Adding upstream version 1.69.0+dfsg1.upstream/1.69.0+dfsg1

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

30 files changed, 505 insertions, 604 deletions

diff --git a/compiler/rustc_builtin_macros/src/format/ast.rs b/compiler/rustc_ast/src/format.rs
index 01dbffa21..d021bea5e 100644
--- a/compiler/rustc_builtin_macros/src/format/ast.rs
+++ b/compiler/rustc_ast/src/format.rs
@@ -1,5 +1,5 @@
-use rustc_ast::ptr::P;
-use rustc_ast::Expr;
+use crate::ptr::P;
+use crate::Expr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::Span;
@@ -39,7 +39,7 @@ use rustc_span::Span;
 /// Basically the "AST" for a complete `format_args!()`.
 ///
 /// E.g., `format_args!("hello {name}");`.
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FormatArgs {
     pub span: Span,
     pub template: Vec<FormatArgsPiece>,
@@ -49,7 +49,7 @@ pub struct FormatArgs {
 /// A piece of a format template string.
 ///
 /// E.g. "hello" or "{name}".
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub enum FormatArgsPiece {
     Literal(Symbol),
     Placeholder(FormatPlaceholder),
@@ -59,7 +59,7 @@ pub enum FormatArgsPiece {
 ///
 /// E.g. `1, 2, name="ferris", n=3`,
 /// but also implicit captured arguments like `x` in `format_args!("{x}")`.
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FormatArguments {
     arguments: Vec<FormatArgument>,
     num_unnamed_args: usize,
@@ -67,6 +67,12 @@ pub struct FormatArguments {
     names: FxHashMap<Symbol, usize>,
 }
 
+// FIXME: Rustdoc has trouble proving Send/Sync for this. See #106930.
+#[cfg(parallel_compiler)]
+unsafe impl Sync for FormatArguments {}
+#[cfg(parallel_compiler)]
+unsafe impl Send for FormatArguments {}
+
 impl FormatArguments {
     pub fn new() -> Self {
         Self {
@@ -121,18 +127,22 @@ impl FormatArguments {
         &self.arguments[..self.num_explicit_args]
     }
 
-    pub fn into_vec(self) -> Vec<FormatArgument> {
-        self.arguments
+    pub fn all_args(&self) -> &[FormatArgument] {
+        &self.arguments[..]
+    }
+
+    pub fn all_args_mut(&mut self) -> &mut [FormatArgument] {
+        &mut self.arguments[..]
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FormatArgument {
     pub kind: FormatArgumentKind,
     pub expr: P<Expr>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub enum FormatArgumentKind {
     /// `format_args(…, arg)`
     Normal,
@@ -152,7 +162,7 @@ impl FormatArgumentKind {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub struct FormatPlaceholder {
     /// Index into [`FormatArgs::arguments`].
     pub argument: FormatArgPosition,
@@ -164,7 +174,7 @@ pub struct FormatPlaceholder {
     pub format_options: FormatOptions,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub struct FormatArgPosition {
     /// Which argument this position refers to (Ok),
     /// or would've referred to if it existed (Err).
@@ -175,7 +185,7 @@ pub struct FormatArgPosition {
     pub span: Option<Span>,
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatArgPositionKind {
     /// `{}` or `{:.*}`
     Implicit,
@@ -185,7 +195,7 @@ pub enum FormatArgPositionKind {
     Named,
 }
 
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq, Hash)]
 pub enum FormatTrait {
     /// `{}`
     Display,
@@ -207,7 +217,7 @@ pub enum FormatTrait {
     UpperHex,
 }
 
-#[derive(Clone, Debug, Default, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Default, Debug, PartialEq, Eq)]
 pub struct FormatOptions {
     /// The width. E.g. `{:5}` or `{:width$}`.
     pub width: Option<FormatCount>,
@@ -217,11 +227,33 @@ pub struct FormatOptions {
     pub alignment: Option<FormatAlignment>,
     /// The fill character. E.g. the `.` in `{:.>10}`.
     pub fill: Option<char>,
-    /// The `+`, `-`, `0`, `#`, `x?` and `X?` flags.
-    pub flags: u32,
+    /// The `+` or `-` flag.
+    pub sign: Option<FormatSign>,
+    /// The `#` flag.
+    pub alternate: bool,
+    /// The `0` flag. E.g. the `0` in `{:02x}`.
+    pub zero_pad: bool,
+    /// The `x` or `X` flag (for `Debug` only). E.g. the `x` in `{:x?}`.
+    pub debug_hex: Option<FormatDebugHex>,
+}
+
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
+pub enum FormatSign {
+    /// The `+` flag.
+    Plus,
+    /// The `-` flag.
+    Minus,
+}
+
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
+pub enum FormatDebugHex {
+    /// The `x` flag in `{:x?}`.
+    Lower,
+    /// The `X` flag in `{:X?}`.
+    Upper,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatAlignment {
     /// `{:<}`
     Left,
@@ -231,7 +263,7 @@ pub enum FormatAlignment {
     Center,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatCount {
     /// `{:5}` or `{:.5}`
     Literal(usize),
diff --git a/compiler/rustc_builtin_macros/Cargo.toml b/compiler/rustc_builtin_macros/Cargo.toml
index 467fa932a..336e14ef9 100644
--- a/compiler/rustc_builtin_macros/Cargo.toml
+++ b/compiler/rustc_builtin_macros/Cargo.toml
@@ -23,5 +23,5 @@ 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 = "0.2.9"
+thin-vec = "0.2.12"
 tracing = "0.1"
diff --git a/compiler/rustc_error_messages/locales/en-US/builtin_macros.ftl b/compiler/rustc_builtin_macros/locales/en-US.ftl
index 4d088e27b..4d088e27b 100644
--- a/compiler/rustc_error_messages/locales/en-US/builtin_macros.ftl
+++ b/compiler/rustc_builtin_macros/locales/en-US.ftl
diff --git a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
index dcf500ddb..ac6697232 100644
--- a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
+++ b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
@@ -6,7 +6,7 @@ use rustc_ast::{Fn, ItemKind, Stmt, TyKind, Unsafe};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Span;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand(
     ecx: &mut ExtCtxt<'_>,
@@ -39,10 +39,10 @@ pub fn expand(
     let span = ecx.with_def_site_ctxt(item.span);
 
     // Generate item statements for the allocator methods.
-    let stmts = vec![generate_handler(ecx, item.ident, span, sig_span)];
+    let stmts = thin_vec![generate_handler(ecx, item.ident, span, sig_span)];
 
     // Generate anonymous constant serving as container for the allocator methods.
-    let const_ty = ecx.ty(sig_span, TyKind::Tup(Vec::new()));
+    let const_ty = ecx.ty(sig_span, TyKind::Tup(ThinVec::new()));
     let const_body = ecx.expr_block(ecx.block(span, stmts));
     let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
     let const_item = if is_stmt {
@@ -67,13 +67,16 @@ fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span
 
     let layout_new = cx.std_path(&[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
     let layout_new = cx.expr_path(cx.path(span, layout_new));
-    let layout =
-        cx.expr_call(span, layout_new, vec![cx.expr_ident(span, size), cx.expr_ident(span, align)]);
+    let layout = cx.expr_call(
+        span,
+        layout_new,
+        thin_vec![cx.expr_ident(span, size), cx.expr_ident(span, align)],
+    );
 
-    let call = cx.expr_call_ident(sig_span, handler, vec![layout]);
+    let call = cx.expr_call_ident(sig_span, handler, thin_vec![layout]);
 
     let never = ast::FnRetTy::Ty(cx.ty(span, TyKind::Never));
-    let params = vec![cx.param(span, size, ty_usize.clone()), cx.param(span, align, ty_usize)];
+    let params = thin_vec![cx.param(span, size, ty_usize.clone()), cx.param(span, align, ty_usize)];
     let decl = cx.fn_decl(params, never);
     let header = FnHeader { unsafety: Unsafe::Yes(span), ..FnHeader::default() };
     let sig = FnSig { decl, header, span: span };
diff --git a/compiler/rustc_builtin_macros/src/asm.rs b/compiler/rustc_builtin_macros/src/asm.rs
index 925392b50..3fdbc9715 100644
--- a/compiler/rustc_builtin_macros/src/asm.rs
+++ b/compiler/rustc_builtin_macros/src/asm.rs
@@ -152,7 +152,7 @@ pub fn parse_asm_args<'a>(
                 ast::InlineAsmOperand::InOut { reg, expr, late: true }
             }
         } else if p.eat_keyword(kw::Const) {
-            let anon_const = p.parse_anon_const_expr()?;
+            let anon_const = p.parse_expr_anon_const()?;
             ast::InlineAsmOperand::Const { anon_const }
         } else if p.eat_keyword(sym::sym) {
             let expr = p.parse_expr()?;
diff --git a/compiler/rustc_builtin_macros/src/assert.rs b/compiler/rustc_builtin_macros/src/assert.rs
index 8555c3593..75af5e2b1 100644
--- a/compiler/rustc_builtin_macros/src/assert.rs
+++ b/compiler/rustc_builtin_macros/src/assert.rs
@@ -11,6 +11,7 @@ use rustc_expand::base::{DummyResult, ExtCtxt, MacEager, MacResult};
 use rustc_parse::parser::Parser;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
+use thin_vec::thin_vec;
 
 pub fn expand_assert<'cx>(
     cx: &'cx mut ExtCtxt<'_>,
@@ -79,7 +80,7 @@ pub fn expand_assert<'cx>(
         let then = cx.expr_call_global(
             call_site_span,
             cx.std_path(&[sym::panicking, sym::panic]),
-            vec![cx.expr_str(
+            thin_vec![cx.expr_str(
                 DUMMY_SP,
                 Symbol::intern(&format!(
                     "assertion failed: {}",
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index 93b07801e..b0b4dda16 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -12,7 +12,7 @@ use rustc_span::{
     symbol::{sym, Ident, Symbol},
     Span,
 };
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub(super) struct Context<'cx, 'a> {
     // An optimization.
@@ -83,12 +83,12 @@ impl<'cx, 'a> Context<'cx, 'a> {
 
         let Self { best_case_captures, capture_decls, cx, local_bind_decls, span, .. } = self;
 
-        let mut assert_then_stmts = Vec::with_capacity(2);
+        let mut assert_then_stmts = ThinVec::with_capacity(2);
         assert_then_stmts.extend(best_case_captures);
         assert_then_stmts.push(self.cx.stmt_expr(panic));
         let assert_then = self.cx.block(span, assert_then_stmts);
 
-        let mut stmts = Vec::with_capacity(4);
+        let mut stmts = ThinVec::with_capacity(4);
         stmts.push(initial_imports);
         stmts.extend(capture_decls.into_iter().map(|c| c.decl));
         stmts.extend(local_bind_decls);
@@ -120,7 +120,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
                 thin_vec![self.cx.attr_nested_word(sym::allow, sym::unused_imports, self.span)],
                 ItemKind::Use(UseTree {
                     prefix: self.cx.path(self.span, self.cx.std_path(&[sym::asserting])),
-                    kind: UseTreeKind::Nested(vec![
+                    kind: UseTreeKind::Nested(thin_vec![
                         nested_tree(self, sym::TryCaptureGeneric),
                         nested_tree(self, sym::TryCapturePrintable),
                     ]),
@@ -136,7 +136,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
         self.cx.expr_call(
             self.span,
             self.cx.expr_path(self.cx.path(self.span, unlikely_path)),
-            vec![self.cx.expr(self.span, ExprKind::Unary(UnOp::Not, cond_expr))],
+            thin_vec![self.cx.expr(self.span, ExprKind::Unary(UnOp::Not, cond_expr))],
         )
     }
 
