Auto merge of #99210 - Dylan-DPC:rollup-879cp1t, r=Dylan-DPC

Rollup of 5 pull requests

Successful merges:

 - #98574 (Lower let-else in MIR)
 - #99011 (`UnsafeCell` blocks niches inside its nested type from being available outside)
 - #99030 (diagnostics: error messages when struct literals fail to parse)
 - #99155 (Keep unstable target features for asm feature checking)
 - #99199 (Refactor: remove an unnecessary `span_to_snippet`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

43 files changed, 480 insertions, 336 deletions

diff --git a/compiler/rustc_ast_lowering/src/block.rs b/compiler/rustc_ast_lowering/src/block.rs
index 9444fffc331..7cbfe143b4d 100644
--- a/compiler/rustc_ast_lowering/src/block.rs
+++ b/compiler/rustc_ast_lowering/src/block.rs
@@ -1,8 +1,8 @@
 use crate::{ImplTraitContext, ImplTraitPosition, LoweringContext};
-use rustc_ast::{AttrVec, Block, BlockCheckMode, Expr, Local, LocalKind, Stmt, StmtKind};
+use rustc_ast::{Block, BlockCheckMode, Local, LocalKind, Stmt, StmtKind};
 use rustc_hir as hir;
 use rustc_session::parse::feature_err;
-use rustc_span::{sym, DesugaringKind};
+use rustc_span::sym;
 
 use smallvec::SmallVec;
 
@@ -36,21 +36,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             match s.kind {
                 StmtKind::Local(ref local) => {
                     let hir_id = self.lower_node_id(s.id);
-                    match &local.kind {
-                        LocalKind::InitElse(init, els) => {
-                            let e = self.lower_let_else(hir_id, local, init, els, tail);
-                            expr = Some(e);
-                            // remaining statements are in let-else expression
-                            break;
-                        }
-                        _ => {
-                            let local = self.lower_local(local);
-                            self.alias_attrs(hir_id, local.hir_id);
-                            let kind = hir::StmtKind::Local(local);
-                            let span = self.lower_span(s.span);
-                            stmts.push(hir::Stmt { hir_id, kind, span });
-                        }
-                    }
+                    let local = self.lower_local(local);
+                    self.alias_attrs(hir_id, local.hir_id);
+                    let kind = hir::StmtKind::Local(local);
+                    let span = self.lower_span(s.span);
+                    stmts.push(hir::Stmt { hir_id, kind, span });
                 }
                 StmtKind::Item(ref it) => {
                     stmts.extend(self.lower_item_ref(it).into_iter().enumerate().map(
@@ -101,10 +91,24 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let init = l.kind.init().map(|init| self.lower_expr(init));
         let hir_id = self.lower_node_id(l.id);
         let pat = self.lower_pat(&l.pat);
+        let els = if let LocalKind::InitElse(_, els) = &l.kind {
+            if !self.tcx.features().let_else {
+                feature_err(
+                    &self.tcx.sess.parse_sess,
+                    sym::let_else,
+                    l.span,
+                    "`let...else` statements are unstable",
+                )
+                .emit();
+            }
+            Some(self.lower_block(els, false))
+        } else {
+            None
+        };
         let span = self.lower_span(l.span);
         let source = hir::LocalSource::Normal;
         self.lower_attrs(hir_id, &l.attrs);
-        self.arena.alloc(hir::Local { hir_id, ty, pat, init, span, source })
+        self.arena.alloc(hir::Local { hir_id, ty, pat, init, els, span, source })
     }
 
     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
@@ -115,59 +119,4 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
         }
     }
-
-    fn lower_let_else(
-        &mut self,
-        stmt_hir_id: hir::HirId,
-        local: &Local,
-        init: &Expr,
-        els: &Block,
-        tail: &[Stmt],
-    ) -> &'hir hir::Expr<'hir> {
-        let ty = local
-            .ty
-            .as_ref()
-            .map(|t| self.lower_ty(t, ImplTraitContext::Disallowed(ImplTraitPosition::Variable)));
-        let span = self.lower_span(local.span);
-        let span = self.mark_span_with_reason(DesugaringKind::LetElse, span, None);
-        let init = self.lower_expr(init);
-        let local_hir_id = self.lower_node_id(local.id);
-        self.lower_attrs(local_hir_id, &local.attrs);
-        let let_expr = {
-            let lex = self.arena.alloc(hir::Let {
-                hir_id: local_hir_id,
-                pat: self.lower_pat(&local.pat),
-                ty,
-                init,
-                span,
-            });
-            self.arena.alloc(self.expr(span, hir::ExprKind::Let(lex), AttrVec::new()))
-        };
-        let then_expr = {
-            let (stmts, expr) = self.lower_stmts(tail);
-            let block = self.block_all(span, stmts, expr);
-            self.arena.alloc(self.expr_block(block, AttrVec::new()))
-        };
-        let else_expr = {
-            let block = self.lower_block(els, false);
-            self.arena.alloc(self.expr_block(block, AttrVec::new()))
-        };
-        self.alias_attrs(let_expr.hir_id, local_hir_id);
-        self.alias_attrs(else_expr.hir_id, local_hir_id);
-        let if_expr = self.arena.alloc(hir::Expr {
-            hir_id: stmt_hir_id,
-            span,
-            kind: hir::ExprKind::If(let_expr, then_expr, Some(else_expr)),
-        });
-        if !self.tcx.features().let_else {
-            feature_err(
-                &self.tcx.sess.parse_sess,
-                sym::let_else,
-                local.span,
-                "`let...else` statements are unstable",
-            )
-            .emit();
-        }
-        if_expr
-    }
 }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index fdf60e60914..4da3096f7c3 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -2146,7 +2146,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             debug_assert!(!a.is_empty());
             self.attrs.insert(hir_id.local_id, a);
         }
-        let local = hir::Local { hir_id, init, pat, source, span: self.lower_span(span), ty: None };
+        let local = hir::Local {
+            hir_id,
+            init,
+            pat,
+            els: None,
+            source,
+            span: self.lower_span(span),
+            ty: None,
+        };
         self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
     }
 
diff --git a/compiler/rustc_attr/src/builtin.rs b/compiler/rustc_attr/src/builtin.rs
index ce7c0eb72cd..6673d75d99d 100644
--- a/compiler/rustc_attr/src/builtin.rs
+++ b/compiler/rustc_attr/src/builtin.rs
@@ -856,7 +856,6 @@ pub enum ReprAttr {
     ReprSimd,
     ReprTransparent,
     ReprAlign(u32),
-    ReprNoNiche,
 }
 
 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
@@ -904,7 +903,6 @@ pub fn parse_repr_attr(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
                     sym::packed => Some(ReprPacked(1)),
                     sym::simd => Some(ReprSimd),
                     sym::transparent => Some(ReprTransparent),
-                    sym::no_niche => Some(ReprNoNiche),
                     sym::align => {
                         let mut err = struct_span_err!(
                             diagnostic,
@@ -943,7 +941,7 @@ pub fn parse_repr_attr(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
                         Ok(literal) => acc.push(ReprPacked(literal)),
                         Err(message) => literal_error = Some(message),
                     };
-                } else if matches!(name, sym::C | sym::simd | sym::transparent | sym::no_niche)
+                } else if matches!(name, sym::C | sym::simd | sym::transparent)
                     || int_type_of_word(name).is_some()
                 {
                     recognised = true;
@@ -1001,7 +999,7 @@ pub fn parse_repr_attr(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
                     } else {
                         if matches!(
                             meta_item.name_or_empty(),
-                            sym::C | sym::simd | sym::transparent | sym::no_niche
+                            sym::C | sym::simd | sym::transparent
                         ) || int_type_of_word(meta_item.name_or_empty()).is_some()
                         {
                             recognised = true;
@@ -1039,7 +1037,7 @@ pub fn parse_repr_attr(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
                         .emit();
                     } else if matches!(
                         meta_item.name_or_empty(),
-                        sym::C | sym::simd | sym::transparent | sym::no_niche
+                        sym::C | sym::simd | sym::transparent
                     ) || int_type_of_word(meta_item.name_or_empty()).is_some()
                     {
                         recognised = true;
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 687ff0fb505..0ceb63477c8 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -1598,21 +1598,18 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             let return_ty = tcx.erase_regions(return_ty);
 
