Merging upstream version 1.75.0+dfsg1.

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

8 files changed, 215 insertions, 197 deletions

diff --git a/compiler/rustc_ast_lowering/Cargo.toml b/compiler/rustc_ast_lowering/Cargo.toml
index 6b0da2565..8cc4521e0 100644
--- a/compiler/rustc_ast_lowering/Cargo.toml
+++ b/compiler/rustc_ast_lowering/Cargo.toml
@@ -7,18 +7,20 @@ edition = "2021"
 doctest = false
 
 [dependencies]
+# tidy-alphabetical-start
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
-rustc_hir = { path = "../rustc_hir" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
+rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
-rustc_middle = { path = "../rustc_middle" }
 rustc_macros = { path = "../rustc_macros" }
+rustc_middle = { path = "../rustc_middle" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
 thin-vec = "0.2.12"
 tracing = "0.1"
+# tidy-alphabetical-end
diff --git a/compiler/rustc_ast_lowering/messages.ftl b/compiler/rustc_ast_lowering/messages.ftl
index 8115c4b55..91591a716 100644
--- a/compiler/rustc_ast_lowering/messages.ftl
+++ b/compiler/rustc_ast_lowering/messages.ftl
@@ -11,8 +11,8 @@ ast_lowering_argument = argument
 ast_lowering_assoc_ty_parentheses =
     parenthesized generic arguments cannot be used in associated type constraints
 
-ast_lowering_async_generators_not_supported =
-    `async` generators are not yet supported
+ast_lowering_async_coroutines_not_supported =
+    `async` coroutines are not yet supported
 
 ast_lowering_async_non_move_closure_not_supported =
     `async` non-`move` closures with parameters are not currently supported
@@ -42,6 +42,9 @@ ast_lowering_clobber_abi_not_supported =
 
 ast_lowering_closure_cannot_be_static = closures cannot be static
 
+ast_lowering_coroutine_too_many_parameters =
+    too many parameters for a coroutine (expected 0 or 1 parameters)
+
 ast_lowering_does_not_support_modifiers =
     the `{$class_name}` register class does not support template modifiers
 
@@ -53,9 +56,6 @@ ast_lowering_functional_record_update_destructuring_assignment =
     functional record updates are not allowed in destructuring assignments
     .suggestion = consider removing the trailing pattern
 
-ast_lowering_generator_too_many_parameters =
-    too many parameters for a generator (expected 0 or 1 parameters)
-
 ast_lowering_generic_type_with_parentheses =
     parenthesized type parameters may only be used with a `Fn` trait
     .label = only `Fn` traits may use parentheses
@@ -99,7 +99,7 @@ ast_lowering_misplaced_double_dot =
     .note = only allowed in tuple, tuple struct, and slice patterns
 
 ast_lowering_misplaced_impl_trait =
-    `impl Trait` only allowed in function and inherent method return types, not in {$position}
+    `impl Trait` only allowed in function and inherent method argument and return types, not in {$position}
 
 ast_lowering_misplaced_relax_trait_bound =
     `?Trait` bounds are only permitted at the point where a type parameter is declared
@@ -136,12 +136,6 @@ ast_lowering_template_modifier = template modifier
 
 ast_lowering_this_not_async = this is not `async`
 
-ast_lowering_trait_fn_async =
-    functions in traits cannot be declared `async`
-    .label = `async` because of this
-    .note = `async` trait functions are not currently supported
-    .note2 = consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 ast_lowering_underscore_expr_lhs_assign =
     in expressions, `_` can only be used on the left-hand side of an assignment
     .label = `_` not allowed here
diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index a63bd4f8a..6e1a9eff5 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -131,8 +131,8 @@ pub struct AwaitOnlyInAsyncFnAndBlocks {
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_generator_too_many_parameters, code = "E0628")]
-pub struct GeneratorTooManyParameters {
+#[diag(ast_lowering_coroutine_too_many_parameters, code = "E0628")]
+pub struct CoroutineTooManyParameters {
     #[primary_span]
     pub fn_decl_span: Span,
 }
@@ -161,8 +161,8 @@ pub struct FunctionalRecordUpdateDestructuringAssignment {
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_async_generators_not_supported, code = "E0727")]
-pub struct AsyncGeneratorsNotSupported {
+#[diag(ast_lowering_async_coroutines_not_supported, code = "E0727")]
+pub struct AsyncCoroutinesNotSupported {
     #[primary_span]
     pub span: Span,
 }
@@ -354,17 +354,6 @@ pub struct InclusiveRangeWithNoEnd {
     pub span: Span,
 }
 
