diff --git a/compiler/rustc_arena/src/lib.rs b/compiler/rustc_arena/src/lib.rs
index e54fcaf6fc1..6f9ecb9cd21 100644
--- a/compiler/rustc_arena/src/lib.rs
+++ b/compiler/rustc_arena/src/lib.rs
@@ -111,7 +111,7 @@ impl<T> Default for TypedArena<T> {
             // alloc() will trigger a grow().
             ptr: Cell::new(ptr::null_mut()),
             end: Cell::new(ptr::null_mut()),
-            chunks: RefCell::new(vec![]),
+            chunks: Default::default(),
             _own: PhantomData,
         }
     }
@@ -325,13 +325,17 @@ unsafe impl<#[may_dangle] T> Drop for TypedArena<T> {
 
 unsafe impl<T: Send> Send for TypedArena<T> {}
 
+/// An arena that can hold objects of multiple different types that impl `Copy`
+/// and/or satisfy `!mem::needs_drop`.
 pub struct DroplessArena {
     /// A pointer to the start of the free space.
     start: Cell<*mut u8>,
 
     /// A pointer to the end of free space.
     ///
-    /// The allocation proceeds from the end of the chunk towards the start.
+    /// The allocation proceeds downwards from the end of the chunk towards the
+    /// start. (This is slightly simpler and faster than allocating upwards,
+    /// see <https://fitzgeraldnick.com/2019/11/01/always-bump-downwards.html>.)
     /// When this pointer crosses the start pointer, a new chunk is allocated.
     end: Cell<*mut u8>,
 
@@ -516,10 +520,14 @@ impl DroplessArena {
     }
 }
 
+// Declare an `Arena` containing one dropless arena and many typed arenas (the
+// types of the typed arenas are specified by the arguments). The dropless
+// arena will be used for any types that impl `Copy`, and also for any of the
+// specified types that satisfy `!mem::needs_drop`.
 #[rustc_macro_transparency = "semitransparent"]
-pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) {
+pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
     #[derive(Default)]
-    pub struct Arena<$tcx> {
+    pub struct Arena<'tcx> {
         pub dropless: $crate::DroplessArena,
         $($name: $crate::TypedArena<$ty>,)*
     }
@@ -532,6 +540,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) {
         ) -> &'a mut [Self];
     }
 
+    // Any type that impls `Copy` can be arena-allocated in the `DroplessArena`.
     impl<'tcx, T: Copy> ArenaAllocatable<'tcx, ()> for T {
         #[inline]
         fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
@@ -544,12 +553,11 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) {
         ) -> &'a mut [Self] {
             arena.dropless.alloc_from_iter(iter)
         }
-
     }
     $(
-        impl<$tcx> ArenaAllocatable<$tcx, $ty> for $ty {
+        impl<'tcx> ArenaAllocatable<'tcx, $ty> for $ty {
             #[inline]
-            fn allocate_on<'a>(self, arena: &'a Arena<$tcx>) -> &'a mut Self {
+            fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
                 if !::std::mem::needs_drop::<Self>() {
                     arena.dropless.alloc(self)
                 } else {
@@ -559,7 +567,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) {
 
             #[inline]
             fn allocate_from_iter<'a>(
-                arena: &'a Arena<$tcx>,
+                arena: &'a Arena<'tcx>,
                 iter: impl ::std::iter::IntoIterator<Item = Self>,
             ) -> &'a mut [Self] {
                 if !::std::mem::needs_drop::<Self>() {
@@ -577,6 +585,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) {
             value.allocate_on(self)
         }
 
+        // Any type that impls `Copy` can have slices be arena-allocated in the `DroplessArena`.
         #[inline]
         pub fn alloc_slice<T: ::std::marker::Copy>(&self, value: &[T]) -> &mut [T] {
             if value.is_empty() {
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index fef6e87bfdb..2b3a538772e 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -84,7 +84,7 @@ mod item;
 mod pat;
 mod path;
 
-rustc_hir::arena_types!(rustc_arena::declare_arena, 'tcx);
+rustc_hir::arena_types!(rustc_arena::declare_arena);
 
 struct LoweringContext<'a, 'hir: 'a> {
     /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
index 7bf378601e0..a92b20f5cb5 100644
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ b/compiler/rustc_const_eval/src/transform/promote_consts.rs
@@ -93,17 +93,8 @@ impl TempState {
 /// returned value in a promoted MIR, unless it's a subset
 /// of a larger candidate.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
-pub enum Candidate {
-    /// Borrow of a constant temporary, candidate for lifetime extension.
-    Ref(Location),
-}
-
-impl Candidate {
-    fn source_info(&self, body: &Body<'_>) -> SourceInfo {
-        match self {
-            Candidate::Ref(location) => *body.source_info(*location),
-        }
-    }
+pub struct Candidate {
+    location: Location,
 }
 
 struct Collector<'a, 'tcx> {
@@ -167,7 +158,7 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
 
         match *rvalue {
             Rvalue::Ref(..) => {
-                self.candidates.push(Candidate::Ref(location));
+                self.candidates.push(Candidate { location });
             }
             _ => {}
         }
@@ -209,36 +200,33 @@ struct Unpromotable;
 
 impl<'tcx> Validator<'_, 'tcx> {
     fn validate_candidate(&self, candidate: Candidate) -> Result<(), Unpromotable> {
-        match candidate {
-            Candidate::Ref(loc) => {
-                let statement = &self.body[loc.block].statements[loc.statement_index];
-                match &statement.kind {
-                    StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
-                        // We can only promote interior borrows of promotable temps (non-temps
-                        // don't get promoted anyway).
-                        self.validate_local(place.local)?;
+        let loc = candidate.location;
+        let statement = &self.body[loc.block].statements[loc.statement_index];
+        match &statement.kind {
+            StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
+                // We can only promote interior borrows of promotable temps (non-temps
+                // don't get promoted anyway).
+                self.validate_local(place.local)?;
 
-                        // The reference operation itself must be promotable.
-                        // (Needs to come after `validate_local` to avoid ICEs.)
-                        self.validate_ref(*kind, place)?;
+                // The reference operation itself must be promotable.
+                // (Needs to come after `validate_local` to avoid ICEs.)
+                self.validate_ref(*kind, place)?;
 
-                        // We do not check all the projections (they do not get promoted anyway),
-                        // but we do stay away from promoting anything involving a dereference.
-                        if place.projection.contains(&ProjectionElem::Deref) {
-                            return Err(Unpromotable);
-                        }
-
-                        // We cannot promote things that need dropping, since the promoted value
-                        // would not get dropped.
-                        if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
-                            return Err(Unpromotable);
-                        }
-
-                        Ok(())
-                    }
-                    _ => bug!(),
+                // We do not check all the projections (they do not get promoted anyway),
+                // but we do stay away from promoting anything involving a dereference.
+                if place.projection.contains(&ProjectionElem::Deref) {
+                    return Err(Unpromotable);
                 }
+
+                // We cannot promote things that need dropping, since the promoted value
+                // would not get dropped.
+                if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
+                    return Err(Unpromotable);
+                }
+
+                Ok(())
             }
+            _ => bug!(),
         }
     }
 
@@ -871,58 +859,55 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                 }))
             };
             let (blocks, local_decls) = self.source.basic_blocks_and_local_decls_mut();
-            match candidate {
-                Candidate::Ref(loc) => {
-                    let statement = &mut blocks[loc.block].statements[loc.statement_index];
-                    match statement.kind {
-                        StatementKind::Assign(box (
-                            _,
-                            Rvalue::Ref(ref mut region, borrow_kind, ref mut place),
-                        )) => {
-                            // Use the underlying local for this (necessarily interior) borrow.
-                            let ty = local_decls.local_decls()[place.local].ty;
-                            let span = statement.source_info.span;
+            let loc = candidate.location;
+            let statement = &mut blocks[loc.block].statements[loc.statement_index];
+            match statement.kind {
+                StatementKind::Assign(box (
+                    _,
+                    Rvalue::Ref(ref mut region, borrow_kind, ref mut place),
+                )) => {
+                    // Use the underlying local for this (necessarily interior) borrow.
+                    let ty = local_decls.local_decls()[place.local].ty;
+                    let span = statement.source_info.span;
 
-                            let ref_ty = tcx.mk_ref(
-                                tcx.lifetimes.re_erased,
-                                ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() },
-                            );
+                    let ref_ty = tcx.mk_ref(
+                        tcx.lifetimes.re_erased,
+                        ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() },
+                    );
 
-                            *region = tcx.lifetimes.re_erased;
+                    *region = tcx.lifetimes.re_erased;
 
-                            let mut projection = vec![PlaceElem::Deref];
-                            projection.extend(place.projection);
-                            place.projection = tcx.intern_place_elems(&projection);
+                    let mut projection = vec![PlaceElem::Deref];
+                    projection.extend(place.projection);
+                    place.projection = tcx.intern_place_elems(&projection);
 
-                            // Create a temp to hold the promoted reference.
-                            // This is because `*r` requires `r` to be a local,
-                            // otherwise we would use the `promoted` directly.
-                            let mut promoted_ref = LocalDecl::new(ref_ty, span);
-                            promoted_ref.source_info = statement.source_info;
-                            let promoted_ref = local_decls.push(promoted_ref);
-                            assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);
+                    // Create a temp to hold the promoted reference.
+                    // This is because `*r` requires `r` to be a local,
+                    // otherwise we would use the `promoted` directly.
+                    let mut promoted_ref = LocalDecl::new(ref_ty, span);
+                    promoted_ref.source_info = statement.source_info;
+                    let promoted_ref = local_decls.push(promoted_ref);
+                    assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);
 
-                            let promoted_ref_statement = Statement {
-                                source_info: statement.source_info,
-                                kind: StatementKind::Assign(Box::new((
-                                    Place::from(promoted_ref),
-                                    Rvalue::Use(promoted_operand(ref_ty, span)),
-                                ))),
-                            };
-                            self.extra_statements.push((loc, promoted_ref_statement));
+                    let promoted_ref_statement = Statement {
+                        source_info: statement.source_info,
+                        kind: StatementKind::Assign(Box::new((
+                            Place::from(promoted_ref),
+                            Rvalue::Use(promoted_operand(ref_ty, span)),
+                        ))),
+                    };
+                    self.extra_statements.push((loc, promoted_ref_statement));
 
