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-rw-r--r--Cargo.lock57
-rw-r--r--compiler/rustc_ast/Cargo.toml2
-rw-r--r--compiler/rustc_ast/src/ast.rs8
-rw-r--r--compiler/rustc_ast/src/mut_visit.rs2
-rw-r--r--compiler/rustc_ast/src/util/literal.rs2
-rw-r--r--compiler/rustc_ast/src/visit.rs2
-rw-r--r--compiler/rustc_ast_lowering/src/expr.rs16
-rw-r--r--compiler/rustc_ast_lowering/src/lib.rs11
-rw-r--r--compiler/rustc_ast_lowering/src/pat.rs1
-rw-r--r--compiler/rustc_ast_passes/src/ast_validation.rs2
-rw-r--r--compiler/rustc_ast_pretty/src/pprust/state.rs11
-rw-r--r--compiler/rustc_builtin_macros/src/autodiff.rs125
-rw-r--r--compiler/rustc_codegen_llvm/src/back/write.rs7
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs161
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs8
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs172
-rw-r--r--compiler/rustc_hir/src/hir.rs6
-rw-r--r--compiler/rustc_hir/src/intravisit.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/check/region.rs12
-rw-r--r--compiler/rustc_hir_pretty/src/lib.rs1
-rw-r--r--compiler/rustc_hir_typeck/src/demand.rs5
-rw-r--r--compiler/rustc_hir_typeck/src/expr.rs3
-rw-r--r--compiler/rustc_hir_typeck/src/expr_use_visitor.rs2
-rw-r--r--compiler/rustc_hir_typeck/src/pat.rs11
-rw-r--r--compiler/rustc_lexer/src/lib.rs1
-rw-r--r--compiler/rustc_lexer/src/unescape.rs438
-rw-r--r--compiler/rustc_lexer/src/unescape/tests.rs286
-rw-r--r--compiler/rustc_lint/src/builtin.rs26
-rw-r--r--compiler/rustc_lint/src/unused.rs3
-rw-r--r--compiler/rustc_middle/src/thir.rs3
-rw-r--r--compiler/rustc_middle/src/thir/visit.rs3
-rw-r--r--compiler/rustc_middle/src/ty/generic_args.rs6
-rw-r--r--compiler/rustc_mir_build/src/builder/matches/match_pair.rs2
-rw-r--r--compiler/rustc_mir_build/src/builder/matches/mod.rs1
-rw-r--r--compiler/rustc_mir_build/src/check_unsafety.rs1
-rw-r--r--compiler/rustc_mir_build/src/thir/pattern/mod.rs2
-rw-r--r--compiler/rustc_mir_build/src/thir/print.rs1
-rw-r--r--compiler/rustc_parse/Cargo.toml1
-rw-r--r--compiler/rustc_parse/src/lexer/mod.rs10
-rw-r--r--compiler/rustc_parse/src/lexer/unescape_error_reporting.rs2
-rw-r--r--compiler/rustc_parse/src/parser/expr.rs2
-rw-r--r--compiler/rustc_parse/src/parser/item.rs4
-rw-r--r--compiler/rustc_parse_format/Cargo.toml1
-rw-r--r--compiler/rustc_parse_format/src/lib.rs10
-rw-r--r--compiler/rustc_passes/src/input_stats.rs2
-rw-r--r--compiler/rustc_passes/src/liveness.rs7
-rw-r--r--compiler/rustc_pattern_analysis/src/rustc.rs2
-rw-r--r--compiler/rustc_resolve/src/late.rs13
-rw-r--r--compiler/rustc_type_ir/Cargo.toml1
-rw-r--r--compiler/rustc_type_ir/src/data_structures/mod.rs1
-rw-r--r--compiler/rustc_type_ir/src/ty_kind.rs8
-rw-r--r--library/Cargo.lock14
-rw-r--r--library/alloc/src/lib.rs1
-rw-r--r--library/alloc/src/raw_vec/mod.rs10
-rw-r--r--library/alloctests/lib.rs2
-rw-r--r--library/core/src/alloc/layout.rs8
-rw-r--r--library/core/src/ptr/unique.rs8
-rw-r--r--library/core/src/slice/iter.rs50
-rw-r--r--library/core/src/slice/mod.rs53
-rw-r--r--library/proc_macro/Cargo.toml1
-rw-r--r--library/proc_macro/src/lib.rs115
-rw-r--r--library/std/src/sys/io/io_slice/iovec.rs2
-rw-r--r--library/std/src/sys/io/mod.rs2
-rw-r--r--library/std/src/sys/stdio/trusty.rs83
-rw-r--r--src/bootstrap/src/lib.rs2
-rw-r--r--src/doc/style-guide/src/expressions.md78
-rw-r--r--src/librustdoc/clean/utils.rs1
m---------src/tools/cargo0
-rw-r--r--src/tools/clippy/clippy_lints/src/equatable_if_let.rs1
-rw-r--r--src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs1
-rw-r--r--src/tools/clippy/clippy_lints/src/matches/single_match.rs1
-rw-r--r--src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs1
-rw-r--r--src/tools/clippy/clippy_lints/src/utils/author.rs1
-rw-r--r--src/tools/clippy/clippy_utils/src/ast_utils/mod.rs1
-rw-r--r--src/tools/clippy/clippy_utils/src/hir_utils.rs1
-rw-r--r--src/tools/clippy/clippy_utils/src/lib.rs1
-rw-r--r--src/tools/rust-analyzer/Cargo.lock9
-rw-r--r--src/tools/rust-analyzer/Cargo.toml1
-rw-r--r--src/tools/rust-analyzer/crates/parser/Cargo.toml1
-rw-r--r--src/tools/rust-analyzer/crates/parser/src/lexed_str.rs10
-rw-r--r--src/tools/rust-analyzer/crates/syntax/Cargo.toml3
-rw-r--r--src/tools/rust-analyzer/crates/syntax/src/ast/token_ext.rs2
-rw-r--r--src/tools/rust-analyzer/crates/syntax/src/lib.rs9
-rw-r--r--src/tools/rust-analyzer/crates/syntax/src/validation.rs8
-rw-r--r--src/tools/rustbook/Cargo.lock151
-rw-r--r--src/tools/rustfmt/src/items.rs6
-rw-r--r--src/tools/rustfmt/src/patterns.rs2
-rw-r--r--src/tools/tidy/src/deps.rs2
-rw-r--r--tests/pretty/autodiff_forward.pp23
-rw-r--r--tests/pretty/autodiff_forward.rs9
-rw-r--r--tests/ui/attributes/invalid-reprs.rs6
-rw-r--r--tests/ui/attributes/invalid-reprs.stderr33
-rw-r--r--tests/ui/macros/stringify.rs2
-rw-r--r--tests/ui/unpretty/expanded-exhaustive.rs5
-rw-r--r--tests/ui/unpretty/expanded-exhaustive.stdout3
95 files changed, 960 insertions, 1229 deletions
diff --git a/Cargo.lock b/Cargo.lock
index 99bd1bff020..52c9269fa87 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -239,9 +239,9 @@ checksum = "5c8214115b7bf84099f1309324e63141d4c5d7cc26862f97a0a857dbefe165bd"
 
 [[package]]
 name = "blake3"
-version = "1.8.0"
+version = "1.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "34a796731680be7931955498a16a10b2270c7762963d5d570fdbfe02dcbf314f"
+checksum = "389a099b34312839e16420d499a9cad9650541715937ffbdd40d36f49e77eeb3"
 dependencies = [
  "arrayref",
  "arrayvec",
@@ -800,9 +800,9 @@ dependencies = [
 
 [[package]]
 name = "ctrlc"
-version = "3.4.5"
+version = "3.4.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "90eeab0aa92f3f9b4e87f258c72b139c207d251f9cbc1080a0086b86a8870dd3"
+checksum = "697b5419f348fd5ae2478e8018cb016c00a5881c7f46c717de98ffd135a5651c"
 dependencies = [
  "nix",
  "windows-sys 0.59.0",
@@ -1079,9 +1079,9 @@ dependencies = [
 
 [[package]]
 name = "env_logger"
-version = "0.11.7"
+version = "0.11.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3716d7a920fb4fac5d84e9d4bce8ceb321e9414b4409da61b07b75c1e3d0697"
+checksum = "13c863f0904021b108aa8b2f55046443e6b1ebde8fd4a15c399893aae4fa069f"
 dependencies = [
  "anstream",
  "anstyle",
@@ -1098,9 +1098,9 @@ checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
 
 [[package]]
 name = "errno"
-version = "0.3.10"
+version = "0.3.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
+checksum = "976dd42dc7e85965fe702eb8164f21f450704bdde31faefd6471dba214cb594e"
 dependencies = [
  "libc",
  "windows-sys 0.59.0",
@@ -1163,12 +1163,12 @@ dependencies = [
 
 [[package]]
 name = "flate2"
-version = "1.1.0"
+version = "1.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "11faaf5a5236997af9848be0bef4db95824b1d534ebc64d0f0c6cf3e67bd38dc"
+checksum = "7ced92e76e966ca2fd84c8f7aa01a4aea65b0eb6648d72f7c8f3e2764a67fece"
 dependencies = [
  "crc32fast",
- "miniz_oxide 0.8.5",
+ "miniz_oxide 0.8.7",
 ]
 
 [[package]]
@@ -1773,9 +1773,9 @@ checksum = "ce23b50ad8242c51a442f3ff322d56b02f08852c77e4c0b4d3fd684abc89c683"
 
 [[package]]
 name = "indexmap"
-version = "2.8.0"
+version = "2.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3954d50fe15b02142bf25d3b8bdadb634ec3948f103d04ffe3031bc8fe9d7058"
+checksum = "cea70ddb795996207ad57735b50c5982d8844f38ba9ee5f1aedcfb708a2aa11e"
 dependencies = [
  "equivalent",
  "hashbrown",
@@ -2252,9 +2252,9 @@ dependencies = [
 
 [[package]]
 name = "miniz_oxide"
-version = "0.8.5"
+version = "0.8.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e3e04debbb59698c15bacbb6d93584a8c0ca9cc3213cb423d31f760d8843ce5"
+checksum = "ff70ce3e48ae43fa075863cef62e8b43b71a4f2382229920e0df362592919430"
 dependencies = [
  "adler2",
 ]
@@ -2506,9 +2506,9 @@ checksum = "d05e27ee213611ffe7d6348b942e8f942b37114c00cc03cec254295a4a17852e"
 
 [[package]]
 name = "openssl-sys"
-version = "0.9.106"
+version = "0.9.107"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8bb61ea9811cc39e3c2069f40b8b8e2e70d8569b361f879786cc7ed48b777cdd"
+checksum = "8288979acd84749c744a9014b4382d42b8f7b2592847b5afb2ed29e5d16ede07"
 dependencies = [
  "cc",
  "libc",
@@ -2970,9 +2970,9 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.5.10"
+version = "0.5.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b8c0c260b63a8219631167be35e6a988e9554dbd323f8bd08439c8ed1302bd1"
+checksum = "d2f103c6d277498fbceb16e84d317e2a400f160f46904d5f5410848c829511a3"
 dependencies = [
  "bitflags",
 ]
@@ -3151,6 +3151,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "357703d41365b4b27c590e3ed91eabb1b663f07c4c084095e60cbed4362dff0d"
 
 [[package]]
+name = "rustc-literal-escaper"
+version = "0.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0041b6238913c41fe704213a4a9329e2f685a156d1781998128b4149c230ad04"
+
+[[package]]
 name = "rustc-main"
 version = "0.0.0"
 dependencies = [
@@ -3242,10 +3248,10 @@ version = "0.0.0"
 dependencies = [
  "bitflags",
  "memchr",
+ "rustc-literal-escaper",
  "rustc_ast_ir",
  "rustc_data_structures",
  "rustc_index",
- "rustc_lexer",
  "rustc_macros",
  "rustc_serialize",
  "rustc_span",
@@ -4200,6 +4206,7 @@ name = "rustc_parse"
 version = "0.0.0"
 dependencies = [
  "bitflags",
+ "rustc-literal-escaper",
  "rustc_ast",
  "rustc_ast_pretty",
  "rustc_data_structures",
@@ -4222,6 +4229,7 @@ dependencies = [
 name = "rustc_parse_format"
 version = "0.0.0"
 dependencies = [
+ "rustc-literal-escaper",
  "rustc_index",
  "rustc_lexer",
 ]
@@ -4581,6 +4589,7 @@ version = "0.0.0"
 dependencies = [
  "bitflags",
  "derive-where",
+ "ena",
  "indexmap",
  "rustc-hash 1.1.0",
  "rustc_ast_ir",
@@ -4918,9 +4927,9 @@ dependencies = [
 
 [[package]]
 name = "smallvec"
-version = "1.14.0"
+version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7fcf8323ef1faaee30a44a340193b1ac6814fd9b7b4e88e9d4519a3e4abe1cfd"
+checksum = "8917285742e9f3e1683f0a9c4e6b57960b7314d0b08d30d1ecd426713ee2eee9"
 
 [[package]]
 name = "socket2"
@@ -5368,9 +5377,9 @@ checksum = "1f3ccbac311fea05f86f61904b462b55fb3df8837a366dfc601a0161d0532f20"
 
 [[package]]
 name = "tokio"
-version = "1.44.1"
+version = "1.44.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f382da615b842244d4b8738c82ed1275e6c5dd90c459a30941cd07080b06c91a"
+checksum = "e6b88822cbe49de4185e3a4cbf8321dd487cf5fe0c5c65695fef6346371e9c48"
 dependencies = [
  "backtrace",
  "bytes",
diff --git a/compiler/rustc_ast/Cargo.toml b/compiler/rustc_ast/Cargo.toml
index 902287d0328..b2d3b90fc44 100644
--- a/compiler/rustc_ast/Cargo.toml
+++ b/compiler/rustc_ast/Cargo.toml
@@ -7,10 +7,10 @@ edition = "2024"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 memchr = "2.7.4"
+rustc-literal-escaper = "0.0.2"
 rustc_ast_ir = { path = "../rustc_ast_ir" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_index = { path = "../rustc_index" }
-rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 97e6879c33e..6362b539fc7 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -563,6 +563,7 @@ impl Pat {
     /// This is intended for use by diagnostics.
     pub fn to_ty(&self) -> Option<P<Ty>> {
         let kind = match &self.kind {
+            PatKind::Missing => unreachable!(),
             // In a type expression `_` is an inference variable.
             PatKind::Wild => TyKind::Infer,
             // An IDENT pattern with no binding mode would be valid as path to a type. E.g. `u32`.
@@ -625,7 +626,8 @@ impl Pat {
             | PatKind::Guard(s, _) => s.walk(it),
 
             // These patterns do not contain subpatterns, skip.
-            PatKind::Wild
+            PatKind::Missing
+            | PatKind::Wild
             | PatKind::Rest
             | PatKind::Never
             | PatKind::Expr(_)
@@ -676,6 +678,7 @@ impl Pat {
     /// Return a name suitable for diagnostics.
     pub fn descr(&self) -> Option<String> {
         match &self.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => Some("_".to_string()),
             PatKind::Ident(BindingMode::NONE, ident, None) => Some(format!("{ident}")),
             PatKind::Ref(pat, mutbl) => pat.descr().map(|d| format!("&{}{d}", mutbl.prefix_str())),
@@ -769,6 +772,9 @@ pub enum RangeSyntax {
 // Adding a new variant? Please update `test_pat` in `tests/ui/macros/stringify.rs`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum PatKind {
+    /// A missing pattern, e.g. for an anonymous param in a bare fn like `fn f(u32)`.
+    Missing,
+
     /// Represents a wildcard pattern (`_`).
     Wild,
 
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index f7d13acdfc4..00934b73a88 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1587,7 +1587,7 @@ pub fn walk_pat<T: MutVisitor>(vis: &mut T, pat: &mut P<Pat>) {
     vis.visit_id(id);
     match kind {
         PatKind::Err(_guar) => {}
-        PatKind::Wild | PatKind::Rest | PatKind::Never => {}
+        PatKind::Missing | PatKind::Wild | PatKind::Rest | PatKind::Never => {}
         PatKind::Ident(_binding_mode, ident, sub) => {
             vis.visit_ident(ident);
             visit_opt(sub, |sub| vis.visit_pat(sub));
diff --git a/compiler/rustc_ast/src/util/literal.rs b/compiler/rustc_ast/src/util/literal.rs
index 6896ac723fa..b8526cf9d95 100644
--- a/compiler/rustc_ast/src/util/literal.rs
+++ b/compiler/rustc_ast/src/util/literal.rs
@@ -2,7 +2,7 @@
 
 use std::{ascii, fmt, str};
 
-use rustc_lexer::unescape::{
+use rustc_literal_escaper::{
     MixedUnit, Mode, byte_from_char, unescape_byte, unescape_char, unescape_mixed, unescape_unicode,
 };
 use rustc_span::{Span, Symbol, kw, sym};
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 1ef92ff8898..ac6aa6b9e72 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -750,7 +750,7 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) -> V::Res
             try_visit!(visitor.visit_pat(subpattern));
             try_visit!(visitor.visit_expr(guard_condition));
         }
-        PatKind::Wild | PatKind::Rest | PatKind::Never => {}
+        PatKind::Missing | PatKind::Wild | PatKind::Rest | PatKind::Never => {}
         PatKind::Err(_guar) => {}
         PatKind::Tuple(elems) | PatKind::Slice(elems) | PatKind::Or(elems) => {
             walk_list!(visitor, visit_pat, elems);
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 80bb1e8fc41..df4fd2ef52f 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -74,14 +74,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     // Merge attributes into the inner expression.
                     if !e.attrs.is_empty() {
                         let old_attrs = self.attrs.get(&ex.hir_id.local_id).copied().unwrap_or(&[]);
-                        self.attrs.insert(
-                            ex.hir_id.local_id,
-                            &*self.arena.alloc_from_iter(
-                                self.lower_attrs_vec(&e.attrs, e.span)
-                                    .into_iter()
-                                    .chain(old_attrs.iter().cloned()),
-                            ),
+                        let attrs = &*self.arena.alloc_from_iter(
+                            self.lower_attrs_vec(&e.attrs, e.span)
+                                .into_iter()
+                                .chain(old_attrs.iter().cloned()),
                         );
+                        if attrs.is_empty() {
+                            return ex;
+                        }
+
+                        self.attrs.insert(ex.hir_id.local_id, attrs);
                     }
                     return ex;
                 }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index d5d6dcd8d63..38190d44fc5 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -1496,18 +1496,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Option<Ident>] {
         self.arena.alloc_from_iter(decl.inputs.iter().map(|param| match param.pat.kind {
-            PatKind::Ident(_, ident, _) => {
-                if ident.name != kw::Empty {
-                    Some(self.lower_ident(ident))
-                } else {
-                    None
-                }
-            }
+            PatKind::Missing => None,
+            PatKind::Ident(_, ident, _) => Some(self.lower_ident(ident)),
             PatKind::Wild => Some(Ident::new(kw::Underscore, self.lower_span(param.pat.span))),
             _ => {
                 self.dcx().span_delayed_bug(
                     param.pat.span,
-                    "non-ident/wild param pat must trigger an error",
+                    "non-missing/ident/wild param pat must trigger an error",
                 );
                 None
             }
diff --git a/compiler/rustc_ast_lowering/src/pat.rs b/compiler/rustc_ast_lowering/src/pat.rs
index 07cc64a1358..f94d788a9b0 100644
--- a/compiler/rustc_ast_lowering/src/pat.rs
+++ b/compiler/rustc_ast_lowering/src/pat.rs
@@ -26,6 +26,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             let pat_hir_id = self.lower_node_id(pattern.id);
             let node = loop {
                 match &pattern.kind {
+                    PatKind::Missing => break hir::PatKind::Missing,
                     PatKind::Wild => break hir::PatKind::Wild,
                     PatKind::Never => break hir::PatKind::Never,
                     PatKind::Ident(binding_mode, ident, sub) => {
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 9916de8b7b1..dc77e7b2834 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -244,7 +244,7 @@ impl<'a> AstValidator<'a> {
     fn check_decl_no_pat(decl: &FnDecl, mut report_err: impl FnMut(Span, Option<Ident>, bool)) {
         for Param { pat, .. } in &decl.inputs {
             match pat.kind {
-                PatKind::Ident(BindingMode::NONE, _, None) | PatKind::Wild => {}
+                PatKind::Missing | PatKind::Ident(BindingMode::NONE, _, None) | PatKind::Wild => {}
                 PatKind::Ident(BindingMode::MUT, ident, None) => {
                     report_err(pat.span, Some(ident), true)
                 }
diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index 3dbfc191f8f..683ad5c66bf 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -1622,9 +1622,9 @@ impl<'a> State<'a> {
     fn print_pat(&mut self, pat: &ast::Pat) {
         self.maybe_print_comment(pat.span.lo());
         self.ann.pre(self, AnnNode::Pat(pat));
-        /* Pat isn't normalized, but the beauty of it
-        is that it doesn't matter */
+        /* Pat isn't normalized, but the beauty of it is that it doesn't matter */
         match &pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => self.word("_"),
             PatKind::Never => self.word("!"),
             PatKind::Ident(BindingMode(by_ref, mutbl), ident, sub) => {
@@ -1946,12 +1946,7 @@ impl<'a> State<'a> {
                 if let Some(eself) = input.to_self() {
                     self.print_explicit_self(&eself);
                 } else {
-                    let invalid = if let PatKind::Ident(_, ident, _) = input.pat.kind {
-                        ident.name == kw::Empty
-                    } else {
-                        false
-                    };
-                    if !invalid {
+                    if !matches!(input.pat.kind, PatKind::Missing) {
                         self.print_pat(&input.pat);
                         self.word(":");
                         self.space();
diff --git a/compiler/rustc_builtin_macros/src/autodiff.rs b/compiler/rustc_builtin_macros/src/autodiff.rs
index 7f99f75b2b9..351413dea49 100644
--- a/compiler/rustc_builtin_macros/src/autodiff.rs
+++ b/compiler/rustc_builtin_macros/src/autodiff.rs
@@ -17,7 +17,7 @@ mod llvm_enzyme {
     use rustc_ast::visit::AssocCtxt::*;
     use rustc_ast::{
         self as ast, AssocItemKind, BindingMode, ExprKind, FnRetTy, FnSig, Generics, ItemKind,
-        MetaItemInner, PatKind, QSelf, TyKind,
+        MetaItemInner, PatKind, QSelf, TyKind, Visibility,
     };
     use rustc_expand::base::{Annotatable, ExtCtxt};
     use rustc_span::{Ident, Span, Symbol, kw, sym};
@@ -72,6 +72,16 @@ mod llvm_enzyme {
         }
     }
 
