Auto merge of #134499 - jieyouxu:rollup-zmaveur, r=jieyouxu

Rollup of 7 pull requests

Successful merges:

 - #133702 (Variants::Single: do not use invalid VariantIdx for uninhabited enums)
 - #134427 (ci: remove duplicate task definition)
 - #134432 (Fix intra doc links not generated inside footnote definitions)
 - #134437 (reduce compiler `Assemble` complexity)
 - #134474 (Forbid overwriting types in typeck)
 - #134477 (move lint_unused_mut into sub-fn)
 - #134491 (Some destructor/drop related tweaks)

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

compiler/rustc_abi/src/callconv.rs

@@ -206,7 +206,7 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
                 let (mut result, mut total) = from_fields_at(*self, Size::ZERO)?;
 
                 match &self.variants {
-                    abi::Variants::Single { .. } => {}
+                    abi::Variants::Single { .. } | abi::Variants::Empty => {}
                     abi::Variants::Multiple { variants, .. } => {
                         // Treat enum variants like union members.
                         // HACK(eddyb) pretend the `enum` field (discriminant)

compiler/rustc_abi/src/layout.rs

@@ -213,8 +213,9 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         &self,
     ) -> LayoutData<FieldIdx, VariantIdx> {
         let dl = self.cx.data_layout();
+        // This is also used for uninhabited enums, so we use `Variants::Empty`.
         LayoutData {
-            variants: Variants::Single { index: VariantIdx::new(0) },
+            variants: Variants::Empty,
             fields: FieldsShape::Primitive,
             backend_repr: BackendRepr::Uninhabited,
             largest_niche: None,
@@ -1004,8 +1005,8 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
                 Variants::Multiple { tag, tag_encoding, tag_field, variants: best_layout.variants }
             }
-            Variants::Single { .. } => {
+            Variants::Single { .. } | Variants::Empty => {
-                panic!("encountered a single-variant enum during multi-variant layout")
+                panic!("encountered a single-variant or empty enum during multi-variant layout")
             }
         };
         Ok(best_layout.layout)

compiler/rustc_abi/src/lib.rs

@@ -1504,10 +1504,12 @@ impl BackendRepr {
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
 #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
 pub enum Variants<FieldIdx: Idx, VariantIdx: Idx> {
+    /// A type with no valid variants. Must be uninhabited.
+    Empty,
+
     /// Single enum variants, structs/tuples, unions, and all non-ADTs.
     Single {
-        /// Always 0 for non-enums/generators.
+        /// Always `0` for types that cannot have multiple variants.
-        /// For enums without a variant, this is an invalid index!
         index: VariantIdx,
     },
 

compiler/rustc_borrowck/src/lib.rs

@@ -334,35 +334,7 @@ fn do_mir_borrowck<'tcx>(
     mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
 
     debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
-    let used_mut = std::mem::take(&mut mbcx.used_mut);
+    mbcx.lint_unused_mut();
-    for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
-        let local_decl = &mbcx.body.local_decls[local];
-        let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
-            ClearCrossCrate::Set(data) => data.lint_root,
-            _ => continue,
-        };
-
-        // Skip over locals that begin with an underscore or have no name
-        match mbcx.local_names[local] {
-            Some(name) => {
-                if name.as_str().starts_with('_') {
-                    continue;
-                }
-            }
-            None => continue,
-        }
-
-        let span = local_decl.source_info.span;
-        if span.desugaring_kind().is_some() {
-            // If the `mut` arises as part of a desugaring, we should ignore it.
-            continue;
-        }
-
-        let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
-
-        tcx.emit_node_span_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
-    }
-
     let tainted_by_errors = mbcx.emit_errors();
 
     let result = BorrowCheckResult {
@@ -2390,6 +2362,38 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         // `BasicBlocks` computes dominators on-demand and caches them.
         self.body.basic_blocks.dominators()
     }
+
+    fn lint_unused_mut(&self) {
+        let tcx = self.infcx.tcx;
+        let body = self.body;
+        for local in body.mut_vars_and_args_iter().filter(|local| !self.used_mut.contains(local)) {
+            let local_decl = &body.local_decls[local];
+            let lint_root = match &body.source_scopes[local_decl.source_info.scope].local_data {
+                ClearCrossCrate::Set(data) => data.lint_root,
+                _ => continue,
+            };
+
+            // Skip over locals that begin with an underscore or have no name
+            match self.local_names[local] {
+                Some(name) => {
+                    if name.as_str().starts_with('_') {
+                        continue;
+                    }
+                }
+                None => continue,
+            }
+
+            let span = local_decl.source_info.span;
+            if span.desugaring_kind().is_some() {
+                // If the `mut` arises as part of a desugaring, we should ignore it.
+                continue;
+            }
+
+            let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
+
+            tcx.emit_node_span_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
+        }
+    }
 }
 
 mod diags {

compiler/rustc_codegen_cranelift/src/discriminant.rs

@@ -18,6 +18,7 @@ pub(crate) fn codegen_set_discriminant<'tcx>(
         return;
     }
     match layout.variants {
+        Variants::Empty => unreachable!("we already handled uninhabited types"),
         Variants::Single { index } => {
             assert_eq!(index, variant_index);
         }
@@ -85,6 +86,7 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
     }
 
     let (tag_scalar, tag_field, tag_encoding) = match &layout.variants {
+        Variants::Empty => unreachable!("we already handled uninhabited types"),
         Variants::Single { index } => {
             let discr_val = layout
                 .ty

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/cpp_like.rs

@@ -212,21 +212,17 @@ pub(super) fn build_enum_type_di_node<'ll, 'tcx>(
         ),
         |cx, enum_type_di_node| {
             match enum_type_and_layout.variants {
-                Variants::Single { index: variant_index } => {
+                Variants::Empty => {
-                    if enum_adt_def.variants().is_empty() {
+                    // We don't generate any members for uninhabited types.
-                        // Uninhabited enums have Variants::Single. We don't generate
+                    return smallvec![];
-                        // any members for them.
-                        return smallvec![];
-                    }
-
-                    build_single_variant_union_fields(
-                        cx,
-                        enum_adt_def,
-                        enum_type_and_layout,
-                        enum_type_di_node,
-                        variant_index,
-                    )
                 }
+                Variants::Single { index: variant_index } => build_single_variant_union_fields(
+                    cx,
+                    enum_adt_def,
+                    enum_type_and_layout,
+                    enum_type_di_node,
+                    variant_index,
+                ),
                 Variants::Multiple {
                     tag_encoding: TagEncoding::Direct,
                     ref variants,
@@ -303,6 +299,7 @@ pub(super) fn build_coroutine_di_node<'ll, 'tcx>(
                 )
             }
             Variants::Single { .. }
+            | Variants::Empty
             | Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, .. } => {
                 bug!(
                     "Encountered coroutine with non-direct-tag layout: {:?}",

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs

@@ -392,7 +392,7 @@ fn compute_discriminant_value<'ll, 'tcx>(
     variant_index: VariantIdx,
 ) -> DiscrResult {
     match enum_type_and_layout.layout.variants() {
-        &Variants::Single { .. } => DiscrResult::NoDiscriminant,
+        &Variants::Single { .. } | &Variants::Empty => DiscrResult::NoDiscriminant,
         &Variants::Multiple { tag_encoding: TagEncoding::Direct, .. } => DiscrResult::Value(
             enum_type_and_layout.ty.discriminant_for_variant(cx.tcx, variant_index).unwrap().val,
         ),

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/native.rs

@@ -358,8 +358,8 @@ fn build_discr_member_di_node<'ll, 'tcx>(
     let containing_scope = enum_or_coroutine_type_di_node;
 
     match enum_or_coroutine_type_and_layout.layout.variants() {
-        // A single-variant enum has no discriminant.
+        // A single-variant or no-variant enum has no discriminant.
-        &Variants::Single { .. } => None,
+        &Variants::Single { .. } | &Variants::Empty => None,
 
         &Variants::Multiple { tag_field, .. } => {
             let tag_base_type = tag_base_type(cx.tcx, enum_or_coroutine_type_and_layout);

compiler/rustc_codegen_llvm/src/type_of.rs

@@ -38,7 +38,7 @@ fn uncached_llvm_type<'a, 'tcx>(
             if let (&ty::Adt(def, _), &Variants::Single { index }) =
                 (layout.ty.kind(), &layout.variants)
             {
-                if def.is_enum() && !def.variants().is_empty() {
+                if def.is_enum() {
                     write!(&mut name, "::{}", def.variant(index).name).unwrap();
                 }
             }

compiler/rustc_codegen_ssa/src/debuginfo/mod.rs

@@ -65,8 +65,8 @@ fn tag_base_type_opt<'tcx>(
     });
 
     match enum_type_and_layout.layout.variants() {
-        // A single-variant enum has no discriminant.
+        // A single-variant or no-variant enum has no discriminant.
-        Variants::Single { .. } => None,
+        Variants::Single { .. } | Variants::Empty => None,
 
         Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, tag, .. } => {
             // Niche tags are always normalized to unsized integers of the correct size.