-#[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_trait_fn_async, code = "E0706")]
-#[note]
-#[note(ast_lowering_note2)]
-pub struct TraitFnAsync {
-    #[primary_span]
-    pub fn_span: Span,
-    #[label]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 pub enum BadReturnTypeNotation {
     #[diag(ast_lowering_bad_return_type_notation_inputs)]
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 57c54f854..0fff9a6be 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1,8 +1,8 @@
 use super::errors::{
-    AsyncGeneratorsNotSupported, AsyncNonMoveClosureNotSupported, AwaitOnlyInAsyncFnAndBlocks,
-    BaseExpressionDoubleDot, ClosureCannotBeStatic, FunctionalRecordUpdateDestructuringAssignment,
-    GeneratorTooManyParameters, InclusiveRangeWithNoEnd, NotSupportedForLifetimeBinderAsyncClosure,
-    UnderscoreExprLhsAssign,
+    AsyncCoroutinesNotSupported, AsyncNonMoveClosureNotSupported, AwaitOnlyInAsyncFnAndBlocks,
+    BaseExpressionDoubleDot, ClosureCannotBeStatic, CoroutineTooManyParameters,
+    FunctionalRecordUpdateDestructuringAssignment, InclusiveRangeWithNoEnd,
+    NotSupportedForLifetimeBinderAsyncClosure, UnderscoreExprLhsAssign,
 };
 use super::ResolverAstLoweringExt;
 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
@@ -15,9 +15,10 @@ 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::source_map::{respan, Spanned};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
+use rustc_span::{DesugaringKind, Span};
 use thin_vec::{thin_vec, ThinVec};
 
 impl<'hir> LoweringContext<'_, 'hir> {
@@ -183,12 +184,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
                     hir::MatchSource::Normal,
                 ),
-                ExprKind::Async(capture_clause, block) => self.make_async_expr(
+                ExprKind::Gen(capture_clause, block, GenBlockKind::Async) => self.make_async_expr(
                     *capture_clause,
                     e.id,
                     None,
                     e.span,
-                    hir::AsyncGeneratorKind::Block,
+                    hir::CoroutineSource::Block,
                     |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
                 ),
                 ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
@@ -317,6 +318,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         rest,
                     )
                 }
+                ExprKind::Gen(capture_clause, block, GenBlockKind::Gen) => self.make_gen_expr(
+                    *capture_clause,
+                    e.id,
+                    None,
+                    e.span,
+                    hir::CoroutineSource::Block,
+                    |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
+                ),
                 ExprKind::Yield(opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
                 ExprKind::Err => hir::ExprKind::Err(
                     self.tcx.sess.delay_span_bug(e.span, "lowered ExprKind::Err"),
@@ -583,7 +592,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    /// Lower an `async` construct to a generator that implements `Future`.
+    /// Lower an `async` construct to a coroutine that implements `Future`.
     ///
     /// This results in:
     ///
@@ -598,7 +607,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         closure_node_id: NodeId,
         ret_ty: Option<hir::FnRetTy<'hir>>,
         span: Span,
-        async_gen_kind: hir::AsyncGeneratorKind,
+        async_coroutine_source: hir::CoroutineSource,
         body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
     ) -> hir::ExprKind<'hir> {
         let output = ret_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span)));
@@ -613,7 +622,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             span: unstable_span,
         };
 
-        // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
+        // The closure/coroutine `FnDecl` takes a single (resume) argument of type `input_ty`.
         let fn_decl = self.arena.alloc(hir::FnDecl {
             inputs: arena_vec![self; input_ty],
             output,
@@ -637,7 +646,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let params = arena_vec![self; param];
 
         let body = self.lower_body(move |this| {
-            this.generator_kind = Some(hir::GeneratorKind::Async(async_gen_kind));
+            this.coroutine_kind = Some(hir::CoroutineKind::Async(async_coroutine_source));
 
             let old_ctx = this.task_context;
             this.task_context = Some(task_context_hid);
@@ -661,6 +670,57 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }))
     }
 