-                            Rvalue::Ref(
-                                tcx.lifetimes.re_erased,
-                                borrow_kind,
-                                Place {
-                                    local: mem::replace(&mut place.local, promoted_ref),
-                                    projection: List::empty(),
-                                },
-                            )
-                        }
-                        _ => bug!(),
-                    }
+                    Rvalue::Ref(
+                        tcx.lifetimes.re_erased,
+                        borrow_kind,
+                        Place {
+                            local: mem::replace(&mut place.local, promoted_ref),
+                            projection: List::empty(),
+                        },
+                    )
                 }
+                _ => bug!(),
             }
         };
 
@@ -964,17 +949,13 @@ pub fn promote_candidates<'tcx>(
 
     let mut extra_statements = vec![];
     for candidate in candidates.into_iter().rev() {
-        match candidate {
-            Candidate::Ref(Location { block, statement_index }) => {
-                if let StatementKind::Assign(box (place, _)) =
-                    &body[block].statements[statement_index].kind
-                {
-                    if let Some(local) = place.as_local() {
-                        if temps[local] == TempState::PromotedOut {
-                            // Already promoted.
-                            continue;
-                        }
-                    }
+        let Location { block, statement_index } = candidate.location;
+        if let StatementKind::Assign(box (place, _)) = &body[block].statements[statement_index].kind
+        {
+            if let Some(local) = place.as_local() {
+                if temps[local] == TempState::PromotedOut {
+                    // Already promoted.
+                    continue;
                 }
             }
         }
@@ -982,7 +963,7 @@ pub fn promote_candidates<'tcx>(
         // Declare return place local so that `mir::Body::new` doesn't complain.
         let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect();
 
-        let mut scope = body.source_scopes[candidate.source_info(body).scope].clone();
+        let mut scope = body.source_scopes[body.source_info(candidate.location).scope].clone();
         scope.parent_scope = None;
 
         let promoted = Body::new(
diff --git a/compiler/rustc_hir/src/arena.rs b/compiler/rustc_hir/src/arena.rs
index 5091a7bccc5..f19ca497d8b 100644
--- a/compiler/rustc_hir/src/arena.rs
+++ b/compiler/rustc_hir/src/arena.rs
@@ -1,52 +1,52 @@
-/// This declares a list of types which can be allocated by `Arena`.
+/// This higher-order macro declares a list of types which can be allocated by `Arena`.
 ///
 /// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]`,
 /// where `T` is the type listed. These impls will appear in the implement_ty_decoder! macro.
 #[macro_export]
 macro_rules! arena_types {
-    ($macro:path, $tcx:lifetime) => (
+    ($macro:path) => (
         $macro!([
             // HIR types
-            [] hir_krate: rustc_hir::Crate<$tcx>,
-            [] arm: rustc_hir::Arm<$tcx>,
-            [] asm_operand: (rustc_hir::InlineAsmOperand<$tcx>, Span),
+            [] hir_krate: rustc_hir::Crate<'tcx>,
+            [] arm: rustc_hir::Arm<'tcx>,
+            [] asm_operand: (rustc_hir::InlineAsmOperand<'tcx>, Span),
             [] asm_template: rustc_ast::InlineAsmTemplatePiece,
             [] attribute: rustc_ast::Attribute,
-            [] block: rustc_hir::Block<$tcx>,
-            [] bare_fn_ty: rustc_hir::BareFnTy<$tcx>,
-            [] body: rustc_hir::Body<$tcx>,
-            [] generic_arg: rustc_hir::GenericArg<$tcx>,
-            [] generic_args: rustc_hir::GenericArgs<$tcx>,
-            [] generic_bound: rustc_hir::GenericBound<$tcx>,
-            [] generic_param: rustc_hir::GenericParam<$tcx>,
-            [] expr: rustc_hir::Expr<$tcx>,
-            [] expr_field: rustc_hir::ExprField<$tcx>,
-            [] pat_field: rustc_hir::PatField<$tcx>,
-            [] fn_decl: rustc_hir::FnDecl<$tcx>,
-            [] foreign_item: rustc_hir::ForeignItem<$tcx>,
+            [] block: rustc_hir::Block<'tcx>,
+            [] bare_fn_ty: rustc_hir::BareFnTy<'tcx>,
+            [] body: rustc_hir::Body<'tcx>,
+            [] generic_arg: rustc_hir::GenericArg<'tcx>,
+            [] generic_args: rustc_hir::GenericArgs<'tcx>,
+            [] generic_bound: rustc_hir::GenericBound<'tcx>,
+            [] generic_param: rustc_hir::GenericParam<'tcx>,
+            [] expr: rustc_hir::Expr<'tcx>,
+            [] expr_field: rustc_hir::ExprField<'tcx>,
+            [] pat_field: rustc_hir::PatField<'tcx>,
+            [] fn_decl: rustc_hir::FnDecl<'tcx>,
+            [] foreign_item: rustc_hir::ForeignItem<'tcx>,
             [] foreign_item_ref: rustc_hir::ForeignItemRef,
-            [] impl_item: rustc_hir::ImplItem<$tcx>,
+            [] impl_item: rustc_hir::ImplItem<'tcx>,
             [] impl_item_ref: rustc_hir::ImplItemRef,
-            [] item: rustc_hir::Item<$tcx>,
-            [] inline_asm: rustc_hir::InlineAsm<$tcx>,
-            [] llvm_inline_asm: rustc_hir::LlvmInlineAsm<$tcx>,
-            [] local: rustc_hir::Local<$tcx>,
-            [] mod_: rustc_hir::Mod<$tcx>,
-            [] owner_info: rustc_hir::OwnerInfo<$tcx>,
-            [] param: rustc_hir::Param<$tcx>,
-            [] pat: rustc_hir::Pat<$tcx>,
-            [] path: rustc_hir::Path<$tcx>,
-            [] path_segment: rustc_hir::PathSegment<$tcx>,
-            [] poly_trait_ref: rustc_hir::PolyTraitRef<$tcx>,
-            [] qpath: rustc_hir::QPath<$tcx>,
-            [] stmt: rustc_hir::Stmt<$tcx>,
-            [] field_def: rustc_hir::FieldDef<$tcx>,
-            [] trait_item: rustc_hir::TraitItem<$tcx>,
+            [] item: rustc_hir::Item<'tcx>,
+            [] inline_asm: rustc_hir::InlineAsm<'tcx>,
+            [] llvm_inline_asm: rustc_hir::LlvmInlineAsm<'tcx>,
+            [] local: rustc_hir::Local<'tcx>,
+            [] mod_: rustc_hir::Mod<'tcx>,
+            [] owner_info: rustc_hir::OwnerInfo<'tcx>,
+            [] param: rustc_hir::Param<'tcx>,
+            [] pat: rustc_hir::Pat<'tcx>,
+            [] path: rustc_hir::Path<'tcx>,
+            [] path_segment: rustc_hir::PathSegment<'tcx>,
+            [] poly_trait_ref: rustc_hir::PolyTraitRef<'tcx>,
+            [] qpath: rustc_hir::QPath<'tcx>,
+            [] stmt: rustc_hir::Stmt<'tcx>,
+            [] field_def: rustc_hir::FieldDef<'tcx>,
+            [] trait_item: rustc_hir::TraitItem<'tcx>,
             [] trait_item_ref: rustc_hir::TraitItemRef,
-            [] ty: rustc_hir::Ty<$tcx>,
-            [] type_binding: rustc_hir::TypeBinding<$tcx>,
-            [] variant: rustc_hir::Variant<$tcx>,
-            [] where_predicate: rustc_hir::WherePredicate<$tcx>,
-        ], $tcx);
+            [] ty: rustc_hir::Ty<'tcx>,
+            [] type_binding: rustc_hir::TypeBinding<'tcx>,
+            [] variant: rustc_hir::Variant<'tcx>,
+            [] where_predicate: rustc_hir::WherePredicate<'tcx>,
+        ]);
     )
 }
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 2bcc2a4f7cf..ee2e190e7cd 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -1,33 +1,33 @@
-/// This declares a list of types which can be allocated by `Arena`.
+/// This higher-order macro declares a list of types which can be allocated by `Arena`.
 ///
 /// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]` where `T` is the type
 /// listed. These impls will appear in the implement_ty_decoder! macro.
 #[macro_export]
 macro_rules! arena_types {
-    ($macro:path, $tcx:lifetime) => (
+    ($macro:path) => (
         $macro!([
             [] layout: rustc_target::abi::Layout,
-            [] fn_abi: rustc_target::abi::call::FnAbi<$tcx, rustc_middle::ty::Ty<$tcx>>,
+            [] fn_abi: rustc_target::abi::call::FnAbi<'tcx, rustc_middle::ty::Ty<'tcx>>,
             // AdtDef are interned and compared by address
             [] adt_def: rustc_middle::ty::AdtDef,
-            [] steal_thir: rustc_data_structures::steal::Steal<rustc_middle::thir::Thir<$tcx>>,
-            [] steal_mir: rustc_data_structures::steal::Steal<rustc_middle::mir::Body<$tcx>>,
-            [decode] mir: rustc_middle::mir::Body<$tcx>,
+            [] steal_thir: rustc_data_structures::steal::Steal<rustc_middle::thir::Thir<'tcx>>,
+            [] steal_mir: rustc_data_structures::steal::Steal<rustc_middle::mir::Body<'tcx>>,
+            [decode] mir: rustc_middle::mir::Body<'tcx>,
             [] steal_promoted:
                 rustc_data_structures::steal::Steal<
                     rustc_index::vec::IndexVec<
                         rustc_middle::mir::Promoted,
-                        rustc_middle::mir::Body<$tcx>
+                        rustc_middle::mir::Body<'tcx>
                     >
                 >,
             [decode] promoted:
                 rustc_index::vec::IndexVec<
                     rustc_middle::mir::Promoted,
-                    rustc_middle::mir::Body<$tcx>
+                    rustc_middle::mir::Body<'tcx>
                 >,
-            [decode] typeck_results: rustc_middle::ty::TypeckResults<$tcx>,
+            [decode] typeck_results: rustc_middle::ty::TypeckResults<'tcx>,
             [decode] borrowck_result:
-                rustc_middle::mir::BorrowCheckResult<$tcx>,
+                rustc_middle::mir::BorrowCheckResult<'tcx>,
             [decode] unsafety_check_result: rustc_middle::mir::UnsafetyCheckResult,
             [decode] code_region: rustc_middle::mir::coverage::CodeRegion,
             [] const_allocs: rustc_middle::mir::interpret::Allocation,
@@ -78,14 +78,14 @@ macro_rules! arena_types {
             [] foreign_modules: Vec<rustc_session::cstore::ForeignModule>,
             [] upvars_mentioned: rustc_data_structures::fx::FxIndexMap<rustc_hir::HirId, rustc_hir::Upvar>,
             [] object_safety_violations: rustc_middle::traits::ObjectSafetyViolation,
-            [] codegen_unit: rustc_middle::mir::mono::CodegenUnit<$tcx>,
+            [] codegen_unit: rustc_middle::mir::mono::CodegenUnit<'tcx>,
             [] attribute: rustc_ast::Attribute,
             [] name_set: rustc_data_structures::fx::FxHashSet<rustc_span::symbol::Symbol>,
             [] hir_id_set: rustc_hir::HirIdSet,
 