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -243,6 +243,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
             return bx.cx().const_poison(cast_to);
         }
         let (tag_scalar, tag_encoding, tag_field) = match self.layout.variants {
+            Variants::Empty => unreachable!("we already handled uninhabited types"),
             Variants::Single { index } => {
                 let discr_val = self
                     .layout
@@ -365,9 +366,9 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
             return;
         }
         match self.layout.variants {
-            Variants::Single { index } => {
+            Variants::Empty => unreachable!("we already handled uninhabited types"),
-                assert_eq!(index, variant_index);
+            Variants::Single { index } => assert_eq!(index, variant_index),
-            }
+
             Variants::Multiple { tag_encoding: TagEncoding::Direct, tag_field, .. } => {
                 let ptr = self.project_field(bx, tag_field);
                 let to =

compiler/rustc_const_eval/src/interpret/discriminant.rs

@@ -44,7 +44,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         }
     }
 
-    /// Read discriminant, return the runtime value as well as the variant index.
+    /// Read discriminant, return the variant index.
     /// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
     ///
     /// Will never return an uninhabited variant.
@@ -65,21 +65,17 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // We use "tag" to refer to how the discriminant is encoded in memory, which can be either
         // straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`).
         let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout().variants {
+            Variants::Empty => {
+                throw_ub!(UninhabitedEnumVariantRead(None));
+            }
             Variants::Single { index } => {
-                // Do some extra checks on enums.
+                if op.layout().is_uninhabited() {
-                if ty.is_enum() {
-                    // Hilariously, `Single` is used even for 0-variant enums.
-                    // (See https://github.com/rust-lang/rust/issues/89765).
-                    if ty.ty_adt_def().unwrap().variants().is_empty() {
-                        throw_ub!(UninhabitedEnumVariantRead(index))
-                    }
                     // For consistency with `write_discriminant`, and to make sure that
                     // `project_downcast` cannot fail due to strange layouts, we declare immediate UB
-                    // for uninhabited variants.
+                    // for uninhabited enums.
-                    if op.layout().for_variant(self, index).is_uninhabited() {
+                    throw_ub!(UninhabitedEnumVariantRead(Some(index)));
-                        throw_ub!(UninhabitedEnumVariantRead(index))
-                    }
                 }
+                // Since the type is inhabited, there must be an index.
                 return interp_ok(index);
             }
             Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
@@ -199,11 +195,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // `uninhabited_enum_branching` MIR pass. It also ensures consistency with
         // `write_discriminant`.
         if op.layout().for_variant(self, index).is_uninhabited() {
-            throw_ub!(UninhabitedEnumVariantRead(index))
+            throw_ub!(UninhabitedEnumVariantRead(Some(index)))
         }
         interp_ok(index)
     }
 
+    /// Read discriminant, return the user-visible discriminant.
+    /// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
     pub fn discriminant_for_variant(
         &self,
         ty: Ty<'tcx>,
@@ -243,6 +241,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         }
 
         match layout.variants {
+            abi::Variants::Empty => unreachable!("we already handled uninhabited types"),
             abi::Variants::Single { .. } => {
                 // The tag of a `Single` enum is like the tag of the niched
                 // variant: there's no tag as the discriminant is encoded

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -302,7 +302,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                     };
                 }
             }
-            Variants::Single { .. } => {}
+            Variants::Single { .. } | Variants::Empty => {}
         }
 
         // Now we know we are projecting to a field, so figure out which one.
@@ -344,6 +344,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                         // Inside a variant
                         PathElem::Field(def.variant(index).fields[FieldIdx::from_usize(field)].name)
                     }
+                    Variants::Empty => panic!("there is no field in Variants::Empty types"),
                     Variants::Multiple { .. } => bug!("we handled variants above"),
                 }
             }
@@ -1010,7 +1011,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
             }
             // Don't forget potential other variants.
             match &layout.variants {
-                Variants::Single { .. } => {
+                Variants::Single { .. } | Variants::Empty => {
                     // Fully handled above.
                 }
                 Variants::Multiple { variants, .. } => {

compiler/rustc_const_eval/src/interpret/visitor.rs

@@ -218,8 +218,8 @@ pub trait ValueVisitor<'tcx, M: Machine<'tcx>>: Sized {
                 // recurse with the inner type
                 self.visit_variant(v, idx, &inner)?;
             }
-            // For single-variant layouts, we already did anything there is to do.
+            // For single-variant layouts, we already did everything there is to do.
-            Variants::Single { .. } => {}
+            Variants::Single { .. } | Variants::Empty => {}
         }
 
         interp_ok(())

compiler/rustc_const_eval/src/util/check_validity_requirement.rs

@@ -155,6 +155,7 @@ fn check_validity_requirement_lax<'tcx>(
     }
 
     match &this.variants {
+        Variants::Empty => return Ok(false),
         Variants::Single { .. } => {
             // All fields of this single variant have already been checked above, there is nothing
             // else to do.

compiler/rustc_hir_analysis/src/check/region.rs

@@ -129,7 +129,7 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
                     let mut prev_cx = visitor.cx;
 
                     visitor.enter_scope(Scope {
-                        id: blk.hir_id.local_id,
+                        local_id: blk.hir_id.local_id,
                         data: ScopeData::Remainder(FirstStatementIndex::new(i)),
                     });
                     visitor.cx.var_parent = visitor.cx.parent;
@@ -154,7 +154,7 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
                     // the first such subscope, which has the block itself as a
                     // parent.
                     visitor.enter_scope(Scope {
-                        id: blk.hir_id.local_id,
+                        local_id: blk.hir_id.local_id,
                         data: ScopeData::Remainder(FirstStatementIndex::new(i)),
                     });
                     visitor.cx.var_parent = visitor.cx.parent;
@@ -184,7 +184,7 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
                 visitor
                     .scope_tree
                     .backwards_incompatible_scope
-                    .insert(local_id, Scope { id: local_id, data: ScopeData::Node });
+                    .insert(local_id, Scope { local_id, data: ScopeData::Node });
             }
             visitor.visit_expr(tail_expr);
         }
@@ -221,7 +221,7 @@ fn resolve_arm<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, arm: &'tcx hir
 }
 
 fn resolve_pat<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, pat: &'tcx hir::Pat<'tcx>) {
-    visitor.record_child_scope(Scope { id: pat.hir_id.local_id, data: ScopeData::Node });
+    visitor.record_child_scope(Scope { local_id: pat.hir_id.local_id, data: ScopeData::Node });
 
     // If this is a binding then record the lifetime of that binding.
     if let PatKind::Binding(..) = pat.kind {
@@ -485,7 +485,7 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
             } else {
                 ScopeData::IfThen
             };
-            visitor.enter_scope(Scope { id: then.hir_id.local_id, data });
+            visitor.enter_scope(Scope { local_id: then.hir_id.local_id, data });
             visitor.cx.var_parent = visitor.cx.parent;
             visitor.visit_expr(cond);
             visitor.visit_expr(then);
@@ -500,7 +500,7 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
             } else {
                 ScopeData::IfThen
             };
-            visitor.enter_scope(Scope { id: then.hir_id.local_id, data });
+            visitor.enter_scope(Scope { local_id: then.hir_id.local_id, data });
             visitor.cx.var_parent = visitor.cx.parent;
             visitor.visit_expr(cond);
             visitor.visit_expr(then);
@@ -516,7 +516,7 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
 
     if let hir::ExprKind::Yield(_, source) = &expr.kind {
         // Mark this expr's scope and all parent scopes as containing `yield`.
-        let mut scope = Scope { id: expr.hir_id.local_id, data: ScopeData::Node };
+        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 { .. }) => {
@@ -803,9 +803,9 @@ impl<'tcx> RegionResolutionVisitor<'tcx> {
         // account for the destruction scope representing the scope of
         // the destructors that run immediately after it completes.
         if self.terminating_scopes.contains(&id) {
-            self.enter_scope(Scope { id, data: ScopeData::Destruction });
+            self.enter_scope(Scope { local_id: id, data: ScopeData::Destruction });
         }
-        self.enter_scope(Scope { id, data: ScopeData::Node });
+        self.enter_scope(Scope { local_id: id, data: ScopeData::Node });
     }
 
     fn enter_body(&mut self, hir_id: hir::HirId, f: impl FnOnce(&mut Self)) {
@@ -822,8 +822,8 @@ impl<'tcx> RegionResolutionVisitor<'tcx> {
         let outer_pessimistic_yield = mem::replace(&mut self.pessimistic_yield, false);
         self.terminating_scopes.insert(hir_id.local_id);
 
-        self.enter_scope(Scope { id: hir_id.local_id, data: ScopeData::CallSite });
+        self.enter_scope(Scope { local_id: hir_id.local_id, data: ScopeData::CallSite });
-        self.enter_scope(Scope { id: hir_id.local_id, data: ScopeData::Arguments });
+        self.enter_scope(Scope { local_id: hir_id.local_id, data: ScopeData::Arguments });
 
         f(self);
 

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -146,18 +146,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         debug!("write_ty({:?}, {:?}) in fcx {}", id, self.resolve_vars_if_possible(ty), self.tag());
         let mut typeck = self.typeck_results.borrow_mut();
         let mut node_ty = typeck.node_types_mut();
-        if let Some(ty) = node_ty.get(id)
-            && let Err(e) = ty.error_reported()
-        {
-            // Do not overwrite nodes that were already marked as `{type error}`. This allows us to
-            // silence unnecessary errors from obligations that were set earlier than a type error
-            // was produced, but that is overwritten by later analysis. This happens in particular
-            // for `Sized` obligations introduced in gather_locals. (#117846)
-            self.set_tainted_by_errors(e);
-            return;
-        }
 