+    // Get information about the function the macro is applied to
+    fn extract_item_info(iitem: &P<ast::Item>) -> Option<(Visibility, FnSig, Ident)> {
+        match &iitem.kind {
+            ItemKind::Fn(box ast::Fn { sig, ident, .. }) => {
+                Some((iitem.vis.clone(), sig.clone(), ident.clone()))
+            }
+            _ => None,
+        }
+    }
+
     pub(crate) fn from_ast(
         ecx: &mut ExtCtxt<'_>,
         meta_item: &ThinVec<MetaItemInner>,
@@ -199,32 +209,26 @@ mod llvm_enzyme {
             return vec![item];
         }
         let dcx = ecx.sess.dcx();
-        // first get the annotable item:
-        let (primal, sig, is_impl): (Ident, FnSig, bool) = match &item {
-            Annotatable::Item(iitem) => {
-                let (ident, sig) = match &iitem.kind {
-                    ItemKind::Fn(box ast::Fn { ident, sig, .. }) => (ident, sig),
-                    _ => {
-                        dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                        return vec![item];
-                    }
-                };
-                (*ident, sig.clone(), false)
-            }
+
+        // first get information about the annotable item:
+        let Some((vis, sig, primal)) = (match &item {
+            Annotatable::Item(iitem) => extract_item_info(iitem),
+            Annotatable::Stmt(stmt) => match &stmt.kind {
+                ast::StmtKind::Item(iitem) => extract_item_info(iitem),
+                _ => None,
+            },
             Annotatable::AssocItem(assoc_item, Impl { of_trait: false }) => {
-                let (ident, sig) = match &assoc_item.kind {
-                    ast::AssocItemKind::Fn(box ast::Fn { ident, sig, .. }) => (ident, sig),
-                    _ => {
-                        dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                        return vec![item];
+                match &assoc_item.kind {
+                    ast::AssocItemKind::Fn(box ast::Fn { sig, ident, .. }) => {
+                        Some((assoc_item.vis.clone(), sig.clone(), ident.clone()))
                     }
-                };
-                (*ident, sig.clone(), true)
-            }
-            _ => {
-                dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                return vec![item];
+                    _ => None,
+                }
             }
+            _ => None,
+        }) else {
+            dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
+            return vec![item];
         };
 
         let meta_item_vec: ThinVec<MetaItemInner> = match meta_item.kind {
@@ -238,15 +242,6 @@ mod llvm_enzyme {
         let has_ret = has_ret(&sig.decl.output);
         let sig_span = ecx.with_call_site_ctxt(sig.span);
 
-        let vis = match &item {
-            Annotatable::Item(iitem) => iitem.vis.clone(),
-            Annotatable::AssocItem(assoc_item, _) => assoc_item.vis.clone(),
-            _ => {
-                dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                return vec![item];
-            }
-        };
-
         // create TokenStream from vec elemtents:
         // meta_item doesn't have a .tokens field
         let mut ts: Vec<TokenTree> = vec![];
@@ -379,6 +374,22 @@ mod llvm_enzyme {
                 }
                 Annotatable::AssocItem(assoc_item.clone(), i)
             }
+            Annotatable::Stmt(ref mut stmt) => {
+                match stmt.kind {
+                    ast::StmtKind::Item(ref mut iitem) => {
+                        if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
+                            iitem.attrs.push(attr);
+                        }
+                        if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind))
+                        {
+                            iitem.attrs.push(inline_never.clone());
+                        }
+                    }
+                    _ => unreachable!("stmt kind checked previously"),
+                };
+
+                Annotatable::Stmt(stmt.clone())
+            }
             _ => {
                 unreachable!("annotatable kind checked previously")
             }
@@ -389,22 +400,40 @@ mod llvm_enzyme {
             delim: rustc_ast::token::Delimiter::Parenthesis,
             tokens: ts,
         });
+
         let d_attr = outer_normal_attr(&rustc_ad_attr, new_id, span);
-        let d_annotatable = if is_impl {
-            let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(asdf);
-            let d_fn = P(ast::AssocItem {
-                attrs: thin_vec![d_attr, inline_never],
-                id: ast::DUMMY_NODE_ID,
-                span,
-                vis,
-                kind: assoc_item,
-                tokens: None,
-            });
-            Annotatable::AssocItem(d_fn, Impl { of_trait: false })
-        } else {
-            let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
-            d_fn.vis = vis;
-            Annotatable::Item(d_fn)
+        let d_annotatable = match &item {
+            Annotatable::AssocItem(_, _) => {
+                let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(asdf);
+                let d_fn = P(ast::AssocItem {
+                    attrs: thin_vec![d_attr, inline_never],
+                    id: ast::DUMMY_NODE_ID,
+                    span,
+                    vis,
+                    kind: assoc_item,
+                    tokens: None,
+                });
+                Annotatable::AssocItem(d_fn, Impl { of_trait: false })
+            }
+            Annotatable::Item(_) => {
+                let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
+                d_fn.vis = vis;
+
+                Annotatable::Item(d_fn)
+            }
+            Annotatable::Stmt(_) => {
+                let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
+                d_fn.vis = vis;
+
+                Annotatable::Stmt(P(ast::Stmt {
+                    id: ast::DUMMY_NODE_ID,
+                    kind: ast::StmtKind::Item(d_fn),
+                    span,
+                }))
+            }
+            _ => {
+                unreachable!("item kind checked previously")
+            }
         };
 
         return vec![orig_annotatable, d_annotatable];
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index bf6138142b6..76d431a4975 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -439,12 +439,9 @@ fn report_inline_asm(
     let span = if cookie == 0 || matches!(cgcx.lto, Lto::Fat | Lto::Thin) {
         SpanData::default()
     } else {
-        let lo = BytePos::from_u32(cookie as u32);
-        let hi = BytePos::from_u32((cookie >> 32) as u32);
         SpanData {
-            lo,
-            // LLVM version < 19 silently truncates the cookie to 32 bits in some situations.
-            hi: if hi.to_u32() != 0 { hi } else { lo },
+            lo: BytePos::from_u32(cookie as u32),
+            hi: BytePos::from_u32((cookie >> 32) as u32),
             ctxt: SyntaxContext::root(),
             parent: None,
         }
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index 9a2473d6cf2..5e62ce285dd 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -5,15 +5,11 @@ use rustc_abi::Align;
 use rustc_codegen_ssa::traits::{
     BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
 };
-use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
-use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_index::IndexVec;
-use rustc_middle::mir;
-use rustc_middle::mir::mono::MonoItemPartitions;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::TyCtxt;
 use rustc_session::RemapFileNameExt;
 use rustc_session::config::RemapPathScopeComponents;
-use rustc_span::def_id::DefIdSet;
 use rustc_span::{SourceFile, StableSourceFileId};
 use tracing::debug;
 
@@ -24,6 +20,7 @@ use crate::llvm;
 
 mod covfun;
 mod spans;
+mod unused;
 
 /// Generates and exports the coverage map, which is embedded in special
 /// linker sections in the final binary.
@@ -76,12 +73,11 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
     // In a single designated CGU, also prepare covfun records for functions
     // in this crate that were instrumented for coverage, but are unused.
     if cx.codegen_unit.is_code_coverage_dead_code_cgu() {
-        let mut unused_instances = gather_unused_function_instances(cx);
-        // Sort the unused instances by symbol name, for the same reason as the used ones.
-        unused_instances.sort_by_cached_key(|&instance| tcx.symbol_name(instance).name);
-        covfun_records.extend(unused_instances.into_iter().filter_map(|instance| {
-            prepare_covfun_record(tcx, &mut global_file_table, instance, false)
-        }));
+        unused::prepare_covfun_records_for_unused_functions(
+            cx,
+            &mut global_file_table,
+            &mut covfun_records,
+        );
     }
 
     // If there are no covfun records for this CGU, don't generate a covmap record.
@@ -100,33 +96,10 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
     // contain multiple covmap records from different compilation units.
     let filenames_hash = llvm_cov::hash_bytes(&filenames_buffer);
 
-    let mut unused_function_names = vec![];
-
     for covfun in &covfun_records {
-        unused_function_names.extend(covfun.mangled_function_name_if_unused());
-
         covfun::generate_covfun_record(cx, filenames_hash, covfun)
     }
 
-    // For unused functions, we need to take their mangled names and store them
-    // in a specially-named global array. LLVM's `InstrProfiling` pass will
-    // detect this global and include those names in its `__llvm_prf_names`
-    // section. (See `llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp`.)
-    if !unused_function_names.is_empty() {
-        assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
-
-        let name_globals = unused_function_names
-            .into_iter()
-            .map(|mangled_function_name| cx.const_str(mangled_function_name).0)
-            .collect::<Vec<_>>();
-        let initializer = cx.const_array(cx.type_ptr(), &name_globals);
-
-        let array = llvm::add_global(cx.llmod, cx.val_ty(initializer), c"__llvm_coverage_names");
-        llvm::set_global_constant(array, true);
-        llvm::set_linkage(array, llvm::Linkage::InternalLinkage);
-        llvm::set_initializer(array, initializer);
-    }
-
     // Generate the coverage map header, which contains the filenames used by
     // this CGU's coverage mappings, and store it in a well-known global.
     // (This is skipped if we returned early due to having no covfun records.)
@@ -249,121 +222,3 @@ fn generate_covmap_record<'ll>(cx: &CodegenCx<'ll, '_>, version: u32, filenames_
 
     cx.add_used_global(covmap_global);
 }
-
-/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
-/// But since we don't want unused functions to disappear from coverage reports, we also scan for
-/// functions that were instrumented but are not participating in codegen.
-///
-/// These unused functions don't need to be codegenned, but we do need to add them to the function
-/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
-/// We also end up adding their symbol names to a special global array that LLVM will include in
-/// its embedded coverage data.
-fn gather_unused_function_instances<'tcx>(cx: &CodegenCx<'_, 'tcx>) -> Vec<ty::Instance<'tcx>> {
-    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
-
-    let tcx = cx.tcx;
-    let usage = prepare_usage_sets(tcx);
-
-    let is_unused_fn = |def_id: LocalDefId| -> bool {
-        // Usage sets expect `DefId`, so convert from `LocalDefId`.
-        let d: DefId = LocalDefId::to_def_id(def_id);
-        // To be potentially eligible for "unused function" mappings, a definition must:
-        // - Be eligible for coverage instrumentation
-        // - Not participate directly in codegen (or have lost all its coverage statements)
-        // - Not have any coverage statements inlined into codegenned functions
-        tcx.is_eligible_for_coverage(def_id)
-            && (!usage.all_mono_items.contains(&d) || usage.missing_own_coverage.contains(&d))
-            && !usage.used_via_inlining.contains(&d)
-    };
-
-    // FIXME(#79651): Consider trying to filter out dummy instantiations of
-    // unused generic functions from library crates, because they can produce
-    // "unused instantiation" in coverage reports even when they are actually
-    // used by some downstream crate in the same binary.
-
-    tcx.mir_keys(())
-        .iter()
-        .copied()
-        .filter(|&def_id| is_unused_fn(def_id))
-        .map(|def_id| make_dummy_instance(tcx, def_id))
-        .collect::<Vec<_>>()
-}
-
-struct UsageSets<'tcx> {
-    all_mono_items: &'tcx DefIdSet,
-    used_via_inlining: FxHashSet<DefId>,
-    missing_own_coverage: FxHashSet<DefId>,
-}
-
-/// Prepare sets of definitions that are relevant to deciding whether something
-/// is an "unused function" for coverage purposes.
-fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
-    let MonoItemPartitions { all_mono_items, codegen_units, .. } =
-        tcx.collect_and_partition_mono_items(());
-
-    // Obtain a MIR body for each function participating in codegen, via an
-    // arbitrary instance.
-    let mut def_ids_seen = FxHashSet::default();
-    let def_and_mir_for_all_mono_fns = codegen_units
-        .iter()
-        .flat_map(|cgu| cgu.items().keys())
-        .filter_map(|item| match item {
-            mir::mono::MonoItem::Fn(instance) => Some(instance),
-            mir::mono::MonoItem::Static(_) | mir::mono::MonoItem::GlobalAsm(_) => None,
-        })
-        // We only need one arbitrary instance per definition.
-        .filter(move |instance| def_ids_seen.insert(instance.def_id()))
-        .map(|instance| {
-            // We don't care about the instance, just its underlying MIR.
-            let body = tcx.instance_mir(instance.def);
-            (instance.def_id(), body)
-        });
-
-    // Functions whose coverage statements were found inlined into other functions.
-    let mut used_via_inlining = FxHashSet::default();
-    // Functions that were instrumented, but had all of their coverage statements
-    // removed by later MIR transforms (e.g. UnreachablePropagation).
-    let mut missing_own_coverage = FxHashSet::default();
-
-    for (def_id, body) in def_and_mir_for_all_mono_fns {
-        let mut saw_own_coverage = false;
-
-        // Inspect every coverage statement in the function's MIR.
-        for stmt in body
-            .basic_blocks
-            .iter()
-            .flat_map(|block| &block.statements)
-            .filter(|stmt| matches!(stmt.kind, mir::StatementKind::Coverage(_)))
-        {
-            if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
-                // This coverage statement was inlined from another function.
-                used_via_inlining.insert(inlined.def_id());
-            } else {
-                // Non-inlined coverage statements belong to the enclosing function.
-                saw_own_coverage = true;
-            }
-        }
-
-        if !saw_own_coverage && body.function_coverage_info.is_some() {
-            missing_own_coverage.insert(def_id);
-        }
-    }
-
-    UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
-}
-
-fn make_dummy_instance<'tcx>(tcx: TyCtxt<'tcx>, local_def_id: LocalDefId) -> ty::Instance<'tcx> {
-    let def_id = local_def_id.to_def_id();
-
-    // Make a dummy instance that fills in all generics with placeholders.
-    ty::Instance::new(
-        def_id,
-        ty::GenericArgs::for_item(tcx, def_id, |param, _| {
-            if let ty::GenericParamDefKind::Lifetime = param.kind {
-                tcx.lifetimes.re_erased.into()
-            } else {
-                tcx.mk_param_from_def(param)
-            }
-        }),
-    )
-}
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
index 048e1988c32..93419c2caad 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
@@ -37,14 +37,6 @@ pub(crate) struct CovfunRecord<'tcx> {
     regions: ffi::Regions,
 }
 
