diff --git a/rust-toolchain b/rust-toolchain
index 719b5eabf89..aa35a7f12d5 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2023-12-12"
+channel = "nightly-2023-12-28"
 components = ["llvm-tools", "rustc-dev"]
diff --git a/src/closures.rs b/src/closures.rs
index f698f494ae5..5bf29441b54 100644
--- a/src/closures.rs
+++ b/src/closures.rs
@@ -448,7 +448,7 @@ fn is_block_closure_forced(context: &RewriteContext<'_>, expr: &ast::Expr) -> bo
 
 fn is_block_closure_forced_inner(expr: &ast::Expr, version: Version) -> bool {
     match expr.kind {
-        ast::ExprKind::If(..) | ast::ExprKind::While(..) | ast::ExprKind::ForLoop(..) => true,
+        ast::ExprKind::If(..) | ast::ExprKind::While(..) | ast::ExprKind::ForLoop { .. } => true,
         ast::ExprKind::Loop(..) if version == Version::Two => true,
         ast::ExprKind::AddrOf(_, _, ref expr)
         | ast::ExprKind::Try(ref expr)
@@ -473,7 +473,7 @@ fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
         | ast::ExprKind::Block(..)
         | ast::ExprKind::While(..)
         | ast::ExprKind::Loop(..)
-        | ast::ExprKind::ForLoop(..)
+        | ast::ExprKind::ForLoop { .. }
         | ast::ExprKind::TryBlock(..) => false,
         _ => true,
     }
diff --git a/src/expr.rs b/src/expr.rs
index a68bd6694ba..7808f891336 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -3,7 +3,7 @@ use std::cmp::min;
 
 use itertools::Itertools;
 use rustc_ast::token::{Delimiter, Lit, LitKind};
-use rustc_ast::{ast, ptr, token};
+use rustc_ast::{ast, ptr, token, ForLoopKind};
 use rustc_span::{BytePos, Span};
 
 use crate::chains::rewrite_chain;
@@ -134,7 +134,7 @@ pub(crate) fn format_expr(
         }
         ast::ExprKind::Let(ref pat, ref expr, _span, _) => rewrite_let(context, shape, pat, expr),
         ast::ExprKind::If(..)
-        | ast::ExprKind::ForLoop(..)
+        | ast::ExprKind::ForLoop { .. }
         | ast::ExprKind::Loop(..)
         | ast::ExprKind::While(..) => to_control_flow(expr, expr_type)
             .and_then(|control_flow| control_flow.rewrite(context, shape)),
@@ -682,9 +682,15 @@ fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow<
                 expr.span,
             ))
         }
-        ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
-            Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
-        }
+        ast::ExprKind::ForLoop {
+            ref pat,
+            ref iter,
+            ref body,
+            label,
+            kind,
+        } => Some(ControlFlow::new_for(
+            pat, iter, body, label, expr.span, kind,
+        )),
         ast::ExprKind::Loop(ref block, label, _) => {
             Some(ControlFlow::new_loop(block, label, expr.span))
         }
@@ -771,6 +777,7 @@ impl<'a> ControlFlow<'a> {
         block: &'a ast::Block,
         label: Option<ast::Label>,
         span: Span,
+        kind: ForLoopKind,
     ) -> ControlFlow<'a> {
         ControlFlow {
             cond: Some(cond),
@@ -778,7 +785,10 @@ impl<'a> ControlFlow<'a> {
             else_block: None,
             label,
             pat: Some(pat),
-            keyword: "for",
+            keyword: match kind {
+                ForLoopKind::For => "for",
+                ForLoopKind::ForAwait => "for await",
+            },
             matcher: "",
             connector: " in",
             allow_single_line: false,
@@ -1364,7 +1374,7 @@ pub(crate) fn can_be_overflowed_expr(
                 || context.config.overflow_delimited_expr()
         }
         ast::ExprKind::If(..)
-        | ast::ExprKind::ForLoop(..)
+        | ast::ExprKind::ForLoop { .. }
         | ast::ExprKind::Loop(..)
         | ast::ExprKind::While(..) => {
             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
diff --git a/src/items.rs b/src/items.rs
index 5d01a2df068..0bcfa3f448b 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -666,7 +666,7 @@ impl<'a> FmtVisitor<'a> {
         let span = mk_sp(lo, field.span.lo());
 