             // to avoid panics
-            if let Some(iter_trait) = tcx.get_diagnostic_item(sym::Iterator) {
-                if self
+            if let Some(iter_trait) = tcx.get_diagnostic_item(sym::Iterator)
+                && self
                     .infcx
                     .type_implements_trait(iter_trait, return_ty, ty_params, self.param_env)
                     .must_apply_modulo_regions()
-                {
-                    if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(return_span) {
-                        err.span_suggestion_hidden(
-                            return_span,
-                            "use `.collect()` to allocate the iterator",
-                            format!("{snippet}.collect::<Vec<_>>()"),
-                            Applicability::MaybeIncorrect,
-                        );
-                    }
-                }
+            {
+                err.span_suggestion_hidden(
+                    return_span.shrink_to_hi(),
+                    "use `.collect()` to allocate the iterator",
+                    ".collect::<Vec<_>>()",
+                    Applicability::MaybeIncorrect,
+                );
             }
         }
 
diff --git a/compiler/rustc_codegen_cranelift/src/lib.rs b/compiler/rustc_codegen_cranelift/src/lib.rs
index be2d3108c5f..3ed3453c6c7 100644
--- a/compiler/rustc_codegen_cranelift/src/lib.rs
+++ b/compiler/rustc_codegen_cranelift/src/lib.rs
@@ -167,7 +167,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
         }
     }
 
-    fn target_features(&self, _sess: &Session) -> Vec<rustc_span::Symbol> {
+    fn target_features(&self, _sess: &Session, _allow_unstable: bool) -> Vec<rustc_span::Symbol> {
         vec![]
     }
 
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
index 399830de84c..c21e0c5a35b 100644
--- a/compiler/rustc_codegen_gcc/src/lib.rs
+++ b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -140,8 +140,8 @@ impl CodegenBackend for GccCodegenBackend {
         )
     }
 
-    fn target_features(&self, sess: &Session) -> Vec<Symbol> {
-        target_features(sess)
+    fn target_features(&self, sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
+        target_features(sess, allow_unstable)
     }
 }
 
@@ -298,12 +298,12 @@ pub fn target_cpu(sess: &Session) -> &str {
     }
 }
 
-pub fn target_features(sess: &Session) -> Vec<Symbol> {
+pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
     supported_target_features(sess)
         .iter()
         .filter_map(
             |&(feature, gate)| {
-                if sess.is_nightly_build() || gate.is_none() { Some(feature) } else { None }
+                if sess.is_nightly_build() || allow_unstable || gate.is_none() { Some(feature) } else { None }
             },
         )
         .filter(|_feature| {
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index a7dd8e16d28..fb196ee9f5d 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -324,8 +324,8 @@ impl CodegenBackend for LlvmCodegenBackend {
         llvm_util::print_version();
     }
 
-    fn target_features(&self, sess: &Session) -> Vec<Symbol> {
-        target_features(sess)
+    fn target_features(&self, sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
+        target_features(sess, allow_unstable)
     }
 
     fn codegen_crate<'tcx>(
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index ce6c6e3215c..5b3b7db12b7 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -233,26 +233,29 @@ pub fn check_tied_features(
 
 // Used to generate cfg variables and apply features
 // Must express features in the way Rust understands them
-pub fn target_features(sess: &Session) -> Vec<Symbol> {
+pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
     let target_machine = create_informational_target_machine(sess);
-    let mut features: Vec<Symbol> =
-        supported_target_features(sess)
-            .iter()
-            .filter_map(|&(feature, gate)| {
-                if sess.is_nightly_build() || gate.is_none() { Some(feature) } else { None }
-            })
-            .filter(|feature| {
-                // check that all features in a given smallvec are enabled
-                for llvm_feature in to_llvm_features(sess, feature) {
-                    let cstr = SmallCStr::new(llvm_feature);
-                    if !unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
-                        return false;
-                    }
+    let mut features: Vec<Symbol> = supported_target_features(sess)
+        .iter()
+        .filter_map(|&(feature, gate)| {
+            if sess.is_nightly_build() || allow_unstable || gate.is_none() {
+                Some(feature)
+            } else {
+                None
+            }
+        })
+        .filter(|feature| {
+            // check that all features in a given smallvec are enabled
+            for llvm_feature in to_llvm_features(sess, feature) {
+                let cstr = SmallCStr::new(llvm_feature);
+                if !unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
+                    return false;
                 }
-                true
-            })
-            .map(|feature| Symbol::intern(feature))
-            .collect();
+            }
+            true
+        })
+        .map(|feature| Symbol::intern(feature))
+        .collect();
 
     // LLVM 14 changed the ABI for i128 arguments to __float/__fix builtins on Win64
     // (see https://reviews.llvm.org/D110413). This unstable target feature is intended for use
diff --git a/compiler/rustc_codegen_ssa/src/traits/backend.rs b/compiler/rustc_codegen_ssa/src/traits/backend.rs
index 1e53c73d1bb..779bd3ea278 100644
--- a/compiler/rustc_codegen_ssa/src/traits/backend.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/backend.rs
@@ -59,7 +59,7 @@ impl<'tcx, T> Backend<'tcx> for T where
 pub trait CodegenBackend {
     fn init(&self, _sess: &Session) {}
     fn print(&self, _req: PrintRequest, _sess: &Session) {}
-    fn target_features(&self, _sess: &Session) -> Vec<Symbol> {
+    fn target_features(&self, _sess: &Session, _allow_unstable: bool) -> Vec<Symbol> {
         vec![]
     }
     fn print_passes(&self) {}
diff --git a/compiler/rustc_const_eval/src/interpret/intern.rs b/compiler/rustc_const_eval/src/interpret/intern.rs
index 9dfdafcb38e..7616e7a63d1 100644
--- a/compiler/rustc_const_eval/src/interpret/intern.rs
+++ b/compiler/rustc_const_eval/src/interpret/intern.rs
@@ -217,7 +217,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: CompileTimeMachine<'mir, 'tcx, const_eval::Memory
         }
 
         if let Some(def) = mplace.layout.ty.ty_adt_def() {
-            if Some(def.did()) == self.ecx.tcx.lang_items().unsafe_cell_type() {
+            if def.is_unsafe_cell() {
                 // We are crossing over an `UnsafeCell`, we can mutate again. This means that
                 // References we encounter inside here are interned as pointing to mutable
                 // allocations.
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index 5114ce5d452..53bc2cc8a69 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -821,7 +821,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
         // Special check preventing `UnsafeCell` in the inner part of constants
         if let Some(def) = op.layout.ty.ty_adt_def() {
             if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { inner: true, .. }))
-                && Some(def.did()) == self.ecx.tcx.lang_items().unsafe_cell_type()
+                && def.is_unsafe_cell()
             {
                 throw_validation_failure!(self.path, { "`UnsafeCell` in a `const`" });
             }
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
index 9941afe5a12..29464cf8c4e 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -96,13 +96,13 @@ impl Qualif for HasMutInterior {
     }
 
     fn in_adt_inherently<'tcx>(
-        cx: &ConstCx<'_, 'tcx>,
+        _cx: &ConstCx<'_, 'tcx>,
         adt: AdtDef<'tcx>,
         _: SubstsRef<'tcx>,
     ) -> bool {
         // Exactly one type, `UnsafeCell`, has the `HasMutInterior` qualif inherently.
         // It arises structurally for all other types.
-        Some(adt.did()) == cx.tcx.lang_items().unsafe_cell_type()
+        adt.is_unsafe_cell()
     }
 }
 