@@ -297,6 +297,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::Continue(_)
             | ExprKind::Err
             | ExprKind::Field(_, _)
+            | ExprKind::FormatArgs(_)
             | ExprKind::ForLoop(_, _, _, _)
             | ExprKind::If(_, _, _)
             | ExprKind::IncludedBytes(..)
@@ -338,7 +339,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
         let init = self.cx.expr_call(
             self.span,
             self.cx.expr_path(self.cx.path(self.span, init_std_path)),
-            vec![],
+            ThinVec::new(),
         );
         let capture = Capture { decl: self.cx.stmt_let(self.span, true, ident, init), ident };
         self.capture_decls.push(capture);
@@ -365,7 +366,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             self.cx.expr_path(
                 self.cx.path(self.span, self.cx.std_path(&[sym::asserting, sym::Wrapper])),
             ),
-            vec![self.cx.expr_path(Path::from_ident(local_bind))],
+            thin_vec![self.cx.expr_path(Path::from_ident(local_bind))],
         );
         let try_capture_call = self
             .cx
@@ -377,7 +378,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
                     ident: Ident::new(sym::try_capture, self.span),
                 },
                 expr_paren(self.cx, self.span, self.cx.expr_addr_of(self.span, wrapper)),
-                vec![expr_addr_of_mut(
+                thin_vec![expr_addr_of_mut(
                     self.cx,
                     self.span,
                     self.cx.expr_path(Path::from_ident(capture)),
@@ -388,7 +389,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
         let local_bind_path = self.cx.expr_path(Path::from_ident(local_bind));
         let rslt = if self.is_consumed {
             let ret = self.cx.stmt_expr(local_bind_path);
-            self.cx.expr_block(self.cx.block(self.span, vec![try_capture_call, ret]))
+            self.cx.expr_block(self.cx.block(self.span, thin_vec![try_capture_call, ret]))
         } else {
             self.best_case_captures.push(try_capture_call);
             local_bind_path
@@ -440,7 +441,7 @@ fn expr_method_call(
     cx: &ExtCtxt<'_>,
     seg: PathSegment,
     receiver: P<Expr>,
-    args: Vec<P<Expr>>,
+    args: ThinVec<P<Expr>>,
     span: Span,
 ) -> P<Expr> {
     cx.expr(span, ExprKind::MethodCall(Box::new(MethodCall { seg, receiver, args, span })))
diff --git a/compiler/rustc_builtin_macros/src/deriving/bounds.rs b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
index 240167146..0481a1189 100644
--- a/compiler/rustc_builtin_macros/src/deriving/bounds.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
@@ -17,6 +17,7 @@ pub fn expand_deriving_copy(
         span,
         path: path_std!(marker::Copy),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: false,
         additional_bounds: Vec::new(),
         supports_unions: true,
         methods: Vec::new(),
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index ef5a75f42..dfee2d3ce 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -6,7 +6,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Span;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_clone(
     cx: &mut ExtCtxt<'_>,
@@ -73,6 +73,7 @@ pub fn expand_deriving_clone(
         span,
         path: path_std!(clone::Clone),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: bounds,
         supports_unions: true,
         methods: vec![MethodDef {
@@ -99,7 +100,7 @@ fn cs_clone_simple(
     substr: &Substructure<'_>,
     is_union: bool,
 ) -> BlockOrExpr {
-    let mut stmts = Vec::new();
+    let mut stmts = ThinVec::new();
     let mut seen_type_names = FxHashSet::default();
     let mut process_variant = |variant: &VariantData| {
         for field in variant.fields() {
@@ -161,7 +162,7 @@ fn cs_clone(
     let all_fields;
     let fn_path = cx.std_path(&[sym::clone, sym::Clone, sym::clone]);
     let subcall = |cx: &mut ExtCtxt<'_>, field: &FieldInfo| {
-        let args = vec![field.self_expr.clone()];
+        let args = thin_vec![field.self_expr.clone()];
         cx.expr_call_global(field.span, fn_path.clone(), args)
     };
 
@@ -199,7 +200,7 @@ fn cs_clone(
                     let call = subcall(cx, field);
                     cx.field_imm(field.span, ident, call)
                 })
-                .collect::<Vec<_>>();
+                .collect::<ThinVec<_>>();
 
             cx.expr_struct(trait_span, ctor_path, fields)
         }
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
index 3e994f037..af9719586 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
@@ -7,7 +7,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_eq(
     cx: &mut ExtCtxt<'_>,
@@ -27,6 +27,7 @@ pub fn expand_deriving_eq(
         span,
         path: path_std!(cmp::Eq),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: true,
         methods: vec![MethodDef {
@@ -55,7 +56,7 @@ fn cs_total_eq_assert(
     trait_span: Span,
     substr: &Substructure<'_>,
 ) -> BlockOrExpr {
-    let mut stmts = Vec::new();
+    let mut stmts = ThinVec::new();
     let mut seen_type_names = FxHashSet::default();
     let mut process_variant = |variant: &ast::VariantData| {
         for field in variant.fields() {
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
index a926fca4e..cfd36f030 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -20,6 +20,7 @@ pub fn expand_deriving_ord(
         span,
         path: path_std!(cmp::Ord),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods: vec![MethodDef {
@@ -63,14 +64,14 @@ pub fn cs_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> Bl
                 let [other_expr] = &field.other_selflike_exprs[..] else {
                         cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
                     };
-                let args = vec![field.self_expr.clone(), other_expr.clone()];
+                let args = thin_vec![field.self_expr.clone(), other_expr.clone()];
                 cx.expr_call_global(field.span, cmp_path.clone(), args)
             }
             CsFold::Combine(span, expr1, expr2) => {
                 let eq_arm = cx.arm(span, cx.pat_path(span, equal_path.clone()), expr1);
                 let neq_arm =
                     cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
-                cx.expr_match(span, expr2, vec![eq_arm, neq_arm])
+                cx.expr_match(span, expr2, thin_vec![eq_arm, neq_arm])
             }
             CsFold::Fieldless => cx.expr_path(equal_path.clone()),
         },
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
index 9051fe0b2..bad47db0d 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -29,16 +29,30 @@ pub fn expand_deriving_partial_eq(
                         cx.span_bug(field.span, "not exactly 2 arguments in `derive(PartialEq)`");
                     };
 
-                    // We received `&T` arguments. Convert them to `T` by
-                    // stripping `&` or adding `*`. This isn't necessary for
-                    // type checking, but it results in much better error
-                    // messages if something goes wrong.
+                    // We received arguments of type `&T`. Convert them to type `T` by stripping
+                    // any leading `&` or adding `*`. This isn't necessary for type checking, but
+                    // it results in better error messages if something goes wrong.
+                    //
+                    // Note: for arguments that look like `&{ x }`, which occur with packed
+                    // structs, this would cause expressions like `{ self.x } == { other.x }`,
+                    // which isn't valid Rust syntax. This wouldn't break compilation because these
+                    // AST nodes are constructed within the compiler. But it would mean that code
+                    // printed by `-Zunpretty=expanded` (or `cargo expand`) would have invalid
+                    // syntax, which would be suboptimal. So we wrap these in parens, giving
+                    // `({ self.x }) == ({ other.x })`, which is valid syntax.
                     let convert = |expr: &P<Expr>| {
                         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, inner) =
                             &expr.kind
                         {
-                            inner.clone()
+                            if let ExprKind::Block(..) = &inner.kind {
+                                // `&{ x }` form: remove the `&`, add parens.
+                                cx.expr_paren(field.span, inner.clone())
+                            } else {
+                                // `&x` form: remove the `&`.
+                                inner.clone()
+                            }
                         } else {
+                            // No leading `&`: add a leading `*`.
                             cx.expr_deref(field.span, expr.clone())
                         }
                     };
@@ -84,6 +98,7 @@ pub fn expand_deriving_partial_eq(
         span,
         path: path_std!(cmp::PartialEq),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods,
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
index c9dc89212..9f4624790 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -1,7 +1,7 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::{path_std, pathvec_std};
-use rustc_ast::MetaItem;
+use rustc_ast::{ExprKind, ItemKind, MetaItem, PatKind};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
@@ -21,6 +21,27 @@ pub fn expand_deriving_partial_ord(
 
     let attrs = thin_vec![cx.attr_word(sym::inline, span)];
 
+    // Order in which to perform matching
+    let tag_then_data = if let Annotatable::Item(item) = item
+        && let ItemKind::Enum(def, _) = &item.kind {
+            let dataful: Vec<bool> = def.variants.iter().map(|v| !v.data.fields().is_empty()).collect();
+            match dataful.iter().filter(|&&b| b).count() {
+                // No data, placing the tag check first makes codegen simpler
+                0 => true,
+                1..=2 => false,
+                _ => {
+                    (0..dataful.len()-1).any(|i| {
+                        if dataful[i] && let Some(idx) = dataful[i+1..].iter().position(|v| *v) {
+                            idx >= 2
+                        } else {
+                            false
+                        }
+                    })
+                }
+            }
+        } else {
+            true
+        };
     let partial_cmp_def = MethodDef {
         name: sym::partial_cmp,
         generics: Bounds::empty(),
@@ -30,7 +51,7 @@ pub fn expand_deriving_partial_ord(
         attributes: attrs,
         fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
         combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
-            cs_partial_cmp(cx, span, substr)
+            cs_partial_cmp(cx, span, substr, tag_then_data)
         })),
     };
 
@@ -38,6 +59,7 @@ pub fn expand_deriving_partial_ord(
         span,
         path: path_std!(cmp::PartialOrd),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: vec![],
         supports_unions: false,
         methods: vec![partial_cmp_def],
@@ -47,7 +69,12 @@ pub fn expand_deriving_partial_ord(
     trait_def.expand(cx, mitem, item, push)
 }
 
-pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
+fn cs_partial_cmp(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    substr: &Substructure<'_>,
+    tag_then_data: bool,
+) -> BlockOrExpr {
     let test_id = Ident::new(sym::cmp, span);
     let equal_path = cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::Equal]));
     let partial_cmp_path = cx.std_path(&[sym::cmp, sym::PartialOrd, sym::partial_cmp]);
@@ -71,15 +98,53 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_
                 let [other_expr] = &field.other_selflike_exprs[..] else {
                         cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
                     };
-                let args = vec![field.self_expr.clone(), other_expr.clone()];
+                let args = thin_vec![field.self_expr.clone(), other_expr.clone()];
                 cx.expr_call_global(field.span, partial_cmp_path.clone(), args)
             }
-            CsFold::Combine(span, expr1, expr2) => {
-                let eq_arm =
-                    cx.arm(span, cx.pat_some(span, cx.pat_path(span, equal_path.clone())), expr1);
-                let neq_arm =
-                    cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
-                cx.expr_match(span, expr2, vec![eq_arm, neq_arm])
+            CsFold::Combine(span, mut expr1, expr2) => {
+                // When the item is an enum, this expands to
+                // ```
+                // match (expr2) {
+                //     Some(Ordering::Equal) => expr1,
+                //     cmp => cmp
+                // }
+                // ```
+                // where `expr2` is `partial_cmp(self_tag, other_tag)`, and `expr1` is a `match`
+                //  against the enum variants. This means that we begin by comparing the enum tags,
+                // before either inspecting their contents (if they match), or returning
+                // the `cmp::Ordering` of comparing the enum tags.
+                // ```
+                // match partial_cmp(self_tag, other_tag) {
+                //     Some(Ordering::Equal) => match (self, other)  {
+                //         (Self::A(self_0), Self::A(other_0)) => partial_cmp(self_0, other_0),
+                //         (Self::B(self_0), Self::B(other_0)) => partial_cmp(self_0, other_0),
+                //         _ => Some(Ordering::Equal)
+                //     }
+                //     cmp => cmp
+                // }
+                // ```
+                // If we have any certain enum layouts, flipping this results in better codegen
+                // ```
+                // match (self, other) {
+                //     (Self::A(self_0), Self::A(other_0)) => partial_cmp(self_0, other_0),
+                //     _ => partial_cmp(self_tag, other_tag)
+                // }
+                // ```
+                // Reference: https://github.com/rust-lang/rust/pull/103659#issuecomment-1328126354
+
+                if !tag_then_data
+                    && let ExprKind::Match(_, arms) = &mut expr1.kind
+                    && let Some(last) = arms.last_mut()
+                    && let PatKind::Wild = last.pat.kind {
+                        last.body = expr2;
+                        expr1
+                } else {
+                    let eq_arm =
+                        cx.arm(span, cx.pat_some(span, cx.pat_path(span, equal_path.clone())), expr1);
+                    let neq_arm =
+                        cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
+                    cx.expr_match(span, expr2, thin_vec![eq_arm, neq_arm])
+                }
             }
             CsFold::Fieldless => cx.expr_some(span, cx.expr_path(equal_path.clone())),
         },
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index e0f487e86..809f9838d 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -7,6 +7,7 @@ use rustc_ast::{self as ast, MetaItem};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_debug(
     cx: &mut ExtCtxt<'_>,
@@ -23,6 +24,7 @@ pub fn expand_deriving_debug(
         span,
         path: path_std!(fmt::Debug),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods: vec![MethodDef {
@@ -75,10 +77,25 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
     // The number of fields that can be handled without an array.
     const CUTOFF: usize = 5;
 
