diff --git a/src/librustc_codegen_ssa/mir/mod.rs b/src/librustc_codegen_ssa/mir/mod.rs
index 1cd01c8c5bcb0..00b4bf96afa59 100644
--- a/src/librustc_codegen_ssa/mir/mod.rs
+++ b/src/librustc_codegen_ssa/mir/mod.rs
@@ -157,7 +157,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     let cleanup_kinds = analyze::cleanup_kinds(&mir);
     // Allocate a `Block` for every basic block, except
     // the start block, if nothing loops back to it.
-    let reentrant_start_block = !mir.predecessors_for(mir::START_BLOCK).is_empty();
+    let reentrant_start_block = !mir.predecessors()[mir::START_BLOCK].is_empty();
     let block_bxs: IndexVec<mir::BasicBlock, Bx::BasicBlock> = mir
         .basic_blocks()
         .indices()
diff --git a/src/librustc_data_structures/box_region.rs b/src/librustc_data_structures/box_region.rs
index edeb4f83c7d7e..eb6f4e8213ec7 100644
--- a/src/librustc_data_structures/box_region.rs
+++ b/src/librustc_data_structures/box_region.rs
@@ -1,4 +1,15 @@
-use std::cell::Cell;
+//! This module provides a way to deal with self-referential data.
+//!
+//! The main idea is to allocate such data in a generator frame and then
+//! give access to it by executing user-provided closures inside that generator.
+//! The module provides a safe abstraction for the latter task.
+//!
+//! The interface consists of two exported macros meant to be used together:
+//! * `declare_box_region_type` wraps a generator inside a struct with `access`
+//!   method which accepts closures.
+//! * `box_region_allow_access` is a helper which should be called inside
+//!   a generator to actually execute those closures.
+
 use std::marker::PhantomData;
 use std::ops::{Generator, GeneratorState};
 use std::pin::Pin;
@@ -14,24 +25,23 @@ impl AccessAction {
 
 #[derive(Copy, Clone)]
 pub enum Action {
+    Initial,
     Access(AccessAction),
     Complete,
 }
 
-thread_local!(pub static BOX_REGION_ARG: Cell<Action> = Cell::new(Action::Complete));
-
 pub struct PinnedGenerator<I, A, R> {
-    generator: Pin<Box<dyn Generator<Yield = YieldType<I, A>, Return = R>>>,
+    generator: Pin<Box<dyn Generator<Action, Yield = YieldType<I, A>, Return = R>>>,
 }
 
 impl<I, A, R> PinnedGenerator<I, A, R> {
-    pub fn new<T: Generator<Yield = YieldType<I, A>, Return = R> + 'static>(
+    pub fn new<T: Generator<Action, Yield = YieldType<I, A>, Return = R> + 'static>(
         generator: T,
     ) -> (I, Self) {
         let mut result = PinnedGenerator { generator: Box::pin(generator) };
 
         // Run it to the first yield to set it up
-        let init = match Pin::new(&mut result.generator).resume(()) {
+        let init = match Pin::new(&mut result.generator).resume(Action::Initial) {
             GeneratorState::Yielded(YieldType::Initial(y)) => y,
             _ => panic!(),
         };
@@ -40,21 +50,17 @@ impl<I, A, R> PinnedGenerator<I, A, R> {
     }
 
     pub unsafe fn access(&mut self, closure: *mut dyn FnMut()) {
-        BOX_REGION_ARG.with(|i| {
-            i.set(Action::Access(AccessAction(closure)));
-        });
-
-        // Call the generator, which in turn will call the closure in BOX_REGION_ARG
-        if let GeneratorState::Complete(_) = Pin::new(&mut self.generator).resume(()) {
+        // Call the generator, which in turn will call the closure
+        if let GeneratorState::Complete(_) =
+            Pin::new(&mut self.generator).resume(Action::Access(AccessAction(closure)))
+        {
             panic!()
         }
     }
 
     pub fn complete(&mut self) -> R {
         // Tell the generator we want it to complete, consuming it and yielding a result
-        BOX_REGION_ARG.with(|i| i.set(Action::Complete));
-
-        let result = Pin::new(&mut self.generator).resume(());
+        let result = Pin::new(&mut self.generator).resume(Action::Complete);
         if let GeneratorState::Complete(r) = result { r } else { panic!() }
     }
 }
@@ -89,7 +95,7 @@ macro_rules! declare_box_region_type {
         >);
 
         impl $name {
-            fn new<T: ::std::ops::Generator<Yield = $yield_type, Return = $retc> + 'static>(
+            fn new<T: ::std::ops::Generator<$crate::box_region::Action, Yield = $yield_type, Return = $retc> + 'static>(
                 generator: T
             ) -> ($reti, Self) {
                 let (initial, pinned) = $crate::box_region::PinnedGenerator::new(generator);
@@ -98,7 +104,7 @@ macro_rules! declare_box_region_type {
 
             $v fn access<F: for<$($lifetimes)*> FnOnce($($args,)*) -> R, R>(&mut self, f: F) -> R {
                 // Turn the FnOnce closure into *mut dyn FnMut()
-                // so we can pass it in to the generator using the BOX_REGION_ARG thread local
+                // so we can pass it in to the generator
                 let mut r = None;
                 let mut f = Some(f);
                 let mut_f: &mut dyn for<$($lifetimes)*> FnMut(($($args,)*)) =
@@ -140,9 +146,9 @@ macro_rules! declare_box_region_type {
 #[macro_export]
 #[allow_internal_unstable(fn_traits)]
 macro_rules! box_region_allow_access {
-    (for($($lifetimes:tt)*), ($($args:ty),*), ($($exprs:expr),*) ) => {
+    (for($($lifetimes:tt)*), ($($args:ty),*), ($($exprs:expr),*), $action:ident) => {
         loop {
-            match $crate::box_region::BOX_REGION_ARG.with(|i| i.get()) {
+            match $action {
                 $crate::box_region::Action::Access(accessor) => {
                     let accessor: &mut dyn for<$($lifetimes)*> FnMut($($args),*) = unsafe {
                         ::std::mem::transmute(accessor.get())
@@ -152,10 +158,11 @@ macro_rules! box_region_allow_access {
                         let marker = $crate::box_region::Marker::<
                             for<$($lifetimes)*> fn(($($args,)*))
                         >::new();
-                        yield $crate::box_region::YieldType::Accessor(marker)
+                        $action = yield $crate::box_region::YieldType::Accessor(marker);
                     };
                 }
                 $crate::box_region::Action::Complete => break,
+                $crate::box_region::Action::Initial => panic!("unexpected box_region action: Initial"),
             }
         }
     }
diff --git a/src/librustc_hir/def.rs b/src/librustc_hir/def.rs
index 3334cc32a52f7..88049f85f45e4 100644
--- a/src/librustc_hir/def.rs
+++ b/src/librustc_hir/def.rs
@@ -77,6 +77,18 @@ pub enum DefKind {
 
     // Macro namespace
     Macro(MacroKind),
+
+    // Not namespaced (or they are, but we don't treat them so)
+    ExternCrate,
+    Use,
+    ForeignMod,
+    AnonConst,
+    Field,
+    LifetimeParam,
+    GlobalAsm,
+    Impl,
+    Closure,
+    Generator,
 }
 
 impl DefKind {
@@ -113,6 +125,16 @@ impl DefKind {
             DefKind::TyParam => "type parameter",
             DefKind::ConstParam => "const parameter",
             DefKind::Macro(macro_kind) => macro_kind.descr(),
+            DefKind::LifetimeParam => "lifetime parameter",
+            DefKind::Use => "import",
+            DefKind::ForeignMod => "foreign module",
+            DefKind::AnonConst => "constant expression",
+            DefKind::Field => "field",
+            DefKind::Impl => "implementation",
+            DefKind::Closure => "closure",
+            DefKind::Generator => "generator",
+            DefKind::ExternCrate => "extern crate",
+            DefKind::GlobalAsm => "global assembly block",
         }
     }
 
@@ -124,7 +146,10 @@ impl DefKind {
             | DefKind::AssocOpaqueTy
             | DefKind::AssocFn
             | DefKind::Enum
-            | DefKind::OpaqueTy => "an",
+            | DefKind::OpaqueTy
+            | DefKind::Impl
+            | DefKind::Use
+            | DefKind::ExternCrate => "an",
             DefKind::Macro(macro_kind) => macro_kind.article(),
             _ => "a",
         }
@@ -155,6 +180,18 @@ impl DefKind {
             | DefKind::AssocConst => ns == Namespace::ValueNS,
 
             DefKind::Macro(..) => ns == Namespace::MacroNS,
+
+            // Not namespaced.
+            DefKind::AnonConst
+            | DefKind::Field
+            | DefKind::LifetimeParam
+            | DefKind::ExternCrate
+            | DefKind::Closure
+            | DefKind::Generator
+            | DefKind::Use
+            | DefKind::ForeignMod
+            | DefKind::GlobalAsm
+            | DefKind::Impl => false,
         }
     }
 }
diff --git a/src/librustc_hir/hir.rs b/src/librustc_hir/hir.rs
index b66e6101b504b..d342f8b0ad21c 100644
--- a/src/librustc_hir/hir.rs
+++ b/src/librustc_hir/hir.rs
@@ -2452,27 +2452,6 @@ pub enum ItemKind<'hir> {
 }
 
 impl ItemKind<'_> {
-    pub fn descr(&self) -> &str {
-        match *self {
-            ItemKind::ExternCrate(..) => "extern crate",
-            ItemKind::Use(..) => "`use` import",
-            ItemKind::Static(..) => "static item",
-            ItemKind::Const(..) => "constant item",
-            ItemKind::Fn(..) => "function",
-            ItemKind::Mod(..) => "module",
-            ItemKind::ForeignMod(..) => "extern block",
-            ItemKind::GlobalAsm(..) => "global asm item",
-            ItemKind::TyAlias(..) => "type alias",
-            ItemKind::OpaqueTy(..) => "opaque type",
-            ItemKind::Enum(..) => "enum",
-            ItemKind::Struct(..) => "struct",
-            ItemKind::Union(..) => "union",
-            ItemKind::Trait(..) => "trait",
-            ItemKind::TraitAlias(..) => "trait alias",
-            ItemKind::Impl { .. } => "implementation",
-        }
-    }
-
     pub fn generics(&self) -> Option<&Generics<'_>> {
         Some(match *self {
             ItemKind::Fn(_, ref generics, _)
@@ -2551,16 +2530,6 @@ pub enum ForeignItemKind<'hir> {
     Type,
 }
 