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index b54f0ef361a..117bdad971a 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -156,9 +156,6 @@ declare_features! (
     (active, intrinsics, "1.0.0", None, None),
     /// Allows using `#[lang = ".."]` attribute for linking items to special compiler logic.
     (active, lang_items, "1.0.0", None, None),
-    /// Allows `#[repr(no_niche)]` (an implementation detail of `rustc`,
-    /// it is not on path for eventual stabilization).
-    (active, no_niche, "1.42.0", None, None),
     /// Allows using `#[omit_gdb_pretty_printer_section]`.
     (active, omit_gdb_pretty_printer_section, "1.5.0", None, None),
     /// Allows using `#[prelude_import]` on glob `use` items.
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 04f585df34c..ed874ae829b 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1316,6 +1316,8 @@ pub struct Local<'hir> {
     pub ty: Option<&'hir Ty<'hir>>,
     /// Initializer expression to set the value, if any.
     pub init: Option<&'hir Expr<'hir>>,
+    /// Else block for a `let...else` binding.
+    pub els: Option<&'hir Block<'hir>>,
     pub hir_id: HirId,
     pub span: Span,
     /// Can be `ForLoopDesugar` if the `let` statement is part of a `for` loop
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 531d9f14040..b5d9769c578 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -472,6 +472,9 @@ pub fn walk_local<'v, V: Visitor<'v>>(visitor: &mut V, local: &'v Local<'v>) {
     walk_list!(visitor, visit_expr, &local.init);
     visitor.visit_id(local.hir_id);
     visitor.visit_pat(&local.pat);
+    if let Some(els) = local.els {
+        visitor.visit_block(els);
+    }
     walk_list!(visitor, visit_ty, &local.ty);
 }
 
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 50acb0270b0..e3c97ec357e 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -883,7 +883,12 @@ impl<'a> State<'a> {
         self.ann.post(self, AnnNode::SubItem(ii.hir_id()))
     }
 
-    pub fn print_local(&mut self, init: Option<&hir::Expr<'_>>, decl: impl Fn(&mut Self)) {
+    pub fn print_local(
+        &mut self,
+        init: Option<&hir::Expr<'_>>,
+        els: Option<&hir::Block<'_>>,
+        decl: impl Fn(&mut Self),
+    ) {
         self.space_if_not_bol();
         self.ibox(INDENT_UNIT);
         self.word_nbsp("let");
@@ -897,6 +902,13 @@ impl<'a> State<'a> {
             self.word_space("=");
             self.print_expr(init);
         }
+
+        if let Some(els) = els {
+            self.nbsp();
+            self.word_space("else");
+            self.print_block(els);
+        }
+
         self.end()
     }
 
@@ -904,7 +916,7 @@ impl<'a> State<'a> {
         self.maybe_print_comment(st.span.lo());
         match st.kind {
             hir::StmtKind::Local(loc) => {
-                self.print_local(loc.init, |this| this.print_local_decl(loc));
+                self.print_local(loc.init, loc.els, |this| this.print_local_decl(loc));
             }
             hir::StmtKind::Item(item) => self.ann.nested(self, Nested::Item(item)),
             hir::StmtKind::Expr(expr) => {
@@ -1404,7 +1416,7 @@ impl<'a> State<'a> {
 
                 // Print `let _t = $init;`:
                 let temp = Ident::from_str("_t");
-                self.print_local(Some(init), |this| this.print_ident(temp));
+                self.print_local(Some(init), None, |this| this.print_ident(temp));
                 self.word(";");
 
                 // Print `_t`:
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 8796ad5a33c..f4b51b5a442 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -48,7 +48,10 @@ pub fn add_configuration(
 ) {
     let tf = sym::target_feature;
 
-    let target_features = codegen_backend.target_features(sess);
+    let unstable_target_features = codegen_backend.target_features(sess, true);
+    sess.unstable_target_features.extend(unstable_target_features.iter().cloned());
+
+    let target_features = codegen_backend.target_features(sess, false);
     sess.target_features.extend(target_features.iter().cloned());
 
     cfg.extend(target_features.into_iter().map(|feat| (tf, Some(feat))));
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index be4843c7ff1..aca481df2e1 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -703,9 +703,8 @@ fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKi
                 return true;
             }
 
-            // Types with a `#[repr(no_niche)]` attribute have their niche hidden.
-            // The attribute is used by the UnsafeCell for example (the only use so far).
-            if def.repr().hide_niche() {
+            // `UnsafeCell` has its niche hidden.
+            if def.is_unsafe_cell() {
                 return false;
             }
 
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 3fe6394ad7e..3e5f6bb8f0b 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -182,6 +182,9 @@ pub enum StmtKind<'tcx> {
         /// `let pat: ty = <INIT>`
         initializer: Option<ExprId>,
 
+        /// `let pat: ty = <INIT> else { <ELSE> }
+        else_block: Option<Block>,
+
         /// The lint level for this `let` statement.
         lint_level: LintLevel,
     },
diff --git a/compiler/rustc_middle/src/thir/visit.rs b/compiler/rustc_middle/src/thir/visit.rs
index c8d09875c28..97249fdd175 100644
--- a/compiler/rustc_middle/src/thir/visit.rs
+++ b/compiler/rustc_middle/src/thir/visit.rs
@@ -167,11 +167,15 @@ pub fn walk_stmt<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, stmt: &Stm
             init_scope: _,
             ref pattern,
             lint_level: _,
+            else_block,
         } => {
             if let Some(init) = initializer {
                 visitor.visit_expr(&visitor.thir()[*init]);
             }
             visitor.visit_pat(pattern);
+            if let Some(block) = else_block {
+                visitor.visit_block(block)
+            }
         }
     }
 }
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index 4cac7670735..809406aff18 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -52,6 +52,8 @@ bitflags! {
         /// Indicates whether the variant list of this ADT is `#[non_exhaustive]`.
         /// (i.e., this flag is never set unless this ADT is an enum).
         const IS_VARIANT_LIST_NON_EXHAUSTIVE = 1 << 8;
+        /// Indicates whether the type is `UnsafeCell`.
+        const IS_UNSAFE_CELL              = 1 << 9;
     }
 }
 
@@ -247,6 +249,9 @@ impl AdtDefData {
         if Some(did) == tcx.lang_items().manually_drop() {
             flags |= AdtFlags::IS_MANUALLY_DROP;
         }
+        if Some(did) == tcx.lang_items().unsafe_cell_type() {
+            flags |= AdtFlags::IS_UNSAFE_CELL;
+        }
 
         AdtDefData { did, variants, flags, repr }
     }
@@ -333,6 +338,12 @@ impl<'tcx> AdtDef<'tcx> {
         self.flags().contains(AdtFlags::IS_BOX)
     }
 
+    /// Returns `true` if this is UnsafeCell<T>.
+    #[inline]
+    pub fn is_unsafe_cell(self) -> bool {
+        self.flags().contains(AdtFlags::IS_UNSAFE_CELL)
+    }
+
     /// Returns `true` if this is `ManuallyDrop<T>`.
     #[inline]
     pub fn is_manually_drop(self) -> bool {
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index f87b6e4212d..1ed41db099c 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -542,14 +542,12 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
             debug!("univariant offset: {:?} field: {:#?}", offset, field);
             offsets[i as usize] = offset;
 
-            if !repr.hide_niche() {
-                if let Some(mut niche) = field.largest_niche {
-                    let available = niche.available(dl);
-                    if available > largest_niche_available {
-                        largest_niche_available = available;
-                        niche.offset += offset;
-                        largest_niche = Some(niche);
-                    }
+            if let Some(mut niche) = field.largest_niche {
+                let available = niche.available(dl);
+                if available > largest_niche_available {
+                    largest_niche_available = available;
+                    niche.offset += offset;
+                    largest_niche = Some(niche);
                 }
             }
 