-        node_ty.insert(id, ty);
+        if let Some(prev) = node_ty.insert(id, ty) {
+            if prev.references_error() {
+                node_ty.insert(id, prev);
+            } else if !ty.references_error() {
+                // Could change this to a bug, but there's lots of diagnostic code re-lowering
+                // or re-typechecking nodes that were already typecked.
+                // Lots of that diagnostics code relies on subtle effects of re-lowering, so we'll
+                // let it keep doing that and just ensure that compilation won't succeed.
+                self.dcx().span_delayed_bug(
+                    self.tcx.hir().span(id),
+                    format!("`{prev}` overridden by `{ty}` for {id:?} in {:?}", self.body_id),
+                );
+            }
+        }
 
         if let Err(e) = ty.error_reported() {
             self.set_tainted_by_errors(e);
@@ -1104,7 +1107,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if let Res::Local(hid) = res {
             let ty = self.local_ty(span, hid);
             let ty = self.normalize(span, ty);
-            self.write_ty(hir_id, ty);
             return (ty, res);
         }
 

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1750,10 +1750,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    pub(in super::super) fn check_decl(&self, decl: Declaration<'tcx>) {
+    pub(in super::super) fn check_decl(&self, decl: Declaration<'tcx>) -> Ty<'tcx> {
         // Determine and write the type which we'll check the pattern against.
         let decl_ty = self.local_ty(decl.span, decl.hir_id);
-        self.write_ty(decl.hir_id, decl_ty);
 
         // Type check the initializer.
         if let Some(ref init) = decl.init {
@@ -1785,11 +1784,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
             self.diverges.set(previous_diverges);
         }
+        decl_ty
     }
 
     /// Type check a `let` statement.
     fn check_decl_local(&self, local: &'tcx hir::LetStmt<'tcx>) {
-        self.check_decl(local.into());
+        let ty = self.check_decl(local.into());
+        self.write_ty(local.hir_id, ty);
         if local.pat.is_never_pattern() {
             self.diverges.set(Diverges::Always {
                 span: local.pat.span,

compiler/rustc_middle/src/middle/region.rs

@@ -84,23 +84,23 @@ use crate::ty::TyCtxt;
 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub struct Scope {
-    pub id: hir::ItemLocalId,
+    pub local_id: hir::ItemLocalId,
     pub data: ScopeData,
 }
 
 impl fmt::Debug for Scope {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.data {
-            ScopeData::Node => write!(fmt, "Node({:?})", self.id),
+            ScopeData::Node => write!(fmt, "Node({:?})", self.local_id),
-            ScopeData::CallSite => write!(fmt, "CallSite({:?})", self.id),
+            ScopeData::CallSite => write!(fmt, "CallSite({:?})", self.local_id),
-            ScopeData::Arguments => write!(fmt, "Arguments({:?})", self.id),
+            ScopeData::Arguments => write!(fmt, "Arguments({:?})", self.local_id),
-            ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.id),
+            ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.local_id),
-            ScopeData::IfThen => write!(fmt, "IfThen({:?})", self.id),
+            ScopeData::IfThen => write!(fmt, "IfThen({:?})", self.local_id),
-            ScopeData::IfThenRescope => write!(fmt, "IfThen[edition2024]({:?})", self.id),
+            ScopeData::IfThenRescope => write!(fmt, "IfThen[edition2024]({:?})", self.local_id),
             ScopeData::Remainder(fsi) => write!(
                 fmt,
                 "Remainder {{ block: {:?}, first_statement_index: {}}}",
-                self.id,
+                self.local_id,
                 fsi.as_u32(),
             ),
         }
@@ -164,18 +164,8 @@ rustc_index::newtype_index! {
 rustc_data_structures::static_assert_size!(ScopeData, 4);
 
 impl Scope {
-    /// Returns an item-local ID associated with this scope.
-    ///
-    /// N.B., likely to be replaced as API is refined; e.g., pnkfelix
-    /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
-    pub fn item_local_id(&self) -> hir::ItemLocalId {
-        self.id
-    }
-
     pub fn hir_id(&self, scope_tree: &ScopeTree) -> Option<HirId> {
-        scope_tree
+        scope_tree.root_body.map(|hir_id| HirId { owner: hir_id.owner, local_id: self.local_id })
-            .root_body
-            .map(|hir_id| HirId { owner: hir_id.owner, local_id: self.item_local_id() })
     }
 
     /// Returns the span of this `Scope`. Note that in general the
@@ -350,7 +340,7 @@ impl ScopeTree {
 
     pub fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
         debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
-        assert!(var != lifetime.item_local_id());
+        assert!(var != lifetime.local_id);
         self.var_map.insert(var, lifetime);
     }
 
@@ -359,7 +349,7 @@ impl ScopeTree {
         match &candidate_type {
             RvalueCandidateType::Borrow { lifetime: Some(lifetime), .. }
             | RvalueCandidateType::Pattern { lifetime: Some(lifetime), .. } => {
-                assert!(var.local_id != lifetime.item_local_id())
+                assert!(var.local_id != lifetime.local_id)
             }
             _ => {}
         }

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -392,7 +392,7 @@ pub enum UndefinedBehaviorInfo<'tcx> {
     /// A discriminant of an uninhabited enum variant is written.
     UninhabitedEnumVariantWritten(VariantIdx),
     /// An uninhabited enum variant is projected.
-    UninhabitedEnumVariantRead(VariantIdx),
+    UninhabitedEnumVariantRead(Option<VariantIdx>),
     /// Trying to set discriminant to the niched variant, but the value does not match.
     InvalidNichedEnumVariantWritten { enum_ty: Ty<'tcx> },
     /// ABI-incompatible argument types.

compiler/rustc_middle/src/ty/layout.rs

@@ -734,21 +734,22 @@ where
         let layout = match this.variants {
             Variants::Single { index }
                 // If all variants but one are uninhabited, the variant layout is the enum layout.
-                if index == variant_index &&
+                if index == variant_index =>
-                // Don't confuse variants of uninhabited enums with the enum itself.
-                // For more details see https://github.com/rust-lang/rust/issues/69763.
-                this.fields != FieldsShape::Primitive =>
             {
                 this.layout
             }
 
-            Variants::Single { index } => {
+            Variants::Single { .. } | Variants::Empty => {
+                // Single-variant and no-variant enums *can* have other variants, but those are
+                // uninhabited. Produce a layout that has the right fields for that variant, so that
+                // the rest of the compiler can project fields etc as usual.
+
                 let tcx = cx.tcx();
                 let typing_env = cx.typing_env();
 
                 // Deny calling for_variant more than once for non-Single enums.
                 if let Ok(original_layout) = tcx.layout_of(typing_env.as_query_input(this.ty)) {
-                    assert_eq!(original_layout.variants, Variants::Single { index });
+                    assert_eq!(original_layout.variants, this.variants);
                 }
 
                 let fields = match this.ty.kind() {
@@ -902,6 +903,7 @@ where
                 ),
 
                 ty::Coroutine(def_id, args) => match this.variants {
+                    Variants::Empty => unreachable!(),
                     Variants::Single { index } => TyMaybeWithLayout::Ty(
                         args.as_coroutine()
                             .state_tys(def_id, tcx)
@@ -927,6 +929,7 @@ where
                             let field = &def.variant(index).fields[FieldIdx::from_usize(i)];
                             TyMaybeWithLayout::Ty(field.ty(tcx, args))
                         }
+                        Variants::Empty => panic!("there is no field in Variants::Empty types"),
 
                         // Discriminant field for enums (where applicable).
                         Variants::Multiple { tag, .. } => {

compiler/rustc_middle/src/ty/rvalue_scopes.rs

@@ -35,7 +35,7 @@ impl RvalueScopes {
         // if there's one. Static items, for instance, won't
         // have an enclosing scope, hence no scope will be
         // returned.
-        let mut id = Scope { id: expr_id, data: ScopeData::Node };
+        let mut id = Scope { local_id: expr_id, data: ScopeData::Node };
         let mut backwards_incompatible = None;
 
         while let Some(&(p, _)) = region_scope_tree.parent_map.get(&id) {
@@ -60,7 +60,7 @@ impl RvalueScopes {
                     if backwards_incompatible.is_none() {
                         backwards_incompatible = region_scope_tree
                             .backwards_incompatible_scope
-                            .get(&p.item_local_id())
+                            .get(&p.local_id)
                             .copied();
                     }
                     id = p
@@ -76,7 +76,7 @@ impl RvalueScopes {
     pub fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
         debug!("record_rvalue_scope(var={var:?}, lifetime={lifetime:?})");
         if let Some(lifetime) = lifetime {
-            assert!(var != lifetime.item_local_id());
+            assert!(var != lifetime.local_id);
         }
         self.map.insert(var, lifetime);
     }

compiler/rustc_mir_build/src/builder/expr/as_temp.rs

@@ -75,11 +75,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     LocalInfo::BlockTailTemp(tail_info)
                 }
 