+    fn expr_for_field(
+        cx: &ExtCtxt<'_>,
+        field: &FieldInfo,
+        index: usize,
+        len: usize,
+    ) -> ast::ptr::P<ast::Expr> {
+        if index < len - 1 {
+            field.self_expr.clone()
+        } else {
+            // Unsized types need an extra indirection, but only the last field
+            // may be unsized.
+            cx.expr_addr_of(field.span, field.self_expr.clone())
+        }
+    }
+
     if fields.is_empty() {
         // Special case for no fields.
         let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
-        let expr = cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]);
+        let expr = cx.expr_call_global(span, fn_path_write_str, thin_vec![fmt, name]);
         BlockOrExpr::new_expr(expr)
     } else if fields.len() <= CUTOFF {
         // Few enough fields that we can use a specific-length method.
@@ -89,7 +106,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         };
         let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
 
-        let mut args = Vec::with_capacity(2 + fields.len() * args_per_field);
+        let mut args = ThinVec::with_capacity(2 + fields.len() * args_per_field);
         args.extend([fmt, name]);
         for i in 0..fields.len() {
             let field = &fields[i];
@@ -97,47 +114,48 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
                 let name = cx.expr_str(field.span, field.name.unwrap().name);
                 args.push(name);
             }
-            // Use an extra indirection to make sure this works for unsized types.
-            let field = cx.expr_addr_of(field.span, field.self_expr.clone());
+
+            let field = expr_for_field(cx, field, i, fields.len());
             args.push(field);
         }
         let expr = cx.expr_call_global(span, fn_path_debug, args);
         BlockOrExpr::new_expr(expr)
     } else {
         // Enough fields that we must use the any-length method.
-        let mut name_exprs = Vec::with_capacity(fields.len());
-        let mut value_exprs = Vec::with_capacity(fields.len());
+        let mut name_exprs = ThinVec::with_capacity(fields.len());
+        let mut value_exprs = ThinVec::with_capacity(fields.len());
 
-        for field in fields {
+        for i in 0..fields.len() {
+            let field = &fields[i];
             if is_struct {
                 name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
             }
 
-            // Use an extra indirection to make sure this works for unsized types.
-            let field = cx.expr_addr_of(field.span, field.self_expr.clone());
+            let field = expr_for_field(cx, field, i, fields.len());
             value_exprs.push(field);
         }
 
         // `let names: &'static _ = &["field1", "field2"];`
-        let names_let = if is_struct {
+        let names_let = is_struct.then(|| {
             let lt_static = Some(cx.lifetime_static(span));
             let ty_static_ref = cx.ty_ref(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
-            Some(cx.stmt_let_ty(
+            cx.stmt_let_ty(
                 span,
                 false,
                 Ident::new(sym::names, span),
                 Some(ty_static_ref),
                 cx.expr_array_ref(span, name_exprs),
-            ))
-        } else {
-            None
-        };
+            )
+        });
 
         // `let values: &[&dyn Debug] = &[&&self.field1, &&self.field2];`
         let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
         let ty_dyn_debug = cx.ty(
             span,
-            ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
+            ast::TyKind::TraitObject(
+                vec![cx.trait_bound(path_debug, false)],
+                ast::TraitObjectSyntax::Dyn,
+            ),
         );
         let ty_slice = cx.ty(
             span,
@@ -160,7 +178,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         };
         let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
 
-        let mut args = Vec::with_capacity(4);
+        let mut args = ThinVec::with_capacity(4);
         args.push(fmt);
         args.push(name);
         if is_struct {
@@ -169,7 +187,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         args.push(cx.expr_ident(span, Ident::new(sym::values, span)));
         let expr = cx.expr_call_global(span, fn_path_debug_internal, args);
 
-        let mut stmts = Vec::with_capacity(3);
+        let mut stmts = ThinVec::with_capacity(2);
         if is_struct {
             stmts.push(names_let.unwrap());
         }
@@ -206,18 +224,18 @@ fn show_fieldless_enum(
             let pat = match &v.data {
                 ast::VariantData::Tuple(fields, _) => {
                     debug_assert!(fields.is_empty());
-                    cx.pat_tuple_struct(span, variant_path, vec![])
+                    cx.pat_tuple_struct(span, variant_path, ThinVec::new())
                 }
                 ast::VariantData::Struct(fields, _) => {
                     debug_assert!(fields.is_empty());
-                    cx.pat_struct(span, variant_path, vec![])
+                    cx.pat_struct(span, variant_path, ThinVec::new())
                 }
                 ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
             };
             cx.arm(span, pat, cx.expr_str(span, v.ident.name))
         })
-        .collect::<Vec<_>>();
+        .collect::<ThinVec<_>>();
     let name = cx.expr_match(span, cx.expr_self(span), arms);
     let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
-    BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]))
+    BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, thin_vec![fmt, name]))
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/decodable.rs b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
index 5f9519dad..3921533c8 100644
--- a/compiler/rustc_builtin_macros/src/deriving/decodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
@@ -3,12 +3,12 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::pathvec_std;
-
 use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, Expr, MetaItem, Mutability};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_rustc_decodable(
     cx: &mut ExtCtxt<'_>,
@@ -25,6 +25,7 @@ pub fn expand_deriving_rustc_decodable(
         span,
         path: Path::new_(vec![krate, sym::Decodable], vec![], PathKind::Global),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods: vec![MethodDef {
@@ -95,7 +96,7 @@ fn decodable_substructure(
                         cx.expr_call_global(
                             span,
                             fn_read_struct_field_path.clone(),
-                            vec![
+                            thin_vec![
                                 blkdecoder.clone(),
                                 cx.expr_str(span, name),
                                 cx.expr_usize(span, field),
@@ -111,7 +112,7 @@ fn decodable_substructure(
             cx.expr_call_global(
                 trait_span,
                 fn_read_struct_path,
-                vec![
+                thin_vec![
                     decoder,
                     cx.expr_str(trait_span, substr.type_ident.name),
                     cx.expr_usize(trait_span, nfields),
@@ -122,8 +123,8 @@ fn decodable_substructure(
         StaticEnum(_, fields) => {
             let variant = Ident::new(sym::i, trait_span);
 
-            let mut arms = Vec::with_capacity(fields.len() + 1);
-            let mut variants = Vec::with_capacity(fields.len());
+            let mut arms = ThinVec::with_capacity(fields.len() + 1);
+            let mut variants = ThinVec::with_capacity(fields.len());
 
             let fn_read_enum_variant_arg_path: Vec<_> =
                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
@@ -140,7 +141,7 @@ fn decodable_substructure(
                             cx.expr_call_global(
                                 span,
                                 fn_read_enum_variant_arg_path.clone(),
-                                vec![blkdecoder.clone(), idx, exprdecode.clone()],
+                                thin_vec![blkdecoder.clone(), idx, exprdecode.clone()],
                             ),
                         )
                     });
@@ -161,7 +162,7 @@ fn decodable_substructure(
             let result = cx.expr_call_global(
                 trait_span,
                 fn_read_enum_variant_path,
-                vec![blkdecoder, variant_array_ref, lambda],
+                thin_vec![blkdecoder, variant_array_ref, lambda],
             );
             let fn_read_enum_path: Vec<_> =
                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
@@ -169,7 +170,7 @@ fn decodable_substructure(
             cx.expr_call_global(
                 trait_span,
                 fn_read_enum_path,
-                vec![
+                thin_vec![
                     decoder,
                     cx.expr_str(trait_span, substr.type_ident.name),
                     cx.lambda1(trait_span, result, blkarg),
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
index 182707472..4d753a2ed 100644
--- a/compiler/rustc_builtin_macros/src/deriving/default.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -8,7 +8,7 @@ use rustc_span::symbol::Ident;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::Span;
 use smallvec::SmallVec;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_default(
     cx: &mut ExtCtxt<'_>,
@@ -25,6 +25,7 @@ pub fn expand_deriving_default(
         span,
         path: Path::new(vec![kw::Default, sym::Default]),
         skip_path_as_bound: has_a_default_variant(item),
+        needs_copy_as_bound_if_packed: false,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods: vec![MethodDef {
@@ -59,7 +60,7 @@ fn default_struct_substructure(
 ) -> BlockOrExpr {
     // Note that `kw::Default` is "default" and `sym::Default` is "Default"!
     let default_ident = cx.std_path(&[kw::Default, sym::Default, kw::Default]);
-    let default_call = |span| cx.expr_call_global(span, default_ident.clone(), Vec::new());
+    let default_call = |span| cx.expr_call_global(span, default_ident.clone(), ThinVec::new());
 
     let expr = match summary {
         Unnamed(_, false) => cx.expr_ident(trait_span, substr.type_ident),
diff --git a/compiler/rustc_builtin_macros/src/deriving/encodable.rs b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
index 2afeed927..a3b11309d 100644
--- a/compiler/rustc_builtin_macros/src/deriving/encodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
@@ -88,11 +88,11 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::pathvec_std;
-
 use rustc_ast::{AttrVec, ExprKind, MetaItem, Mutability};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_rustc_encodable(
     cx: &mut ExtCtxt<'_>,
@@ -109,6 +109,7 @@ pub fn expand_deriving_rustc_encodable(
         span,
         path: Path::new_(vec![krate, sym::Encodable], vec![], PathKind::Global),
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods: vec![MethodDef {
@@ -168,19 +169,20 @@ fn encodable_substructure(
         Struct(_, fields) => {
             let fn_emit_struct_field_path =
                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct_field]);
-            let mut stmts = Vec::new();
+            let mut stmts = ThinVec::new();
             for (i, &FieldInfo { name, ref self_expr, span, .. }) in fields.iter().enumerate() {
                 let name = match name {
                     Some(id) => id.name,
                     None => Symbol::intern(&format!("_field{}", i)),
                 };
                 let self_ref = cx.expr_addr_of(span, self_expr.clone());
-                let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
+                let enc =
+                    cx.expr_call(span, fn_path.clone(), thin_vec![self_ref, blkencoder.clone()]);
                 let lambda = cx.lambda1(span, enc, blkarg);
                 let call = cx.expr_call_global(
                     span,
                     fn_emit_struct_field_path.clone(),
-                    vec![
+                    thin_vec![
                         blkencoder.clone(),
                         cx.expr_str(span, name),
                         cx.expr_usize(span, i),
@@ -202,7 +204,7 @@ fn encodable_substructure(
 