-impl<'tcx> CovfunRecord<'tcx> {
-    /// FIXME(Zalathar): Make this the responsibility of the code that determines
-    /// which functions are unused.
-    pub(crate) fn mangled_function_name_if_unused(&self) -> Option<&'tcx str> {
-        (!self.is_used).then_some(self.mangled_function_name)
-    }
-}
-
 pub(crate) fn prepare_covfun_record<'tcx>(
     tcx: TyCtxt<'tcx>,
     global_file_table: &mut GlobalFileTable,
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs
new file mode 100644
index 00000000000..ab030f5b615
--- /dev/null
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs
@@ -0,0 +1,172 @@
+use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, ConstCodegenMethods};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_middle::mir;
+use rustc_middle::mir::mono::MonoItemPartitions;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::def_id::DefIdSet;
+
+use crate::common::CodegenCx;
+use crate::coverageinfo::mapgen::GlobalFileTable;
+use crate::coverageinfo::mapgen::covfun::{CovfunRecord, prepare_covfun_record};
+use crate::llvm;
+
+/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
+/// But since we don't want unused functions to disappear from coverage reports, we also scan for
+/// functions that were instrumented but are not participating in codegen.
+///
+/// These unused functions don't need to be codegenned, but we do need to add them to the function
+/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
+/// We also end up adding their symbol names to a special global array that LLVM will include in
+/// its embedded coverage data.
+pub(crate) fn prepare_covfun_records_for_unused_functions<'tcx>(
+    cx: &CodegenCx<'_, 'tcx>,
+    global_file_table: &mut GlobalFileTable,
+    covfun_records: &mut Vec<CovfunRecord<'tcx>>,
+) {
+    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
+
+    let mut unused_instances = gather_unused_function_instances(cx);
+    // Sort the unused instances by symbol name, so that their order isn't hash-sensitive.
+    unused_instances.sort_by_key(|instance| instance.symbol_name);
+
+    // Try to create a covfun record for each unused function.
+    let mut name_globals = Vec::with_capacity(unused_instances.len());
+    covfun_records.extend(unused_instances.into_iter().filter_map(|unused| try {
+        let record = prepare_covfun_record(cx.tcx, global_file_table, unused.instance, false)?;
+        // If successful, also store its symbol name in a global constant.
+        name_globals.push(cx.const_str(unused.symbol_name.name).0);
+        record
+    }));
+
+    // Store the names of unused functions in a specially-named global array.
+    // LLVM's `InstrProfilling` pass will detect this array, and include the
+    // referenced names in its `__llvm_prf_names` section.
+    // (See `llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp`.)
+    if !name_globals.is_empty() {
+        let initializer = cx.const_array(cx.type_ptr(), &name_globals);
+
+        let array = llvm::add_global(cx.llmod, cx.val_ty(initializer), c"__llvm_coverage_names");
+        llvm::set_global_constant(array, true);
+        llvm::set_linkage(array, llvm::Linkage::InternalLinkage);
+        llvm::set_initializer(array, initializer);
+    }
+}
+
+/// Holds a dummy function instance along with its symbol name, to avoid having
+/// to repeatedly query for the name.
+struct UnusedInstance<'tcx> {
+    instance: ty::Instance<'tcx>,
+    symbol_name: ty::SymbolName<'tcx>,
+}
+
+fn gather_unused_function_instances<'tcx>(cx: &CodegenCx<'_, 'tcx>) -> Vec<UnusedInstance<'tcx>> {
+    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
+
+    let tcx = cx.tcx;
+    let usage = prepare_usage_sets(tcx);
+
+    let is_unused_fn = |def_id: LocalDefId| -> bool {
+        // Usage sets expect `DefId`, so convert from `LocalDefId`.
+        let d: DefId = LocalDefId::to_def_id(def_id);
+        // To be potentially eligible for "unused function" mappings, a definition must:
+        // - Be eligible for coverage instrumentation
+        // - Not participate directly in codegen (or have lost all its coverage statements)
+        // - Not have any coverage statements inlined into codegenned functions
+        tcx.is_eligible_for_coverage(def_id)
+            && (!usage.all_mono_items.contains(&d) || usage.missing_own_coverage.contains(&d))
+            && !usage.used_via_inlining.contains(&d)
+    };
+
+    // FIXME(#79651): Consider trying to filter out dummy instantiations of
+    // unused generic functions from library crates, because they can produce
+    // "unused instantiation" in coverage reports even when they are actually
+    // used by some downstream crate in the same binary.
+
+    tcx.mir_keys(())
+        .iter()
+        .copied()
+        .filter(|&def_id| is_unused_fn(def_id))
+        .map(|def_id| make_dummy_instance(tcx, def_id))
+        .map(|instance| UnusedInstance { instance, symbol_name: tcx.symbol_name(instance) })
+        .collect::<Vec<_>>()
+}
+
+struct UsageSets<'tcx> {
+    all_mono_items: &'tcx DefIdSet,
+    used_via_inlining: FxHashSet<DefId>,
+    missing_own_coverage: FxHashSet<DefId>,
+}
+
+/// Prepare sets of definitions that are relevant to deciding whether something
+/// is an "unused function" for coverage purposes.
+fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
+    let MonoItemPartitions { all_mono_items, codegen_units, .. } =
+        tcx.collect_and_partition_mono_items(());
+
+    // Obtain a MIR body for each function participating in codegen, via an
+    // arbitrary instance.
+    let mut def_ids_seen = FxHashSet::default();
+    let def_and_mir_for_all_mono_fns = codegen_units
+        .iter()
+        .flat_map(|cgu| cgu.items().keys())
+        .filter_map(|item| match item {
+            mir::mono::MonoItem::Fn(instance) => Some(instance),
+            mir::mono::MonoItem::Static(_) | mir::mono::MonoItem::GlobalAsm(_) => None,
+        })
+        // We only need one arbitrary instance per definition.
+        .filter(move |instance| def_ids_seen.insert(instance.def_id()))
+        .map(|instance| {
+            // We don't care about the instance, just its underlying MIR.
+            let body = tcx.instance_mir(instance.def);
+            (instance.def_id(), body)
+        });
+
+    // Functions whose coverage statements were found inlined into other functions.
+    let mut used_via_inlining = FxHashSet::default();
+    // Functions that were instrumented, but had all of their coverage statements
+    // removed by later MIR transforms (e.g. UnreachablePropagation).
+    let mut missing_own_coverage = FxHashSet::default();
+
+    for (def_id, body) in def_and_mir_for_all_mono_fns {
+        let mut saw_own_coverage = false;
+
+        // Inspect every coverage statement in the function's MIR.
+        for stmt in body
+            .basic_blocks
+            .iter()
+            .flat_map(|block| &block.statements)
+            .filter(|stmt| matches!(stmt.kind, mir::StatementKind::Coverage(_)))
+        {
+            if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
+                // This coverage statement was inlined from another function.
+                used_via_inlining.insert(inlined.def_id());
+            } else {
+                // Non-inlined coverage statements belong to the enclosing function.
+                saw_own_coverage = true;
+            }
+        }
+
+        if !saw_own_coverage && body.function_coverage_info.is_some() {
+            missing_own_coverage.insert(def_id);
+        }
+    }
+
+    UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
+}
+
+fn make_dummy_instance<'tcx>(tcx: TyCtxt<'tcx>, local_def_id: LocalDefId) -> ty::Instance<'tcx> {
+    let def_id = local_def_id.to_def_id();
+
+    // Make a dummy instance that fills in all generics with placeholders.
+    ty::Instance::new(
+        def_id,
+        ty::GenericArgs::for_item(tcx, def_id, |param, _| {
+            if let ty::GenericParamDefKind::Lifetime = param.kind {
+                tcx.lifetimes.re_erased.into()
+            } else {
+                tcx.mk_param_from_def(param)
+            }
+        }),
+    )
+}
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 1a6c15b66a4..74957b4651a 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1555,6 +1555,7 @@ impl<'hir> Pat<'hir> {
 
         use PatKind::*;
         match self.kind {
+            Missing => unreachable!(),
             Wild | Never | Expr(_) | Range(..) | Binding(.., None) | Err(_) => true,
             Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) | Guard(s, _) => s.walk_short_(it),
             Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk_short_(it)),
@@ -1582,7 +1583,7 @@ impl<'hir> Pat<'hir> {
 
         use PatKind::*;
         match self.kind {
-            Wild | Never | Expr(_) | Range(..) | Binding(.., None) | Err(_) => {}
+            Missing | Wild | Never | Expr(_) | Range(..) | Binding(.., None) | Err(_) => {}
             Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) | Guard(s, _) => s.walk_(it),
             Struct(_, fields, _) => fields.iter().for_each(|field| field.pat.walk_(it)),
             TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().for_each(|p| p.walk_(it)),
@@ -1720,6 +1721,9 @@ pub enum TyPatKind<'hir> {
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum PatKind<'hir> {
+    /// A missing pattern, e.g. for an anonymous param in a bare fn like `fn f(u32)`.
+    Missing,
+
     /// Represents a wildcard pattern (i.e., `_`).
     Wild,
 
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 506358341b5..ea3f396761b 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -744,7 +744,7 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat<'v>) -> V:
             visit_opt!(visitor, visit_pat_expr, lower_bound);
             visit_opt!(visitor, visit_pat_expr, upper_bound);
         }
-        PatKind::Never | PatKind::Wild | PatKind::Err(_) => (),
+        PatKind::Missing | PatKind::Never | PatKind::Wild | PatKind::Err(_) => (),
         PatKind::Slice(prepatterns, ref slice_pattern, postpatterns) => {
             walk_list!(visitor, visit_pat, prepatterns);
             visit_opt!(visitor, visit_pat, slice_pattern);
diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
index cf66ab708bb..d230f9f0fc6 100644
--- a/compiler/rustc_hir_analysis/src/check/region.rs
+++ b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -446,14 +446,11 @@ fn resolve_expr<'tcx>(
         // Mark this expr's scope and all parent scopes as containing `yield`.
         let mut scope = Scope { local_id: expr.hir_id.local_id, data: ScopeData::Node };
         loop {
-            let span = match expr.kind {
-                hir::ExprKind::Yield(expr, hir::YieldSource::Await { .. }) => {
-                    expr.span.shrink_to_hi().to(expr.span)
-                }
-                _ => expr.span,
+            let data = YieldData {
+                span: expr.span,
+                expr_and_pat_count: visitor.expr_and_pat_count,
+                source: *source,
             };
-            let data =
-                YieldData { span, expr_and_pat_count: visitor.expr_and_pat_count, source: *source };
             match visitor.scope_tree.yield_in_scope.get_mut(&scope) {
                 Some(yields) => yields.push(data),
                 None => {
@@ -626,6 +623,7 @@ fn resolve_local<'tcx>(
 
             PatKind::Ref(_, _)
             | PatKind::Binding(hir::BindingMode(hir::ByRef::No, _), ..)
+            | PatKind::Missing
             | PatKind::Wild
             | PatKind::Never
             | PatKind::Expr(_)
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 8c0c17f7a7d..29214196c3d 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -1868,6 +1868,7 @@ impl<'a> State<'a> {
         // Pat isn't normalized, but the beauty of it
         // is that it doesn't matter
         match pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => self.word("_"),
             PatKind::Never => self.word("!"),
             PatKind::Binding(BindingMode(by_ref, mutbl), _, ident, sub) => {
diff --git a/compiler/rustc_hir_typeck/src/demand.rs b/compiler/rustc_hir_typeck/src/demand.rs
index b845e2190ef..fec45995410 100644
--- a/compiler/rustc_hir_typeck/src/demand.rs
+++ b/compiler/rustc_hir_typeck/src/demand.rs
@@ -865,10 +865,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // `&'name Ty` -> `&'name mut Ty` or `&Ty` -> `&mut Ty`
                 vec![(
                     ty_ref.1.ty.span.shrink_to_lo(),
-                    format!(
-                        "{}mut ",
-                        if ty_ref.0.ident.span.lo() == ty_ref.0.ident.span.hi() { "" } else { " " },
-                    ),
+                    format!("{}mut ", if ty_ref.0.ident.span.is_empty() { "" } else { " " },),
                 )]
             };
             sugg.extend([
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 45ab8e03db5..952a2e231e4 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -482,7 +482,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             // All of these constitute a read, or match on something that isn't `!`,
             // which would require a `NeverToAny` coercion.
-            hir::PatKind::Binding(_, _, _, _)
+            hir::PatKind::Missing
+            | hir::PatKind::Binding(_, _, _, _)
             | hir::PatKind::Struct(_, _, _)
             | hir::PatKind::TupleStruct(_, _, _)
             | hir::PatKind::Tuple(_, _)
diff --git a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
index 64176dacb73..27df8f0e98a 100644
--- a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
+++ b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
@@ -611,6 +611,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         for pat in pats {
             self.cat_pattern(discr_place.clone(), pat, &mut |place, pat| {
                 match &pat.kind {
+                    PatKind::Missing => unreachable!(),
                     PatKind::Binding(.., opt_sub_pat) => {
                         // If the opt_sub_pat is None, then the binding does not count as
                         // a wildcard for the purpose of borrowing discr.
@@ -1832,6 +1833,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
             | PatKind::Expr(..)
             | PatKind::Range(..)
             | PatKind::Never
+            | PatKind::Missing
             | PatKind::Wild
             | PatKind::Err(_) => {
                 // always ok
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index 9766ceda569..8641348bffb 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -341,7 +341,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
 
         let ty = match pat.kind {
-            PatKind::Wild | PatKind::Err(_) => expected,
+            PatKind::Missing | PatKind::Wild | PatKind::Err(_) => expected,
             // We allow any type here; we ensure that the type is uninhabited during match checking.
             PatKind::Never => expected,
             PatKind::Expr(PatExpr { kind: PatExprKind::Path(qpath), hir_id, span }) => {
@@ -505,9 +505,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             },
 
             // Ref patterns are complicated, we handle them in `check_pat_ref`.
-            PatKind::Ref(..) => AdjustMode::Pass,
+            PatKind::Ref(..)
+            // No need to do anything on a missing pattern.
+            | PatKind::Missing
             // A `_` pattern works with any expected type, so there's no need to do anything.
-            PatKind::Wild
+            | PatKind::Wild
             // A malformed pattern doesn't have an expected type, so let's just accept any type.
             | PatKind::Err(_)
             // Bindings also work with whatever the expected type is,
@@ -1032,7 +1034,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         | PatKind::Tuple(..)
                         | PatKind::Slice(..) => "binding",
 
-                        PatKind::Wild
+                        PatKind::Missing
+                        | PatKind::Wild
                         | PatKind::Never
                         | PatKind::Binding(..)
                         | PatKind::Box(..)
diff --git a/compiler/rustc_lexer/src/lib.rs b/compiler/rustc_lexer/src/lib.rs
index 61638e45253..f9c71b2fa65 100644
--- a/compiler/rustc_lexer/src/lib.rs
+++ b/compiler/rustc_lexer/src/lib.rs
@@ -26,7 +26,6 @@
 // tidy-alphabetical-end
 
 mod cursor;
-pub mod unescape;
 
