Merging upstream version 1.67.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 625 insertions, 705 deletions

diff --git a/compiler/rustc_ast_lowering/src/asm.rs b/compiler/rustc_ast_lowering/src/asm.rs
index 450cdf246..dfef6ec70 100644
--- a/compiler/rustc_ast_lowering/src/asm.rs
+++ b/compiler/rustc_ast_lowering/src/asm.rs
@@ -11,7 +11,7 @@ use super::LoweringContext;
 
 use rustc_ast::ptr::P;
 use rustc_ast::*;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::definitions::DefPathData;
@@ -71,7 +71,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             .emit();
         }
 
-        let mut clobber_abis = FxHashMap::default();
+        let mut clobber_abis = FxIndexMap::default();
         if let Some(asm_arch) = asm_arch {
             for (abi_name, abi_span) in &asm.clobber_abis {
                 match asm::InlineAsmClobberAbi::parse(asm_arch, &self.tcx.sess.target, *abi_name) {
@@ -123,7 +123,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             .operands
             .iter()
             .map(|(op, op_sp)| {
-                let lower_reg = |reg| match reg {
+                let lower_reg = |&reg: &_| match reg {
                     InlineAsmRegOrRegClass::Reg(reg) => {
                         asm::InlineAsmRegOrRegClass::Reg(if let Some(asm_arch) = asm_arch {
                             asm::InlineAsmReg::parse(asm_arch, reg).unwrap_or_else(|error| {
@@ -152,32 +152,30 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }
                 };
 
-                let op = match *op {
-                    InlineAsmOperand::In { reg, ref expr } => hir::InlineAsmOperand::In {
+                let op = match op {
+                    InlineAsmOperand::In { reg, expr } => hir::InlineAsmOperand::In {
                         reg: lower_reg(reg),
                         expr: self.lower_expr(expr),
                     },
-                    InlineAsmOperand::Out { reg, late, ref expr } => hir::InlineAsmOperand::Out {
+                    InlineAsmOperand::Out { reg, late, expr } => hir::InlineAsmOperand::Out {
                         reg: lower_reg(reg),
-                        late,
+                        late: *late,
                         expr: expr.as_ref().map(|expr| self.lower_expr(expr)),
                     },
-                    InlineAsmOperand::InOut { reg, late, ref expr } => {
-                        hir::InlineAsmOperand::InOut {
-                            reg: lower_reg(reg),
-                            late,
-                            expr: self.lower_expr(expr),
-                        }
-                    }
-                    InlineAsmOperand::SplitInOut { reg, late, ref in_expr, ref out_expr } => {
+                    InlineAsmOperand::InOut { reg, late, expr } => hir::InlineAsmOperand::InOut {
+                        reg: lower_reg(reg),
+                        late: *late,
+                        expr: self.lower_expr(expr),
+                    },
+                    InlineAsmOperand::SplitInOut { reg, late, in_expr, out_expr } => {
                         hir::InlineAsmOperand::SplitInOut {
                             reg: lower_reg(reg),
-                            late,
+                            late: *late,
                             in_expr: self.lower_expr(in_expr),
                             out_expr: out_expr.as_ref().map(|expr| self.lower_expr(expr)),
                         }
                     }
-                    InlineAsmOperand::Const { ref anon_const } => {
+                    InlineAsmOperand::Const { anon_const } => {
                         if !self.tcx.features().asm_const {
                             feature_err(
                                 &sess.parse_sess,
@@ -191,7 +189,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             anon_const: self.lower_anon_const(anon_const),
                         }
                     }
-                    InlineAsmOperand::Sym { ref sym } => {
+                    InlineAsmOperand::Sym { sym } => {
                         let static_def_id = self
                             .resolver
                             .get_partial_res(sym.id)
@@ -224,7 +222,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             // Wrap the expression in an AnonConst.
                             let parent_def_id = self.current_hir_id_owner;
                             let node_id = self.next_node_id();
-                            self.create_def(parent_def_id.def_id, node_id, DefPathData::AnonConst);
+                            self.create_def(
+                                parent_def_id.def_id,
+                                node_id,
+                                DefPathData::AnonConst,
+                                *op_sp,
+                            );
                             let anon_const = AnonConst { id: node_id, value: P(expr) };
                             hir::InlineAsmOperand::SymFn {
                                 anon_const: self.lower_anon_const(&anon_const),
@@ -347,7 +350,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                     skip = true;
 
                                     let idx2 = *o.get();
-                                    let &(ref op2, op_sp2) = &operands[idx2];
+                                    let (ref op2, op_sp2) = operands[idx2];
                                     let Some(asm::InlineAsmRegOrRegClass::Reg(reg2)) = op2.reg() else {
                                         unreachable!();
                                     };
diff --git a/compiler/rustc_ast_lowering/src/block.rs b/compiler/rustc_ast_lowering/src/block.rs
index 12a0cc0d2..d310f72f7 100644
--- a/compiler/rustc_ast_lowering/src/block.rs
+++ b/compiler/rustc_ast_lowering/src/block.rs
@@ -31,8 +31,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let mut stmts = SmallVec::<[hir::Stmt<'hir>; 8]>::new();
         let mut expr = None;
         while let [s, tail @ ..] = ast_stmts {
-            match s.kind {
-                StmtKind::Local(ref local) => {
+            match &s.kind {
+                StmtKind::Local(local) => {
                     let hir_id = self.lower_node_id(s.id);
                     let local = self.lower_local(local);
                     self.alias_attrs(hir_id, local.hir_id);
@@ -40,7 +40,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     let span = self.lower_span(s.span);
                     stmts.push(hir::Stmt { hir_id, kind, span });
                 }
-                StmtKind::Item(ref it) => {
+                StmtKind::Item(it) => {
                     stmts.extend(self.lower_item_ref(it).into_iter().enumerate().map(
                         |(i, item_id)| {
                             let hir_id = match i {
@@ -53,7 +53,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         },
                     ));
                 }
-                StmtKind::Expr(ref e) => {
+                StmtKind::Expr(e) => {
                     let e = self.lower_expr(e);
                     if tail.is_empty() {
                         expr = Some(e);
@@ -65,7 +65,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         stmts.push(hir::Stmt { hir_id, kind, span });
                     }
                 }
-                StmtKind::Semi(ref e) => {
+                StmtKind::Semi(e) => {
                     let e = self.lower_expr(e);
                     let hir_id = self.lower_node_id(s.id);
                     self.alias_attrs(hir_id, e.hir_id);
diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index 157f46501..21c6a2d26 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -277,8 +277,9 @@ pub struct RegisterConflict<'a> {
 pub struct SubTupleBinding<'a> {
     #[primary_span]
     #[label]
-    #[suggestion_verbose(
+    #[suggestion(
         ast_lowering_sub_tuple_binding_suggestion,
+        style = "verbose",
         code = "..",
         applicability = "maybe-incorrect"
     )]
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index ec9c39350..7dd6d5acc 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -14,6 +14,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
 use rustc_hir::definitions::DefPathData;
+use rustc_session::errors::report_lit_error;
 use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::DUMMY_SP;
@@ -30,20 +31,20 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
         ensure_sufficient_stack(|| {
-            let kind = match e.kind {
-                ExprKind::Box(ref inner) => hir::ExprKind::Box(self.lower_expr(inner)),
-                ExprKind::Array(ref exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
-                ExprKind::ConstBlock(ref anon_const) => {
+            let kind = match &e.kind {
+                ExprKind::Box(inner) => hir::ExprKind::Box(self.lower_expr(inner)),
+                ExprKind::Array(exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
+                ExprKind::ConstBlock(anon_const) => {
                     let anon_const = self.lower_anon_const(anon_const);
                     hir::ExprKind::ConstBlock(anon_const)
                 }
-                ExprKind::Repeat(ref expr, ref count) => {
+                ExprKind::Repeat(expr, count) => {
                     let expr = self.lower_expr(expr);
                     let count = self.lower_array_length(count);
                     hir::ExprKind::Repeat(expr, count)
                 }
-                ExprKind::Tup(ref elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
-                ExprKind::Call(ref f, ref args) => {
+                ExprKind::Tup(elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
+                ExprKind::Call(f, args) => {
                     if e.attrs.get(0).map_or(false, |a| a.has_name(sym::rustc_box)) {
                         if let [inner] = &args[..] && e.attrs.len() == 1 {
                             let kind = hir::ExprKind::Box(self.lower_expr(&inner));
@@ -60,7 +61,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         hir::ExprKind::Call(f, self.lower_exprs(args))
                     }
                 }
-                ExprKind::MethodCall(ref seg, ref receiver, ref args, span) => {
+                ExprKind::MethodCall(box MethodCall { seg, receiver, args, span }) => {
                     let hir_seg = self.arena.alloc(self.lower_path_segment(
                         e.span,
                         seg,
@@ -71,81 +72,89 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let receiver = self.lower_expr(receiver);
                     let args =
                         self.arena.alloc_from_iter(args.iter().map(|x| self.lower_expr_mut(x)));
-                    hir::ExprKind::MethodCall(hir_seg, receiver, args, self.lower_span(span))
+                    hir::ExprKind::MethodCall(hir_seg, receiver, args, self.lower_span(*span))
                 }
-                ExprKind::Binary(binop, ref lhs, ref rhs) => {
-                    let binop = self.lower_binop(binop);
+                ExprKind::Binary(binop, lhs, rhs) => {
+                    let binop = self.lower_binop(*binop);
                     let lhs = self.lower_expr(lhs);
                     let rhs = self.lower_expr(rhs);
                     hir::ExprKind::Binary(binop, lhs, rhs)
                 }
-                ExprKind::Unary(op, ref ohs) => {
-                    let op = self.lower_unop(op);
+                ExprKind::Unary(op, ohs) => {
+                    let op = self.lower_unop(*op);
                     let ohs = self.lower_expr(ohs);
                     hir::ExprKind::Unary(op, ohs)
                 }
-                ExprKind::Lit(ref l) => {
-                    hir::ExprKind::Lit(respan(self.lower_span(l.span), l.kind.clone()))
+                ExprKind::Lit(token_lit) => {
+                    let lit_kind = match LitKind::from_token_lit(*token_lit) {
+                        Ok(lit_kind) => lit_kind,
+                        Err(err) => {
+                            report_lit_error(&self.tcx.sess.parse_sess, err, *token_lit, e.span);
+                            LitKind::Err
+                        }
+                    };
+                    hir::ExprKind::Lit(respan(self.lower_span(e.span), lit_kind))
                 }
-                ExprKind::Cast(ref expr, ref ty) => {
+                ExprKind::IncludedBytes(bytes) => hir::ExprKind::Lit(respan(
+                    self.lower_span(e.span),
+                    LitKind::ByteStr(bytes.clone()),
+                )),
+                ExprKind::Cast(expr, ty) => {
                     let expr = self.lower_expr(expr);
                     let ty =
                         self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
                     hir::ExprKind::Cast(expr, ty)
                 }
-                ExprKind::Type(ref expr, ref ty) => {
+                ExprKind::Type(expr, ty) => {
                     let expr = self.lower_expr(expr);
                     let ty =
                         self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
                     hir::ExprKind::Type(expr, ty)
                 }
-                ExprKind::AddrOf(k, m, ref ohs) => {
+                ExprKind::AddrOf(k, m, ohs) => {
                     let ohs = self.lower_expr(ohs);
-                    hir::ExprKind::AddrOf(k, m, ohs)
+                    hir::ExprKind::AddrOf(*k, *m, ohs)
                 }
-                ExprKind::Let(ref pat, ref scrutinee, span) => {
+                ExprKind::Let(pat, scrutinee, span) => {
                     hir::ExprKind::Let(self.arena.alloc(hir::Let {
                         hir_id: self.next_id(),
-                        span: self.lower_span(span),
+                        span: self.lower_span(*span),
                         pat: self.lower_pat(pat),
                         ty: None,
                         init: self.lower_expr(scrutinee),
                     }))
                 }
-                ExprKind::If(ref cond, ref then, ref else_opt) => {
+                ExprKind::If(cond, then, else_opt) => {
                     self.lower_expr_if(cond, then, else_opt.as_deref())
                 }
-                ExprKind::While(ref cond, ref body, opt_label) => {
-                    self.with_loop_scope(e.id, |this| {
-                        let span =
-                            this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
-                        this.lower_expr_while_in_loop_scope(span, cond, body, opt_label)
-                    })
-                }
-                ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
+                ExprKind::While(cond, body, opt_label) => self.with_loop_scope(e.id, |this| {
+                    let span = this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
+                    this.lower_expr_while_in_loop_scope(span, cond, body, *opt_label)
+                }),
+                ExprKind::Loop(body, opt_label, span) => self.with_loop_scope(e.id, |this| {
                     hir::ExprKind::Loop(
                         this.lower_block(body, false),
-                        this.lower_label(opt_label),
+                        this.lower_label(*opt_label),
                         hir::LoopSource::Loop,
-                        DUMMY_SP,
+                        this.lower_span(*span),
                     )
                 }),
-                ExprKind::TryBlock(ref body) => self.lower_expr_try_block(body),
-                ExprKind::Match(ref expr, ref arms) => hir::ExprKind::Match(
+                ExprKind::TryBlock(body) => self.lower_expr_try_block(body),
+                ExprKind::Match(expr, arms) => hir::ExprKind::Match(
                     self.lower_expr(expr),
                     self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
                     hir::MatchSource::Normal,
                 ),
-                ExprKind::Async(capture_clause, closure_node_id, ref block) => self
-                    .make_async_expr(
-                        capture_clause,
-                        closure_node_id,
-                        None,
-                        block.span,
-                        hir::AsyncGeneratorKind::Block,
-                        |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
-                    ),
-                ExprKind::Await(ref expr) => {
+                ExprKind::Async(capture_clause, closure_node_id, block) => self.make_async_expr(
+                    *capture_clause,
+                    None,
+                    *closure_node_id,
+                    None,
+                    e.span,
+                    hir::AsyncGeneratorKind::Block,
+                    |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
+                ),
+                ExprKind::Await(expr) => {
                     let dot_await_span = if expr.span.hi() < e.span.hi() {
                         let span_with_whitespace = self
                             .tcx
@@ -160,66 +169,67 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     };
                     self.lower_expr_await(dot_await_span, expr)
                 }
-                ExprKind::Closure(
-                    ref binder,
+                ExprKind::Closure(box Closure {
+                    binder,
                     capture_clause,
                     asyncness,
                     movability,
-                    ref decl,
-                    ref body,
+                    fn_decl,
+                    body,
                     fn_decl_span,
-                ) => {
+                    fn_arg_span,
+                }) => {
                     if let Async::Yes { closure_id, .. } = asyncness {
                         self.lower_expr_async_closure(
                             binder,
-                            capture_clause,
+                            *capture_clause,
                             e.id,
-                            closure_id,
-                            decl,
+                            *closure_id,
+                            fn_decl,
                             body,
-                            fn_decl_span,
+                            *fn_decl_span,
+                            *fn_arg_span,
                         )
                     } else {
                         self.lower_expr_closure(
                             binder,
-                            capture_clause,
+                            *capture_clause,
                             e.id,
-                            movability,
-                            decl,
+                            *movability,
+                            fn_decl,
                             body,
-                            fn_decl_span,
+                            *fn_decl_span,
+                            *fn_arg_span,
                         )
                     }
                 }
-                ExprKind::Block(ref blk, opt_label) => {
-                    let opt_label = self.lower_label(opt_label);
+                ExprKind::Block(blk, opt_label) => {
+                    let opt_label = self.lower_label(*opt_label);
                     hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
                 }
-                ExprKind::Assign(ref el, ref er, span) => {
-                    self.lower_expr_assign(el, er, span, e.span)
-                }
-                ExprKind::AssignOp(op, ref el, ref er) => hir::ExprKind::AssignOp(
-                    self.lower_binop(op),
+                ExprKind::Assign(el, er, span) => self.lower_expr_assign(el, er, *span, e.span),
+                ExprKind::AssignOp(op, el, er) => hir::ExprKind::AssignOp(
+                    self.lower_binop(*op),
                     self.lower_expr(el),
                     self.lower_expr(er),
                 ),
-                ExprKind::Field(ref el, ident) => {
-                    hir::ExprKind::Field(self.lower_expr(el), self.lower_ident(ident))
+                ExprKind::Field(el, ident) => {
+                    hir::ExprKind::Field(self.lower_expr(el), self.lower_ident(*ident))
                 }
-                ExprKind::Index(ref el, ref er) => {
+                ExprKind::Index(el, er) => {
                     hir::ExprKind::Index(self.lower_expr(el), self.lower_expr(er))
                 }
-                ExprKind::Range(Some(ref e1), Some(ref e2), RangeLimits::Closed) => {
+                ExprKind::Range(Some(e1), Some(e2), RangeLimits::Closed) => {
                     self.lower_expr_range_closed(e.span, e1, e2)
                 }
-                ExprKind::Range(ref e1, ref e2, lims) => {
-                    self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), lims)
+                ExprKind::Range(e1, e2, lims) => {
+                    self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), *lims)
                 }
                 ExprKind::Underscore => {
                     self.tcx.sess.emit_err(UnderscoreExprLhsAssign { span: e.span });
                     hir::ExprKind::Err
                 }
-                ExprKind::Path(ref qself, ref path) => {
+                ExprKind::Path(qself, path) => {
                     let qpath = self.lower_qpath(
                         e.id,
                         qself,
@@ -229,22 +239,22 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     );
                     hir::ExprKind::Path(qpath)
                 }
-                ExprKind::Break(opt_label, ref opt_expr) => {
+                ExprKind::Break(opt_label, opt_expr) => {
                     let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
-                    hir::ExprKind::Break(self.lower_jump_destination(e.id, opt_label), opt_expr)
+                    hir::ExprKind::Break(self.lower_jump_destination(e.id, *opt_label), opt_expr)
                 }
                 ExprKind::Continue(opt_label) => {
-                    hir::ExprKind::Continue(self.lower_jump_destination(e.id, opt_label))
+                    hir::ExprKind::Continue(self.lower_jump_destination(e.id, *opt_label))
                 }
-                ExprKind::Ret(ref e) => {
+                ExprKind::Ret(e) => {
                     let e = e.as_ref().map(|x| self.lower_expr(x));
                     hir::ExprKind::Ret(e)
                 }
-                ExprKind::Yeet(ref sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
-                ExprKind::InlineAsm(ref asm) => {
+                ExprKind::Yeet(sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
+                ExprKind::InlineAsm(asm) => {
                     hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
                 }
-                ExprKind::Struct(ref se) => {
+                ExprKind::Struct(se) => {
                     let rest = match &se.rest {
                         StructRest::Base(e) => Some(self.lower_expr(e)),
                         StructRest::Rest(sp) => {
@@ -266,10 +276,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         rest,
                     )
                 }
-                ExprKind::Yield(ref opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
+                ExprKind::Yield(opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
                 ExprKind::Err => hir::ExprKind::Err,
-                ExprKind::Try(ref sub_expr) => self.lower_expr_try(e.span, sub_expr),
-                ExprKind::Paren(ref ex) => {
+                ExprKind::Try(sub_expr) => self.lower_expr_try(e.span, sub_expr),
+                ExprKind::Paren(ex) => {
                     let mut ex = self.lower_expr_mut(ex);
                     // Include parens in span, but only if it is a super-span.
                     if e.span.contains(ex.span) {
@@ -294,8 +304,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
                 // Desugar `ExprForLoop`
                 // from: `[opt_ident]: for <pat> in <head> <body>`
-                ExprKind::ForLoop(ref pat, ref head, ref body, opt_label) => {
-                    return self.lower_expr_for(e, pat, head, body, opt_label);
+                ExprKind::ForLoop(pat, head, body, opt_label) => {
+                    return self.lower_expr_for(e, pat, head, body, *opt_label);
                 }
                 ExprKind::MacCall(_) => panic!("{:?} shouldn't exist here", e.span),
             };
@@ -346,7 +356,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         args: Vec<AstP<Expr>>,
         legacy_args_idx: &[usize],
     ) -> hir::ExprKind<'hir> {
-        let ExprKind::Path(None, ref mut path) = f.kind else {
+        let ExprKind::Path(None, path) = &mut f.kind else {
             unreachable!();
         };
 