             // unit structs have no fields and need to return Ok()
             let blk = if stmts.is_empty() {
-                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
+                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, ThinVec::new()));
                 cx.lambda1(trait_span, ok, blkarg)
             } else {
                 cx.lambda_stmts_1(trait_span, stmts, blkarg)
@@ -214,7 +216,7 @@ fn encodable_substructure(
             let expr = cx.expr_call_global(
                 trait_span,
                 fn_emit_struct_path,
-                vec![
+                thin_vec![
                     encoder,
                     cx.expr_str(trait_span, substr.type_ident.name),
                     cx.expr_usize(trait_span, fields.len()),
@@ -235,19 +237,22 @@ fn encodable_substructure(
             let fn_emit_enum_variant_arg_path: Vec<_> =
                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant_arg]);
 
-            let mut stmts = Vec::new();
+            let mut stmts = ThinVec::new();
             if !fields.is_empty() {
                 let last = fields.len() - 1;
                 for (i, &FieldInfo { ref self_expr, span, .. }) in fields.iter().enumerate() {
                     let self_ref = cx.expr_addr_of(span, self_expr.clone());
-                    let enc =
-                        cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
+                    let enc = cx.expr_call(
+                        span,
+                        fn_path.clone(),
+                        thin_vec![self_ref, blkencoder.clone()],
+                    );
                     let lambda = cx.lambda1(span, enc, blkarg);
 
                     let call = cx.expr_call_global(
                         span,
                         fn_emit_enum_variant_arg_path.clone(),
-                        vec![blkencoder.clone(), cx.expr_usize(span, i), lambda],
+                        thin_vec![blkencoder.clone(), cx.expr_usize(span, i), lambda],
                     );
                     let call = if i != last {
                         cx.expr_try(span, call)
@@ -257,7 +262,7 @@ fn encodable_substructure(
                     stmts.push(cx.stmt_expr(call));
                 }
             } else {
-                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
+                let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, ThinVec::new()));
                 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
                 stmts.push(cx.stmt_expr(ret_ok));
             }
@@ -271,7 +276,7 @@ fn encodable_substructure(
             let call = cx.expr_call_global(
                 trait_span,
                 fn_emit_enum_variant_path,
-                vec![
+                thin_vec![
                     blkencoder,
                     name,
                     cx.expr_usize(trait_span, *idx),
@@ -286,9 +291,9 @@ fn encodable_substructure(
             let expr = cx.expr_call_global(
                 trait_span,
                 fn_emit_enum_path,
-                vec![encoder, cx.expr_str(trait_span, substr.type_ident.name), blk],
+                thin_vec![encoder, cx.expr_str(trait_span, substr.type_ident.name), blk],
             );
-            BlockOrExpr::new_mixed(vec![me], Some(expr))
+            BlockOrExpr::new_mixed(thin_vec![me], Some(expr))
         }
 
         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index 17b7ac0eb..1f819beeb 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -165,18 +165,19 @@ pub use SubstructureFields::*;
 use crate::deriving;
 use rustc_ast::ptr::P;
 use rustc_ast::{
-    self as ast, BindingAnnotation, ByRef, EnumDef, Expr, Generics, Mutability, PatKind,
+    self as ast, BindingAnnotation, ByRef, EnumDef, Expr, GenericArg, GenericParamKind, Generics,
+    Mutability, PatKind, TyKind, VariantData,
 };
-use rustc_ast::{GenericArg, GenericParamKind, VariantData};
 use rustc_attr as attr;
 use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_session::lint::builtin::BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use std::cell::RefCell;
 use std::iter;
 use std::ops::Not;
 use std::vec;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 use ty::{Bounds, Path, Ref, Self_, Ty};
 
 pub mod ty;
@@ -191,6 +192,9 @@ pub struct TraitDef<'a> {
     /// Whether to skip adding the current trait as a bound to the type parameters of the type.
     pub skip_path_as_bound: bool,
 
+    /// Whether `Copy` is needed as an additional bound on type parameters in a packed struct.
+    pub needs_copy_as_bound_if_packed: bool,
+
     /// Additional bounds required of any type parameters of the type,
     /// other than the current trait
     pub additional_bounds: Vec<Ty>,
@@ -314,7 +318,7 @@ pub fn combine_substructure(
 }
 
 struct TypeParameter {
-    bound_generic_params: Vec<ast::GenericParam>,
+    bound_generic_params: ThinVec<ast::GenericParam>,
     ty: P<ast::Ty>,
 }
 
@@ -324,18 +328,18 @@ struct TypeParameter {
 /// avoiding the insertion of any unnecessary blocks.
 ///
 /// The statements come before the expression.
-pub struct BlockOrExpr(Vec<ast::Stmt>, Option<P<Expr>>);
+pub struct BlockOrExpr(ThinVec<ast::Stmt>, Option<P<Expr>>);
 
 impl BlockOrExpr {
-    pub fn new_stmts(stmts: Vec<ast::Stmt>) -> BlockOrExpr {
+    pub fn new_stmts(stmts: ThinVec<ast::Stmt>) -> BlockOrExpr {
         BlockOrExpr(stmts, None)
     }
 
     pub fn new_expr(expr: P<Expr>) -> BlockOrExpr {
-        BlockOrExpr(vec![], Some(expr))
+        BlockOrExpr(ThinVec::new(), Some(expr))
     }
 
-    pub fn new_mixed(stmts: Vec<ast::Stmt>, expr: Option<P<Expr>>) -> BlockOrExpr {
+    pub fn new_mixed(stmts: ThinVec<ast::Stmt>, expr: Option<P<Expr>>) -> BlockOrExpr {
         BlockOrExpr(stmts, expr)
     }
 
@@ -351,7 +355,7 @@ impl BlockOrExpr {
     fn into_expr(self, cx: &ExtCtxt<'_>, span: Span) -> P<Expr> {
         if self.0.is_empty() {
             match self.1 {
-                None => cx.expr_block(cx.block(span, vec![])),
+                None => cx.expr_block(cx.block(span, ThinVec::new())),
                 Some(expr) => expr,
             }
         } else if self.0.len() == 1
@@ -381,7 +385,7 @@ fn find_type_parameters(
     struct Visitor<'a, 'b> {
         cx: &'a ExtCtxt<'b>,
         ty_param_names: &'a [Symbol],
-        bound_generic_params_stack: Vec<ast::GenericParam>,
+        bound_generic_params_stack: ThinVec<ast::GenericParam>,
         type_params: Vec<TypeParameter>,
     }
 
@@ -418,7 +422,7 @@ fn find_type_parameters(
     let mut visitor = Visitor {
         cx,
         ty_param_names,
-        bound_generic_params_stack: Vec::new(),
+        bound_generic_params_stack: ThinVec::new(),
         type_params: Vec::new(),
     };
     visit::Visitor::visit_ty(&mut visitor, ty);
@@ -455,18 +459,6 @@ impl<'a> TraitDef<'a> {
                     }
                     false
                 });
-                let has_no_type_params = match &item.kind {
-                    ast::ItemKind::Struct(_, generics)
-                    | ast::ItemKind::Enum(_, generics)
-                    | ast::ItemKind::Union(_, generics) => !generics
-                        .params
-                        .iter()
-                        .any(|param| matches!(param.kind, ast::GenericParamKind::Type { .. })),
-                    _ => unreachable!(),
-                };
-                let container_id = cx.current_expansion.id.expn_data().parent.expect_local();
-                let copy_fields =
-                    is_packed && has_no_type_params && cx.resolver.has_derive_copy(container_id);
 
                 let newitem = match &item.kind {
                     ast::ItemKind::Struct(struct_def, generics) => self.expand_struct_def(
@@ -475,7 +467,7 @@ impl<'a> TraitDef<'a> {
                         item.ident,
                         generics,
                         from_scratch,
-                        copy_fields,
+                        is_packed,
                     ),
                     ast::ItemKind::Enum(enum_def, generics) => {
                         // We ignore `is_packed` here, because `repr(packed)`
@@ -493,7 +485,7 @@ impl<'a> TraitDef<'a> {
                                 item.ident,
                                 generics,
                                 from_scratch,
-                                copy_fields,
+                                is_packed,
                             )
                         } else {
                             cx.span_err(mitem.span, "this trait cannot be derived for unions");
@@ -565,6 +557,7 @@ impl<'a> TraitDef<'a> {
         generics: &Generics,
         field_tys: Vec<P<ast::Ty>>,
         methods: Vec<P<ast::AssocItem>>,
+        is_packed: bool,
     ) -> P<ast::Item> {
         let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
 
@@ -601,26 +594,46 @@ impl<'a> TraitDef<'a> {
         let span = generics.span.with_ctxt(ctxt);
 
         // Create the generic parameters
-        let params: Vec<_> = generics
+        let params: ThinVec<_> = generics
             .params
             .iter()
             .map(|param| match &param.kind {
                 GenericParamKind::Lifetime { .. } => param.clone(),
                 GenericParamKind::Type { .. } => {
-                    // I don't think this can be moved out of the loop, since
-                    // a GenericBound requires an ast id
-                    let bounds: Vec<_> =
-                    // extra restrictions on the generics parameters to the
-                    // type being derived upon
-                    self.additional_bounds.iter().map(|p| {
-                        cx.trait_bound(p.to_path(cx, self.span, type_ident, generics))
-                    }).chain(
-                        // require the current trait
-                        self.skip_path_as_bound.not().then(|| cx.trait_bound(trait_path.clone()))
-                    ).chain(
-                        // also add in any bounds from the declaration
-                        param.bounds.iter().cloned()
-                    ).collect();
+                    // Extra restrictions on the generics parameters to the
+                    // type being derived upon.
+                    let bounds: Vec<_> = self
+                        .additional_bounds
+                        .iter()
+                        .map(|p| {
+                            cx.trait_bound(
+                                p.to_path(cx, self.span, type_ident, generics),
+                                self.is_const,
+                            )
+                        })
+                        .chain(
+                            // Add a bound for the current trait.
+                            self.skip_path_as_bound
+                                .not()
+                                .then(|| cx.trait_bound(trait_path.clone(), self.is_const)),
+                        )
+                        .chain({
+                            // Add a `Copy` bound if required.
+                            if is_packed && self.needs_copy_as_bound_if_packed {
+                                let p = deriving::path_std!(marker::Copy);
+                                Some(cx.trait_bound(
+                                    p.to_path(cx, self.span, type_ident, generics),
+                                    self.is_const,
+                                ))
+                            } else {
+                                None
+                            }
+                        })
+                        .chain(
+                            // Also add in any bounds from the declaration.
+                            param.bounds.iter().cloned(),
+                        )
+                        .collect();
 
                     cx.typaram(param.ident.span.with_ctxt(ctxt), param.ident, bounds, None)
                 }
@@ -689,11 +702,25 @@ impl<'a> TraitDef<'a> {
                         let mut bounds: Vec<_> = self
                             .additional_bounds
                             .iter()
-                            .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                            .map(|p| {
+                                cx.trait_bound(
+                                    p.to_path(cx, self.span, type_ident, generics),
+                                    self.is_const,
+                                )
+                            })
                             .collect();
 
-                        // require the current trait
-                        bounds.push(cx.trait_bound(trait_path.clone()));
+                        // Require the current trait.
+                        bounds.push(cx.trait_bound(trait_path.clone(), self.is_const));
+
+                        // Add a `Copy` bound if required.
+                        if is_packed && self.needs_copy_as_bound_if_packed {
+                            let p = deriving::path_std!(marker::Copy);
+                            bounds.push(cx.trait_bound(
+                                p.to_path(cx, self.span, type_ident, generics),
+                                self.is_const,
+                            ));
+                        }
 
                         let predicate = ast::WhereBoundPredicate {
                             span: self.span,
@@ -734,8 +761,7 @@ impl<'a> TraitDef<'a> {
         let path = cx.path_all(self.span, false, vec![type_ident], self_params);
         let self_type = cx.ty_path(path);
 