@@ -1078,6 +1076,29 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
 
                     let mut st = self.univariant_uninterned(ty, &variants[v], &def.repr(), kind)?;
                     st.variants = Variants::Single { index: v };
+
+                    if def.is_unsafe_cell() {
+                        let hide_niches = |scalar: &mut _| match scalar {
+                            Scalar::Initialized { value, valid_range } => {
+                                *valid_range = WrappingRange::full(value.size(dl))
+                            }
+                            // Already doesn't have any niches
+                            Scalar::Union { .. } => {}
+                        };
+                        match &mut st.abi {
+                            Abi::Uninhabited => {}
+                            Abi::Scalar(scalar) => hide_niches(scalar),
+                            Abi::ScalarPair(a, b) => {
+                                hide_niches(a);
+                                hide_niches(b);
+                            }
+                            Abi::Vector { element, count: _ } => hide_niches(element),
+                            Abi::Aggregate { sized: _ } => {}
+                        }
+                        st.largest_niche = None;
+                        return Ok(tcx.intern_layout(st));
+                    }
+
                     let (start, end) = self.tcx.layout_scalar_valid_range(def.did());
                     match st.abi {
                         Abi::Scalar(ref mut scalar) | Abi::ScalarPair(ref mut scalar, _) => {
@@ -1106,11 +1127,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                             }
 
                             // Update `largest_niche` if we have introduced a larger niche.
-                            let niche = if def.repr().hide_niche() {
-                                None
-                            } else {
-                                Niche::from_scalar(dl, Size::ZERO, *scalar)
-                            };
+                            let niche = Niche::from_scalar(dl, Size::ZERO, *scalar);
                             if let Some(niche) = niche {
                                 match st.largest_niche {
                                     Some(largest_niche) => {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index f15108fb750..c2c7b3df844 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1720,11 +1720,9 @@ bitflags! {
         const IS_TRANSPARENT     = 1 << 2;
         // Internal only for now. If true, don't reorder fields.
         const IS_LINEAR          = 1 << 3;
-        // If true, don't expose any niche to type's context.
-        const HIDE_NICHE         = 1 << 4;
         // If true, the type's layout can be randomized using
         // the seed stored in `ReprOptions.layout_seed`
-        const RANDOMIZE_LAYOUT   = 1 << 5;
+        const RANDOMIZE_LAYOUT   = 1 << 4;
         // Any of these flags being set prevent field reordering optimisation.
         const IS_UNOPTIMISABLE   = ReprFlags::IS_C.bits
                                  | ReprFlags::IS_SIMD.bits
@@ -1781,7 +1779,6 @@ impl ReprOptions {
                         ReprFlags::empty()
                     }
                     attr::ReprTransparent => ReprFlags::IS_TRANSPARENT,
-                    attr::ReprNoNiche => ReprFlags::HIDE_NICHE,
                     attr::ReprSimd => ReprFlags::IS_SIMD,
                     attr::ReprInt(i) => {
                         size = Some(i);
@@ -1834,11 +1831,6 @@ impl ReprOptions {
         self.flags.contains(ReprFlags::IS_LINEAR)
     }
 
-    #[inline]
-    pub fn hide_niche(&self) -> bool {
-        self.flags.contains(ReprFlags::HIDE_NICHE)
-    }
-
     /// Returns the discriminant type, given these `repr` options.
     /// This must only be called on enums!
     pub fn discr_type(&self) -> attr::IntType {
diff --git a/compiler/rustc_mir_build/src/build/block.rs b/compiler/rustc_mir_build/src/build/block.rs
index a83328c0cab..cb8be51a085 100644
--- a/compiler/rustc_mir_build/src/build/block.rs
+++ b/compiler/rustc_mir_build/src/build/block.rs
@@ -99,6 +99,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     ref pattern,
                     initializer,
                     lint_level,
+                    else_block,
                 } => {
                     let ignores_expr_result = matches!(*pattern.kind, PatKind::Wild);
                     this.block_context.push(BlockFrame::Statement { ignores_expr_result });
@@ -124,18 +125,30 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                 |this| {
                                     let scope = (*init_scope, source_info);
                                     this.in_scope(scope, *lint_level, |this| {
-                                        this.declare_bindings(
-                                            visibility_scope,
-                                            remainder_span,
-                                            pattern,
-                                            ArmHasGuard(false),
-                                            Some((None, initializer_span)),
-                                        );
-                                        this.expr_into_pattern(block, pattern.clone(), init)
+                                        if let Some(else_block) = else_block {
+                                            this.ast_let_else(
+                                                block,
+                                                init,
+                                                initializer_span,
+                                                else_block,
+                                                visibility_scope,
+                                                remainder_span,
+                                                pattern,
+                                            )
+                                        } else {
+                                            this.declare_bindings(
+                                                visibility_scope,
+                                                remainder_span,
+                                                pattern,
+                                                ArmHasGuard(false),
+                                                Some((None, initializer_span)),
+                                            );
+                                            this.expr_into_pattern(block, pattern.clone(), init) // irrefutable pattern
+                                        }
                                     })
-                                }
+                                },
                             )
-                        );
+                        )
                     } else {
                         let scope = (*init_scope, source_info);
                         unpack!(this.in_scope(scope, *lint_level, |this| {
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 1628f1a4b85..7067a48b783 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -1615,7 +1615,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // those N possible outcomes, create a (initially empty)
         // vector of candidates. Those are the candidates that still
         // apply if the test has that particular outcome.
-        debug!("match_candidates: test={:?} match_pair={:?}", test, match_pair);
+        debug!("test_candidates: test={:?} match_pair={:?}", test, match_pair);
         let mut target_candidates: Vec<Vec<&mut Candidate<'pat, 'tcx>>> = vec![];
         target_candidates.resize_with(test.targets(), Default::default);
 
@@ -1635,8 +1635,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
         // at least the first candidate ought to be tested
         assert!(total_candidate_count > candidates.len());
-        debug!("tested_candidates: {}", total_candidate_count - candidates.len());
-        debug!("untested_candidates: {}", candidates.len());
+        debug!("test_candidates: tested_candidates: {}", total_candidate_count - candidates.len());
+        debug!("test_candidates: untested_candidates: {}", candidates.len());
 
         // HACK(matthewjasper) This is a closure so that we can let the test
         // create its blocks before the rest of the match. This currently
@@ -2274,4 +2274,75 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         debug!("declare_binding: vars={:?}", locals);
         self.var_indices.insert(var_id, locals);
     }
+
+    pub(crate) fn ast_let_else(
+        &mut self,
+        mut block: BasicBlock,
+        init: &Expr<'tcx>,
+        initializer_span: Span,
+        else_block: &Block,
+        visibility_scope: Option<SourceScope>,
+        remainder_span: Span,
+        pattern: &Pat<'tcx>,
+    ) -> BlockAnd<()> {
+        let scrutinee = unpack!(block = self.lower_scrutinee(block, init, initializer_span));
+        let pat = Pat { ty: init.ty, span: else_block.span, kind: Box::new(PatKind::Wild) };
+        let mut wildcard = Candidate::new(scrutinee.clone(), &pat, false);
+        self.declare_bindings(
+            visibility_scope,
+            remainder_span,
+            pattern,
+            ArmHasGuard(false),
+            Some((None, initializer_span)),
+        );
+        let mut candidate = Candidate::new(scrutinee.clone(), pattern, false);
+        let fake_borrow_temps = self.lower_match_tree(
+            block,
+            initializer_span,
+            pattern.span,
+            false,
+            &mut [&mut candidate, &mut wildcard],
+        );
+        // This block is for the matching case
+        let matching = self.bind_pattern(
+            self.source_info(pattern.span),
+            candidate,
+            None,
+            &fake_borrow_temps,
+            initializer_span,
+            None,
+            None,
+            None,
+        );
+        // This block is for the failure case
+        let failure = self.bind_pattern(
+            self.source_info(else_block.span),
+            wildcard,
+            None,
+            &fake_borrow_temps,
+            initializer_span,
+            None,
+            None,
+            None,
+        );
+        // This place is not really used because this destination place
+        // should never be used to take values at the end of the failure
+        // block.
+        let dummy_place = Place { local: RETURN_PLACE, projection: ty::List::empty() };
+        let failure_block;
+        unpack!(
+            failure_block = self.ast_block(
+                dummy_place,
+                failure,
+                else_block,
+                self.source_info(else_block.span),
+            )
+        );
+        self.cfg.terminate(
+            failure_block,
+            self.source_info(else_block.span),
+            TerminatorKind::Unreachable,
+        );
+        matching.unit()
+    }
 }
diff --git a/compiler/rustc_mir_build/src/thir/cx/block.rs b/compiler/rustc_mir_build/src/thir/cx/block.rs
index 59750d5d0b8..dccaa61ed89 100644
--- a/compiler/rustc_mir_build/src/thir/cx/block.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/block.rs
@@ -74,6 +74,8 @@ impl<'tcx> Cx<'tcx> {
                             )),
                         };
 