 #[cfg(test)]
 mod tests;
diff --git a/compiler/rustc_lexer/src/unescape.rs b/compiler/rustc_lexer/src/unescape.rs
deleted file mode 100644
index d6ea4249247..00000000000
--- a/compiler/rustc_lexer/src/unescape.rs
+++ /dev/null
@@ -1,438 +0,0 @@
-//! Utilities for validating string and char literals and turning them into
-//! values they represent.
-
-use std::ops::Range;
-use std::str::Chars;
-
-use Mode::*;
-
-#[cfg(test)]
-mod tests;
-
-/// Errors and warnings that can occur during string unescaping. They mostly
-/// relate to malformed escape sequences, but there are a few that are about
-/// other problems.
-#[derive(Debug, PartialEq, Eq)]
-pub enum EscapeError {
-    /// Expected 1 char, but 0 were found.
-    ZeroChars,
-    /// Expected 1 char, but more than 1 were found.
-    MoreThanOneChar,
-
-    /// Escaped '\' character without continuation.
-    LoneSlash,
-    /// Invalid escape character (e.g. '\z').
-    InvalidEscape,
-    /// Raw '\r' encountered.
-    BareCarriageReturn,
-    /// Raw '\r' encountered in raw string.
-    BareCarriageReturnInRawString,
-    /// Unescaped character that was expected to be escaped (e.g. raw '\t').
-    EscapeOnlyChar,
-
-    /// Numeric character escape is too short (e.g. '\x1').
-    TooShortHexEscape,
-    /// Invalid character in numeric escape (e.g. '\xz')
-    InvalidCharInHexEscape,
-    /// Character code in numeric escape is non-ascii (e.g. '\xFF').
-    OutOfRangeHexEscape,
-
-    /// '\u' not followed by '{'.
-    NoBraceInUnicodeEscape,
-    /// Non-hexadecimal value in '\u{..}'.
-    InvalidCharInUnicodeEscape,
-    /// '\u{}'
-    EmptyUnicodeEscape,
-    /// No closing brace in '\u{..}', e.g. '\u{12'.
-    UnclosedUnicodeEscape,
-    /// '\u{_12}'
-    LeadingUnderscoreUnicodeEscape,
-    /// More than 6 characters in '\u{..}', e.g. '\u{10FFFF_FF}'
-    OverlongUnicodeEscape,
-    /// Invalid in-bound unicode character code, e.g. '\u{DFFF}'.
-    LoneSurrogateUnicodeEscape,
-    /// Out of bounds unicode character code, e.g. '\u{FFFFFF}'.
-    OutOfRangeUnicodeEscape,
-
-    /// Unicode escape code in byte literal.
-    UnicodeEscapeInByte,
-    /// Non-ascii character in byte literal, byte string literal, or raw byte string literal.
-    NonAsciiCharInByte,
-
-    // `\0` in a C string literal.
-    NulInCStr,
-
-    /// After a line ending with '\', the next line contains whitespace
-    /// characters that are not skipped.
-    UnskippedWhitespaceWarning,
-
-    /// After a line ending with '\', multiple lines are skipped.
-    MultipleSkippedLinesWarning,
-}
-
-impl EscapeError {
-    /// Returns true for actual errors, as opposed to warnings.
-    pub fn is_fatal(&self) -> bool {
-        !matches!(
-            self,
-            EscapeError::UnskippedWhitespaceWarning | EscapeError::MultipleSkippedLinesWarning
-        )
-    }
-}
-
-/// Takes the contents of a unicode-only (non-mixed-utf8) literal (without
-/// quotes) and produces a sequence of escaped characters or errors.
-///
-/// Values are returned by invoking `callback`. For `Char` and `Byte` modes,
-/// the callback will be called exactly once.
-pub fn unescape_unicode<F>(src: &str, mode: Mode, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<char, EscapeError>),
-{
-    match mode {
-        Char | Byte => {
-            let mut chars = src.chars();
-            let res = unescape_char_or_byte(&mut chars, mode);
-            callback(0..(src.len() - chars.as_str().len()), res);
-        }
-        Str | ByteStr => unescape_non_raw_common(src, mode, callback),
-        RawStr | RawByteStr => check_raw_common(src, mode, callback),
-        RawCStr => check_raw_common(src, mode, &mut |r, mut result| {
-            if let Ok('\0') = result {
-                result = Err(EscapeError::NulInCStr);
-            }
-            callback(r, result)
-        }),
-        CStr => unreachable!(),
-    }
-}
-
-/// Used for mixed utf8 string literals, i.e. those that allow both unicode
-/// chars and high bytes.
-pub enum MixedUnit {
-    /// Used for ASCII chars (written directly or via `\x00`..`\x7f` escapes)
-    /// and Unicode chars (written directly or via `\u` escapes).
-    ///
-    /// For example, if '¥' appears in a string it is represented here as
-    /// `MixedUnit::Char('¥')`, and it will be appended to the relevant byte
-    /// string as the two-byte UTF-8 sequence `[0xc2, 0xa5]`
-    Char(char),
-
-    /// Used for high bytes (`\x80`..`\xff`).
-    ///
-    /// For example, if `\xa5` appears in a string it is represented here as
-    /// `MixedUnit::HighByte(0xa5)`, and it will be appended to the relevant
-    /// byte string as the single byte `0xa5`.
-    HighByte(u8),
-}
-
-impl From<char> for MixedUnit {
-    fn from(c: char) -> Self {
-        MixedUnit::Char(c)
-    }
-}
-
-impl From<u8> for MixedUnit {
-    fn from(n: u8) -> Self {
-        if n.is_ascii() { MixedUnit::Char(n as char) } else { MixedUnit::HighByte(n) }
-    }
-}
-
-/// Takes the contents of a mixed-utf8 literal (without quotes) and produces
-/// a sequence of escaped characters or errors.
-///
-/// Values are returned by invoking `callback`.
-pub fn unescape_mixed<F>(src: &str, mode: Mode, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<MixedUnit, EscapeError>),
-{
-    match mode {
-        CStr => unescape_non_raw_common(src, mode, &mut |r, mut result| {
-            if let Ok(MixedUnit::Char('\0')) = result {
-                result = Err(EscapeError::NulInCStr);
-            }
-            callback(r, result)
-        }),
-        Char | Byte | Str | RawStr | ByteStr | RawByteStr | RawCStr => unreachable!(),
-    }
-}
-
-/// Takes a contents of a char literal (without quotes), and returns an
-/// unescaped char or an error.
-pub fn unescape_char(src: &str) -> Result<char, EscapeError> {
-    unescape_char_or_byte(&mut src.chars(), Char)
-}
-
-/// Takes a contents of a byte literal (without quotes), and returns an
-/// unescaped byte or an error.
-pub fn unescape_byte(src: &str) -> Result<u8, EscapeError> {
-    unescape_char_or_byte(&mut src.chars(), Byte).map(byte_from_char)
-}
-
-/// What kind of literal do we parse.
-#[derive(Debug, Clone, Copy, PartialEq)]
-pub enum Mode {
-    Char,
-
-    Byte,
-
-    Str,
-    RawStr,
-
-    ByteStr,
-    RawByteStr,
-
-    CStr,
-    RawCStr,
-}
-
-impl Mode {
-    pub fn in_double_quotes(self) -> bool {
-        match self {
-            Str | RawStr | ByteStr | RawByteStr | CStr | RawCStr => true,
-            Char | Byte => false,
-        }
-    }
-
-    /// Are `\x80`..`\xff` allowed?
-    fn allow_high_bytes(self) -> bool {
-        match self {
-            Char | Str => false,
-            Byte | ByteStr | CStr => true,
-            RawStr | RawByteStr | RawCStr => unreachable!(),
-        }
-    }
-
-    /// Are unicode (non-ASCII) chars allowed?
-    #[inline]
-    fn allow_unicode_chars(self) -> bool {
-        match self {
-            Byte | ByteStr | RawByteStr => false,
-            Char | Str | RawStr | CStr | RawCStr => true,
-        }
-    }
-
-    /// Are unicode escapes (`\u`) allowed?
-    fn allow_unicode_escapes(self) -> bool {
-        match self {
-            Byte | ByteStr => false,
-            Char | Str | CStr => true,
-            RawByteStr | RawStr | RawCStr => unreachable!(),
-        }
-    }
-
-    pub fn prefix_noraw(self) -> &'static str {
-        match self {
-            Char | Str | RawStr => "",
-            Byte | ByteStr | RawByteStr => "b",
-            CStr | RawCStr => "c",
-        }
-    }
-}
-
-fn scan_escape<T: From<char> + From<u8>>(
-    chars: &mut Chars<'_>,
-    mode: Mode,
-) -> Result<T, EscapeError> {
-    // Previous character was '\\', unescape what follows.
-    let res: char = match chars.next().ok_or(EscapeError::LoneSlash)? {
-        '"' => '"',
-        'n' => '\n',
-        'r' => '\r',
-        't' => '\t',
-        '\\' => '\\',
-        '\'' => '\'',
-        '0' => '\0',
-        'x' => {
-            // Parse hexadecimal character code.
-
-            let hi = chars.next().ok_or(EscapeError::TooShortHexEscape)?;
-            let hi = hi.to_digit(16).ok_or(EscapeError::InvalidCharInHexEscape)?;
-
-            let lo = chars.next().ok_or(EscapeError::TooShortHexEscape)?;
-            let lo = lo.to_digit(16).ok_or(EscapeError::InvalidCharInHexEscape)?;
-
-            let value = (hi * 16 + lo) as u8;
-
-            return if !mode.allow_high_bytes() && !value.is_ascii() {
-                Err(EscapeError::OutOfRangeHexEscape)
-            } else {
-                // This may be a high byte, but that will only happen if `T` is
-                // `MixedUnit`, because of the `allow_high_bytes` check above.
-                Ok(T::from(value))
-            };
-        }
-        'u' => return scan_unicode(chars, mode.allow_unicode_escapes()).map(T::from),
-        _ => return Err(EscapeError::InvalidEscape),
-    };
-    Ok(T::from(res))
-}
-
-fn scan_unicode(chars: &mut Chars<'_>, allow_unicode_escapes: bool) -> Result<char, EscapeError> {
-    // We've parsed '\u', now we have to parse '{..}'.
-
-    if chars.next() != Some('{') {
-        return Err(EscapeError::NoBraceInUnicodeEscape);
-    }
-
-    // First character must be a hexadecimal digit.
-    let mut n_digits = 1;
-    let mut value: u32 = match chars.next().ok_or(EscapeError::UnclosedUnicodeEscape)? {
-        '_' => return Err(EscapeError::LeadingUnderscoreUnicodeEscape),
-        '}' => return Err(EscapeError::EmptyUnicodeEscape),
-        c => c.to_digit(16).ok_or(EscapeError::InvalidCharInUnicodeEscape)?,
-    };
-
-    // First character is valid, now parse the rest of the number
-    // and closing brace.
-    loop {
-        match chars.next() {
-            None => return Err(EscapeError::UnclosedUnicodeEscape),
-            Some('_') => continue,
-            Some('}') => {
-                if n_digits > 6 {
-                    return Err(EscapeError::OverlongUnicodeEscape);
-                }
-
-                // Incorrect syntax has higher priority for error reporting
-                // than unallowed value for a literal.
-                if !allow_unicode_escapes {
-                    return Err(EscapeError::UnicodeEscapeInByte);
-                }
-
-                break std::char::from_u32(value).ok_or({
-                    if value > 0x10FFFF {
-                        EscapeError::OutOfRangeUnicodeEscape
-                    } else {
-                        EscapeError::LoneSurrogateUnicodeEscape
-                    }
-                });
-            }
-            Some(c) => {
-                let digit: u32 = c.to_digit(16).ok_or(EscapeError::InvalidCharInUnicodeEscape)?;
-                n_digits += 1;
-                if n_digits > 6 {
-                    // Stop updating value since we're sure that it's incorrect already.
-                    continue;
-                }
-                value = value * 16 + digit;
-            }
-        };
-    }
-}
-
-#[inline]
-fn ascii_check(c: char, allow_unicode_chars: bool) -> Result<char, EscapeError> {
-    if allow_unicode_chars || c.is_ascii() { Ok(c) } else { Err(EscapeError::NonAsciiCharInByte) }
-}
-
-fn unescape_char_or_byte(chars: &mut Chars<'_>, mode: Mode) -> Result<char, EscapeError> {
-    let c = chars.next().ok_or(EscapeError::ZeroChars)?;
-    let res = match c {
-        '\\' => scan_escape(chars, mode),
-        '\n' | '\t' | '\'' => Err(EscapeError::EscapeOnlyChar),
-        '\r' => Err(EscapeError::BareCarriageReturn),
-        _ => ascii_check(c, mode.allow_unicode_chars()),
-    }?;
-    if chars.next().is_some() {
-        return Err(EscapeError::MoreThanOneChar);
-    }
-    Ok(res)
-}
-
-/// Takes a contents of a string literal (without quotes) and produces a
-/// sequence of escaped characters or errors.
-fn unescape_non_raw_common<F, T: From<char> + From<u8>>(src: &str, mode: Mode, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<T, EscapeError>),
-{
-    let mut chars = src.chars();
-    let allow_unicode_chars = mode.allow_unicode_chars(); // get this outside the loop
-
-    // The `start` and `end` computation here is complicated because
-    // `skip_ascii_whitespace` makes us to skip over chars without counting
-    // them in the range computation.
-    while let Some(c) = chars.next() {
-        let start = src.len() - chars.as_str().len() - c.len_utf8();
-        let res = match c {
-            '\\' => {
-                match chars.clone().next() {
-                    Some('\n') => {
-                        // Rust language specification requires us to skip whitespaces
-                        // if unescaped '\' character is followed by '\n'.
-                        // For details see [Rust language reference]
-                        // (https://doc.rust-lang.org/reference/tokens.html#string-literals).
-                        skip_ascii_whitespace(&mut chars, start, &mut |range, err| {
-                            callback(range, Err(err))
-                        });
-                        continue;
-                    }
-                    _ => scan_escape::<T>(&mut chars, mode),
-                }
-            }
-            '"' => Err(EscapeError::EscapeOnlyChar),
-            '\r' => Err(EscapeError::BareCarriageReturn),
-            _ => ascii_check(c, allow_unicode_chars).map(T::from),
-        };
-        let end = src.len() - chars.as_str().len();
-        callback(start..end, res);
-    }
-}
-
-fn skip_ascii_whitespace<F>(chars: &mut Chars<'_>, start: usize, callback: &mut F)
-where
-    F: FnMut(Range<usize>, EscapeError),
-{
-    let tail = chars.as_str();
-    let first_non_space = tail
-        .bytes()
-        .position(|b| b != b' ' && b != b'\t' && b != b'\n' && b != b'\r')
-        .unwrap_or(tail.len());
-    if tail[1..first_non_space].contains('\n') {
-        // The +1 accounts for the escaping slash.
-        let end = start + first_non_space + 1;
-        callback(start..end, EscapeError::MultipleSkippedLinesWarning);
-    }
-    let tail = &tail[first_non_space..];
-    if let Some(c) = tail.chars().next() {
-        if c.is_whitespace() {
-            // For error reporting, we would like the span to contain the character that was not
-            // skipped. The +1 is necessary to account for the leading \ that started the escape.
-            let end = start + first_non_space + c.len_utf8() + 1;
-            callback(start..end, EscapeError::UnskippedWhitespaceWarning);
-        }
-    }
-    *chars = tail.chars();
-}
-
-/// Takes a contents of a string literal (without quotes) and produces a
-/// sequence of characters or errors.
-/// NOTE: Raw strings do not perform any explicit character escaping, here we
-/// only produce errors on bare CR.
-fn check_raw_common<F>(src: &str, mode: Mode, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<char, EscapeError>),
-{
-    let mut chars = src.chars();
-    let allow_unicode_chars = mode.allow_unicode_chars(); // get this outside the loop
-
-    // The `start` and `end` computation here matches the one in
-    // `unescape_non_raw_common` for consistency, even though this function
-    // doesn't have to worry about skipping any chars.
-    while let Some(c) = chars.next() {
-        let start = src.len() - chars.as_str().len() - c.len_utf8();
-        let res = match c {
-            '\r' => Err(EscapeError::BareCarriageReturnInRawString),
-            _ => ascii_check(c, allow_unicode_chars),
-        };
-        let end = src.len() - chars.as_str().len();
-        callback(start..end, res);
-    }
-}
-
-#[inline]
-pub fn byte_from_char(c: char) -> u8 {
-    let res = c as u32;
-    debug_assert!(res <= u8::MAX as u32, "guaranteed because of ByteStr");
-    res as u8
-}
diff --git a/compiler/rustc_lexer/src/unescape/tests.rs b/compiler/rustc_lexer/src/unescape/tests.rs
deleted file mode 100644
index 5b99495f475..00000000000
--- a/compiler/rustc_lexer/src/unescape/tests.rs
+++ /dev/null
@@ -1,286 +0,0 @@
-use super::*;
-
-#[test]
-fn test_unescape_char_bad() {
-    fn check(literal_text: &str, expected_error: EscapeError) {
-        assert_eq!(unescape_char(literal_text), Err(expected_error));
-    }
-
-    check("", EscapeError::ZeroChars);
-    check(r"\", EscapeError::LoneSlash);
-
-    check("\n", EscapeError::EscapeOnlyChar);
-    check("\t", EscapeError::EscapeOnlyChar);
-    check("'", EscapeError::EscapeOnlyChar);
-    check("\r", EscapeError::BareCarriageReturn);
-
-    check("spam", EscapeError::MoreThanOneChar);
-    check(r"\x0ff", EscapeError::MoreThanOneChar);
-    check(r#"\"a"#, EscapeError::MoreThanOneChar);
-    check(r"\na", EscapeError::MoreThanOneChar);
-    check(r"\ra", EscapeError::MoreThanOneChar);
-    check(r"\ta", EscapeError::MoreThanOneChar);
-    check(r"\\a", EscapeError::MoreThanOneChar);
-    check(r"\'a", EscapeError::MoreThanOneChar);
-    check(r"\0a", EscapeError::MoreThanOneChar);
-    check(r"\u{0}x", EscapeError::MoreThanOneChar);
-    check(r"\u{1F63b}}", EscapeError::MoreThanOneChar);
-
-    check(r"\v", EscapeError::InvalidEscape);
-    check(r"\💩", EscapeError::InvalidEscape);
-    check(r"\●", EscapeError::InvalidEscape);
-    check("\\\r", EscapeError::InvalidEscape);
-
-    check(r"\x", EscapeError::TooShortHexEscape);
-    check(r"\x0", EscapeError::TooShortHexEscape);
-    check(r"\xf", EscapeError::TooShortHexEscape);
-    check(r"\xa", EscapeError::TooShortHexEscape);
-    check(r"\xx", EscapeError::InvalidCharInHexEscape);
-    check(r"\xы", EscapeError::InvalidCharInHexEscape);
-    check(r"\x🦀", EscapeError::InvalidCharInHexEscape);
-    check(r"\xtt", EscapeError::InvalidCharInHexEscape);
-    check(r"\xff", EscapeError::OutOfRangeHexEscape);
-    check(r"\xFF", EscapeError::OutOfRangeHexEscape);
-    check(r"\x80", EscapeError::OutOfRangeHexEscape);
-
-    check(r"\u", EscapeError::NoBraceInUnicodeEscape);
-    check(r"\u[0123]", EscapeError::NoBraceInUnicodeEscape);
-    check(r"\u{0x}", EscapeError::InvalidCharInUnicodeEscape);
-    check(r"\u{", EscapeError::UnclosedUnicodeEscape);
-    check(r"\u{0000", EscapeError::UnclosedUnicodeEscape);
-    check(r"\u{}", EscapeError::EmptyUnicodeEscape);
-    check(r"\u{_0000}", EscapeError::LeadingUnderscoreUnicodeEscape);
-    check(r"\u{0000000}", EscapeError::OverlongUnicodeEscape);
-    check(r"\u{FFFFFF}", EscapeError::OutOfRangeUnicodeEscape);
-    check(r"\u{ffffff}", EscapeError::OutOfRangeUnicodeEscape);
-    check(r"\u{ffffff}", EscapeError::OutOfRangeUnicodeEscape);
-
-    check(r"\u{DC00}", EscapeError::LoneSurrogateUnicodeEscape);
-    check(r"\u{DDDD}", EscapeError::LoneSurrogateUnicodeEscape);
-    check(r"\u{DFFF}", EscapeError::LoneSurrogateUnicodeEscape);
-
-    check(r"\u{D800}", EscapeError::LoneSurrogateUnicodeEscape);
-    check(r"\u{DAAA}", EscapeError::LoneSurrogateUnicodeEscape);
-    check(r"\u{DBFF}", EscapeError::LoneSurrogateUnicodeEscape);
-}
-
-#[test]
-fn test_unescape_char_good() {
-    fn check(literal_text: &str, expected_char: char) {
-        assert_eq!(unescape_char(literal_text), Ok(expected_char));
-    }
-
-    check("a", 'a');
-    check("ы", 'ы');
-    check("🦀", '🦀');
-
-    check(r#"\""#, '"');
-    check(r"\n", '\n');
-    check(r"\r", '\r');
-    check(r"\t", '\t');
-    check(r"\\", '\\');
-    check(r"\'", '\'');
-    check(r"\0", '\0');
-
-    check(r"\x00", '\0');
-    check(r"\x5a", 'Z');
-    check(r"\x5A", 'Z');
-    check(r"\x7f", 127 as char);
-
-    check(r"\u{0}", '\0');
-    check(r"\u{000000}", '\0');
-    check(r"\u{41}", 'A');
-    check(r"\u{0041}", 'A');
-    check(r"\u{00_41}", 'A');
-    check(r"\u{4__1__}", 'A');
-    check(r"\u{1F63b}", '😻');
-}
-
-#[test]
-fn test_unescape_str_warn() {
-    fn check(literal: &str, expected: &[(Range<usize>, Result<char, EscapeError>)]) {
-        let mut unescaped = Vec::with_capacity(literal.len());
-        unescape_unicode(literal, Mode::Str, &mut |range, res| unescaped.push((range, res)));
-        assert_eq!(unescaped, expected);
-    }
-
-    // Check we can handle escaped newlines at the end of a file.
-    check("\\\n", &[]);
-    check("\\\n ", &[]);
-
-    check(
-        "\\\n \u{a0} x",
-        &[
-            (0..5, Err(EscapeError::UnskippedWhitespaceWarning)),
-            (3..5, Ok('\u{a0}')),
-            (5..6, Ok(' ')),
-            (6..7, Ok('x')),
-        ],
-    );
-    check("\\\n  \n  x", &[(0..7, Err(EscapeError::MultipleSkippedLinesWarning)), (7..8, Ok('x'))]);
-}
-
-#[test]
-fn test_unescape_str_good() {
-    fn check(literal_text: &str, expected: &str) {
-        let mut buf = Ok(String::with_capacity(literal_text.len()));
-        unescape_unicode(literal_text, Mode::Str, &mut |range, c| {
-            if let Ok(b) = &mut buf {
-                match c {
-                    Ok(c) => b.push(c),
-                    Err(e) => buf = Err((range, e)),
-                }
-            }
-        });
-        assert_eq!(buf.as_deref(), Ok(expected))
-    }
-
-    check("foo", "foo");
-    check("", "");
-    check(" \t\n", " \t\n");
-
-    check("hello \\\n     world", "hello world");
-    check("thread's", "thread's")
-}
-
-#[test]
-fn test_unescape_byte_bad() {
-    fn check(literal_text: &str, expected_error: EscapeError) {
-        assert_eq!(unescape_byte(literal_text), Err(expected_error));
-    }
-
-    check("", EscapeError::ZeroChars);
-    check(r"\", EscapeError::LoneSlash);
-
-    check("\n", EscapeError::EscapeOnlyChar);
-    check("\t", EscapeError::EscapeOnlyChar);
-    check("'", EscapeError::EscapeOnlyChar);
-    check("\r", EscapeError::BareCarriageReturn);
-
-    check("spam", EscapeError::MoreThanOneChar);
-    check(r"\x0ff", EscapeError::MoreThanOneChar);
-    check(r#"\"a"#, EscapeError::MoreThanOneChar);
-    check(r"\na", EscapeError::MoreThanOneChar);
-    check(r"\ra", EscapeError::MoreThanOneChar);
-    check(r"\ta", EscapeError::MoreThanOneChar);
-    check(r"\\a", EscapeError::MoreThanOneChar);
-    check(r"\'a", EscapeError::MoreThanOneChar);
-    check(r"\0a", EscapeError::MoreThanOneChar);
-
-    check(r"\v", EscapeError::InvalidEscape);
-    check(r"\💩", EscapeError::InvalidEscape);
-    check(r"\●", EscapeError::InvalidEscape);
-
-    check(r"\x", EscapeError::TooShortHexEscape);
-    check(r"\x0", EscapeError::TooShortHexEscape);
-    check(r"\xa", EscapeError::TooShortHexEscape);
-    check(r"\xf", EscapeError::TooShortHexEscape);
-    check(r"\xx", EscapeError::InvalidCharInHexEscape);
-    check(r"\xы", EscapeError::InvalidCharInHexEscape);
-    check(r"\x🦀", EscapeError::InvalidCharInHexEscape);
-    check(r"\xtt", EscapeError::InvalidCharInHexEscape);
-
-    check(r"\u", EscapeError::NoBraceInUnicodeEscape);
-    check(r"\u[0123]", EscapeError::NoBraceInUnicodeEscape);
-    check(r"\u{0x}", EscapeError::InvalidCharInUnicodeEscape);
-    check(r"\u{", EscapeError::UnclosedUnicodeEscape);
-    check(r"\u{0000", EscapeError::UnclosedUnicodeEscape);
-    check(r"\u{}", EscapeError::EmptyUnicodeEscape);
-    check(r"\u{_0000}", EscapeError::LeadingUnderscoreUnicodeEscape);
-    check(r"\u{0000000}", EscapeError::OverlongUnicodeEscape);
-
-    check("ы", EscapeError::NonAsciiCharInByte);
-    check("🦀", EscapeError::NonAsciiCharInByte);
-
-    check(r"\u{0}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{000000}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{41}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{0041}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{00_41}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{4__1__}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{1F63b}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{0}x", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{1F63b}}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{FFFFFF}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{ffffff}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{ffffff}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{DC00}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{DDDD}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{DFFF}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{D800}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{DAAA}", EscapeError::UnicodeEscapeInByte);
-    check(r"\u{DBFF}", EscapeError::UnicodeEscapeInByte);
-}
-
-#[test]
-fn test_unescape_byte_good() {
-    fn check(literal_text: &str, expected_byte: u8) {
-        assert_eq!(unescape_byte(literal_text), Ok(expected_byte));
-    }
-
-    check("a", b'a');
-
-    check(r#"\""#, b'"');
-    check(r"\n", b'\n');
-    check(r"\r", b'\r');
-    check(r"\t", b'\t');
-    check(r"\\", b'\\');
-    check(r"\'", b'\'');
-    check(r"\0", b'\0');
-
-    check(r"\x00", b'\0');
-    check(r"\x5a", b'Z');
-    check(r"\x5A", b'Z');
-    check(r"\x7f", 127);
-    check(r"\x80", 128);
-    check(r"\xff", 255);
-    check(r"\xFF", 255);
-}
-
-#[test]
-fn test_unescape_byte_str_good() {
-    fn check(literal_text: &str, expected: &[u8]) {
-        let mut buf = Ok(Vec::with_capacity(literal_text.len()));
-        unescape_unicode(literal_text, Mode::ByteStr, &mut |range, c| {
-            if let Ok(b) = &mut buf {
-                match c {
-                    Ok(c) => b.push(byte_from_char(c)),
-                    Err(e) => buf = Err((range, e)),
-                }
-            }
-        });
-        assert_eq!(buf.as_deref(), Ok(expected))
-    }
-
-    check("foo", b"foo");
-    check("", b"");
-    check(" \t\n", b" \t\n");
-
-    check("hello \\\n     world", b"hello world");
-    check("thread's", b"thread's")
-}
-
-#[test]
-fn test_unescape_raw_str() {
-    fn check(literal: &str, expected: &[(Range<usize>, Result<char, EscapeError>)]) {
-        let mut unescaped = Vec::with_capacity(literal.len());
-        unescape_unicode(literal, Mode::RawStr, &mut |range, res| unescaped.push((range, res)));
-        assert_eq!(unescaped, expected);
-    }
-
-    check("\r", &[(0..1, Err(EscapeError::BareCarriageReturnInRawString))]);
-    check("\rx", &[(0..1, Err(EscapeError::BareCarriageReturnInRawString)), (1..2, Ok('x'))]);
-}
-
-#[test]
-fn test_unescape_raw_byte_str() {
-    fn check(literal: &str, expected: &[(Range<usize>, Result<char, EscapeError>)]) {
-        let mut unescaped = Vec::with_capacity(literal.len());
-        unescape_unicode(literal, Mode::RawByteStr, &mut |range, res| unescaped.push((range, res)));
-        assert_eq!(unescaped, expected);
-    }
-
-    check("\r", &[(0..1, Err(EscapeError::BareCarriageReturnInRawString))]);
-    check("🦀", &[(0..4, Err(EscapeError::NonAsciiCharInByte))]);
-    check("🦀a", &[(0..4, Err(EscapeError::NonAsciiCharInByte)), (4..5, Ok('a'))]);
-}
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index dae0efcbbc4..38c2bf54432 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -779,21 +779,19 @@ impl EarlyLintPass for AnonymousParameters {
         }
         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
             for arg in sig.decl.inputs.iter() {
-                if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
-                    if ident.name == kw::Empty {
-                        let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
+                if let ast::PatKind::Missing = arg.pat.kind {
+                    let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
 