-impl ForeignItemKind<'hir> {
-    pub fn descriptive_variant(&self) -> &str {
-        match *self {
-            ForeignItemKind::Fn(..) => "foreign function",
-            ForeignItemKind::Static(..) => "foreign static item",
-            ForeignItemKind::Type => "foreign type",
-        }
-    }
-}
-
 /// A variable captured by a closure.
 #[derive(Debug, Copy, Clone, RustcEncodable, RustcDecodable, HashStable_Generic)]
 pub struct Upvar {
diff --git a/src/librustc_infer/infer/error_reporting/need_type_info.rs b/src/librustc_infer/infer/error_reporting/need_type_info.rs
index 53f52038ed022..1986838e4016c 100644
--- a/src/librustc_infer/infer/error_reporting/need_type_info.rs
+++ b/src/librustc_infer/infer/error_reporting/need_type_info.rs
@@ -207,12 +207,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         .get_opt_name()
                         .map(|parent_symbol| parent_symbol.to_string());
 
-                    let type_parent_desc = self
-                        .tcx
-                        .def_kind(parent_def_id)
-                        .map(|parent_def_kind| parent_def_kind.descr(parent_def_id));
-
-                    (parent_name, type_parent_desc)
+                    (parent_name, Some(self.tcx.def_kind(parent_def_id).descr(parent_def_id)))
                 } else {
                     (None, None)
                 };
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index 4c054795136b9..4b09148eab61f 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -109,7 +109,8 @@ pub fn configure_and_expand(
     // its contents but the results of name resolution on those contents. Hopefully we'll push
     // this back at some point.
     let crate_name = crate_name.to_string();
-    let (result, resolver) = BoxedResolver::new(static move || {
+    let (result, resolver) = BoxedResolver::new(static move |mut action| {
+        let _ = action;
         let sess = &*sess;
         let resolver_arenas = Resolver::arenas();
         let res = configure_and_expand_inner(
@@ -126,11 +127,11 @@ pub fn configure_and_expand(
                 panic!()
             }
             Ok((krate, resolver)) => {
-                yield BoxedResolver::initial_yield(Ok(krate));
+                action = yield BoxedResolver::initial_yield(Ok(krate));
                 resolver
             }
         };
-        box_region_allow_access!(for(), (&mut Resolver<'_>), (&mut resolver));
+        box_region_allow_access!(for(), (&mut Resolver<'_>), (&mut resolver), action);
         resolver.into_outputs()
     });
     result.map(|k| (k, resolver))
diff --git a/src/librustc_metadata/rmeta/decoder.rs b/src/librustc_metadata/rmeta/decoder.rs
index 1fb260f66fa3b..39d8213f2629b 100644
--- a/src/librustc_metadata/rmeta/decoder.rs
+++ b/src/librustc_metadata/rmeta/decoder.rs
@@ -562,8 +562,8 @@ impl MetadataBlob {
 }
 
 impl EntryKind {
-    fn def_kind(&self) -> Option<DefKind> {
-        Some(match *self {
+    fn def_kind(&self) -> DefKind {
+        match *self {
             EntryKind::Const(..) => DefKind::Const,
             EntryKind::AssocConst(..) => DefKind::AssocConst,
             EntryKind::ImmStatic
@@ -587,14 +587,13 @@ impl EntryKind {
             EntryKind::Enum(..) => DefKind::Enum,
             EntryKind::MacroDef(_) => DefKind::Macro(MacroKind::Bang),
             EntryKind::ForeignType => DefKind::ForeignTy,
-
-            EntryKind::ForeignMod
-            | EntryKind::GlobalAsm
-            | EntryKind::Impl(_)
-            | EntryKind::Field
-            | EntryKind::Generator(_)
-            | EntryKind::Closure => return None,
-        })
+            EntryKind::Impl(_) => DefKind::Impl,
+            EntryKind::Closure => DefKind::Closure,
+            EntryKind::ForeignMod => DefKind::ForeignMod,
+            EntryKind::GlobalAsm => DefKind::GlobalAsm,
+            EntryKind::Field => DefKind::Field,
+            EntryKind::Generator(_) => DefKind::Generator,
+        }
     }
 }
 
@@ -679,11 +678,11 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
-    fn def_kind(&self, index: DefIndex) -> Option<DefKind> {
+    fn def_kind(&self, index: DefIndex) -> DefKind {
         if !self.is_proc_macro(index) {
             self.kind(index).def_kind()
         } else {
-            Some(DefKind::Macro(macro_kind(self.raw_proc_macro(index))))
+            DefKind::Macro(macro_kind(self.raw_proc_macro(index)))
         }
     }
 
@@ -1009,20 +1008,19 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                             .get(self, child_index)
                             .unwrap_or(Lazy::empty());
                         for child_index in child_children.decode((self, sess)) {
-                            if let Some(kind) = self.def_kind(child_index) {
-                                callback(Export {
-                                    res: Res::Def(kind, self.local_def_id(child_index)),
-                                    ident: self.item_ident(child_index, sess),
-                                    vis: self.get_visibility(child_index),
-                                    span: self
-                                        .root
-                                        .tables
-                                        .span
-                                        .get(self, child_index)
-                                        .unwrap()
-                                        .decode((self, sess)),
-                                });
-                            }
+                            let kind = self.def_kind(child_index);
+                            callback(Export {
+                                res: Res::Def(kind, self.local_def_id(child_index)),
+                                ident: self.item_ident(child_index, sess),
+                                vis: self.get_visibility(child_index),
+                                span: self
+                                    .root
+                                    .tables
+                                    .span
+                                    .get(self, child_index)
+                                    .unwrap()
+                                    .decode((self, sess)),
+                            });
                         }
                         continue;
                     }
@@ -1033,10 +1031,8 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
                 let def_key = self.def_key(child_index);
                 let span = self.get_span(child_index, sess);
-                if let (Some(kind), true) = (
-                    self.def_kind(child_index),
-                    def_key.disambiguated_data.data.get_opt_name().is_some(),
-                ) {
+                if def_key.disambiguated_data.data.get_opt_name().is_some() {
+                    let kind = self.def_kind(child_index);
                     let ident = self.item_ident(child_index, sess);
                     let vis = self.get_visibility(child_index);
                     let def_id = self.local_def_id(child_index);
diff --git a/src/librustc_middle/hir/map/mod.rs b/src/librustc_middle/hir/map/mod.rs
index aee80b6e14e14..1c71fc57bea5a 100644
--- a/src/librustc_middle/hir/map/mod.rs
+++ b/src/librustc_middle/hir/map/mod.rs
@@ -6,7 +6,7 @@ use crate::ty::TyCtxt;
 use rustc_ast::ast::{self, Name, NodeId};
 use rustc_data_structures::svh::Svh;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, Definitions};
 use rustc_hir::intravisit;
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
@@ -227,10 +227,14 @@ impl<'hir> Map<'hir> {
         self.tcx.definitions.opt_local_def_id_to_hir_id(def_id)
     }
 
-    pub fn def_kind(&self, hir_id: HirId) -> Option<DefKind> {
-        let node = self.find(hir_id)?;
+    pub fn def_kind(&self, local_def_id: LocalDefId) -> DefKind {
+        // FIXME(eddyb) support `find` on the crate root.
+        if local_def_id.to_def_id().index == CRATE_DEF_INDEX {
+            return DefKind::Mod;
+        }
 
