Merging upstream version 1.71.1+dfsg1.

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

7 files changed, 170 insertions, 132 deletions

diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index 3e9f9b436..72dc52a63 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -108,7 +108,7 @@ pub struct BaseExpressionDoubleDot {
 pub struct AwaitOnlyInAsyncFnAndBlocks {
     #[primary_span]
     #[label]
-    pub dot_await_span: Span,
+    pub await_kw_span: Span,
     #[label(ast_lowering_this_not_async)]
     pub item_span: Option<Span>,
 }
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 1b1c4765b..5e0ab80c6 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -121,12 +121,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             LitKind::Err
                         }
                     };
-                    hir::ExprKind::Lit(respan(self.lower_span(e.span), lit_kind))
+                    let lit = self.arena.alloc(respan(self.lower_span(e.span), lit_kind));
+                    hir::ExprKind::Lit(lit)
+                }
+                ExprKind::IncludedBytes(bytes) => {
+                    let lit = self.arena.alloc(respan(
+                        self.lower_span(e.span),
+                        LitKind::ByteStr(bytes.clone(), StrStyle::Cooked),
+                    ));
+                    hir::ExprKind::Lit(lit)
                 }
-                ExprKind::IncludedBytes(bytes) => hir::ExprKind::Lit(respan(
-                    self.lower_span(e.span),
-                    LitKind::ByteStr(bytes.clone(), StrStyle::Cooked),
-                )),
                 ExprKind::Cast(expr, ty) => {
                     let expr = self.lower_expr(expr);
                     let ty =
@@ -181,21 +185,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     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
-                            .sess
-                            .source_map()
-                            .span_extend_while(expr.span, char::is_whitespace)
-                            .unwrap_or(expr.span);
-                        span_with_whitespace.shrink_to_hi().with_hi(e.span.hi())
-                    } else {
-                        // this is a recovered `await expr`
-                        e.span
-                    };
-                    self.lower_expr_await(dot_await_span, expr)
-                }
+                ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
                 ExprKind::Closure(box Closure {
                     binder,
                     capture_clause,
@@ -285,6 +275,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
                 }
                 ExprKind::FormatArgs(fmt) => self.lower_format_args(e.span, fmt),
+                ExprKind::OffsetOf(container, fields) => hir::ExprKind::OffsetOf(
+                    self.lower_ty(
+                        container,
+                        &mut ImplTraitContext::Disallowed(ImplTraitPosition::OffsetOf),
+                    ),
+                    self.arena.alloc_from_iter(fields.iter().map(|&ident| self.lower_ident(ident))),
+                ),
                 ExprKind::Struct(se) => {
                     let rest = match &se.rest {
                         StructRest::Base(e) => Some(self.lower_expr(e)),
@@ -699,18 +696,18 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ///     }
     /// }
     /// ```
-    fn lower_expr_await(&mut self, dot_await_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
-        let full_span = expr.span.to(dot_await_span);
+    fn lower_expr_await(&mut self, await_kw_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
+        let full_span = expr.span.to(await_kw_span);
         match self.generator_kind {
             Some(hir::GeneratorKind::Async(_)) => {}
             Some(hir::GeneratorKind::Gen) | None => {
                 self.tcx.sess.emit_err(AwaitOnlyInAsyncFnAndBlocks {
-                    dot_await_span,
+                    await_kw_span,
                     item_span: self.current_item,
                 });
             }
         }
-        let span = self.mark_span_with_reason(DesugaringKind::Await, dot_await_span, None);
+        let span = self.mark_span_with_reason(DesugaringKind::Await, await_kw_span, None);
         let gen_future_span = self.mark_span_with_reason(
             DesugaringKind::Await,
             full_span,
@@ -847,13 +844,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let awaitee_arm = self.arm(awaitee_pat, loop_expr);
 
         // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
-        let into_future_span = self.mark_span_with_reason(
-            DesugaringKind::Await,
-            dot_await_span,
-            self.allow_into_future.clone(),
-        );
         let into_future_expr = self.expr_call_lang_item_fn(
-            into_future_span,
+            span,
             hir::LangItem::IntoFutureIntoFuture,
             arena_vec![self; expr],
             Some(expr_hir_id),
@@ -1746,40 +1738,31 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     pub(super) fn expr_usize(&mut self, sp: Span, value: usize) -> hir::Expr<'hir> {
-        self.expr(
-            sp,
-            hir::ExprKind::Lit(hir::Lit {
-                span: sp,
-                node: ast::LitKind::Int(
-                    value as u128,
-                    ast::LitIntType::Unsigned(ast::UintTy::Usize),
-                ),
-            }),
-        )
+        let lit = self.arena.alloc(hir::Lit {
+            span: sp,
+            node: ast::LitKind::Int(value as u128, ast::LitIntType::Unsigned(ast::UintTy::Usize)),
+        });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_u32(&mut self, sp: Span, value: u32) -> hir::Expr<'hir> {
-        self.expr(
-            sp,
-            hir::ExprKind::Lit(hir::Lit {
-                span: sp,
-                node: ast::LitKind::Int(value.into(), ast::LitIntType::Unsigned(ast::UintTy::U32)),
-            }),
-        )
+        let lit = self.arena.alloc(hir::Lit {
+            span: sp,
+            node: ast::LitKind::Int(value.into(), ast::LitIntType::Unsigned(ast::UintTy::U32)),
+        });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_char(&mut self, sp: Span, value: char) -> hir::Expr<'hir> {
-        self.expr(sp, hir::ExprKind::Lit(hir::Lit { span: sp, node: ast::LitKind::Char(value) }))
+        let lit = self.arena.alloc(hir::Lit { span: sp, node: ast::LitKind::Char(value) });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_str(&mut self, sp: Span, value: Symbol) -> hir::Expr<'hir> {
-        self.expr(
-            sp,
-            hir::ExprKind::Lit(hir::Lit {
-                span: sp,
-                node: ast::LitKind::Str(value, ast::StrStyle::Cooked),
-            }),
-        )
+        let lit = self
+            .arena
+            .alloc(hir::Lit { span: sp, node: ast::LitKind::Str(value, ast::StrStyle::Cooked) });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_call_mut(
diff --git a/compiler/rustc_ast_lowering/src/format.rs b/compiler/rustc_ast_lowering/src/format.rs
index c41bdc440..afcf8b15c 100644
--- a/compiler/rustc_ast_lowering/src/format.rs
+++ b/compiler/rustc_ast_lowering/src/format.rs
@@ -186,7 +186,7 @@ enum ArgumentType {
 /// Generates:
 ///
 /// ```text
-///     <core::fmt::ArgumentV1>::new_…(arg)
+///     <core::fmt::Argument>::new_…(arg)
 /// ```
 fn make_argument<'hir>(
     ctx: &mut LoweringContext<'_, 'hir>,
@@ -220,19 +220,19 @@ fn make_argument<'hir>(
 /// Generates:
 ///
 /// ```text
-///     <core::fmt::rt::v1::Count>::Is(…)
+///     <core::fmt::rt::Count>::Is(…)
 /// ```
 ///
 /// or
 ///
 /// ```text
-///     <core::fmt::rt::v1::Count>::Param(…)
+///     <core::fmt::rt::Count>::Param(…)
 /// ```
 ///
 /// or
 ///
 /// ```text
-///     <core::fmt::rt::v1::Count>::Implied
+///     <core::fmt::rt::Count>::Implied
 /// ```
 fn make_count<'hir>(
     ctx: &mut LoweringContext<'_, 'hir>,
@@ -278,13 +278,13 @@ fn make_count<'hir>(
 /// Generates
 ///
 /// ```text
-///     <core::fmt::rt::v1::Argument::new(
+///     <core::fmt::rt::Placeholder::new(
 ///         …usize, // position
 ///         '…', // fill
-///         <core::fmt::rt::v1::Alignment>::…, // alignment
+///         <core::fmt::rt::Alignment>::…, // alignment
 ///         …u32, // flags
-///         <core::fmt::rt::v1::Count::…>, // width
-///         <core::fmt::rt::v1::Count::…>, // precision
+///         <core::fmt::rt::Count::…>, // width
+///         <core::fmt::rt::Count::…>, // precision
 ///     )
 /// ```
 fn make_format_spec<'hir>(
@@ -327,7 +327,7 @@ fn make_format_spec<'hir>(
             None => sym::Unknown,
         },
     );
-    // This needs to match `FlagV1` in library/core/src/fmt/mod.rs.
+    // This needs to match `Flag` in library/core/src/fmt/rt.rs.
     let flags: u32 = ((sign == Some(FormatSign::Plus)) as u32)
         | ((sign == Some(FormatSign::Minus)) as u32) << 1
         | (alternate as u32) << 2
@@ -438,7 +438,7 @@ fn expand_format_args<'hir>(
     // If the args array contains exactly all the original arguments once,
     // in order, we can use a simple array instead of a `match` construction.
     // However, if there's a yield point in any argument except the first one,
-    // we don't do this, because an ArgumentV1 cannot be kept across yield points.
+    // we don't do this, because an Argument cannot be kept across yield points.
     //
     // This is an optimization, speeding up compilation about 1-2% in some cases.
     // See https://github.com/rust-lang/rust/pull/106770#issuecomment-1380790609
@@ -446,12 +446,35 @@ fn expand_format_args<'hir>(
         && argmap.iter().enumerate().all(|(i, (&(j, _), _))| i == j)
         && arguments.iter().skip(1).all(|arg| !may_contain_yield_point(&arg.expr));
 