-                _ if let Some(Scope { data: ScopeData::IfThenRescope, id }) =
+                _ if let Some(Scope { data: ScopeData::IfThenRescope, local_id }) =
                     temp_lifetime.temp_lifetime =>
                 {
                     LocalInfo::IfThenRescopeTemp {
-                        if_then: HirId { owner: this.hir_id.owner, local_id: id },
+                        if_then: HirId { owner: this.hir_id.owner, local_id },
                     }
                 }
 

compiler/rustc_mir_build/src/builder/mod.rs

@@ -531,9 +531,9 @@ fn construct_fn<'tcx>(
     );
 
     let call_site_scope =
-        region::Scope { id: body.id().hir_id.local_id, data: region::ScopeData::CallSite };
+        region::Scope { local_id: body.id().hir_id.local_id, data: region::ScopeData::CallSite };
     let arg_scope =
-        region::Scope { id: body.id().hir_id.local_id, data: region::ScopeData::Arguments };
+        region::Scope { local_id: body.id().hir_id.local_id, data: region::ScopeData::Arguments };
     let source_info = builder.source_info(span);
     let call_site_s = (call_site_scope, source_info);
     let _: BlockAnd<()> = builder.in_scope(call_site_s, LintLevel::Inherited, |builder| {

compiler/rustc_mir_build/src/builder/scope.rs

@@ -89,7 +89,7 @@ use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::middle::region;
 use rustc_middle::mir::*;
 use rustc_middle::thir::{ExprId, LintLevel};
-use rustc_middle::{bug, span_bug, ty};
+use rustc_middle::{bug, span_bug};
 use rustc_session::lint::Level;
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Span};
@@ -1119,10 +1119,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         region_scope: region::Scope,
         local: Local,
     ) {
-        if !self.local_decls[local].ty.has_significant_drop(self.tcx, ty::TypingEnv {
+        if !self.local_decls[local].ty.has_significant_drop(self.tcx, self.typing_env()) {
-            typing_mode: ty::TypingMode::non_body_analysis(),
-            param_env: self.param_env,
-        }) {
             return;
         }
         for scope in self.scopes.scopes.iter_mut().rev() {

compiler/rustc_mir_build/src/thir/cx/block.rs

@@ -16,7 +16,7 @@ impl<'tcx> Cx<'tcx> {
         let block = Block {
             targeted_by_break: block.targeted_by_break,
             region_scope: region::Scope {
-                id: block.hir_id.local_id,
+                local_id: block.hir_id.local_id,
                 data: region::ScopeData::Node,
             },
             span: block.span,
@@ -51,7 +51,7 @@ impl<'tcx> Cx<'tcx> {
                         let stmt = Stmt {
                             kind: StmtKind::Expr {
                                 scope: region::Scope {
-                                    id: hir_id.local_id,
+                                    local_id: hir_id.local_id,
                                     data: region::ScopeData::Node,
                                 },
                                 expr: self.mirror_expr(expr),
@@ -65,7 +65,7 @@ impl<'tcx> Cx<'tcx> {
                     }
                     hir::StmtKind::Let(local) => {
                         let remainder_scope = region::Scope {
-                            id: block_id,
+                            local_id: block_id,
                             data: region::ScopeData::Remainder(region::FirstStatementIndex::new(
                                 index,
                             )),
@@ -108,7 +108,7 @@ impl<'tcx> Cx<'tcx> {
                             kind: StmtKind::Let {
                                 remainder_scope,
                                 init_scope: region::Scope {
-                                    id: hir_id.local_id,
+                                    local_id: hir_id.local_id,
                                     data: region::ScopeData::Node,
                                 },
                                 pattern,

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -45,7 +45,7 @@ impl<'tcx> Cx<'tcx> {
     #[instrument(level = "trace", skip(self, hir_expr))]
     pub(super) fn mirror_expr_inner(&mut self, hir_expr: &'tcx hir::Expr<'tcx>) -> ExprId {
         let expr_scope =
-            region::Scope { id: hir_expr.hir_id.local_id, data: region::ScopeData::Node };
+            region::Scope { local_id: hir_expr.hir_id.local_id, data: region::ScopeData::Node };
 
         trace!(?hir_expr.hir_id, ?hir_expr.span);
 
@@ -814,14 +814,20 @@ impl<'tcx> Cx<'tcx> {
             hir::ExprKind::Become(call) => ExprKind::Become { value: self.mirror_expr(call) },
             hir::ExprKind::Break(dest, ref value) => match dest.target_id {
                 Ok(target_id) => ExprKind::Break {
-                    label: region::Scope { id: target_id.local_id, data: region::ScopeData::Node },
+                    label: region::Scope {
+                        local_id: target_id.local_id,
+                        data: region::ScopeData::Node,
+                    },
                     value: value.map(|value| self.mirror_expr(value)),
                 },
                 Err(err) => bug!("invalid loop id for break: {}", err),
             },
             hir::ExprKind::Continue(dest) => match dest.target_id {
                 Ok(loop_id) => ExprKind::Continue {
-                    label: region::Scope { id: loop_id.local_id, data: region::ScopeData::Node },
+                    label: region::Scope {
+                        local_id: loop_id.local_id,
+                        data: region::ScopeData::Node,
+                    },
                 },
                 Err(err) => bug!("invalid loop id for continue: {}", err),
             },
@@ -831,7 +837,7 @@ impl<'tcx> Cx<'tcx> {
             },
             hir::ExprKind::If(cond, then, else_opt) => ExprKind::If {
                 if_then_scope: region::Scope {
-                    id: then.hir_id.local_id,
+                    local_id: then.hir_id.local_id,
                     data: {
                         if expr.span.at_least_rust_2024() {
                             region::ScopeData::IfThenRescope
@@ -1021,7 +1027,7 @@ impl<'tcx> Cx<'tcx> {
             guard: arm.guard.as_ref().map(|g| self.mirror_expr(g)),
             body: self.mirror_expr(arm.body),
             lint_level: LintLevel::Explicit(arm.hir_id),
-            scope: region::Scope { id: arm.hir_id.local_id, data: region::ScopeData::Node },
+            scope: region::Scope { local_id: arm.hir_id.local_id, data: region::ScopeData::Node },
             span: arm.span,
         };
         self.thir.arms.push(arm)

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -35,7 +35,6 @@
 //! Likewise, applying the optimisation can create a lot of new MIR, so we bound the instruction
 //! cost by `MAX_COST`.
 
-use rustc_abi::{TagEncoding, Variants};
 use rustc_arena::DroplessArena;
 use rustc_const_eval::const_eval::DummyMachine;
 use rustc_const_eval::interpret::{ImmTy, Immediate, InterpCx, OpTy, Projectable};
@@ -565,31 +564,15 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             StatementKind::SetDiscriminant { box place, variant_index } => {
                 let Some(discr_target) = self.map.find_discr(place.as_ref()) else { return };
                 let enum_ty = place.ty(self.body, self.tcx).ty;
-                // `SetDiscriminant` may be a no-op if the assigned variant is the untagged variant
+                // `SetDiscriminant` guarantees that the discriminant is now `variant_index`.
-                // of a niche encoding. If we cannot ensure that we write to the discriminant, do
+                // Even if the discriminant write does nothing due to niches, it is UB to set the
-                // nothing.
+                // discriminant when the data does not encode the desired discriminant.
-                let Ok(enum_layout) = self.ecx.layout_of(enum_ty) else {
+                let Some(discr) =
+                    self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()
+                else {
                     return;
                 };
-                let writes_discriminant = match enum_layout.variants {
+                self.process_immediate(bb, discr_target, discr, state);
-                    Variants::Single { index } => {
-                        assert_eq!(index, *variant_index);
-                        true
-                    }
-                    Variants::Multiple { tag_encoding: TagEncoding::Direct, .. } => true,
-                    Variants::Multiple {
-                        tag_encoding: TagEncoding::Niche { untagged_variant, .. },
-                        ..
-                    } => *variant_index != untagged_variant,
-                };
-                if writes_discriminant {
-                    let Some(discr) =
-                        self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()
-                    else {
-                        return;
-                    };
-                    self.process_immediate(bb, discr_target, discr, state);
-                }
             }
             // If we expect `lhs ?= true`, we have an opportunity if we assume `lhs == true`.
             StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume(

compiler/rustc_mir_transform/src/large_enums.rs

@@ -216,7 +216,7 @@ impl EnumSizeOpt {
         };
         let layout = tcx.layout_of(typing_env.as_query_input(ty)).ok()?;
         let variants = match &layout.variants {
-            Variants::Single { .. } => return None,
+            Variants::Single { .. } | Variants::Empty => return None,
             Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, .. } => return None,
 