+    /// Lower a `gen` construct to a generator that implements `Iterator`.
+    ///
+    /// This results in:
+    ///
+    /// ```text
+    /// static move? |()| -> () {
+    ///     <body>
+    /// }
+    /// ```
+    pub(super) fn make_gen_expr(
+        &mut self,
+        capture_clause: CaptureBy,
+        closure_node_id: NodeId,
+        _yield_ty: Option<hir::FnRetTy<'hir>>,
+        span: Span,
+        coroutine_source: hir::CoroutineSource,
+        body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
+    ) -> hir::ExprKind<'hir> {
+        let output = hir::FnRetTy::DefaultReturn(self.lower_span(span));
+
+        // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
+        let fn_decl = self.arena.alloc(hir::FnDecl {
+            inputs: &[],
+            output,
+            c_variadic: false,
+            implicit_self: hir::ImplicitSelfKind::None,
+            lifetime_elision_allowed: false,
+        });
+
+        let body = self.lower_body(move |this| {
+            this.coroutine_kind = Some(hir::CoroutineKind::Gen(coroutine_source));
+
+            let res = body(this);
+            (&[], res)
+        });
+
+        // `static |()| -> () { body }`:
+        hir::ExprKind::Closure(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(Movability::Movable),
+            constness: hir::Constness::NotConst,
+        }))
+    }
+
     /// Forwards a possible `#[track_caller]` annotation from `outer_hir_id` to
     /// `inner_hir_id` in case the `async_fn_track_caller` feature is enabled.
     pub(super) fn maybe_forward_track_caller(
@@ -673,12 +733,18 @@ impl<'hir> LoweringContext<'_, 'hir> {
             && let Some(attrs) = self.attrs.get(&outer_hir_id.local_id)
             && attrs.into_iter().any(|attr| attr.has_name(sym::track_caller))
         {
-            let unstable_span =
-                self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
+            let unstable_span = self.mark_span_with_reason(
+                DesugaringKind::Async,
+                span,
+                self.allow_gen_future.clone(),
+            );
             self.lower_attrs(
                 inner_hir_id,
                 &[Attribute {
-                    kind: AttrKind::Normal(ptr::P(NormalAttr::from_ident(Ident::new(sym::track_caller, span)))),
+                    kind: AttrKind::Normal(ptr::P(NormalAttr::from_ident(Ident::new(
+                        sym::track_caller,
+                        span,
+                    )))),
                     id: self.tcx.sess.parse_sess.attr_id_generator.mk_attr_id(),
                     style: AttrStyle::Outer,
                     span: unstable_span,
@@ -704,9 +770,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
     /// ```
     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 => {
+        match self.coroutine_kind {
+            Some(hir::CoroutineKind::Async(_)) => {}
+            Some(hir::CoroutineKind::Coroutine) | Some(hir::CoroutineKind::Gen(_)) | None => {
                 self.tcx.sess.emit_err(AwaitOnlyInAsyncFnAndBlocks {
                     await_kw_span,
                     item_span: self.current_item,
@@ -881,19 +947,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> hir::ExprKind<'hir> {
         let (binder_clause, generic_params) = self.lower_closure_binder(binder);
 
-        let (body_id, generator_option) = self.with_new_scopes(move |this| {
+        let (body_id, coroutine_option) = self.with_new_scopes(move |this| {
             let prev = this.current_item;
             this.current_item = Some(fn_decl_span);
-            let mut generator_kind = None;
+            let mut coroutine_kind = None;
             let body_id = this.lower_fn_body(decl, |this| {
                 let e = this.lower_expr_mut(body);
-                generator_kind = this.generator_kind;
+                coroutine_kind = this.coroutine_kind;
                 e
             });
-            let generator_option =
-                this.generator_movability_for_fn(&decl, fn_decl_span, generator_kind, movability);
+            let coroutine_option =
+                this.coroutine_movability_for_fn(&decl, fn_decl_span, coroutine_kind, movability);
             this.current_item = prev;
-            (body_id, generator_option)
+            (body_id, coroutine_option)
         });
 
         let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
@@ -909,29 +975,29 @@ impl<'hir> LoweringContext<'_, 'hir> {
             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,
+            movability: coroutine_option,
             constness: self.lower_constness(constness),
         });
 