             // Interned types
-            [] tys: rustc_middle::ty::TyS<$tcx>,
-            [] predicates: rustc_middle::ty::PredicateInner<$tcx>,
+            [] tys: rustc_middle::ty::TyS<'tcx>,
+            [] predicates: rustc_middle::ty::PredicateInner<'tcx>,
 
             // Note that this deliberately duplicates items in the `rustc_hir::arena`,
             // since we need to allocate this type on both the `rustc_hir` arena
@@ -97,8 +97,8 @@ macro_rules! arena_types {
             [decode] used_trait_imports: rustc_data_structures::fx::FxHashSet<rustc_hir::def_id::LocalDefId>,
 
             [] dep_kind: rustc_middle::dep_graph::DepKindStruct,
-        ], $tcx);
+        ]);
     )
 }
 
-arena_types!(rustc_arena::declare_arena, 'tcx);
+arena_types!(rustc_arena::declare_arena);
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 434008ecb1f..3f2b987b1e6 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -417,17 +417,17 @@ macro_rules! __impl_decoder_methods {
 macro_rules! impl_arena_allocatable_decoder {
     ([]$args:tt) => {};
     ([decode $(, $attrs:ident)*]
-     [[$name:ident: $ty:ty], $tcx:lifetime]) => {
-        impl<$tcx, D: TyDecoder<$tcx>> RefDecodable<$tcx, D> for $ty {
+     [$name:ident: $ty:ty]) => {
+        impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for $ty {
             #[inline]
-            fn decode(decoder: &mut D) -> Result<&$tcx Self, D::Error> {
+            fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
                 decode_arena_allocable(decoder)
             }
         }
 
-        impl<$tcx, D: TyDecoder<$tcx>> RefDecodable<$tcx, D> for [$ty] {
+        impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [$ty] {
             #[inline]
-            fn decode(decoder: &mut D) -> Result<&$tcx Self, D::Error> {
+            fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
                 decode_arena_allocable_slice(decoder)
             }
         }
@@ -438,15 +438,15 @@ macro_rules! impl_arena_allocatable_decoder {
 }
 
 macro_rules! impl_arena_allocatable_decoders {
-    ([$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
+    ([$($a:tt $name:ident: $ty:ty,)*]) => {
         $(
-            impl_arena_allocatable_decoder!($a [[$name: $ty], $tcx]);
+            impl_arena_allocatable_decoder!($a [$name: $ty]);
         )*
     }
 }
 
-rustc_hir::arena_types!(impl_arena_allocatable_decoders, 'tcx);
-arena_types!(impl_arena_allocatable_decoders, 'tcx);
+rustc_hir::arena_types!(impl_arena_allocatable_decoders);
+arena_types!(impl_arena_allocatable_decoders);
 
 #[macro_export]
 macro_rules! implement_ty_decoder {
diff --git a/compiler/rustc_typeck/src/check/callee.rs b/compiler/rustc_typeck/src/check/callee.rs
index 5d22e300774..635ed938193 100644
--- a/compiler/rustc_typeck/src/check/callee.rs
+++ b/compiler/rustc_typeck/src/check/callee.rs
@@ -349,9 +349,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ty::FnPtr(sig) => (sig, None),
             ref t => {
                 let mut unit_variant = None;
+                let mut removal_span = call_expr.span;
                 if let ty::Adt(adt_def, ..) = t {
                     if adt_def.is_enum() {
                         if let hir::ExprKind::Call(expr, _) = call_expr.kind {
+                            removal_span =
+                                expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
                             unit_variant =
                                 self.tcx.sess.source_map().span_to_snippet(expr.span).ok();
                         }
@@ -379,14 +382,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 );
 
                 if let Some(ref path) = unit_variant {
-                    err.span_suggestion(
-                        call_expr.span,
+                    err.span_suggestion_verbose(
+                        removal_span,
                         &format!(
-                            "`{}` is a unit variant, you need to write it \
-                                 without the parentheses",
+                            "`{}` is a unit variant, you need to write it without the parentheses",
                             path
                         ),
-                        path.to_string(),
+                        String::new(),
                         Applicability::MachineApplicable,
                     );
                 }
diff --git a/library/core/src/char/convert.rs b/library/core/src/char/convert.rs
index 8fc6b1af924..c4046d7496f 100644
--- a/library/core/src/char/convert.rs
+++ b/library/core/src/char/convert.rs
@@ -51,8 +51,13 @@ use super::MAX;
 #[must_use]
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-pub fn from_u32(i: u32) -> Option<char> {
-    char::try_from(i).ok()
+#[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
+pub const fn from_u32(i: u32) -> Option<char> {
+    // FIXME: once Result::ok is const fn, use it here
+    match char_try_from_u32(i) {
+        Ok(c) => Some(c),
+        Err(_) => None,
+    }
 }
 
 /// Converts a `u32` to a `char`, ignoring validity.
@@ -91,7 +96,8 @@ pub fn from_u32(i: u32) -> Option<char> {
 #[inline]
 #[must_use]
 #[stable(feature = "char_from_unchecked", since = "1.5.0")]
-pub unsafe fn from_u32_unchecked(i: u32) -> char {
+#[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
+pub const unsafe fn from_u32_unchecked(i: u32) -> char {
     // SAFETY: the caller must guarantee that `i` is a valid char value.
     if cfg!(debug_assertions) { char::from_u32(i).unwrap() } else { unsafe { transmute(i) } }
 }
@@ -248,18 +254,23 @@ impl FromStr for char {
     }
 }
 
+#[inline]
+const fn char_try_from_u32(i: u32) -> Result<char, CharTryFromError> {
+    if (i > MAX as u32) || (i >= 0xD800 && i <= 0xDFFF) {
+        Err(CharTryFromError(()))
+    } else {
+        // SAFETY: checked that it's a legal unicode value
+        Ok(unsafe { transmute(i) })
+    }
+}
+
 #[stable(feature = "try_from", since = "1.34.0")]
 impl TryFrom<u32> for char {
     type Error = CharTryFromError;
 
     #[inline]
     fn try_from(i: u32) -> Result<Self, Self::Error> {
-        if (i > MAX as u32) || (i >= 0xD800 && i <= 0xDFFF) {
-            Err(CharTryFromError(()))
-        } else {
-            // SAFETY: checked that it's a legal unicode value
-            Ok(unsafe { transmute(i) })
-        }
+        char_try_from_u32(i)
     }
 }
 
@@ -327,7 +338,8 @@ impl fmt::Display for CharTryFromError {
 #[inline]
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
-pub fn from_digit(num: u32, radix: u32) -> Option<char> {
+#[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
+pub const fn from_digit(num: u32, radix: u32) -> Option<char> {
     if radix > 36 {
         panic!("from_digit: radix is too high (maximum 36)");
     }
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index 3c4972bd3c9..d5ad0c385c7 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -136,9 +136,10 @@ impl char {
     /// assert_eq!(None, c);
     /// ```
     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+    #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
     #[must_use]
     #[inline]
-    pub fn from_u32(i: u32) -> Option<char> {
+    pub const fn from_u32(i: u32) -> Option<char> {
         super::convert::from_u32(i)
     }
 
@@ -178,9 +179,10 @@ impl char {
     /// assert_eq!('❤', c);
     /// ```
     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+    #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
     #[must_use]
     #[inline]
-    pub unsafe fn from_u32_unchecked(i: u32) -> char {
+    pub const unsafe fn from_u32_unchecked(i: u32) -> char {
         // SAFETY: the safety contract must be upheld by the caller.
         unsafe { super::convert::from_u32_unchecked(i) }
     }
@@ -235,9 +237,10 @@ impl char {
     /// let _c = char::from_digit(1, 37);
     /// ```
     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+    #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
     #[must_use]
     #[inline]
-    pub fn from_digit(num: u32, radix: u32) -> Option<char> {
+    pub const fn from_digit(num: u32, radix: u32) -> Option<char> {
         super::convert::from_digit(num, radix)
     }
 
@@ -331,10 +334,11 @@ impl char {
     /// let _ = '1'.to_digit(37);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_char_convert", issue = "89259")]
     #[must_use = "this returns the result of the operation, \
                   without modifying the original"]
     #[inline]
-    pub fn to_digit(self, radix: u32) -> Option<u32> {
+    pub const fn to_digit(self, radix: u32) -> Option<u32> {
         assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
         // If not a digit, a number greater than radix will be created.
         let mut digit = (self as u32).wrapping_sub('0' as u32);
@@ -345,7 +349,8 @@ impl char {
             // Force the 6th bit to be set to ensure ascii is lower case.
             digit = (self as u32 | 0b10_0000).wrapping_sub('a' as u32).saturating_add(10);
         }
-        (digit < radix).then_some(digit)
+        // FIXME: once then_some is const fn, use it here
+        if digit < radix { Some(digit) } else { None }
     }
 
     /// Returns an iterator that yields the hexadecimal Unicode escape of a
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 3b0872378c6..4a64e2e2d10 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -105,6 +105,7 @@
 #![feature(const_bigint_helper_methods)]
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
+#![feature(const_char_convert)]
 #![feature(const_discriminant)]
 #![feature(const_eval_select)]
 #![feature(const_float_bits_conv)]
diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index 1417d860c47..9a8f1e44f1f 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -1430,4 +1430,8 @@ fn create_dir_long_paths() {
     // This will fail if the path isn't converted to verbatim.
     path.push("a");
     fs::create_dir(&path).unwrap();
+
+    // #90940: Ensure an empty path returns the "Not Found" error.
+    let path = Path::new("");
+    assert_eq!(path.canonicalize().unwrap_err().kind(), crate::io::ErrorKind::NotFound);
 }
diff --git a/library/std/src/sys/windows/path.rs b/library/std/src/sys/windows/path.rs
index 460c1eff778..d0b7d9e7377 100644
--- a/library/std/src/sys/windows/path.rs
+++ b/library/std/src/sys/windows/path.rs
@@ -174,8 +174,8 @@ pub(crate) fn maybe_verbatim(path: &Path) -> io::Result<Vec<u16>> {
     const UNC_PREFIX: &[u16] = &[SEP, SEP, QUERY, SEP, U, N, C, SEP];
 
     let mut path = to_u16s(path)?;
-    if path.starts_with(VERBATIM_PREFIX) || path.starts_with(NT_PREFIX) {
-        // Early return for paths that are already verbatim.
+    if path.starts_with(VERBATIM_PREFIX) || path.starts_with(NT_PREFIX) || path == &[0] {
+        // Early return for paths that are already verbatim or empty.
         return Ok(path);
     } else if path.len() < LEGACY_MAX_PATH {
         // Early return if an absolute path is less < 260 UTF-16 code units.
diff --git a/library/std/src/sys/windows/path/tests.rs b/library/std/src/sys/windows/path/tests.rs
index c6c84519f41..425c2011b32 100644
--- a/library/std/src/sys/windows/path/tests.rs
+++ b/library/std/src/sys/windows/path/tests.rs
@@ -91,7 +91,6 @@ fn verbatim() {
     // Make sure opening a drive will work.
     check("Z:", "Z:");
 