@@ -359,7 +369,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let node_id = self.next_node_id();
 
                 // Add a definition for the in-band const def.
-                self.create_def(parent_def_id.def_id, node_id, DefPathData::AnonConst);
+                self.create_def(parent_def_id.def_id, node_id, DefPathData::AnonConst, f.span);
 
                 let anon_const = AnonConst { id: node_id, value: arg };
                 generic_args.push(AngleBracketedArg::Arg(GenericArg::Const(anon_const)));
@@ -426,18 +436,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let lhs = self.lower_cond(lhs);
                 let rhs = self.lower_cond(rhs);
 
-                self.arena.alloc(self.expr(
-                    cond.span,
-                    hir::ExprKind::Binary(op, lhs, rhs),
-                    AttrVec::new(),
-                ))
+                self.arena.alloc(self.expr(cond.span, hir::ExprKind::Binary(op, lhs, rhs)))
             }
             ExprKind::Let(..) => self.lower_expr(cond),
             _ => {
                 let cond = self.lower_expr(cond);
                 let reason = DesugaringKind::CondTemporary;
                 let span_block = self.mark_span_with_reason(reason, cond.span, None);
-                self.expr_drop_temps(span_block, cond, AttrVec::new())
+                self.expr_drop_temps(span_block, cond)
             }
         }
     }
@@ -467,12 +473,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> hir::ExprKind<'hir> {
         let lowered_cond = self.with_loop_condition_scope(|t| t.lower_cond(cond));
         let then = self.lower_block_expr(body);
-        let expr_break = self.expr_break(span, AttrVec::new());
+        let expr_break = self.expr_break(span);
         let stmt_break = self.stmt_expr(span, expr_break);
         let else_blk = self.block_all(span, arena_vec![self; stmt_break], None);
-        let else_expr = self.arena.alloc(self.expr_block(else_blk, AttrVec::new()));
+        let else_expr = self.arena.alloc(self.expr_block(else_blk));
         let if_kind = hir::ExprKind::If(lowered_cond, self.arena.alloc(then), Some(else_expr));
-        let if_expr = self.expr(span, if_kind, AttrVec::new());
+        let if_expr = self.expr(span, if_kind);
         let block = self.block_expr(self.arena.alloc(if_expr));
         let span = self.lower_span(span.with_hi(cond.span.hi()));
         let opt_label = self.lower_label(opt_label);
@@ -528,22 +534,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
         expr: &'hir hir::Expr<'hir>,
         overall_span: Span,
     ) -> &'hir hir::Expr<'hir> {
-        let constructor = self.arena.alloc(self.expr_lang_item_path(
-            method_span,
-            lang_item,
-            AttrVec::new(),
-            None,
-        ));
+        let constructor = self.arena.alloc(self.expr_lang_item_path(method_span, lang_item, None));
         self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
     }
 
     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
         let pat = self.lower_pat(&arm.pat);
         let guard = arm.guard.as_ref().map(|cond| {
-            if let ExprKind::Let(ref pat, ref scrutinee, span) = cond.kind {
+            if let ExprKind::Let(pat, scrutinee, span) = &cond.kind {
                 hir::Guard::IfLet(self.arena.alloc(hir::Let {
                     hir_id: self.next_id(),
-                    span: self.lower_span(span),
+                    span: self.lower_span(*span),
                     pat: self.lower_pat(pat),
                     ty: None,
                     init: self.lower_expr(scrutinee),
@@ -563,37 +564,35 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    /// Lower an `async` construct to a generator that is then wrapped so it implements `Future`.
+    /// Lower an `async` construct to a generator that implements `Future`.
     ///
     /// This results in:
     ///
     /// ```text
-    /// std::future::from_generator(static move? |_task_context| -> <ret_ty> {
+    /// std::future::identity_future(static move? |_task_context| -> <ret_ty> {
     ///     <body>
     /// })
     /// ```
     pub(super) fn make_async_expr(
         &mut self,
         capture_clause: CaptureBy,
+        outer_hir_id: Option<hir::HirId>,
         closure_node_id: NodeId,
-        ret_ty: Option<AstP<Ty>>,
+        ret_ty: Option<hir::FnRetTy<'hir>>,
         span: Span,
         async_gen_kind: hir::AsyncGeneratorKind,
         body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
     ) -> hir::ExprKind<'hir> {
-        let output = match ret_ty {
-            Some(ty) => hir::FnRetTy::Return(
-                self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::AsyncBlock)),
-            ),
-            None => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
-        };
+        let output = ret_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span)));
 
-        // Resume argument type. We let the compiler infer this to simplify the lowering. It is
-        // fully constrained by `future::from_generator`.
+        // Resume argument type: `ResumeTy`
+        let unstable_span =
+            self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
+        let resume_ty = hir::QPath::LangItem(hir::LangItem::ResumeTy, unstable_span, None);
         let input_ty = hir::Ty {
             hir_id: self.next_id(),
-            kind: hir::TyKind::Infer,
-            span: self.lower_span(span),
+            kind: hir::TyKind::Path(resume_ty),
+            span: unstable_span,
         };
 
         // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
@@ -602,6 +601,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             output,
             c_variadic: false,
             implicit_self: hir::ImplicitSelfKind::None,
+            lifetime_elision_allowed: false,
         });
 
         // Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
@@ -631,35 +631,63 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // `static |_task_context| -> <ret_ty> { body }`:
         let generator_kind = {
             let c = self.arena.alloc(hir::Closure {
+                def_id: self.local_def_id(closure_node_id),
                 binder: hir::ClosureBinder::Default,
                 capture_clause,
                 bound_generic_params: &[],
                 fn_decl,
                 body,
                 fn_decl_span: self.lower_span(span),
+                fn_arg_span: None,
                 movability: Some(hir::Movability::Static),
             });
 
             hir::ExprKind::Closure(c)
         };
-        let generator = hir::Expr {
-            hir_id: self.lower_node_id(closure_node_id),
-            kind: generator_kind,
-            span: self.lower_span(span),
-        };
 
-        // `future::from_generator`:
+        let hir_id = self.lower_node_id(closure_node_id);
         let unstable_span =
             self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
-        let gen_future = self.expr_lang_item_path(
-            unstable_span,
-            hir::LangItem::FromGenerator,
-            AttrVec::new(),
-            None,
-        );
 
-        // `future::from_generator(generator)`:
-        hir::ExprKind::Call(self.arena.alloc(gen_future), arena_vec![self; generator])
+        if self.tcx.features().closure_track_caller
+            && let Some(outer_hir_id) = outer_hir_id
+            && let Some(attrs) = self.attrs.get(&outer_hir_id.local_id)
+            && attrs.into_iter().any(|attr| attr.has_name(sym::track_caller))
+        {
+            self.lower_attrs(
+                hir_id,
+                &[Attribute {
+                    kind: AttrKind::Normal(ptr::P(NormalAttr {
+                        item: AttrItem {
+                            path: Path::from_ident(Ident::new(sym::track_caller, span)),
+                            args: AttrArgs::Empty,
+                            tokens: None,
+                        },
+                        tokens: None,
+                    })),
+                    id: self.tcx.sess.parse_sess.attr_id_generator.mk_attr_id(),
+                    style: AttrStyle::Outer,
+                    span: unstable_span,
+                }],
+            );
+        }
+
+        let generator = hir::Expr { hir_id, kind: generator_kind, span: self.lower_span(span) };
+
+        // FIXME(swatinem):
+        // For some reason, the async block needs to flow through *any*
+        // call (like the identity function), as otherwise type and lifetime
+        // inference have a hard time figuring things out.
+        // Without this, we would get:
+        // E0720 in src/test/ui/impl-trait/in-trait/default-body-with-rpit.rs
+        // E0700 in src/test/ui/self/self_lifetime-async.rs
+
+        // `future::identity_future`:
+        let identity_future =
+            self.expr_lang_item_path(unstable_span, hir::LangItem::IdentityFuture, None);
+
+        // `future::identity_future(generator)`:
+        hir::ExprKind::Call(self.arena.alloc(identity_future), arena_vec![self; generator])
     }
 