-        let attr = cx.attr_word(sym::automatically_derived, self.span);
-        let attrs = thin_vec![attr];
+        let attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
         let opt_trait_ref = Some(trait_ref);
 
         cx.item(
@@ -762,7 +788,7 @@ impl<'a> TraitDef<'a> {
         type_ident: Ident,
         generics: &Generics,
         from_scratch: bool,
-        copy_fields: bool,
+        is_packed: bool,
     ) -> P<ast::Item> {
         let field_tys: Vec<P<ast::Ty>> =
             struct_def.fields().iter().map(|field| field.ty.clone()).collect();
@@ -790,7 +816,7 @@ impl<'a> TraitDef<'a> {
                         type_ident,
                         &selflike_args,
                         &nonselflike_args,
-                        copy_fields,
+                        is_packed,
                     )
                 };
 
@@ -806,7 +832,7 @@ impl<'a> TraitDef<'a> {
             })
             .collect();
 
-        self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
+        self.create_derived_impl(cx, type_ident, generics, field_tys, methods, is_packed)
     }
 
     fn expand_enum_def(
@@ -861,7 +887,8 @@ impl<'a> TraitDef<'a> {
             })
             .collect();
 
-        self.create_derived_impl(cx, type_ident, generics, field_tys, methods)
+        let is_packed = false; // enums are never packed
+        self.create_derived_impl(cx, type_ident, generics, field_tys, methods, is_packed)
     }
 }
 
@@ -908,19 +935,17 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'_>,
         type_ident: Ident,
         generics: &Generics,
-    ) -> (Option<ast::ExplicitSelf>, Vec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
-        let mut selflike_args = Vec::new();
+    ) -> (Option<ast::ExplicitSelf>, ThinVec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
+        let mut selflike_args = ThinVec::new();
         let mut nonselflike_args = Vec::new();
         let mut nonself_arg_tys = Vec::new();
         let span = trait_.span;
 
-        let explicit_self = if self.explicit_self {
+        let explicit_self = self.explicit_self.then(|| {
             let (self_expr, explicit_self) = ty::get_explicit_self(cx, span);
             selflike_args.push(self_expr);
-            Some(explicit_self)
-        } else {
-            None
-        };
+            explicit_self
+        });
 
         for (ty, name) in self.nonself_args.iter() {
             let ast_ty = ty.to_ty(cx, span, type_ident, generics);
@@ -1011,8 +1036,8 @@ impl<'a> MethodDef<'a> {
     /// ```
     /// But if the struct is `repr(packed)`, we can't use something like
     /// `&self.x` because that might cause an unaligned ref. So for any trait
-    /// method that takes a reference, if the struct impls `Copy` then we use a
-    /// local block to force a copy:
+    /// method that takes a reference, we use a local block to force a copy.
+    /// This requires that the field impl `Copy`.
     /// ```
     /// # struct A { x: u8, y: u8 }
     /// impl PartialEq for A {
@@ -1027,10 +1052,6 @@ impl<'a> MethodDef<'a> {
     ///         ::core::hash::Hash::hash(&{ self.y }, state)
     ///     }
     /// }
-    /// ```
-    /// If the struct doesn't impl `Copy`, we use the normal `&self.x`. This
-    /// only works if the fields match the alignment required by the
-    /// `packed(N)` attribute. (We'll get errors later on if not.)
     fn expand_struct_method_body<'b>(
         &self,
         cx: &mut ExtCtxt<'_>,
@@ -1039,12 +1060,12 @@ impl<'a> MethodDef<'a> {
         type_ident: Ident,
         selflike_args: &[P<Expr>],
         nonselflike_args: &[P<Expr>],
-        copy_fields: bool,
+        is_packed: bool,
     ) -> BlockOrExpr {
         assert!(selflike_args.len() == 1 || selflike_args.len() == 2);
 
         let selflike_fields =
-            trait_.create_struct_field_access_fields(cx, selflike_args, struct_def, copy_fields);
+            trait_.create_struct_field_access_fields(cx, selflike_args, struct_def, is_packed);
         self.call_substructure_method(
             cx,
             trait_,
@@ -1112,7 +1133,7 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'b>,
         enum_def: &'b EnumDef,
         type_ident: Ident,
-        selflike_args: Vec<P<Expr>>,
+        selflike_args: ThinVec<P<Expr>>,
         nonselflike_args: &[P<Expr>],
     ) -> BlockOrExpr {
         let span = trait_.span;
@@ -1125,7 +1146,7 @@ impl<'a> MethodDef<'a> {
         // There is no sensible code to be generated for *any* deriving on a
         // zero-variant enum. So we just generate a failing expression.
         if variants.is_empty() {
-            return BlockOrExpr(vec![], Some(deriving::call_unreachable(cx, span)));
+            return BlockOrExpr(ThinVec::new(), Some(deriving::call_unreachable(cx, span)));
         }
 
         let prefixes = iter::once("__self".to_string())
@@ -1161,13 +1182,13 @@ impl<'a> MethodDef<'a> {
             let other_selflike_exprs = tag_exprs;
             let tag_field = FieldInfo { span, name: None, self_expr, other_selflike_exprs };
 
-            let tag_let_stmts: Vec<_> = iter::zip(&tag_idents, &selflike_args)
+            let tag_let_stmts: ThinVec<_> = iter::zip(&tag_idents, &selflike_args)
                 .map(|(&ident, selflike_arg)| {
                     let variant_value = deriving::call_intrinsic(
                         cx,
                         span,
                         sym::discriminant_value,
-                        vec![selflike_arg.clone()],
+                        thin_vec![selflike_arg.clone()],
                     );
                     cx.stmt_let(span, false, ident, variant_value)
                 })
@@ -1226,7 +1247,7 @@ impl<'a> MethodDef<'a> {
         // (Variant2, Variant2, ...) => Body2
         // ...
         // where each tuple has length = selflike_args.len()
-        let mut match_arms: Vec<ast::Arm> = variants
+        let mut match_arms: ThinVec<ast::Arm> = variants
             .iter()
             .enumerate()
             .filter(|&(_, v)| !(unify_fieldless_variants && v.data.fields().is_empty()))
@@ -1239,7 +1260,7 @@ impl<'a> MethodDef<'a> {
                 let sp = variant.span.with_ctxt(trait_.span.ctxt());
                 let variant_path = cx.path(sp, vec![type_ident, variant.ident]);
                 let by_ref = ByRef::No; // because enums can't be repr(packed)
-                let mut subpats: Vec<_> = trait_.create_struct_patterns(
+                let mut subpats = trait_.create_struct_patterns(
                     cx,
                     variant_path,
                     &variant.data,
@@ -1315,7 +1336,7 @@ impl<'a> MethodDef<'a> {
         //          ...
         //          _ => ::core::intrinsics::unreachable()
         //      }
-        let get_match_expr = |mut selflike_args: Vec<P<Expr>>| {
+        let get_match_expr = |mut selflike_args: ThinVec<P<Expr>>| {
             let match_arg = if selflike_args.len() == 1 {
                 selflike_args.pop().unwrap()
             } else {
@@ -1341,7 +1362,7 @@ impl<'a> MethodDef<'a> {
             tag_let_stmts.append(&mut tag_check_plus_match.0);
             BlockOrExpr(tag_let_stmts, tag_check_plus_match.1)
         } else {
-            BlockOrExpr(vec![], Some(get_match_expr(selflike_args)))
+            BlockOrExpr(ThinVec::new(), Some(get_match_expr(selflike_args)))
         }
     }
 
@@ -1406,7 +1427,7 @@ impl<'a> TraitDef<'a> {
         struct_def: &'a VariantData,
         prefixes: &[String],
         by_ref: ByRef,
-    ) -> Vec<P<ast::Pat>> {
+    ) -> ThinVec<P<ast::Pat>> {
         prefixes
             .iter()
             .map(|prefix| {
@@ -1514,7 +1535,7 @@ impl<'a> TraitDef<'a> {
         cx: &mut ExtCtxt<'_>,
         selflike_args: &[P<Expr>],
         struct_def: &'a VariantData,
-        copy_fields: bool,
+        is_packed: bool,
     ) -> Vec<FieldInfo> {
         self.create_fields(struct_def, |i, struct_field, sp| {
             selflike_args
@@ -1533,10 +1554,54 @@ impl<'a> TraitDef<'a> {
                             }),
                         ),
                     );
-                    if copy_fields {
-                        field_expr = cx.expr_block(
-                            cx.block(struct_field.span, vec![cx.stmt_expr(field_expr)]),
-                        );
+                    if is_packed {
+                        // In general, fields in packed structs are copied via a
+                        // block, e.g. `&{self.0}`. The two exceptions are `[u8]`
+                        // and `str` fields, which cannot be copied and also never
+                        // cause unaligned references. These exceptions are allowed
+                        // to handle the `FlexZeroSlice` type in the `zerovec`
+                        // crate within `icu4x-0.9.0`.
+                        //
+                        // Once use of `icu4x-0.9.0` has dropped sufficiently, this
+                        // exception should be removed.
+                        let is_simple_path = |ty: &P<ast::Ty>, sym| {
+                            if let TyKind::Path(None, ast::Path { segments, .. }) = &ty.kind &&
+                                let [seg] = segments.as_slice() &&
+                                seg.ident.name == sym && seg.args.is_none()
+                            {
+                                true
+                            } else {
+                                false
+                            }
+                        };
+
+                        let exception = if let TyKind::Slice(ty) = &struct_field.ty.kind &&
+                            is_simple_path(ty, sym::u8)
+                        {
+                            Some("byte")
+                        } else if is_simple_path(&struct_field.ty, sym::str) {
+                            Some("string")
+                        } else {
+                            None
+                        };
+
+                        if let Some(ty) = exception {
+                            cx.sess.parse_sess.buffer_lint_with_diagnostic(
+                                BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
+                                sp,
+                                ast::CRATE_NODE_ID,
+                                &format!(
+                                    "{} slice in a packed struct that derives a built-in trait",
+                                    ty
+                                ),
+                                rustc_lint_defs::BuiltinLintDiagnostics::ByteSliceInPackedStructWithDerive
+                            );
+                        } else {
+                            // Wrap the expression in `{...}`, causing a copy.
+                            field_expr = cx.expr_block(
+                                cx.block(struct_field.span, thin_vec![cx.stmt_expr(field_expr)]),
+                            );
+                        }
                     }
                     cx.expr_addr_of(sp, field_expr)
                 })
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
index c6f5f5d08..26f91b714 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
@@ -9,6 +9,7 @@ use rustc_expand::base::ExtCtxt;
 use rustc_span::source_map::{respan, DUMMY_SP};
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::Span;
+use thin_vec::ThinVec;
 
 /// A path, e.g., `::std::option::Option::<i32>` (global). Has support
 /// for type parameters.
@@ -102,7 +103,7 @@ impl Ty {
             Path(p) => p.to_ty(cx, span, self_ty, self_generics),
             Self_ => cx.ty_path(self.to_path(cx, span, self_ty, self_generics)),
             Unit => {
-                let ty = ast::TyKind::Tup(vec![]);
+                let ty = ast::TyKind::Tup(ThinVec::new());
                 cx.ty(span, ty)
             }
         }
@@ -154,7 +155,7 @@ fn mk_ty_param(
         .iter()
         .map(|b| {
             let path = b.to_path(cx, span, self_ident, self_generics);
-            cx.trait_bound(path)
+            cx.trait_bound(path, false)
         })
         .collect();
     cx.typaram(span, Ident::new(name, span), bounds, None)
@@ -185,7 +186,11 @@ impl Bounds {
 