-    // An empty path or a path that contains null are not valid paths.
-    assert!(maybe_verbatim(Path::new("")).is_err());
+    // A path that contains null is not a valid path.
     assert!(maybe_verbatim(Path::new("\0")).is_err());
 }
diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 38d3c7aec49..22f2e405a1e 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -1119,17 +1119,22 @@ class RustBuild(object):
                     raise Exception("{} not found".format(vendor_dir))
 
         if self.use_vendored_sources:
+            config = ("[source.crates-io]\n"
+                      "replace-with = 'vendored-sources'\n"
+                      "registry = 'https://example.com'\n"
+                      "\n"
+                      "[source.vendored-sources]\n"
+                      "directory = '{}/vendor'\n"
+                      .format(self.rust_root))
             if not os.path.exists('.cargo'):
                 os.makedirs('.cargo')
-            with output('.cargo/config') as cargo_config:
-                cargo_config.write(
-                    "[source.crates-io]\n"
-                    "replace-with = 'vendored-sources'\n"
-                    "registry = 'https://example.com'\n"
-                    "\n"
-                    "[source.vendored-sources]\n"
-                    "directory = '{}/vendor'\n"
-                    .format(self.rust_root))
+                with output('.cargo/config') as cargo_config:
+                    cargo_config.write(config)
+            else:
+                print('info: using vendored source, but .cargo/config is already present.')
+                print('      Reusing the current configuration file. But you may want to '
+                      'configure vendoring like this:')
+                print(config)
         else:
             if os.path.exists('.cargo'):
                 shutil.rmtree('.cargo')
diff --git a/src/test/ui/byte-literals.rs b/src/test/ui/array-slice-vec/byte-literals.rs
similarity index 100%
rename from src/test/ui/byte-literals.rs
rename to src/test/ui/array-slice-vec/byte-literals.rs
diff --git a/src/test/ui/suffixed-literal-meta.rs b/src/test/ui/attributes/suffixed-literal-meta.rs
similarity index 100%
rename from src/test/ui/suffixed-literal-meta.rs
rename to src/test/ui/attributes/suffixed-literal-meta.rs
diff --git a/src/test/ui/suffixed-literal-meta.stderr b/src/test/ui/attributes/suffixed-literal-meta.stderr
similarity index 100%
rename from src/test/ui/suffixed-literal-meta.stderr
rename to src/test/ui/attributes/suffixed-literal-meta.stderr
diff --git a/src/test/ui/operator-multidispatch.rs b/src/test/ui/binop/operator-multidispatch.rs
similarity index 100%
rename from src/test/ui/operator-multidispatch.rs
rename to src/test/ui/binop/operator-multidispatch.rs
diff --git a/src/test/ui/operator-overloading.rs b/src/test/ui/binop/operator-overloading.rs
similarity index 100%
rename from src/test/ui/operator-overloading.rs
rename to src/test/ui/binop/operator-overloading.rs
diff --git a/src/test/ui/placement-syntax.rs b/src/test/ui/binop/placement-syntax.rs
similarity index 100%
rename from src/test/ui/placement-syntax.rs
rename to src/test/ui/binop/placement-syntax.rs
diff --git a/src/test/ui/placement-syntax.stderr b/src/test/ui/binop/placement-syntax.stderr
similarity index 100%
rename from src/test/ui/placement-syntax.stderr
rename to src/test/ui/binop/placement-syntax.stderr
diff --git a/src/test/ui/immut-function-arguments.rs b/src/test/ui/borrowck/immut-function-arguments.rs
similarity index 100%
rename from src/test/ui/immut-function-arguments.rs
rename to src/test/ui/borrowck/immut-function-arguments.rs
diff --git a/src/test/ui/immut-function-arguments.stderr b/src/test/ui/borrowck/immut-function-arguments.stderr
similarity index 100%
rename from src/test/ui/immut-function-arguments.stderr
rename to src/test/ui/borrowck/immut-function-arguments.stderr
diff --git a/src/test/ui/kindck-implicit-close-over-mut-var.rs b/src/test/ui/borrowck/kindck-implicit-close-over-mut-var.rs
similarity index 100%
rename from src/test/ui/kindck-implicit-close-over-mut-var.rs
rename to src/test/ui/borrowck/kindck-implicit-close-over-mut-var.rs
diff --git a/src/test/ui/crt-static-on-works.rs b/src/test/ui/cfg/crt-static-on-works.rs
similarity index 100%
rename from src/test/ui/crt-static-on-works.rs
rename to src/test/ui/cfg/crt-static-on-works.rs
diff --git a/src/test/ui/once-move-out-on-heap.rs b/src/test/ui/closures/once-move-out-on-heap.rs
similarity index 100%
rename from src/test/ui/once-move-out-on-heap.rs
rename to src/test/ui/closures/once-move-out-on-heap.rs
diff --git a/src/test/ui/auxiliary/llvm_pr32379.rs b/src/test/ui/codegen/auxiliary/llvm_pr32379.rs
similarity index 100%
rename from src/test/ui/auxiliary/llvm_pr32379.rs
rename to src/test/ui/codegen/auxiliary/llvm_pr32379.rs
diff --git a/src/test/ui/init-large-type.rs b/src/test/ui/codegen/init-large-type.rs
similarity index 100%
rename from src/test/ui/init-large-type.rs
rename to src/test/ui/codegen/init-large-type.rs
diff --git a/src/test/ui/llvm-pr32379.rs b/src/test/ui/codegen/llvm-pr32379.rs
similarity index 100%
rename from src/test/ui/llvm-pr32379.rs
rename to src/test/ui/codegen/llvm-pr32379.rs
diff --git a/src/test/ui/retslot-cast.rs b/src/test/ui/coercion/retslot-cast.rs
similarity index 100%
rename from src/test/ui/retslot-cast.rs
rename to src/test/ui/coercion/retslot-cast.rs
diff --git a/src/test/ui/retslot-cast.stderr b/src/test/ui/coercion/retslot-cast.stderr
similarity index 100%
rename from src/test/ui/retslot-cast.stderr
rename to src/test/ui/coercion/retslot-cast.stderr
diff --git a/src/test/ui/const-generics/invariant.nll.stderr b/src/test/ui/const-generics/invariant.nll.stderr
new file mode 100644
index 00000000000..ce0fad10471
--- /dev/null
+++ b/src/test/ui/const-generics/invariant.nll.stderr
@@ -0,0 +1,26 @@
+warning: conflicting implementations of trait `SadBee` for type `for<'a> fn(&'a ())`
+  --> $DIR/invariant.rs:14:1
+   |
+LL | impl SadBee for for<'a> fn(&'a ()) {
+   | ---------------------------------- first implementation here
+...
+LL | impl SadBee for fn(&'static ()) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `for<'a> fn(&'a ())`
+   |
+   = note: `#[warn(coherence_leak_check)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #56105 <https://github.com/rust-lang/rust/issues/56105>
+   = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
+
+error[E0308]: mismatched types
+  --> $DIR/invariant.rs:27:5
+   |
+LL |     v
+   |     ^ one type is more general than the other
+   |
+   = note: expected reference `&Foo<fn(&())>`
+              found reference `&Foo<for<'a> fn(&'a ())>`
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/const-generics/invariant.rs b/src/test/ui/const-generics/invariant.rs
new file mode 100644
index 00000000000..ee191b65c2c
--- /dev/null
+++ b/src/test/ui/const-generics/invariant.rs
@@ -0,0 +1,33 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+use std::marker::PhantomData;
+
+trait SadBee {
+    const ASSOC: usize;
+}
+// fn(&'static ())` is a supertype of `for<'a> fn(&'a ())` while
+// we allow two different impls for these types, leading
+// to different const eval results.
+impl SadBee for for<'a> fn(&'a ()) {
+    const ASSOC: usize = 0;
+}
+impl SadBee for fn(&'static ()) {
+    //~^ WARNING conflicting implementations of trait
+    //~| WARNING this was previously accepted
+    const ASSOC: usize = 100;
+}
+
+struct Foo<T: SadBee>([u8; <T as SadBee>::ASSOC], PhantomData<T>)
+where
+    [(); <T as SadBee>::ASSOC]: ;
+
+fn covariant(
+    v: &'static Foo<for<'a> fn(&'a ())>
+) -> &'static Foo<fn(&'static ())> {
+    v //~ ERROR mismatched types
+}
+
+fn main() {
+    let y = covariant(&Foo([], PhantomData));
+    println!("{:?}", y.0);
+}
diff --git a/src/test/ui/const-generics/invariant.stderr b/src/test/ui/const-generics/invariant.stderr
new file mode 100644
index 00000000000..318c885e6a6
--- /dev/null
+++ b/src/test/ui/const-generics/invariant.stderr
@@ -0,0 +1,26 @@
+warning: conflicting implementations of trait `SadBee` for type `for<'a> fn(&'a ())`
+  --> $DIR/invariant.rs:14:1
+   |
+LL | impl SadBee for for<'a> fn(&'a ()) {
+   | ---------------------------------- first implementation here
+...
+LL | impl SadBee for fn(&'static ()) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `for<'a> fn(&'a ())`
+   |
+   = note: `#[warn(coherence_leak_check)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #56105 <https://github.com/rust-lang/rust/issues/56105>
+   = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
+
+error[E0308]: mismatched types
+  --> $DIR/invariant.rs:27:5
+   |
+LL |     v
+   |     ^ one type is more general than the other
+   |
+   = note: expected reference `&'static Foo<fn(&'static ())>`
+              found reference `&'static Foo<for<'a> fn(&'a ())>`
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/cleanup-arm-conditional.rs b/src/test/ui/dropck/cleanup-arm-conditional.rs
similarity index 100%
rename from src/test/ui/cleanup-arm-conditional.rs
rename to src/test/ui/dropck/cleanup-arm-conditional.rs
diff --git a/src/test/ui/edition-keywords-2015-2018.rs b/src/test/ui/editions/edition-keywords-2015-2018.rs
similarity index 100%
rename from src/test/ui/edition-keywords-2015-2018.rs
rename to src/test/ui/editions/edition-keywords-2015-2018.rs
diff --git a/src/test/ui/edition-keywords-2018-2018.rs b/src/test/ui/editions/edition-keywords-2018-2018.rs
similarity index 100%
rename from src/test/ui/edition-keywords-2018-2018.rs
rename to src/test/ui/editions/edition-keywords-2018-2018.rs
diff --git a/src/test/ui/empty/empty-struct-unit-expr.stderr b/src/test/ui/empty/empty-struct-unit-expr.stderr
index 26bfc4355fa..81651c5bf6f 100644
--- a/src/test/ui/empty/empty-struct-unit-expr.stderr
+++ b/src/test/ui/empty/empty-struct-unit-expr.stderr
@@ -22,8 +22,9 @@ LL |     let e4 = E::Empty4();
    |
 help: `E::Empty4` is a unit variant, you need to write it without the parentheses
    |
-LL |     let e4 = E::Empty4;
-   |              ~~~~~~~~~
+LL -     let e4 = E::Empty4();
+LL +     let e4 = E::Empty4;
+   | 
 