         let variant_body = match field.data {
-            ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => format_struct(
+            ast::VariantData::Tuple(..) | ast::VariantData::Struct { .. } => format_struct(
                 &context,
                 &StructParts::from_variant(field, &context),
                 self.block_indent,
@@ -1094,7 +1094,7 @@ fn enum_variant_span(variant: &ast::Variant, context: &RewriteContext<'_>) -> Sp
     if let Some(ref anon_const) = variant.disr_expr {
         let span_before_consts = variant.span.until(anon_const.value.span);
         let hi = match &variant.data {
-            Struct(..) => context
+            Struct { .. } => context
                 .snippet_provider
                 .span_after_last(span_before_consts, "}"),
             Tuple(..) => context
@@ -1114,12 +1114,12 @@ fn format_struct(
     offset: Indent,
     one_line_width: Option<usize>,
 ) -> Option<String> {
-    match *struct_parts.def {
+    match struct_parts.def {
         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
-        ast::VariantData::Tuple(ref fields, _) => {
+        ast::VariantData::Tuple(fields, _) => {
             format_tuple_struct(context, struct_parts, fields, offset)
         }
-        ast::VariantData::Struct(ref fields, _) => {
+        ast::VariantData::Struct { fields, .. } => {
             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
         }
     }
diff --git a/src/matches.rs b/src/matches.rs
index e6692d78161..72386f0a097 100644
--- a/src/matches.rs
+++ b/src/matches.rs
@@ -591,7 +591,7 @@ fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
         ast::ExprKind::If(..) => false,
         // We do not allow collapsing a block around expression with condition
         // to avoid it being cluttered with match arm.
-        ast::ExprKind::ForLoop(..) | ast::ExprKind::While(..) => false,
+        ast::ExprKind::ForLoop { .. } | ast::ExprKind::While(..) => false,
         ast::ExprKind::Loop(..)
         | ast::ExprKind::Match(..)
         | ast::ExprKind::Block(..)
diff --git a/src/overflow.rs b/src/overflow.rs
index 11060f46666..2f9705ec943 100644
--- a/src/overflow.rs
+++ b/src/overflow.rs
@@ -421,7 +421,7 @@ impl<'a> Context<'a> {
                     // When overflowing the expressions which consists of a control flow
                     // expression, avoid condition to use multi line.
                     ast::ExprKind::If(..)
-                    | ast::ExprKind::ForLoop(..)
+                    | ast::ExprKind::ForLoop { .. }
                     | ast::ExprKind::Loop(..)
                     | ast::ExprKind::While(..)
                     | ast::ExprKind::Match(..) => {
diff --git a/src/parse/macros/cfg_if.rs b/src/parse/macros/cfg_if.rs
index cbc4c90b8f9..bafef7b0f46 100644
--- a/src/parse/macros/cfg_if.rs
+++ b/src/parse/macros/cfg_if.rs
@@ -67,7 +67,7 @@ fn parse_cfg_if_inner<'a>(
                 Ok(None) => continue,
                 Err(err) => {
                     err.cancel();
-                    parser.sess.span_diagnostic.reset_err_count();
+                    parser.sess.dcx.reset_err_count();
                     return Err(
                         "Expected item inside cfg_if block, but failed to parse it as an item",
                     );
diff --git a/src/parse/macros/lazy_static.rs b/src/parse/macros/lazy_static.rs
index a8c2feec453..8b1dc6694d6 100644
--- a/src/parse/macros/lazy_static.rs
+++ b/src/parse/macros/lazy_static.rs
@@ -16,8 +16,8 @@ pub(crate) fn parse_lazy_static(
         ($method:ident $(,)* $($arg:expr),* $(,)*) => {
             match parser.$method($($arg,)*) {
                 Ok(val) => {
-                    if parser.sess.span_diagnostic.has_errors().is_some() {
-                        parser.sess.span_diagnostic.reset_err_count();
+                    if parser.sess.dcx.has_errors().is_some() {
+                        parser.sess.dcx.reset_err_count();
                         return None;
                     } else {
                         val
@@ -25,7 +25,7 @@ pub(crate) fn parse_lazy_static(
                 }
                 Err(err) => {
                     err.cancel();
-                    parser.sess.span_diagnostic.reset_err_count();
+                    parser.sess.dcx.reset_err_count();
                     return None;
                 }
             }
diff --git a/src/parse/macros/mod.rs b/src/parse/macros/mod.rs
index 7a802f7a88e..2dd2622174f 100644
--- a/src/parse/macros/mod.rs
+++ b/src/parse/macros/mod.rs
@@ -28,8 +28,8 @@ fn parse_macro_arg<'a, 'b: 'a>(parser: &'a mut Parser<'b>) -> Option<MacroArg> {
             let mut cloned_parser = (*parser).clone();
             match $parser(&mut cloned_parser) {
                 Ok(x) => {
-                    if parser.sess.span_diagnostic.has_errors().is_some() {
-                        parser.sess.span_diagnostic.reset_err_count();
+                    if parser.sess.dcx.has_errors().is_some() {
+                        parser.sess.dcx.reset_err_count();
                     } else {
                         // Parsing succeeded.
                         *parser = cloned_parser;
@@ -38,7 +38,7 @@ fn parse_macro_arg<'a, 'b: 'a>(parser: &'a mut Parser<'b>) -> Option<MacroArg> {
                 }
                 Err(e) => {
                     e.cancel();
-                    parser.sess.span_diagnostic.reset_err_count();
+                    parser.sess.dcx.reset_err_count();
                 }
             }
         };
diff --git a/src/parse/session.rs b/src/parse/session.rs
index 162a8caf373..646d2d132a8 100644
--- a/src/parse/session.rs
+++ b/src/parse/session.rs
@@ -4,7 +4,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
 use rustc_errors::emitter::{DynEmitter, Emitter, EmitterWriter};
 use rustc_errors::translation::Translate;
-use rustc_errors::{ColorConfig, Diagnostic, Handler, Level as DiagnosticLevel};
+use rustc_errors::{ColorConfig, DiagCtxt, Diagnostic, Level as DiagnosticLevel};
 use rustc_session::parse::ParseSess as RawParseSess;
 use rustc_span::{
     source_map::{FilePathMapping, SourceMap},
@@ -118,13 +118,13 @@ impl From<Color> for ColorConfig {
     }
 }
 