         hir::ExprKind::Closure(c)
     }
 
-    fn generator_movability_for_fn(
+    fn coroutine_movability_for_fn(
         &mut self,
         decl: &FnDecl,
         fn_decl_span: Span,
-        generator_kind: Option<hir::GeneratorKind>,
+        coroutine_kind: Option<hir::CoroutineKind>,
         movability: Movability,
     ) -> Option<hir::Movability> {
-        match generator_kind {
-            Some(hir::GeneratorKind::Gen) => {
+        match coroutine_kind {
+            Some(hir::CoroutineKind::Coroutine) => {
                 if decl.inputs.len() > 1 {
-                    self.tcx.sess.emit_err(GeneratorTooManyParameters { fn_decl_span });
+                    self.tcx.sess.emit_err(CoroutineTooManyParameters { fn_decl_span });
                 }
                 Some(movability)
             }
-            Some(hir::GeneratorKind::Async(_)) => {
-                panic!("non-`async` closure body turned `async` during lowering");
+            Some(hir::CoroutineKind::Gen(_)) | Some(hir::CoroutineKind::Async(_)) => {
+                panic!("non-`async`/`gen` closure body turned `async`/`gen` during lowering");
             }
             None => {
                 if movability == Movability::Static {
@@ -999,7 +1065,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     inner_closure_id,
                     async_ret_ty,
                     body.span,
-                    hir::AsyncGeneratorKind::Closure,
+                    hir::CoroutineSource::Closure,
                     |this| this.with_new_scopes(|this| this.lower_expr_mut(body)),
                 );
                 let hir_id = this.lower_node_id(inner_closure_id);
@@ -1102,7 +1168,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
         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) {
-                if let Some(res) = partial_res.full_res() && !res.expected_in_tuple_struct_pat() {
+                if let Some(res) = partial_res.full_res()
+                    && !res.expected_in_tuple_struct_pat()
+                {
                     return None;
                 }
             }
@@ -1122,7 +1190,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
         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) {
-                if let Some(res) = partial_res.full_res() && !res.expected_in_unit_struct_pat() {
+                if let Some(res) = partial_res.full_res()
+                    && !res.expected_in_unit_struct_pat()
+                {
                     return None;
                 }
             }
@@ -1434,12 +1504,23 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
-        match self.generator_kind {
-            Some(hir::GeneratorKind::Gen) => {}
-            Some(hir::GeneratorKind::Async(_)) => {
-                self.tcx.sess.emit_err(AsyncGeneratorsNotSupported { span });
+        match self.coroutine_kind {
+            Some(hir::CoroutineKind::Gen(_)) => {}
+            Some(hir::CoroutineKind::Async(_)) => {
+                self.tcx.sess.emit_err(AsyncCoroutinesNotSupported { span });
+            }
+            Some(hir::CoroutineKind::Coroutine) | None => {
+                if !self.tcx.features().coroutines {
+                    rustc_session::parse::feature_err(
+                        &self.tcx.sess.parse_sess,
+                        sym::coroutines,
+                        span,
+                        "yield syntax is experimental",
+                    )
+                    .emit();
+                }
+                self.coroutine_kind = Some(hir::CoroutineKind::Coroutine)
             }
-            None => self.generator_kind = Some(hir::GeneratorKind::Gen),
         }
 