-        Some(match node {
+        let hir_id = self.local_def_id_to_hir_id(local_def_id);
+        match self.get(hir_id) {
             Node::Item(item) => match item.kind {
                 ItemKind::Static(..) => DefKind::Static,
                 ItemKind::Const(..) => DefKind::Const,
@@ -243,11 +247,11 @@ impl<'hir> Map<'hir> {
                 ItemKind::Union(..) => DefKind::Union,
                 ItemKind::Trait(..) => DefKind::Trait,
                 ItemKind::TraitAlias(..) => DefKind::TraitAlias,
-                ItemKind::ExternCrate(_)
-                | ItemKind::Use(..)
-                | ItemKind::ForeignMod(..)
-                | ItemKind::GlobalAsm(..)
-                | ItemKind::Impl { .. } => return None,
+                ItemKind::ExternCrate(_) => DefKind::ExternCrate,
+                ItemKind::Use(..) => DefKind::Use,
+                ItemKind::ForeignMod(..) => DefKind::ForeignMod,
+                ItemKind::GlobalAsm(..) => DefKind::GlobalAsm,
+                ItemKind::Impl { .. } => DefKind::Impl,
             },
             Node::ForeignItem(item) => match item.kind {
                 ForeignItemKind::Fn(..) => DefKind::Fn,
@@ -268,7 +272,7 @@ impl<'hir> Map<'hir> {
             Node::Variant(_) => DefKind::Variant,
             Node::Ctor(variant_data) => {
                 // FIXME(eddyb) is this even possible, if we have a `Node::Ctor`?
-                variant_data.ctor_hir_id()?;
+                assert_ne!(variant_data.ctor_hir_id(), None);
 
                 let ctor_of = match self.find(self.get_parent_node(hir_id)) {
                     Some(Node::Item(..)) => def::CtorOf::Struct,
@@ -277,10 +281,20 @@ impl<'hir> Map<'hir> {
                 };
                 DefKind::Ctor(ctor_of, def::CtorKind::from_hir(variant_data))
             }
-            Node::AnonConst(_)
-            | Node::Field(_)
-            | Node::Expr(_)
-            | Node::Stmt(_)
+            Node::AnonConst(_) => DefKind::AnonConst,
+            Node::Field(_) => DefKind::Field,
+            Node::Expr(expr) => match expr.kind {
+                ExprKind::Closure(.., None) => DefKind::Closure,
+                ExprKind::Closure(.., Some(_)) => DefKind::Generator,
+                _ => bug!("def_kind: unsupported node: {}", self.node_to_string(hir_id)),
+            },
+            Node::MacroDef(_) => DefKind::Macro(MacroKind::Bang),
+            Node::GenericParam(param) => match param.kind {
+                GenericParamKind::Lifetime { .. } => DefKind::LifetimeParam,
+                GenericParamKind::Type { .. } => DefKind::TyParam,
+                GenericParamKind::Const { .. } => DefKind::ConstParam,
+            },
+            Node::Stmt(_)
             | Node::PathSegment(_)
             | Node::Ty(_)
             | Node::TraitRef(_)
@@ -292,14 +306,8 @@ impl<'hir> Map<'hir> {
             | Node::Lifetime(_)
             | Node::Visibility(_)
             | Node::Block(_)
-            | Node::Crate(_) => return None,
-            Node::MacroDef(_) => DefKind::Macro(MacroKind::Bang),
-            Node::GenericParam(param) => match param.kind {
-                GenericParamKind::Lifetime { .. } => return None,
-                GenericParamKind::Type { .. } => DefKind::TyParam,
-                GenericParamKind::Const { .. } => DefKind::ConstParam,
-            },
-        })
+            | Node::Crate(_) => bug!("def_kind: unsupported node: {}", self.node_to_string(hir_id)),
+        }
     }
 
     fn find_entry(&self, id: HirId) -> Option<Entry<'hir>> {
@@ -1082,6 +1090,5 @@ fn hir_id_to_string(map: &Map<'_>, id: HirId) -> String {
 }
 
 pub fn provide(providers: &mut Providers<'_>) {
-    providers.def_kind =
-        |tcx, def_id| tcx.hir().def_kind(tcx.hir().as_local_hir_id(def_id.expect_local()));
+    providers.def_kind = |tcx, def_id| tcx.hir().def_kind(def_id.expect_local());
 }
diff --git a/src/librustc_middle/middle/stability.rs b/src/librustc_middle/middle/stability.rs
index 9d95a700313d6..54c05bca3bd2b 100644
--- a/src/librustc_middle/middle/stability.rs
+++ b/src/librustc_middle/middle/stability.rs
@@ -246,7 +246,7 @@ pub enum EvalResult {
 fn skip_stability_check_due_to_privacy(tcx: TyCtxt<'_>, mut def_id: DefId) -> bool {
     // Check if `def_id` is a trait method.
     match tcx.def_kind(def_id) {
-        Some(DefKind::AssocFn) | Some(DefKind::AssocTy) | Some(DefKind::AssocConst) => {
+        DefKind::AssocFn | DefKind::AssocTy | DefKind::AssocConst => {
             if let ty::TraitContainer(trait_def_id) = tcx.associated_item(def_id).container {
                 // Trait methods do not declare visibility (even
                 // for visibility info in cstore). Use containing
diff --git a/src/librustc_middle/mir/mod.rs b/src/librustc_middle/mir/mod.rs
index 341fec0c07b36..34c05ec59f388 100644
--- a/src/librustc_middle/mir/mod.rs
+++ b/src/librustc_middle/mir/mod.rs
@@ -23,14 +23,12 @@ use rustc_ast::ast::Name;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::graph::dominators::{dominators, Dominators};
 use rustc_data_structures::graph::{self, GraphSuccessors};
-use rustc_data_structures::sync::MappedLockGuard;
 use rustc_index::bit_set::BitMatrix;
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_macros::HashStable;
 use rustc_serialize::{Decodable, Encodable};
 use rustc_span::symbol::Symbol;
 use rustc_span::{Span, DUMMY_SP};
-use smallvec::SmallVec;
 use std::borrow::Cow;
 use std::fmt::{self, Debug, Display, Formatter, Write};
 use std::ops::{Index, IndexMut};
@@ -170,7 +168,7 @@ pub struct Body<'tcx> {
     /// FIXME(oli-obk): rewrite the promoted during promotion to eliminate the cell components.
     pub ignore_interior_mut_in_const_validation: bool,
 
-    pub predecessor_cache: PredecessorCache,
+    predecessor_cache: PredecessorCache,
 }
 
 impl<'tcx> Body<'tcx> {
@@ -398,15 +396,6 @@ impl<'tcx> Body<'tcx> {
         Location { block: bb, statement_index: self[bb].statements.len() }
     }
 
-    #[inline]
-    pub fn predecessors_for(
-        &self,
-        bb: BasicBlock,
-    ) -> impl std::ops::Deref<Target = SmallVec<[BasicBlock; 4]>> + '_ {
-        let predecessors = self.predecessor_cache.compute(&self.basic_blocks);
-        MappedLockGuard::map(predecessors, |preds| &mut preds[bb])
-    }
-
     #[inline]
     pub fn predecessors(&self) -> impl std::ops::Deref<Target = Predecessors> + '_ {
         self.predecessor_cache.compute(&self.basic_blocks)
@@ -2684,7 +2673,7 @@ impl graph::GraphPredecessors<'graph> for Body<'tcx> {
 impl graph::WithPredecessors for Body<'tcx> {
     #[inline]
     fn predecessors(&self, node: Self::Node) -> <Self as graph::GraphPredecessors<'_>>::Iter {
-        self.predecessors_for(node).clone().into_iter()
+        self.predecessors()[node].clone().into_iter()
     }
 }
 
diff --git a/src/librustc_middle/mir/predecessors.rs b/src/librustc_middle/mir/predecessors.rs
index 629b5c2efb711..9508365886aa7 100644
--- a/src/librustc_middle/mir/predecessors.rs
+++ b/src/librustc_middle/mir/predecessors.rs
@@ -1,5 +1,7 @@
+//! Lazily compute the reverse control-flow graph for the MIR.
+
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_data_structures::sync::{Lock, LockGuard, MappedLockGuard};
+use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_index::vec::IndexVec;
 use rustc_serialize as serialize;
 use smallvec::SmallVec;
@@ -10,40 +12,49 @@ use crate::mir::{BasicBlock, BasicBlockData};
 pub type Predecessors = IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>>;
 
 #[derive(Clone, Debug)]
-pub struct PredecessorCache {
-    cache: Lock<Option<Predecessors>>,
+pub(super) struct PredecessorCache {
+    cache: Lock<Option<Lrc<Predecessors>>>,
 }
 
 impl PredecessorCache {
     #[inline]
-    pub fn new() -> Self {
+    pub(super) fn new() -> Self {
         PredecessorCache { cache: Lock::new(None) }
     }
 
+    /// Invalidates the predecessor cache.
+    ///
+    /// Invalidating the predecessor cache requires mutating the MIR, which in turn requires a
+    /// unique reference (`&mut`) to the `mir::Body`. Because of this, we can assume that all
+    /// callers of `invalidate` have a unique reference to the MIR and thus to the predecessor
+    /// cache. This means we don't actually need to take a lock when `invalidate` is called.
     #[inline]
-    pub fn invalidate(&mut self) {
+    pub(super) fn invalidate(&mut self) {
         *self.cache.get_mut() = None;
     }
 
+    /// Returns a ref-counted smart pointer containing the predecessor graph for this MIR.
+    ///
+    /// We use ref-counting instead of a mapped `LockGuard` here to ensure that the lock for
+    /// `cache` is only held inside this function. As long as no other locks are taken while
+    /// computing the predecessor graph, deadlock is impossible.
     #[inline]
-    pub fn compute(
+    pub(super) fn compute(
         &self,
         basic_blocks: &IndexVec<BasicBlock, BasicBlockData<'_>>,
-    ) -> MappedLockGuard<'_, Predecessors> {
-        LockGuard::map(self.cache.lock(), |cache| {
-            cache.get_or_insert_with(|| {
-                let mut preds = IndexVec::from_elem(SmallVec::new(), basic_blocks);
-                for (bb, data) in basic_blocks.iter_enumerated() {
-                    if let Some(term) = &data.terminator {
-                        for &succ in term.successors() {
-                            preds[succ].push(bb);
-                        }
+    ) -> Lrc<Predecessors> {
+        Lrc::clone(self.cache.lock().get_or_insert_with(|| {
+            let mut preds = IndexVec::from_elem(SmallVec::new(), basic_blocks);
+            for (bb, data) in basic_blocks.iter_enumerated() {
+                if let Some(term) = &data.terminator {
+                    for &succ in term.successors() {
+                        preds[succ].push(bb);
                     }
                 }
+            }
 