 error[E0618]: expected function, found `empty_struct::XEmpty2`
   --> $DIR/empty-struct-unit-expr.rs:18:15
@@ -43,8 +44,9 @@ LL |     let xe4 = XE::XEmpty4();
    |
 help: `XE::XEmpty4` is a unit variant, you need to write it without the parentheses
    |
-LL |     let xe4 = XE::XEmpty4;
-   |               ~~~~~~~~~~~
+LL -     let xe4 = XE::XEmpty4();
+LL +     let xe4 = XE::XEmpty4;
+   | 
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/error-codes/E0618.stderr b/src/test/ui/error-codes/E0618.stderr
index db1b3f09837..a3a90968df7 100644
--- a/src/test/ui/error-codes/E0618.stderr
+++ b/src/test/ui/error-codes/E0618.stderr
@@ -11,8 +11,9 @@ LL |     X::Entry();
    |
 help: `X::Entry` is a unit variant, you need to write it without the parentheses
    |
-LL |     X::Entry;
-   |     ~~~~~~~~
+LL -     X::Entry();
+LL +     X::Entry;
+   | 
 
 error[E0618]: expected function, found `i32`
   --> $DIR/E0618.rs:9:5
diff --git a/src/test/ui/export.rs b/src/test/ui/export.rs
deleted file mode 100644
index 73ceec6803a..00000000000
--- a/src/test/ui/export.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-mod foo {
-    pub fn x(y: isize) { log(debug, y); }
-    //~^ ERROR cannot find function `log` in this scope
-    //~| ERROR cannot find value `debug` in this scope
-    fn z(y: isize) { log(debug, y); }
-    //~^ ERROR cannot find function `log` in this scope
-    //~| ERROR cannot find value `debug` in this scope
-}
-
-fn main() { foo::z(10); } //~ ERROR function `z` is private
diff --git a/src/test/ui/export.stderr b/src/test/ui/export.stderr
deleted file mode 100644
index 23c29b31c6a..00000000000
--- a/src/test/ui/export.stderr
+++ /dev/null
@@ -1,40 +0,0 @@
-error[E0425]: cannot find function `log` in this scope
-  --> $DIR/export.rs:2:26
-   |
-LL |     pub fn x(y: isize) { log(debug, y); }
-   |                          ^^^ not found in this scope
-
-error[E0425]: cannot find value `debug` in this scope
-  --> $DIR/export.rs:2:30
-   |
-LL |     pub fn x(y: isize) { log(debug, y); }
-   |                              ^^^^^ not found in this scope
-
-error[E0425]: cannot find function `log` in this scope
-  --> $DIR/export.rs:5:22
-   |
-LL |     fn z(y: isize) { log(debug, y); }
-   |                      ^^^ not found in this scope
-
-error[E0425]: cannot find value `debug` in this scope
-  --> $DIR/export.rs:5:26
-   |
-LL |     fn z(y: isize) { log(debug, y); }
-   |                          ^^^^^ not found in this scope
-
-error[E0603]: function `z` is private
-  --> $DIR/export.rs:10:18
-   |
-LL | fn main() { foo::z(10); }
-   |                  ^ private function
-   |
-note: the function `z` is defined here
-  --> $DIR/export.rs:5:5
-   |
-LL |     fn z(y: isize) { log(debug, y); }
-   |     ^^^^^^^^^^^^^^
-
-error: aborting due to 5 previous errors
-
-Some errors have detailed explanations: E0425, E0603.
-For more information about an error, try `rustc --explain E0425`.
diff --git a/src/test/ui/expr-block-slot.rs b/src/test/ui/expr-block-slot.rs
deleted file mode 100644
index 54bcbb328b0..00000000000
--- a/src/test/ui/expr-block-slot.rs
+++ /dev/null
@@ -1,13 +0,0 @@
-// run-pass
-// Regression test for issue #377
-
-
-struct A { a: isize }
-struct V { v: isize }
-
-pub fn main() {
-    let a = { let b = A {a: 3}; b };
-    assert_eq!(a.a, 3);
-    let c = { let d = V {v: 3}; d };
-    assert_eq!(c.v, 3);
-}
diff --git a/src/test/ui/auxiliary/no-mangle-associated-fn.rs b/src/test/ui/extern/auxiliary/no-mangle-associated-fn.rs
similarity index 100%
rename from src/test/ui/auxiliary/no-mangle-associated-fn.rs
rename to src/test/ui/extern/auxiliary/no-mangle-associated-fn.rs
diff --git a/src/test/ui/no-mangle-associated-fn.rs b/src/test/ui/extern/no-mangle-associated-fn.rs
similarity index 100%
rename from src/test/ui/no-mangle-associated-fn.rs
rename to src/test/ui/extern/no-mangle-associated-fn.rs
diff --git a/src/test/ui/fun-call-variants.rs b/src/test/ui/fn/fun-call-variants.rs
similarity index 100%
rename from src/test/ui/fun-call-variants.rs
rename to src/test/ui/fn/fun-call-variants.rs
diff --git a/src/test/ui/break-outside-loop.rs b/src/test/ui/for-loop-while/break-outside-loop.rs
similarity index 100%
rename from src/test/ui/break-outside-loop.rs
rename to src/test/ui/for-loop-while/break-outside-loop.rs
diff --git a/src/test/ui/break-outside-loop.stderr b/src/test/ui/for-loop-while/break-outside-loop.stderr
similarity index 100%
rename from src/test/ui/break-outside-loop.stderr
rename to src/test/ui/for-loop-while/break-outside-loop.stderr
diff --git a/src/test/ui/break-while-condition.rs b/src/test/ui/for-loop-while/break-while-condition.rs
similarity index 100%
rename from src/test/ui/break-while-condition.rs
rename to src/test/ui/for-loop-while/break-while-condition.rs
diff --git a/src/test/ui/break-while-condition.stderr b/src/test/ui/for-loop-while/break-while-condition.stderr
similarity index 100%
rename from src/test/ui/break-while-condition.stderr
rename to src/test/ui/for-loop-while/break-while-condition.stderr
diff --git a/src/test/ui/thread-local-not-in-prelude.rs b/src/test/ui/hygiene/thread-local-not-in-prelude.rs
similarity index 100%
rename from src/test/ui/thread-local-not-in-prelude.rs
rename to src/test/ui/hygiene/thread-local-not-in-prelude.rs
diff --git a/src/test/ui/absolute-paths-in-nested-use-groups.rs b/src/test/ui/imports/absolute-paths-in-nested-use-groups.rs
similarity index 100%
rename from src/test/ui/absolute-paths-in-nested-use-groups.rs
rename to src/test/ui/imports/absolute-paths-in-nested-use-groups.rs
diff --git a/src/test/ui/absolute-paths-in-nested-use-groups.stderr b/src/test/ui/imports/absolute-paths-in-nested-use-groups.stderr
similarity index 100%
rename from src/test/ui/absolute-paths-in-nested-use-groups.stderr
rename to src/test/ui/imports/absolute-paths-in-nested-use-groups.stderr
diff --git a/src/test/ui/reexport-star.rs b/src/test/ui/imports/reexport-star.rs
similarity index 100%
rename from src/test/ui/reexport-star.rs
rename to src/test/ui/imports/reexport-star.rs
diff --git a/src/test/ui/newlambdas-ret-infer.rs b/src/test/ui/inference/newlambdas-ret-infer.rs
similarity index 100%
rename from src/test/ui/newlambdas-ret-infer.rs
rename to src/test/ui/inference/newlambdas-ret-infer.rs
diff --git a/src/test/ui/newlambdas-ret-infer2.rs b/src/test/ui/inference/newlambdas-ret-infer2.rs
similarity index 100%
rename from src/test/ui/newlambdas-ret-infer2.rs
rename to src/test/ui/inference/newlambdas-ret-infer2.rs
diff --git a/src/test/ui/range-type-infer.rs b/src/test/ui/inference/range-type-infer.rs
similarity index 100%
rename from src/test/ui/range-type-infer.rs
rename to src/test/ui/inference/range-type-infer.rs
diff --git a/src/test/ui/tutorial-suffix-inference-test.rs b/src/test/ui/inference/tutorial-suffix-inference-test.rs
similarity index 100%
rename from src/test/ui/tutorial-suffix-inference-test.rs
rename to src/test/ui/inference/tutorial-suffix-inference-test.rs
diff --git a/src/test/ui/tutorial-suffix-inference-test.stderr b/src/test/ui/inference/tutorial-suffix-inference-test.stderr
similarity index 100%
rename from src/test/ui/tutorial-suffix-inference-test.stderr
rename to src/test/ui/inference/tutorial-suffix-inference-test.stderr
diff --git a/src/test/ui/type-infer-generalize-ty-var.rs b/src/test/ui/inference/type-infer-generalize-ty-var.rs
similarity index 100%
rename from src/test/ui/type-infer-generalize-ty-var.rs
rename to src/test/ui/inference/type-infer-generalize-ty-var.rs
diff --git a/src/test/ui/leak-unique-as-tydesc.rs b/src/test/ui/leak-unique-as-tydesc.rs
deleted file mode 100644
index 322f726156d..00000000000
--- a/src/test/ui/leak-unique-as-tydesc.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-// run-pass
-// pretty-expanded FIXME #23616
-
-fn leaky<T>(_t: T) { }
-
-pub fn main() {
-    let x = Box::new(10);
-    leaky::<Box<isize>>(x);
-}
diff --git a/src/test/ui/auxiliary/link-cfg-works-transitive-dylib.rs b/src/test/ui/linkage-attr/auxiliary/link-cfg-works-transitive-dylib.rs
similarity index 100%
rename from src/test/ui/auxiliary/link-cfg-works-transitive-dylib.rs
rename to src/test/ui/linkage-attr/auxiliary/link-cfg-works-transitive-dylib.rs
diff --git a/src/test/ui/auxiliary/link-cfg-works-transitive-rlib.rs b/src/test/ui/linkage-attr/auxiliary/link-cfg-works-transitive-rlib.rs
similarity index 100%
rename from src/test/ui/auxiliary/link-cfg-works-transitive-rlib.rs
rename to src/test/ui/linkage-attr/auxiliary/link-cfg-works-transitive-rlib.rs
diff --git a/src/test/ui/link-cfg-works.rs b/src/test/ui/linkage-attr/link-cfg-works.rs
similarity index 100%
rename from src/test/ui/link-cfg-works.rs
rename to src/test/ui/linkage-attr/link-cfg-works.rs
diff --git a/src/test/ui/lint-cap.rs b/src/test/ui/lint/lint-cap.rs
similarity index 100%
rename from src/test/ui/lint-cap.rs
rename to src/test/ui/lint/lint-cap.rs
diff --git a/src/test/ui/liveness-assign-imm-local-after-ret.rs b/src/test/ui/liveness/liveness-assign-imm-local-after-ret.rs
similarity index 100%
rename from src/test/ui/liveness-assign-imm-local-after-ret.rs
rename to src/test/ui/liveness/liveness-assign-imm-local-after-ret.rs
diff --git a/src/test/ui/match-on-negative-integer-ranges.rs b/src/test/ui/match/match-on-negative-integer-ranges.rs
similarity index 100%
rename from src/test/ui/match-on-negative-integer-ranges.rs
rename to src/test/ui/match/match-on-negative-integer-ranges.rs
diff --git a/src/test/ui/issue-73914.rs b/src/test/ui/mir/issue-73914.rs
similarity index 100%
rename from src/test/ui/issue-73914.rs
rename to src/test/ui/mir/issue-73914.rs
diff --git a/src/test/ui/assignment-operator-unimplemented.rs b/src/test/ui/mismatched_types/assignment-operator-unimplemented.rs
similarity index 100%
rename from src/test/ui/assignment-operator-unimplemented.rs
rename to src/test/ui/mismatched_types/assignment-operator-unimplemented.rs
diff --git a/src/test/ui/assignment-operator-unimplemented.stderr b/src/test/ui/mismatched_types/assignment-operator-unimplemented.stderr
similarity index 100%
rename from src/test/ui/assignment-operator-unimplemented.stderr
rename to src/test/ui/mismatched_types/assignment-operator-unimplemented.stderr
diff --git a/src/test/ui/float-literal-inference-restrictions.rs b/src/test/ui/mismatched_types/float-literal-inference-restrictions.rs
similarity index 100%