-                        let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
-                            (snip.as_str(), Applicability::MachineApplicable)
-                        } else {
-                            ("<type>", Applicability::HasPlaceholders)
-                        };
-                        cx.emit_span_lint(
-                            ANONYMOUS_PARAMETERS,
-                            arg.pat.span,
-                            BuiltinAnonymousParams { suggestion: (arg.pat.span, appl), ty_snip },
-                        );
-                    }
+                    let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
+                        (snip.as_str(), Applicability::MachineApplicable)
+                    } else {
+                        ("<type>", Applicability::HasPlaceholders)
+                    };
+                    cx.emit_span_lint(
+                        ANONYMOUS_PARAMETERS,
+                        arg.pat.span,
+                        BuiltinAnonymousParams { suggestion: (arg.pat.span, appl), ty_snip },
+                    );
                 }
             }
         }
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 7b43aac90c7..806bca78f78 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -1201,7 +1201,8 @@ impl EarlyLintPass for UnusedParens {
             // Do not lint on `(..)` as that will result in the other arms being useless.
             Paren(_)
             // The other cases do not contain sub-patterns.
-            | Wild | Never | Rest | Expr(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) | Err(_) => {},
+            | Missing | Wild | Never | Rest | Expr(..) | MacCall(..) | Range(..) | Ident(.., None)
+            | Path(..) | Err(_) => {},
             // These are list-like patterns; parens can always be removed.
             TupleStruct(_, _, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps {
                 self.check_unused_parens_pat(cx, p, false, false, keep_space);
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index bc49c197ef8..c168142fb1e 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -747,6 +747,9 @@ pub struct Ascription<'tcx> {
 
 #[derive(Clone, Debug, HashStable, TypeVisitable)]
 pub enum PatKind<'tcx> {
+    /// A missing pattern, e.g. for an anonymous param in a bare fn like `fn f(u32)`.
+    Missing,
+
     /// A wildcard pattern: `_`.
     Wild,
 
diff --git a/compiler/rustc_middle/src/thir/visit.rs b/compiler/rustc_middle/src/thir/visit.rs
index 7d62ab7970d..f3da2a5cc8e 100644
--- a/compiler/rustc_middle/src/thir/visit.rs
+++ b/compiler/rustc_middle/src/thir/visit.rs
@@ -250,7 +250,8 @@ pub(crate) fn for_each_immediate_subpat<'a, 'tcx>(
     mut callback: impl FnMut(&'a Pat<'tcx>),
 ) {
     match &pat.kind {
-        PatKind::Wild
+        PatKind::Missing
+        | PatKind::Wild
         | PatKind::Binding { subpattern: None, .. }
         | PatKind::Constant { value: _ }
         | PatKind::Range(_)
diff --git a/compiler/rustc_middle/src/ty/generic_args.rs b/compiler/rustc_middle/src/ty/generic_args.rs
index e87859a55ed..9c1ff134f0f 100644
--- a/compiler/rustc_middle/src/ty/generic_args.rs
+++ b/compiler/rustc_middle/src/ty/generic_args.rs
@@ -396,14 +396,14 @@ impl<'tcx> GenericArgs<'tcx> {
         InlineConstArgs { args: self }
     }
 
-    /// Creates an `GenericArgs` that maps each generic parameter to itself.
+    /// Creates a [`GenericArgs`] that maps each generic parameter to itself.
     pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: impl Into<DefId>) -> GenericArgsRef<'tcx> {
         Self::for_item(tcx, def_id.into(), |param, _| tcx.mk_param_from_def(param))
     }
 
-    /// Creates an `GenericArgs` for generic parameter definitions,
+    /// Creates a [`GenericArgs`] for generic parameter definitions,
     /// by calling closures to obtain each kind.
-    /// The closures get to observe the `GenericArgs` as they're
+    /// The closures get to observe the [`GenericArgs`] as they're
     /// being built, which can be used to correctly
     /// replace defaults of generic parameters.
     pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> GenericArgsRef<'tcx>
diff --git a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
index fcfacf1e1f8..9670c1716f5 100644
--- a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
@@ -118,7 +118,7 @@ impl<'tcx> MatchPairTree<'tcx> {
         let place = place_builder.try_to_place(cx);
         let mut subpairs = Vec::new();
         let test_case = match pattern.kind {
-            PatKind::Wild | PatKind::Error(_) => None,
+            PatKind::Missing | PatKind::Wild | PatKind::Error(_) => None,
 
             PatKind::Or { ref pats } => Some(TestCase::Or {
                 pats: pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect(),
diff --git a/compiler/rustc_mir_build/src/builder/matches/mod.rs b/compiler/rustc_mir_build/src/builder/matches/mod.rs
index 3acf2a6a2a6..977d4f3e931 100644
--- a/compiler/rustc_mir_build/src/builder/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/mod.rs
@@ -920,6 +920,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             PatKind::Constant { .. }
             | PatKind::Range { .. }
+            | PatKind::Missing
             | PatKind::Wild
             | PatKind::Never
             | PatKind::Error(_) => {}
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index b52d0d1e300..b6a856a6eb4 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -315,6 +315,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
     fn visit_pat(&mut self, pat: &'a Pat<'tcx>) {
         if self.in_union_destructure {
             match pat.kind {
+                PatKind::Missing => unreachable!(),
                 // binding to a variable allows getting stuff out of variable
                 PatKind::Binding { .. }
                 // match is conditional on having this value
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index 7ceeebbb70d..73d60cf4442 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -284,6 +284,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         let mut span = pat.span;
 
         let kind = match pat.kind {
+            hir::PatKind::Missing => PatKind::Missing,
+
             hir::PatKind::Wild => PatKind::Wild,
 
             hir::PatKind::Never => PatKind::Never,
diff --git a/compiler/rustc_mir_build/src/thir/print.rs b/compiler/rustc_mir_build/src/thir/print.rs
index aa8d2e5897e..37248941e2c 100644
--- a/compiler/rustc_mir_build/src/thir/print.rs
+++ b/compiler/rustc_mir_build/src/thir/print.rs
@@ -664,6 +664,7 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
         print_indented!(self, "kind: PatKind {", depth_lvl);
 
         match pat_kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => {
                 print_indented!(self, "Wild", depth_lvl + 1);
             }
diff --git a/compiler/rustc_parse/Cargo.toml b/compiler/rustc_parse/Cargo.toml
index c9dcab0c871..6504081f0b9 100644
--- a/compiler/rustc_parse/Cargo.toml
+++ b/compiler/rustc_parse/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
+rustc-literal-escaper = "0.0.2"
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_data_structures = { path = "../rustc_data_structures" }
diff --git a/compiler/rustc_parse/src/lexer/mod.rs b/compiler/rustc_parse/src/lexer/mod.rs
index 1d17290e1c7..4935fc03256 100644
--- a/compiler/rustc_parse/src/lexer/mod.rs
+++ b/compiler/rustc_parse/src/lexer/mod.rs
@@ -6,8 +6,8 @@ use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
 use rustc_errors::codes::*;
 use rustc_errors::{Applicability, Diag, DiagCtxtHandle, StashKey};
-use rustc_lexer::unescape::{self, EscapeError, Mode};
 use rustc_lexer::{Base, Cursor, DocStyle, LiteralKind, RawStrError};
+use rustc_literal_escaper::{EscapeError, Mode, unescape_mixed, unescape_unicode};
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::{
     RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX, RUST_2024_GUARDED_STRING_INCOMPATIBLE_SYNTAX,
@@ -970,9 +970,7 @@ impl<'psess, 'src> Lexer<'psess, 'src> {
         postfix_len: u32,
     ) -> (token::LitKind, Symbol) {
         self.cook_common(kind, mode, start, end, prefix_len, postfix_len, |src, mode, callback| {
-            unescape::unescape_unicode(src, mode, &mut |span, result| {
-                callback(span, result.map(drop))
-            })
+            unescape_unicode(src, mode, &mut |span, result| callback(span, result.map(drop)))
         })
     }
 
@@ -986,9 +984,7 @@ impl<'psess, 'src> Lexer<'psess, 'src> {
         postfix_len: u32,
     ) -> (token::LitKind, Symbol) {
         self.cook_common(kind, mode, start, end, prefix_len, postfix_len, |src, mode, callback| {
-            unescape::unescape_mixed(src, mode, &mut |span, result| {
-                callback(span, result.map(drop))
-            })
+            unescape_mixed(src, mode, &mut |span, result| callback(span, result.map(drop)))
         })
     }
 }
diff --git a/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs b/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
index 2e066f0179c..ec59a1a0131 100644
--- a/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
+++ b/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
@@ -4,7 +4,7 @@ use std::iter::once;
 use std::ops::Range;
 
 use rustc_errors::{Applicability, DiagCtxtHandle, ErrorGuaranteed};
-use rustc_lexer::unescape::{EscapeError, Mode};
+use rustc_literal_escaper::{EscapeError, Mode};
 use rustc_span::{BytePos, Span};
 use tracing::debug;
 
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 841d967d934..9c457f150a3 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -21,7 +21,7 @@ use rustc_ast::{
 };
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{Applicability, Diag, PResult, StashKey, Subdiagnostic};
-use rustc_lexer::unescape::unescape_char;
+use rustc_literal_escaper::unescape_char;
 use rustc_macros::Subdiagnostic;
 use rustc_session::errors::{ExprParenthesesNeeded, report_lit_error};
 use rustc_session::lint::BuiltinLintDiag;
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 9405b58ab3b..3647bf2c378 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -2987,9 +2987,7 @@ impl<'a> Parser<'a> {
                 }
                 match ty {
                     Ok(ty) => {
-                        let ident = Ident::new(kw::Empty, this.prev_token.span);
-                        let bm = BindingMode::NONE;
-                        let pat = this.mk_pat_ident(ty.span, bm, ident);
+                        let pat = this.mk_pat(ty.span, PatKind::Missing);
                         (pat, ty)
                     }
                     // If this is a C-variadic argument and we hit an error, return the error.
diff --git a/compiler/rustc_parse_format/Cargo.toml b/compiler/rustc_parse_format/Cargo.toml
index 289e062fb5e..52f23c00d4b 100644
--- a/compiler/rustc_parse_format/Cargo.toml
+++ b/compiler/rustc_parse_format/Cargo.toml
@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
+rustc-literal-escaper = "0.0.2"
 rustc_lexer = { path = "../rustc_lexer" }
 # tidy-alphabetical-end
 
diff --git a/compiler/rustc_parse_format/src/lib.rs b/compiler/rustc_parse_format/src/lib.rs
index 97931742985..c59e6cb5c33 100644
--- a/compiler/rustc_parse_format/src/lib.rs
+++ b/compiler/rustc_parse_format/src/lib.rs
@@ -18,7 +18,7 @@
 pub use Alignment::*;
 pub use Count::*;
 pub use Position::*;
-use rustc_lexer::unescape;
+use rustc_literal_escaper::{Mode, unescape_unicode};
 
 // Note: copied from rustc_span
 /// Range inside of a `Span` used for diagnostics when we only have access to relative positions.
@@ -1094,11 +1094,9 @@ fn find_width_map_from_snippet(
 fn unescape_string(string: &str) -> Option<String> {
     let mut buf = String::new();
     let mut ok = true;
-    unescape::unescape_unicode(string, unescape::Mode::Str, &mut |_, unescaped_char| {
-        match unescaped_char {
-            Ok(c) => buf.push(c),
-            Err(_) => ok = false,
-        }
+    unescape_unicode(string, Mode::Str, &mut |_, unescaped_char| match unescaped_char {
+        Ok(c) => buf.push(c),
+        Err(_) => ok = false,
     });
 
     ok.then_some(buf)
diff --git a/compiler/rustc_passes/src/input_stats.rs b/compiler/rustc_passes/src/input_stats.rs
index 1278e98afcf..71815448172 100644
--- a/compiler/rustc_passes/src/input_stats.rs
+++ b/compiler/rustc_passes/src/input_stats.rs
@@ -295,6 +295,7 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
         record_variants!(
             (self, p, p.kind, Some(p.hir_id), hir, Pat, PatKind),
             [
+                Missing,
                 Wild,
                 Binding,
                 Struct,
@@ -597,6 +598,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
         record_variants!(
             (self, p, p.kind, None, ast, Pat, PatKind),
             [
+                Missing,
                 Wild,
                 Ident,
                 Struct,
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs
index ed70d9ee91f..06eb76c30c5 100644
--- a/compiler/rustc_passes/src/liveness.rs
+++ b/compiler/rustc_passes/src/liveness.rs
@@ -96,7 +96,7 @@ use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self, RootVariableMinCaptureList, Ty, TyCtxt};
 use rustc_session::lint;
-use rustc_span::{BytePos, Span, Symbol, kw, sym};
+use rustc_span::{BytePos, Span, Symbol, sym};
 use tracing::{debug, instrument};
 
 use self::LiveNodeKind::*;
@@ -1481,9 +1481,6 @@ impl<'tcx> Liveness<'_, 'tcx> {
 
     fn should_warn(&self, var: Variable) -> Option<String> {
         let name = self.ir.variable_name(var);
-        if name == kw::Empty {
-            return None;
-        }
         let name = name.as_str();
         if name.as_bytes()[0] == b'_' {
             return None;
@@ -1655,7 +1652,7 @@ impl<'tcx> Liveness<'_, 'tcx> {
                 // `&'name Ty` -> `&'name mut Ty` or `&Ty` -> `&mut Ty`
                 Some(mut_ty.ty.span.shrink_to_lo())
             };
-            let pre = if lt.ident.span.lo() == lt.ident.span.hi() { "" } else { " " };
+            let pre = if lt.ident.span.is_empty() { "" } else { " " };
             Some(errors::UnusedAssignSuggestion {
                 ty_span,
                 pre,
diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index 31c4ee0fa0b..88d45ead295 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -460,7 +460,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             PatKind::AscribeUserType { subpattern, .. }
             | PatKind::ExpandedConstant { subpattern, .. } => return self.lower_pat(subpattern),
             PatKind::Binding { subpattern: Some(subpat), .. } => return self.lower_pat(subpat),
-            PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
+            PatKind::Missing | PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
                 ctor = Wildcard;
                 fields = vec![];
                 arity = 0;
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 20e19caf909..1389e8c811e 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -4009,22 +4009,17 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             self.report_error(ident.span, error(ident));
         }
 
-        // Record as bound if it's valid:
-        let ident_valid = ident.name != kw::Empty;
-        if ident_valid {
-            bindings.last_mut().unwrap().1.insert(ident);
-        }
+        // Record as bound.
+        bindings.last_mut().unwrap().1.insert(ident);
 
         if already_bound_or {
             // `Variant1(a) | Variant2(a)`, ok
             // Reuse definition from the first `a`.
             self.innermost_rib_bindings(ValueNS)[&ident]
         } else {
+            // A completely fresh binding is added to the set.
             let res = Res::Local(pat_id);
-            if ident_valid {
-                // A completely fresh binding add to the set if it's valid.
-                self.innermost_rib_bindings(ValueNS).insert(ident, res);
-            }
+            self.innermost_rib_bindings(ValueNS).insert(ident, res);
             res
         }
     }
diff --git a/compiler/rustc_type_ir/Cargo.toml b/compiler/rustc_type_ir/Cargo.toml
index 4adf7157926..83d3d78298e 100644
--- a/compiler/rustc_type_ir/Cargo.toml
+++ b/compiler/rustc_type_ir/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2024"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 derive-where = "1.2.7"
+ena = "0.14.3"
 indexmap = "2.0.0"
 rustc-hash = "1.1.0"
 rustc_ast_ir = { path = "../rustc_ast_ir", default-features = false }
diff --git a/compiler/rustc_type_ir/src/data_structures/mod.rs b/compiler/rustc_type_ir/src/data_structures/mod.rs
index 30c67d10d0e..a72669cbd18 100644
--- a/compiler/rustc_type_ir/src/data_structures/mod.rs
+++ b/compiler/rustc_type_ir/src/data_structures/mod.rs
@@ -1,5 +1,6 @@
 use std::hash::BuildHasherDefault;
 
+pub use ena::unify::{NoError, UnifyKey, UnifyValue};
 use rustc_hash::FxHasher;
 pub use rustc_hash::{FxHashMap as HashMap, FxHashSet as HashSet};
 
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index d35b22d517c..753a72a051a 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -6,9 +6,8 @@ use rustc_ast_ir::Mutability;
 #[cfg(feature = "nightly")]
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 #[cfg(feature = "nightly")]
-use rustc_data_structures::unify::{NoError, UnifyKey, UnifyValue};
-#[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
+use rustc_type_ir::data_structures::{NoError, UnifyKey, UnifyValue};
 use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
 
 use self::TyKind::*;
@@ -796,7 +795,6 @@ pub enum InferTy {
 
 /// Raw `TyVid` are used as the unification key for `sub_relations`;
 /// they carry no values.
-#[cfg(feature = "nightly")]
 impl UnifyKey for TyVid {
     type Value = ();
     #[inline]
@@ -812,7 +810,6 @@ impl UnifyKey for TyVid {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyValue for IntVarValue {
     type Error = NoError;
 
@@ -832,7 +829,6 @@ impl UnifyValue for IntVarValue {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyKey for IntVid {
     type Value = IntVarValue;
     #[inline] // make this function eligible for inlining - it is quite hot.
@@ -848,7 +844,6 @@ impl UnifyKey for IntVid {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyValue for FloatVarValue {
     type Error = NoError;
 
@@ -866,7 +861,6 @@ impl UnifyValue for FloatVarValue {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyKey for FloatVid {
     type Value = FloatVarValue;
     #[inline]
diff --git a/library/Cargo.lock b/library/Cargo.lock
index 23d9d926eba..ad634e9f794 100644
--- a/library/Cargo.lock
+++ b/library/Cargo.lock
@@ -176,9 +176,9 @@ dependencies = [
 
 [[package]]
 name = "miniz_oxide"
-version = "0.8.5"
+version = "0.8.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e3e04debbb59698c15bacbb6d93584a8c0ca9cc3213cb423d31f760d8843ce5"
+checksum = "ff70ce3e48ae43fa075863cef62e8b43b71a4f2382229920e0df362592919430"
 dependencies = [
  "adler2",
  "compiler_builtins",
@@ -235,6 +235,7 @@ name = "proc_macro"
 version = "0.0.0"
 dependencies = [
  "core",
+ "rustc-literal-escaper",
  "std",
 ]
 
@@ -311,6 +312,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "rustc-literal-escaper"
+version = "0.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0041b6238913c41fe704213a4a9329e2f685a156d1781998128b4149c230ad04"
+dependencies = [
+ "rustc-std-workspace-std",
+]
+
+[[package]]
 name = "rustc-std-workspace-alloc"
 version = "1.99.0"
 dependencies = [
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index f0cdb1e4e0f..04858667230 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -135,6 +135,7 @@
 #![feature(pattern)]
 #![feature(pin_coerce_unsized_trait)]
 #![feature(pointer_like_trait)]
+#![feature(ptr_alignment_type)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
 #![feature(set_ptr_value)]
diff --git a/library/alloc/src/raw_vec/mod.rs b/library/alloc/src/raw_vec/mod.rs
index 99ebc5c4bfc..a989e5b55b3 100644
--- a/library/alloc/src/raw_vec/mod.rs
+++ b/library/alloc/src/raw_vec/mod.rs
@@ -6,7 +6,7 @@
 
 use core::marker::PhantomData;
 use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties};
-use core::ptr::{self, NonNull, Unique};
+use core::ptr::{self, Alignment, NonNull, Unique};
 use core::{cmp, hint};
 
 #[cfg(not(no_global_oom_handling))]
@@ -177,7 +177,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// the returned `RawVec`.
     #[inline]
     pub(crate) const fn new_in(alloc: A) -> Self {
-        Self { inner: RawVecInner::new_in(alloc, align_of::<T>()), _marker: PhantomData }
+        Self { inner: RawVecInner::new_in(alloc, Alignment::of::<T>()), _marker: PhantomData }
     }
 