-    let args = if use_simple_array {
+    let args = if arguments.is_empty() {
+        // Generate:
+        //    &<core::fmt::Argument>::none()
+        //
+        // Note:
+        //     `none()` just returns `[]`. We use `none()` rather than `[]` to limit the lifetime.
+        //
+        //     This makes sure that this still fails to compile, even when the argument is inlined:
+        //
+        //     ```
+        //     let f = format_args!("{}", "a");
+        //     println!("{f}"); // error E0716
+        //     ```
+        //
+        //     Cases where keeping the object around is allowed, such as `format_args!("a")`,
+        //     are handled above by the `allow_const` case.
+        let none_fn = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+            macsp,
+            hir::LangItem::FormatArgument,
+            sym::none,
+        ));
+        let none = ctx.expr_call(macsp, none_fn, &[]);
+        ctx.expr(macsp, hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, none))
+    } else if use_simple_array {
         // Generate:
         //     &[
-        //         <core::fmt::ArgumentV1>::new_display(&arg0),
-        //         <core::fmt::ArgumentV1>::new_lower_hex(&arg1),
-        //         <core::fmt::ArgumentV1>::new_debug(&arg2),
+        //         <core::fmt::Argument>::new_display(&arg0),
+        //         <core::fmt::Argument>::new_lower_hex(&arg1),
+        //         <core::fmt::Argument>::new_debug(&arg2),
         //         …
         //     ]
         let elements: Vec<_> = arguments
@@ -477,9 +500,9 @@ fn expand_format_args<'hir>(
         // Generate:
         //     &match (&arg0, &arg1, &…) {
         //         args => [
-        //             <core::fmt::ArgumentV1>::new_display(args.0),
-        //             <core::fmt::ArgumentV1>::new_lower_hex(args.1),
-        //             <core::fmt::ArgumentV1>::new_debug(args.0),
+        //             <core::fmt::Argument>::new_display(args.0),
+        //             <core::fmt::Argument>::new_lower_hex(args.1),
+        //             <core::fmt::Argument>::new_debug(args.0),
         //             …
         //         ]
         //     }
@@ -583,7 +606,7 @@ fn may_contain_yield_point(e: &ast::Expr) -> bool {
 