-fn default_handler(
+fn default_dcx(
     source_map: Lrc<SourceMap>,
     ignore_path_set: Lrc<IgnorePathSet>,
     can_reset: Lrc<AtomicBool>,
     show_parse_errors: bool,
     color: Color,
-) -> Handler {
+) -> DiagCtxt {
     let supports_color = term::stderr().map_or(false, |term| term.supports_color());
     let emit_color = if supports_color {
         ColorConfig::from(color)
@@ -141,7 +141,7 @@ fn default_handler(
         );
         Box::new(EmitterWriter::stderr(emit_color, fallback_bundle).sm(Some(source_map.clone())))
     };
-    Handler::with_emitter(Box::new(SilentOnIgnoredFilesEmitter {
+    DiagCtxt::with_emitter(Box::new(SilentOnIgnoredFilesEmitter {
         has_non_ignorable_parser_errors: false,
         source_map,
         emitter,
@@ -159,14 +159,14 @@ impl ParseSess {
         let source_map = Lrc::new(SourceMap::new(FilePathMapping::empty()));
         let can_reset_errors = Lrc::new(AtomicBool::new(false));
 
-        let handler = default_handler(
+        let dcx = default_dcx(
             Lrc::clone(&source_map),
             Lrc::clone(&ignore_path_set),
             Lrc::clone(&can_reset_errors),
             config.show_parse_errors(),
             config.color(),
         );
-        let parse_sess = RawParseSess::with_span_handler(handler, source_map);
+        let parse_sess = RawParseSess::with_dcx(dcx, source_map);
 
         Ok(ParseSess {
             parse_sess,
@@ -218,7 +218,7 @@ impl ParseSess {
     }
 
     pub(crate) fn set_silent_emitter(&mut self) {
-        self.parse_sess.span_diagnostic = Handler::with_emitter(silent_emitter());
+        self.parse_sess.dcx = DiagCtxt::with_emitter(silent_emitter());
     }
 
     pub(crate) fn span_to_filename(&self, span: Span) -> FileName {
@@ -284,10 +284,8 @@ impl ParseSess {
 // Methods that should be restricted within the parse module.
 impl ParseSess {
     pub(super) fn emit_diagnostics(&self, diagnostics: Vec<Diagnostic>) {
-        for mut diagnostic in diagnostics {
-            self.parse_sess
-                .span_diagnostic
-                .emit_diagnostic(&mut diagnostic);
+        for diagnostic in diagnostics {
+            self.parse_sess.dcx.emit_diagnostic(diagnostic);
         }
     }
 
@@ -296,11 +294,11 @@ impl ParseSess {
     }
 
     pub(super) fn has_errors(&self) -> bool {
-        self.parse_sess.span_diagnostic.has_errors().is_some()
+        self.parse_sess.dcx.has_errors().is_some()
     }
 
     pub(super) fn reset_errors(&self) {
-        self.parse_sess.span_diagnostic.reset_err_count();
+        self.parse_sess.dcx.reset_err_count();
     }
 }
 