     /// Desugar `<expr>.await` into:
@@ -759,7 +787,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let break_x = self.with_loop_scope(loop_node_id, move |this| {
                 let expr_break =
                     hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
-                this.arena.alloc(this.expr(gen_future_span, expr_break, AttrVec::new()))
+                this.arena.alloc(this.expr(gen_future_span, expr_break))
             });
             self.arm(ready_pat, break_x)
         };
@@ -792,17 +820,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let yield_expr = self.expr(
                 span,
                 hir::ExprKind::Yield(unit, hir::YieldSource::Await { expr: Some(expr_hir_id) }),
-                AttrVec::new(),
             );
             let yield_expr = self.arena.alloc(yield_expr);
 
             if let Some(task_context_hid) = self.task_context {
                 let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
-                let assign = self.expr(
-                    span,
-                    hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span)),
-                    AttrVec::new(),
-                );
+                let assign =
+                    self.expr(span, hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span)));
                 self.stmt_expr(span, assign)
             } else {
                 // Use of `await` outside of an async context. Return `yield_expr` so that we can
@@ -860,6 +884,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         decl: &FnDecl,
         body: &Expr,
         fn_decl_span: Span,
+        fn_arg_span: Span,
     ) -> hir::ExprKind<'hir> {
         let (binder_clause, generic_params) = self.lower_closure_binder(binder);
 
@@ -880,15 +905,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
         // Lower outside new scope to preserve `is_in_loop_condition`.
-        let fn_decl = self.lower_fn_decl(decl, None, fn_decl_span, FnDeclKind::Closure, None);
+        let fn_decl = self.lower_fn_decl(decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
+            def_id: self.local_def_id(closure_id),
             binder: binder_clause,
             capture_clause,
             bound_generic_params,
             fn_decl,
             body: body_id,
             fn_decl_span: self.lower_span(fn_decl_span),
+            fn_arg_span: Some(self.lower_span(fn_arg_span)),
             movability: generator_option,
         });
 
@@ -927,8 +954,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> (hir::ClosureBinder, &'c [GenericParam]) {
         let (binder, params) = match binder {
             ClosureBinder::NotPresent => (hir::ClosureBinder::Default, &[][..]),
-            &ClosureBinder::For { span, ref generic_params } => {
-                let span = self.lower_span(span);
+            ClosureBinder::For { span, generic_params } => {
+                let span = self.lower_span(*span);
                 (hir::ClosureBinder::For { span }, &**generic_params)
             }
         };
@@ -945,6 +972,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         decl: &FnDecl,
         body: &Expr,
         fn_decl_span: Span,
+        fn_arg_span: Span,
     ) -> hir::ExprKind<'hir> {
         if let &ClosureBinder::For { span, .. } = binder {
             self.tcx.sess.emit_err(NotSupportedForLifetimeBinderAsyncClosure { span });
@@ -962,19 +990,27 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
 
             // Transform `async |x: u8| -> X { ... }` into
-            // `|x: u8| future_from_generator(|| -> X { ... })`.
+            // `|x: u8| identity_future(|| -> X { ... })`.
             let body_id = this.lower_fn_body(&outer_decl, |this| {
-                let async_ret_ty =
-                    if let FnRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
+                let async_ret_ty = if let FnRetTy::Ty(ty) = &decl.output {
+                    let itctx = ImplTraitContext::Disallowed(ImplTraitPosition::AsyncBlock);
+                    Some(hir::FnRetTy::Return(this.lower_ty(&ty, &itctx)))
+                } else {
+                    None
+                };
+
                 let async_body = this.make_async_expr(
                     capture_clause,
+                    // FIXME(nbdd0121): This should also use a proper HIR id so `#[track_caller]`
+                    // can be applied on async closures as well.
+                    None,
                     inner_closure_id,
                     async_ret_ty,
                     body.span,
                     hir::AsyncGeneratorKind::Closure,
                     |this| this.with_new_scopes(|this| this.lower_expr_mut(body)),
                 );
-                this.expr(fn_decl_span, async_body, AttrVec::new())
+                this.expr(fn_decl_span, async_body)
             });
             body_id
         });
@@ -984,15 +1020,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // have to conserve the state of being inside a loop condition for the
         // closure argument types.
         let fn_decl =
-            self.lower_fn_decl(&outer_decl, None, fn_decl_span, FnDeclKind::Closure, None);
+            self.lower_fn_decl(&outer_decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
+            def_id: self.local_def_id(closure_id),
             binder: binder_clause,
             capture_clause,
             bound_generic_params,
             fn_decl,
             body,
             fn_decl_span: self.lower_span(fn_decl_span),
+            fn_arg_span: Some(self.lower_span(fn_arg_span)),
             movability: None,
         });
         hir::ExprKind::Closure(c)
@@ -1065,7 +1103,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn extract_tuple_struct_path<'a>(
         &mut self,
         expr: &'a Expr,
-    ) -> Option<(&'a Option<QSelf>, &'a Path)> {
+    ) -> Option<(&'a Option<AstP<QSelf>>, &'a Path)> {
         if let ExprKind::Path(qself, path) = &expr.kind {
             // Does the path resolve to something disallowed in a tuple struct/variant pattern?
             if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
@@ -1085,7 +1123,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn extract_unit_struct_path<'a>(
         &mut self,
         expr: &'a Expr,
-    ) -> Option<(&'a Option<QSelf>, &'a Path)> {
+    ) -> Option<(&'a Option<AstP<QSelf>>, &'a Path)> {
         if let ExprKind::Path(qself, path) = &expr.kind {
             // Does the path resolve to something disallowed in a unit struct/variant pattern?
             if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
@@ -1232,7 +1270,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let ident = self.expr_ident(lhs.span, ident, binding);
         let assign =
             hir::ExprKind::Assign(self.lower_expr(lhs), ident, self.lower_span(eq_sign_span));
-        let expr = self.expr(lhs.span, assign, AttrVec::new());
+        let expr = self.expr(lhs.span, assign);
         assignments.push(self.stmt_expr(lhs.span, expr));
         pat
     }
@@ -1273,8 +1311,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let e2 = self.lower_expr_mut(e2);
         let fn_path =
             hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, self.lower_span(span), None);
-        let fn_expr =
-            self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), AttrVec::new()));
+        let fn_expr = self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path)));
         hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
     }
 
@@ -1446,8 +1483,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         // `None => break`
         let none_arm = {
-            let break_expr =
-                self.with_loop_scope(e.id, |this| this.expr_break_alloc(for_span, AttrVec::new()));
+            let break_expr = self.with_loop_scope(e.id, |this| this.expr_break_alloc(for_span));
             let pat = self.pat_none(for_span);
             self.arm(pat, break_expr)
         };
@@ -1456,7 +1492,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let some_arm = {
             let some_pat = self.pat_some(pat_span, pat);
             let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
-            let body_expr = self.arena.alloc(self.expr_block(body_block, AttrVec::new()));
+            let body_expr = self.arena.alloc(self.expr_block(body_block));
             self.arm(some_pat, body_expr)
         };
 
@@ -1519,7 +1555,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // surrounding scope of the `match` since the `match` is not a terminating scope.
         //
         // Also, add the attributes to the outer returned expr node.
-        self.expr_drop_temps_mut(for_span, match_expr, e.attrs.clone())
+        let expr = self.expr_drop_temps_mut(for_span, match_expr);
+        self.lower_attrs(expr.hir_id, &e.attrs);
+        expr
     }
 
     /// Desugar `ExprKind::Try` from: `<expr>?` into:
@@ -1561,28 +1599,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
         };
 
         // `#[allow(unreachable_code)]`
-        let attr = {
-            // `allow(unreachable_code)`
-            let allow = {
-                let allow_ident = Ident::new(sym::allow, self.lower_span(span));
-                let uc_ident = Ident::new(sym::unreachable_code, self.lower_span(span));
-                let uc_nested = attr::mk_nested_word_item(uc_ident);
-                attr::mk_list_item(allow_ident, vec![uc_nested])
-            };
-            attr::mk_attr_outer(&self.tcx.sess.parse_sess.attr_id_generator, allow)
-        };
+        let attr = attr::mk_attr_nested_word(
+            &self.tcx.sess.parse_sess.attr_id_generator,
+            AttrStyle::Outer,
+            sym::allow,
+            sym::unreachable_code,
+            self.lower_span(span),
+        );
         let attrs: AttrVec = thin_vec![attr];
 
         // `ControlFlow::Continue(val) => #[allow(unreachable_code)] val,`
         let continue_arm = {
             let val_ident = Ident::with_dummy_span(sym::val);
             let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
-            let val_expr = self.arena.alloc(self.expr_ident_with_attrs(
-                span,
-                val_ident,
-                val_pat_nid,
-                attrs.clone(),
-            ));
+            let val_expr = self.expr_ident(span, val_ident, val_pat_nid);
+            self.lower_attrs(val_expr.hir_id, &attrs);
             let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
             self.arm(continue_pat, val_expr)
         };
@@ -1608,15 +1639,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         hir::Destination { label: None, target_id },
                         Some(from_residual_expr),
                     ),
-                    attrs,
                 ))
             } else {
-                self.arena.alloc(self.expr(
-                    try_span,
-                    hir::ExprKind::Ret(Some(from_residual_expr)),
-                    attrs,
-                ))
+                self.arena.alloc(self.expr(try_span, hir::ExprKind::Ret(Some(from_residual_expr))))
             };
+            self.lower_attrs(ret_expr.hir_id, &attrs);
 
             let break_pat = self.pat_cf_break(try_span, residual_local);
             self.arm(break_pat, ret_expr)
@@ -1681,18 +1708,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         span: Span,
         expr: &'hir hir::Expr<'hir>,
-        attrs: AttrVec,
     ) -> &'hir hir::Expr<'hir> {
-        self.arena.alloc(self.expr_drop_temps_mut(span, expr, attrs))
+        self.arena.alloc(self.expr_drop_temps_mut(span, expr))
     }
 
     pub(super) fn expr_drop_temps_mut(
         &mut self,
         span: Span,
         expr: &'hir hir::Expr<'hir>,
-        attrs: AttrVec,
     ) -> hir::Expr<'hir> {
-        self.expr(span, hir::ExprKind::DropTemps(expr), attrs)
+        self.expr(span, hir::ExprKind::DropTemps(expr))
     }
 
     fn expr_match(
@@ -1702,29 +1727,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
         arms: &'hir [hir::Arm<'hir>],
         source: hir::MatchSource,
     ) -> hir::Expr<'hir> {
-        self.expr(span, hir::ExprKind::Match(arg, arms, source), AttrVec::new())
+        self.expr(span, hir::ExprKind::Match(arg, arms, source))
     }
 
-    fn expr_break(&mut self, span: Span, attrs: AttrVec) -> hir::Expr<'hir> {
+    fn expr_break(&mut self, span: Span) -> hir::Expr<'hir> {
         let expr_break = hir::ExprKind::Break(self.lower_loop_destination(None), None);
-        self.expr(span, expr_break, attrs)
+        self.expr(span, expr_break)
     }
 
-    fn expr_break_alloc(&mut self, span: Span, attrs: AttrVec) -> &'hir hir::Expr<'hir> {
-        let expr_break = self.expr_break(span, attrs);
+    fn expr_break_alloc(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
+        let expr_break = self.expr_break(span);
         self.arena.alloc(expr_break)
     }
 
     fn expr_mut_addr_of(&mut self, span: Span, e: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
-        self.expr(
-            span,
-            hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e),
-            AttrVec::new(),
-        )
+        self.expr(span, hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e))
     }
 
     fn expr_unit(&mut self, sp: Span) -> &'hir hir::Expr<'hir> {
-        self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[]), AttrVec::new()))
+        self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[])))
     }
 
     fn expr_call_mut(
@@ -1733,7 +1754,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         e: &'hir hir::Expr<'hir>,
         args: &'hir [hir::Expr<'hir>],
     ) -> hir::Expr<'hir> {
-        self.expr(span, hir::ExprKind::Call(e, args), AttrVec::new())
+        self.expr(span, hir::ExprKind::Call(e, args))
     }
 
     fn expr_call(
@@ -1752,8 +1773,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         args: &'hir [hir::Expr<'hir>],
         hir_id: Option<hir::HirId>,
     ) -> hir::Expr<'hir> {
-        let path =
-            self.arena.alloc(self.expr_lang_item_path(span, lang_item, AttrVec::new(), hir_id));
+        let path = self.arena.alloc(self.expr_lang_item_path(span, lang_item, hir_id));
         self.expr_call_mut(span, path, args)
     }
 
@@ -1771,13 +1791,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         span: Span,
         lang_item: hir::LangItem,
-        attrs: AttrVec,
         hir_id: Option<hir::HirId>,
     ) -> hir::Expr<'hir> {
         self.expr(
             span,
             hir::ExprKind::Path(hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id)),
-            attrs,
         )
     }
 
@@ -1792,19 +1810,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     pub(super) fn expr_ident_mut(
         &mut self,
-        sp: Span,
-        ident: Ident,
-        binding: hir::HirId,
-    ) -> hir::Expr<'hir> {
-        self.expr_ident_with_attrs(sp, ident, binding, AttrVec::new())
-    }
-
-    fn expr_ident_with_attrs(
-        &mut self,
         span: Span,
         ident: Ident,
         binding: hir::HirId,
-        attrs: AttrVec,
     ) -> hir::Expr<'hir> {
         let hir_id = self.next_id();
         let res = Res::Local(binding);
@@ -1817,7 +1825,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }),
         ));
 
-        self.expr(span, expr_path, attrs)
+        self.expr(span, expr_path)
     }
 
     fn expr_unsafe(&mut self, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
@@ -1836,32 +1844,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 }),
                 None,
             ),
-            AttrVec::new(),
         )
     }
 
     fn expr_block_empty(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
         let blk = self.block_all(span, &[], None);
-        let expr = self.expr_block(blk, AttrVec::new());
+        let expr = self.expr_block(blk);
         self.arena.alloc(expr)
     }
 
-    pub(super) fn expr_block(
-        &mut self,
-        b: &'hir hir::Block<'hir>,
-        attrs: AttrVec,
-    ) -> hir::Expr<'hir> {
-        self.expr(b.span, hir::ExprKind::Block(b, None), attrs)
+    pub(super) fn expr_block(&mut self, b: &'hir hir::Block<'hir>) -> hir::Expr<'hir> {
+        self.expr(b.span, hir::ExprKind::Block(b, None))
     }
 