     impl Visitor<'_> for MayContainYieldPoint {
         fn visit_expr(&mut self, e: &ast::Expr) {
-            if let ast::ExprKind::Await(_) | ast::ExprKind::Yield(_) = e.kind {
+            if let ast::ExprKind::Await(_, _) | ast::ExprKind::Yield(_) = e.kind {
                 self.0 = true;
             } else {
                 visit::walk_expr(self, e);
diff --git a/compiler/rustc_ast_lowering/src/index.rs b/compiler/rustc_ast_lowering/src/index.rs
index f7fe0d771..2e66c81eb 100644
--- a/compiler/rustc_ast_lowering/src/index.rs
+++ b/compiler/rustc_ast_lowering/src/index.rs
@@ -5,7 +5,7 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_hir::definitions;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::*;
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::{Idx, IndexVec};
 use rustc_middle::span_bug;
 use rustc_session::Session;
 use rustc_span::source_map::SourceMap;
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index f89e254a2..08ee3761b 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -12,7 +12,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_hir::PredicateOrigin;
-use rustc_index::vec::{Idx, IndexSlice, IndexVec};
+use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::source_map::DesugaringKind;
@@ -83,15 +83,14 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             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, sym::closure_track_caller][..].into()),
-            allow_into_future: Some([sym::into_future][..].into()),
             generics_def_id_map: Default::default(),
         };
         lctx.with_hir_id_owner(owner, |lctx| f(lctx));
 
         for (def_id, info) in lctx.children {
-            self.owners.ensure_contains_elem(def_id, || hir::MaybeOwner::Phantom);
-            debug_assert!(matches!(self.owners[def_id], hir::MaybeOwner::Phantom));
-            self.owners[def_id] = info;
+            let owner = self.owners.ensure_contains_elem(def_id, || hir::MaybeOwner::Phantom);
+            debug_assert!(matches!(owner, hir::MaybeOwner::Phantom));
+            *owner = info;
         }
     }
 
@@ -99,8 +98,8 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
         &mut self,
         def_id: LocalDefId,
     ) -> hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>> {
-        self.owners.ensure_contains_elem(def_id, || hir::MaybeOwner::Phantom);
-        if let hir::MaybeOwner::Phantom = self.owners[def_id] {
+        let owner = self.owners.ensure_contains_elem(def_id, || hir::MaybeOwner::Phantom);
+        if let hir::MaybeOwner::Phantom = owner {
             let node = self.ast_index[def_id];
             match node {
                 AstOwner::NonOwner => {}
@@ -138,12 +137,10 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             // Evaluate with the lifetimes in `params` in-scope.
             // 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 { of_trait, .. }) => {
-                    lctx.is_in_trait_impl = of_trait.is_some();
-                }
-                _ => {}
-            };
+
+            if let hir::ItemKind::Impl(impl_) = parent_hir.node().expect_item().kind {
+                lctx.is_in_trait_impl = impl_.of_trait.is_some();
+            }
 
             match ctxt {
                 AssocCtxt::Trait => hir::OwnerNode::TraitItem(lctx.lower_trait_item(item)),
@@ -308,7 +305,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             );
                             this.arena.alloc(this.ty(span, hir::TyKind::Err(guar)))
                         }
-                        Some(ty) => this.lower_ty(ty, &ImplTraitContext::TypeAliasesOpaqueTy),
+                        Some(ty) => this.lower_ty(
+                            ty,
+                            &ImplTraitContext::TypeAliasesOpaqueTy { in_assoc_ty: false },
+                        ),
                     },
                 );
                 hir::ItemKind::TyAlias(ty, generics)
@@ -445,7 +445,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
             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_rules }, macro_kind)
+                let macro_def = self.arena.alloc(ast::MacroDef { body, macro_rules: *macro_rules });
+                hir::ItemKind::Macro(macro_def, macro_kind)
             }
             ItemKind::MacCall(..) => {
                 panic!("`TyMac` should have been expanded by now")
@@ -854,7 +855,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             hir::ImplItemKind::Type(ty)
                         }
                         Some(ty) => {
-                            let ty = this.lower_ty(ty, &ImplTraitContext::TypeAliasesOpaqueTy);
+                            let ty = this.lower_ty(
+                                ty,
+                                &ImplTraitContext::TypeAliasesOpaqueTy { in_assoc_ty: true },
+                            );
                             hir::ImplItemKind::Type(ty)
                         }
                     },
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index f7ae96b7c..8d4f96639 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -55,13 +55,13 @@ use rustc_data_structures::sync::Lrc;
 use rustc_errors::{
     DiagnosticArgFromDisplay, DiagnosticMessage, Handler, StashKey, SubdiagnosticMessage,
 };
+use rustc_fluent_macro::fluent_messages;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
-use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
+use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::definitions::DefPathData;
 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
-use rustc_index::vec::{Idx, IndexSlice, IndexVec};
-use rustc_macros::fluent_messages;
+use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_middle::{
     span_bug,
     ty::{ResolverAstLowering, TyCtxt},
@@ -136,7 +136,6 @@ struct LoweringContext<'a, 'hir> {
 
     allow_try_trait: Option<Lrc<[Symbol]>>,
     allow_gen_future: Option<Lrc<[Symbol]>>,
-    allow_into_future: Option<Lrc<[Symbol]>>,
 