         Generics {
             params,
-            where_clause: ast::WhereClause { has_where_token: false, predicates: Vec::new(), span },
+            where_clause: ast::WhereClause {
+                has_where_token: false,
+                predicates: ThinVec::new(),
+                span,
+            },
             span,
         }
     }
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
index f8570d8f8..4eee573db 100644
--- a/compiler/rustc_builtin_macros/src/deriving/hash.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -1,11 +1,11 @@
 use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::{path_std, pathvec_std};
-
 use rustc_ast::{AttrVec, MetaItem, Mutability};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 pub fn expand_deriving_hash(
     cx: &mut ExtCtxt<'_>,
@@ -24,6 +24,7 @@ pub fn expand_deriving_hash(
         span,
         path,
         skip_path_as_bound: false,
+        needs_copy_as_bound_if_packed: true,
         additional_bounds: Vec::new(),
         supports_unions: false,
         methods: vec![MethodDef {
@@ -59,7 +60,7 @@ fn hash_substructure(
 
             cx.expr_path(cx.path_global(span, strs))
         };
-        let expr = cx.expr_call(span, hash_path, vec![expr, state_expr.clone()]);
+        let expr = cx.expr_call(span, hash_path, thin_vec![expr, state_expr.clone()]);
         cx.stmt_expr(expr)
     };
 
@@ -71,7 +72,7 @@ fn hash_substructure(
         }
         EnumTag(tag_field, match_expr) => {
             assert!(tag_field.other_selflike_exprs.is_empty());
-            let stmts = vec![call_hash(tag_field.span, tag_field.self_expr.clone())];
+            let stmts = thin_vec![call_hash(tag_field.span, tag_field.self_expr.clone())];
             (stmts, match_expr.clone())
         }
         _ => cx.span_bug(trait_span, "impossible substructure in `derive(Hash)`"),
diff --git a/compiler/rustc_builtin_macros/src/deriving/mod.rs b/compiler/rustc_builtin_macros/src/deriving/mod.rs
index de657e4e6..d34336e76 100644
--- a/compiler/rustc_builtin_macros/src/deriving/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/mod.rs
@@ -6,6 +6,7 @@ use rustc_ast::{GenericArg, Impl, ItemKind, MetaItem};
 use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
+use thin_vec::{thin_vec, ThinVec};
 
 macro path_local($x:ident) {
     generic::ty::Path::new_local(sym::$x)
@@ -92,7 +93,7 @@ fn call_intrinsic(
     cx: &ExtCtxt<'_>,
     span: Span,
     intrinsic: Symbol,
-    args: Vec<P<ast::Expr>>,
+    args: ThinVec<P<ast::Expr>>,
 ) -> P<ast::Expr> {
     let span = cx.with_def_site_ctxt(span);
     let path = cx.std_path(&[sym::intrinsics, intrinsic]);
@@ -103,10 +104,10 @@ fn call_intrinsic(
 fn call_unreachable(cx: &ExtCtxt<'_>, span: Span) -> P<ast::Expr> {
     let span = cx.with_def_site_ctxt(span);
     let path = cx.std_path(&[sym::intrinsics, sym::unreachable]);
-    let call = cx.expr_call_global(span, path, vec![]);
+    let call = cx.expr_call_global(span, path, ThinVec::new());
 
     cx.expr_block(P(ast::Block {
-        stmts: vec![cx.stmt_expr(call)],
+        stmts: thin_vec![cx.stmt_expr(call)],
         id: ast::DUMMY_NODE_ID,
         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
         span,
@@ -202,7 +203,7 @@ fn inject_impl_of_structural_trait(
             generics,
             of_trait: Some(trait_ref),
             self_ty: self_type,
-            items: Vec::new(),
+            items: ThinVec::new(),
         })),
     );
 
@@ -211,7 +212,7 @@ fn inject_impl_of_structural_trait(
 
 fn assert_ty_bounds(
     cx: &mut ExtCtxt<'_>,
-    stmts: &mut Vec<ast::Stmt>,
+    stmts: &mut ThinVec<ast::Stmt>,
     ty: P<ast::Ty>,
     span: Span,
     assert_path: &[Symbol],
diff --git a/compiler/rustc_builtin_macros/src/env.rs b/compiler/rustc_builtin_macros/src/env.rs
index e5a5e6069..f011cb754 100644
--- a/compiler/rustc_builtin_macros/src/env.rs
+++ b/compiler/rustc_builtin_macros/src/env.rs
@@ -8,8 +8,8 @@ use rustc_ast::{self as ast, GenericArg};
 use rustc_expand::base::{self, *};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
-
 use std::env;
+use thin_vec::thin_vec;
 
 pub fn expand_option_env<'cx>(
     cx: &'cx mut ExtCtxt<'_>,
@@ -41,7 +41,7 @@ pub fn expand_option_env<'cx>(
         Some(value) => cx.expr_call_global(
             sp,
             cx.std_path(&[sym::option, sym::Option, sym::Some]),
-            vec![cx.expr_str(sp, value)],
+            thin_vec![cx.expr_str(sp, value)],
         ),
     };
     MacEager::expr(e)
@@ -53,7 +53,7 @@ pub fn expand_env<'cx>(
     tts: TokenStream,
 ) -> Box<dyn base::MacResult + 'cx> {
     let mut exprs = match get_exprs_from_tts(cx, tts) {
-        Some(exprs) if exprs.is_empty() => {
+        Some(exprs) if exprs.is_empty() || exprs.len() > 2 => {
             cx.span_err(sp, "env! takes 1 or 2 arguments");
             return DummyResult::any(sp);
         }
@@ -64,28 +64,48 @@ pub fn expand_env<'cx>(
     let Some((var, _style)) = expr_to_string(cx, exprs.next().unwrap(), "expected string literal") else {
         return DummyResult::any(sp);
     };
-    let msg = match exprs.next() {
-        None => Symbol::intern(&format!("environment variable `{}` not defined", var)),
+
+    let custom_msg = match exprs.next() {
+        None => None,
         Some(second) => match expr_to_string(cx, second, "expected string literal") {
             None => return DummyResult::any(sp),
-            Some((s, _style)) => s,
+            Some((s, _style)) => Some(s),
         },
     };
 
-    if exprs.next().is_some() {
-        cx.span_err(sp, "env! takes 1 or 2 arguments");
-        return DummyResult::any(sp);
-    }
-
     let sp = cx.with_def_site_ctxt(sp);
     let value = env::var(var.as_str()).ok().as_deref().map(Symbol::intern);
     cx.sess.parse_sess.env_depinfo.borrow_mut().insert((var, value));
     let e = match value {
         None => {
-            cx.span_err(sp, msg.as_str());
+            let (msg, help) = match custom_msg {
+                None => (
+                    format!("environment variable `{var}` not defined at compile time"),
+                    Some(help_for_missing_env_var(var.as_str())),
+                ),
+                Some(s) => (s.to_string(), None),
+            };
+            let mut diag = cx.struct_span_err(sp, &msg);
+            if let Some(help) = help {
+                diag.help(help);
+            }
+            diag.emit();
             return DummyResult::any(sp);
         }
         Some(value) => cx.expr_str(sp, value),
     };
     MacEager::expr(e)
 }
+
+fn help_for_missing_env_var(var: &str) -> String {
+    if var.starts_with("CARGO_")
+        || var.starts_with("DEP_")
+        || matches!(var, "OUT_DIR" | "OPT_LEVEL" | "PROFILE" | "HOST" | "TARGET")
+    {
+        format!(
+            "Cargo sets build script variables at run time. Use `std::env::var(\"{var}\")` instead"
+        )
+    } else {
+        format!("Use `std::env::var(\"{var}\")` to read the variable at run time")
+    }
+}
diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
index 9f4bbbc62..e93a23394 100644
--- a/compiler/rustc_builtin_macros/src/format.rs
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -1,7 +1,11 @@
 use rustc_ast::ptr::P;
 use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
-use rustc_ast::Expr;
+use rustc_ast::{
+    Expr, ExprKind, FormatAlignment, FormatArgPosition, FormatArgPositionKind, FormatArgs,
+    FormatArgsPiece, FormatArgument, FormatArgumentKind, FormatArguments, FormatCount,
+    FormatDebugHex, FormatOptions, FormatPlaceholder, FormatSign, FormatTrait,
+};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, Applicability, MultiSpan, PResult};
 use rustc_expand::base::{self, *};
@@ -12,21 +16,15 @@ use rustc_span::{BytePos, InnerSpan, Span};
 use rustc_lint_defs::builtin::NAMED_ARGUMENTS_USED_POSITIONALLY;
 use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiagnostics, LintId};
 
-mod ast;
-use ast::*;
-
-mod expand;
-use expand::expand_parsed_format_args;
-
 // The format_args!() macro is expanded in three steps:
 //  1. First, `parse_args` will parse the `(literal, arg, arg, name=arg, name=arg)` syntax,
 //     but doesn't parse the template (the literal) itself.
 //  2. Second, `make_format_args` will parse the template, the format options, resolve argument references,
-//     produce diagnostics, and turn the whole thing into a `FormatArgs` structure.
-//  3. Finally, `expand_parsed_format_args` will turn that `FormatArgs` structure
-//     into the expression that the macro expands to.
+//     produce diagnostics, and turn the whole thing into a `FormatArgs` AST node.
+//  3. Much later, in AST lowering (rustc_ast_lowering), that `FormatArgs` structure will be turned
+//     into the expression of type `core::fmt::Arguments`.
 
-// See format/ast.rs for the FormatArgs structure and glossary.
+// See rustc_ast/src/format.rs for the FormatArgs structure and glossary.
 