             Variants::Multiple { variants, .. } if variants.len() <= 1 => return None,

compiler/rustc_mir_transform/src/unreachable_enum_branching.rs

@@ -54,6 +54,10 @@ fn variant_discriminants<'tcx>(
     tcx: TyCtxt<'tcx>,
 ) -> FxHashSet<u128> {
     match &layout.variants {
+        Variants::Empty => {
+            // Uninhabited, no valid discriminant.
+            FxHashSet::default()
+        }
         Variants::Single { index } => {
             let mut res = FxHashSet::default();
             res.insert(

compiler/rustc_smir/src/rustc_smir/convert/abi.rs

@@ -167,6 +167,7 @@ impl<'tcx> Stable<'tcx> for rustc_abi::Variants<rustc_abi::FieldIdx, rustc_abi::
             rustc_abi::Variants::Single { index } => {
                 VariantsShape::Single { index: index.stable(tables) }
             }
+            rustc_abi::Variants::Empty => VariantsShape::Empty,
             rustc_abi::Variants::Multiple { tag, tag_encoding, tag_field, variants } => {
                 VariantsShape::Multiple {
                     tag: tag.stable(tables),

compiler/rustc_target/src/callconv/loongarch.rs

@@ -116,7 +116,7 @@ where
             FieldsShape::Arbitrary { .. } => {
                 match arg_layout.variants {
                     abi::Variants::Multiple { .. } => return Err(CannotUseFpConv),
-                    abi::Variants::Single { .. } => (),
+                    abi::Variants::Single { .. } | abi::Variants::Empty => (),
                 }
                 for i in arg_layout.fields.index_by_increasing_offset() {
                     let field = arg_layout.field(cx, i);

compiler/rustc_target/src/callconv/riscv.rs

@@ -122,7 +122,7 @@ where
             FieldsShape::Arbitrary { .. } => {
                 match arg_layout.variants {
                     abi::Variants::Multiple { .. } => return Err(CannotUseFpConv),
-                    abi::Variants::Single { .. } => (),
+                    abi::Variants::Single { .. } | abi::Variants::Empty => (),
                 }
                 for i in arg_layout.fields.index_by_increasing_offset() {
                     let field = arg_layout.field(cx, i);

compiler/rustc_target/src/callconv/x86_64.rs

@@ -65,7 +65,7 @@ where
                 }
 
                 match &layout.variants {
-                    abi::Variants::Single { .. } => {}
+                    abi::Variants::Single { .. } | abi::Variants::Empty => {}
                     abi::Variants::Multiple { variants, .. } => {
                         // Treat enum variants like union members.
                         for variant_idx in variants.indices() {

compiler/rustc_transmute/src/layout/tree.rs

@@ -338,16 +338,11 @@ pub(crate) mod rustc {
                 };
 
             match layout.variants() {
+                Variants::Empty => Ok(Self::uninhabited()),
                 Variants::Single { index } => {
-                    // Hilariously, `Single` is used even for 0-variant enums;
+                    // `Variants::Single` on enums with variants denotes that
-                    // `index` is just junk in that case.
+                    // the enum delegates its layout to the variant at `index`.
-                    if ty.ty_adt_def().unwrap().variants().is_empty() {
+                    layout_of_variant(*index, None)
-                        Ok(Self::uninhabited())
-                    } else {
-                        // `Variants::Single` on enums with variants denotes that
-                        // the enum delegates its layout to the variant at `index`.
-                        layout_of_variant(*index, None)
-                    }
                 }
                 Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
                     // `Variants::Multiple` denotes an enum with multiple
@@ -500,6 +495,10 @@ pub(crate) mod rustc {
         (ty, layout): (Ty<'tcx>, Layout<'tcx>),
         i: FieldIdx,
     ) -> Ty<'tcx> {
+        // We cannot use `ty_and_layout_field` to retrieve the field type, since
+        // `ty_and_layout_field` erases regions in the returned type. We must
+        // not erase regions here, since we may need to ultimately emit outlives
+        // obligations as a consequence of the transmutability analysis.
         match ty.kind() {
             ty::Adt(def, args) => {
                 match layout.variants {
@@ -507,6 +506,7 @@ pub(crate) mod rustc {
                         let field = &def.variant(index).fields[i];
                         field.ty(cx.tcx(), args)
                     }
+                    Variants::Empty => panic!("there is no field in Variants::Empty types"),
                     // Discriminant field for enums (where applicable).
                     Variants::Multiple { tag, .. } => {
                         assert_eq!(i.as_usize(), 0);

compiler/rustc_ty_utils/src/layout.rs

@@ -1104,15 +1104,13 @@ fn variant_info_for_adt<'tcx>(
     };
 
     match layout.variants {
+        Variants::Empty => (vec![], None),
+
         Variants::Single { index } => {
-            if !adt_def.variants().is_empty() && layout.fields != FieldsShape::Primitive {
+            debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variant(index).name);
-                debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variant(index).name);
+            let variant_def = &adt_def.variant(index);
-                let variant_def = &adt_def.variant(index);
+            let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
-                let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
+            (vec![build_variant_info(Some(variant_def.name), &fields, layout)], None)
-                (vec![build_variant_info(Some(variant_def.name), &fields, layout)], None)
-            } else {
-                (vec![], None)
-            }
         }
 
         Variants::Multiple { tag, ref tag_encoding, .. } => {

compiler/rustc_ty_utils/src/layout/invariant.rs

@@ -241,63 +241,81 @@ pub(super) fn layout_sanity_check<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLayou
 
     check_layout_abi(cx, layout);
 
-    if let Variants::Multiple { variants, tag, tag_encoding, .. } = &layout.variants {
+    match &layout.variants {
-        if let TagEncoding::Niche { niche_start, untagged_variant, niche_variants } = tag_encoding {
+        Variants::Empty => {
-            let niche_size = tag.size(cx);
+            assert!(layout.is_uninhabited());
-            assert!(*niche_start <= niche_size.unsigned_int_max());
+        }
-            for (idx, variant) in variants.iter_enumerated() {
+        Variants::Single { index } => {
-                // Ensure all inhabited variants are accounted for.
+            if let Some(variants) = layout.ty.variant_range(tcx) {
-                if !variant.is_uninhabited() {
+                assert!(variants.contains(index));
-                    assert!(idx == *untagged_variant || niche_variants.contains(&idx));
+            } else {
-                }
+                // Types without variants use `0` as dummy variant index.
+                assert!(index.as_u32() == 0);
             }
         }
-        for variant in variants.iter() {
+        Variants::Multiple { variants, tag, tag_encoding, .. } => {
-            // No nested "multiple".
+            if let TagEncoding::Niche { niche_start, untagged_variant, niche_variants } =
-            assert_matches!(variant.variants, Variants::Single { .. });
+                tag_encoding
-            // Variants should have the same or a smaller size as the full thing,
-            // and same for alignment.
-            if variant.size > layout.size {
-                bug!(
-                    "Type with size {} bytes has variant with size {} bytes: {layout:#?}",
-                    layout.size.bytes(),
-                    variant.size.bytes(),
-                )
-            }
-            if variant.align.abi > layout.align.abi {
-                bug!(
-                    "Type with alignment {} bytes has variant with alignment {} bytes: {layout:#?}",
-                    layout.align.abi.bytes(),
-                    variant.align.abi.bytes(),
-                )
-            }
-            // Skip empty variants.
-            if variant.size == Size::ZERO || variant.fields.count() == 0 || variant.is_uninhabited()
             {
-                // These are never actually accessed anyway, so we can skip the coherence check
+                let niche_size = tag.size(cx);
-                // for them. They also fail that check, since they have
+                assert!(*niche_start <= niche_size.unsigned_int_max());
-                // `Aggregate`/`Uninhabited` ABI even when the main type is
+                for (idx, variant) in variants.iter_enumerated() {
-                // `Scalar`/`ScalarPair`. (Note that sometimes, variants with fields have size
+                    // Ensure all inhabited variants are accounted for.
-                // 0, and sometimes, variants without fields have non-0 size.)
+                    if !variant.is_uninhabited() {
-                continue;
+                        assert!(idx == *untagged_variant || niche_variants.contains(&idx));
-            }
+                    }
-            // The top-level ABI and the ABI of the variants should be coherent.
+                }
-            let scalar_coherent =
+            }
-                |s1: Scalar, s2: Scalar| s1.size(cx) == s2.size(cx) && s1.align(cx) == s2.align(cx);
+            for variant in variants.iter() {
-            let abi_coherent = match (layout.backend_repr, variant.backend_repr) {
+                // No nested "multiple".
-                (BackendRepr::Scalar(s1), BackendRepr::Scalar(s2)) => scalar_coherent(s1, s2),
+                assert_matches!(variant.variants, Variants::Single { .. });
-                (BackendRepr::ScalarPair(a1, b1), BackendRepr::ScalarPair(a2, b2)) => {
+                // Variants should have the same or a smaller size as the full thing,
-                    scalar_coherent(a1, a2) && scalar_coherent(b1, b2)
+                // and same for alignment.
+                if variant.size > layout.size {
+                    bug!(
+                        "Type with size {} bytes has variant with size {} bytes: {layout:#?}",
+                        layout.size.bytes(),
+                        variant.size.bytes(),
+                    )
+                }
+                if variant.align.abi > layout.align.abi {
+                    bug!(
+                        "Type with alignment {} bytes has variant with alignment {} bytes: {layout:#?}",
+                        layout.align.abi.bytes(),
+                        variant.align.abi.bytes(),
+                    )
+                }
+                // Skip empty variants.
+                if variant.size == Size::ZERO
+                    || variant.fields.count() == 0
+                    || variant.is_uninhabited()
+                {
+                    // These are never actually accessed anyway, so we can skip the coherence check
+                    // for them. They also fail that check, since they have
+                    // `Aggregate`/`Uninhabited` ABI even when the main type is
+                    // `Scalar`/`ScalarPair`. (Note that sometimes, variants with fields have size
+                    // 0, and sometimes, variants without fields have non-0 size.)
+                    continue;
+                }
+                // The top-level ABI and the ABI of the variants should be coherent.
+                let scalar_coherent = |s1: Scalar, s2: Scalar| {
+                    s1.size(cx) == s2.size(cx) && s1.align(cx) == s2.align(cx)
+                };
+                let abi_coherent = match (layout.backend_repr, variant.backend_repr) {
+                    (BackendRepr::Scalar(s1), BackendRepr::Scalar(s2)) => scalar_coherent(s1, s2),
+                    (BackendRepr::ScalarPair(a1, b1), BackendRepr::ScalarPair(a2, b2)) => {
+                        scalar_coherent(a1, a2) && scalar_coherent(b1, b2)
+                    }
+                    (BackendRepr::Uninhabited, _) => true,
+                    (BackendRepr::Memory { .. }, _) => true,
+                    _ => false,
+                };
+                if !abi_coherent {
+                    bug!(
+                        "Variant ABI is incompatible with top-level ABI:\nvariant={:#?}\nTop-level: {layout:#?}",
+                        variant
+                    );
                 }
-                (BackendRepr::Uninhabited, _) => true,
-                (BackendRepr::Memory { .. }, _) => true,
-                _ => false,
-            };
-            if !abi_coherent {
-                bug!(
-                    "Variant ABI is incompatible with top-level ABI:\nvariant={:#?}\nTop-level: {layout:#?}",
-                    variant
-                );
             }
         }
     }