@@ -372,7 +370,7 @@ mod tests {
 
         fn build_diagnostic(level: DiagnosticLevel, span: Option<MultiSpan>) -> Diagnostic {
             let mut diag = Diagnostic::new(level, "");
-            diag.message.clear();
+            diag.messages.clear();
             if let Some(span) = span {
                 diag.span = span;
             }
diff --git a/src/patterns.rs b/src/patterns.rs
index 8504999b8ff..0fa6edaa5d7 100644
--- a/src/patterns.rs
+++ b/src/patterns.rs
@@ -259,9 +259,15 @@ impl Rewrite for Pat {
                 None,
                 None,
             ),
-            PatKind::Struct(ref qself, ref path, ref fields, ellipsis) => {
-                rewrite_struct_pat(qself, path, fields, ellipsis, self.span, context, shape)
-            }
+            PatKind::Struct(ref qself, ref path, ref fields, rest) => rewrite_struct_pat(
+                qself,
+                path,
+                fields,
+                rest == ast::PatFieldsRest::Rest,
+                self.span,
+                context,
+                shape,
+            ),
             PatKind::MacCall(ref mac) => {
                 rewrite_macro(mac, None, context, shape, MacroPosition::Pat)
             }
diff --git a/src/types.rs b/src/types.rs
index a5a4244903c..cd2582e66be 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -537,28 +537,19 @@ impl Rewrite for ast::Lifetime {
 impl Rewrite for ast::GenericBound {
     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
         match *self {
-            ast::GenericBound::Trait(ref poly_trait_ref, trait_bound_modifier) => {
+            ast::GenericBound::Trait(ref poly_trait_ref, modifiers) => {
                 let snippet = context.snippet(self.span());
                 let has_paren = snippet.starts_with('(') && snippet.ends_with(')');
-                let rewrite = match trait_bound_modifier {
-                    ast::TraitBoundModifier::None => poly_trait_ref.rewrite(context, shape),
-                    ast::TraitBoundModifier::Maybe => poly_trait_ref
-                        .rewrite(context, shape.offset_left(1)?)
-                        .map(|s| format!("?{}", s)),
-                    ast::TraitBoundModifier::MaybeConst(_) => poly_trait_ref
-                        .rewrite(context, shape.offset_left(7)?)
-                        .map(|s| format!("~const {}", s)),
-                    ast::TraitBoundModifier::MaybeConstMaybe => poly_trait_ref
-                        .rewrite(context, shape.offset_left(8)?)
-                        .map(|s| format!("~const ?{}", s)),
-                    ast::TraitBoundModifier::Negative => poly_trait_ref
-                        .rewrite(context, shape.offset_left(1)?)
-                        .map(|s| format!("!{}", s)),
-                    ast::TraitBoundModifier::MaybeConstNegative => poly_trait_ref
-                        .rewrite(context, shape.offset_left(8)?)
-                        .map(|s| format!("~const !{}", s)),
-                };
-                rewrite.map(|s| if has_paren { format!("({})", s) } else { s })
+                let mut constness = modifiers.constness.as_str().to_string();
+                if !constness.is_empty() {
+                    constness.push(' ');
+                }
+                let polarity = modifiers.polarity.as_str();
+                let shape = shape.offset_left(constness.len() + polarity.len())?;
+                poly_trait_ref
+                    .rewrite(context, shape)
+                    .map(|s| format!("{constness}{polarity}{s}"))
+                    .map(|s| if has_paren { format!("({})", s) } else { s })
             }
             ast::GenericBound::Outlives(ref lifetime) => lifetime.rewrite(context, shape),
         }
diff --git a/src/utils.rs b/src/utils.rs
index 7d7bbf11529..642b6603b1e 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -295,7 +295,7 @@ pub(crate) fn semicolon_for_stmt(
 ) -> bool {
     match stmt.kind {
         ast::StmtKind::Semi(ref expr) => match expr.kind {
-            ast::ExprKind::While(..) | ast::ExprKind::Loop(..) | ast::ExprKind::ForLoop(..) => {
+            ast::ExprKind::While(..) | ast::ExprKind::Loop(..) | ast::ExprKind::ForLoop { .. } => {
                 false
             }
             ast::ExprKind::Break(..) | ast::ExprKind::Continue(..) | ast::ExprKind::Ret(..) => {
@@ -476,7 +476,7 @@ pub(crate) fn is_block_expr(context: &RewriteContext<'_>, expr: &ast::Expr, repr
         | ast::ExprKind::ConstBlock(..)
         | ast::ExprKind::Gen(..)
         | ast::ExprKind::Loop(..)
-        | ast::ExprKind::ForLoop(..)
+        | ast::ExprKind::ForLoop { .. }
         | ast::ExprKind::TryBlock(..)
         | ast::ExprKind::Match(..) => repr.contains('\n'),
         ast::ExprKind::Paren(ref expr)