-                preds
-            })
-        })
+            Lrc::new(preds)
+        }))
     }
 }
 
diff --git a/src/librustc_middle/query/mod.rs b/src/librustc_middle/query/mod.rs
index 51bbb9016b6a2..8b0509e314ce6 100644
--- a/src/librustc_middle/query/mod.rs
+++ b/src/librustc_middle/query/mod.rs
@@ -620,7 +620,7 @@ rustc_queries! {
             cache_on_disk_if { true }
         }
 
-        query def_kind(_: DefId) -> Option<DefKind> {}
+        query def_kind(_: DefId) -> DefKind {}
         query def_span(_: DefId) -> Span {
             // FIXME(mw): DefSpans are not really inputs since they are derived from
             // HIR. But at the moment HIR hashing still contains some hacks that allow
diff --git a/src/librustc_middle/ty/context.rs b/src/librustc_middle/ty/context.rs
index 7797374259cb7..eae4055877b2a 100644
--- a/src/librustc_middle/ty/context.rs
+++ b/src/librustc_middle/ty/context.rs
@@ -48,7 +48,7 @@ use rustc_errors::ErrorReported;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
-use rustc_hir::definitions::{DefPathData, DefPathHash, Definitions};
+use rustc_hir::definitions::{DefPathHash, Definitions};
 use rustc_hir::lang_items;
 use rustc_hir::lang_items::PanicLocationLangItem;
 use rustc_hir::{HirId, Node, TraitCandidate};
@@ -1492,21 +1492,13 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Returns a displayable description and article for the given `def_id` (e.g. `("a", "struct")`).
     pub fn article_and_description(&self, def_id: DefId) -> (&'static str, &'static str) {
-        self.def_kind(def_id)
-            .map(|def_kind| (def_kind.article(), def_kind.descr(def_id)))
-            .unwrap_or_else(|| match self.def_key(def_id).disambiguated_data.data {
-                DefPathData::ClosureExpr => match self.generator_kind(def_id) {
-                    None => ("a", "closure"),
-                    Some(rustc_hir::GeneratorKind::Async(..)) => ("an", "async closure"),
-                    Some(rustc_hir::GeneratorKind::Gen) => ("a", "generator"),
-                },
-                DefPathData::LifetimeNs(..) => ("a", "lifetime"),
-                DefPathData::Impl => ("an", "implementation"),
-                DefPathData::TypeNs(..) | DefPathData::ValueNs(..) | DefPathData::MacroNs(..) => {
-                    unreachable!()
-                }
-                _ => bug!("article_and_description called on def_id {:?}", def_id),
-            })
+        match self.def_kind(def_id) {
+            DefKind::Generator => match self.generator_kind(def_id).unwrap() {
+                rustc_hir::GeneratorKind::Async(..) => ("an", "async closure"),
+                rustc_hir::GeneratorKind::Gen => ("a", "generator"),
+            },
+            def_kind => (def_kind.article(), def_kind.descr(def_id)),
+        }
     }
 }
 
diff --git a/src/librustc_middle/ty/mod.rs b/src/librustc_middle/ty/mod.rs
index b785f79e1f35e..d6c8ccf5ea62a 100644
--- a/src/librustc_middle/ty/mod.rs
+++ b/src/librustc_middle/ty/mod.rs
@@ -2680,7 +2680,7 @@ impl<'tcx> TyCtxt<'tcx> {
             }
         } else {
             match self.def_kind(def_id) {
-                Some(DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy) => true,
+                DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy => true,
                 _ => false,
             }
         };
diff --git a/src/librustc_middle/ty/print/pretty.rs b/src/librustc_middle/ty/print/pretty.rs
index 8c8d20655f96f..2d2704fc2bd89 100644
--- a/src/librustc_middle/ty/print/pretty.rs
+++ b/src/librustc_middle/ty/print/pretty.rs
@@ -888,7 +888,7 @@ pub trait PrettyPrinter<'tcx>:
                     p!(write("::{:?}", promoted));
                 } else {
                     match self.tcx().def_kind(did) {
-                        Some(DefKind::Static | DefKind::Const | DefKind::AssocConst) => {
+                        DefKind::Static | DefKind::Const | DefKind::AssocConst => {
                             p!(print_value_path(did, substs))
                         }
                         _ => {
diff --git a/src/librustc_middle/ty/util.rs b/src/librustc_middle/ty/util.rs
index 4b10a8ba8210b..b46caf7985208 100644
--- a/src/librustc_middle/ty/util.rs
+++ b/src/librustc_middle/ty/util.rs
@@ -16,7 +16,6 @@ use rustc_errors::ErrorReported;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
-use rustc_hir::definitions::DefPathData;
 use rustc_macros::HashStable;
 use rustc_span::Span;
 use rustc_target::abi::{Integer, Size, TargetDataLayout};
@@ -446,24 +445,24 @@ impl<'tcx> TyCtxt<'tcx> {
     /// those are not yet phased out). The parent of the closure's
     /// `DefId` will also be the context where it appears.
     pub fn is_closure(self, def_id: DefId) -> bool {
-        self.def_key(def_id).disambiguated_data.data == DefPathData::ClosureExpr
+        matches!(self.def_kind(def_id), DefKind::Closure | DefKind::Generator)
     }
 
     /// Returns `true` if `def_id` refers to a trait (i.e., `trait Foo { ... }`).
     pub fn is_trait(self, def_id: DefId) -> bool {
-        self.def_kind(def_id) == Some(DefKind::Trait)
+        self.def_kind(def_id) == DefKind::Trait
     }
 
     /// Returns `true` if `def_id` refers to a trait alias (i.e., `trait Foo = ...;`),
     /// and `false` otherwise.
     pub fn is_trait_alias(self, def_id: DefId) -> bool {
-        self.def_kind(def_id) == Some(DefKind::TraitAlias)
+        self.def_kind(def_id) == DefKind::TraitAlias
     }
 
     /// Returns `true` if this `DefId` refers to the implicit constructor for
     /// a tuple struct like `struct Foo(u32)`, and `false` otherwise.
     pub fn is_constructor(self, def_id: DefId) -> bool {
-        self.def_key(def_id).disambiguated_data.data == DefPathData::Ctor
+        matches!(self.def_kind(def_id), DefKind::Ctor(..))
     }
 
     /// Given the def-ID of a fn or closure, returns the def-ID of
diff --git a/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs b/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs
index 6cc4ee432a58c..d424d0525fdd8 100644
--- a/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs
+++ b/src/librustc_mir/borrow_check/diagnostics/conflict_errors.rs
@@ -1269,7 +1269,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             location: Location,
         ) -> impl Iterator<Item = Location> + 'a {
             if location.statement_index == 0 {
-                let predecessors = body.predecessors_for(location.block).to_vec();
+                let predecessors = body.predecessors()[location.block].to_vec();
                 Either::Left(predecessors.into_iter().map(move |bb| body.terminator_loc(bb)))
             } else {
                 Either::Right(std::iter::once(Location {
diff --git a/src/librustc_mir/borrow_check/region_infer/values.rs b/src/librustc_mir/borrow_check/region_infer/values.rs
index 57a3fa6f79b50..6cd814962c613 100644
--- a/src/librustc_mir/borrow_check/region_infer/values.rs
+++ b/src/librustc_mir/borrow_check/region_infer/values.rs
@@ -89,7 +89,7 @@ impl RegionValueElements {
             // If this is a basic block head, then the predecessors are
             // the terminators of other basic blocks
             stack.extend(
-                body.predecessors_for(block)
+                body.predecessors()[block]
                     .iter()
                     .map(|&pred_bb| body.terminator_loc(pred_bb))
                     .map(|pred_loc| self.point_from_location(pred_loc)),
diff --git a/src/librustc_mir/borrow_check/type_check/liveness/trace.rs b/src/librustc_mir/borrow_check/type_check/liveness/trace.rs
index af09dc5b8039e..ec52a08c7b216 100644
--- a/src/librustc_mir/borrow_check/type_check/liveness/trace.rs
+++ b/src/librustc_mir/borrow_check/type_check/liveness/trace.rs
@@ -303,7 +303,7 @@ impl LivenessResults<'me, 'typeck, 'flow, 'tcx> {
         }
 
         let body = self.cx.body;
-        for &pred_block in body.predecessors_for(block).iter() {
+        for &pred_block in body.predecessors()[block].iter() {
             debug!("compute_drop_live_points_for_block: pred_block = {:?}", pred_block,);
 
             // Check whether the variable is (at least partially)
diff --git a/src/librustc_mir/const_eval/eval_queries.rs b/src/librustc_mir/const_eval/eval_queries.rs
index 6d0a02ee3a47f..b6d10d1e3701d 100644
--- a/src/librustc_mir/const_eval/eval_queries.rs
+++ b/src/librustc_mir/const_eval/eval_queries.rs
@@ -341,7 +341,7 @@ pub fn const_eval_raw_provider<'tcx>(
                     // because any code that existed before validation could not have failed
                     // validation thus preventing such a hard error from being a backwards
                     // compatibility hazard
-                    Some(DefKind::Const | DefKind::AssocConst) => {
+                    DefKind::Const | DefKind::AssocConst => {
                         let hir_id = tcx.hir().as_local_hir_id(def_id.expect_local());
                         err.report_as_lint(
                             tcx.at(tcx.def_span(def_id)),
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 45abde4347728..a497a6784ff6b 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -632,7 +632,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             // FIXME: The above is likely untrue. See
             // <https://github.com/rust-lang/rust/pull/70004#issuecomment-602022110>. Is it
             // okay to ignore `StorageDead`/`StorageLive` annotations during CTFE?
-            Some(DefKind::Static | DefKind::Const | DefKind::AssocConst) => {}
+            DefKind::Static | DefKind::Const | DefKind::AssocConst => {}
             _ => {
                 // Mark locals that use `Storage*` annotations as dead on function entry.
                 let always_live = AlwaysLiveLocals::new(self.body());
diff --git a/src/librustc_mir/interpret/memory.rs b/src/librustc_mir/interpret/memory.rs
index 9b2b7196fc0e9..0d0ed465c1cc6 100644
--- a/src/librustc_mir/interpret/memory.rs
+++ b/src/librustc_mir/interpret/memory.rs
@@ -400,7 +400,18 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
 