compiler/stable_mir/src/abi.rs

@@ -180,6 +180,9 @@ impl FieldsShape {
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize)]
 pub enum VariantsShape {
+    /// A type with no valid variants. Must be uninhabited.
+    Empty,
+
     /// Single enum variants, structs/tuples, unions, and all non-ADTs.
     Single { index: VariantIdx },
 

src/bootstrap/src/core/build_steps/compile.rs

@@ -1897,12 +1897,6 @@ impl Step for Assemble {
             });
         }
 
-        let lld_install = if builder.config.lld_enabled {
-            Some(builder.ensure(llvm::Lld { target: target_compiler.host }))
-        } else {
-            None
-        };
-
         let stage = target_compiler.stage;
         let host = target_compiler.host;
         let (host_info, dir_name) = if build_compiler.host == host {
@@ -1963,22 +1957,11 @@ impl Step for Assemble {
 
         copy_codegen_backends_to_sysroot(builder, build_compiler, target_compiler);
 
-        if let Some(lld_install) = lld_install {
+        if builder.config.lld_enabled {
-            let src_exe = exe("lld", target_compiler.host);
+            builder.ensure(crate::core::build_steps::tool::LldWrapper {
-            let dst_exe = exe("rust-lld", target_compiler.host);
+                build_compiler,
-            builder.copy_link(&lld_install.join("bin").join(src_exe), &libdir_bin.join(dst_exe));
+                target_compiler,
-            let self_contained_lld_dir = libdir_bin.join("gcc-ld");
-            t!(fs::create_dir_all(&self_contained_lld_dir));
-            let lld_wrapper_exe = builder.ensure(crate::core::build_steps::tool::LldWrapper {
-                compiler: build_compiler,
-                target: target_compiler.host,
             });
-            for name in crate::LLD_FILE_NAMES {
-                builder.copy_link(
-                    &lld_wrapper_exe,
-                    &self_contained_lld_dir.join(exe(name, target_compiler.host)),
-                );
-            }
         }
 
         if builder.config.llvm_enabled(target_compiler.host) && builder.config.llvm_tools_enabled {

src/bootstrap/src/core/build_steps/tool.rs

@@ -1,8 +1,8 @@
 use std::path::PathBuf;
 use std::{env, fs};
 
-use crate::core::build_steps::compile;
 use crate::core::build_steps::toolstate::ToolState;
+use crate::core::build_steps::{compile, llvm};
 use crate::core::builder;
 use crate::core::builder::{Builder, Cargo as CargoCommand, RunConfig, ShouldRun, Step};
 use crate::core::config::TargetSelection;
@@ -722,21 +722,27 @@ impl Step for Cargo {
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
 pub struct LldWrapper {
-    pub compiler: Compiler,
+    pub build_compiler: Compiler,
-    pub target: TargetSelection,
+    pub target_compiler: Compiler,
 }
 
 impl Step for LldWrapper {
-    type Output = PathBuf;
+    type Output = ();
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.never()
     }
 
-    fn run(self, builder: &Builder<'_>) -> PathBuf {
+    fn run(self, builder: &Builder<'_>) {
-        builder.ensure(ToolBuild {
+        if builder.config.dry_run() {
-            compiler: self.compiler,
+            return;
-            target: self.target,
+        }
+
+        let target = self.target_compiler.host;
+
+        let executable = builder.ensure(ToolBuild {
+            compiler: self.build_compiler,
+            target,
             tool: "lld-wrapper",
             mode: Mode::ToolStd,
             path: "src/tools/lld-wrapper",
@@ -744,7 +750,22 @@ impl Step for LldWrapper {
             extra_features: Vec::new(),
             allow_features: "",
             cargo_args: Vec::new(),
-        })
+        });
+
+        let libdir_bin = builder.sysroot_target_bindir(self.target_compiler, target);
+        t!(fs::create_dir_all(&libdir_bin));
+
+        let lld_install = builder.ensure(llvm::Lld { target });
+        let src_exe = exe("lld", target);
+        let dst_exe = exe("rust-lld", target);
+
+        builder.copy_link(&lld_install.join("bin").join(src_exe), &libdir_bin.join(dst_exe));
+        let self_contained_lld_dir = libdir_bin.join("gcc-ld");
+        t!(fs::create_dir_all(&self_contained_lld_dir));
+
+        for name in crate::LLD_FILE_NAMES {
+            builder.copy_link(&executable, &self_contained_lld_dir.join(exe(name, target)));
+        }
     }
 }
 

src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile

@@ -28,4 +28,6 @@ RUN echo "optimize = false" >> /config/nopt-std-config.toml
 
 ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu --disable-optimize-tests
 ARG SCRIPT_ARG
-ENV SCRIPT=${SCRIPT_ARG}
+COPY scripts/stage_2_test_set1.sh /scripts/
+COPY scripts/stage_2_test_set2.sh /scripts/
+ENV SCRIPT ${SCRIPT_ARG}

src/ci/docker/host-x86_64/i686-gnu/Dockerfile

@@ -25,4 +25,6 @@ RUN sh /scripts/sccache.sh
 
 ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu
 ARG SCRIPT_ARG
-ENV SCRIPT=${SCRIPT_ARG}
+COPY scripts/stage_2_test_set1.sh /scripts/
+COPY scripts/stage_2_test_set2.sh /scripts/
+ENV SCRIPT /scripts/${SCRIPT_ARG}

src/ci/docker/host-x86_64/x86_64-gnu-llvm-18/Dockerfile

@@ -60,9 +60,12 @@ COPY scripts/build-gccjit.sh /scripts/
 RUN /scripts/build-gccjit.sh /scripts
 
 ARG SCRIPT_ARG
-COPY scripts/add_dummy_commit.sh /tmp/add_dummy_commit.sh
+
-COPY scripts/x86_64-gnu-llvm.sh /tmp/x86_64-gnu-llvm.sh
+COPY scripts/add_dummy_commit.sh /tmp/
-COPY scripts/x86_64-gnu-llvm1.sh /tmp/x86_64-gnu-llvm1.sh
+COPY scripts/x86_64-gnu-llvm.sh /tmp/
-COPY scripts/x86_64-gnu-llvm2.sh /tmp/x86_64-gnu-llvm2.sh
+COPY scripts/x86_64-gnu-llvm2.sh /tmp/
-COPY scripts/x86_64-gnu-llvm3.sh /tmp/x86_64-gnu-llvm3.sh
+COPY scripts/x86_64-gnu-llvm3.sh /tmp/
-ENV SCRIPT /tmp/${SCRIPT_ARG}
+COPY scripts/stage_2_test_set1.sh /tmp/
+COPY scripts/stage_2_test_set2.sh /tmp/
+
+ENV SCRIPT "/tmp/add_dummy_commit.sh && /tmp/${SCRIPT_ARG}"

src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile

@@ -60,9 +60,12 @@ COPY scripts/build-gccjit.sh /scripts/
 RUN /scripts/build-gccjit.sh /scripts
 
 ARG SCRIPT_ARG
-COPY scripts/add_dummy_commit.sh /tmp/add_dummy_commit.sh
+
-COPY scripts/x86_64-gnu-llvm.sh /tmp/x86_64-gnu-llvm.sh
+COPY scripts/add_dummy_commit.sh /tmp/
-COPY scripts/x86_64-gnu-llvm1.sh /tmp/x86_64-gnu-llvm1.sh
+COPY scripts/x86_64-gnu-llvm.sh /tmp/
-COPY scripts/x86_64-gnu-llvm2.sh /tmp/x86_64-gnu-llvm2.sh
+COPY scripts/x86_64-gnu-llvm2.sh /tmp/
-COPY scripts/x86_64-gnu-llvm3.sh /tmp/x86_64-gnu-llvm3.sh
+COPY scripts/x86_64-gnu-llvm3.sh /tmp/
-ENV SCRIPT /tmp/${SCRIPT_ARG}
+COPY scripts/stage_2_test_set1.sh /tmp/
+COPY scripts/stage_2_test_set2.sh /tmp/
+
+ENV SCRIPT "/tmp/add_dummy_commit.sh && /tmp/${SCRIPT_ARG}"

src/ci/docker/scripts/stage_2_test_set1.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -ex
+
+# Run a subset of tests. Used to run tests in parallel in multiple jobs.
+
+../x.py --stage 2 test \
+  --skip compiler \
+  --skip src

src/ci/docker/scripts/stage_2_test_set2.sh

@@ -2,7 +2,7 @@
 
 set -ex
 
-/tmp/add_dummy_commit.sh
+# Run a subset of tests. Used to run tests in parallel in multiple jobs.
 