-    pub(super) fn expr(
-        &mut self,
-        span: Span,
-        kind: hir::ExprKind<'hir>,
-        attrs: AttrVec,
-    ) -> hir::Expr<'hir> {
+    pub(super) fn expr(&mut self, span: Span, kind: hir::ExprKind<'hir>) -> hir::Expr<'hir> {
         let hir_id = self.next_id();
-        self.lower_attrs(hir_id, &attrs);
         hir::Expr { hir_id, kind, span: self.lower_span(span) }
     }
 
diff --git a/compiler/rustc_ast_lowering/src/index.rs b/compiler/rustc_ast_lowering/src/index.rs
index f1851d7b4..fe0bd4381 100644
--- a/compiler/rustc_ast_lowering/src/index.rs
+++ b/compiler/rustc_ast_lowering/src/index.rs
@@ -77,7 +77,7 @@ impl<'a, 'hir> NodeCollector<'a, 'hir> {
             if hir_id.owner != self.owner {
                 span_bug!(
                     span,
-                    "inconsistent DepNode at `{:?}` for `{:?}`: \
+                    "inconsistent HirId at `{:?}` for `{:?}`: \
                      current_dep_node_owner={} ({:?}), hir_id.owner={} ({:?})",
                     self.source_map.span_to_diagnostic_string(span),
                     node,
@@ -145,7 +145,7 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
     fn visit_item(&mut self, i: &'hir Item<'hir>) {
         debug_assert_eq!(i.owner_id, self.owner);
         self.with_parent(i.hir_id(), |this| {
-            if let ItemKind::Struct(ref struct_def, _) = i.kind {
+            if let ItemKind::Struct(struct_def, _) = &i.kind {
                 // If this is a tuple or unit-like struct, register the constructor.
                 if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
                     this.insert(i.span, ctor_hir_id, Node::Ctor(struct_def));
@@ -303,12 +303,12 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
     }
 
     fn visit_lifetime(&mut self, lifetime: &'hir Lifetime) {
-        self.insert(lifetime.span, lifetime.hir_id, Node::Lifetime(lifetime));
+        self.insert(lifetime.ident.span, lifetime.hir_id, Node::Lifetime(lifetime));
     }
 
     fn visit_variant(&mut self, v: &'hir Variant<'hir>) {
-        self.insert(v.span, v.id, Node::Variant(v));
-        self.with_parent(v.id, |this| {
+        self.insert(v.span, v.hir_id, Node::Variant(v));
+        self.with_parent(v.hir_id, |this| {
             // Register the constructor of this variant.
             if let Some(ctor_hir_id) = v.data.ctor_hir_id() {
                 this.insert(v.span, ctor_hir_id, Node::Ctor(&v.data));
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 76316a574..d73d6d391 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -6,7 +6,6 @@ use super::{FnDeclKind, LoweringContext, ParamMode};
 use rustc_ast::ptr::P;
 use rustc_ast::visit::AssocCtxt;
 use rustc_ast::*;
-use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sorted_map::SortedMap;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -20,8 +19,7 @@ use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{Span, Symbol};
 use rustc_target::spec::abi;
 use smallvec::{smallvec, SmallVec};
-
-use std::iter;
+use thin_vec::ThinVec;
 
 pub(super) struct ItemLowerer<'a, 'hir> {
     pub(super) tcx: TyCtxt<'hir>,
@@ -67,7 +65,7 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             // HirId handling.
             bodies: Vec::new(),
             attrs: SortedMap::default(),
-            children: FxHashMap::default(),
+            children: Vec::default(),
             current_hir_id_owner: hir::CRATE_OWNER_ID,
             item_local_id_counter: hir::ItemLocalId::new(0),
             node_id_to_local_id: Default::default(),
@@ -86,7 +84,7 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             impl_trait_defs: Vec::new(),
             impl_trait_bounds: Vec::new(),
             allow_try_trait: Some([sym::try_trait_v2, sym::yeet_desugar_details][..].into()),
-            allow_gen_future: Some([sym::gen_future][..].into()),
+            allow_gen_future: Some([sym::gen_future, sym::closure_track_caller][..].into()),
             allow_into_future: Some([sym::into_future][..].into()),
             generics_def_id_map: Default::default(),
         };
@@ -143,7 +141,7 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             // This is used to track which lifetimes have already been defined,
             // and which need to be replicated when lowering an async fn.
             match parent_hir.node().expect_item().kind {
-                hir::ItemKind::Impl(hir::Impl { ref of_trait, .. }) => {
+                hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
                     lctx.is_in_trait_impl = of_trait.is_some();
                 }
                 _ => {}
@@ -179,37 +177,23 @@ impl<'hir> LoweringContext<'_, 'hir> {
     pub(super) fn lower_item_ref(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
         let mut node_ids =
             smallvec![hir::ItemId { owner_id: hir::OwnerId { def_id: self.local_def_id(i.id) } }];
-        if let ItemKind::Use(ref use_tree) = &i.kind {
-            self.lower_item_id_use_tree(use_tree, i.id, &mut node_ids);
+        if let ItemKind::Use(use_tree) = &i.kind {
+            self.lower_item_id_use_tree(use_tree, &mut node_ids);
         }
         node_ids
     }
 
-    fn lower_item_id_use_tree(
-        &mut self,
-        tree: &UseTree,
-        base_id: NodeId,
-        vec: &mut SmallVec<[hir::ItemId; 1]>,
-    ) {
-        match tree.kind {
-            UseTreeKind::Nested(ref nested_vec) => {
+    fn lower_item_id_use_tree(&mut self, tree: &UseTree, vec: &mut SmallVec<[hir::ItemId; 1]>) {
+        match &tree.kind {
+            UseTreeKind::Nested(nested_vec) => {
                 for &(ref nested, id) in nested_vec {
                     vec.push(hir::ItemId {
                         owner_id: hir::OwnerId { def_id: self.local_def_id(id) },
                     });
-                    self.lower_item_id_use_tree(nested, id, vec);
-                }
-            }
-            UseTreeKind::Glob => {}
-            UseTreeKind::Simple(_, id1, id2) => {
-                for (_, &id) in
-                    iter::zip(self.expect_full_res_from_use(base_id).skip(1), &[id1, id2])
-                {
-                    vec.push(hir::ItemId {
-                        owner_id: hir::OwnerId { def_id: self.local_def_id(id) },
-                    });
+                    self.lower_item_id_use_tree(nested, vec);
                 }
             }
+            UseTreeKind::Simple(..) | UseTreeKind::Glob => {}
         }
     }
 
@@ -239,26 +223,26 @@ impl<'hir> LoweringContext<'_, 'hir> {
         vis_span: Span,
         i: &ItemKind,
     ) -> hir::ItemKind<'hir> {
-        match *i {
-            ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
-            ItemKind::Use(ref use_tree) => {
+        match i {
+            ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(*orig_name),
+            ItemKind::Use(use_tree) => {
                 // Start with an empty prefix.
-                let prefix = Path { segments: vec![], span: use_tree.span, tokens: None };
+                let prefix = Path { segments: ThinVec::new(), span: use_tree.span, tokens: None };
 
                 self.lower_use_tree(use_tree, &prefix, id, vis_span, ident, attrs)
             }
-            ItemKind::Static(ref t, m, ref e) => {
+            ItemKind::Static(t, m, e) => {
                 let (ty, body_id) = self.lower_const_item(t, span, e.as_deref());
-                hir::ItemKind::Static(ty, m, body_id)
+                hir::ItemKind::Static(ty, *m, body_id)
             }
-            ItemKind::Const(_, ref t, ref e) => {
+            ItemKind::Const(_, t, e) => {
                 let (ty, body_id) = self.lower_const_item(t, span, e.as_deref());
                 hir::ItemKind::Const(ty, body_id)
             }
             ItemKind::Fn(box Fn {
-                sig: FnSig { ref decl, header, span: fn_sig_span },
-                ref generics,
-                ref body,
+                sig: FnSig { decl, header, span: fn_sig_span },
+                generics,
+                body,
                 ..
             }) => {
                 self.with_new_scopes(|this| {
@@ -269,43 +253,41 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     // only cares about the input argument patterns in the function
                     // declaration (decl), not the return types.
                     let asyncness = header.asyncness;
-                    let body_id =
-                        this.lower_maybe_async_body(span, &decl, asyncness, body.as_deref());
+                    let body_id = this.lower_maybe_async_body(
+                        span,
+                        hir_id,
+                        &decl,
+                        asyncness,
+                        body.as_deref(),
+                    );
 
                     let mut itctx = ImplTraitContext::Universal;
                     let (generics, decl) = this.lower_generics(generics, id, &mut itctx, |this| {
                         let ret_id = asyncness.opt_return_id();
-                        this.lower_fn_decl(&decl, Some(id), fn_sig_span, FnDeclKind::Fn, ret_id)
+                        this.lower_fn_decl(&decl, id, *fn_sig_span, FnDeclKind::Fn, ret_id)
                     });
                     let sig = hir::FnSig {
                         decl,
-                        header: this.lower_fn_header(header),
-                        span: this.lower_span(fn_sig_span),
+                        header: this.lower_fn_header(*header),
+                        span: this.lower_span(*fn_sig_span),
                     };
                     hir::ItemKind::Fn(sig, generics, body_id)
                 })
             }
-            ItemKind::Mod(_, ref mod_kind) => match mod_kind {
+            ItemKind::Mod(_, mod_kind) => match mod_kind {
                 ModKind::Loaded(items, _, spans) => {
                     hir::ItemKind::Mod(self.lower_mod(items, spans))
                 }
                 ModKind::Unloaded => panic!("`mod` items should have been loaded by now"),
             },
-            ItemKind::ForeignMod(ref fm) => hir::ItemKind::ForeignMod {
+            ItemKind::ForeignMod(fm) => hir::ItemKind::ForeignMod {
                 abi: fm.abi.map_or(abi::Abi::FALLBACK, |abi| self.lower_abi(abi)),
                 items: self
                     .arena
                     .alloc_from_iter(fm.items.iter().map(|x| self.lower_foreign_item_ref(x))),
             },
-            ItemKind::GlobalAsm(ref asm) => {
-                hir::ItemKind::GlobalAsm(self.lower_inline_asm(span, asm))
-            }
-            ItemKind::TyAlias(box TyAlias {
-                ref generics,
-                where_clauses,
-                ty: Some(ref ty),
-                ..
-            }) => {
+            ItemKind::GlobalAsm(asm) => hir::ItemKind::GlobalAsm(self.lower_inline_asm(span, asm)),
+            ItemKind::TyAlias(box TyAlias { generics, where_clauses, ty: Some(ty), .. }) => {
                 // We lower
                 //
                 // type Foo = impl Trait
@@ -315,7 +297,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // type Foo = Foo1
                 // opaque type Foo1: Trait
                 let mut generics = generics.clone();
-                add_ty_alias_where_clause(&mut generics, where_clauses, true);
+                add_ty_alias_where_clause(&mut generics, *where_clauses, true);
                 let (generics, ty) = self.lower_generics(
                     &generics,
                     id,
@@ -324,9 +306,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 hir::ItemKind::TyAlias(ty, generics)
             }
-            ItemKind::TyAlias(box TyAlias {
-                ref generics, ref where_clauses, ty: None, ..
-            }) => {
+            ItemKind::TyAlias(box TyAlias { generics, where_clauses, ty: None, .. }) => {
                 let mut generics = generics.clone();
                 add_ty_alias_where_clause(&mut generics, *where_clauses, true);
                 let (generics, ty) = self.lower_generics(
@@ -337,7 +317,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 hir::ItemKind::TyAlias(ty, generics)
             }
-            ItemKind::Enum(ref enum_definition, ref generics) => {
+            ItemKind::Enum(enum_definition, generics) => {
                 let (generics, variants) = self.lower_generics(
                     generics,
                     id,
@@ -350,7 +330,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 hir::ItemKind::Enum(hir::EnumDef { variants }, generics)
             }
-            ItemKind::Struct(ref struct_def, ref generics) => {
+            ItemKind::Struct(struct_def, generics) => {
                 let (generics, struct_def) = self.lower_generics(
                     generics,
                     id,
@@ -359,7 +339,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 hir::ItemKind::Struct(struct_def, generics)
             }
-            ItemKind::Union(ref vdata, ref generics) => {
+            ItemKind::Union(vdata, generics) => {
                 let (generics, vdata) = self.lower_generics(
                     generics,
                     id,
@@ -373,10 +353,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 polarity,
                 defaultness,
                 constness,
-                generics: ref ast_generics,
-                of_trait: ref trait_ref,
-                self_ty: ref ty,
-                items: ref impl_items,
+                generics: ast_generics,
+                of_trait: trait_ref,
+                self_ty: ty,
+                items: impl_items,
             }) => {
                 // Lower the "impl header" first. This ordering is important
                 // for in-band lifetimes! Consider `'a` here:
@@ -414,30 +394,24 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // `defaultness.has_value()` is never called for an `impl`, always `true` in order
                 // to not cause an assertion failure inside the `lower_defaultness` function.
                 let has_val = true;
-                let (defaultness, defaultness_span) = self.lower_defaultness(defaultness, has_val);
+                let (defaultness, defaultness_span) = self.lower_defaultness(*defaultness, has_val);
                 let polarity = match polarity {
                     ImplPolarity::Positive => ImplPolarity::Positive,
-                    ImplPolarity::Negative(s) => ImplPolarity::Negative(self.lower_span(s)),
+                    ImplPolarity::Negative(s) => ImplPolarity::Negative(self.lower_span(*s)),
                 };
                 hir::ItemKind::Impl(self.arena.alloc(hir::Impl {
-                    unsafety: self.lower_unsafety(unsafety),
+                    unsafety: self.lower_unsafety(*unsafety),
                     polarity,
                     defaultness,
                     defaultness_span,
-                    constness: self.lower_constness(constness),
+                    constness: self.lower_constness(*constness),
                     generics,
                     of_trait: trait_ref,
                     self_ty: lowered_ty,
                     items: new_impl_items,
                 }))
             }
-            ItemKind::Trait(box Trait {
-                is_auto,
-                unsafety,
-                ref generics,
-                ref bounds,
-                ref items,
-            }) => {
+            ItemKind::Trait(box Trait { is_auto, unsafety, generics, bounds, items }) => {
                 let (generics, (unsafety, items, bounds)) = self.lower_generics(
                     generics,
                     id,
@@ -450,13 +424,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         let items = this.arena.alloc_from_iter(
                             items.iter().map(|item| this.lower_trait_item_ref(item)),
                         );
-                        let unsafety = this.lower_unsafety(unsafety);
+                        let unsafety = this.lower_unsafety(*unsafety);
                         (unsafety, items, bounds)
                     },
                 );
-                hir::ItemKind::Trait(is_auto, unsafety, generics, bounds, items)
+                hir::ItemKind::Trait(*is_auto, unsafety, generics, bounds, items)
             }
-            ItemKind::TraitAlias(ref generics, ref bounds) => {
+            ItemKind::TraitAlias(generics, bounds) => {
                 let (generics, bounds) = self.lower_generics(
                     generics,
                     id,
@@ -470,10 +444,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 hir::ItemKind::TraitAlias(generics, bounds)
             }
-            ItemKind::MacroDef(MacroDef { ref body, macro_rules }) => {
-                let body = P(self.lower_mac_args(body));
+            ItemKind::MacroDef(MacroDef { body, macro_rules }) => {
+                let body = P(self.lower_delim_args(body));
                 let macro_kind = self.resolver.decl_macro_kind(self.local_def_id(id));
-                hir::ItemKind::Macro(ast::MacroDef { body, macro_rules }, macro_kind)
+                hir::ItemKind::Macro(ast::MacroDef { body, macro_rules: *macro_rules }, macro_kind)
             }
             ItemKind::MacCall(..) => {
                 panic!("`TyMac` should have been expanded by now")
@@ -505,7 +479,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let segments = prefix.segments.iter().chain(path.segments.iter()).cloned().collect();
 
         match tree.kind {
-            UseTreeKind::Simple(rename, id1, id2) => {
+            UseTreeKind::Simple(rename) => {
                 *ident = tree.ident();
 