+                        let else_block = local.els.map(|els| self.mirror_block(els));
+
                         let mut pattern = self.pattern_from_hir(local.pat);
                         debug!(?pattern);
 
@@ -110,6 +112,7 @@ impl<'tcx> Cx<'tcx> {
                                 },
                                 pattern,
                                 initializer: local.init.map(|init| self.mirror_expr(init)),
+                                else_block,
                                 lint_level: LintLevel::Explicit(local.hir_id),
                             },
                             opt_destruction_scope: opt_dxn_ext,
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index 75fd156ebfd..5bd1fad0bcb 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -21,7 +21,7 @@ use rustc_session::lint::builtin::{
 };
 use rustc_session::Session;
 use rustc_span::source_map::Spanned;
-use rustc_span::{BytePos, DesugaringKind, ExpnKind, Span};
+use rustc_span::{BytePos, Span};
 
 pub(crate) fn check_match(tcx: TyCtxt<'_>, def_id: DefId) {
     let body_id = match def_id.as_local() {
@@ -77,6 +77,10 @@ impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, '_, 'tcx> {
 
     fn visit_local(&mut self, loc: &'tcx hir::Local<'tcx>) {
         intravisit::walk_local(self, loc);
+        let els = loc.els;
+        if let Some(init) = loc.init && els.is_some() {
+            self.check_let(&loc.pat, init, loc.span);
+        }
 
         let (msg, sp) = match loc.source {
             hir::LocalSource::Normal => ("local binding", Some(loc.span)),
@@ -84,7 +88,9 @@ impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, '_, 'tcx> {
             hir::LocalSource::AwaitDesugar => ("`await` future binding", None),
             hir::LocalSource::AssignDesugar(_) => ("destructuring assignment binding", None),
         };
-        self.check_irrefutable(&loc.pat, msg, sp);
+        if els.is_none() {
+            self.check_irrefutable(&loc.pat, msg, sp);
+        }
     }
 
     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
@@ -1125,17 +1131,16 @@ fn let_source_parent(tcx: TyCtxt<'_>, parent: HirId, pat_id: Option<HirId>) -> L
         }) if Some(*hir_id) == pat_id => {
             return LetSource::IfLetGuard;
         }
-        hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Let(..), span, .. }) => {
-            let expn_data = span.ctxt().outer_expn_data();
-            if let ExpnKind::Desugaring(DesugaringKind::LetElse) = expn_data.kind {
-                return LetSource::LetElse(expn_data.call_site);
-            }
-        }
         _ => {}
     }
 
     let parent_parent = hir.get_parent_node(parent);
     let parent_parent_node = hir.get(parent_parent);
+    if let hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(_), span, .. }) =
+        parent_parent_node
+    {
+        return LetSource::LetElse(*span);
+    }
 
     let parent_parent_parent = hir.get_parent_node(parent_parent);
     let parent_parent_parent_parent = hir.get_parent_node(parent_parent_parent);
diff --git a/compiler/rustc_mir_transform/src/remove_uninit_drops.rs b/compiler/rustc_mir_transform/src/remove_uninit_drops.rs
index efa45883eab..c48aa9a90ef 100644
--- a/compiler/rustc_mir_transform/src/remove_uninit_drops.rs
+++ b/compiler/rustc_mir_transform/src/remove_uninit_drops.rs
@@ -102,7 +102,7 @@ fn is_needs_drop_and_init<'tcx>(
     let field_needs_drop_and_init = |(f, f_ty, mpi)| {
         let child = move_path_children_matching(move_data, mpi, |x| x.is_field_to(f));
         let Some(mpi) = child else {
-            return f_ty.needs_drop(tcx, param_env);
+            return Ty::needs_drop(f_ty, tcx, param_env);
         };
 
         is_needs_drop_and_init(tcx, param_env, maybe_inits, move_data, f_ty, mpi)
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index f9387e29262..0d9c57908c1 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -3028,6 +3028,11 @@ impl<'a> Parser<'a> {
                 }
             };
 
+            let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
+            // A shorthand field can be turned into a full field with `:`.
+            // We should point this out.
+            self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
+
             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
                 Ok(_) => {
                     if let Some(f) = parsed_field.or(recovery_field) {
@@ -3048,6 +3053,19 @@ impl<'a> Parser<'a> {
                                 ",",
                                 Applicability::MachineApplicable,
                             );
+                        } else if is_shorthand
+                            && (AssocOp::from_token(&self.token).is_some()
+                                || matches!(&self.token.kind, token::OpenDelim(_))
+                                || self.token.kind == token::Dot)
+                        {
+                            // Looks like they tried to write a shorthand, complex expression.
+                            let ident = parsed_field.expect("is_shorthand implies Some").ident;
+                            e.span_suggestion(
+                                ident.span.shrink_to_lo(),
+                                "try naming a field",
+                                &format!("{ident}: "),
+                                Applicability::HasPlaceholders,
+                            );
                         }
                     }
                     if !recover {
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index d0723c68a77..20d03d797fe 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -1808,21 +1808,6 @@ impl CheckAttrVisitor<'_> {
                         _ => ("a", "struct, enum, or union"),
                     }
                 }
-                sym::no_niche => {
-                    if !self.tcx.features().enabled(sym::no_niche) {
-                        feature_err(
-                            &self.tcx.sess.parse_sess,
-                            sym::no_niche,
-                            hint.span(),
-                            "the attribute `repr(no_niche)` is currently unstable",
-                        )
-                        .emit();
-                    }
-                    match target {
-                        Target::Struct | Target::Enum => continue,
-                        _ => ("a", "struct or enum"),
-                    }
-                }
                 sym::i8
                 | sym::u8
                 | sym::i16
@@ -1870,10 +1855,8 @@ impl CheckAttrVisitor<'_> {
         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
         let hint_spans = hints.iter().map(|hint| hint.span());
 
-        // Error on repr(transparent, <anything else apart from no_niche>).
-        let non_no_niche = |hint: &&NestedMetaItem| hint.name_or_empty() != sym::no_niche;
-        let non_no_niche_count = hints.iter().filter(non_no_niche).count();
-        if is_transparent && non_no_niche_count > 1 {
+        // Error on repr(transparent, <anything else>).
+        if is_transparent && hints.len() > 1 {
             let hint_spans: Vec<_> = hint_spans.clone().collect();
             struct_span_err!(
                 self.tcx.sess,
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs
index 0070c0699a4..eed3e1579a2 100644
--- a/compiler/rustc_passes/src/liveness.rs
+++ b/compiler/rustc_passes/src/liveness.rs
@@ -278,7 +278,7 @@ impl<'tcx> IrMaps<'tcx> {
                     pats.extend(inner_pat.iter());
                 }
                 Struct(_, fields, _) => {
-                    let (short, not_short): (Vec<&_>, Vec<&_>) =
+                    let (short, not_short): (Vec<_>, _) =
                         fields.iter().partition(|f| f.is_shorthand);
                     shorthand_field_ids.extend(short.iter().map(|f| f.pat.hir_id));
                     pats.extend(not_short.iter().map(|f| f.pat));
@@ -298,7 +298,7 @@ impl<'tcx> IrMaps<'tcx> {
             }
         }
 
-        return shorthand_field_ids;
+        shorthand_field_ids
     }
 
     fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
@@ -368,6 +368,9 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
 
     fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
         self.add_from_pat(&local.pat);
+        if local.els.is_some() {
+            self.add_live_node_for_node(local.hir_id, ExprNode(local.span, local.hir_id));
+        }
         intravisit::walk_local(self, local);
     }
 
@@ -800,8 +803,40 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 // initialization, which is mildly more complex than checking
                 // once at the func header but otherwise equivalent.
 