         let expr =
diff --git a/compiler/rustc_ast_lowering/src/format.rs b/compiler/rustc_ast_lowering/src/format.rs
index afcf8b15c..c7d0719e7 100644
--- a/compiler/rustc_ast_lowering/src/format.rs
+++ b/compiler/rustc_ast_lowering/src/format.rs
@@ -61,9 +61,12 @@ fn flatten_format_args(mut fmt: Cow<'_, FormatArgs>) -> Cow<'_, FormatArgs> {
             let remaining_args = args.split_off(arg_index + 1);
             let old_arg_offset = args.len();
             let mut fmt2 = &mut args.pop().unwrap().expr; // The inner FormatArgs.
-            let fmt2 = loop { // Unwrap the Expr to get to the FormatArgs.
+            let fmt2 = loop {
+                // Unwrap the Expr to get to the FormatArgs.
                 match &mut fmt2.kind {
-                    ExprKind::Paren(inner) | ExprKind::AddrOf(BorrowKind::Ref, _, inner) => fmt2 = inner,
+                    ExprKind::Paren(inner) | ExprKind::AddrOf(BorrowKind::Ref, _, inner) => {
+                        fmt2 = inner
+                    }
                     ExprKind::FormatArgs(fmt2) => break fmt2,
                     _ => unreachable!(),
                 }
@@ -410,15 +413,11 @@ fn expand_format_args<'hir>(
     let format_options = use_format_options.then(|| {
         // Generate:
         //     &[format_spec_0, format_spec_1, format_spec_2]
-        let elements: Vec<_> = fmt
-            .template
-            .iter()
-            .filter_map(|piece| {
-                let FormatArgsPiece::Placeholder(placeholder) = piece else { return None };
-                Some(make_format_spec(ctx, macsp, placeholder, &mut argmap))
-            })
-            .collect();
-        ctx.expr_array_ref(macsp, ctx.arena.alloc_from_iter(elements))
+        let elements = ctx.arena.alloc_from_iter(fmt.template.iter().filter_map(|piece| {
+            let FormatArgsPiece::Placeholder(placeholder) = piece else { return None };
+            Some(make_format_spec(ctx, macsp, placeholder, &mut argmap))
+        }));
+        ctx.expr_array_ref(macsp, elements)
     });
 
     let arguments = fmt.arguments.all_args();
@@ -477,10 +476,8 @@ fn expand_format_args<'hir>(
         //         <core::fmt::Argument>::new_debug(&arg2),
         //         …
         //     ]
-        let elements: Vec<_> = arguments
-            .iter()
-            .zip(argmap)
-            .map(|(arg, ((_, ty), placeholder_span))| {
+        let elements = ctx.arena.alloc_from_iter(arguments.iter().zip(argmap).map(
+            |(arg, ((_, ty), placeholder_span))| {
                 let placeholder_span =
                     placeholder_span.unwrap_or(arg.expr.span).with_ctxt(macsp.ctxt());
                 let arg_span = match arg.kind {
@@ -493,9 +490,9 @@ fn expand_format_args<'hir>(
                     hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, arg),
                 ));
                 make_argument(ctx, placeholder_span, ref_arg, ty)
-            })
-            .collect();
-        ctx.expr_array_ref(macsp, ctx.arena.alloc_from_iter(elements))
+            },
+        ));
+        ctx.expr_array_ref(macsp, elements)
     } else {
         // Generate:
         //     &match (&arg0, &arg1, &…) {
@@ -528,19 +525,14 @@ fn expand_format_args<'hir>(
                 make_argument(ctx, placeholder_span, arg, ty)
             },
         ));
-        let elements: Vec<_> = arguments
-            .iter()
-            .map(|arg| {
-                let arg_expr = ctx.lower_expr(&arg.expr);
-                ctx.expr(
-                    arg.expr.span.with_ctxt(macsp.ctxt()),
-                    hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, arg_expr),
-                )
-            })
-            .collect();
-        let args_tuple = ctx
-            .arena
-            .alloc(ctx.expr(macsp, hir::ExprKind::Tup(ctx.arena.alloc_from_iter(elements))));
+        let elements = ctx.arena.alloc_from_iter(arguments.iter().map(|arg| {
+            let arg_expr = ctx.lower_expr(&arg.expr);
+            ctx.expr(
+                arg.expr.span.with_ctxt(macsp.ctxt()),
+                hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, arg_expr),
+            )
+        }));
+        let args_tuple = ctx.arena.alloc(ctx.expr(macsp, hir::ExprKind::Tup(elements)));
         let array = ctx.arena.alloc(ctx.expr(macsp, hir::ExprKind::Array(args)));
         let match_arms = ctx.arena.alloc_from_iter([ctx.arm(args_pat, array)]);
         let match_expr = ctx.arena.alloc(ctx.expr_match(
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index edc1e2f0b..9a70e6d7c 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -16,9 +16,8 @@ use rustc_hir::PredicateOrigin;
 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;
 use rustc_span::symbol::{kw, sym, Ident};
-use rustc_span::{Span, Symbol};
+use rustc_span::{DesugaringKind, Span, Symbol};
 use rustc_target::spec::abi;
 use smallvec::{smallvec, SmallVec};
 use thin_vec::ThinVec;
@@ -82,7 +81,7 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             is_in_loop_condition: false,
             is_in_trait_impl: false,
             is_in_dyn_type: false,
-            generator_kind: None,
+            coroutine_kind: None,
             task_context: None,
             current_item: None,
             impl_trait_defs: Vec::new(),
@@ -974,7 +973,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         value: hir::Expr<'hir>,
     ) -> hir::BodyId {
         let body = hir::Body {
-            generator_kind: self.generator_kind,
+            coroutine_kind: self.coroutine_kind,
             params,
             value: self.arena.alloc(value),
         };
@@ -988,12 +987,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         f: impl FnOnce(&mut Self) -> (&'hir [hir::Param<'hir>], hir::Expr<'hir>),
     ) -> hir::BodyId {
-        let prev_gen_kind = self.generator_kind.take();
+        let prev_coroutine_kind = self.coroutine_kind.take();
         let task_context = self.task_context.take();
         let (parameters, result) = f(self);
         let body_id = self.record_body(parameters, result);
         self.task_context = task_context;
-        self.generator_kind = prev_gen_kind;
+        self.coroutine_kind = prev_coroutine_kind;
         body_id
     }
 