rename from src/test/ui/float-literal-inference-restrictions.rs
rename to src/test/ui/mismatched_types/float-literal-inference-restrictions.rs
diff --git a/src/test/ui/float-literal-inference-restrictions.stderr b/src/test/ui/mismatched_types/float-literal-inference-restrictions.stderr
similarity index 100%
rename from src/test/ui/float-literal-inference-restrictions.stderr
rename to src/test/ui/mismatched_types/float-literal-inference-restrictions.stderr
diff --git a/src/test/ui/newtype-temporary.rs b/src/test/ui/newtype-temporary.rs
deleted file mode 100644
index 8ee75b2fef1..00000000000
--- a/src/test/ui/newtype-temporary.rs
+++ /dev/null
@@ -1,12 +0,0 @@
-// run-pass
-
-#[derive(PartialEq, Debug)]
-struct Foo(usize);
-
-fn foo() -> Foo {
-    Foo(42)
-}
-
-pub fn main() {
-    assert_eq!(foo(), Foo(42));
-}
diff --git a/src/test/ui/lub-if.nll.stderr b/src/test/ui/nll/lub-if.nll.stderr
similarity index 100%
rename from src/test/ui/lub-if.nll.stderr
rename to src/test/ui/nll/lub-if.nll.stderr
diff --git a/src/test/ui/lub-if.rs b/src/test/ui/nll/lub-if.rs
similarity index 100%
rename from src/test/ui/lub-if.rs
rename to src/test/ui/nll/lub-if.rs
diff --git a/src/test/ui/lub-if.stderr b/src/test/ui/nll/lub-if.stderr
similarity index 100%
rename from src/test/ui/lub-if.stderr
rename to src/test/ui/nll/lub-if.stderr
diff --git a/src/test/ui/non-legacy-modes.rs b/src/test/ui/non-legacy-modes.rs
deleted file mode 100644
index 38c83e00a6a..00000000000
--- a/src/test/ui/non-legacy-modes.rs
+++ /dev/null
@@ -1,22 +0,0 @@
-// run-pass
-
-struct X {
-    repr: isize
-}
-
-fn apply<T, F>(x: T, f: F) where F: FnOnce(T) {
-    f(x);
-}
-
-fn check_int(x: isize) {
-    assert_eq!(x, 22);
-}
-
-fn check_struct(x: X) {
-    check_int(x.repr);
-}
-
-pub fn main() {
-    apply(22, check_int);
-    apply(X {repr: 22}, check_struct);
-}
diff --git a/src/test/ui/overloaded-calls-nontuple.rs b/src/test/ui/overloaded/overloaded-calls-nontuple.rs
similarity index 100%
rename from src/test/ui/overloaded-calls-nontuple.rs
rename to src/test/ui/overloaded/overloaded-calls-nontuple.rs
diff --git a/src/test/ui/overloaded-calls-nontuple.stderr b/src/test/ui/overloaded/overloaded-calls-nontuple.stderr
similarity index 100%
rename from src/test/ui/overloaded-calls-nontuple.stderr
rename to src/test/ui/overloaded/overloaded-calls-nontuple.stderr
diff --git a/src/test/ui/attribute-with-no-generics-in-parameter-list.rs b/src/test/ui/parser/attribute-with-no-generics-in-parameter-list.rs
similarity index 100%
rename from src/test/ui/attribute-with-no-generics-in-parameter-list.rs
rename to src/test/ui/parser/attribute-with-no-generics-in-parameter-list.rs
diff --git a/src/test/ui/attribute-with-no-generics-in-parameter-list.stderr b/src/test/ui/parser/attribute-with-no-generics-in-parameter-list.stderr
similarity index 100%
rename from src/test/ui/attribute-with-no-generics-in-parameter-list.stderr
rename to src/test/ui/parser/attribute-with-no-generics-in-parameter-list.stderr
diff --git a/src/test/ui/dyn-trait-compatibility.rs b/src/test/ui/parser/dyn-trait-compatibility.rs
similarity index 100%
rename from src/test/ui/dyn-trait-compatibility.rs
rename to src/test/ui/parser/dyn-trait-compatibility.rs
diff --git a/src/test/ui/dyn-trait-compatibility.stderr b/src/test/ui/parser/dyn-trait-compatibility.stderr
similarity index 100%
rename from src/test/ui/dyn-trait-compatibility.stderr
rename to src/test/ui/parser/dyn-trait-compatibility.stderr
diff --git a/src/test/ui/operator-associativity.rs b/src/test/ui/parser/operator-associativity.rs
similarity index 100%
rename from src/test/ui/operator-associativity.rs
rename to src/test/ui/parser/operator-associativity.rs
diff --git a/src/test/ui/ignore-all-the-things.rs b/src/test/ui/pattern/ignore-all-the-things.rs
similarity index 100%
rename from src/test/ui/ignore-all-the-things.rs
rename to src/test/ui/pattern/ignore-all-the-things.rs
diff --git a/src/test/ui/auxiliary/impl_privacy_xc_2.rs b/src/test/ui/privacy/auxiliary/impl_privacy_xc_2.rs
similarity index 100%
rename from src/test/ui/auxiliary/impl_privacy_xc_2.rs
rename to src/test/ui/privacy/auxiliary/impl_privacy_xc_2.rs
diff --git a/src/test/ui/auxiliary/reachable-unnameable-items.rs b/src/test/ui/privacy/auxiliary/reachable-unnameable-items.rs
similarity index 100%
rename from src/test/ui/auxiliary/reachable-unnameable-items.rs
rename to src/test/ui/privacy/auxiliary/reachable-unnameable-items.rs
diff --git a/src/test/ui/export-tag-variant.rs b/src/test/ui/privacy/export-tag-variant.rs
similarity index 100%
rename from src/test/ui/export-tag-variant.rs
rename to src/test/ui/privacy/export-tag-variant.rs
diff --git a/src/test/ui/export-tag-variant.stderr b/src/test/ui/privacy/export-tag-variant.stderr
similarity index 100%
rename from src/test/ui/export-tag-variant.stderr
rename to src/test/ui/privacy/export-tag-variant.stderr
diff --git a/src/test/ui/impl-privacy-xc-2.rs b/src/test/ui/privacy/impl-privacy-xc-2.rs
similarity index 100%
rename from src/test/ui/impl-privacy-xc-2.rs
rename to src/test/ui/privacy/impl-privacy-xc-2.rs
diff --git a/src/test/ui/reachable-unnameable-items.rs b/src/test/ui/privacy/reachable-unnameable-items.rs
similarity index 100%
rename from src/test/ui/reachable-unnameable-items.rs
rename to src/test/ui/privacy/reachable-unnameable-items.rs
diff --git a/src/test/ui/core-run-destroy.rs b/src/test/ui/process/core-run-destroy.rs
similarity index 100%
rename from src/test/ui/core-run-destroy.rs
rename to src/test/ui/process/core-run-destroy.rs
diff --git a/src/test/ui/multi-panic.rs b/src/test/ui/process/multi-panic.rs
similarity index 100%
rename from src/test/ui/multi-panic.rs
rename to src/test/ui/process/multi-panic.rs
diff --git a/src/test/ui/no-stdio.rs b/src/test/ui/process/no-stdio.rs
similarity index 100%
rename from src/test/ui/no-stdio.rs
rename to src/test/ui/process/no-stdio.rs
diff --git a/src/test/ui/try-wait.rs b/src/test/ui/process/try-wait.rs
similarity index 100%
rename from src/test/ui/try-wait.rs
rename to src/test/ui/process/try-wait.rs
diff --git a/src/test/ui/pure-sum.rs b/src/test/ui/pure-sum.rs
deleted file mode 100644
index 2f2ece75ebe..00000000000
--- a/src/test/ui/pure-sum.rs
+++ /dev/null
@@ -1,51 +0,0 @@
-// run-pass
-
-#![allow(dead_code)]
-// Check that functions can modify local state.
-
-// pretty-expanded FIXME #23616
-
-fn sums_to(v: Vec<isize> , sum: isize) -> bool {
-    let mut i = 0;
-    let mut sum0 = 0;
-    while i < v.len() {
-        sum0 += v[i];
-        i += 1;
-    }
-    return sum0 == sum;
-}
-
-fn sums_to_using_uniq(v: Vec<isize> , sum: isize) -> bool {
-    let mut i = 0;
-    let mut sum0: Box<_> = 0.into();
-    while i < v.len() {
-        *sum0 += v[i];
-        i += 1;
-    }
-    return *sum0 == sum;
-}
-
-fn sums_to_using_rec(v: Vec<isize> , sum: isize) -> bool {
-    let mut i = 0;
-    let mut sum0 = F {f: 0};
-    while i < v.len() {
-        sum0.f += v[i];
-        i += 1;
-    }
-    return sum0.f == sum;
-}
-
-struct F<T> { f: T }
-
-fn sums_to_using_uniq_rec(v: Vec<isize> , sum: isize) -> bool {
-    let mut i = 0;
-    let mut sum0 = F::<Box<_>> {f: 0.into() };
-    while i < v.len() {
-        *sum0.f += v[i];
-        i += 1;
-    }
-    return *sum0.f == sum;
-}
-
-pub fn main() {
-}
diff --git a/src/test/ui/wf-bound-region-in-object-type.rs b/src/test/ui/regions/wf-bound-region-in-object-type.rs
similarity index 100%
rename from src/test/ui/wf-bound-region-in-object-type.rs
rename to src/test/ui/regions/wf-bound-region-in-object-type.rs
diff --git a/src/test/ui/auxiliary/blind-item-mixed-crate-use-item-foo.rs b/src/test/ui/resolve/auxiliary/blind-item-mixed-crate-use-item-foo.rs
similarity index 100%
rename from src/test/ui/auxiliary/blind-item-mixed-crate-use-item-foo.rs
rename to src/test/ui/resolve/auxiliary/blind-item-mixed-crate-use-item-foo.rs
diff --git a/src/test/ui/auxiliary/blind-item-mixed-crate-use-item-foo2.rs b/src/test/ui/resolve/auxiliary/blind-item-mixed-crate-use-item-foo2.rs
similarity index 100%
rename from src/test/ui/auxiliary/blind-item-mixed-crate-use-item-foo2.rs
rename to src/test/ui/resolve/auxiliary/blind-item-mixed-crate-use-item-foo2.rs
diff --git a/src/test/ui/blind-item-mixed-crate-use-item.rs b/src/test/ui/resolve/blind-item-mixed-crate-use-item.rs
similarity index 100%
rename from src/test/ui/blind-item-mixed-crate-use-item.rs
rename to src/test/ui/resolve/blind-item-mixed-crate-use-item.rs
diff --git a/src/test/ui/blind-item-mixed-use-item.rs b/src/test/ui/resolve/blind-item-mixed-use-item.rs
similarity index 100%
rename from src/test/ui/blind-item-mixed-use-item.rs
rename to src/test/ui/resolve/blind-item-mixed-use-item.rs
diff --git a/src/test/ui/export-fully-qualified.rs b/src/test/ui/resolve/export-fully-qualified.rs
similarity index 100%
rename from src/test/ui/export-fully-qualified.rs
rename to src/test/ui/resolve/export-fully-qualified.rs
diff --git a/src/test/ui/export-fully-qualified.stderr b/src/test/ui/resolve/export-fully-qualified.stderr
similarity index 100%
rename from src/test/ui/export-fully-qualified.stderr
rename to src/test/ui/resolve/export-fully-qualified.stderr
diff --git a/src/test/ui/no-std-1.rs b/src/test/ui/resolve/no-std-1.rs
similarity index 100%
rename from src/test/ui/no-std-1.rs
rename to src/test/ui/resolve/no-std-1.rs
diff --git a/src/test/ui/no-std-2.rs b/src/test/ui/resolve/no-std-2.rs
similarity index 100%
rename from src/test/ui/no-std-2.rs
rename to src/test/ui/resolve/no-std-2.rs
diff --git a/src/test/ui/no-std-3.rs b/src/test/ui/resolve/no-std-3.rs
similarity index 100%
rename from src/test/ui/no-std-3.rs
rename to src/test/ui/resolve/no-std-3.rs
diff --git a/src/test/ui/pathless-extern-ok.rs b/src/test/ui/resolve/pathless-extern-ok.rs
similarity index 100%
rename from src/test/ui/pathless-extern-ok.rs
rename to src/test/ui/resolve/pathless-extern-ok.rs
diff --git a/src/test/ui/resolve/privacy-enum-ctor.stderr b/src/test/ui/resolve/privacy-enum-ctor.stderr
index 06c52befd52..c93ba915efb 100644
--- a/src/test/ui/resolve/privacy-enum-ctor.stderr
+++ b/src/test/ui/resolve/privacy-enum-ctor.stderr
@@ -340,8 +340,9 @@ LL |         let _ = Z::Unit();
    |
 help: `Z::Unit` is a unit variant, you need to write it without the parentheses
    |
-LL |         let _ = Z::Unit;
-   |                 ~~~~~~~
+LL -         let _ = Z::Unit();
+LL +         let _ = Z::Unit;
+   | 
 