-                let succ = self.propagate_through_opt_expr(local.init, succ);
-                self.define_bindings_in_pat(&local.pat, succ)
+                if let Some(els) = local.els {
+                    // Eventually, `let pat: ty = init else { els };` is mostly equivalent to
+                    // `let (bindings, ...) = match init { pat => (bindings, ...), _ => els };`
+                    // except that extended lifetime applies at the `init` location.
+                    //
+                    //       (e)
+                    //        |
+                    //        v
+                    //      (expr)
+                    //      /   \
+                    //     |     |
+                    //     v     v
+                    // bindings  els
+                    //     |
+                    //     v
+                    // ( succ )
+                    //
+                    if let Some(init) = local.init {
+                        let else_ln = self.propagate_through_block(els, succ);
+                        let ln = self.live_node(local.hir_id, local.span);
+                        self.init_from_succ(ln, succ);
+                        self.merge_from_succ(ln, else_ln);
+                        let succ = self.propagate_through_expr(init, ln);
+                        self.define_bindings_in_pat(&local.pat, succ)
+                    } else {
+                        span_bug!(
+                            stmt.span,
+                            "variable is uninitialized but an unexpected else branch is found"
+                        )
+                    }
+                } else {
+                    let succ = self.propagate_through_opt_expr(local.init, succ);
+                    self.define_bindings_in_pat(&local.pat, succ)
+                }
             }
             hir::StmtKind::Item(..) => succ,
             hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
@@ -1121,7 +1156,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         //     (rvalue)          ||       (rvalue)
         //         |             ||           |
         //         v             ||           v
-        // (write of place)     ||   (place components)
+        // (write of place)      ||   (place components)
         //         |             ||           |
         //         v             ||           v
         //      (succ)           ||        (succ)
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 2851b08cd93..a820f700869 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -508,7 +508,7 @@ impl<'a> Resolver<'a> {
                     E0401,
                     "can't use generic parameters from outer function",
                 );
-                err.span_label(span, "use of generic parameter from outer function".to_string());
+                err.span_label(span, "use of generic parameter from outer function");
 
                 let sm = self.session.source_map();
                 match outer_res {
@@ -990,7 +990,7 @@ impl<'a> Resolver<'a> {
                     E0735,
                     "generic parameters cannot use `Self` in their defaults"
                 );
-                err.span_label(span, "`Self` in generic parameter default".to_string());
+                err.span_label(span, "`Self` in generic parameter default");
                 err
             }
             ResolutionError::UnreachableLabel { name, definition_span, suggestion } => {
diff --git a/compiler/rustc_save_analysis/src/dump_visitor.rs b/compiler/rustc_save_analysis/src/dump_visitor.rs
index 6eb2f2d929d..a4175f4c5f3 100644
--- a/compiler/rustc_save_analysis/src/dump_visitor.rs
+++ b/compiler/rustc_save_analysis/src/dump_visitor.rs
@@ -82,14 +82,7 @@ impl<'tcx> DumpVisitor<'tcx> {
     pub fn new(save_ctxt: SaveContext<'tcx>) -> DumpVisitor<'tcx> {
         let span_utils = SpanUtils::new(&save_ctxt.tcx.sess);
         let dumper = Dumper::new(save_ctxt.config.clone());
-        DumpVisitor {
-            tcx: save_ctxt.tcx,
-            save_ctxt,
-            dumper,
-            span: span_utils,
-            // mac_defs: FxHashSet::default(),
-            // macro_calls: FxHashSet::default(),
-        }
+        DumpVisitor { tcx: save_ctxt.tcx, save_ctxt, dumper, span: span_utils }
     }
 
     pub fn analysis(&self) -> &rls_data::Analysis {
@@ -1425,9 +1418,10 @@ impl<'tcx> Visitor<'tcx> for DumpVisitor<'tcx> {
         self.process_macro_use(l.span);
         self.process_var_decl(&l.pat);
 
-        // Just walk the initializer and type (don't want to walk the pattern again).
+        // Just walk the initializer, the else branch and type (don't want to walk the pattern again).
         walk_list!(self, visit_ty, &l.ty);
         walk_list!(self, visit_expr, &l.init);
+        walk_list!(self, visit_block, l.els);
     }
 
     fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 1cccef2f64f..16f4a099d80 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -194,6 +194,9 @@ pub struct Session {
 
     /// Set of enabled features for the current target.
     pub target_features: FxHashSet<Symbol>,
+
+    /// Set of enabled features for the current target, including unstable ones.
+    pub unstable_target_features: FxHashSet<Symbol>,
 }
 
 pub struct PerfStats {
@@ -1390,6 +1393,7 @@ pub fn build_session(
         miri_unleashed_features: Lock::new(Default::default()),
         asm_arch,
         target_features: FxHashSet::default(),
+        unstable_target_features: FxHashSet::default(),
     };
 
     validate_commandline_args_with_session_available(&sess);
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index 3df4dfb74b3..29879c48b04 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -1141,7 +1141,6 @@ pub enum DesugaringKind {
     Async,
     Await,
     ForLoop,
-    LetElse,
     WhileLoop,
 }
 
@@ -1157,7 +1156,6 @@ impl DesugaringKind {
             DesugaringKind::YeetExpr => "`do yeet` expression",
             DesugaringKind::OpaqueTy => "`impl Trait`",
             DesugaringKind::ForLoop => "`for` loop",
-            DesugaringKind::LetElse => "`let...else`",
             DesugaringKind::WhileLoop => "`while` loop",
         }
     }
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 9b6967621f1..99912b491cb 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -980,7 +980,6 @@ symbols! {
         no_link,
         no_main,
         no_mangle,
-        no_niche,
         no_sanitize,
         no_stack_check,
         no_start,
@@ -1153,7 +1152,6 @@ symbols! {
         repr128,
         repr_align,
         repr_align_enum,
-        repr_no_niche,
         repr_packed,
         repr_simd,
         repr_transparent,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 33585de6001..b08fc482186 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -1311,7 +1311,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         visitor.visit_body(&body);
 
         let typeck_results = self.in_progress_typeck_results.map(|t| t.borrow()).unwrap();
-        let Some(liberated_sig) = typeck_results.liberated_fn_sigs().get(fn_hir_id) else { return false; };
+        let Some(liberated_sig) = typeck_results.liberated_fn_sigs().get(fn_hir_id).copied() else { return false; };
 
         let ret_types = visitor
             .returns
diff --git a/compiler/rustc_typeck/src/check/expr.rs b/compiler/rustc_typeck/src/check/expr.rs
index 1d3608048f2..30b76b922c7 100644
--- a/compiler/rustc_typeck/src/check/expr.rs
+++ b/compiler/rustc_typeck/src/check/expr.rs
@@ -997,26 +997,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         coerce.coerce(self, &self.misc(sp), then_expr, then_ty);
 
         if let Some(else_expr) = opt_else_expr {
-            let else_ty = if sp.desugaring_kind() == Some(DesugaringKind::LetElse) {
-                // todo introduce `check_expr_with_expectation(.., Expectation::LetElse)`
-                //   for errors that point to the offending expression rather than the entire block.
-                //   We could use `check_expr_eq_type(.., tcx.types.never)`, but then there is no
-                //   way to detect that the expected type originated from let-else and provide
-                //   a customized error.
-                let else_ty = self.check_expr(else_expr);
-                let cause = self.cause(else_expr.span, ObligationCauseCode::LetElse);
-
-                if let Some(mut err) =
-                    self.demand_eqtype_with_origin(&cause, self.tcx.types.never, else_ty)
-                {
-                    err.emit();
-                    self.tcx.ty_error()
-                } else {
-                    else_ty
-                }
-            } else {
-                self.check_expr_with_expectation(else_expr, expected)
-            };
+            let else_ty = self.check_expr_with_expectation(else_expr, expected);
             let else_diverges = self.diverges.get();
 
             let opt_suggest_box_span = self.opt_suggest_box_span(else_ty, orig_expected);
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs b/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
index a7c7089234a..60ee2233ed9 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
@@ -1215,6 +1215,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.check_pat_top(&decl.pat, decl_ty, ty_span, origin_expr);
         let pat_ty = self.node_ty(decl.pat.hir_id);
         self.overwrite_local_ty_if_err(decl.hir_id, decl.pat, decl_ty, pat_ty);
+
+        if let Some(blk) = decl.els {
+            let previous_diverges = self.diverges.get();
+            let else_ty = self.check_block_with_expected(blk, NoExpectation);
+            let cause = self.cause(blk.span, ObligationCauseCode::LetElse);
+            if let Some(mut err) =
+                self.demand_eqtype_with_origin(&cause, self.tcx.types.never, else_ty)
+            {
+                err.emit();
+            }
+            self.diverges.set(previous_diverges);
+        }
     }
 