                 // We can still be zero-sized in this branch, in which case we have to
                 // return `None`.
-                if size.bytes() == 0 { None } else { Some(ptr) }
+                if size.bytes() == 0 {
+                    // We may be reading from a static.
+                    // In order to ensure that `static FOO: Type = FOO;` causes a cycle error
+                    // instead of magically pulling *any* ZST value from the ether, we need to
+                    // actually access the referenced allocation. The caller is likely
+                    // to short-circuit on `None`, so we trigger the access here to
+                    // make sure it happens.
+                    self.get_raw(ptr.alloc_id)?;
+                    None
+                } else {
+                    Some(ptr)
+                }
             }
         })
     }
diff --git a/src/librustc_mir/interpret/operand.rs b/src/librustc_mir/interpret/operand.rs
index 8188106b5f187..4d76a23005065 100644
--- a/src/librustc_mir/interpret/operand.rs
+++ b/src/librustc_mir/interpret/operand.rs
@@ -248,13 +248,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
         };
 
+        let alloc = self.memory.get_raw(ptr.alloc_id)?;
+
         match mplace.layout.abi {
             Abi::Scalar(..) => {
-                let scalar = self.memory.get_raw(ptr.alloc_id)?.read_scalar(
-                    self,
-                    ptr,
-                    mplace.layout.size,
-                )?;
+                let scalar = alloc.read_scalar(self, ptr, mplace.layout.size)?;
                 Ok(Some(ImmTy { imm: scalar.into(), layout: mplace.layout }))
             }
             Abi::ScalarPair(ref a, ref b) => {
@@ -267,8 +265,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let b_offset = a_size.align_to(b.align(self).abi);
                 assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields
                 let b_ptr = ptr.offset(b_offset, self)?;
-                let a_val = self.memory.get_raw(ptr.alloc_id)?.read_scalar(self, a_ptr, a_size)?;
-                let b_val = self.memory.get_raw(ptr.alloc_id)?.read_scalar(self, b_ptr, b_size)?;
+                let a_val = alloc.read_scalar(self, a_ptr, a_size)?;
+                let b_val = alloc.read_scalar(self, b_ptr, b_size)?;
                 Ok(Some(ImmTy { imm: Immediate::ScalarPair(a_val, b_val), layout: mplace.layout }))
             }
             _ => Ok(None),
diff --git a/src/librustc_mir/monomorphize/partitioning.rs b/src/librustc_mir/monomorphize/partitioning.rs
index cad5b114ae455..db1ea72c0a531 100644
--- a/src/librustc_mir/monomorphize/partitioning.rs
+++ b/src/librustc_mir/monomorphize/partitioning.rs
@@ -779,7 +779,7 @@ fn compute_codegen_unit_name(
                 cgu_def_id = Some(DefId { krate: def_id.krate, index: CRATE_DEF_INDEX });
             }
             break;
-        } else if tcx.def_kind(current_def_id) == Some(DefKind::Mod) {
+        } else if tcx.def_kind(current_def_id) == DefKind::Mod {
             if cgu_def_id.is_none() {
                 cgu_def_id = Some(current_def_id);
             }
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index a3465b021826c..bad0b94f3ece7 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -69,10 +69,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
         let hir_id = tcx.hir().as_local_hir_id(source.def_id().expect_local());
 
         let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some();
-        let is_assoc_const = match tcx.def_kind(source.def_id()) {
-            Some(DefKind::AssocConst) => true,
-            _ => false,
-        };
+        let is_assoc_const = tcx.def_kind(source.def_id()) == DefKind::AssocConst;
 
         // Only run const prop on functions, methods, closures and associated constants
         if !is_fn_like && !is_assoc_const {
diff --git a/src/librustc_mir/util/pretty.rs b/src/librustc_mir/util/pretty.rs
index 6c852d9e36709..8829b10d5dd79 100644
--- a/src/librustc_mir/util/pretty.rs
+++ b/src/librustc_mir/util/pretty.rs
@@ -807,17 +807,17 @@ fn write_mir_sig(
     trace!("write_mir_sig: {:?}", src.instance);
     let kind = tcx.def_kind(src.def_id());
     let is_function = match kind {
-        Some(DefKind::Fn | DefKind::AssocFn | DefKind::Ctor(..)) => true,
+        DefKind::Fn | DefKind::AssocFn | DefKind::Ctor(..) => true,
         _ => tcx.is_closure(src.def_id()),
     };
     match (kind, src.promoted) {
         (_, Some(i)) => write!(w, "{:?} in ", i)?,
-        (Some(DefKind::Const | DefKind::AssocConst), _) => write!(w, "const ")?,
-        (Some(DefKind::Static), _) => {
+        (DefKind::Const | DefKind::AssocConst, _) => write!(w, "const ")?,
+        (DefKind::Static, _) => {
             write!(w, "static {}", if tcx.is_mutable_static(src.def_id()) { "mut " } else { "" })?
         }
         (_, _) if is_function => write!(w, "fn ")?,
-        (None, _) => {} // things like anon const, not an item
+        (DefKind::AnonConst, _) => {} // things like anon const, not an item
         _ => bug!("Unexpected def kind {:?}", kind),
     }
 
diff --git a/src/librustc_passes/dead.rs b/src/librustc_passes/dead.rs
index 6d1fbd6c868c5..3b778cacefe13 100644
--- a/src/librustc_passes/dead.rs
+++ b/src/librustc_passes/dead.rs
@@ -553,12 +553,13 @@ impl DeadVisitor<'tcx> {
         id: hir::HirId,
         span: rustc_span::Span,
         name: ast::Name,
-        node_type: &str,
         participle: &str,
     ) {
         if !name.as_str().starts_with('_') {
             self.tcx.struct_span_lint_hir(lint::builtin::DEAD_CODE, id, span, |lint| {
-                lint.build(&format!("{} is never {}: `{}`", node_type, participle, name)).emit()
+                let def_id = self.tcx.hir().local_def_id(id);
+                let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
+                lint.build(&format!("{} is never {}: `{}`", descr, participle, name)).emit()
             });
         }
     }
@@ -604,7 +605,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
                 hir::ItemKind::Struct(..) => "constructed", // Issue #52325
                 _ => "used",
             };
-            self.warn_dead_code(item.hir_id, span, item.ident.name, item.kind.descr(), participle);
+            self.warn_dead_code(item.hir_id, span, item.ident.name, participle);
         } else {
             // Only continue if we didn't warn
             intravisit::walk_item(self, item);
@@ -618,13 +619,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
         id: hir::HirId,
     ) {
         if self.should_warn_about_variant(&variant) {
-            self.warn_dead_code(
-                variant.id,
-                variant.span,
-                variant.ident.name,
-                "variant",
-                "constructed",
-            );
+            self.warn_dead_code(variant.id, variant.span, variant.ident.name, "constructed");
         } else {
             intravisit::walk_variant(self, variant, g, id);
         }
@@ -632,20 +627,14 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
 
     fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem<'tcx>) {
         if self.should_warn_about_foreign_item(fi) {
-            self.warn_dead_code(
-                fi.hir_id,
-                fi.span,
-                fi.ident.name,
-                fi.kind.descriptive_variant(),
-                "used",
-            );
+            self.warn_dead_code(fi.hir_id, fi.span, fi.ident.name, "used");
         }
         intravisit::walk_foreign_item(self, fi);
     }
 
     fn visit_struct_field(&mut self, field: &'tcx hir::StructField<'tcx>) {
         if self.should_warn_about_field(&field) {
-            self.warn_dead_code(field.hir_id, field.span, field.ident.name, "field", "read");
+            self.warn_dead_code(field.hir_id, field.span, field.ident.name, "read");
         }
         intravisit::walk_struct_field(self, field);
     }
@@ -658,7 +647,6 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
                         impl_item.hir_id,
                         impl_item.span,
                         impl_item.ident.name,
-                        "associated const",
                         "used",
                     );
                 }
@@ -667,13 +655,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
             hir::ImplItemKind::Fn(_, body_id) => {
                 if !self.symbol_is_live(impl_item.hir_id) {
                     let span = self.tcx.sess.source_map().guess_head_span(impl_item.span);
-                    self.warn_dead_code(
-                        impl_item.hir_id,
-                        span,
-                        impl_item.ident.name,
-                        "method",
-                        "used",
-                    );
+                    self.warn_dead_code(impl_item.hir_id, span, impl_item.ident.name, "used");
                 }
                 self.visit_nested_body(body_id)
             }
diff --git a/src/librustc_passes/stability.rs b/src/librustc_passes/stability.rs
index 2e48fd9d659bd..ad9934d379ac5 100644
--- a/src/librustc_passes/stability.rs
+++ b/src/librustc_passes/stability.rs
@@ -337,12 +337,14 @@ struct MissingStabilityAnnotations<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> MissingStabilityAnnotations<'a, 'tcx> {
-    fn check_missing_stability(&self, hir_id: HirId, span: Span, name: &str) {
+    fn check_missing_stability(&self, hir_id: HirId, span: Span) {
         let stab = self.tcx.stability().local_stability(hir_id);
         let is_error =
             !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(hir_id);
         if is_error {
-            self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", name));
+            let def_id = self.tcx.hir().local_def_id(hir_id);
+            let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
+            self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
         }
     }
 }
@@ -362,42 +364,42 @@ impl<'a, 'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'a, 'tcx> {
             // optional. They inherit stability from their parents when unannotated.
             hir::ItemKind::Impl { of_trait: None, .. } | hir::ItemKind::ForeignMod(..) => {}
 