@@ -1202,11 +1201,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
 
             let async_expr = this.make_async_expr(
-                CaptureBy::Value,
+                CaptureBy::Value { move_kw: rustc_span::DUMMY_SP },
                 closure_id,
                 None,
                 body.span,
-                hir::AsyncGeneratorKind::Fn,
+                hir::CoroutineSource::Fn,
                 |this| {
                     // Create a block from the user's function body:
                     let user_body = this.lower_block_expr(body);
@@ -1387,10 +1386,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // Desugar `~const` bound in generics into an additional `const host: bool` param
         // if the effects feature is enabled. This needs to be done before we lower where
         // clauses since where clauses need to bind to the DefId of the host param
-        let host_param_parts = if let Const::Yes(span) = constness && self.tcx.features().effects {
-            if let Some(param) = generics.params.iter().find(|x| {
-                x.attrs.iter().any(|x| x.has_name(sym::rustc_host))
-            }) {
+        let host_param_parts = if let Const::Yes(span) = constness
+            && self.tcx.features().effects
+        {
+            if let Some(param) =
+                generics.params.iter().find(|x| x.attrs.iter().any(|x| x.has_name(sym::rustc_host)))
+            {
                 // user has manually specified a `rustc_host` param, in this case, we set
                 // the param id so that lowering logic can use that. But we don't create
                 // another host param, so this gives `None`.
@@ -1399,7 +1400,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
             } else {
                 let param_node_id = self.next_node_id();
                 let hir_id = self.next_id();
-                let def_id = self.create_def(self.local_def_id(parent_node_id), param_node_id, DefPathData::TypeNs(sym::host), span);
+                let def_id = self.create_def(
+                    self.local_def_id(parent_node_id),
+                    param_node_id,
+                    DefPathData::TypeNs(sym::host),
+                    span,
+                );
                 self.host_param_id = Some(def_id);
                 Some((span, hir_id, def_id))
             }
@@ -1623,12 +1629,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     .lower_generic_params(bound_generic_params, hir::GenericParamSource::Binder),
                 bounded_ty: self
                     .lower_ty(bounded_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Bound)),
-                bounds: self.arena.alloc_from_iter(bounds.iter().map(|bound| {
-                    self.lower_param_bound(
-                        bound,
-                        &ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
-                    )
-                })),
+                bounds: self.lower_param_bounds(
+                    bounds,
+                    &ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
+                ),
                 span: self.lower_span(*span),
                 origin: PredicateOrigin::WhereClause,
             }),
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 85ab5e722..a88493acf 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -30,6 +30,9 @@
 //! get confused if the spans from leaf AST nodes occur in multiple places
 //! in the HIR, especially for multiple identifiers.
 