                 // First, apply the prefix to the path.
@@ -521,66 +495,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     }
                 }
 
-                let mut resolutions = self.expect_full_res_from_use(id).fuse();
-                // We want to return *something* from this function, so hold onto the first item
-                // for later.
-                let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
-
-                // Here, we are looping over namespaces, if they exist for the definition
-                // being imported. We only handle type and value namespaces because we
-                // won't be dealing with macros in the rest of the compiler.
-                // Essentially a single `use` which imports two names is desugared into
-                // two imports.
-                for new_node_id in [id1, id2] {
-                    let new_id = self.local_def_id(new_node_id);
-                    let Some(res) = resolutions.next() else {
-                        // Associate an HirId to both ids even if there is no resolution.
-                        let _old = self.children.insert(
-                            new_id,
-                            hir::MaybeOwner::NonOwner(hir::HirId::make_owner(new_id)),
-                        );
-                        debug_assert!(_old.is_none());
-                        continue;
-                    };
-                    let ident = *ident;
-                    let mut path = path.clone();
-                    for seg in &mut path.segments {
-                        // Give the cloned segment the same resolution information
-                        // as the old one (this is needed for stability checking).
-                        let new_id = self.next_node_id();
-                        self.resolver.clone_res(seg.id, new_id);
-                        seg.id = new_id;
-                    }
-                    let span = path.span;
-
-                    self.with_hir_id_owner(new_node_id, |this| {
-                        let res = this.lower_res(res);
-                        let path = this.lower_path_extra(res, &path, ParamMode::Explicit);
-                        let kind = hir::ItemKind::Use(path, hir::UseKind::Single);
-                        if let Some(attrs) = attrs {
-                            this.attrs.insert(hir::ItemLocalId::new(0), attrs);
-                        }
-
-                        let item = hir::Item {
-                            owner_id: hir::OwnerId { def_id: new_id },
-                            ident: this.lower_ident(ident),
-                            kind,
-                            vis_span,
-                            span: this.lower_span(span),
-                        };
-                        hir::OwnerNode::Item(this.arena.alloc(item))
-                    });
-                }
-
-                let path = self.lower_path_extra(ret_res, &path, ParamMode::Explicit);
+                let res =
+                    self.expect_full_res_from_use(id).map(|res| self.lower_res(res)).collect();
+                let path = self.lower_use_path(res, &path, ParamMode::Explicit);
                 hir::ItemKind::Use(path, hir::UseKind::Single)
             }
             UseTreeKind::Glob => {
-                let path = self.lower_path(
-                    id,
-                    &Path { segments, span: path.span, tokens: None },
-                    ParamMode::Explicit,
-                );
+                let res = self.expect_full_res(id);
+                let res = smallvec![self.lower_res(res)];
+                let path = Path { segments, span: path.span, tokens: None };
+                let path = self.lower_use_path(res, &path, ParamMode::Explicit);
                 hir::ItemKind::Use(path, hir::UseKind::Glob)
             }
             UseTreeKind::Nested(ref trees) => {
@@ -650,9 +574,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     });
                 }
 
-                let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
-                let res = self.lower_res(res);
-                let path = self.lower_path_extra(res, &prefix, ParamMode::Explicit);
+                let res =
+                    self.expect_full_res_from_use(id).map(|res| self.lower_res(res)).collect();
+                let path = self.lower_use_path(res, &prefix, ParamMode::Explicit);
                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
             }
         }
@@ -665,8 +589,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let item = hir::ForeignItem {
             owner_id,
             ident: self.lower_ident(i.ident),
-            kind: match i.kind {
-                ForeignItemKind::Fn(box Fn { ref sig, ref generics, .. }) => {
+            kind: match &i.kind {
+                ForeignItemKind::Fn(box Fn { sig, generics, .. }) => {
                     let fdec = &sig.decl;
                     let mut itctx = ImplTraitContext::Universal;
                     let (generics, (fn_dec, fn_args)) =
@@ -675,7 +599,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                 // Disallow `impl Trait` in foreign items.
                                 this.lower_fn_decl(
                                     fdec,
-                                    None,
+                                    i.id,
                                     sig.span,
                                     FnDeclKind::ExternFn,
                                     None,
@@ -686,10 +610,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
                 }
-                ForeignItemKind::Static(ref t, m, _) => {
+                ForeignItemKind::Static(t, m, _) => {
                     let ty =
                         self.lower_ty(t, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
-                    hir::ForeignItemKind::Static(ty, m)
+                    hir::ForeignItemKind::Static(ty, *m)
                 }
                 ForeignItemKind::TyAlias(..) => hir::ForeignItemKind::Type,
                 ForeignItemKind::MacCall(_) => panic!("macro shouldn't exist here"),
@@ -709,11 +633,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     fn lower_variant(&mut self, v: &Variant) -> hir::Variant<'hir> {
-        let id = self.lower_node_id(v.id);
-        self.lower_attrs(id, &v.attrs);
+        let hir_id = self.lower_node_id(v.id);
+        self.lower_attrs(hir_id, &v.attrs);
         hir::Variant {
-            id,
-            data: self.lower_variant_data(id, &v.data),
+            hir_id,
+            def_id: self.local_def_id(v.id),
+            data: self.lower_variant_data(hir_id, &v.data),
             disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
             ident: self.lower_ident(v.ident),
             span: self.lower_span(v.span),
@@ -725,32 +650,33 @@ impl<'hir> LoweringContext<'_, 'hir> {
         parent_id: hir::HirId,
         vdata: &VariantData,
     ) -> hir::VariantData<'hir> {
-        match *vdata {
-            VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
+        match vdata {
+            VariantData::Struct(fields, recovered) => hir::VariantData::Struct(
                 self.arena
                     .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_field_def(f))),
-                recovered,
+                *recovered,
             ),
-            VariantData::Tuple(ref fields, id) => {
-                let ctor_id = self.lower_node_id(id);
+            VariantData::Tuple(fields, id) => {
+                let ctor_id = self.lower_node_id(*id);
                 self.alias_attrs(ctor_id, parent_id);
                 hir::VariantData::Tuple(
                     self.arena.alloc_from_iter(
                         fields.iter().enumerate().map(|f| self.lower_field_def(f)),
                     ),
                     ctor_id,
+                    self.local_def_id(*id),
                 )
             }
             VariantData::Unit(id) => {
-                let ctor_id = self.lower_node_id(id);
+                let ctor_id = self.lower_node_id(*id);
                 self.alias_attrs(ctor_id, parent_id);
-                hir::VariantData::Unit(ctor_id)
+                hir::VariantData::Unit(ctor_id, self.local_def_id(*id))
             }
         }
     }
 
     fn lower_field_def(&mut self, (index, f): (usize, &FieldDef)) -> hir::FieldDef<'hir> {
-        let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
+        let ty = if let TyKind::Path(qself, path) = &f.ty.kind {
             let t = self.lower_path_ty(
                 &f.ty,
                 qself,
@@ -767,6 +693,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         hir::FieldDef {
             span: self.lower_span(f.span),
             hir_id,
+            def_id: self.local_def_id(f.id),
             ident: match f.ident {
                 Some(ident) => self.lower_ident(ident),
                 // FIXME(jseyfried): positional field hygiene.
@@ -779,15 +706,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_trait_item(&mut self, i: &AssocItem) -> &'hir hir::TraitItem<'hir> {
         let hir_id = self.lower_node_id(i.id);
+        self.lower_attrs(hir_id, &i.attrs);
         let trait_item_def_id = hir_id.expect_owner();
 
-        let (generics, kind, has_default) = match i.kind {
-            AssocItemKind::Const(_, ref ty, ref default) => {
+        let (generics, kind, has_default) = match &i.kind {
+            AssocItemKind::Const(_, ty, default) => {
                 let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
                 let body = default.as_ref().map(|x| self.lower_const_body(i.span, Some(x)));
                 (hir::Generics::empty(), hir::TraitItemKind::Const(ty, body), body.is_some())
             }
-            AssocItemKind::Fn(box Fn { ref sig, ref generics, body: None, .. }) => {
+            AssocItemKind::Fn(box Fn { sig, generics, body: None, .. }) => {
                 let asyncness = sig.header.asyncness;
                 let names = self.lower_fn_params_to_names(&sig.decl);
                 let (generics, sig) = self.lower_method_sig(
@@ -799,10 +727,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 (generics, hir::TraitItemKind::Fn(sig, hir::TraitFn::Required(names)), false)
             }
-            AssocItemKind::Fn(box Fn { ref sig, ref generics, body: Some(ref body), .. }) => {
+            AssocItemKind::Fn(box Fn { sig, generics, body: Some(body), .. }) => {
                 let asyncness = sig.header.asyncness;
                 let body_id =
-                    self.lower_maybe_async_body(i.span, &sig.decl, asyncness, Some(&body));
+                    self.lower_maybe_async_body(i.span, hir_id, &sig.decl, asyncness, Some(&body));
                 let (generics, sig) = self.lower_method_sig(
                     generics,
                     sig,
@@ -812,15 +740,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 (generics, hir::TraitItemKind::Fn(sig, hir::TraitFn::Provided(body_id)), true)
             }
-            AssocItemKind::Type(box TyAlias {
-                ref generics,
-                where_clauses,
-                ref bounds,
-                ref ty,
-                ..
-            }) => {
+            AssocItemKind::Type(box TyAlias { generics, where_clauses, bounds, ty, .. }) => {
                 let mut generics = generics.clone();
-                add_ty_alias_where_clause(&mut generics, where_clauses, false);
+                add_ty_alias_where_clause(&mut generics, *where_clauses, false);
                 let (generics, kind) = self.lower_generics(
                     &generics,
                     i.id,
@@ -843,7 +765,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
             AssocItemKind::MacCall(..) => panic!("macro item shouldn't exist at this point"),
         };
 
-        self.lower_attrs(hir_id, &i.attrs);
         let item = hir::TraitItem {
             owner_id: trait_item_def_id,
             ident: self.lower_ident(i.ident),
@@ -875,13 +796,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     /// Construct `ExprKind::Err` for the given `span`.
     pub(crate) fn expr_err(&mut self, span: Span) -> hir::Expr<'hir> {
-        self.expr(span, hir::ExprKind::Err, AttrVec::new())
+        self.expr(span, hir::ExprKind::Err)
     }
 
     fn lower_impl_item(&mut self, i: &AssocItem) -> &'hir hir::ImplItem<'hir> {
         // Since `default impl` is not yet implemented, this is always true in impls.
         let has_value = true;
         let (defaultness, _) = self.lower_defaultness(i.kind.defaultness(), has_value);
+        let hir_id = self.lower_node_id(i.id);
+        self.lower_attrs(hir_id, &i.attrs);
 
         let (generics, kind) = match &i.kind {
             AssocItemKind::Const(_, ty, expr) => {
@@ -894,8 +817,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
             AssocItemKind::Fn(box Fn { sig, generics, body, .. }) => {
                 self.current_item = Some(i.span);
                 let asyncness = sig.header.asyncness;
-                let body_id =
-                    self.lower_maybe_async_body(i.span, &sig.decl, asyncness, body.as_deref());
+                let body_id = self.lower_maybe_async_body(
+                    i.span,
+                    hir_id,
+                    &sig.decl,
+                    asyncness,
+                    body.as_deref(),
+                );
                 let (generics, sig) = self.lower_method_sig(
                     generics,
                     sig,
@@ -928,8 +856,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
             AssocItemKind::MacCall(..) => panic!("`TyMac` should have been expanded by now"),
         };
 
-        let hir_id = self.lower_node_id(i.id);
-        self.lower_attrs(hir_id, &i.attrs);
         let item = hir::ImplItem {
             owner_id: hir_id.expect_owner(),
             ident: self.lower_ident(i.ident),
@@ -1062,6 +988,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_maybe_async_body(
         &mut self,
         span: Span,
+        fn_id: hir::HirId,
         decl: &FnDecl,
         asyncness: Async,
         body: Option<&Block>,
@@ -1212,6 +1139,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
             let async_expr = this.make_async_expr(
                 CaptureBy::Value,
+                Some(fn_id),
                 closure_id,
                 None,
                 body.span,
@@ -1223,11 +1151,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     // Transform into `drop-temps { <user-body> }`, an expression:
                     let desugared_span =
                         this.mark_span_with_reason(DesugaringKind::Async, user_body.span, None);
-                    let user_body = this.expr_drop_temps(
-                        desugared_span,
-                        this.arena.alloc(user_body),
-                        AttrVec::new(),
-                    );
+                    let user_body =
+                        this.expr_drop_temps(desugared_span, this.arena.alloc(user_body));
 
                     // As noted above, create the final block like
                     //
@@ -1244,14 +1169,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         Some(user_body),
                     );
 
-                    this.expr_block(body, AttrVec::new())
+                    this.expr_block(body)
                 },
             );
 
-            (
-                this.arena.alloc_from_iter(parameters),
-                this.expr(body.span, async_expr, AttrVec::new()),
-            )
+            (this.arena.alloc_from_iter(parameters), this.expr(body.span, async_expr))
         })
     }
 