     /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
     /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
@@ -248,7 +247,7 @@ enum ImplTraitContext {
         in_trait: bool,
     },
     /// Impl trait in type aliases.
-    TypeAliasesOpaqueTy,
+    TypeAliasesOpaqueTy { in_assoc_ty: bool },
     /// `impl Trait` is unstably accepted in this position.
     FeatureGated(ImplTraitPosition, Symbol),
     /// `impl Trait` is not accepted in this position.
@@ -283,6 +282,7 @@ enum ImplTraitPosition {
     FieldTy,
     Cast,
     ImplSelf,
+    OffsetOf,
 }
 
 impl std::fmt::Display for ImplTraitPosition {
@@ -313,6 +313,7 @@ impl std::fmt::Display for ImplTraitPosition {
             ImplTraitPosition::FieldTy => "field types",
             ImplTraitPosition::Cast => "cast types",
             ImplTraitPosition::ImplSelf => "impl headers",
+            ImplTraitPosition::OffsetOf => "`offset_of!` params",
         };
 
         write!(f, "{name}")
@@ -332,10 +333,7 @@ enum FnDeclKind {
 
 impl FnDeclKind {
     fn param_impl_trait_allowed(&self) -> bool {
-        match self {
-            FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
-            _ => false,
-        }
+        matches!(self, FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait)
     }
 
     fn return_impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
@@ -371,8 +369,8 @@ fn index_crate<'a>(
     krate: &'a Crate,
 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
     let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
-    indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
-    indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
+    *indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner) =
+        AstOwner::Crate(krate);
     visit::walk_crate(&mut indexer, krate);
     return indexer.index;
 
@@ -389,22 +387,21 @@ fn index_crate<'a>(
 
         fn visit_item(&mut self, item: &'a ast::Item) {
             let def_id = self.node_id_to_def_id[&item.id];
-            self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
-            self.index[def_id] = AstOwner::Item(item);
+            *self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner) = AstOwner::Item(item);
             visit::walk_item(self, item)
         }
 
         fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
             let def_id = self.node_id_to_def_id[&item.id];
-            self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
-            self.index[def_id] = AstOwner::AssocItem(item, ctxt);
+            *self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner) =
+                AstOwner::AssocItem(item, ctxt);
             visit::walk_assoc_item(self, item, ctxt);
         }
 
         fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
             let def_id = self.node_id_to_def_id[&item.id];
-            self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
-            self.index[def_id] = AstOwner::ForeignItem(item);
+            *self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner) =
+                AstOwner::ForeignItem(item);
             visit::walk_foreign_item(self, item);
         }
     }
@@ -438,6 +435,7 @@ pub fn lower_to_hir(tcx: TyCtxt<'_>, (): ()) -> hir::Crate<'_> {
     // Queries that borrow `resolver_for_lowering`.
     tcx.ensure_with_value().output_filenames(());
     tcx.ensure_with_value().early_lint_checks(());
+    tcx.ensure_with_value().debugger_visualizers(LOCAL_CRATE);
     let (mut resolver, krate) = tcx.resolver_for_lowering(()).steal();
 