-            _ => self.check_missing_stability(i.hir_id, i.span, i.kind.descr()),
+            _ => self.check_missing_stability(i.hir_id, i.span),
         }
 
         intravisit::walk_item(self, i)
     }
 
     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
-        self.check_missing_stability(ti.hir_id, ti.span, "item");
+        self.check_missing_stability(ti.hir_id, ti.span);
         intravisit::walk_trait_item(self, ti);
     }
 
     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
         let impl_def_id = self.tcx.hir().local_def_id(self.tcx.hir().get_parent_item(ii.hir_id));
         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
-            self.check_missing_stability(ii.hir_id, ii.span, "item");
+            self.check_missing_stability(ii.hir_id, ii.span);
         }
         intravisit::walk_impl_item(self, ii);
     }
 
     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
-        self.check_missing_stability(var.id, var.span, "variant");
+        self.check_missing_stability(var.id, var.span);
         intravisit::walk_variant(self, var, g, item_id);
     }
 
     fn visit_struct_field(&mut self, s: &'tcx StructField<'tcx>) {
-        self.check_missing_stability(s.hir_id, s.span, "field");
+        self.check_missing_stability(s.hir_id, s.span);
         intravisit::walk_struct_field(self, s);
     }
 
     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
-        self.check_missing_stability(i.hir_id, i.span, i.kind.descriptive_variant());
+        self.check_missing_stability(i.hir_id, i.span);
         intravisit::walk_foreign_item(self, i);
     }
 
     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef<'tcx>) {
-        self.check_missing_stability(md.hir_id, md.span, "macro");
+        self.check_missing_stability(md.hir_id, md.span);
     }
 }
 
@@ -585,7 +587,7 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
     if tcx.stability().staged_api[&LOCAL_CRATE] {
         let krate = tcx.hir().krate();
         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
-        missing.check_missing_stability(hir::CRATE_HIR_ID, krate.item.span, "crate");
+        missing.check_missing_stability(hir::CRATE_HIR_ID, krate.item.span);
         intravisit::walk_crate(&mut missing, krate);
         krate.visit_all_item_likes(&mut missing.as_deep_visitor());
     }
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index b1fbba7e1a7b3..e4501b5c3b562 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -1,6 +1,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
+#![feature(or_patterns)]
 #![recursion_limit = "256"]
 
 use rustc_ast::ast::Ident;
@@ -537,11 +538,10 @@ impl EmbargoVisitor<'tcx> {
         for item_id in module.item_ids {
             let hir_id = item_id.id;
             let item_def_id = self.tcx.hir().local_def_id(hir_id);
-            if let Some(def_kind) = self.tcx.def_kind(item_def_id) {
-                let item = self.tcx.hir().expect_item(hir_id);
-                let vis = ty::Visibility::from_hir(&item.vis, hir_id, self.tcx);
-                self.update_macro_reachable_def(hir_id, def_kind, vis, defining_mod);
-            }
+            let def_kind = self.tcx.def_kind(item_def_id);
+            let item = self.tcx.hir().expect_item(hir_id);
+            let vis = ty::Visibility::from_hir(&item.vis, hir_id, self.tcx);
+            self.update_macro_reachable_def(hir_id, def_kind, vis, defining_mod);
         }
         if let Some(exports) = self.tcx.module_exports(module_def_id) {
             for export in exports {
@@ -613,7 +613,7 @@ impl EmbargoVisitor<'tcx> {
             }
 
             // These have type privacy, so are not reachable unless they're
-            // public
+            // public, or are not namespaced at all.
             DefKind::AssocConst
             | DefKind::AssocTy
             | DefKind::AssocOpaqueTy
@@ -626,7 +626,17 @@ impl EmbargoVisitor<'tcx> {
             | DefKind::AssocFn
             | DefKind::Trait
             | DefKind::TyParam
-            | DefKind::Variant => (),
+            | DefKind::Variant
+            | DefKind::LifetimeParam
+            | DefKind::ExternCrate
+            | DefKind::Use
+            | DefKind::ForeignMod
+            | DefKind::AnonConst
+            | DefKind::Field
+            | DefKind::GlobalAsm
+            | DefKind::Impl
+            | DefKind::Closure
+            | DefKind::Generator => (),
         }
     }
 
diff --git a/src/librustc_resolve/build_reduced_graph.rs b/src/librustc_resolve/build_reduced_graph.rs
index f9156be3f4ada..bd484fc7a90cf 100644
--- a/src/librustc_resolve/build_reduced_graph.rs
+++ b/src/librustc_resolve/build_reduced_graph.rs
@@ -906,7 +906,21 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             Res::Def(DefKind::Macro(..), _) | Res::NonMacroAttr(..) => {
                 self.r.define(parent, ident, MacroNS, (res, vis, span, expansion))
             }
-            Res::Def(DefKind::TyParam | DefKind::ConstParam, _)
+            Res::Def(
+                DefKind::TyParam
+                | DefKind::ConstParam
+                | DefKind::ExternCrate
+                | DefKind::Use
+                | DefKind::ForeignMod
+                | DefKind::AnonConst
+                | DefKind::Field
+                | DefKind::LifetimeParam
+                | DefKind::GlobalAsm
+                | DefKind::Closure
+                | DefKind::Impl
+                | DefKind::Generator,
+                _,
+            )
             | Res::Local(..)
             | Res::SelfTy(..)
             | Res::SelfCtor(..)
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 77aa7230aa893..26ea75ad7ef64 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -2504,10 +2504,8 @@ impl<'a> Resolver<'a> {
         }
 
         let container = match parent.kind {
-            ModuleKind::Def(DefKind::Mod, _, _) => "module",
-            ModuleKind::Def(DefKind::Trait, _, _) => "trait",
+            ModuleKind::Def(kind, _, _) => kind.descr(parent.def_id().unwrap()),
             ModuleKind::Block(..) => "block",
-            _ => "enum",
         };
 
         let old_noun = match old_binding.is_import() {
diff --git a/src/librustc_save_analysis/lib.rs b/src/librustc_save_analysis/lib.rs
index 1939b6261d57b..8456a0304fec6 100644
--- a/src/librustc_save_analysis/lib.rs
+++ b/src/librustc_save_analysis/lib.rs
@@ -760,9 +760,23 @@ impl<'l, 'tcx> SaveContext<'l, 'tcx> {
             Res::Def(HirDefKind::Mod, def_id) => {
                 Some(Ref { kind: RefKind::Mod, span, ref_id: id_from_def_id(def_id) })
             }
-            Res::PrimTy(..)
+
+            Res::Def(
+                HirDefKind::Macro(..)
+                | HirDefKind::ExternCrate
+                | HirDefKind::ForeignMod
+                | HirDefKind::LifetimeParam
+                | HirDefKind::AnonConst
+                | HirDefKind::Use
+                | HirDefKind::Field
+                | HirDefKind::GlobalAsm
+                | HirDefKind::Impl
+                | HirDefKind::Closure
+                | HirDefKind::Generator,
+                _,
+            )
+            | Res::PrimTy(..)
             | Res::SelfTy(..)
-            | Res::Def(HirDefKind::Macro(..), _)
             | Res::ToolMod
             | Res::NonMacroAttr(..)
             | Res::SelfCtor(..)
diff --git a/src/librustc_trait_selection/traits/error_reporting/suggestions.rs b/src/librustc_trait_selection/traits/error_reporting/suggestions.rs
index 88b9d257795f7..19260f4d573ac 100644
--- a/src/librustc_trait_selection/traits/error_reporting/suggestions.rs
+++ b/src/librustc_trait_selection/traits/error_reporting/suggestions.rs
@@ -1487,7 +1487,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 // ```
                 debug!("parent_def_kind: {:?}", self.tcx.def_kind(parent_did));
                 let is_raw_borrow_inside_fn_like_call = match self.tcx.def_kind(parent_did) {
-                    Some(DefKind::Fn | DefKind::Ctor(..)) => target_ty.is_unsafe_ptr(),
+                    DefKind::Fn | DefKind::Ctor(..) => target_ty.is_unsafe_ptr(),
                     _ => false,
                 };
 