     /// Like `with_capacity`, but parameterized over the choice of
@@ -409,8 +409,8 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
 
 impl<A: Allocator> RawVecInner<A> {
     #[inline]
-    const fn new_in(alloc: A, align: usize) -> Self {
-        let ptr = unsafe { core::mem::transmute(align) };
+    const fn new_in(alloc: A, align: Alignment) -> Self {
+        let ptr = Unique::from_non_null(NonNull::without_provenance(align.as_nonzero()));
         // `cap: 0` means "unallocated". zero-sized types are ignored.
         Self { ptr, cap: ZERO_CAP, alloc }
     }
@@ -465,7 +465,7 @@ impl<A: Allocator> RawVecInner<A> {
 
         // Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
         if layout.size() == 0 {
-            return Ok(Self::new_in(alloc, elem_layout.align()));
+            return Ok(Self::new_in(alloc, elem_layout.alignment()));
         }
 
         if let Err(err) = alloc_guard(layout.size()) {
diff --git a/library/alloctests/lib.rs b/library/alloctests/lib.rs
index 6ce8a6d9ca1..56e60ed4c84 100644
--- a/library/alloctests/lib.rs
+++ b/library/alloctests/lib.rs
@@ -28,6 +28,8 @@
 #![feature(iter_next_chunk)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array_transpose)]
+#![feature(nonnull_provenance)]
+#![feature(ptr_alignment_type)]
 #![feature(ptr_internals)]
 #![feature(sized_type_properties)]
 #![feature(slice_iter_mut_as_mut_slice)]
diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
index 1595a3af883..e8a03aadc33 100644
--- a/library/core/src/alloc/layout.rs
+++ b/library/core/src/alloc/layout.rs
@@ -520,6 +520,14 @@ impl Layout {
             unsafe { Ok(Layout::from_size_align_unchecked(array_size, align.as_usize())) }
         }
     }
+
+    /// Perma-unstable access to `align` as `Alignment` type.
+    #[unstable(issue = "none", feature = "std_internals")]
+    #[doc(hidden)]
+    #[inline]
+    pub const fn alignment(&self) -> Alignment {
+        self.align
+    }
 }
 
 #[stable(feature = "alloc_layout", since = "1.28.0")]
diff --git a/library/core/src/ptr/unique.rs b/library/core/src/ptr/unique.rs
index 4810ebe01f9..d688ce2a07a 100644
--- a/library/core/src/ptr/unique.rs
+++ b/library/core/src/ptr/unique.rs
@@ -100,6 +100,12 @@ impl<T: ?Sized> Unique<T> {
         }
     }
 
+    /// Create a new `Unique` from a `NonNull` in const context.
+    #[inline]
+    pub const fn from_non_null(pointer: NonNull<T>) -> Self {
+        Unique { pointer, _marker: PhantomData }
+    }
+
     /// Acquires the underlying `*mut` pointer.
     #[must_use = "`self` will be dropped if the result is not used"]
     #[inline]
@@ -202,6 +208,6 @@ impl<T: ?Sized> From<NonNull<T>> for Unique<T> {
     /// This conversion is infallible since `NonNull` cannot be null.
     #[inline]
     fn from(pointer: NonNull<T>) -> Self {
-        Unique { pointer, _marker: PhantomData }
+        Unique::from_non_null(pointer)
     }
 }
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index d48248749c2..f507ee563ac 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -1380,14 +1380,16 @@ impl<'a, T> Iterator for Windows<'a, T> {
 
     #[inline]
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
-        let (end, overflow) = self.size.get().overflowing_add(n);
-        if end > self.v.len() || overflow {
-            self.v = &[];
-            None
-        } else {
-            let nth = &self.v[n..end];
-            self.v = &self.v[n + 1..];
+        let size = self.size.get();
+        if let Some(rest) = self.v.get(n..)
+            && let Some(nth) = rest.get(..size)
+        {
+            self.v = &rest[1..];
             Some(nth)
+        } else {
+            // setting length to 0 is cheaper than overwriting the pointer when assigning &[]
+            self.v = &self.v[..0]; // cheaper than &[]
+            None
         }
     }
 
@@ -1427,7 +1429,7 @@ impl<'a, T> DoubleEndedIterator for Windows<'a, T> {
     fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
         let (end, overflow) = self.v.len().overflowing_sub(n);
         if end < self.size.get() || overflow {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             let ret = &self.v[end - self.size.get()..end];
@@ -1536,17 +1538,15 @@ impl<'a, T> Iterator for Chunks<'a, T> {
     #[inline]
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
         let (start, overflow) = n.overflowing_mul(self.chunk_size);
-        if start >= self.v.len() || overflow {
-            self.v = &[];
-            None
-        } else {
-            let end = match start.checked_add(self.chunk_size) {
-                Some(sum) => cmp::min(self.v.len(), sum),
-                None => self.v.len(),
-            };
-            let nth = &self.v[start..end];
-            self.v = &self.v[end..];
+        // min(len) makes a wrong start harmless, but enables optimizing this to brachless code
+        let chunk_start = &self.v[start.min(self.v.len())..];
+        let (nth, remainder) = chunk_start.split_at(self.chunk_size.min(chunk_start.len()));
+        if !overflow && start < self.v.len() {
+            self.v = remainder;
             Some(nth)
+        } else {
+            self.v = &self.v[..0]; // cheaper than &[]
+            None
         }
     }
 
@@ -1609,7 +1609,7 @@ impl<'a, T> DoubleEndedIterator for Chunks<'a, T> {
     fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
         let len = self.len();
         if n >= len {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             let start = (len - 1 - n) * self.chunk_size;
@@ -1933,7 +1933,7 @@ impl<'a, T> Iterator for ChunksExact<'a, T> {
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
         let (start, overflow) = n.overflowing_mul(self.chunk_size);
         if start >= self.v.len() || overflow {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             let (_, snd) = self.v.split_at(start);
@@ -1971,7 +1971,7 @@ impl<'a, T> DoubleEndedIterator for ChunksExact<'a, T> {
     fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
         let len = self.len();
         if n >= len {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             let start = (len - 1 - n) * self.chunk_size;
@@ -2638,7 +2638,7 @@ impl<'a, T> Iterator for RChunks<'a, T> {
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
         let (end, overflow) = n.overflowing_mul(self.chunk_size);
         if end >= self.v.len() || overflow {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             // Can't underflow because of the check above
@@ -2695,7 +2695,7 @@ impl<'a, T> DoubleEndedIterator for RChunks<'a, T> {
     fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
         let len = self.len();
         if n >= len {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             // can't underflow because `n < len`
@@ -3023,7 +3023,7 @@ impl<'a, T> Iterator for RChunksExact<'a, T> {
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
         let (end, overflow) = n.overflowing_mul(self.chunk_size);
         if end >= self.v.len() || overflow {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             let (fst, _) = self.v.split_at(self.v.len() - end);
@@ -3062,7 +3062,7 @@ impl<'a, T> DoubleEndedIterator for RChunksExact<'a, T> {
     fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
         let len = self.len();
         if n >= len {
-            self.v = &[];
+            self.v = &self.v[..0]; // cheaper than &[]
             None
         } else {
             // now that we know that `n` corresponds to a chunk,
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index e54840c8fcc..c7e8d5f989d 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -8,7 +8,7 @@
 
 use crate::cmp::Ordering::{self, Equal, Greater, Less};
 use crate::intrinsics::{exact_div, unchecked_sub};
-use crate::mem::{self, SizedTypeProperties};
+use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::num::NonZero;
 use crate::ops::{OneSidedRange, OneSidedRangeBound, Range, RangeBounds, RangeInclusive};
 use crate::panic::const_panic;
@@ -4579,7 +4579,7 @@ impl<T> [T] {
         // or generate worse code otherwise. This is also why we need to go
         // through a raw pointer here.
         let slice: *mut [T] = self;
-        let mut arr: mem::MaybeUninit<[&mut I::Output; N]> = mem::MaybeUninit::uninit();
+        let mut arr: MaybeUninit<[&mut I::Output; N]> = MaybeUninit::uninit();
         let arr_ptr = arr.as_mut_ptr();
 
         // SAFETY: We expect `indices` to contain disjunct values that are
@@ -4764,6 +4764,55 @@ impl<T> [T] {
     }
 }
 
+impl<T> [MaybeUninit<T>] {
+    /// Transmutes the mutable uninitialized slice to a mutable uninitialized slice of
+    /// another type, ensuring alignment of the types is maintained.
+    ///
+    /// This is a safe wrapper around [`slice::align_to_mut`], so inherits the same
+    /// guarantees as that method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(align_to_uninit_mut)]
+    /// use std::mem::MaybeUninit;
+    ///
+    /// pub struct BumpAllocator<'scope> {
+    ///     memory: &'scope mut [MaybeUninit<u8>],
+    /// }
+    ///
+    /// impl<'scope> BumpAllocator<'scope> {
+    ///     pub fn new(memory: &'scope mut [MaybeUninit<u8>]) -> Self {
+    ///         Self { memory }
+    ///     }
+    ///     pub fn try_alloc_uninit<T>(&mut self) -> Option<&'scope mut MaybeUninit<T>> {
+    ///         let first_end = self.memory.as_ptr().align_offset(align_of::<T>()) + size_of::<T>();
+    ///         let prefix = self.memory.split_off_mut(..first_end)?;
+    ///         Some(&mut prefix.align_to_uninit_mut::<T>().1[0])
+    ///     }
+    ///     pub fn try_alloc_u32(&mut self, value: u32) -> Option<&'scope mut u32> {
+    ///         let uninit = self.try_alloc_uninit()?;
+    ///         Some(uninit.write(value))
+    ///     }
+    /// }
+    ///
+    /// let mut memory = [MaybeUninit::<u8>::uninit(); 10];
+    /// let mut allocator = BumpAllocator::new(&mut memory);
+    /// let v = allocator.try_alloc_u32(42);
+    /// assert_eq!(v, Some(&mut 42));
+    /// ```
+    #[unstable(feature = "align_to_uninit_mut", issue = "139062")]
+    #[inline]
+    #[must_use]
+    pub fn align_to_uninit_mut<U>(&mut self) -> (&mut Self, &mut [MaybeUninit<U>], &mut Self) {
+        // SAFETY: `MaybeUninit` is transparent. Correct size and alignment are guaranteed by
+        // `align_to_mut` itself. Therefore the only thing that we have to ensure for a safe
+        // `transmute` is that the values are valid for the types involved. But for `MaybeUninit`
+        // any values are valid, so this operation is safe.
+        unsafe { self.align_to_mut() }
+    }
+}
+
 impl<T, const N: usize> [[T; N]] {
     /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
     ///
diff --git a/library/proc_macro/Cargo.toml b/library/proc_macro/Cargo.toml
index 72cb4e4166f..b8bc2a3af4c 100644
--- a/library/proc_macro/Cargo.toml
+++ b/library/proc_macro/Cargo.toml
@@ -9,3 +9,4 @@ std = { path = "../std" }
 # `core` when resolving doc links. Without this line a different `core` will be
 # loaded from sysroot causing duplicate lang items and other similar errors.
 core = { path = "../core" }
+rustc-literal-escaper = { version = "0.0.2", features = ["rustc-dep-of-std"] }
diff --git a/library/proc_macro/src/lib.rs b/library/proc_macro/src/lib.rs
index d9141eab591..f1cf0c5a2db 100644
--- a/library/proc_macro/src/lib.rs
+++ b/library/proc_macro/src/lib.rs
@@ -27,6 +27,7 @@
 #![feature(panic_can_unwind)]
 #![feature(restricted_std)]
 #![feature(rustc_attrs)]
+#![feature(stmt_expr_attributes)]
 #![feature(extend_one)]
 #![recursion_limit = "256"]
 #![allow(internal_features)]
@@ -51,11 +52,24 @@ use std::{error, fmt};
 
 #[unstable(feature = "proc_macro_diagnostic", issue = "54140")]
 pub use diagnostic::{Diagnostic, Level, MultiSpan};
+#[unstable(feature = "proc_macro_value", issue = "136652")]
+pub use rustc_literal_escaper::EscapeError;
+use rustc_literal_escaper::{MixedUnit, Mode, byte_from_char, unescape_mixed, unescape_unicode};
 #[unstable(feature = "proc_macro_totokens", issue = "130977")]
 pub use to_tokens::ToTokens;
 
 use crate::escape::{EscapeOptions, escape_bytes};
 
+/// Errors returned when trying to retrieve a literal unescaped value.
+#[unstable(feature = "proc_macro_value", issue = "136652")]
+#[derive(Debug, PartialEq, Eq)]
+pub enum ConversionErrorKind {
+    /// The literal failed to be escaped, take a look at [`EscapeError`] for more information.
+    FailedToUnescape(EscapeError),
+    /// Trying to convert a literal with the wrong type.
+    InvalidLiteralKind,
+}
+
 /// Determines whether proc_macro has been made accessible to the currently
 /// running program.
 ///
@@ -1451,6 +1465,107 @@ impl Literal {
             }
         })
     }
+
+    /// Returns the unescaped string value if the current literal is a string or a string literal.
+    #[unstable(feature = "proc_macro_value", issue = "136652")]
+    pub fn str_value(&self) -> Result<String, ConversionErrorKind> {
+        self.0.symbol.with(|symbol| match self.0.kind {
+            bridge::LitKind::Str => {
+                if symbol.contains('\\') {
+                    let mut buf = String::with_capacity(symbol.len());
+                    let mut error = None;
+                    // Force-inlining here is aggressive but the closure is
+                    // called on every char in the string, so it can be hot in
+                    // programs with many long strings containing escapes.
+                    unescape_unicode(
+                        symbol,
+                        Mode::Str,
+                        &mut #[inline(always)]
+                        |_, c| match c {
+                            Ok(c) => buf.push(c),
+                            Err(err) => {
+                                if err.is_fatal() {
+                                    error = Some(ConversionErrorKind::FailedToUnescape(err));
+                                }
+                            }
+                        },
+                    );
+                    if let Some(error) = error { Err(error) } else { Ok(buf) }
+                } else {
+                    Ok(symbol.to_string())
+                }
+            }
+            bridge::LitKind::StrRaw(_) => Ok(symbol.to_string()),
+            _ => Err(ConversionErrorKind::InvalidLiteralKind),
+        })
+    }
+
+    /// Returns the unescaped string value if the current literal is a c-string or a c-string
+    /// literal.
+    #[unstable(feature = "proc_macro_value", issue = "136652")]
+    pub fn cstr_value(&self) -> Result<Vec<u8>, ConversionErrorKind> {
+        self.0.symbol.with(|symbol| match self.0.kind {
+            bridge::LitKind::CStr => {
+                let mut error = None;
+                let mut buf = Vec::with_capacity(symbol.len());
+
+                unescape_mixed(symbol, Mode::CStr, &mut |_span, c| match c {
+                    Ok(MixedUnit::Char(c)) => {
+                        buf.extend_from_slice(c.encode_utf8(&mut [0; 4]).as_bytes())
+                    }
+                    Ok(MixedUnit::HighByte(b)) => buf.push(b),
+                    Err(err) => {
+                        if err.is_fatal() {
+                            error = Some(ConversionErrorKind::FailedToUnescape(err));
+                        }
+                    }
+                });
+                if let Some(error) = error {
+                    Err(error)
+                } else {
+                    buf.push(0);
+                    Ok(buf)
+                }
+            }
+            bridge::LitKind::CStrRaw(_) => {
+                // Raw strings have no escapes so we can convert the symbol
+                // directly to a `Lrc<u8>` after appending the terminating NUL
+                // char.
+                let mut buf = symbol.to_owned().into_bytes();
+                buf.push(0);
+                Ok(buf)
+            }
+            _ => Err(ConversionErrorKind::InvalidLiteralKind),
+        })
+    }
+
+    /// Returns the unescaped string value if the current literal is a byte string or a byte string
+    /// literal.
+    #[unstable(feature = "proc_macro_value", issue = "136652")]
+    pub fn byte_str_value(&self) -> Result<Vec<u8>, ConversionErrorKind> {
+        self.0.symbol.with(|symbol| match self.0.kind {
+            bridge::LitKind::ByteStr => {
+                let mut buf = Vec::with_capacity(symbol.len());
+                let mut error = None;
+
+                unescape_unicode(symbol, Mode::ByteStr, &mut |_, c| match c {
+                    Ok(c) => buf.push(byte_from_char(c)),
+                    Err(err) => {
+                        if err.is_fatal() {
+                            error = Some(ConversionErrorKind::FailedToUnescape(err));
+                        }
+                    }
+                });
+                if let Some(error) = error { Err(error) } else { Ok(buf) }
+            }
+            bridge::LitKind::ByteStrRaw(_) => {
+                // Raw strings have no escapes so we can convert the symbol
+                // directly to a `Lrc<u8>`.
+                Ok(symbol.to_owned().into_bytes())
+            }
+            _ => Err(ConversionErrorKind::InvalidLiteralKind),
+        })
+    }
 }
 
 /// Parse a single literal from its stringified representation.
diff --git a/library/std/src/sys/io/io_slice/iovec.rs b/library/std/src/sys/io/io_slice/iovec.rs
index 072191315f7..df56358969a 100644
--- a/library/std/src/sys/io/io_slice/iovec.rs
+++ b/library/std/src/sys/io/io_slice/iovec.rs
@@ -1,6 +1,6 @@
 #[cfg(target_os = "hermit")]
 use hermit_abi::iovec;
-#[cfg(target_family = "unix")]
+#[cfg(any(target_family = "unix", target_os = "trusty"))]
 use libc::iovec;
 
 use crate::ffi::c_void;
diff --git a/library/std/src/sys/io/mod.rs b/library/std/src/sys/io/mod.rs
index e00b479109f..4d0365d42fd 100644
--- a/library/std/src/sys/io/mod.rs
+++ b/library/std/src/sys/io/mod.rs
@@ -2,7 +2,7 @@
 
 mod io_slice {
     cfg_if::cfg_if! {
-        if #[cfg(any(target_family = "unix", target_os = "hermit", target_os = "solid_asp3"))] {
+        if #[cfg(any(target_family = "unix", target_os = "hermit", target_os = "solid_asp3", target_os = "trusty"))] {
             mod iovec;
             pub use iovec::*;
         } else if #[cfg(target_os = "windows")] {
diff --git a/library/std/src/sys/stdio/trusty.rs b/library/std/src/sys/stdio/trusty.rs
index d393e95394d..e05461aa44a 100644
--- a/library/std/src/sys/stdio/trusty.rs
+++ b/library/std/src/sys/stdio/trusty.rs
@@ -1,21 +1,14 @@
-use crate::io;
+#[expect(dead_code)]
+#[path = "unsupported.rs"]
+mod unsupported_stdio;
 
-pub struct Stdin;
+use crate::cmp;
+use crate::io::{self, IoSlice};
+
+pub type Stdin = unsupported_stdio::Stdin;
 pub struct Stdout;
 pub struct Stderr;
 
-impl Stdin {
-    pub const fn new() -> Stdin {
-        Stdin
-    }
-}
-
-impl io::Read for Stdin {
-    fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> {
-        Ok(0)
-    }
-}
-
 impl Stdout {
     pub const fn new() -> Stdout {
         Stdout
@@ -24,7 +17,16 @@ impl Stdout {
 
 impl io::Write for Stdout {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        _write(libc::STDOUT_FILENO, buf)
+        write(libc::STDOUT_FILENO, buf)
+    }
+
+    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
+        write_vectored(libc::STDOUT_FILENO, bufs)
+    }
+
+    #[inline]
+    fn is_write_vectored(&self) -> bool {
+        true
     }
 
     fn flush(&mut self) -> io::Result<()> {
@@ -40,7 +42,16 @@ impl Stderr {
 
 impl io::Write for Stderr {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        _write(libc::STDERR_FILENO, buf)
+        write(libc::STDERR_FILENO, buf)
+    }
+
+    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
+        write_vectored(libc::STDERR_FILENO, bufs)
+    }
+
+    #[inline]
+    fn is_write_vectored(&self) -> bool {
+        true
     }
 
     fn flush(&mut self) -> io::Result<()> {
@@ -48,7 +59,7 @@ impl io::Write for Stderr {
     }
 }
 
-pub const STDIN_BUF_SIZE: usize = 0;
+pub const STDIN_BUF_SIZE: usize = unsupported_stdio::STDIN_BUF_SIZE;
 
 pub fn is_ebadf(_err: &io::Error) -> bool {
     true
@@ -58,24 +69,24 @@ pub fn panic_output() -> Option<impl io::Write> {
     Some(Stderr)
 }
 
-fn _write(fd: i32, message: &[u8]) -> io::Result<usize> {
-    let mut iov = libc::iovec { iov_base: message.as_ptr() as *mut _, iov_len: message.len() };
-    loop {
-        // SAFETY: syscall, safe arguments.
-        let ret = unsafe { libc::writev(fd, &iov, 1) };
-        if ret < 0 {
-            return Err(io::Error::last_os_error());
-        }
-        let ret = ret as usize;
-        if ret > iov.iov_len {
-            return Err(io::Error::last_os_error());
-        }
-        if ret == iov.iov_len {
-            return Ok(message.len());
-        }
-        // SAFETY: ret has been checked to be less than the length of
-        // the buffer
-        iov.iov_base = unsafe { iov.iov_base.add(ret) };
-        iov.iov_len -= ret;
+fn write(fd: i32, buf: &[u8]) -> io::Result<usize> {
+    let iov = libc::iovec { iov_base: buf.as_ptr() as *mut _, iov_len: buf.len() };
+    // SAFETY: syscall, safe arguments.
+    let ret = unsafe { libc::writev(fd, &iov, 1) };
+    // This check includes ret < 0, since the length is at most isize::MAX.
+    if ret as usize > iov.iov_len {
+        return Err(io::Error::last_os_error());
+    }
+    Ok(ret as usize)
+}
+
+fn write_vectored(fd: i32, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
+    let iov = bufs.as_ptr() as *const libc::iovec;
+    let len = cmp::min(bufs.len(), libc::c_int::MAX as usize) as libc::c_int;
+    // SAFETY: syscall, safe arguments.
+    let ret = unsafe { libc::writev(fd, iov, len) };
+    if ret < 0 {
+        return Err(io::Error::last_os_error());
     }
+    Ok(ret as usize)
 }
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index 843d474f92d..7c60e042142 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -748,7 +748,7 @@ impl Build {
             features.push("llvm");
         }
         // keep in sync with `bootstrap/compile.rs:rustc_cargo_env`
-        if self.config.rust_randomize_layout {
+        if self.config.rust_randomize_layout && check("rustc_randomized_layouts") {
             features.push("rustc_randomized_layouts");
         }
 
diff --git a/src/doc/style-guide/src/expressions.md b/src/doc/style-guide/src/expressions.md
index 12037b5992e..031e59d86e1 100644
--- a/src/doc/style-guide/src/expressions.md
+++ b/src/doc/style-guide/src/expressions.md
@@ -521,8 +521,11 @@ self.pre_comment.as_ref().map_or(
 
 ## Control flow expressions
 
-This section covers `if`, `if let`, `loop`, `while`, `while let`, and `for`
-expressions.
+This section covers `for` and `loop` expressions, as well as `if` and `while`
+expressions with their sub-expression variants. This includes those with a
+single `let` sub-expression (i.e. `if let` and `while let`)
+as well as "let-chains": those with one or more `let` sub-expressions and
+one or more bool-type conditions (i.e.  `if a && let Some(b) = c`).
 