 error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:43:16
@@ -374,8 +375,9 @@ LL |     let _: E = m::E::Unit();
    |
 help: `m::E::Unit` is a unit variant, you need to write it without the parentheses
    |
-LL |     let _: E = m::E::Unit;
-   |                ~~~~~~~~~~
+LL -     let _: E = m::E::Unit();
+LL +     let _: E = m::E::Unit;
+   | 
 
 error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:51:16
@@ -408,8 +410,9 @@ LL |     let _: E = E::Unit();
    |
 help: `E::Unit` is a unit variant, you need to write it without the parentheses
    |
-LL |     let _: E = E::Unit;
-   |                ~~~~~~~
+LL -     let _: E = E::Unit();
+LL +     let _: E = E::Unit;
+   | 
 
 error: aborting due to 23 previous errors
 
diff --git a/src/test/ui/atomic-print.rs b/src/test/ui/runtime/atomic-print.rs
similarity index 100%
rename from src/test/ui/atomic-print.rs
rename to src/test/ui/runtime/atomic-print.rs
diff --git a/src/test/ui/backtrace-debuginfo-aux.rs b/src/test/ui/runtime/backtrace-debuginfo-aux.rs
similarity index 100%
rename from src/test/ui/backtrace-debuginfo-aux.rs
rename to src/test/ui/runtime/backtrace-debuginfo-aux.rs
diff --git a/src/test/ui/backtrace-debuginfo.rs b/src/test/ui/runtime/backtrace-debuginfo.rs
similarity index 100%
rename from src/test/ui/backtrace-debuginfo.rs
rename to src/test/ui/runtime/backtrace-debuginfo.rs
diff --git a/src/test/ui/native-print-no-runtime.rs b/src/test/ui/runtime/native-print-no-runtime.rs
similarity index 100%
rename from src/test/ui/native-print-no-runtime.rs
rename to src/test/ui/runtime/native-print-no-runtime.rs
diff --git a/src/test/ui/stability-in-private-module.rs b/src/test/ui/stability-attribute/stability-in-private-module.rs
similarity index 100%
rename from src/test/ui/stability-in-private-module.rs
rename to src/test/ui/stability-attribute/stability-in-private-module.rs
diff --git a/src/test/ui/stability-in-private-module.stderr b/src/test/ui/stability-attribute/stability-in-private-module.stderr
similarity index 100%
rename from src/test/ui/stability-in-private-module.stderr
rename to src/test/ui/stability-attribute/stability-in-private-module.stderr
diff --git a/src/test/ui/auxiliary/extern-statics.rs b/src/test/ui/static/auxiliary/extern-statics.rs
similarity index 100%
rename from src/test/ui/auxiliary/extern-statics.rs
rename to src/test/ui/static/auxiliary/extern-statics.rs
diff --git a/src/test/ui/safe-extern-statics-mut.mir.stderr b/src/test/ui/static/safe-extern-statics-mut.mir.stderr
similarity index 100%
rename from src/test/ui/safe-extern-statics-mut.mir.stderr
rename to src/test/ui/static/safe-extern-statics-mut.mir.stderr
diff --git a/src/test/ui/safe-extern-statics-mut.rs b/src/test/ui/static/safe-extern-statics-mut.rs
similarity index 100%
rename from src/test/ui/safe-extern-statics-mut.rs
rename to src/test/ui/static/safe-extern-statics-mut.rs
diff --git a/src/test/ui/safe-extern-statics-mut.thir.stderr b/src/test/ui/static/safe-extern-statics-mut.thir.stderr
similarity index 100%
rename from src/test/ui/safe-extern-statics-mut.thir.stderr
rename to src/test/ui/static/safe-extern-statics-mut.thir.stderr
diff --git a/src/test/ui/safe-extern-statics.mir.stderr b/src/test/ui/static/safe-extern-statics.mir.stderr
similarity index 100%
rename from src/test/ui/safe-extern-statics.mir.stderr
rename to src/test/ui/static/safe-extern-statics.mir.stderr
diff --git a/src/test/ui/safe-extern-statics.rs b/src/test/ui/static/safe-extern-statics.rs
similarity index 100%
rename from src/test/ui/safe-extern-statics.rs
rename to src/test/ui/static/safe-extern-statics.rs
diff --git a/src/test/ui/safe-extern-statics.thir.stderr b/src/test/ui/static/safe-extern-statics.thir.stderr
similarity index 100%
rename from src/test/ui/safe-extern-statics.thir.stderr
rename to src/test/ui/static/safe-extern-statics.thir.stderr
diff --git a/src/test/ui/thread-local-in-ctfe.rs b/src/test/ui/static/thread-local-in-ctfe.rs
similarity index 100%
rename from src/test/ui/thread-local-in-ctfe.rs
rename to src/test/ui/static/thread-local-in-ctfe.rs
diff --git a/src/test/ui/thread-local-in-ctfe.stderr b/src/test/ui/static/thread-local-in-ctfe.stderr
similarity index 100%
rename from src/test/ui/thread-local-in-ctfe.stderr
rename to src/test/ui/static/thread-local-in-ctfe.stderr
diff --git a/src/test/ui/matches2021.rs b/src/test/ui/stdlib-unit-tests/matches2021.rs
similarity index 100%
rename from src/test/ui/matches2021.rs
rename to src/test/ui/stdlib-unit-tests/matches2021.rs
diff --git a/src/test/ui/minmax-stability-issue-23687.rs b/src/test/ui/stdlib-unit-tests/minmax-stability-issue-23687.rs
similarity index 100%
rename from src/test/ui/minmax-stability-issue-23687.rs
rename to src/test/ui/stdlib-unit-tests/minmax-stability-issue-23687.rs
diff --git a/src/test/ui/not-sync.rs b/src/test/ui/stdlib-unit-tests/not-sync.rs
similarity index 100%
rename from src/test/ui/not-sync.rs
rename to src/test/ui/stdlib-unit-tests/not-sync.rs
diff --git a/src/test/ui/not-sync.stderr b/src/test/ui/stdlib-unit-tests/not-sync.stderr
similarity index 100%
rename from src/test/ui/not-sync.stderr
rename to src/test/ui/stdlib-unit-tests/not-sync.stderr
diff --git a/src/test/ui/raw-fat-ptr.rs b/src/test/ui/stdlib-unit-tests/raw-fat-ptr.rs
similarity index 100%
rename from src/test/ui/raw-fat-ptr.rs
rename to src/test/ui/stdlib-unit-tests/raw-fat-ptr.rs
diff --git a/src/test/ui/volatile-fat-ptr.rs b/src/test/ui/stdlib-unit-tests/volatile-fat-ptr.rs
similarity index 100%
rename from src/test/ui/volatile-fat-ptr.rs
rename to src/test/ui/stdlib-unit-tests/volatile-fat-ptr.rs
diff --git a/src/test/ui/syntax-trait-polarity-feature-gate.rs b/src/test/ui/syntax-trait-polarity-feature-gate.rs
deleted file mode 100644
index 4a3b24383ab..00000000000
--- a/src/test/ui/syntax-trait-polarity-feature-gate.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-use std::marker::Send;
-
-struct TestType;
-
-trait TestTrait {}
-
-impl !Send for TestType {}
-//~^ ERROR negative trait bounds
-
-fn main() {}
diff --git a/src/test/ui/syntax-trait-polarity-feature-gate.stderr b/src/test/ui/syntax-trait-polarity-feature-gate.stderr
deleted file mode 100644
index 3562deecbd5..00000000000
--- a/src/test/ui/syntax-trait-polarity-feature-gate.stderr
+++ /dev/null
@@ -1,12 +0,0 @@
-error[E0658]: negative trait bounds are not yet fully implemented; use marker types for now