@@ -1266,7 +1188,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let header = self.lower_fn_header(sig.header);
         let mut itctx = ImplTraitContext::Universal;
         let (generics, decl) = self.lower_generics(generics, id, &mut itctx, |this| {
-            this.lower_fn_decl(&sig.decl, Some(id), sig.span, kind, is_async)
+            this.lower_fn_decl(&sig.decl, id, sig.span, kind, is_async)
         });
         (generics, hir::FnSig { header, decl, span: self.lower_span(sig.span) })
     }
@@ -1352,7 +1274,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // keep track of the Span info. Now, `add_implicitly_sized` in `AstConv` checks both param bounds and
         // where clauses for `?Sized`.
         for pred in &generics.where_clause.predicates {
-            let WherePredicate::BoundPredicate(ref bound_pred) = *pred else {
+            let WherePredicate::BoundPredicate(bound_pred) = pred else {
                 continue;
             };
             let compute_is_param = || {
@@ -1498,10 +1420,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 }))
             }
             GenericParamKind::Lifetime => {
-                let ident_span = self.lower_span(ident.span);
                 let ident = self.lower_ident(ident);
                 let lt_id = self.next_node_id();
-                let lifetime = self.new_named_lifetime(id, lt_id, ident_span, ident);
+                let lifetime = self.new_named_lifetime(id, lt_id, ident);
                 Some(hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
                     lifetime,
                     span,
@@ -1513,11 +1434,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate<'hir> {
-        match *pred {
+        match pred {
             WherePredicate::BoundPredicate(WhereBoundPredicate {
-                ref bound_generic_params,
-                ref bounded_ty,
-                ref bounds,
+                bound_generic_params,
+                bounded_ty,
+                bounds,
                 span,
             }) => hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
                 hir_id: self.next_id(),
@@ -1530,29 +1451,27 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         &ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
                     )
                 })),
-                span: self.lower_span(span),
+                span: self.lower_span(*span),
                 origin: PredicateOrigin::WhereClause,
             }),
-            WherePredicate::RegionPredicate(WhereRegionPredicate {
-                ref lifetime,
-                ref bounds,
-                span,
-            }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
-                span: self.lower_span(span),
-                lifetime: self.lower_lifetime(lifetime),
-                bounds: self.lower_param_bounds(
-                    bounds,
-                    &ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
-                ),
-                in_where_clause: true,
-            }),
-            WherePredicate::EqPredicate(WhereEqPredicate { ref lhs_ty, ref rhs_ty, span }) => {
+            WherePredicate::RegionPredicate(WhereRegionPredicate { lifetime, bounds, span }) => {
+                hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
+                    span: self.lower_span(*span),
+                    lifetime: self.lower_lifetime(lifetime),
+                    bounds: self.lower_param_bounds(
+                        bounds,
+                        &ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
+                    ),
+                    in_where_clause: true,
+                })
+            }
+            WherePredicate::EqPredicate(WhereEqPredicate { lhs_ty, rhs_ty, span }) => {
                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
                     lhs_ty: self
                         .lower_ty(lhs_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type)),
                     rhs_ty: self
                         .lower_ty(rhs_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type)),
-                    span: self.lower_span(span),
+                    span: self.lower_span(*span),
                 })
             }
         }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index ff29d15f1..4fa18907f 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -34,7 +34,6 @@
 #![feature(let_chains)]
 #![feature(never_type)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 
@@ -61,8 +60,8 @@ use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_hir::definitions::DefPathData;
 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
 use rustc_index::vec::{Idx, IndexVec};
+use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
-use rustc_middle::{bug, span_bug};
 use rustc_session::parse::feature_err;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::DesugaringKind;
@@ -107,7 +106,7 @@ struct LoweringContext<'a, 'hir> {
     /// Attributes inside the owner being lowered.
     attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
     /// Collect items that were created by lowering the current owner.
-    children: FxHashMap<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
+    children: Vec<(LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>)>,
 
     generator_kind: Option<hir::GeneratorKind>,
 
@@ -260,6 +259,8 @@ enum ImplTraitContext {
     },
     /// Impl trait in type aliases.
     TypeAliasesOpaqueTy,
+    /// `impl Trait` is unstably accepted in this position.
+    FeatureGated(ImplTraitPosition, Symbol),
     /// `impl Trait` is not accepted in this position.
     Disallowed(ImplTraitPosition),
 }
@@ -328,7 +329,14 @@ enum FnDeclKind {
 }
 
 impl FnDeclKind {
-    fn impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
+    fn param_impl_trait_allowed(&self) -> bool {
+        match self {
+            FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
+            _ => false,
+        }
+    }
+
+    fn return_impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
         match self {
             FnDeclKind::Fn | FnDeclKind::Inherent => true,
             FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
@@ -481,6 +489,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         parent: LocalDefId,
         node_id: ast::NodeId,
         data: DefPathData,
+        span: Span,
     ) -> LocalDefId {
         debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
         assert!(
@@ -491,7 +500,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.tcx.hir().def_key(self.local_def_id(node_id)),
         );
 
-        let def_id = self.tcx.create_def(parent, data);
+        let def_id = self.tcx.at(span).create_def(parent, data).def_id();
 
         debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
         self.resolver.node_id_to_def_id.insert(node_id, def_id);
@@ -611,8 +620,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.impl_trait_defs = current_impl_trait_defs;
         self.impl_trait_bounds = current_impl_trait_bounds;
 
-        let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
-        debug_assert!(_old.is_none())
+        debug_assert!(self.children.iter().find(|(id, _)| id == &def_id).is_none());
+        self.children.push((def_id, hir::MaybeOwner::Owner(info)));
     }
 
     /// Installs the remapping `remap` in scope while `f` is being executed.
@@ -719,8 +728,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                 assert_ne!(local_id, hir::ItemLocalId::new(0));
                 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
-                    // Do not override a `MaybeOwner::Owner` that may already here.
-                    self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
+                    self.children.push((def_id, hir::MaybeOwner::NonOwner(hir_id)));
                     self.local_id_to_def_id.insert(local_id, def_id);
                 }
 
@@ -818,6 +826,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     self.current_hir_id_owner.def_id,
                     param,
                     DefPathData::LifetimeNs(kw::UnderscoreLifetime),
+                    ident.span,
                 );
                 debug!(?_def_id);
 
@@ -830,8 +839,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             ),
         };
         let hir_id = self.lower_node_id(node_id);
+        let def_id = self.local_def_id(node_id);
         Some(hir::GenericParam {
             hir_id,
+            def_id,
             name,
             span: self.lower_span(ident.span),
             pure_wrt_drop: false,
@@ -911,7 +922,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
                 item: AttrItem {
                     path: normal.item.path.clone(),
-                    args: self.lower_mac_args(&normal.item.args),
+                    args: self.lower_attr_args(&normal.item.args),
                     tokens: None,
                 },
                 tokens: None,
@@ -931,51 +942,39 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         }
     }
 
-    fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
-        match *args {
-            MacArgs::Empty => MacArgs::Empty,
-            MacArgs::Delimited(dspan, delim, ref tokens) => {
-                // This is either a non-key-value attribute, or a `macro_rules!` body.
-                // We either not have any nonterminals present (in the case of an attribute),
-                // or have tokens available for all nonterminals in the case of a nested
-                // `macro_rules`: e.g:
-                //
-                // ```rust
-                // macro_rules! outer {
-                //     ($e:expr) => {
-                //         macro_rules! inner {
-                //             () => { $e }
-                //         }
-                //     }
-                // }
-                // ```
-                //
-                // In both cases, we don't want to synthesize any tokens
-                MacArgs::Delimited(dspan, delim, tokens.flattened())
-            }
+    fn lower_attr_args(&self, args: &AttrArgs) -> AttrArgs {
+        match args {
+            AttrArgs::Empty => AttrArgs::Empty,
+            AttrArgs::Delimited(args) => AttrArgs::Delimited(self.lower_delim_args(args)),
             // This is an inert key-value attribute - it will never be visible to macros
             // after it gets lowered to HIR. Therefore, we can extract literals to handle
             // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
-            MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
+            AttrArgs::Eq(eq_span, AttrArgsEq::Ast(expr)) => {
                 // In valid code the value always ends up as a single literal. Otherwise, a dummy
                 // literal suffices because the error is handled elsewhere.
-                let lit = if let ExprKind::Lit(lit) = &expr.kind {
-                    lit.clone()
+                let lit = if let ExprKind::Lit(token_lit) = expr.kind
+                    && let Ok(lit) = MetaItemLit::from_token_lit(token_lit, expr.span)
+                {
+                    lit
                 } else {
-                    Lit {
+                    MetaItemLit {
                         token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
                         kind: LitKind::Err,
                         span: DUMMY_SP,
                     }
                 };
-                MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
+                AttrArgs::Eq(*eq_span, AttrArgsEq::Hir(lit))
             }
-            MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
+            AttrArgs::Eq(_, AttrArgsEq::Hir(lit)) => {
                 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
             }
         }
     }
 
+    fn lower_delim_args(&self, args: &DelimArgs) -> DelimArgs {
+        DelimArgs { dspan: args.dspan, delim: args.delim, tokens: args.tokens.flattened() }
+    }
+
     /// Given an associated type constraint like one of these:
     ///
     /// ```ignore (illustrative)
@@ -994,12 +993,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     ) -> hir::TypeBinding<'hir> {
         debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
         // lower generic arguments of identifier in constraint
-        let gen_args = if let Some(ref gen_args) = constraint.gen_args {
+        let gen_args = if let Some(gen_args) = &constraint.gen_args {
             let gen_args_ctor = match gen_args {
-                GenericArgs::AngleBracketed(ref data) => {
+                GenericArgs::AngleBracketed(data) => {
                     self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
                 }
-                GenericArgs::Parenthesized(ref data) => {
+                GenericArgs::Parenthesized(data) => {
                     self.emit_bad_parenthesized_trait_in_assoc_ty(data);
                     let aba = self.ast_arena.aba.alloc(data.as_angle_bracketed_args());
                     self.lower_angle_bracketed_parameter_data(aba, ParamMode::Explicit, itctx).0
@@ -1011,15 +1010,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         };
         let itctx_tait = &ImplTraitContext::TypeAliasesOpaqueTy;
 
-        let kind = match constraint.kind {
-            AssocConstraintKind::Equality { ref term } => {
+        let kind = match &constraint.kind {
+            AssocConstraintKind::Equality { term } => {
                 let term = match term {
-                    Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
-                    Term::Const(ref c) => self.lower_anon_const(c).into(),
+                    Term::Ty(ty) => self.lower_ty(ty, itctx).into(),
+                    Term::Const(c) => self.lower_anon_const(c).into(),
                 };
                 hir::TypeBindingKind::Equality { term }
             }
-            AssocConstraintKind::Bound { ref bounds } => {
+            AssocConstraintKind::Bound { bounds } => {
                 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
                 let (desugar_to_impl_trait, itctx) = match itctx {
                     // We are in the return position:
@@ -1129,7 +1128,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         match arg {
             ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(&lt)),
             ast::GenericArg::Type(ty) => {
-                match ty.kind {
+                match &ty.kind {
                     TyKind::Infer if self.tcx.features().generic_arg_infer => {
                         return GenericArg::Infer(hir::InferArg {
                             hir_id: self.lower_node_id(ty.id),
@@ -1140,7 +1139,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     // parsing. We try to resolve that ambiguity by attempting resolution in both the
                     // type and value namespaces. If we resolved the path in the value namespace, we
                     // transform it into a generic const argument.
-                    TyKind::Path(ref qself, ref path) => {
+                    TyKind::Path(qself, path) => {
                         if let Some(res) = self
                             .resolver
                             .get_partial_res(ty.id)
@@ -1156,15 +1155,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                                 let parent_def_id = self.current_hir_id_owner;
                                 let node_id = self.next_node_id();
+                                let span = self.lower_span(ty.span);
 
                                 // Add a definition for the in-band const def.
-                                self.create_def(
+                                let def_id = self.create_def(
                                     parent_def_id.def_id,
                                     node_id,
                                     DefPathData::AnonConst,
+                                    span,
                                 );
 
-                                let span = self.lower_span(ty.span);
                                 let path_expr = Expr {
                                     id: ty.id,
                                     kind: ExprKind::Path(qself.clone(), path.clone()),
@@ -1174,6 +1174,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 };
 