diff --git a/src/librustc_traits/lowering/mod.rs b/src/librustc_traits/lowering/mod.rs
index 4f3eba9995638..19765c36ae26a 100644
--- a/src/librustc_traits/lowering/mod.rs
+++ b/src/librustc_traits/lowering/mod.rs
@@ -150,10 +150,10 @@ crate fn program_clauses_for(tcx: TyCtxt<'_>, def_id: DefId) -> Clauses<'_> {
     // FIXME(eddyb) this should only be using `def_kind`.
     match tcx.def_key(def_id).disambiguated_data.data {
         DefPathData::TypeNs(..) => match tcx.def_kind(def_id) {
-            Some(DefKind::Trait | DefKind::TraitAlias) => program_clauses_for_trait(tcx, def_id),
+            DefKind::Trait | DefKind::TraitAlias => program_clauses_for_trait(tcx, def_id),
             // FIXME(eddyb) deduplicate this `associated_item` call with
             // `program_clauses_for_associated_type_{value,def}`.
-            Some(DefKind::AssocTy) => match tcx.associated_item(def_id).container {
+            DefKind::AssocTy => match tcx.associated_item(def_id).container {
                 ty::AssocItemContainer::ImplContainer(_) => {
                     program_clauses_for_associated_type_value(tcx, def_id)
                 }
@@ -161,13 +161,11 @@ crate fn program_clauses_for(tcx: TyCtxt<'_>, def_id: DefId) -> Clauses<'_> {
                     program_clauses_for_associated_type_def(tcx, def_id)
                 }
             },
-            Some(
-                DefKind::Struct
-                | DefKind::Enum
-                | DefKind::TyAlias
-                | DefKind::Union
-                | DefKind::OpaqueTy,
-            ) => program_clauses_for_type_def(tcx, def_id),
+            DefKind::Struct
+            | DefKind::Enum
+            | DefKind::TyAlias
+            | DefKind::Union
+            | DefKind::OpaqueTy => program_clauses_for_type_def(tcx, def_id),
             _ => List::empty(),
         },
         DefPathData::Impl => program_clauses_for_impl(tcx, def_id),
diff --git a/src/librustc_typeck/check/dropck.rs b/src/librustc_typeck/check/dropck.rs
index 078401ee6a815..478a848cf09dd 100644
--- a/src/librustc_typeck/check/dropck.rs
+++ b/src/librustc_typeck/check/dropck.rs
@@ -94,10 +94,7 @@ fn ensure_drop_params_and_item_params_correspond<'tcx>(
             }
             Err(_) => {
                 let item_span = tcx.def_span(self_type_did);
-                let self_descr = tcx
-                    .def_kind(self_type_did)
-                    .map(|kind| kind.descr(self_type_did))
-                    .unwrap_or("type");
+                let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
                 struct_span_err!(
                     tcx.sess,
                     drop_impl_span,
@@ -244,10 +241,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
 
         if !assumptions_in_impl_context.iter().any(predicate_matches_closure) {
             let item_span = tcx.hir().span(self_type_hir_id);
-            let self_descr = tcx
-                .def_kind(self_type_did)
-                .map(|kind| kind.descr(self_type_did.to_def_id()))
-                .unwrap_or("type");
+            let self_descr = tcx.def_kind(self_type_did).descr(self_type_did.to_def_id());
             struct_span_err!(
                 tcx.sess,
                 *predicate_sp,
diff --git a/src/librustc_typeck/check/expr.rs b/src/librustc_typeck/check/expr.rs
index 2bca5e7582526..d287589789e2d 100644
--- a/src/librustc_typeck/check/expr.rs
+++ b/src/librustc_typeck/check/expr.rs
@@ -1564,10 +1564,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         base_did: DefId,
     ) {
         let struct_path = self.tcx().def_path_str(base_did);
-        let kind_name = match self.tcx().def_kind(base_did) {
-            Some(def_kind) => def_kind.descr(base_did),
-            _ => " ",
-        };
+        let kind_name = self.tcx().def_kind(base_did).descr(base_did);
         let mut err = struct_span_err!(
             self.tcx().sess,
             field.span,
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index b7e86c0791f63..d631d3c33405e 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -831,6 +831,13 @@ fn primary_body_of(
 }
 
 fn has_typeck_tables(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+    // FIXME(#71104) some `LocalDefId` do not seem to have a corresponding `HirId`.
+    if let Some(def_id) = def_id.as_local() {
+        if tcx.hir().opt_local_def_id_to_hir_id(def_id).is_none() {
+            return false;
+        }
+    }
+
     // Closures' tables come from their outermost function,
     // as they are part of the same "inference environment".
     let outer_def_id = tcx.closure_base_def_id(def_id);
@@ -838,11 +845,8 @@ fn has_typeck_tables(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
         return tcx.has_typeck_tables(outer_def_id);
     }
 
-    // FIXME(#71104) Should really be using just `as_local_hir_id` but
-    // some `LocalDefId` do not seem to have a corresponding HirId.
-    if let Some(id) =
-        def_id.as_local().and_then(|def_id| tcx.hir().opt_local_def_id_to_hir_id(def_id))
-    {
+    if let Some(def_id) = def_id.as_local() {
+        let id = tcx.hir().local_def_id_to_hir_id(def_id);
         primary_body_of(tcx, id).is_some()
     } else {
         false
@@ -4971,15 +4975,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
                 Some(Node::Ctor(hir::VariantData::Tuple(fields, _))) => {
                     sugg_call = fields.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
-                    match def_id
-                        .as_local()
-                        .map(|def_id| hir.as_local_hir_id(def_id))
-                        .and_then(|hir_id| hir.def_kind(hir_id))
-                    {
-                        Some(hir::def::DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
+                    match def_id.as_local().map(|def_id| hir.def_kind(def_id)) {
+                        Some(DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
                             msg = "instantiate this tuple variant";
                         }
-                        Some(hir::def::DefKind::Ctor(hir::def::CtorOf::Struct, _)) => {
+                        Some(DefKind::Ctor(CtorOf::Struct, _)) => {
                             msg = "instantiate this tuple struct";
                         }
                         _ => {}
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 6208c14710183..cd098936ed6a5 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -278,7 +278,7 @@ fn build_type_alias_type(cx: &DocContext<'_>, did: DefId) -> Option<clean::Type>
 }
 
 pub fn build_ty(cx: &DocContext, did: DefId) -> Option<clean::Type> {
-    match cx.tcx.def_kind(did)? {
+    match cx.tcx.def_kind(did) {
         DefKind::Struct | DefKind::Union | DefKind::Enum | DefKind::Const | DefKind::Static => {
             Some(cx.tcx.type_of(did).clean(cx))
         }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 63ab0ef5f1728..55c32e917f25c 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -2135,7 +2135,7 @@ impl Clean<Vec<Item>> for doctree::Impl<'_> {
 
         let for_ = self.for_.clean(cx);
         let type_alias = for_.def_id().and_then(|did| match cx.tcx.def_kind(did) {
-            Some(DefKind::TyAlias) => Some(cx.tcx.type_of(did).clean(cx)),
+            DefKind::TyAlias => Some(cx.tcx.type_of(did).clean(cx)),
             _ => None,
         });
         let make_item = |trait_: Option<Type>, for_: Type, items: Vec<Item>| Item {
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index ec5ac48ffe4a8..c4e4802db6c07 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -209,7 +209,7 @@ pub fn get_real_types(
                                 res.extend(adds);
                             } else if !ty.is_full_generic() {
                                 if let Some(kind) =
-                                    ty.def_id().and_then(|did| cx.tcx.def_kind(did).clean(cx))
+                                    ty.def_id().map(|did| cx.tcx.def_kind(did).clean(cx))
                                 {
                                     res.insert((ty, kind));
                                 }
@@ -226,9 +226,7 @@ pub fn get_real_types(
                     if !adds.is_empty() {
                         res.extend(adds);
                     } else if !ty.is_full_generic() {
-                        if let Some(kind) =
-                            ty.def_id().and_then(|did| cx.tcx.def_kind(did).clean(cx))
-                        {
+                        if let Some(kind) = ty.def_id().map(|did| cx.tcx.def_kind(did).clean(cx)) {
                             res.insert((ty.clone(), kind));
                         }
                     }
@@ -236,7 +234,7 @@ pub fn get_real_types(
             }
         }
     } else {
-        if let Some(kind) = arg.def_id().and_then(|did| cx.tcx.def_kind(did).clean(cx)) {
+        if let Some(kind) = arg.def_id().map(|did| cx.tcx.def_kind(did).clean(cx)) {
             res.insert((arg.clone(), kind));
         }
         if let Some(gens) = arg.generics() {
@@ -246,9 +244,7 @@ pub fn get_real_types(
                     if !adds.is_empty() {
                         res.extend(adds);
                     }
-                } else if let Some(kind) =
-                    gen.def_id().and_then(|did| cx.tcx.def_kind(did).clean(cx))
-                {
+                } else if let Some(kind) = gen.def_id().map(|did| cx.tcx.def_kind(did).clean(cx)) {
                     res.insert((gen.clone(), kind));
                 }
             }
@@ -275,7 +271,7 @@ pub fn get_all_types(
         if !args.is_empty() {
             all_types.extend(args);
         } else {
-            if let Some(kind) = arg.type_.def_id().and_then(|did| cx.tcx.def_kind(did).clean(cx)) {
+            if let Some(kind) = arg.type_.def_id().map(|did| cx.tcx.def_kind(did).clean(cx)) {
                 all_types.insert((arg.type_.clone(), kind));
             }
         }
@@ -285,9 +281,7 @@ pub fn get_all_types(
         FnRetTy::Return(ref return_type) => {
             let mut ret = get_real_types(generics, &return_type, cx, 0);
             if ret.is_empty() {
-                if let Some(kind) =
-                    return_type.def_id().and_then(|did| cx.tcx.def_kind(did).clean(cx))
-                {
+                if let Some(kind) = return_type.def_id().map(|did| cx.tcx.def_kind(did).clean(cx)) {
                     ret.insert((return_type.clone(), kind));
                 }
             }
diff --git a/src/test/ui/associated-const/associated-const-dead-code.rs b/src/test/ui/associated-const/associated-const-dead-code.rs
index c47e474d2dd74..e659bdb83f9c1 100644
--- a/src/test/ui/associated-const/associated-const-dead-code.rs
+++ b/src/test/ui/associated-const/associated-const-dead-code.rs
@@ -4,7 +4,7 @@ struct MyFoo;
 