 // Only used in parse_args and report_invalid_references,
 // to indicate how a referred argument was used.
@@ -437,7 +435,16 @@ pub fn make_format_args(
                     format_options: FormatOptions {
                         fill: format.fill,
                         alignment,
-                        flags: format.flags,
+                        sign: format.sign.map(|s| match s {
+                            parse::Sign::Plus => FormatSign::Plus,
+                            parse::Sign::Minus => FormatSign::Minus,
+                        }),
+                        alternate: format.alternate,
+                        zero_pad: format.zero_pad,
+                        debug_hex: format.debug_hex.map(|s| match s {
+                            parse::DebugHex::Lower => FormatDebugHex::Lower,
+                            parse::DebugHex::Upper => FormatDebugHex::Upper,
+                        }),
                         precision,
                         width,
                     },
@@ -850,7 +857,7 @@ fn expand_format_args_impl<'cx>(
     match parse_args(ecx, sp, tts) {
         Ok((efmt, args)) => {
             if let Ok(format_args) = make_format_args(ecx, efmt, args, nl) {
-                MacEager::expr(expand_parsed_format_args(ecx, format_args))
+                MacEager::expr(ecx.expr(sp, ExprKind::FormatArgs(P(format_args))))
             } else {
                 MacEager::expr(DummyResult::raw_expr(sp, true))
             }
diff --git a/compiler/rustc_builtin_macros/src/format/expand.rs b/compiler/rustc_builtin_macros/src/format/expand.rs
deleted file mode 100644
index 9dde5efcb..000000000
--- a/compiler/rustc_builtin_macros/src/format/expand.rs
+++ /dev/null
@@ -1,353 +0,0 @@
-use super::*;
-use rustc_ast as ast;
-use rustc_ast::visit::{self, Visitor};
-use rustc_ast::{BlockCheckMode, UnsafeSource};
-use rustc_data_structures::fx::FxIndexSet;
-use rustc_span::{sym, symbol::kw};
-
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-enum ArgumentType {
-    Format(FormatTrait),
-    Usize,
-}
-
-fn make_argument(ecx: &ExtCtxt<'_>, sp: Span, arg: P<ast::Expr>, ty: ArgumentType) -> P<ast::Expr> {
-    // Generate:
-    //     ::core::fmt::ArgumentV1::new_…(arg)
-    use ArgumentType::*;
-    use FormatTrait::*;
-    ecx.expr_call_global(
-        sp,
-        ecx.std_path(&[
-            sym::fmt,
-            sym::ArgumentV1,
-            match ty {
-                Format(Display) => sym::new_display,
-                Format(Debug) => sym::new_debug,
-                Format(LowerExp) => sym::new_lower_exp,
-                Format(UpperExp) => sym::new_upper_exp,
-                Format(Octal) => sym::new_octal,
-                Format(Pointer) => sym::new_pointer,
-                Format(Binary) => sym::new_binary,
-                Format(LowerHex) => sym::new_lower_hex,
-                Format(UpperHex) => sym::new_upper_hex,
-                Usize => sym::from_usize,
-            },
-        ]),
-        vec![arg],
-    )
-}
-
-fn make_count(
-    ecx: &ExtCtxt<'_>,
-    sp: Span,
-    count: &Option<FormatCount>,
-    argmap: &mut FxIndexSet<(usize, ArgumentType)>,
-) -> P<ast::Expr> {
-    // Generate:
-    //     ::core::fmt::rt::v1::Count::…(…)
-    match count {
-        Some(FormatCount::Literal(n)) => ecx.expr_call_global(
-            sp,
-            ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Count, sym::Is]),
-            vec![ecx.expr_usize(sp, *n)],
-        ),
-        Some(FormatCount::Argument(arg)) => {
-            if let Ok(arg_index) = arg.index {
-                let (i, _) = argmap.insert_full((arg_index, ArgumentType::Usize));
-                ecx.expr_call_global(
-                    sp,
-                    ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Count, sym::Param]),
-                    vec![ecx.expr_usize(sp, i)],
-                )
-            } else {
-                DummyResult::raw_expr(sp, true)
-            }
-        }
-        None => ecx.expr_path(ecx.path_global(
-            sp,
-            ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Count, sym::Implied]),
-        )),
-    }
-}
-
-fn make_format_spec(
-    ecx: &ExtCtxt<'_>,
-    sp: Span,
-    placeholder: &FormatPlaceholder,
-    argmap: &mut FxIndexSet<(usize, ArgumentType)>,
-) -> P<ast::Expr> {
-    // Generate:
-    //     ::core::fmt::rt::v1::Argument {
-    //         position: 0usize,
-    //         format: ::core::fmt::rt::v1::FormatSpec {
-    //             fill: ' ',
-    //             align: ::core::fmt::rt::v1::Alignment::Unknown,
-    //             flags: 0u32,
-    //             precision: ::core::fmt::rt::v1::Count::Implied,
-    //             width: ::core::fmt::rt::v1::Count::Implied,
-    //         },
-    //     }
-    let position = match placeholder.argument.index {
-        Ok(arg_index) => {
-            let (i, _) =
-                argmap.insert_full((arg_index, ArgumentType::Format(placeholder.format_trait)));
-            ecx.expr_usize(sp, i)
-        }
-        Err(_) => DummyResult::raw_expr(sp, true),
-    };
-    let fill = ecx.expr_char(sp, placeholder.format_options.fill.unwrap_or(' '));
-    let align = ecx.expr_path(ecx.path_global(
-        sp,
-        ecx.std_path(&[
-            sym::fmt,
-            sym::rt,
-            sym::v1,
-            sym::Alignment,
-            match placeholder.format_options.alignment {
-                Some(FormatAlignment::Left) => sym::Left,
-                Some(FormatAlignment::Right) => sym::Right,
-                Some(FormatAlignment::Center) => sym::Center,
-                None => sym::Unknown,
-            },
-        ]),
-    ));
-    let flags = ecx.expr_u32(sp, placeholder.format_options.flags);
-    let prec = make_count(ecx, sp, &placeholder.format_options.precision, argmap);
-    let width = make_count(ecx, sp, &placeholder.format_options.width, argmap);
-    ecx.expr_struct(
-        sp,
-        ecx.path_global(sp, ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::Argument])),
-        vec![
-            ecx.field_imm(sp, Ident::new(sym::position, sp), position),
-            ecx.field_imm(
-                sp,
-                Ident::new(sym::format, sp),
-                ecx.expr_struct(
-                    sp,
-                    ecx.path_global(
-                        sp,
-                        ecx.std_path(&[sym::fmt, sym::rt, sym::v1, sym::FormatSpec]),
-                    ),
-                    vec![
-                        ecx.field_imm(sp, Ident::new(sym::fill, sp), fill),
-                        ecx.field_imm(sp, Ident::new(sym::align, sp), align),
-                        ecx.field_imm(sp, Ident::new(sym::flags, sp), flags),
-                        ecx.field_imm(sp, Ident::new(sym::precision, sp), prec),
-                        ecx.field_imm(sp, Ident::new(sym::width, sp), width),
-                    ],
-                ),
-            ),
-        ],
-    )
-}
-
-pub fn expand_parsed_format_args(ecx: &mut ExtCtxt<'_>, fmt: FormatArgs) -> P<ast::Expr> {
-    let macsp = ecx.with_def_site_ctxt(ecx.call_site());
-
-    let lit_pieces = ecx.expr_array_ref(
-        fmt.span,
-        fmt.template
-            .iter()
-            .enumerate()
-            .filter_map(|(i, piece)| match piece {
-                &FormatArgsPiece::Literal(s) => Some(ecx.expr_str(fmt.span, s)),
-                &FormatArgsPiece::Placeholder(_) => {
-                    // Inject empty string before placeholders when not already preceded by a literal piece.
-                    if i == 0 || matches!(fmt.template[i - 1], FormatArgsPiece::Placeholder(_)) {
-                        Some(ecx.expr_str(fmt.span, kw::Empty))
-                    } else {
-                        None
-                    }
-                }
-            })
-            .collect(),
-    );
-
-    // Whether we'll use the `Arguments::new_v1_formatted` form (true),
-    // or the `Arguments::new_v1` form (false).
-    let mut use_format_options = false;
-
-    // Create a list of all _unique_ (argument, format trait) combinations.
-    // E.g. "{0} {0:x} {0} {1}" -> [(0, Display), (0, LowerHex), (1, Display)]
-    let mut argmap = FxIndexSet::default();
-    for piece in &fmt.template {
-        let FormatArgsPiece::Placeholder(placeholder) = piece else { continue };
-        if placeholder.format_options != Default::default() {
-            // Can't use basic form if there's any formatting options.
-            use_format_options = true;
-        }
-        if let Ok(index) = placeholder.argument.index {
-            if !argmap.insert((index, ArgumentType::Format(placeholder.format_trait))) {
-                // Duplicate (argument, format trait) combination,
-                // which we'll only put once in the args array.
-                use_format_options = true;
-            }
-        }
-    }
-
-    let format_options = use_format_options.then(|| {
-        // Generate:
-        //     &[format_spec_0, format_spec_1, format_spec_2]
-        ecx.expr_array_ref(
-            macsp,
-            fmt.template
-                .iter()
-                .filter_map(|piece| {
-                    let FormatArgsPiece::Placeholder(placeholder) = piece else { return None };
-                    Some(make_format_spec(ecx, macsp, placeholder, &mut argmap))
-                })
-                .collect(),
-        )
-    });
-
-    let arguments = fmt.arguments.into_vec();
-
-    // 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.
-    let use_simple_array = argmap.len() == arguments.len()
-        && 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 {
-        // Generate:
-        //     &[
-        //         ::core::fmt::ArgumentV1::new_display(&arg0),
-        //         ::core::fmt::ArgumentV1::new_lower_hex(&arg1),
-        //         ::core::fmt::ArgumentV1::new_debug(&arg2),
-        //     ]
-        ecx.expr_array_ref(
-            macsp,
-            arguments
-                .into_iter()
-                .zip(argmap)
-                .map(|(arg, (_, ty))| {
-                    let sp = arg.expr.span.with_ctxt(macsp.ctxt());
-                    make_argument(ecx, sp, ecx.expr_addr_of(sp, arg.expr), ty)
-                })
-                .collect(),
-        )
-    } else {
-        // Generate:
-        //     match (&arg0, &arg1, &arg2) {
-        //         args => &[
-        //             ::core::fmt::ArgumentV1::new_display(args.0),
-        //             ::core::fmt::ArgumentV1::new_lower_hex(args.1),
-        //             ::core::fmt::ArgumentV1::new_debug(args.0),
-        //         ]
-        //     }
-        let args_ident = Ident::new(sym::args, macsp);
-        let args = argmap
-            .iter()
-            .map(|&(arg_index, ty)| {
-                if let Some(arg) = arguments.get(arg_index) {
-                    let sp = arg.expr.span.with_ctxt(macsp.ctxt());
-                    make_argument(
-                        ecx,
-                        sp,
-                        ecx.expr_field(
-                            sp,
-                            ecx.expr_ident(macsp, args_ident),
-                            Ident::new(sym::integer(arg_index), macsp),
-                        ),
-                        ty,
-                    )
-                } else {
-                    DummyResult::raw_expr(macsp, true)
-                }
-            })
-            .collect();
-        ecx.expr_addr_of(
-            macsp,
-            ecx.expr_match(
-                macsp,
-                ecx.expr_tuple(
-                    macsp,
-                    arguments
-                        .into_iter()
-                        .map(|arg| {
-                            ecx.expr_addr_of(arg.expr.span.with_ctxt(macsp.ctxt()), arg.expr)
-                        })
-                        .collect(),
-                ),
-                vec![ecx.arm(macsp, ecx.pat_ident(macsp, args_ident), ecx.expr_array(macsp, args))],
-            ),
-        )
-    };
-
-    if let Some(format_options) = format_options {
-        // Generate:
-        //     ::core::fmt::Arguments::new_v1_formatted(
-        //         lit_pieces,
-        //         args,
-        //         format_options,
-        //         unsafe { ::core::fmt::UnsafeArg::new() }
-        //     )
-        ecx.expr_call_global(
-            macsp,
-            ecx.std_path(&[sym::fmt, sym::Arguments, sym::new_v1_formatted]),
-            vec![
-                lit_pieces,
-                args,
-                format_options,
-                ecx.expr_block(P(ast::Block {
-                    stmts: vec![ecx.stmt_expr(ecx.expr_call_global(
-                        macsp,
-                        ecx.std_path(&[sym::fmt, sym::UnsafeArg, sym::new]),
-                        Vec::new(),
-                    ))],
-                    id: ast::DUMMY_NODE_ID,
-                    rules: BlockCheckMode::Unsafe(UnsafeSource::CompilerGenerated),
-                    span: macsp,
-                    tokens: None,
-                    could_be_bare_literal: false,
-                })),
-            ],
-        )
-    } else {
-        // Generate:
-        //     ::core::fmt::Arguments::new_v1(
-        //         lit_pieces,
-        //         args,
-        //     )
-        ecx.expr_call_global(
-            macsp,
-            ecx.std_path(&[sym::fmt, sym::Arguments, sym::new_v1]),
-            vec![lit_pieces, args],
-        )
-    }
-}
-
-fn may_contain_yield_point(e: &ast::Expr) -> bool {
-    struct MayContainYieldPoint(bool);
-
-    impl Visitor<'_> for MayContainYieldPoint {
-        fn visit_expr(&mut self, e: &ast::Expr) {
-            if let ast::ExprKind::Await(_) | ast::ExprKind::Yield(_) = e.kind {
-                self.0 = true;
-            } else {
-                visit::walk_expr(self, e);
-            }
-        }
-
-        fn visit_mac_call(&mut self, _: &ast::MacCall) {
-            self.0 = true;
-        }
-
-        fn visit_attribute(&mut self, _: &ast::Attribute) {
-            // Conservatively assume this may be a proc macro attribute in
-            // expression position.
-            self.0 = true;
-        }
-
-        fn visit_item(&mut self, _: &ast::Item) {
-            // Do not recurse into nested items.
-        }
-    }
-
-    let mut visitor = MayContainYieldPoint(false);
-    visitor.visit_expr(e);
-    visitor.0
-}
diff --git a/compiler/rustc_builtin_macros/src/global_allocator.rs b/compiler/rustc_builtin_macros/src/global_allocator.rs
index f8761653b..41b51bae7 100644
--- a/compiler/rustc_builtin_macros/src/global_allocator.rs
+++ b/compiler/rustc_builtin_macros/src/global_allocator.rs
@@ -9,7 +9,7 @@ use rustc_ast::{Fn, ItemKind, Mutability, Stmt, Ty, TyKind, Unsafe};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand(
     ecx: &mut ExtCtxt<'_>,
@@ -47,7 +47,7 @@ pub fn expand(
     let stmts = ALLOCATOR_METHODS.iter().map(|method| f.allocator_fn(method)).collect();
 
