiedError<_>>(())
+   |           +++++++++++++++++++++++++
 
 error: aborting due to previous error
 

src/test/ui/inference/need_type_info/channel.rs

@@ -0,0 +1,19 @@
+// Test that we suggest specifying the generic argument of `channel`
+// instead of the return type of that function, which is a lot more
+// complex.
+use std::sync::mpsc::channel;
+
+fn no_tuple() {
+    let _data =
+        channel(); //~ ERROR type annotations needed
+}
+
+fn tuple() {
+    let (_sender, _receiver) =
+        channel(); //~ ERROR type annotations needed
+}
+
+fn main() {
+    no_tuple();
+    tuple();
+}

src/test/ui/inference/need_type_info/channel.stderr

@@ -0,0 +1,25 @@
+error[E0282]: type annotations needed
+  --> $DIR/channel.rs:8:9
+   |
+LL |         channel();
+   |         ^^^^^^^ cannot infer type of the type parameter `T` declared on the function `channel`
+   |
+help: consider specifying the generic argument
+   |
+LL |         channel::<T>();
+   |                +++++
+
+error[E0282]: type annotations needed
+  --> $DIR/channel.rs:13:9
+   |
+LL |         channel();
+   |         ^^^^^^^ cannot infer type of the type parameter `T` declared on the function `channel`
+   |
+help: consider specifying the generic argument
+   |
+LL |         channel::<T>();
+   |                +++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0282`.

src/test/ui/issues/issue-23041.stderr

@@ -1,8 +1,13 @@
 error[E0282]: type annotations needed
-  --> $DIR/issue-23041.rs:6:22
+  --> $DIR/issue-23041.rs:6:7
    |
 LL |     b.downcast_ref::<fn(_)->_>();
-   |                      ^^^^^^^^ cannot infer type
+   |       ^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the associated function `downcast_ref`
+   |
+help: consider specifying the generic arguments
+   |
+LL |     b.downcast_ref::<fn(_) -> _>();
+   |                   ~~~~~~~~~~~~~~
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-24013.stderr

@@ -1,8 +1,13 @@
 error[E0282]: type annotations needed
-  --> $DIR/issue-24013.rs:5:20
+  --> $DIR/issue-24013.rs:5:13
    |
 LL |     unsafe {swap::<&mut _>(transmute(&a), transmute(&b))};
-   |                    ^^^^^^ cannot infer type
+   |             ^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `swap`
+   |
+help: consider specifying the generic arguments
+   |
+LL |     unsafe {swap::<&mut _>(transmute(&a), transmute(&b))};
+   |                 ~~~~~~~~~~
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-25368.rs

@@ -5,10 +5,10 @@
 struct Foo<T> {foo: PhantomData<T>}
 
 fn main() {
-    let (tx, rx) = //~ ERROR type annotations needed
+    let (tx, rx) =
         channel();
-    // FIXME(#89862): Suggest adding a generic argument to `channel` instead
     spawn(move || {
         tx.send(Foo{ foo: PhantomData });
+        //~^ ERROR type annotations needed
     });
 }

src/test/ui/issues/issue-25368.stderr

@@ -1,13 +1,13 @@
-error[E0282]: type annotations needed for `(Sender<Foo<T>>, std::sync::mpsc::Receiver<Foo<T>>)`
-  --> $DIR/issue-25368.rs:8:9
+error[E0282]: type annotations needed
+  --> $DIR/issue-25368.rs:11:27
    |
-LL |     let (tx, rx) =
-   |         ^^^^^^^^
+LL |         tx.send(Foo{ foo: PhantomData });
+   |                           ^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the struct `PhantomData`
    |
-help: consider giving this pattern a type, where the type for type parameter `T` is specified
+help: consider specifying the generic argument
    |
-LL |     let (tx, rx): (Sender<Foo<T>>, std::sync::mpsc::Receiver<Foo<T>>) =
-   |                 +++++++++++++++++++++++++++++++++++++++++++++++++++++
+LL |         tx.send(Foo{ foo: PhantomData::<T> });
+   |                                      +++++
 
 error: aborting due to previous error
 

src/test/ui/methods/method-ambig-one-trait-unknown-int-type.stderr

@@ -13,7 +13,7 @@ error[E0283]: type annotations needed
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:26:7
    |
 LL |     x.foo();
-   |       ^^^ cannot infer type for struct `Vec<_>`
+   |       ^^^
    |
 note: multiple `impl`s satisfying `Vec<_>: Foo` found
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:9:1
@@ -23,6 +23,10 @@ LL | impl Foo for Vec<usize> {
 ...
 LL | impl Foo for Vec<isize> {
    | ^^^^^^^^^^^^^^^^^^^^^^^
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     <Vec<T> as Foo>::foo(&x);
+   |     ++++++++++++++++++++++ ~
 
 error[E0308]: mismatched types
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:33:20