+#![cfg_attr(not(bootstrap), allow(internal_features))]
+#![cfg_attr(not(bootstrap), feature(rustdoc_internals))]
+#![cfg_attr(not(bootstrap), doc(rust_logo))]
 #![feature(box_patterns)]
 #![feature(let_chains)]
 #![feature(never_type)]
@@ -40,7 +43,7 @@
 #[macro_use]
 extern crate tracing;
 
-use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait, TraitFnAsync};
+use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait};
 
 use rustc_ast::ptr::P;
 use rustc_ast::visit;
@@ -68,9 +71,8 @@ use rustc_middle::{
 };
 use rustc_session::parse::{add_feature_diagnostics, feature_err};
 use rustc_span::hygiene::MacroKind;
-use rustc_span::source_map::DesugaringKind;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{DesugaringKind, Span, DUMMY_SP};
 use smallvec::SmallVec;
 use std::collections::hash_map::Entry;
 use thin_vec::ThinVec;
@@ -108,10 +110,10 @@ struct LoweringContext<'a, 'hir> {
     /// Collect items that were created by lowering the current owner.
     children: Vec<(LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>)>,
 
-    generator_kind: Option<hir::GeneratorKind>,
+    coroutine_kind: Option<hir::CoroutineKind>,
 
     /// When inside an `async` context, this is the `HirId` of the
-    /// `task_context` local bound to the resume argument of the generator.
+    /// `task_context` local bound to the resume argument of the coroutine.
     task_context: Option<hir::HirId>,
 
     /// Used to get the current `fn`'s def span to point to when using `await`
@@ -271,8 +273,6 @@ enum ImplTraitPosition {
     ClosureReturn,
     PointerReturn,
     FnTraitReturn,
-    TraitReturn,
-    ImplReturn,
     GenericDefault,
     ConstTy,
     StaticTy,
@@ -302,8 +302,6 @@ impl std::fmt::Display for ImplTraitPosition {
             ImplTraitPosition::ClosureReturn => "closure return types",
             ImplTraitPosition::PointerReturn => "`fn` pointer return types",
             ImplTraitPosition::FnTraitReturn => "`Fn` trait return types",
-            ImplTraitPosition::TraitReturn => "trait method return types",
-            ImplTraitPosition::ImplReturn => "`impl` method return types",
             ImplTraitPosition::GenericDefault => "generic parameter defaults",
             ImplTraitPosition::ConstTy => "const types",
             ImplTraitPosition::StaticTy => "static types",
@@ -334,20 +332,9 @@ impl FnDeclKind {
         matches!(self, FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait)
     }
 
-    fn return_impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
+    fn return_impl_trait_allowed(&self) -> bool {
         match self {
-            FnDeclKind::Fn | FnDeclKind::Inherent => true,
-            FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
-            FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
-            _ => false,
-        }
-    }
-
-    fn async_fn_allowed(&self, tcx: TyCtxt<'_>) -> bool {
-        match self {
-            FnDeclKind::Fn | FnDeclKind::Inherent => true,
-            FnDeclKind::Impl if tcx.features().async_fn_in_trait => true,
-            FnDeclKind::Trait if tcx.features().async_fn_in_trait => true,
+            FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
             _ => false,
         }
     }
@@ -1229,7 +1216,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                     hir_id: this.lower_node_id(node_id),
                                     body: this.lower_const_body(path_expr.span, Some(&path_expr)),
                                 });
-                                return GenericArg::Const(ConstArg { value: ct, span });
+                                return GenericArg::Const(ConstArg {
+                                    value: ct,
+                                    span,
+                                    is_desugared_from_effects: false,
+                                });
                             }
                         }
                     }
@@ -1240,6 +1231,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
                 value: self.lower_anon_const(&ct),
                 span: self.lower_span(ct.value.span),
+                is_desugared_from_effects: false,
             }),
         }
     }
@@ -1271,7 +1263,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     &PolyTraitRef {
                         bound_generic_params: ThinVec::new(),
                         trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
-                        span: t.span
+                        span: t.span,
                     },
                     itctx,
                     ast::Const::No,
@@ -1749,14 +1741,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
-        // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
-        // as they are not explicit in HIR/Ty function signatures.
-        // (instead, the `c_variadic` flag is set to `true`)
-        let mut inputs = &decl.inputs[..];
-        if decl.c_variadic() {
-            inputs = &inputs[..inputs.len() - 1];
-        }
-        self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
+        self.arena.alloc_from_iter(decl.inputs.iter().map(|param| match param.pat.kind {
             PatKind::Ident(_, ident, _) => self.lower_ident(ident),
             _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
         }))
@@ -1805,53 +1790,30 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.lower_ty_direct(&param.ty, &itctx)
         }));
 