                                 let ct = self.with_new_scopes(|this| hir::AnonConst {
+                                    def_id,
                                     hir_id: this.lower_node_id(node_id),
                                     body: this.lower_const_body(path_expr.span, Some(&path_expr)),
                                 });
@@ -1200,7 +1201,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_path_ty(
         &mut self,
         t: &Ty,
-        qself: &Option<QSelf>,
+        qself: &Option<ptr::P<QSelf>>,
         path: &Path,
         param_mode: ParamMode,
         itctx: &ImplTraitContext,
@@ -1246,12 +1247,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_ty_direct(&mut self, t: &Ty, itctx: &ImplTraitContext) -> hir::Ty<'hir> {
-        let kind = match t.kind {
+        let kind = match &t.kind {
             TyKind::Infer => hir::TyKind::Infer,
             TyKind::Err => hir::TyKind::Err,
-            TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
-            TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
-            TyKind::Rptr(ref region, ref mt) => {
+            TyKind::Slice(ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
+            TyKind::Ptr(mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
+            TyKind::Rptr(region, mt) => {
                 let region = region.unwrap_or_else(|| {
                     let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
                         self.resolver.get_lifetime_res(t.id)
@@ -1261,30 +1262,30 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     } else {
                         self.next_node_id()
                     };
-                    let span = self.tcx.sess.source_map().start_point(t.span);
+                    let span = self.tcx.sess.source_map().start_point(t.span).shrink_to_hi();
                     Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
                 });
                 let lifetime = self.lower_lifetime(&region);
                 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
             }
-            TyKind::BareFn(ref f) => {
+            TyKind::BareFn(f) => {
                 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
                 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
                     generic_params,
                     unsafety: self.lower_unsafety(f.unsafety),
                     abi: self.lower_extern(f.ext),
-                    decl: self.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
+                    decl: self.lower_fn_decl(&f.decl, t.id, t.span, FnDeclKind::Pointer, None),
                     param_names: self.lower_fn_params_to_names(&f.decl),
                 }))
             }
             TyKind::Never => hir::TyKind::Never,
-            TyKind::Tup(ref tys) => hir::TyKind::Tup(
+            TyKind::Tup(tys) => hir::TyKind::Tup(
                 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
             ),
-            TyKind::Paren(ref ty) => {
+            TyKind::Paren(ty) => {
                 return self.lower_ty_direct(ty, itctx);
             }
-            TyKind::Path(ref qself, ref path) => {
+            TyKind::Path(qself, path) => {
                 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
             }
             TyKind::ImplicitSelf => {
@@ -1304,48 +1305,46 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }),
                 ))
             }
-            TyKind::Array(ref ty, ref length) => {
+            TyKind::Array(ty, length) => {
                 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
             }
-            TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
-            TyKind::TraitObject(ref bounds, kind) => {
+            TyKind::Typeof(expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
+            TyKind::TraitObject(bounds, kind) => {
                 let mut lifetime_bound = None;
                 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
                     let bounds =
-                        this.arena.alloc_from_iter(bounds.iter().filter_map(
-                            |bound| match *bound {
-                                GenericBound::Trait(
-                                    ref ty,
-                                    TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
-                                ) => Some(this.lower_poly_trait_ref(ty, itctx)),
-                                // `~const ?Bound` will cause an error during AST validation
-                                // anyways, so treat it like `?Bound` as compilation proceeds.
-                                GenericBound::Trait(
-                                    _,
-                                    TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
-                                ) => None,
-                                GenericBound::Outlives(ref lifetime) => {
-                                    if lifetime_bound.is_none() {
-                                        lifetime_bound = Some(this.lower_lifetime(lifetime));
-                                    }
-                                    None
+                        this.arena.alloc_from_iter(bounds.iter().filter_map(|bound| match bound {
+                            GenericBound::Trait(
+                                ty,
+                                TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
+                            ) => Some(this.lower_poly_trait_ref(ty, itctx)),
+                            // `~const ?Bound` will cause an error during AST validation
+                            // anyways, so treat it like `?Bound` as compilation proceeds.
+                            GenericBound::Trait(
+                                _,
+                                TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
+                            ) => None,
+                            GenericBound::Outlives(lifetime) => {
+                                if lifetime_bound.is_none() {
+                                    lifetime_bound = Some(this.lower_lifetime(lifetime));
                                 }
-                            },
-                        ));
+                                None
+                            }
+                        }));
                     let lifetime_bound =
                         lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
                     (bounds, lifetime_bound)
                 });
-                hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
+                hir::TyKind::TraitObject(bounds, lifetime_bound, *kind)
             }
-            TyKind::ImplTrait(def_node_id, ref bounds) => {
+            TyKind::ImplTrait(def_node_id, bounds) => {
                 let span = t.span;
                 match itctx {
                     ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
                         .lower_opaque_impl_trait(
                             span,
                             *origin,
-                            def_node_id,
+                            *def_node_id,
                             bounds,
                             *in_trait,
                             itctx,
@@ -1353,38 +1352,37 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
                         span,
                         hir::OpaqueTyOrigin::TyAlias,
-                        def_node_id,
+                        *def_node_id,
                         bounds,
                         false,
                         itctx,
                     ),
                     ImplTraitContext::Universal => {
+                        let span = t.span;
                         self.create_def(
                             self.current_hir_id_owner.def_id,
-                            def_node_id,
+                            *def_node_id,
                             DefPathData::ImplTrait,
+                            span,
                         );
-                        let span = t.span;
                         let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
                         let (param, bounds, path) =
-                            self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
+                            self.lower_generic_and_bounds(*def_node_id, span, ident, bounds);
                         self.impl_trait_defs.push(param);
                         if let Some(bounds) = bounds {
                             self.impl_trait_bounds.push(bounds);
                         }
                         path
                     }
-                    ImplTraitContext::Disallowed(
-                        position @ (ImplTraitPosition::TraitReturn | ImplTraitPosition::ImplReturn),
-                    ) => {
+                    ImplTraitContext::FeatureGated(position, feature) => {
                         self.tcx
                             .sess
                             .create_feature_err(
                                 MisplacedImplTrait {
                                     span: t.span,
-                                    position: DiagnosticArgFromDisplay(&position),
+                                    position: DiagnosticArgFromDisplay(position),
                                 },
-                                sym::return_position_impl_trait_in_trait,
+                                *feature,
                             )
                             .emit();
                         hir::TyKind::Err
@@ -1392,7 +1390,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     ImplTraitContext::Disallowed(position) => {
                         self.tcx.sess.emit_err(MisplacedImplTrait {
                             span: t.span,
-                            position: DiagnosticArgFromDisplay(&position),
+                            position: DiagnosticArgFromDisplay(position),
                         });
                         hir::TyKind::Err
                     }
@@ -1457,17 +1455,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // frequently opened issues show.
         let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
 
-        let opaque_ty_def_id = match origin {
-            hir::OpaqueTyOrigin::TyAlias => self.create_def(
-                self.current_hir_id_owner.def_id,
-                opaque_ty_node_id,
-                DefPathData::ImplTrait,
-            ),
-            hir::OpaqueTyOrigin::FnReturn(fn_def_id) => {
-                self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait)
-            }
-            hir::OpaqueTyOrigin::AsyncFn(..) => bug!("unreachable"),
-        };
+        let opaque_ty_def_id = self.create_def(
+            self.current_hir_id_owner.def_id,
+            opaque_ty_node_id,
+            DefPathData::ImplTrait,
+            opaque_ty_span,
+        );
         debug!(?opaque_ty_def_id);
 
         // Contains the new lifetime definitions created for the TAIT (if any).
@@ -1521,6 +1514,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                         hir::GenericParam {
                             hir_id,
+                            def_id: lctx.local_def_id(new_node_id),
                             name,
                             span: lifetime.ident.span,
                             pure_wrt_drop: false,
@@ -1559,15 +1553,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let lifetimes =
             self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
                 let id = self.next_node_id();
-                let span = lifetime.ident.span;
-
-                let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
-                    Ident::with_dummy_span(kw::UnderscoreLifetime)
-                } else {
-                    lifetime.ident
-                };
-
-                let l = self.new_named_lifetime(lifetime.id, id, span, ident);
+                let l = self.new_named_lifetime(lifetime.id, id, lifetime.ident);
                 hir::GenericArg::Lifetime(l)
             }));
         debug!(?lifetimes);
@@ -1627,6 +1613,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             parent_def_id,
                             node_id,
                             DefPathData::LifetimeNs(lifetime.ident.name),
+                            lifetime.ident.span,
                         );
                         remapping.insert(old_def_id, new_def_id);
 
@@ -1643,6 +1630,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             parent_def_id,
                             node_id,
                             DefPathData::LifetimeNs(kw::UnderscoreLifetime),
+                            lifetime.ident.span,
                         );
                         remapping.insert(old_def_id, new_def_id);
 
@@ -1692,7 +1680,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_fn_decl(
         &mut self,
         decl: &FnDecl,
-        fn_node_id: Option<NodeId>,
+        fn_node_id: NodeId,
         fn_span: Span,
         kind: FnDeclKind,
         make_ret_async: Option<(NodeId, Span)>,
@@ -1707,23 +1695,21 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             inputs = &inputs[..inputs.len() - 1];
         }
         let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
-            if fn_node_id.is_some() {
-                self.lower_ty_direct(&param.ty, &ImplTraitContext::Universal)
+            let itctx = if kind.param_impl_trait_allowed() {
+                ImplTraitContext::Universal
             } else {
-                self.lower_ty_direct(
-                    &param.ty,
-                    &ImplTraitContext::Disallowed(match kind {
-                        FnDeclKind::Fn | FnDeclKind::Inherent => {
-                            unreachable!("fn should allow in-band lifetimes")
-                        }
-                        FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
-                        FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
-                        FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
-                        FnDeclKind::Trait => ImplTraitPosition::TraitParam,
-                        FnDeclKind::Impl => ImplTraitPosition::ImplParam,
-                    }),
-                )
-            }
+                ImplTraitContext::Disallowed(match kind {
+                    FnDeclKind::Fn | FnDeclKind::Inherent => {
+                        unreachable!("fn should allow APIT")
+                    }
+                    FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
+                    FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
+                    FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
+                    FnDeclKind::Trait => ImplTraitPosition::TraitParam,
+                    FnDeclKind::Impl => ImplTraitPosition::ImplParam,
+                })
+            };
+            self.lower_ty_direct(&param.ty, &itctx)
         }));
 
         let output = if let Some((ret_id, span)) = make_ret_async {
@@ -1746,22 +1732,21 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
             self.lower_async_fn_ret_ty(
                 &decl.output,
-                fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
+                fn_node_id,
                 ret_id,
                 matches!(kind, FnDeclKind::Trait),
             )
         } else {
-            match decl.output {
-                FnRetTy::Ty(ref ty) => {
-                    let mut context = match fn_node_id {
-                        Some(fn_node_id) if kind.impl_trait_allowed(self.tcx) => {
-                            let fn_def_id = self.local_def_id(fn_node_id);
-                            ImplTraitContext::ReturnPositionOpaqueTy {
-                                origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                                in_trait: matches!(kind, FnDeclKind::Trait),
-                            }
+            match &decl.output {
+                FnRetTy::Ty(ty) => {
+                    let context = if kind.return_impl_trait_allowed(self.tcx) {
+                        let fn_def_id = self.local_def_id(fn_node_id);
+                        ImplTraitContext::ReturnPositionOpaqueTy {
+                            origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
+                            in_trait: matches!(kind, FnDeclKind::Trait),
                         }
-                        _ => ImplTraitContext::Disallowed(match kind {
+                    } else {
+                        let position = match kind {
                             FnDeclKind::Fn | FnDeclKind::Inherent => {
                                 unreachable!("fn should allow in-band lifetimes")
                             }
@@ -1770,11 +1755,18 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
                             FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
                             FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
-                        }),
+                        };
+                        match kind {
+                            FnDeclKind::Trait | FnDeclKind::Impl => ImplTraitContext::FeatureGated(
+                                position,
+                                sym::return_position_impl_trait_in_trait,
+                            ),
+                            _ => ImplTraitContext::Disallowed(position),
+                        }
                     };
-                    hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
+                    hir::FnRetTy::Return(self.lower_ty(ty, &context))
                 }
-                FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
+                FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(*span)),
             }
         };
 
@@ -1782,26 +1774,23 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             inputs,
             output,
             c_variadic,
+            lifetime_elision_allowed: self.resolver.lifetime_elision_allowed.contains(&fn_node_id),
             implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
                 let is_mutable_pat = matches!(
                     arg.pat.kind,
                     PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
                 );
 
-                match arg.ty.kind {
+                match &arg.ty.kind {
                     TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
                     TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
                     // Given we are only considering `ImplicitSelf` types, we needn't consider
                     // the case where we have a mutable pattern to a reference as that would
                     // no longer be an `ImplicitSelf`.
-                    TyKind::Rptr(_, ref mt)
-                        if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
-                    {
-                        hir::ImplicitSelfKind::MutRef
-                    }
-                    TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
-                        hir::ImplicitSelfKind::ImmRef
-                    }
+                    TyKind::Rptr(_, mt) if mt.ty.kind.is_implicit_self() => match mt.mutbl {
+                        hir::Mutability::Not => hir::ImplicitSelfKind::ImmRef,
+                        hir::Mutability::Mut => hir::ImplicitSelfKind::MutRef,
+                    },
                     _ => hir::ImplicitSelfKind::None,
                 }
             }),
@@ -1828,9 +1817,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
 
-        let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
         let fn_def_id = self.local_def_id(fn_node_id);
 
+        let opaque_ty_def_id =
+            self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait, opaque_ty_span);
+
         // When we create the opaque type for this async fn, it is going to have
         // to capture all the lifetimes involved in the signature (including in the
         // return type). This is done by introducing lifetime parameters for:
@@ -1889,6 +1880,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 opaque_ty_def_id,
                 inner_node_id,
                 DefPathData::LifetimeNs(ident.name),
+                ident.span,
             );
             new_remapping.insert(outer_def_id, inner_def_id);
 
@@ -1953,7 +1945,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     output,
                     span,
                     if in_trait && !this.tcx.features().return_position_impl_trait_in_trait {
-                        ImplTraitContext::Disallowed(ImplTraitPosition::TraitReturn)
+                        ImplTraitContext::FeatureGated(
+                            ImplTraitPosition::TraitReturn,
+                            sym::return_position_impl_trait_in_trait,
+                        )
                     } else {
                         ImplTraitContext::ReturnPositionOpaqueTy {
                             origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
@@ -1978,6 +1973,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                         hir::GenericParam {
                             hir_id,
+                            def_id: this.local_def_id(new_node_id),
                             name,
                             span: lifetime.ident.span,
                             pure_wrt_drop: false,
@@ -2024,18 +2020,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
             |(_, lifetime, res)| {
                 let id = self.next_node_id();
-                let span = lifetime.ident.span;
-
-                let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
-                    Ident::with_dummy_span(kw::UnderscoreLifetime)
-                } else {
-                    lifetime.ident
-                };
-
                 let res = res.unwrap_or(
                     self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
                 );
-                hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, span, ident, res))
+                hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, lifetime.ident, res))
             },
         ));
 
@@ -2105,43 +2093,40 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
-        let span = self.lower_span(l.ident.span);
         let ident = self.lower_ident(l.ident);
-        self.new_named_lifetime(l.id, l.id, span, ident)
+        self.new_named_lifetime(l.id, l.id, ident)
     }
 
     #[instrument(level = "debug", skip(self))]
     fn new_named_lifetime_with_res(
         &mut self,
         id: NodeId,
-        span: Span,
         ident: Ident,
         res: LifetimeRes,
     ) -> &'hir hir::Lifetime {
-        let name = match res {
+        let res = match res {
             LifetimeRes::Param { param, .. } => {
-                let p_name = ParamName::Plain(ident);
                 let param = self.get_remapped_def_id(param);
-
-                hir::LifetimeName::Param(param, p_name)
+                hir::LifetimeName::Param(param)
             }
             LifetimeRes::Fresh { param, .. } => {
-                debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
                 let param = self.local_def_id(param);
-
-                hir::LifetimeName::Param(param, ParamName::Fresh)
+                hir::LifetimeName::Param(param)
             }
             LifetimeRes::Infer => hir::LifetimeName::Infer,
             LifetimeRes::Static => hir::LifetimeName::Static,
             LifetimeRes::Error => hir::LifetimeName::Error,
-            res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
+            res => panic!(
+                "Unexpected lifetime resolution {:?} for {:?} at {:?}",
+                res, ident, ident.span
+            ),
         };
 
-        debug!(?name);
+        debug!(?res);
         self.arena.alloc(hir::Lifetime {
             hir_id: self.lower_node_id(id),
-            span: self.lower_span(span),
-            name,
+            ident: self.lower_ident(ident),
+            res,
         })
     }
 