     let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
@@ -1193,13 +1191,15 @@ 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(qself, path) => {
+                    TyKind::Path(None, path) => {
                         if let Some(res) = self
                             .resolver
                             .get_partial_res(ty.id)
                             .and_then(|partial_res| partial_res.full_res())
                         {
-                            if !res.matches_ns(Namespace::TypeNS) {
+                            if !res.matches_ns(Namespace::TypeNS)
+                                && path.is_potential_trivial_const_arg()
+                            {
                                 debug!(
                                     "lower_generic_arg: Lowering type argument as const argument: {:?}",
                                     ty,
@@ -1221,7 +1221,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                                 let path_expr = Expr {
                                     id: ty.id,
-                                    kind: ExprKind::Path(qself.clone(), path.clone()),
+                                    kind: ExprKind::Path(None, path.clone()),
                                     span,
                                     attrs: AttrVec::new(),
                                     tokens: None,
@@ -1371,13 +1371,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         this.arena.alloc_from_iter(bounds.iter().filter_map(|bound| match bound {
                             GenericBound::Trait(
                                 ty,
-                                TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
+                                TraitBoundModifier::None
+                                | TraitBoundModifier::MaybeConst
+                                | TraitBoundModifier::Negative,
                             ) => 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,
+                                TraitBoundModifier::Maybe
+                                | TraitBoundModifier::MaybeConstMaybe
+                                | TraitBoundModifier::MaybeConstNegative,
                             ) => None,
                             GenericBound::Outlives(lifetime) => {
                                 if lifetime_bound.is_none() {
@@ -1404,14 +1408,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             *in_trait,
                             itctx,
                         ),
-                    ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
-                        span,
-                        hir::OpaqueTyOrigin::TyAlias,
-                        *def_node_id,
-                        bounds,
-                        false,
-                        itctx,
-                    ),
+                    &ImplTraitContext::TypeAliasesOpaqueTy { in_assoc_ty } => self
+                        .lower_opaque_impl_trait(
+                            span,
+                            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty },
+                            *def_node_id,
+                            bounds,
+                            false,
+                            itctx,
+                        ),
                     ImplTraitContext::Universal => {
                         let span = t.span;
                         self.create_def(
@@ -1420,7 +1425,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             DefPathData::ImplTrait,
                             span,
                         );
-                        let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
+
+                        // HACK: pprust breaks strings with newlines when the type
+                        // gets too long. We don't want these to show up in compiler
+                        // output or built artifacts, so replace them here...
+                        // Perhaps we should instead format APITs more robustly.
+                        let ident = Ident::from_str_and_span(
+                            &pprust::ty_to_string(t).replace('\n', " "),
+                            span,
+                        );
+
                         let (param, bounds, path) = self.lower_universal_param_and_bounds(
                             *def_node_id,
                             span,
@@ -1476,6 +1490,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// Given a function definition like:
     ///
     /// ```rust
+    /// use std::fmt::Debug;
+    ///
     /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
     ///     x
     /// }
@@ -1483,13 +1499,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     ///
     /// we will create a TAIT definition in the HIR like
     ///
-    /// ```
+    /// ```rust,ignore (pseudo-Rust)
     /// type TestReturn<'a, T, 'x> = impl Debug + 'x
     /// ```
     ///
     /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
     ///
-    /// ```rust
+    /// ```rust,ignore (pseudo-Rust)
     /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
     /// ```
     ///
@@ -1529,13 +1545,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
         // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
         // exactly which ones those are.
-        let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
-            // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
-            Vec::new()
-        } else {
-            // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
-            // we only keep the lifetimes that appear in the `impl Debug` itself:
-            lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
+        let lifetimes_to_remap = match origin {
+            hir::OpaqueTyOrigin::TyAlias { .. } => {
+                // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
+                Vec::new()
+            }
+            hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..) => {
+                // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
+                // we only keep the lifetimes that appear in the `impl Debug` itself:
+                lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
+            }
         };
         debug!(?lifetimes_to_remap);
 
@@ -2424,11 +2443,20 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             TraitBoundModifier::None => hir::TraitBoundModifier::None,
             TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
 
+            TraitBoundModifier::Negative => {
+                if self.tcx.features().negative_bounds {
+                    hir::TraitBoundModifier::Negative
+                } else {
+                    hir::TraitBoundModifier::None
+                }
+            }
+
             // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
             // placeholder for compilation to proceed.
             TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
                 hir::TraitBoundModifier::Maybe
             }
+            TraitBoundModifier::MaybeConstNegative => hir::TraitBoundModifier::MaybeConst,
         }
     }
 
diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index 8eb84c036..441282c05 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -136,7 +136,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         self.diagnostic().span_bug(
             p.span,
-            &format!(
+            format!(
                 "lower_qpath: no final extension segment in {}..{}",
                 proj_start,
                 p.segments.len()