     /// Type check a `let` statement.
@@ -1236,8 +1248,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let old_has_errors = self.has_errors.replace(false);
 
         match stmt.kind {
-            hir::StmtKind::Local(ref l) => {
-                self.check_decl_local(&l);
+            hir::StmtKind::Local(l) => {
+                self.check_decl_local(l);
             }
             // Ignore for now.
             hir::StmtKind::Item(_) => {}
diff --git a/compiler/rustc_typeck/src/check/gather_locals.rs b/compiler/rustc_typeck/src/check/gather_locals.rs
index 576dc6f127c..8f34a970f6f 100644
--- a/compiler/rustc_typeck/src/check/gather_locals.rs
+++ b/compiler/rustc_typeck/src/check/gather_locals.rs
@@ -16,19 +16,20 @@ pub(super) struct Declaration<'a> {
     pub ty: Option<&'a hir::Ty<'a>>,
     pub span: Span,
     pub init: Option<&'a hir::Expr<'a>>,
+    pub els: Option<&'a hir::Block<'a>>,
 }
 
 impl<'a> From<&'a hir::Local<'a>> for Declaration<'a> {
     fn from(local: &'a hir::Local<'a>) -> Self {
-        let hir::Local { hir_id, pat, ty, span, init, .. } = *local;
-        Declaration { hir_id, pat, ty, span, init }
+        let hir::Local { hir_id, pat, ty, span, init, els, source: _ } = *local;
+        Declaration { hir_id, pat, ty, span, init, els }
     }
 }
 
 impl<'a> From<&'a hir::Let<'a>> for Declaration<'a> {
     fn from(let_expr: &'a hir::Let<'a>) -> Self {
         let hir::Let { hir_id, pat, ty, span, init } = *let_expr;
-        Declaration { hir_id, pat, ty, span, init: Some(init) }
+        Declaration { hir_id, pat, ty, span, init: Some(init), els: None }
     }
 }
 
@@ -101,7 +102,7 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherLocalsVisitor<'a, 'tcx> {
     // Add explicitly-declared locals.
     fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
         self.declare(local.into());
-        intravisit::walk_local(self, local);
+        intravisit::walk_local(self, local)
     }
 
     fn visit_let_expr(&mut self, let_expr: &'tcx hir::Let<'tcx>) {
diff --git a/compiler/rustc_typeck/src/check/region.rs b/compiler/rustc_typeck/src/check/region.rs
index 9f1368a3e07..a1a92c62ad2 100644
--- a/compiler/rustc_typeck/src/check/region.rs
+++ b/compiler/rustc_typeck/src/check/region.rs
@@ -460,6 +460,7 @@ fn resolve_local<'tcx>(
     visitor: &mut RegionResolutionVisitor<'tcx>,
     pat: Option<&'tcx hir::Pat<'tcx>>,
     init: Option<&'tcx hir::Expr<'tcx>>,
+    els: Option<&'tcx hir::Block<'tcx>>,
 ) {
     debug!("resolve_local(pat={:?}, init={:?})", pat, init);
 
@@ -537,13 +538,18 @@ fn resolve_local<'tcx>(
         }
     }
 
-    // Make sure we visit the initializer first, so expr_and_pat_count remains correct
+    // Make sure we visit the initializer first, so expr_and_pat_count remains correct.
+    // The correct order, as shared between generator_interior, drop_ranges and intravisitor,
+    // is to walk initializer, followed by pattern bindings, finally followed by the `else` block.
     if let Some(expr) = init {
         visitor.visit_expr(expr);
     }
     if let Some(pat) = pat {
         visitor.visit_pat(pat);
     }
+    if let Some(els) = els {
+        visitor.visit_block(els);
+    }
 
     /// Returns `true` if `pat` match the `P&` non-terminal.
     ///
@@ -764,7 +770,7 @@ impl<'tcx> Visitor<'tcx> for RegionResolutionVisitor<'tcx> {
             // (i.e., `'static`), which means that after `g` returns, it drops,
             // and all the associated destruction scope rules apply.
             self.cx.var_parent = None;
-            resolve_local(self, None, Some(&body.value));
+            resolve_local(self, None, Some(&body.value), None);
         }
 
         if body.generator_kind.is_some() {
@@ -791,7 +797,7 @@ impl<'tcx> Visitor<'tcx> for RegionResolutionVisitor<'tcx> {
         resolve_expr(self, ex);
     }
     fn visit_local(&mut self, l: &'tcx Local<'tcx>) {
-        resolve_local(self, Some(&l.pat), l.init);
+        resolve_local(self, Some(&l.pat), l.init, l.els)
     }
 }
 
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index 44b9c8392f8..9795be1a912 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -3196,7 +3196,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
 /// Computes the set of target features used in a function for the purposes of
 /// inline assembly.
 fn asm_target_features<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx FxHashSet<Symbol> {
-    let mut target_features = tcx.sess.target_features.clone();
+    let mut target_features = tcx.sess.unstable_target_features.clone();
     if tcx.def_kind(did).has_codegen_attrs() {
         let attrs = tcx.codegen_fn_attrs(did);
         target_features.extend(&attrs.target_features);
diff --git a/compiler/rustc_typeck/src/expr_use_visitor.rs b/compiler/rustc_typeck/src/expr_use_visitor.rs
index 920e3d578c8..9d7420acd26 100644
--- a/compiler/rustc_typeck/src/expr_use_visitor.rs
+++ b/compiler/rustc_typeck/src/expr_use_visitor.rs
@@ -2,7 +2,10 @@
 //! normal visitor, which just walks the entire body in one shot, the
 //! `ExprUseVisitor` determines how expressions are being used.
 
+use std::slice::from_ref;
+
 use hir::def::DefKind;
+use hir::Expr;
 // Export these here so that Clippy can use them.
 pub use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection};
 
@@ -252,96 +255,16 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
             }
 
             hir::ExprKind::Let(hir::Let { pat, init, .. }) => {
-                self.walk_local(init, pat, |t| t.borrow_expr(init, ty::ImmBorrow));
+                self.walk_local(init, pat, None, |t| t.borrow_expr(init, ty::ImmBorrow))
             }
 