@@ -2150,11 +2135,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &mut self,
         id: NodeId,
         new_id: NodeId,
-        span: Span,
         ident: Ident,
     ) -> &'hir hir::Lifetime {
         let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
-        self.new_named_lifetime_with_res(new_id, span, ident, res)
+        self.new_named_lifetime_with_res(new_id, ident, res)
     }
 
     fn lower_generic_params_mut<'s>(
@@ -2176,6 +2160,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.lower_attrs(hir_id, &param.attrs);
         hir::GenericParam {
             hir_id,
+            def_id: self.local_def_id(param.id),
             name,
             span: self.lower_span(param.span()),
             pure_wrt_drop: self.tcx.sess.contains_name(&param.attrs, sym::may_dangle),
@@ -2188,7 +2173,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &mut self,
         param: &GenericParam,
     ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
-        match param.kind {
+        match &param.kind {
             GenericParamKind::Lifetime => {
                 // AST resolution emitted an error on those parameters, so we lower them using
                 // `ParamName::Error`.
@@ -2204,7 +2189,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                 (param_name, kind)
             }
-            GenericParamKind::Type { ref default, .. } => {
+            GenericParamKind::Type { default, .. } => {
                 let kind = hir::GenericParamKind::Type {
                     default: default.as_ref().map(|x| {
                         self.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
@@ -2214,7 +2199,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
             }
-            GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
+            GenericParamKind::Const { ty, kw_span: _, default } => {
                 let ty = self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
                 let default = default.as_ref().map(|def| self.lower_anon_const(def));
                 (
@@ -2280,6 +2265,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // Set the name to `impl Bound1 + Bound2`.
         let param = hir::GenericParam {
             hir_id: self.lower_node_id(node_id),
+            def_id,
             name: ParamName::Plain(self.lower_ident(ident)),
             pure_wrt_drop: false,
             span: self.lower_span(span),
@@ -2315,7 +2301,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// has no attributes and is not targeted by a `break`.
     fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
         let block = self.lower_block(b, false);
-        self.expr_block(block, AttrVec::new())
+        self.expr_block(block)
     }
 
     fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
@@ -2340,6 +2326,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
         self.with_new_scopes(|this| hir::AnonConst {
+            def_id: this.local_def_id(c.id),
             hir_id: this.lower_node_id(c.id),
             body: this.lower_const_body(c.value.span, Some(&c.value)),
         })
@@ -2563,8 +2550,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
         let r = hir::Lifetime {
             hir_id: self.next_id(),
-            span: self.lower_span(span),
-            name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
+            ident: Ident::new(kw::Empty, self.lower_span(span)),
+            res: hir::LifetimeName::ImplicitObjectLifetimeDefault,
         };
         debug!("elided_dyn_bound: r={:?}", r);
         self.arena.alloc(r)
diff --git a/compiler/rustc_ast_lowering/src/pat.rs b/compiler/rustc_ast_lowering/src/pat.rs
index 1af1633b5..16b012630 100644
--- a/compiler/rustc_ast_lowering/src/pat.rs
+++ b/compiler/rustc_ast_lowering/src/pat.rs
@@ -22,16 +22,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         ensure_sufficient_stack(|| {
             // loop here to avoid recursion
             let node = loop {
-                match pattern.kind {
+                match &pattern.kind {
                     PatKind::Wild => break hir::PatKind::Wild,
-                    PatKind::Ident(binding_mode, ident, ref sub) => {
-                        let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
-                        break self.lower_pat_ident(pattern, binding_mode, ident, lower_sub);
+                    PatKind::Ident(binding_mode, ident, sub) => {
+                        let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(s));
+                        break self.lower_pat_ident(pattern, *binding_mode, *ident, lower_sub);
                     }
-                    PatKind::Lit(ref e) => {
+                    PatKind::Lit(e) => {
                         break hir::PatKind::Lit(self.lower_expr_within_pat(e, false));
                     }
-                    PatKind::TupleStruct(ref qself, ref path, ref pats) => {
+                    PatKind::TupleStruct(qself, path, pats) => {
                         let qpath = self.lower_qpath(
                             pattern.id,
                             qself,
@@ -42,12 +42,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
                         break hir::PatKind::TupleStruct(qpath, pats, ddpos);
                     }
-                    PatKind::Or(ref pats) => {
+                    PatKind::Or(pats) => {
                         break hir::PatKind::Or(
                             self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat_mut(x))),
                         );
                     }
-                    PatKind::Path(ref qself, ref path) => {
+                    PatKind::Path(qself, path) => {
                         let qpath = self.lower_qpath(
                             pattern.id,
                             qself,
@@ -57,7 +57,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         );
                         break hir::PatKind::Path(qpath);
                     }
-                    PatKind::Struct(ref qself, ref path, ref fields, etc) => {
+                    PatKind::Struct(qself, path, fields, etc) => {
                         let qpath = self.lower_qpath(
                             pattern.id,
                             qself,
@@ -78,32 +78,32 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 span: self.lower_span(f.span),
                             }
                         }));
-                        break hir::PatKind::Struct(qpath, fs, etc);
+                        break hir::PatKind::Struct(qpath, fs, *etc);
                     }
-                    PatKind::Tuple(ref pats) => {
+                    PatKind::Tuple(pats) => {
                         let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
                         break hir::PatKind::Tuple(pats, ddpos);
                     }
-                    PatKind::Box(ref inner) => {
+                    PatKind::Box(inner) => {
                         break hir::PatKind::Box(self.lower_pat(inner));
                     }
-                    PatKind::Ref(ref inner, mutbl) => {
-                        break hir::PatKind::Ref(self.lower_pat(inner), mutbl);
+                    PatKind::Ref(inner, mutbl) => {
+                        break hir::PatKind::Ref(self.lower_pat(inner), *mutbl);
                     }
-                    PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => {
+                    PatKind::Range(e1, e2, Spanned { node: end, .. }) => {
                         break hir::PatKind::Range(
                             e1.as_deref().map(|e| self.lower_expr_within_pat(e, true)),
                             e2.as_deref().map(|e| self.lower_expr_within_pat(e, true)),
                             self.lower_range_end(end, e2.is_some()),
                         );
                     }
-                    PatKind::Slice(ref pats) => break self.lower_pat_slice(pats),
+                    PatKind::Slice(pats) => break self.lower_pat_slice(pats),
                     PatKind::Rest => {
                         // If we reach here the `..` pattern is not semantically allowed.
                         break self.ban_illegal_rest_pat(pattern.span);
                     }
                     // return inner to be processed in next loop
-                    PatKind::Paren(ref inner) => pattern = inner,
+                    PatKind::Paren(inner) => pattern = inner,
                     PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", pattern.span),
                 }
             };
@@ -126,7 +126,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // Note that unlike for slice patterns,
             // where `xs @ ..` is a legal sub-slice pattern,
             // it is not a legal sub-tuple pattern.
-            match pat.kind {
+            match &pat.kind {
                 // Found a sub-tuple rest pattern
                 PatKind::Rest => {
                     rest = Some((idx, pat.span));
@@ -134,12 +134,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 }
                 // Found a sub-tuple pattern `$binding_mode $ident @ ..`.
                 // This is not allowed as a sub-tuple pattern
-                PatKind::Ident(ref _bm, ident, Some(ref sub)) if sub.is_rest() => {
+                PatKind::Ident(_, ident, Some(sub)) if sub.is_rest() => {
                     let sp = pat.span;
                     self.tcx.sess.emit_err(SubTupleBinding {
                         span: sp,
                         ident_name: ident.name,
-                        ident,
+                        ident: *ident,
                         ctx,
                     });
                 }
@@ -176,7 +176,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let mut prev_rest_span = None;
 
         // Lowers `$bm $ident @ ..` to `$bm $ident @ _`.
-        let lower_rest_sub = |this: &mut Self, pat, ann, ident, sub| {
+        let lower_rest_sub = |this: &mut Self, pat, &ann, &ident, sub| {
             let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
             let node = this.lower_pat_ident(pat, ann, ident, lower_sub);
             this.pat_with_node_id_of(pat, node)
@@ -185,7 +185,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let mut iter = pats.iter();
         // Lower all the patterns until the first occurrence of a sub-slice pattern.
         for pat in iter.by_ref() {
-            match pat.kind {
+            match &pat.kind {
                 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
                 PatKind::Rest => {
                     prev_rest_span = Some(pat.span);
@@ -194,7 +194,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 }
                 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
                 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
-                PatKind::Ident(ann, ident, Some(ref sub)) if sub.is_rest() => {
+                PatKind::Ident(ann, ident, Some(sub)) if sub.is_rest() => {
                     prev_rest_span = Some(sub.span);
                     slice = Some(self.arena.alloc(lower_rest_sub(self, pat, ann, ident, sub)));
                     break;
@@ -207,9 +207,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // Lower all the patterns after the first sub-slice pattern.
         for pat in iter {
             // There was a previous subslice pattern; make sure we don't allow more.
-            let rest_span = match pat.kind {
+            let rest_span = match &pat.kind {
                 PatKind::Rest => Some(pat.span),
-                PatKind::Ident(ann, ident, Some(ref sub)) if sub.is_rest() => {
+                PatKind::Ident(ann, ident, Some(sub)) if sub.is_rest() => {
                     // #69103: Lower into `binding @ _` as above to avoid ICEs.
                     after.push(lower_rest_sub(self, pat, ann, ident, sub));
                     Some(sub.span)
@@ -322,10 +322,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     // m!(S);
     // ```
     fn lower_expr_within_pat(&mut self, expr: &Expr, allow_paths: bool) -> &'hir hir::Expr<'hir> {
-        match expr.kind {
-            ExprKind::Lit(..) | ExprKind::ConstBlock(..) | ExprKind::Err => {}
+        match &expr.kind {
+            ExprKind::Lit(..)
+            | ExprKind::ConstBlock(..)
+            | ExprKind::IncludedBytes(..)
+            | ExprKind::Err => {}
             ExprKind::Path(..) if allow_paths => {}
-            ExprKind::Unary(UnOp::Neg, ref inner) if matches!(inner.kind, ExprKind::Lit(_)) => {}
+            ExprKind::Unary(UnOp::Neg, inner) if matches!(inner.kind, ExprKind::Lit(_)) => {}
             _ => {
                 self.tcx.sess.emit_err(ArbitraryExpressionInPattern { span: expr.span });
                 return self.arena.alloc(self.expr_err(expr.span));
diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index 888776ccc..592fc5aa6 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -9,17 +9,17 @@ use rustc_ast::{self as ast, *};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, PartialRes, Res};
 use rustc_hir::GenericArg;
-use rustc_span::symbol::{kw, Ident};
+use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span, DUMMY_SP};
 
-use smallvec::smallvec;
+use smallvec::{smallvec, SmallVec};
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
     #[instrument(level = "trace", skip(self))]
     pub(crate) fn lower_qpath(
         &mut self,
         id: NodeId,
-        qself: &Option<QSelf>,
+        qself: &Option<ptr::P<QSelf>>,
         p: &Path,
         param_mode: ParamMode,
         itctx: &ImplTraitContext,
@@ -144,13 +144,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         );
     }
 
-    pub(crate) fn lower_path_extra(
+    pub(crate) fn lower_use_path(
         &mut self,
-        res: Res,
+        res: SmallVec<[Res; 3]>,
         p: &Path,
         param_mode: ParamMode,
-    ) -> &'hir hir::Path<'hir> {
-        self.arena.alloc(hir::Path {
+    ) -> &'hir hir::UsePath<'hir> {
+        self.arena.alloc(hir::UsePath {
             res,
             segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
                 self.lower_path_segment(
@@ -165,17 +165,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         })
     }
 
-    pub(crate) fn lower_path(
-        &mut self,
-        id: NodeId,
-        p: &Path,
-        param_mode: ParamMode,
-    ) -> &'hir hir::Path<'hir> {
-        let res = self.expect_full_res(id);
-        let res = self.lower_res(res);
-        self.lower_path_extra(res, p, param_mode)
-    }
-
     pub(crate) fn lower_path_segment(
         &mut self,
         path_span: Span,
@@ -185,13 +174,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         itctx: &ImplTraitContext,
     ) -> hir::PathSegment<'hir> {
         debug!("path_span: {:?}, lower_path_segment(segment: {:?})", path_span, segment,);
-        let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
-            match **generic_args {
-                GenericArgs::AngleBracketed(ref data) => {
+        let (mut generic_args, infer_args) = if let Some(generic_args) = segment.args.as_deref() {
+            match generic_args {
+                GenericArgs::AngleBracketed(data) => {
                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
                 }
-                GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
-                    ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
+                GenericArgs::Parenthesized(data) => match parenthesized_generic_args {
+                    ParenthesizedGenericArgs::Ok => {
+                        self.lower_parenthesized_parameter_data(data, itctx)
+                    }
                     ParenthesizedGenericArgs::Err => {
                         // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
                         let sub = if !data.inputs.is_empty() {
@@ -307,7 +298,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let id = NodeId::from_u32(i);
                 let l = self.lower_lifetime(&Lifetime {
                     id,
-                    ident: Ident::new(kw::UnderscoreLifetime, elided_lifetime_span),
+                    ident: Ident::new(kw::Empty, elided_lifetime_span),
                 });
                 GenericArg::Lifetime(l)
             }),
@@ -344,6 +335,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_parenthesized_parameter_data(
         &mut self,
         data: &ParenthesizedArgs,
+        itctx: &ImplTraitContext,
     ) -> (GenericArgsCtor<'hir>, bool) {
         // Switch to `PassThrough` mode for anonymous lifetimes; this
         // means that we permit things like `&Ref<T>`, where `Ref` has
@@ -355,6 +347,24 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.lower_ty_direct(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam))
         }));
         let output_ty = match output {
+            // Only allow `impl Trait` in return position. i.e.:
+            // ```rust
+            // fn f(_: impl Fn() -> impl Debug) -> impl Fn() -> impl Debug
+            // //      disallowed --^^^^^^^^^^        allowed --^^^^^^^^^^
+            // ```
+            FnRetTy::Ty(ty) if matches!(itctx, ImplTraitContext::ReturnPositionOpaqueTy { .. }) => {
+                if self.tcx.features().impl_trait_in_fn_trait_return {
+                    self.lower_ty(&ty, itctx)
+                } else {
+                    self.lower_ty(
+                        &ty,
+                        &ImplTraitContext::FeatureGated(
+                            ImplTraitPosition::FnTraitReturn,
+                            sym::impl_trait_in_fn_trait_return,
+                        ),
+                    )
+                }
+            }
             FnRetTy::Ty(ty) => {
                 self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitReturn))
             }