 Put the keyword, any initial clauses, and the opening brace of the block all on
 a single line, if they fit. Apply the usual rules for [block
@@ -548,10 +551,11 @@ if let ... {
 }
 ```
 
-If the control line needs to be broken, prefer to break before the `=` in `*
-let` expressions and before `in` in a `for` expression; block-indent the
-following line. If the control line is broken for any reason, put the opening
-brace on its own line, not indented. Examples:
+If the control line needs to be broken, then prefer breaking after the `=` for any
+`let` sub-expression in an `if` or `while` expression that does not fit,
+and before `in` in a `for` expression; the following line should be block indented.
+If the control line is broken for any reason, then the opening brace should be on its
+own line and not indented. Examples:
 
 ```rust
 while let Some(foo)
@@ -572,6 +576,68 @@ if a_long_expression
 {
     ...
 }
+
+if let Some(a) = b
+    && another_long_expression
+    && a_third_long_expression
+{
+    // ...
+}
+
+if let Some(relatively_long_thing)
+    = a_long_expression
+    && another_long_expression
+    && a_third_long_expression
+{
+    // ...
+}
+
+if some_expr
+    && another_long_expression
+    && let Some(relatively_long_thing) =
+        a_long_long_long_long_long_long_really_reallllllllllyyyyyyy_long_expression
+    && a_third_long_expression
+{
+    // ...
+}
+```
+
+A let-chain control line is allowed to be formatted on a single line provided
+it only consists of two clauses, with the first, left-hand side operand being a literal or an
+`ident` (which can optionally be preceded by any number of unary prefix operators),
+and the second, right-hand side operand being a single-line `let` clause. Otherwise,
+the control line must be broken and formatted according to the above rules. For example:
+
+```rust
+if a && let Some(b) = foo() {
+    // ...
+}
+
+if true && let Some(b) = foo() {
+    // ...
+}
+
+let operator = if !from_hir_call && let Some(p) = parent {
+    // ...
+};
+
+if let Some(b) = foo()
+    && a
+{
+    // ..
+}
+
+if foo()
+    && let Some(b) = bar
+{
+    // ...
+}
+
+if gen_pos != GenericArgPosition::Type
+    && let Some(b) = gen_args.bindings.first()
+{
+    // ..
+}
 ```
 
 Where the initial clause spans multiple lines and ends with one or more closing
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index f81db58950c..afcca81a485 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -304,6 +304,7 @@ pub(crate) fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
 
     Symbol::intern(&match &p.kind {
         // FIXME(never_patterns): does this make sense?
+        PatKind::Missing => unreachable!(),
         PatKind::Wild
         | PatKind::Err(_)
         | PatKind::Never
diff --git a/src/tools/cargo b/src/tools/cargo
-Subproject a6c604d1b8a2f2a8ff1f3ba6092f9fda42f4b7e
+Subproject 0e93c5bf6a1d5ee7bc2af63d1afb16cd2879360
diff --git a/src/tools/clippy/clippy_lints/src/equatable_if_let.rs b/src/tools/clippy/clippy_lints/src/equatable_if_let.rs
index cd9ab2764ac..3afb687040f 100644
--- a/src/tools/clippy/clippy_lints/src/equatable_if_let.rs
+++ b/src/tools/clippy/clippy_lints/src/equatable_if_let.rs
@@ -45,6 +45,7 @@ fn unary_pattern(pat: &Pat<'_>) -> bool {
         pats.iter().all(unary_pattern)
     }
     match &pat.kind {
+        PatKind::Missing => unreachable!(),
         PatKind::Slice(_, _, _)
         | PatKind::Range(_, _, _)
         | PatKind::Binding(..)
diff --git a/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs b/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs
index 250f17fa902..a21597ffb93 100644
--- a/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs
@@ -253,6 +253,7 @@ fn iter_matching_struct_fields<'a>(
 impl<'a> NormalizedPat<'a> {
     fn from_pat(cx: &LateContext<'_>, arena: &'a DroplessArena, pat: &'a Pat<'_>) -> Self {
         match pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild | PatKind::Binding(.., None) => Self::Wild,
             PatKind::Binding(.., Some(pat))
             | PatKind::Box(pat)
diff --git a/src/tools/clippy/clippy_lints/src/matches/single_match.rs b/src/tools/clippy/clippy_lints/src/matches/single_match.rs
index 56fbd626eef..836c46240ce 100644
--- a/src/tools/clippy/clippy_lints/src/matches/single_match.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/single_match.rs
@@ -406,6 +406,7 @@ impl<'a> PatState<'a> {
                 pats.iter().map(|p| p.pat),
             ),
 
+            PatKind::Missing => unreachable!(),
             PatKind::Wild
             | PatKind::Binding(_, _, _, None)
             | PatKind::Expr(_)
diff --git a/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs b/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
index f43715d6752..8966e6851ac 100644
--- a/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
+++ b/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
@@ -224,6 +224,7 @@ fn transform_with_focus_on_idx(alternatives: &mut ThinVec<P<Pat>>, focus_idx: us
 
     // We're trying to find whatever kind (~"constructor") we found in `alternatives[start..]`.
     let changed = match &mut focus_kind {
+        Missing => unreachable!(),
         // These pattern forms are "leafs" and do not have sub-patterns.
         // Therefore they are not some form of constructor `C`,
         // with which a pattern `C(p_0)` may be formed,
diff --git a/src/tools/clippy/clippy_lints/src/utils/author.rs b/src/tools/clippy/clippy_lints/src/utils/author.rs
index 4309cd2c9ab..b7dcd2ffb0e 100644
--- a/src/tools/clippy/clippy_lints/src/utils/author.rs
+++ b/src/tools/clippy/clippy_lints/src/utils/author.rs
@@ -676,6 +676,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
         }
 
         match pat.value.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => kind!("Wild"),
             PatKind::Never => kind!("Never"),
             PatKind::Binding(ann, _, name, sub) => {
diff --git a/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs b/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
index eba576392eb..c5dce26143b 100644
--- a/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
+++ b/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
@@ -33,6 +33,7 @@ pub fn eq_id(l: Ident, r: Ident) -> bool {
 pub fn eq_pat(l: &Pat, r: &Pat) -> bool {
     use PatKind::*;
     match (&l.kind, &r.kind) {
+        (Missing, _) | (_, Missing) => unreachable!(),
         (Paren(l), _) => eq_pat(l, r),
         (_, Paren(r)) => eq_pat(l, r),
         (Wild, Wild) | (Rest, Rest) => true,
diff --git a/src/tools/clippy/clippy_utils/src/hir_utils.rs b/src/tools/clippy/clippy_utils/src/hir_utils.rs
index 9938e64d242..b813cd361ed 100644
--- a/src/tools/clippy/clippy_utils/src/hir_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/hir_utils.rs
@@ -1124,6 +1124,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
     pub fn hash_pat(&mut self, pat: &Pat<'_>) {
         std::mem::discriminant(&pat.kind).hash(&mut self.s);
         match pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Binding(BindingMode(by_ref, mutability), _, _, pat) => {
                 std::mem::discriminant(&by_ref).hash(&mut self.s);
                 std::mem::discriminant(&mutability).hash(&mut self.s);
diff --git a/src/tools/clippy/clippy_utils/src/lib.rs b/src/tools/clippy/clippy_utils/src/lib.rs
index 6d2c2a2d692..bcb0f8349e2 100644
--- a/src/tools/clippy/clippy_utils/src/lib.rs
+++ b/src/tools/clippy/clippy_utils/src/lib.rs
@@ -1858,6 +1858,7 @@ pub fn is_refutable(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
     }
 
     match pat.kind {
+        PatKind::Missing => unreachable!(),
         PatKind::Wild | PatKind::Never => false, // If `!` typechecked then the type is empty, so not refutable.
         PatKind::Binding(_, _, _, pat) => pat.is_some_and(|pat| is_refutable(cx, pat)),
         PatKind::Box(pat) | PatKind::Ref(pat, _) => is_refutable(cx, pat),
diff --git a/src/tools/rust-analyzer/Cargo.lock b/src/tools/rust-analyzer/Cargo.lock
index 1e1d68f7782..745a8097c8a 100644
--- a/src/tools/rust-analyzer/Cargo.lock
+++ b/src/tools/rust-analyzer/Cargo.lock
@@ -1270,6 +1270,7 @@ dependencies = [
  "edition",
  "expect-test",
  "ra-ap-rustc_lexer",
+ "rustc-literal-escaper",
  "stdx",
  "tracing",
 ]
@@ -1744,6 +1745,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "583034fd73374156e66797ed8e5b0d5690409c9226b22d87cb7f19821c05d152"
 
 [[package]]
+name = "rustc-literal-escaper"
+version = "0.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0041b6238913c41fe704213a4a9329e2f685a156d1781998128b4149c230ad04"
+
+[[package]]
 name = "rustc-stable-hash"
 version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1978,10 +1985,10 @@ dependencies = [
  "indexmap",
  "itertools",
  "parser",
- "ra-ap-rustc_lexer",
  "rayon",
  "rowan",
  "rustc-hash 2.0.0",
+ "rustc-literal-escaper",
  "rustc_apfloat",
  "smol_str",
  "stdx",
diff --git a/src/tools/rust-analyzer/Cargo.toml b/src/tools/rust-analyzer/Cargo.toml
index ce2d66000e3..e2219139765 100644
--- a/src/tools/rust-analyzer/Cargo.toml
+++ b/src/tools/rust-analyzer/Cargo.toml
@@ -136,6 +136,7 @@ pulldown-cmark-to-cmark = "10.0.4"
 pulldown-cmark = { version = "0.9.0", default-features = false }
 rayon = "1.8.0"
 rustc-hash = "2.0.0"
+rustc-literal-escaper = "0.0.2"
 semver = "1.0.14"
 serde = { version = "1.0.192" }
 serde_derive = { version = "1.0.192" }
diff --git a/src/tools/rust-analyzer/crates/parser/Cargo.toml b/src/tools/rust-analyzer/crates/parser/Cargo.toml
index a36a39dbee6..114a66add63 100644
--- a/src/tools/rust-analyzer/crates/parser/Cargo.toml
+++ b/src/tools/rust-analyzer/crates/parser/Cargo.toml
@@ -14,6 +14,7 @@ rust-version.workspace = true
 [dependencies]
 drop_bomb = "0.1.5"
 ra-ap-rustc_lexer.workspace = true
+rustc-literal-escaper.workspace = true
 tracing = { workspace = true, optional = true }
 
 edition.workspace = true
diff --git a/src/tools/rust-analyzer/crates/parser/src/lexed_str.rs b/src/tools/rust-analyzer/crates/parser/src/lexed_str.rs
index c97596d5097..b0bbc2fa5ff 100644
--- a/src/tools/rust-analyzer/crates/parser/src/lexed_str.rs
+++ b/src/tools/rust-analyzer/crates/parser/src/lexed_str.rs
@@ -10,7 +10,7 @@
 
 use std::ops;
 
-use rustc_lexer::unescape::{EscapeError, Mode};
+use rustc_literal_escaper::{EscapeError, Mode, unescape_byte, unescape_char, unescape_mixed, unescape_unicode};
 
 use crate::{
     Edition,
@@ -282,7 +282,7 @@ impl<'a> Converter<'a> {
                     let text = &self.res.text[self.offset + 1..][..len - 1];
                     let i = text.rfind('\'').unwrap();
                     let text = &text[..i];
-                    if let Err(e) = rustc_lexer::unescape::unescape_char(text) {
+                    if let Err(e) = unescape_char(text) {
                         err = error_to_diagnostic_message(e, Mode::Char);
                     }
                 }
@@ -295,7 +295,7 @@ impl<'a> Converter<'a> {
                     let text = &self.res.text[self.offset + 2..][..len - 2];
                     let i = text.rfind('\'').unwrap();
                     let text = &text[..i];
-                    if let Err(e) = rustc_lexer::unescape::unescape_byte(text) {
+                    if let Err(e) = unescape_byte(text) {
                         err = error_to_diagnostic_message(e, Mode::Byte);
                     }
                 }
@@ -402,14 +402,14 @@ fn unescape_string_error_message(text: &str, mode: Mode) -> &'static str {
     let mut error_message = "";
     match mode {
         Mode::CStr => {
-            rustc_lexer::unescape::unescape_mixed(text, mode, &mut |_, res| {
+            unescape_mixed(text, mode, &mut |_, res| {
                 if let Err(e) = res {
                     error_message = error_to_diagnostic_message(e, mode);
                 }
             });
         }
         Mode::ByteStr | Mode::Str => {
-            rustc_lexer::unescape::unescape_unicode(text, mode, &mut |_, res| {
+            unescape_unicode(text, mode, &mut |_, res| {
                 if let Err(e) = res {
                     error_message = error_to_diagnostic_message(e, mode);
                 }
diff --git a/src/tools/rust-analyzer/crates/syntax/Cargo.toml b/src/tools/rust-analyzer/crates/syntax/Cargo.toml
index 3fe6e01dc3c..6b356398204 100644
--- a/src/tools/rust-analyzer/crates/syntax/Cargo.toml
+++ b/src/tools/rust-analyzer/crates/syntax/Cargo.toml
@@ -17,13 +17,12 @@ either.workspace = true
 itertools.workspace = true
 rowan = "=0.15.15"
 rustc-hash.workspace = true
+rustc-literal-escaper.workspace = true
 indexmap.workspace = true
 smol_str.workspace = true
 triomphe.workspace = true
 tracing.workspace = true
 
-ra-ap-rustc_lexer.workspace = true
-
 parser.workspace = true
 stdx.workspace = true
 
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/token_ext.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/token_ext.rs
index df851ab5b25..08bffb9e3aa 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/token_ext.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/token_ext.rs
@@ -2,7 +2,7 @@
 
 use std::{borrow::Cow, num::ParseIntError};
 
-use rustc_lexer::unescape::{
+use rustc_literal_escaper::{
     unescape_byte, unescape_char, unescape_mixed, unescape_unicode, EscapeError, MixedUnit, Mode,
 };
 use stdx::always;
diff --git a/src/tools/rust-analyzer/crates/syntax/src/lib.rs b/src/tools/rust-analyzer/crates/syntax/src/lib.rs
index c9e9f468dca..21f1ea5f913 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/lib.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/lib.rs
@@ -19,13 +19,6 @@
 //! [RFC]: <https://github.com/rust-lang/rfcs/pull/2256>
 //! [Swift]: <https://github.com/apple/swift/blob/13d593df6f359d0cb2fc81cfaac273297c539455/lib/Syntax/README.md>
 
-#![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
-
-#[cfg(not(feature = "in-rust-tree"))]
-extern crate ra_ap_rustc_lexer as rustc_lexer;
-#[cfg(feature = "in-rust-tree")]
-extern crate rustc_lexer;
-
 mod parsing;
 mod ptr;
 mod syntax_error;
@@ -64,7 +57,7 @@ pub use rowan::{
     api::Preorder, Direction, GreenNode, NodeOrToken, SyntaxText, TextRange, TextSize,
     TokenAtOffset, WalkEvent,
 };
-pub use rustc_lexer::unescape;
+pub use rustc_literal_escaper as unescape;
 pub use smol_str::{format_smolstr, SmolStr, SmolStrBuilder, ToSmolStr};
 
 /// `Parse` is the result of the parsing: a syntax tree and a collection of
diff --git a/src/tools/rust-analyzer/crates/syntax/src/validation.rs b/src/tools/rust-analyzer/crates/syntax/src/validation.rs
index 85eefac734b..71c5f9a946d 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/validation.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/validation.rs
@@ -5,7 +5,7 @@
 mod block;
 
 use rowan::Direction;
-use rustc_lexer::unescape::{self, unescape_mixed, unescape_unicode, Mode};
+use rustc_literal_escaper::{unescape_mixed, unescape_unicode, EscapeError, Mode};
 
 use crate::{
     algo,
@@ -44,8 +44,8 @@ pub(crate) fn validate(root: &SyntaxNode, errors: &mut Vec<SyntaxError>) {
     }
 }
 
-fn rustc_unescape_error_to_string(err: unescape::EscapeError) -> (&'static str, bool) {
-    use unescape::EscapeError as EE;
+fn rustc_unescape_error_to_string(err: EscapeError) -> (&'static str, bool) {
+    use rustc_literal_escaper::EscapeError as EE;
 
     #[rustfmt::skip]
     let err_message = match err {
@@ -127,7 +127,7 @@ fn validate_literal(literal: ast::Literal, acc: &mut Vec<SyntaxError>) {
     let text = token.text();
 
     // FIXME: lift this lambda refactor to `fn` (https://github.com/rust-lang/rust-analyzer/pull/2834#discussion_r366199205)
-    let mut push_err = |prefix_len, off, err: unescape::EscapeError| {
+    let mut push_err = |prefix_len, off, err: EscapeError| {
         let off = token.text_range().start() + TextSize::try_from(off + prefix_len).unwrap();
         let (message, is_err) = rustc_unescape_error_to_string(err);
         // FIXME: Emit lexer warnings
diff --git a/src/tools/rustbook/Cargo.lock b/src/tools/rustbook/Cargo.lock
index 08011e1d427..09bbbd61de5 100644
--- a/src/tools/rustbook/Cargo.lock
+++ b/src/tools/rustbook/Cargo.lock
@@ -156,9 +156,9 @@ checksum = "1628fb46dfa0b37568d12e5edd512553eccf6a22a78e8bde00bb4aed84d5bdbf"
 
 [[package]]
 name = "cc"
-version = "1.2.17"
+version = "1.2.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1fcb57c740ae1daf453ae85f16e37396f672b039e00d9d866e07ddb24e328e3a"
+checksum = "525046617d8376e3db1deffb079e91cef90a89fc3ca5c185bbf8c9ecdd15cd5c"
 dependencies = [
  "shlex",
 ]
@@ -185,9 +185,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.5.32"
+version = "4.5.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6088f3ae8c3608d19260cd7445411865a485688711b78b5be70d78cd96136f83"