 ../x.py --stage 2 test \
   --skip tests \

src/ci/docker/scripts/x86_64-gnu-llvm.sh

@@ -2,8 +2,6 @@
 
 set -ex
 
-/tmp/add_dummy_commit.sh
-
 # NOTE: intentionally uses all of `x.py`, `x`, and `x.ps1` to make sure they all work on Linux.
 ../x.py --stage 2 test --skip src/tools/tidy
 

src/ci/docker/scripts/x86_64-gnu-llvm2.sh

@@ -2,13 +2,9 @@
 
 set -ex
 
-/tmp/add_dummy_commit.sh
-
 ##### Test stage 2 #####
 
-../x.py --stage 2 test \
+/tmp/stage_2_test_set1.sh
-  --skip compiler \
-  --skip src
 
 # Run the `mir-opt` tests again but this time for a 32-bit target.
 # This enforces that tests using `// EMIT_MIR_FOR_EACH_BIT_WIDTH` have

src/ci/github-actions/jobs.yml

@@ -58,22 +58,6 @@ envs:
     NO_DEBUG_ASSERTIONS: 1
     NO_OVERFLOW_CHECKS: 1
 
-  # Different set of tests to run tests in parallel in multiple jobs.
-  stage_2_test_set1: &stage_2_test_set1
-    DOCKER_SCRIPT: >-
-      python3 ../x.py --stage 2 test
-      --skip compiler
-      --skip src
-
-  stage_2_test_set2: &stage_2_test_set2
-    DOCKER_SCRIPT: >-
-      python3 ../x.py --stage 2 test
-      --skip tests
-      --skip coverage-map
-      --skip coverage-run
-      --skip library
-      --skip tidyselftest
-
   production:
     &production
     DEPLOY_BUCKET: rust-lang-ci2
@@ -234,14 +218,14 @@ auto:
   - image: i686-gnu-1
     env:
       IMAGE: i686-gnu
-      <<: *stage_2_test_set1
+      DOCKER_SCRIPT: stage_2_test_set1.sh
     <<: *job-linux-4c
 
   # Skip tests that run in i686-gnu-1
   - image: i686-gnu-2
     env:
       IMAGE: i686-gnu
-      <<: *stage_2_test_set2
+      DOCKER_SCRIPT: stage_2_test_set2.sh
     <<: *job-linux-4c
 
   # The i686-gnu-nopt job is split into multiple jobs to run tests in parallel.
@@ -249,7 +233,7 @@ auto:
   - image: i686-gnu-nopt-1
     env:
       IMAGE: i686-gnu-nopt
-      <<: *stage_2_test_set1
+      DOCKER_SCRIPT: /scripts/stage_2_test_set1.sh
     <<: *job-linux-4c
 
   # Skip tests that run in i686-gnu-nopt-1
@@ -258,12 +242,7 @@ auto:
       IMAGE: i686-gnu-nopt
       DOCKER_SCRIPT: >-
         python3 ../x.py test --stage 0 --config /config/nopt-std-config.toml library/std &&
-        python3 ../x.py --stage 2 test
+        /scripts/stage_2_test_set2.sh
-        --skip tests
-        --skip coverage-map
-        --skip coverage-run
-        --skip library
-        --skip tidyselftest
     <<: *job-linux-4c
 
   - image: mingw-check
@@ -319,7 +298,7 @@ auto:
     env:
       RUST_BACKTRACE: 1
       IMAGE: x86_64-gnu-llvm-19
-      DOCKER_SCRIPT: x86_64-gnu-llvm1.sh
+      DOCKER_SCRIPT: stage_2_test_set1.sh
     <<: *job-linux-4c
 
   # Skip tests that run in x86_64-gnu-llvm-19-{1,3}
@@ -345,7 +324,7 @@ auto:
       RUST_BACKTRACE: 1
       READ_ONLY_SRC: "0"
       IMAGE: x86_64-gnu-llvm-18
-      DOCKER_SCRIPT: x86_64-gnu-llvm1.sh
+      DOCKER_SCRIPT: stage_2_test_set1.sh
     <<: *job-linux-4c
 
   # Skip tests that run in x86_64-gnu-llvm-18-{1,3}

src/librustdoc/html/markdown.rs

@@ -344,35 +344,48 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for CodeBlocks<'_, 'a, I> {
 }
 
 /// Make headings links with anchor IDs and build up TOC.
-struct LinkReplacer<'a, I: Iterator<Item = Event<'a>>> {
+struct LinkReplacerInner<'a> {
-    inner: I,
     links: &'a [RenderedLink],
     shortcut_link: Option<&'a RenderedLink>,
 }
 
+struct LinkReplacer<'a, I: Iterator<Item = Event<'a>>> {
+    iter: I,
+    inner: LinkReplacerInner<'a>,
+}
+
 impl<'a, I: Iterator<Item = Event<'a>>> LinkReplacer<'a, I> {
     fn new(iter: I, links: &'a [RenderedLink]) -> Self {
-        LinkReplacer { inner: iter, links, shortcut_link: None }
+        LinkReplacer { iter, inner: { LinkReplacerInner { links, shortcut_link: None } } }
     }
 }
 
-impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
+// FIXME: Once we have specialized trait impl (for `Iterator` impl on `LinkReplacer`),
-    type Item = Event<'a>;
+// we can remove this type and move back `LinkReplacerInner` fields into `LinkReplacer`.
+struct SpannedLinkReplacer<'a, I: Iterator<Item = SpannedEvent<'a>>> {
+    iter: I,
+    inner: LinkReplacerInner<'a>,
+}
 
-    fn next(&mut self) -> Option<Self::Item> {
+impl<'a, I: Iterator<Item = SpannedEvent<'a>>> SpannedLinkReplacer<'a, I> {
-        let mut event = self.inner.next();
+    fn new(iter: I, links: &'a [RenderedLink]) -> Self {
+        SpannedLinkReplacer { iter, inner: { LinkReplacerInner { links, shortcut_link: None } } }
+    }
+}
 
+impl<'a> LinkReplacerInner<'a> {
+    fn handle_event(&mut self, event: &mut Event<'a>) {
         // Replace intra-doc links and remove disambiguators from shortcut links (`[fn@f]`).
-        match &mut event {
+        match event {
             // This is a shortcut link that was resolved by the broken_link_callback: `[fn@f]`
             // Remove any disambiguator.
-            Some(Event::Start(Tag::Link {
+            Event::Start(Tag::Link {
                 // [fn@f] or [fn@f][]
                 link_type: LinkType::ShortcutUnknown | LinkType::CollapsedUnknown,
                 dest_url,
                 title,
                 ..
-            })) => {
+            }) => {
                 debug!("saw start of shortcut link to {dest_url} with title {title}");
                 // If this is a shortcut link, it was resolved by the broken_link_callback.
                 // So the URL will already be updated properly.
@@ -389,13 +402,13 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
                 }
             }
             // Now that we're done with the shortcut link, don't replace any more text.
-            Some(Event::End(TagEnd::Link)) if self.shortcut_link.is_some() => {
+            Event::End(TagEnd::Link) if self.shortcut_link.is_some() => {
                 debug!("saw end of shortcut link");
                 self.shortcut_link = None;
             }
             // Handle backticks in inline code blocks, but only if we're in the middle of a shortcut link.
             // [`fn@f`]
-            Some(Event::Code(text)) => {
+            Event::Code(text) => {
                 trace!("saw code {text}");
                 if let Some(link) = self.shortcut_link {
                     // NOTE: this only replaces if the code block is the *entire* text.
@@ -418,7 +431,7 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
             }
             // Replace plain text in links, but only in the middle of a shortcut link.
             // [fn@f]
-            Some(Event::Text(text)) => {
+            Event::Text(text) => {
                 trace!("saw text {text}");
                 if let Some(link) = self.shortcut_link {
                     // NOTE: same limitations as `Event::Code`
@@ -434,7 +447,7 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
             }
             // If this is a link, but not a shortcut link,
             // replace the URL, since the broken_link_callback was not called.
-            Some(Event::Start(Tag::Link { dest_url, title, .. })) => {
+            Event::Start(Tag::Link { dest_url, title, .. }) => {
                 if let Some(link) =
                     self.links.iter().find(|&link| *link.original_text == **dest_url)
                 {
@@ -447,12 +460,33 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
             // Anything else couldn't have been a valid Rust path, so no need to replace the text.
             _ => {}
         }
+    }
+}
 
+impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
+    type Item = Event<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut event = self.iter.next();
+        if let Some(ref mut event) = event {
+            self.inner.handle_event(event);
+        }
         // Yield the modified event
         event
     }
 }
 