     // Generate anonymous constant serving as container for the allocator methods.
-    let const_ty = ecx.ty(ty_span, TyKind::Tup(Vec::new()));
+    let const_ty = ecx.ty(ty_span, TyKind::Tup(ThinVec::new()));
     let const_body = ecx.expr_block(ecx.block(span, stmts));
     let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
     let const_item = if is_stmt {
@@ -70,7 +70,7 @@ struct AllocFnFactory<'a, 'b> {
 
 impl AllocFnFactory<'_, '_> {
     fn allocator_fn(&self, method: &AllocatorMethod) -> Stmt {
-        let mut abi_args = Vec::new();
+        let mut abi_args = ThinVec::new();
         let mut i = 0;
         let mut mk = || {
             let name = Ident::from_str_and_span(&format!("arg{}", i), self.span);
@@ -99,7 +99,7 @@ impl AllocFnFactory<'_, '_> {
         self.cx.stmt_item(self.ty_span, item)
     }
 
-    fn call_allocator(&self, method: Symbol, mut args: Vec<P<Expr>>) -> P<Expr> {
+    fn call_allocator(&self, method: Symbol, mut args: ThinVec<P<Expr>>) -> P<Expr> {
         let method = self.cx.std_path(&[sym::alloc, sym::GlobalAlloc, method]);
         let method = self.cx.expr_path(self.cx.path(self.ty_span, method));
         let allocator = self.cx.path_ident(self.ty_span, self.global);
@@ -117,7 +117,7 @@ impl AllocFnFactory<'_, '_> {
     fn arg_ty(
         &self,
         ty: &AllocatorTy,
-        args: &mut Vec<Param>,
+        args: &mut ThinVec<Param>,
         ident: &mut dyn FnMut() -> Ident,
     ) -> P<Expr> {
         match *ty {
@@ -134,7 +134,7 @@ impl AllocFnFactory<'_, '_> {
                 let layout_new = self.cx.expr_path(self.cx.path(self.span, layout_new));
                 let size = self.cx.expr_ident(self.span, size);
                 let align = self.cx.expr_ident(self.span, align);
-                let layout = self.cx.expr_call(self.span, layout_new, vec![size, align]);
+                let layout = self.cx.expr_call(self.span, layout_new, thin_vec![size, align]);
                 layout
             }
 
@@ -168,7 +168,7 @@ impl AllocFnFactory<'_, '_> {
                 (self.ptr_u8(), expr)
             }
 
-            AllocatorTy::Unit => (self.cx.ty(self.span, TyKind::Tup(Vec::new())), expr),
+            AllocatorTy::Unit => (self.cx.ty(self.span, TyKind::Tup(ThinVec::new())), expr),
 
             AllocatorTy::Layout | AllocatorTy::Usize | AllocatorTy::Ptr => {
                 panic!("can't convert `AllocatorTy` to an output")
diff --git a/compiler/rustc_builtin_macros/src/lib.rs b/compiler/rustc_builtin_macros/src/lib.rs
index 75cfac723..8afb6e560 100644
--- a/compiler/rustc_builtin_macros/src/lib.rs
+++ b/compiler/rustc_builtin_macros/src/lib.rs
@@ -21,8 +21,10 @@ extern crate tracing;
 
 use crate::deriving::*;
 
+use rustc_errors::{DiagnosticMessage, SubdiagnosticMessage};
 use rustc_expand::base::{MacroExpanderFn, ResolverExpand, SyntaxExtensionKind};
 use rustc_expand::proc_macro::BangProcMacro;
+use rustc_macros::fluent_messages;
 use rustc_span::symbol::sym;
 
 mod alloc_error_handler;
@@ -54,6 +56,8 @@ pub mod proc_macro_harness;
 pub mod standard_library_imports;
 pub mod test_harness;
 
+fluent_messages! { "../locales/en-US.ftl" }
+
 pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
     let mut register = |name, kind| resolver.register_builtin_macro(name, kind);
     macro register_bang($($name:ident: $f:expr,)*) {
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
index 21c8caa65..bc513607d 100644
--- a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -11,6 +11,7 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use smallvec::smallvec;
 use std::mem;
+use thin_vec::{thin_vec, ThinVec};
 
 struct ProcMacroDerive {
     id: NodeId,
@@ -314,11 +315,14 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
                     cx.expr_call(
                         span,
                         proc_macro_ty_method_path(cx, custom_derive),
-                        vec![
+                        thin_vec![
                             cx.expr_str(span, cd.trait_name),
                             cx.expr_array_ref(
                                 span,
-                                cd.attrs.iter().map(|&s| cx.expr_str(span, s)).collect::<Vec<_>>(),
+                                cd.attrs
+                                    .iter()
+                                    .map(|&s| cx.expr_str(span, s))
+                                    .collect::<ThinVec<_>>(),
                             ),
                             local_path(cx, cd.function_name),
                         ],
@@ -335,7 +339,7 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
                     cx.expr_call(
                         span,
                         proc_macro_ty_method_path(cx, ident),
-                        vec![
+                        thin_vec![
                             cx.expr_str(span, ca.function_name.name),
                             local_path(cx, ca.function_name),
                         ],
@@ -371,13 +375,13 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
         });
 
     let block = cx.expr_block(
-        cx.block(span, vec![cx.stmt_item(span, krate), cx.stmt_item(span, decls_static)]),
+        cx.block(span, thin_vec![cx.stmt_item(span, krate), cx.stmt_item(span, decls_static)]),
     );
 
     let anon_constant = cx.item_const(
         span,
         Ident::new(kw::Underscore, span),
-        cx.ty(span, ast::TyKind::Tup(Vec::new())),
+        cx.ty(span, ast::TyKind::Tup(ThinVec::new())),
         block,
     );
 
diff --git a/compiler/rustc_builtin_macros/src/standard_library_imports.rs b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
index f73f20c84..e67c0dba6 100644
--- a/compiler/rustc_builtin_macros/src/standard_library_imports.rs
+++ b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
@@ -62,7 +62,7 @@ pub fn inject(
     // the one with the prelude.
     let name = names[0];
 
-    let root = (edition == Edition2015).then(|| kw::PathRoot);
+    let root = (edition == Edition2015).then_some(kw::PathRoot);
 
     let import_path = root
         .iter()
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index 729ae4071..e02c7e6c0 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -10,7 +10,7 @@ use rustc_session::Session;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
 use std::iter;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 /// #[test_case] is used by custom test authors to mark tests
 /// When building for test, it needs to make the item public and gensym the name
@@ -179,19 +179,19 @@ pub fn expand_test_or_bench(
         cx.expr_call(
             sp,
             cx.expr_path(test_path("StaticBenchFn")),
-            vec![
+            thin_vec![
                 // |b| self::test::assert_test_result(
                 cx.lambda1(
                     sp,
                     cx.expr_call(
                         sp,
                         cx.expr_path(test_path("assert_test_result")),
-                        vec![
+                        thin_vec![
                             // super::$test_fn(b)
                             cx.expr_call(
                                 ret_ty_sp,
                                 cx.expr_path(cx.path(sp, vec![item.ident])),
-                                vec![cx.expr_ident(sp, b)],
+                                thin_vec![cx.expr_ident(sp, b)],
                             ),
                         ],
                     ),
@@ -203,7 +203,7 @@ pub fn expand_test_or_bench(
         cx.expr_call(
             sp,
             cx.expr_path(test_path("StaticTestFn")),
-            vec![
+            thin_vec![
                 // || {
                 cx.lambda0(
                     sp,
@@ -211,12 +211,12 @@ pub fn expand_test_or_bench(
                     cx.expr_call(
                         sp,
                         cx.expr_path(test_path("assert_test_result")),
-                        vec![
+                        thin_vec![
                             // $test_fn()
                             cx.expr_call(
                                 ret_ty_sp,
                                 cx.expr_path(cx.path(sp, vec![item.ident])),
-                                vec![],
+                                ThinVec::new(),
                             ), // )
                         ],
                     ), // }
@@ -249,21 +249,21 @@ pub fn expand_test_or_bench(
                 cx.expr_struct(
                     sp,
                     test_path("TestDescAndFn"),
-                    vec![
+                    thin_vec![
                         // desc: test::TestDesc {
                         field(
                             "desc",
                             cx.expr_struct(
                                 sp,
                                 test_path("TestDesc"),
-                                vec![
+                                thin_vec![
                                     // name: "path::to::test"
                                     field(
                                         "name",
                                         cx.expr_call(
                                             sp,
                                             cx.expr_path(test_path("StaticTestName")),
-                                            vec![cx.expr_str(sp, test_path_symbol)],
+                                            thin_vec![cx.expr_str(sp, test_path_symbol)],
                                         ),
                                     ),
                                     // ignore: true | false
@@ -300,7 +300,7 @@ pub fn expand_test_or_bench(
                                             ShouldPanic::Yes(Some(sym)) => cx.expr_call(
                                                 sp,
                                                 cx.expr_path(should_panic_path("YesWithMessage")),
-                                                vec![cx.expr_str(sp, sym)],
+                                                thin_vec![cx.expr_str(sp, sym)],
                                             ),
                                         },
                                     ),
diff --git a/compiler/rustc_builtin_macros/src/test_harness.rs b/compiler/rustc_builtin_macros/src/test_harness.rs
index ad8871080..d8e3db9e8 100644
--- a/compiler/rustc_builtin_macros/src/test_harness.rs
+++ b/compiler/rustc_builtin_macros/src/test_harness.rs
@@ -14,7 +14,8 @@ use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::PanicStrategy;
 use smallvec::{smallvec, SmallVec};
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
+use tracing::debug;
 
 use std::{iter, mem};
 
@@ -299,7 +300,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     test_runner.span = sp;
 
     let test_main_path_expr = ecx.expr_path(test_runner);
-    let call_test_main = ecx.expr_call(sp, test_main_path_expr, vec![mk_tests_slice(cx, sp)]);
+    let call_test_main = ecx.expr_call(sp, test_main_path_expr, thin_vec![mk_tests_slice(cx, sp)]);
     let call_test_main = ecx.stmt_expr(call_test_main);
 
     // extern crate test
@@ -312,16 +313,16 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     let main_attr = ecx.attr_word(sym::rustc_main, sp);
 
     // pub fn main() { ... }
-    let main_ret_ty = ecx.ty(sp, ast::TyKind::Tup(vec![]));
+    let main_ret_ty = ecx.ty(sp, ast::TyKind::Tup(ThinVec::new()));
 
     // If no test runner is provided we need to import the test crate
     let main_body = if cx.test_runner.is_none() {
-        ecx.block(sp, vec![test_extern_stmt, call_test_main])
+        ecx.block(sp, thin_vec![test_extern_stmt, call_test_main])
     } else {
-        ecx.block(sp, vec![call_test_main])
+        ecx.block(sp, thin_vec![call_test_main])
     };
 
-    let decl = ecx.fn_decl(vec![], ast::FnRetTy::Ty(main_ret_ty));
+    let decl = ecx.fn_decl(ThinVec::new(), ast::FnRetTy::Ty(main_ret_ty));
     let sig = ast::FnSig { decl, header: ast::FnHeader::default(), span: sp };
     let defaultness = ast::Defaultness::Final;
     let main = ast::ItemKind::Fn(Box::new(ast::Fn {