+checksum = "d8aa86934b44c19c50f87cc2790e19f54f7a67aedb64101c2e1a2e5ecfb73944"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -195,9 +195,9 @@ dependencies = [
 
 [[package]]
 name = "clap_builder"
-version = "4.5.32"
+version = "4.5.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "22a7ef7f676155edfb82daa97f99441f3ebf4a58d5e32f295a56259f1b6facc8"
+checksum = "2414dbb2dd0695280da6ea9261e327479e9d37b0630f6b53ba2a11c60c679fd9"
 dependencies = [
  "anstream",
  "anstyle",
@@ -275,9 +275,9 @@ dependencies = [
 
 [[package]]
 name = "darling"
-version = "0.20.10"
+version = "0.20.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6f63b86c8a8826a49b8c21f08a2d07338eec8d900540f8630dc76284be802989"
+checksum = "fc7f46116c46ff9ab3eb1597a45688b6715c6e628b5c133e288e709a29bcb4ee"
 dependencies = [
  "darling_core",
  "darling_macro",
@@ -285,9 +285,9 @@ dependencies = [
 
 [[package]]
 name = "darling_core"
-version = "0.20.10"
+version = "0.20.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "95133861a8032aaea082871032f5815eb9e98cef03fa916ab4500513994df9e5"
+checksum = "0d00b9596d185e565c2207a0b01f8bd1a135483d02d9b7b0a54b11da8d53412e"
 dependencies = [
  "fnv",
  "ident_case",
@@ -299,9 +299,9 @@ dependencies = [
 
 [[package]]
 name = "darling_macro"
-version = "0.20.10"
+version = "0.20.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d336a2a514f6ccccaa3e09b02d41d35330c07ddf03a62165fcec10bb561c7806"
+checksum = "fc34b93ccb385b40dc71c6fceac4b2ad23662c7eeb248cf10d529b7e055b6ead"
 dependencies = [
  "darling_core",
  "quote",
@@ -413,9 +413,9 @@ dependencies = [
 
 [[package]]
 name = "env_logger"
-version = "0.11.7"
+version = "0.11.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3716d7a920fb4fac5d84e9d4bce8ceb321e9414b4409da61b07b75c1e3d0697"
+checksum = "13c863f0904021b108aa8b2f55046443e6b1ebde8fd4a15c399893aae4fa069f"
 dependencies = [
  "anstream",
  "anstyle",
@@ -432,9 +432,9 @@ checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
 
 [[package]]
 name = "errno"
-version = "0.3.10"
+version = "0.3.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
+checksum = "976dd42dc7e85965fe702eb8164f21f450704bdde31faefd6471dba214cb594e"
 dependencies = [
  "libc",
  "windows-sys",
@@ -455,9 +455,9 @@ checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
 
 [[package]]
 name = "flate2"
-version = "1.1.0"
+version = "1.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "11faaf5a5236997af9848be0bef4db95824b1d534ebc64d0f0c6cf3e67bd38dc"
+checksum = "7ced92e76e966ca2fd84c8f7aa01a4aea65b0eb6648d72f7c8f3e2764a67fece"
 dependencies = [
  "crc32fast",
  "miniz_oxide",
@@ -584,14 +584,15 @@ dependencies = [
 
 [[package]]
 name = "iana-time-zone"
-version = "0.1.61"
+version = "0.1.63"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "235e081f3925a06703c2d0117ea8b91f042756fd6e7a6e5d901e8ca1a996b220"
+checksum = "b0c919e5debc312ad217002b8048a17b7d83f80703865bbfcfebb0458b0b27d8"
 dependencies = [
  "android_system_properties",
  "core-foundation-sys",
  "iana-time-zone-haiku",
  "js-sys",
+ "log",
  "wasm-bindgen",
  "windows-core",
 ]
@@ -646,9 +647,9 @@ dependencies = [
 
 [[package]]
 name = "icu_locid_transform_data"
-version = "1.5.0"
+version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fdc8ff3388f852bede6b579ad4e978ab004f139284d7b28715f773507b946f6e"
+checksum = "7515e6d781098bf9f7205ab3fc7e9709d34554ae0b21ddbcb5febfa4bc7df11d"
 
 [[package]]
 name = "icu_normalizer"
@@ -670,9 +671,9 @@ dependencies = [
 
 [[package]]
 name = "icu_normalizer_data"
-version = "1.5.0"
+version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f8cafbf7aa791e9b22bec55a167906f9e1215fd475cd22adfcf660e03e989516"
+checksum = "c5e8338228bdc8ab83303f16b797e177953730f601a96c25d10cb3ab0daa0cb7"
 
 [[package]]
 name = "icu_properties"
@@ -691,9 +692,9 @@ dependencies = [
 
 [[package]]
 name = "icu_properties_data"
-version = "1.5.0"
+version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "67a8effbc3dd3e4ba1afa8ad918d5684b8868b3b26500753effea8d2eed19569"
+checksum = "85fb8799753b75aee8d2a21d7c14d9f38921b54b3dbda10f5a3c7a7b82dba5e2"
 
 [[package]]
 name = "icu_provider"
@@ -752,9 +753,9 @@ dependencies = [
 
 [[package]]
 name = "indexmap"
-version = "2.8.0"
+version = "2.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3954d50fe15b02142bf25d3b8bdadb634ec3948f103d04ffe3031bc8fe9d7058"
+checksum = "cea70ddb795996207ad57735b50c5982d8844f38ba9ee5f1aedcfb708a2aa11e"
 dependencies = [
  "equivalent",
  "hashbrown",
@@ -861,9 +862,9 @@ dependencies = [
 
 [[package]]
 name = "log"
-version = "0.4.26"
+version = "0.4.27"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "30bde2b3dc3671ae49d8e2e9f044c7c005836e7a023ee57cffa25ab82764bb9e"
+checksum = "13dc2df351e3202783a1fe0d44375f7295ffb4049267b0f3018346dc122a1d94"
 
 [[package]]
 name = "mac"
@@ -980,9 +981,9 @@ checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
 
 [[package]]
 name = "miniz_oxide"
-version = "0.8.5"
+version = "0.8.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e3e04debbb59698c15bacbb6d93584a8c0ca9cc3213cb423d31f760d8843ce5"
+checksum = "ff70ce3e48ae43fa075863cef62e8b43b71a4f2382229920e0df362592919430"
 dependencies = [
  "adler2",
 ]
@@ -1028,9 +1029,9 @@ dependencies = [
 
 [[package]]
 name = "once_cell"
-version = "1.21.1"
+version = "1.21.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d75b0bedcc4fe52caa0e03d9f1151a323e4aa5e2d78ba3580400cd3c9e2bc4bc"
+checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
 
 [[package]]
 name = "onig"
@@ -1103,9 +1104,9 @@ checksum = "e3148f5046208a5d56bcfc03053e3ca6334e51da8dfb19b6cdc8b306fae3283e"
 
 [[package]]
 name = "pest"
-version = "2.7.15"
+version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8b7cafe60d6cf8e62e1b9b2ea516a089c008945bb5a275416789e7db0bc199dc"
+checksum = "198db74531d58c70a361c42201efde7e2591e976d518caf7662a47dc5720e7b6"
 dependencies = [
  "memchr",
  "thiserror 2.0.12",
@@ -1114,9 +1115,9 @@ dependencies = [
 
 [[package]]
 name = "pest_derive"
-version = "2.7.15"
+version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "816518421cfc6887a0d62bf441b6ffb4536fcc926395a69e1a85852d4363f57e"
+checksum = "d725d9cfd79e87dccc9341a2ef39d1b6f6353d68c4b33c177febbe1a402c97c5"
 dependencies = [
  "pest",
  "pest_generator",
@@ -1124,9 +1125,9 @@ dependencies = [
 
 [[package]]
 name = "pest_generator"
-version = "2.7.15"
+version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7d1396fd3a870fc7838768d171b4616d5c91f6cc25e377b673d714567d99377b"
+checksum = "db7d01726be8ab66ab32f9df467ae8b1148906685bbe75c82d1e65d7f5b3f841"
 dependencies = [
  "pest",
  "pest_meta",
@@ -1137,9 +1138,9 @@ dependencies = [
 
 [[package]]
 name = "pest_meta"
-version = "2.7.15"
+version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e1e58089ea25d717bfd31fb534e4f3afcc2cc569c70de3e239778991ea3b7dea"
+checksum = "7f9f832470494906d1fca5329f8ab5791cc60beb230c74815dff541cbd2b5ca0"
 dependencies = [
  "once_cell",
  "pest",
@@ -1316,9 +1317,9 @@ checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
 
 [[package]]
 name = "redox_syscall"
-version = "0.5.10"
+version = "0.5.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b8c0c260b63a8219631167be35e6a988e9554dbd323f8bd08439c8ed1302bd1"
+checksum = "d2f103c6d277498fbceb16e84d317e2a400f160f46904d5f5410848c829511a3"
 dependencies = [
  "bitflags 2.9.0",
 ]
@@ -1366,9 +1367,9 @@ dependencies = [
 
 [[package]]
 name = "rustix"
-version = "1.0.3"
+version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e56a18552996ac8d29ecc3b190b4fdbb2d91ca4ec396de7bbffaf43f3d637e96"
+checksum = "d97817398dd4bb2e6da002002db259209759911da105da92bec29ccb12cf58bf"
 dependencies = [
  "bitflags 2.9.0",
  "errno",
@@ -1476,9 +1477,9 @@ checksum = "56199f7ddabf13fe5074ce809e7d3f42b42ae711800501b5b16ea82ad029c39d"
 
 [[package]]
 name = "smallvec"
-version = "1.14.0"
+version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7fcf8323ef1faaee30a44a340193b1ac6814fd9b7b4e88e9d4519a3e4abe1cfd"
+checksum = "8917285742e9f3e1683f0a9c4e6b57960b7314d0b08d30d1ecd426713ee2eee9"
 
 [[package]]
 name = "stable_deref_trait"
@@ -1488,9 +1489,9 @@ checksum = "a8f112729512f8e442d81f95a8a7ddf2b7c6b8a1a6f509a95864142b30cab2d3"
 
 [[package]]
 name = "string_cache"
-version = "0.8.8"
+version = "0.8.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "938d512196766101d333398efde81bc1f37b00cb42c2f8350e5df639f040bbbe"
+checksum = "bf776ba3fa74f83bf4b63c3dcbbf82173db2632ed8452cb2d891d33f459de70f"
 dependencies = [
  "new_debug_unreachable",
  "parking_lot",
@@ -1879,11 +1880,37 @@ checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
 [[package]]
 name = "windows-core"
-version = "0.52.0"
+version = "0.61.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "33ab640c8d7e35bf8ba19b884ba838ceb4fba93a4e8c65a9059d08afcfc683d9"
+checksum = "4763c1de310c86d75a878046489e2e5ba02c649d185f21c67d4cf8a56d098980"
 dependencies = [
- "windows-targets",
+ "windows-implement",
+ "windows-interface",
+ "windows-link",
+ "windows-result",
+ "windows-strings",
+]
+
+[[package]]
+name = "windows-implement"
+version = "0.60.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a47fddd13af08290e67f4acabf4b459f647552718f683a7b415d290ac744a836"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "windows-interface"
+version = "0.59.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bd9211b69f8dcdfa817bfd14bf1c97c9188afa36f4750130fcdf3f400eca9fa8"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
 ]
 
 [[package]]
@@ -1893,6 +1920,24 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "76840935b766e1b0a05c0066835fb9ec80071d4c09a16f6bd5f7e655e3c14c38"
 
 [[package]]
+name = "windows-result"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c64fd11a4fd95df68efcfee5f44a294fe71b8bc6a91993e2791938abcc712252"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-strings"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a2ba9642430ee452d5a7aa78d72907ebe8cfda358e8cb7918a2050581322f97"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
 name = "windows-sys"
 version = "0.59.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/src/tools/rustfmt/src/items.rs b/src/tools/rustfmt/src/items.rs
index 322af97d9dc..5c3be769f9e 100644
--- a/src/tools/rustfmt/src/items.rs
+++ b/src/tools/rustfmt/src/items.rs
@@ -2442,11 +2442,7 @@ pub(crate) fn span_hi_for_param(context: &RewriteContext<'_>, param: &ast::Param
 }
 
 pub(crate) fn is_named_param(param: &ast::Param) -> bool {
-    if let ast::PatKind::Ident(_, ident, _) = param.pat.kind {
-        ident.name != symbol::kw::Empty
-    } else {
-        true
-    }
+    !matches!(param.pat.kind, ast::PatKind::Missing)
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
diff --git a/src/tools/rustfmt/src/patterns.rs b/src/tools/rustfmt/src/patterns.rs
index 8dc94574503..cb3879f4be8 100644
--- a/src/tools/rustfmt/src/patterns.rs
+++ b/src/tools/rustfmt/src/patterns.rs
@@ -42,6 +42,7 @@ pub(crate) fn is_short_pattern(
 
 fn is_short_pattern_inner(context: &RewriteContext<'_>, pat: &ast::Pat) -> bool {
     match &pat.kind {
+        ast::PatKind::Missing => unreachable!(),
         ast::PatKind::Rest | ast::PatKind::Never | ast::PatKind::Wild | ast::PatKind::Err(_) => {
             true
         }
@@ -100,6 +101,7 @@ impl Rewrite for Pat {
 
     fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
         match self.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Or(ref pats) => {
                 let pat_strs = pats
                     .iter()
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 8f761d349cc..682ab4875a1 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -361,6 +361,7 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "regex-syntax",
     "rustc-demangle",
     "rustc-hash",
+    "rustc-literal-escaper",
     "rustc-rayon",
     "rustc-rayon-core",
     "rustc-stable-hash",
@@ -486,6 +487,7 @@ const PERMITTED_STDLIB_DEPENDENCIES: &[&str] = &[
     "rand_core",
     "rand_xorshift",
     "rustc-demangle",
+    "rustc-literal-escaper",
     "shlex",
     "syn",
     "unicode-ident",
diff --git a/tests/pretty/autodiff_forward.pp b/tests/pretty/autodiff_forward.pp
index 4b2fb6166ff..713b8f541ae 100644
--- a/tests/pretty/autodiff_forward.pp
+++ b/tests/pretty/autodiff_forward.pp
@@ -29,6 +29,8 @@ pub fn f1(x: &[f64], y: f64) -> f64 {
     // Make sure, that we add the None for the default return.
 
 
+    // We want to make sure that we can use the macro for functions defined inside of functions
+
     ::core::panicking::panic("not implemented")
 }
 #[rustc_autodiff(Forward, 1, Dual, Const, Dual)]
@@ -158,4 +160,25 @@ fn f8_1(x: &f32, bx_0: &f32) -> f32 {
     ::core::hint::black_box((bx_0,));
     ::core::hint::black_box(<f32>::default())
 }
+pub fn f9() {
+    #[rustc_autodiff]
+    #[inline(never)]
+    fn inner(x: f32) -> f32 { x * x }
+    #[rustc_autodiff(Forward, 1, Dual, Dual)]
+    #[inline(never)]
+    fn d_inner_2(x: f32, bx_0: f32) -> (f32, f32) {
+        unsafe { asm!("NOP", options(pure, nomem)); };
+        ::core::hint::black_box(inner(x));
+        ::core::hint::black_box((bx_0,));
+        ::core::hint::black_box(<(f32, f32)>::default())
+    }
+    #[rustc_autodiff(Forward, 1, Dual, DualOnly)]
+    #[inline(never)]
+    fn d_inner_1(x: f32, bx_0: f32) -> f32 {
+        unsafe { asm!("NOP", options(pure, nomem)); };
+        ::core::hint::black_box(inner(x));
+        ::core::hint::black_box((bx_0,));
+        ::core::hint::black_box(<f32>::default())
+    }
+}
 fn main() {}
diff --git a/tests/pretty/autodiff_forward.rs b/tests/pretty/autodiff_forward.rs
index a765738c2a8..5a0660a08e5 100644
--- a/tests/pretty/autodiff_forward.rs
+++ b/tests/pretty/autodiff_forward.rs
@@ -54,4 +54,13 @@ fn f8(x: &f32) -> f32 {
     unimplemented!()
 }
 
+// We want to make sure that we can use the macro for functions defined inside of functions
+pub fn f9() {
+    #[autodiff(d_inner_1, Forward, Dual, DualOnly)]
+    #[autodiff(d_inner_2, Forward, Dual, Dual)]
+    fn inner(x: f32) -> f32 {
+        x * x
+    }
+}
+
 fn main() {}
diff --git a/tests/ui/attributes/invalid-reprs.rs b/tests/ui/attributes/invalid-reprs.rs
new file mode 100644
index 00000000000..95ed14b5491
--- /dev/null
+++ b/tests/ui/attributes/invalid-reprs.rs
@@ -0,0 +1,6 @@
+fn main() {
+    let y = #[repr(uwu(4))]
+    //~^ ERROR attributes on expressions are experimental
+    //~| ERROR unrecognized representation hint
+    (&id(5)); //~ ERROR: cannot find function `id` in this scope
+}
diff --git a/tests/ui/attributes/invalid-reprs.stderr b/tests/ui/attributes/invalid-reprs.stderr
new file mode 100644
index 00000000000..415b969b244
--- /dev/null
+++ b/tests/ui/attributes/invalid-reprs.stderr
@@ -0,0 +1,33 @@
+error[E0658]: attributes on expressions are experimental
+  --> $DIR/invalid-reprs.rs:2:13
+   |
+LL |     let y = #[repr(uwu(4))]
+   |             ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
+   = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0425]: cannot find function `id` in this scope
+  --> $DIR/invalid-reprs.rs:5:7
+   |
+LL |     (&id(5));
+   |       ^^ not found in this scope
+   |
+help: consider importing this function
+   |
+LL + use std::process::id;
+   |
+
+error[E0552]: unrecognized representation hint
+  --> $DIR/invalid-reprs.rs:2:20
+   |
+LL |     let y = #[repr(uwu(4))]
+   |                    ^^^^^^
+   |
+   = help: valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0425, E0552, E0658.
+For more information about an error, try `rustc --explain E0425`.
diff --git a/tests/ui/macros/stringify.rs b/tests/ui/macros/stringify.rs
index 40033f546d3..3490d3efc59 100644
--- a/tests/ui/macros/stringify.rs
+++ b/tests/ui/macros/stringify.rs
@@ -515,6 +515,8 @@ fn test_meta() {
 
 #[test]
 fn test_pat() {
+    // PatKind::Missing: untestable in isolation.
+
     // PatKind::Wild
     c1!(pat, [ _ ], "_");
 
diff --git a/tests/ui/unpretty/expanded-exhaustive.rs b/tests/ui/unpretty/expanded-exhaustive.rs
index 31af323ecda..4d1f12e3490 100644
--- a/tests/ui/unpretty/expanded-exhaustive.rs
+++ b/tests/ui/unpretty/expanded-exhaustive.rs
@@ -574,6 +574,11 @@ mod items {
 }
 
 mod patterns {
+    /// PatKind::Missing
+    fn pat_missing() {
+        let _: fn(u32, T, &str);
+    }
+
     /// PatKind::Wild
     fn pat_wild() {
         let _;
diff --git a/tests/ui/unpretty/expanded-exhaustive.stdout b/tests/ui/unpretty/expanded-exhaustive.stdout
index 19ae66f7a07..d8da941a340 100644
--- a/tests/ui/unpretty/expanded-exhaustive.stdout
+++ b/tests/ui/unpretty/expanded-exhaustive.stdout
@@ -363,6 +363,7 @@ mod expressions {
 
 
 
+
         { builtin # offset_of(T, field) };
     }
     /// ExprKind::MacCall
@@ -517,6 +518,8 @@ mod items {
     }
 }
 mod patterns {
+    /// PatKind::Missing
+    fn pat_missing() { let _: fn(u32, T, &str); }
     /// PatKind::Wild
     fn pat_wild() { let _; }
     /// PatKind::Ident