+impl<'a, I: Iterator<Item = SpannedEvent<'a>>> Iterator for SpannedLinkReplacer<'a, I> {
+    type Item = SpannedEvent<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let Some((mut event, range)) = self.iter.next() else { return None };
+        self.inner.handle_event(&mut event);
+        // Yield the modified event
+        Some((event, range))
+    }
+}
+
 /// Wrap HTML tables into `<div>` to prevent having the doc blocks width being too big.
 struct TableWrapper<'a, I: Iterator<Item = Event<'a>>> {
     inner: I,
@@ -1339,9 +1373,9 @@ impl<'a> Markdown<'a> {
 
         ids.handle_footnotes(|ids, existing_footnotes| {
             let p = HeadingLinks::new(p, None, ids, heading_offset);
+            let p = SpannedLinkReplacer::new(p, links);
             let p = footnotes::Footnotes::new(p, existing_footnotes);
-            let p = LinkReplacer::new(p.map(|(ev, _)| ev), links);
+            let p = TableWrapper::new(p.map(|(ev, _)| ev));
-            let p = TableWrapper::new(p);
             CodeBlocks::new(p, codes, edition, playground)
         })
     }

src/tools/miri/src/helpers.rs

@@ -605,7 +605,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                             // `UnsafeCell` action.
                             (self.unsafe_cell_action)(v)
                         }
-                        Variants::Single { .. } => {
+                        Variants::Single { .. } | Variants::Empty => {
                             // Proceed further, try to find where exactly that `UnsafeCell`
                             // is hiding.
                             self.walk_value(v)

src/tools/rust-analyzer/crates/hir-ty/src/mir/eval.rs

@@ -813,7 +813,7 @@ impl Evaluator<'_> {
                 ProjectionElem::Field(Either::Left(f)) => {
                     let layout = self.layout(&prev_ty)?;
                     let variant_layout = match &layout.variants {
-                        Variants::Single { .. } => &layout,
+                        Variants::Single { .. } | Variants::Empty => &layout,
                         Variants::Multiple { variants, .. } => {
                             &variants[match f.parent {
                                 hir_def::VariantId::EnumVariantId(it) => {
@@ -1638,6 +1638,7 @@ impl Evaluator<'_> {
             return Ok(0);
         };
         match &layout.variants {
+            Variants::Empty => unreachable!(),
             Variants::Single { index } => {
                 let r = self.const_eval_discriminant(self.db.enum_data(e).variants[index.0].0)?;
                 Ok(r)
@@ -1800,7 +1801,7 @@ impl Evaluator<'_> {
         }
         let layout = self.layout_adt(adt, subst)?;
         Ok(match &layout.variants {
-            Variants::Single { .. } => (layout.size.bytes_usize(), layout, None),
+            Variants::Single { .. } | Variants::Empty => (layout.size.bytes_usize(), layout, None),
             Variants::Multiple { variants, tag, tag_encoding, .. } => {
                 let enum_variant_id = match it {
                     VariantId::EnumVariantId(it) => it,

src/tools/rust-analyzer/crates/hir-ty/src/utils.rs

@@ -334,6 +334,7 @@ pub(crate) fn detect_variant_from_bytes<'a>(
     e: EnumId,
 ) -> Option<(EnumVariantId, &'a Layout)> {
     let (var_id, var_layout) = match &layout.variants {
+        hir_def::layout::Variants::Empty => unreachable!(),
         hir_def::layout::Variants::Single { index } => {
             (db.enum_data(e).variants[index.0].0, layout)
         }

tests/mir-opt/set_no_discriminant.f.JumpThreading.diff

@@ -10,7 +10,8 @@
           _2 = E::<char>::A;
           discriminant(_2) = 1;
           _1 = discriminant(_2);
-          switchInt(copy _1) -> [0: bb1, otherwise: bb2];
+-         switchInt(copy _1) -> [0: bb1, otherwise: bb2];
++         goto -> bb2;
       }
   
       bb1: {

tests/mir-opt/set_no_discriminant.generic.JumpThreading.diff

@@ -10,7 +10,8 @@
           _2 = E::<T>::A;
           discriminant(_2) = 1;
           _1 = discriminant(_2);
-          switchInt(copy _1) -> [0: bb1, otherwise: bb2];
+-         switchInt(copy _1) -> [0: bb1, otherwise: bb2];
++         goto -> bb2;
       }
   
       bb1: {

tests/mir-opt/set_no_discriminant.rs

@@ -1,5 +1,6 @@
 // `SetDiscriminant` does not actually write anything if the chosen variant is the untagged variant
-// of a niche encoding. Verify that we do not thread over this case.
+// of a niche encoding. However, it is UB to call `SetDiscriminant` with the untagged variant if the
+// value currently encodes a different variant. Verify that we do correctly thread in this case.
 //@ test-mir-pass: JumpThreading
 
 #![feature(custom_mir)]
@@ -16,20 +17,21 @@ enum E<T> {
 #[custom_mir(dialect = "runtime")]
 pub fn f() -> usize {
     // CHECK-LABEL: fn f(
-    // CHECK-NOT: goto
+    // CHECK-NOT: switchInt
-    // CHECK: switchInt(
+    // CHECK: goto
-    // CHECK-NOT: goto
+    // CHECK-NOT: switchInt
     mir! {
         let a: isize;
         let e: E<char>;
         {
             e = E::A;
-            SetDiscriminant(e, 1);
+            SetDiscriminant(e, 1); // UB!
             a = Discriminant(e);
             match a {
                 0 => bb0,
                 _ => bb1,
             }
+
         }
         bb0 = {
             RET = 0;
@@ -46,15 +48,15 @@ pub fn f() -> usize {
 #[custom_mir(dialect = "runtime")]
 pub fn generic<T>() -> usize {
     // CHECK-LABEL: fn generic(
-    // CHECK-NOT: goto
+    // CHECK-NOT: switchInt
-    // CHECK: switchInt(
+    // CHECK: goto
-    // CHECK-NOT: goto
+    // CHECK-NOT: switchInt
     mir! {
         let a: isize;
         let e: E<T>;
         {
             e = E::A;
-            SetDiscriminant(e, 1);
+            SetDiscriminant(e, 1); // UB!
             a = Discriminant(e);
             match a {
                 0 => bb0,
@@ -72,6 +74,7 @@ pub fn generic<T>() -> usize {
     }
 }
 
+// CHECK-LABEL: fn main(
 fn main() {
     assert_eq!(f(), 0);
     assert_eq!(generic::<char>(), 0);

tests/rustdoc/intra-doc/link-in-footnotes-132208.rs

@@ -0,0 +1,24 @@
+// Rustdoc has multiple passes and if the footnote pass is run before the link replacer
+// one, intra doc links are not generated inside footnote definitions. This test
+// therefore ensures that intra-doc link are correctly generated inside footnote
+// definitions.
+//
+// Regression test for <https://github.com/rust-lang/rust/issues/132208>.
+
+#![crate_name = "foo"]
+
+//@ has 'foo/index.html'
+//@ has - '//*[@class="docblock"]//a[@href="struct.Bar.html"]' 'a'
+//@ has - '//*[@class="docblock"]//*[@class="footnotes"]//a[@href="struct.Foo.html"]' 'b'
+
+//! [a]: crate::Bar
+//! [b]: crate::Foo
+//!
+//! link in body: [a]
+//!
+//! see footnote[^1]
+//!
+//! [^1]: link in footnote: [b]
+
+pub struct Bar;
+pub struct Foo;

tests/ui/pattern/slice-pattern-refutable.stderr

@@ -1,13 +1,15 @@
 error[E0282]: type annotations needed
-  --> $DIR/slice-pattern-refutable.rs:14:9
+  --> $DIR/slice-pattern-refutable.rs:14:28
    |
 LL |     let [a, b, c] = Zeroes.into() else {
-   |         ^^^^^^^^^
+   |         ---------          ^^^^
+   |         |
+   |         type must be known at this point
    |
-help: consider giving this pattern a type
+help: try using a fully qualified path to specify the expected types
    |
-LL |     let [a, b, c]: /* Type */ = Zeroes.into() else {
+LL |     let [a, b, c] = <Zeroes as Into<T>>::into(Zeroes) else {
-   |                  ++++++++++++
+   |                     ++++++++++++++++++++++++++      ~
 
 error[E0282]: type annotations needed
   --> $DIR/slice-pattern-refutable.rs:21:31

tests/ui/pattern/slice-patterns-ambiguity.stderr

@@ -1,13 +1,15 @@
-error[E0282]: type annotations needed for `&_`
+error[E0282]: type annotations needed
-  --> $DIR/slice-patterns-ambiguity.rs:25:9
+  --> $DIR/slice-patterns-ambiguity.rs:25:26
    |
 LL |     let &[a, b] = Zeroes.into() else {
-   |         ^^^^^^^
+   |          ------          ^^^^
+   |          |
+   |          type must be known at this point
    |
-help: consider giving this pattern a type, where the placeholders `_` are specified
+help: try using a fully qualified path to specify the expected types
    |
-LL |     let &[a, b]: &_ = Zeroes.into() else {
+LL |     let &[a, b] = <Zeroes as Into<&_>>::into(Zeroes) else {
-   |                ++++
+   |                   +++++++++++++++++++++++++++      ~
 
 error[E0282]: type annotations needed
   --> $DIR/slice-patterns-ambiguity.rs:32:29