             hir::ExprKind::Match(ref discr, arms, _) => {
                 let discr_place = return_if_err!(self.mc.cat_expr(discr));
-
-                // Matching should not always be considered a use of the place, hence
-                // discr does not necessarily need to be borrowed.
-                // We only want to borrow discr if the pattern contain something other
-                // than wildcards.
-                let ExprUseVisitor { ref mc, body_owner: _, delegate: _ } = *self;
-                let mut needs_to_be_read = false;
-                for arm in arms.iter() {
-                    return_if_err!(mc.cat_pattern(discr_place.clone(), arm.pat, |place, pat| {
-                        match &pat.kind {
-                            PatKind::Binding(.., opt_sub_pat) => {
-                                // If the opt_sub_pat is None, than the binding does not count as
-                                // a wildcard for the purpose of borrowing discr.
-                                if opt_sub_pat.is_none() {
-                                    needs_to_be_read = true;
-                                }
-                            }
-                            PatKind::Path(qpath) => {
-                                // A `Path` pattern is just a name like `Foo`. This is either a
-                                // named constant or else it refers to an ADT variant
-
-                                let res = self.mc.typeck_results.qpath_res(qpath, pat.hir_id);
-                                match res {
-                                    Res::Def(DefKind::Const, _)
-                                    | Res::Def(DefKind::AssocConst, _) => {
-                                        // Named constants have to be equated with the value
-                                        // being matched, so that's a read of the value being matched.
-                                        //
-                                        // FIXME: We don't actually  reads for ZSTs.
-                                        needs_to_be_read = true;
-                                    }
-                                    _ => {
-                                        // Otherwise, this is a struct/enum variant, and so it's
-                                        // only a read if we need to read the discriminant.
-                                        needs_to_be_read |= is_multivariant_adt(place.place.ty());
-                                    }
-                                }
-                            }
-                            PatKind::TupleStruct(..) | PatKind::Struct(..) | PatKind::Tuple(..) => {
-                                // For `Foo(..)`, `Foo { ... }` and `(...)` patterns, check if we are matching
-                                // against a multivariant enum or struct. In that case, we have to read
-                                // the discriminant. Otherwise this kind of pattern doesn't actually
-                                // read anything (we'll get invoked for the `...`, which may indeed
-                                // perform some reads).
-
-                                let place_ty = place.place.ty();
-                                needs_to_be_read |= is_multivariant_adt(place_ty);
-                            }
-                            PatKind::Lit(_) | PatKind::Range(..) => {
-                                // If the PatKind is a Lit or a Range then we want
-                                // to borrow discr.
-                                needs_to_be_read = true;
-                            }
-                            PatKind::Or(_)
-                            | PatKind::Box(_)
-                            | PatKind::Slice(..)
-                            | PatKind::Ref(..)
-                            | PatKind::Wild => {
-                                // If the PatKind is Or, Box, Slice or Ref, the decision is made later
-                                // as these patterns contains subpatterns
-                                // If the PatKind is Wild, the decision is made based on the other patterns being
-                                // examined
-                            }
-                        }
-                    }));
-                }
-
-                if needs_to_be_read {
-                    self.borrow_expr(discr, ty::ImmBorrow);
-                } else {
-                    let closure_def_id = match discr_place.place.base {
-                        PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id.to_def_id()),
-                        _ => None,
-                    };
-
-                    self.delegate.fake_read(
-                        &discr_place,
-                        FakeReadCause::ForMatchedPlace(closure_def_id),
-                        discr_place.hir_id,
-                    );
-
-                    // We always want to walk the discriminant. We want to make sure, for instance,
-                    // that the discriminant has been initialized.
-                    self.walk_expr(discr);
-                }
+                self.maybe_read_scrutinee(
+                    discr,
+                    discr_place.clone(),
+                    arms.iter().map(|arm| arm.pat),
+                );
 
                 // treatment of the discriminant is handled while walking the arms.
                 for arm in arms {
@@ -453,8 +376,8 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
 
     fn walk_stmt(&mut self, stmt: &hir::Stmt<'_>) {
         match stmt.kind {
-            hir::StmtKind::Local(hir::Local { pat, init: Some(expr), .. }) => {
-                self.walk_local(expr, pat, |_| {});
+            hir::StmtKind::Local(hir::Local { pat, init: Some(expr), els, .. }) => {
+                self.walk_local(expr, pat, *els, |_| {})
             }
 
             hir::StmtKind::Local(_) => {}
@@ -470,13 +393,114 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
         }
     }
 
-    fn walk_local<F>(&mut self, expr: &hir::Expr<'_>, pat: &hir::Pat<'_>, mut f: F)
-    where
+    fn maybe_read_scrutinee<'t>(
+        &mut self,
+        discr: &Expr<'_>,
+        discr_place: PlaceWithHirId<'tcx>,
+        pats: impl Iterator<Item = &'t hir::Pat<'t>>,
+    ) {
+        // Matching should not always be considered a use of the place, hence
+        // discr does not necessarily need to be borrowed.
+        // We only want to borrow discr if the pattern contain something other
+        // than wildcards.
+        let ExprUseVisitor { ref mc, body_owner: _, delegate: _ } = *self;
+        let mut needs_to_be_read = false;
+        for pat in pats {
+            return_if_err!(mc.cat_pattern(discr_place.clone(), pat, |place, pat| {
+                match &pat.kind {
+                    PatKind::Binding(.., opt_sub_pat) => {
+                        // If the opt_sub_pat is None, than the binding does not count as
+                        // a wildcard for the purpose of borrowing discr.
+                        if opt_sub_pat.is_none() {
+                            needs_to_be_read = true;
+                        }
+                    }
+                    PatKind::Path(qpath) => {
+                        // A `Path` pattern is just a name like `Foo`. This is either a
+                        // named constant or else it refers to an ADT variant
+
+                        let res = self.mc.typeck_results.qpath_res(qpath, pat.hir_id);
+                        match res {
+                            Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => {
+                                // Named constants have to be equated with the value
+                                // being matched, so that's a read of the value being matched.
+                                //
+                                // FIXME: We don't actually  reads for ZSTs.
+                                needs_to_be_read = true;
+                            }
+                            _ => {
+                                // Otherwise, this is a struct/enum variant, and so it's
+                                // only a read if we need to read the discriminant.
+                                needs_to_be_read |= is_multivariant_adt(place.place.ty());
+                            }
+                        }
+                    }
+                    PatKind::TupleStruct(..) | PatKind::Struct(..) | PatKind::Tuple(..) => {
+                        // For `Foo(..)`, `Foo { ... }` and `(...)` patterns, check if we are matching
+                        // against a multivariant enum or struct. In that case, we have to read
+                        // the discriminant. Otherwise this kind of pattern doesn't actually
+                        // read anything (we'll get invoked for the `...`, which may indeed
+                        // perform some reads).
+
+                        let place_ty = place.place.ty();
+                        needs_to_be_read |= is_multivariant_adt(place_ty);
+                    }
+                    PatKind::Lit(_) | PatKind::Range(..) => {
+                        // If the PatKind is a Lit or a Range then we want
+                        // to borrow discr.
+                        needs_to_be_read = true;
+                    }
+                    PatKind::Or(_)
+                    | PatKind::Box(_)
+                    | PatKind::Slice(..)
+                    | PatKind::Ref(..)
+                    | PatKind::Wild => {
+                        // If the PatKind is Or, Box, Slice or Ref, the decision is made later
+                        // as these patterns contains subpatterns
+                        // If the PatKind is Wild, the decision is made based on the other patterns being
+                        // examined
+                    }
+                }
+            }));
+        }
+
+        if needs_to_be_read {
+            self.borrow_expr(discr, ty::ImmBorrow);
+        } else {
+            let closure_def_id = match discr_place.place.base {
+                PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id.to_def_id()),
+                _ => None,
+            };
+
+            self.delegate.fake_read(
+                &discr_place,
+                FakeReadCause::ForMatchedPlace(closure_def_id),
+                discr_place.hir_id,
+            );
+
+            // We always want to walk the discriminant. We want to make sure, for instance,
+            // that the discriminant has been initialized.
+            self.walk_expr(discr);
+        }
+    }
+
+    fn walk_local<F>(
+        &mut self,
+        expr: &hir::Expr<'_>,
+        pat: &hir::Pat<'_>,
+        els: Option<&hir::Block<'_>>,
+        mut f: F,
+    ) where
         F: FnMut(&mut Self),
     {
         self.walk_expr(expr);
         let expr_place = return_if_err!(self.mc.cat_expr(expr));
         f(self);
+        if let Some(els) = els {
+            // borrowing because we need to test the descriminant
+            self.maybe_read_scrutinee(expr, expr_place.clone(), from_ref(pat).iter());
+            self.walk_block(els)
+        }
         self.walk_irrefutable_pat(&expr_place, &pat);
     }
 
@@ -667,7 +691,7 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
         let ExprUseVisitor { ref mc, body_owner: _, ref mut delegate } = *self;
         return_if_err!(mc.cat_pattern(discr_place.clone(), pat, |place, pat| {
             if let PatKind::Binding(_, canonical_id, ..) = pat.kind {
-                debug!("walk_pat: binding place={:?} pat={:?}", place, pat,);
+                debug!("walk_pat: binding place={:?} pat={:?}", place, pat);
                 if let Some(bm) =
                     mc.typeck_results.extract_binding_mode(tcx.sess, pat.hir_id, pat.span)
                 {