-        let output = if let Some((ret_id, span)) = make_ret_async {
-            if !kind.async_fn_allowed(self.tcx) {
-                match kind {
-                    FnDeclKind::Trait | FnDeclKind::Impl => {
-                        self.tcx
-                            .sess
-                            .create_feature_err(
-                                TraitFnAsync { fn_span, span },
-                                sym::async_fn_in_trait,
-                            )
-                            .emit();
-                    }
-                    _ => {
-                        self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
-                    }
-                }
-            }
-
+        let output = if let Some((ret_id, _span)) = make_ret_async {
             let fn_def_id = self.local_def_id(fn_node_id);
-            self.lower_async_fn_ret_ty(&decl.output, fn_def_id, ret_id, kind)
+            self.lower_async_fn_ret_ty(&decl.output, fn_def_id, ret_id, kind, fn_span)
         } else {
             match &decl.output {
                 FnRetTy::Ty(ty) => {
-                    let context = if kind.return_impl_trait_allowed(self.tcx) {
+                    let context = if kind.return_impl_trait_allowed() {
                         let fn_def_id = self.local_def_id(fn_node_id);
                         ImplTraitContext::ReturnPositionOpaqueTy {
                             origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
                             fn_kind: kind,
                         }
                     } else {
-                        let position = match kind {
-                            FnDeclKind::Fn | FnDeclKind::Inherent => {
-                                unreachable!("fn should allow in-band lifetimes")
+                        ImplTraitContext::Disallowed(match kind {
+                            FnDeclKind::Fn
+                            | FnDeclKind::Inherent
+                            | FnDeclKind::Trait
+                            | FnDeclKind::Impl => {
+                                unreachable!("fn should allow return-position impl trait in traits")
                             }
                             FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
                             FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
                             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, &context))
                 }
@@ -1901,8 +1863,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         fn_def_id: LocalDefId,
         opaque_ty_node_id: NodeId,
         fn_kind: FnDeclKind,
+        fn_span: Span,
     ) -> hir::FnRetTy<'hir> {
-        let span = self.lower_span(output.span());
+        let span = self.lower_span(fn_span);
         let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
 
         let captured_lifetimes: Vec<_> = self
@@ -1923,18 +1886,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let future_bound = this.lower_async_fn_output_type_to_future_bound(
                     output,
                     span,
-                    if let FnDeclKind::Trait = fn_kind
-                        && !this.tcx.features().return_position_impl_trait_in_trait
-                    {
-                        ImplTraitContext::FeatureGated(
-                            ImplTraitPosition::TraitReturn,
-                            sym::return_position_impl_trait_in_trait,
-                        )
-                    } else {
-                        ImplTraitContext::ReturnPositionOpaqueTy {
-                            origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                            fn_kind,
-                        }
+                    ImplTraitContext::ReturnPositionOpaqueTy {
+                        origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
+                        fn_kind,
                     },
                 );
                 arena_vec![this; future_bound]
@@ -2568,6 +2522,7 @@ impl<'hir> GenericArgsCtor<'hir> {
         self.args.push(hir::GenericArg::Const(hir::ConstArg {
             value: hir::AnonConst { def_id, hir_id, body },
             span,
+            is_desugared_from_effects: true,
         }))
     }
 
diff --git a/compiler/rustc_ast_lowering/src/lifetime_collector.rs b/compiler/rustc_ast_lowering/src/lifetime_collector.rs
index 6f75419c3..d66bba517 100644
--- a/compiler/rustc_ast_lowering/src/lifetime_collector.rs
+++ b/compiler/rustc_ast_lowering/src/lifetime_collector.rs
@@ -82,7 +82,8 @@ impl<'ast> Visitor<'ast> for LifetimeCollectVisitor<'ast> {
                 // We can sometimes encounter bare trait objects
                 // which are represented in AST as paths.
                 if let Some(partial_res) = self.resolver.get_partial_res(t.id)
-                    && let Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _)) = partial_res.full_res()
+                    && let Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _)) =
+                        partial_res.full_res()
                 {
                     self.current_binders.push(t.id);
                     visit::walk_ty(self, t);