-  --> $DIR/syntax-trait-polarity-feature-gate.rs:7:6
-   |
-LL | impl !Send for TestType {}
-   |      ^^^^^
-   |
-   = note: see issue #68318 <https://github.com/rust-lang/rust/issues/68318> for more information
-   = help: add `#![feature(negative_impls)]` to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/tail-direct.rs b/src/test/ui/tail-direct.rs
deleted file mode 100644
index c67c5b7a555..00000000000
--- a/src/test/ui/tail-direct.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-// run-pass
-
-pub fn main() { assert!((even(42))); assert!((odd(45))); }
-
-fn even(n: isize) -> bool { if n == 0 { return true; } else { return odd(n - 1); } }
-
-fn odd(n: isize) -> bool { if n == 0 { return false; } else { return even(n - 1); } }
diff --git a/src/test/ui/clone-with-exterior.rs b/src/test/ui/threads-sendsync/clone-with-exterior.rs
similarity index 100%
rename from src/test/ui/clone-with-exterior.rs
rename to src/test/ui/threads-sendsync/clone-with-exterior.rs
diff --git a/src/test/ui/tcp-stress.rs b/src/test/ui/threads-sendsync/tcp-stress.rs
similarity index 100%
rename from src/test/ui/tcp-stress.rs
rename to src/test/ui/threads-sendsync/tcp-stress.rs
diff --git a/src/test/ui/alignment-gep-tup-like-1.rs b/src/test/ui/traits/alignment-gep-tup-like-1.rs
similarity index 100%
rename from src/test/ui/alignment-gep-tup-like-1.rs
rename to src/test/ui/traits/alignment-gep-tup-like-1.rs
diff --git a/src/test/ui/cycle-generic-bound.rs b/src/test/ui/traits/cycle-generic-bound.rs
similarity index 100%
rename from src/test/ui/cycle-generic-bound.rs
rename to src/test/ui/traits/cycle-generic-bound.rs
diff --git a/src/test/ui/early-vtbl-resolution.rs b/src/test/ui/traits/early-vtbl-resolution.rs
similarity index 100%
rename from src/test/ui/early-vtbl-resolution.rs
rename to src/test/ui/traits/early-vtbl-resolution.rs
diff --git a/src/test/ui/map-types.rs b/src/test/ui/traits/map-types.rs
similarity index 100%
rename from src/test/ui/map-types.rs
rename to src/test/ui/traits/map-types.rs
diff --git a/src/test/ui/map-types.stderr b/src/test/ui/traits/map-types.stderr
similarity index 100%
rename from src/test/ui/map-types.stderr
rename to src/test/ui/traits/map-types.stderr
diff --git a/src/test/ui/no_send-struct.rs b/src/test/ui/traits/no_send-struct.rs
similarity index 100%
rename from src/test/ui/no_send-struct.rs
rename to src/test/ui/traits/no_send-struct.rs
diff --git a/src/test/ui/no_send-struct.stderr b/src/test/ui/traits/no_send-struct.stderr
similarity index 100%
rename from src/test/ui/no_send-struct.stderr
rename to src/test/ui/traits/no_send-struct.stderr
diff --git a/src/test/ui/try-is-identifier-edition2015.rs b/src/test/ui/try-block/try-is-identifier-edition2015.rs
similarity index 100%
rename from src/test/ui/try-is-identifier-edition2015.rs
rename to src/test/ui/try-block/try-is-identifier-edition2015.rs
diff --git a/src/test/ui/type-alias-enum-variants/incorrect-variant-form-through-alias-caught.stderr b/src/test/ui/type-alias-enum-variants/incorrect-variant-form-through-alias-caught.stderr
index e918551020c..0cf020861c7 100644
--- a/src/test/ui/type-alias-enum-variants/incorrect-variant-form-through-alias-caught.stderr
+++ b/src/test/ui/type-alias-enum-variants/incorrect-variant-form-through-alias-caught.stderr
@@ -29,8 +29,9 @@ LL |     Alias::Unit();
    |
 help: `Alias::Unit` is a unit variant, you need to write it without the parentheses
    |
-LL |     Alias::Unit;
-   |     ~~~~~~~~~~~
+LL -     Alias::Unit();
+LL +     Alias::Unit;
+   | 
 
 error[E0164]: expected tuple struct or tuple variant, found unit variant `Alias::Unit`
   --> $DIR/incorrect-variant-form-through-alias-caught.rs:17:9
diff --git a/src/test/ui/type-ascription.rs b/src/test/ui/type/type-ascription.rs
similarity index 100%
rename from src/test/ui/type-ascription.rs
rename to src/test/ui/type/type-ascription.rs
diff --git a/src/test/ui/no-type-for-node-ice.rs b/src/test/ui/typeck/no-type-for-node-ice.rs
similarity index 100%
rename from src/test/ui/no-type-for-node-ice.rs
rename to src/test/ui/typeck/no-type-for-node-ice.rs
diff --git a/src/test/ui/no-type-for-node-ice.stderr b/src/test/ui/typeck/no-type-for-node-ice.stderr
similarity index 100%
rename from src/test/ui/no-type-for-node-ice.stderr
rename to src/test/ui/typeck/no-type-for-node-ice.stderr
diff --git a/src/test/ui/project-cache-issue-37154.rs b/src/test/ui/typeck/project-cache-issue-37154.rs
similarity index 100%
rename from src/test/ui/project-cache-issue-37154.rs
rename to src/test/ui/typeck/project-cache-issue-37154.rs
diff --git a/src/test/ui/ufcs-type-params.rs b/src/test/ui/typeck/ufcs-type-params.rs
similarity index 100%
rename from src/test/ui/ufcs-type-params.rs
rename to src/test/ui/typeck/ufcs-type-params.rs
diff --git a/src/test/ui/unify-return-ty.rs b/src/test/ui/typeck/unify-return-ty.rs
similarity index 100%
rename from src/test/ui/unify-return-ty.rs
rename to src/test/ui/typeck/unify-return-ty.rs
diff --git a/src/test/ui/maybe-bounds-where.rs b/src/test/ui/unsized/maybe-bounds-where.rs
similarity index 100%
rename from src/test/ui/maybe-bounds-where.rs
rename to src/test/ui/unsized/maybe-bounds-where.rs
diff --git a/src/test/ui/maybe-bounds-where.stderr b/src/test/ui/unsized/maybe-bounds-where.stderr
similarity index 100%
rename from src/test/ui/maybe-bounds-where.stderr
rename to src/test/ui/unsized/maybe-bounds-where.stderr
diff --git a/src/test/ui/wasm-import-module.rs b/src/test/ui/wasm/wasm-import-module.rs
similarity index 100%
rename from src/test/ui/wasm-import-module.rs
rename to src/test/ui/wasm/wasm-import-module.rs
diff --git a/src/test/ui/wasm-import-module.stderr b/src/test/ui/wasm/wasm-import-module.stderr
similarity index 100%
rename from src/test/ui/wasm-import-module.stderr
rename to src/test/ui/wasm/wasm-import-module.stderr
diff --git a/src/tools/tidy/src/ui_tests.rs b/src/tools/tidy/src/ui_tests.rs
index 681b2486d07..248d4f1583f 100644
--- a/src/tools/tidy/src/ui_tests.rs
+++ b/src/tools/tidy/src/ui_tests.rs
@@ -7,9 +7,9 @@ use std::path::Path;
 
 const ENTRY_LIMIT: usize = 1000;
 // FIXME: The following limits should be reduced eventually.
-const ROOT_ENTRY_LIMIT: usize = 1102;
+const ROOT_ENTRY_LIMIT: usize = 983;
 const ISSUES_ENTRY_LIMIT: usize = 2310;
-const PARSER_LIMIT: usize = 1005;
+const PARSER_LIMIT: usize = 1010;
 
 fn check_entries(path: &Path, bad: &mut bool) {
     let dirs = walkdir::WalkDir::new(&path.join("test/ui"))