 impl MyFoo {
     const BAR: u32 = 1;
-    //~^ ERROR associated const is never used: `BAR`
+    //~^ ERROR associated constant is never used: `BAR`
 }
 
 fn main() {
diff --git a/src/test/ui/associated-const/associated-const-dead-code.stderr b/src/test/ui/associated-const/associated-const-dead-code.stderr
index 172aed733fca9..9b6bbb68a71f7 100644
--- a/src/test/ui/associated-const/associated-const-dead-code.stderr
+++ b/src/test/ui/associated-const/associated-const-dead-code.stderr
@@ -1,4 +1,4 @@
-error: associated const is never used: `BAR`
+error: associated constant is never used: `BAR`
   --> $DIR/associated-const-dead-code.rs:6:5
    |
 LL |     const BAR: u32 = 1;
diff --git a/src/test/ui/consts/recursive-zst-static.rs b/src/test/ui/consts/recursive-zst-static.rs
index df7562bd9f5d2..768df58e1e32e 100644
--- a/src/test/ui/consts/recursive-zst-static.rs
+++ b/src/test/ui/consts/recursive-zst-static.rs
@@ -1,6 +1,10 @@
-// build-pass
+// This test ensures that we do not allow ZST statics to initialize themselves without ever
+// actually creating a value of that type. This is important, as the ZST may have private fields
+// that users can reasonably expect to only get initialized by their own code. Thus unsafe code
+// can depend on this fact and will thus do unsound things when it is violated.
+// See https://github.com/rust-lang/rust/issues/71078 for more details.
 
-static FOO: () = FOO;
+static FOO: () = FOO; //~ cycle detected when const-evaluating `FOO`
 
 fn main() {
     FOO
diff --git a/src/test/ui/consts/recursive-zst-static.stderr b/src/test/ui/consts/recursive-zst-static.stderr
new file mode 100644
index 0000000000000..e21dcf691ab0a
--- /dev/null
+++ b/src/test/ui/consts/recursive-zst-static.stderr
@@ -0,0 +1,21 @@
+error[E0391]: cycle detected when const-evaluating `FOO`
+  --> $DIR/recursive-zst-static.rs:7:18
+   |
+LL | static FOO: () = FOO;
+   |                  ^^^
+   |
+note: ...which requires const-evaluating `FOO`...
+  --> $DIR/recursive-zst-static.rs:7:1
+   |
+LL | static FOO: () = FOO;
+   | ^^^^^^^^^^^^^^^^^^^^^
+   = note: ...which again requires const-evaluating `FOO`, completing the cycle
+note: cycle used when const-evaluating + checking `FOO`
+  --> $DIR/recursive-zst-static.rs:7:1
+   |
+LL | static FOO: () = FOO;
+   | ^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0391`.
diff --git a/src/test/ui/issues/issue-17718-const-naming.rs b/src/test/ui/issues/issue-17718-const-naming.rs
index d30b95843f300..7386478f9f08c 100644
--- a/src/test/ui/issues/issue-17718-const-naming.rs
+++ b/src/test/ui/issues/issue-17718-const-naming.rs
@@ -3,6 +3,6 @@
 
 const foo: isize = 3;
 //~^ ERROR: should have an upper case name
-//~^^ ERROR: constant item is never used
+//~^^ ERROR: constant is never used
 
 fn main() {}
diff --git a/src/test/ui/issues/issue-17718-const-naming.stderr b/src/test/ui/issues/issue-17718-const-naming.stderr
index 4c0aa0553ebd2..ce4ebcb5e3ef6 100644
--- a/src/test/ui/issues/issue-17718-const-naming.stderr
+++ b/src/test/ui/issues/issue-17718-const-naming.stderr
@@ -1,4 +1,4 @@
-error: constant item is never used: `foo`
+error: constant is never used: `foo`
   --> $DIR/issue-17718-const-naming.rs:4:1
    |
 LL | const foo: isize = 3;
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-1.rs b/src/test/ui/lint/dead-code/lint-dead-code-1.rs
index 09977f8df51cf..896147fcc7738 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-1.rs
+++ b/src/test/ui/lint/dead-code/lint-dead-code-1.rs
@@ -17,14 +17,14 @@ mod foo2 {
 }
 
 pub static pub_static: isize = 0;
-static priv_static: isize = 0; //~ ERROR: static item is never used
+static priv_static: isize = 0; //~ ERROR: static is never used
 const used_static: isize = 0;
 pub static used_static2: isize = used_static;
 const USED_STATIC: isize = 0;
 const STATIC_USED_IN_ENUM_DISCRIMINANT: isize = 10;
 
 pub const pub_const: isize = 0;
-const priv_const: isize = 0; //~ ERROR: constant item is never used
+const priv_const: isize = 0; //~ ERROR: constant is never used
 const used_const: isize = 0;
 pub const used_const2: isize = used_const;
 const USED_CONST: isize = 1;
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-1.stderr b/src/test/ui/lint/dead-code/lint-dead-code-1.stderr
index 0a08aa6da9ac0..af97ea98b2b6d 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-1.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-1.stderr
@@ -10,13 +10,13 @@ note: the lint level is defined here
 LL | #![deny(dead_code)]
    |         ^^^^^^^^^
 
-error: static item is never used: `priv_static`
+error: static is never used: `priv_static`
   --> $DIR/lint-dead-code-1.rs:20:1
    |
 LL | static priv_static: isize = 0;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: constant item is never used: `priv_const`
+error: constant is never used: `priv_const`
   --> $DIR/lint-dead-code-1.rs:27:1
    |
 LL | const priv_const: isize = 0;
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-3.rs b/src/test/ui/lint/dead-code/lint-dead-code-3.rs
index 4397522f3f32f..6826d2cd67eb9 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-3.rs
+++ b/src/test/ui/lint/dead-code/lint-dead-code-3.rs
@@ -12,7 +12,7 @@ extern {
 
 struct Foo; //~ ERROR: struct is never constructed
 impl Foo {
-    fn foo(&self) { //~ ERROR: method is never used
+    fn foo(&self) { //~ ERROR: associated function is never used
         bar()
     }
 }
@@ -58,7 +58,7 @@ mod blah {
 
 enum c_void {} //~ ERROR: enum is never used
 extern {
-    fn free(p: *const c_void); //~ ERROR: foreign function is never used
+    fn free(p: *const c_void); //~ ERROR: function is never used
 }
 
 // Check provided method
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-3.stderr b/src/test/ui/lint/dead-code/lint-dead-code-3.stderr
index aab25c481e6c7..a2614a0bf74b3 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-3.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-3.stderr
@@ -10,7 +10,7 @@ note: the lint level is defined here
 LL | #![deny(dead_code)]
    |         ^^^^^^^^^
 
-error: method is never used: `foo`
+error: associated function is never used: `foo`
   --> $DIR/lint-dead-code-3.rs:15:5
    |
 LL |     fn foo(&self) {
@@ -28,7 +28,7 @@ error: enum is never used: `c_void`
 LL | enum c_void {}
    |      ^^^^^^
 
-error: foreign function is never used: `free`
+error: function is never used: `free`
   --> $DIR/lint-dead-code-3.rs:61:5
    |
 LL |     fn free(p: *const c_void);
diff --git a/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.rs b/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.rs
index 8f750ae62f5e4..38faa24691604 100644
--- a/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.rs
+++ b/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.rs
@@ -1,4 +1,4 @@
 #![feature(staged_api)]
-//~^ ERROR crate has missing stability attribute
+//~^ ERROR module has missing stability attribute
 
 fn main() {}
diff --git a/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.stderr b/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.stderr
index b6c9564e904c4..c7ade234d3dcc 100644
--- a/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.stderr
+++ b/src/test/ui/stability-attribute/missing-stability-attr-at-top-level.stderr
@@ -1,4 +1,4 @@
-error: crate has missing stability attribute
+error: module has missing stability attribute
   --> $DIR/missing-stability-attr-at-top-level.rs:1:1
    |
 LL | / #![feature(staged_api)]
diff --git a/src/test/ui/unsized/return-unsized-from-trait-method.rs b/src/test/ui/unsized/return-unsized-from-trait-method.rs
new file mode 100644
index 0000000000000..2d265d5db5c14
--- /dev/null
+++ b/src/test/ui/unsized/return-unsized-from-trait-method.rs
@@ -0,0 +1,16 @@
+// ignore-tidy-linelength
+
+// regression test for #26376
+
+trait Foo {
+    fn foo(&self) -> [u8];
+}
+
+fn foo(f: Option<&dyn Foo>) {
+    if let Some(f) = f {
+        let _ = f.foo();
+        //~^ ERROR cannot move a value of type [u8]: the size of [u8] cannot be statically determined
+    }
+}
+
+fn main() { foo(None) }
diff --git a/src/test/ui/unsized/return-unsized-from-trait-method.stderr b/src/test/ui/unsized/return-unsized-from-trait-method.stderr
new file mode 100644
index 0000000000000..7ecdd28616674
--- /dev/null
+++ b/src/test/ui/unsized/return-unsized-from-trait-method.stderr
@@ -0,0 +1,9 @@
+error[E0161]: cannot move a value of type [u8]: the size of [u8] cannot be statically determined
+  --> $DIR/return-unsized-from-trait-method.rs:11:17
+   |
+LL |         let _ = f.foo();
+   |                 ^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0161`.