Auto merge of #72202 - Dylan-DPC:rollup-6lbxh1s, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - #71910 (Fix unused_parens false positive when using binary operations)
 - #72087 (Fix hang in lexical_region_resolve)
 - #72126 (Change `WorkProduct::saved_files` to an `Option`.)
 - #72127 (add long error explanation for E0228)
 - #72141 (Warn against thread::sleep in async fn)
 - #72170 (use `require_lang_item` over `unwrap`.)
 - #72191 (Clean up E0589 explanation)
 - #72194 (Don't ICE on missing `Unsize` impl)

Failed merges:

r? @ghost

src/librustc_codegen_ssa/back/write.rs

@@ -21,7 +21,7 @@ use rustc_errors::{DiagnosticId, FatalError, Handler, Level};
 use rustc_fs_util::link_or_copy;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_incremental::{
-    copy_cgu_workproducts_to_incr_comp_cache_dir, in_incr_comp_dir, in_incr_comp_dir_sess,
+    copy_cgu_workproduct_to_incr_comp_cache_dir, in_incr_comp_dir, in_incr_comp_dir_sess,
 };
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::middle::cstore::EncodedMetadata;
@@ -465,17 +465,13 @@ fn copy_all_cgu_workproducts_to_incr_comp_cache_dir(
         return work_products;
     }
 
-    let _timer = sess.timer("incr_comp_copy_cgu_workproducts");
+    let _timer = sess.timer("copy_all_cgu_workproducts_to_incr_comp_cache_dir");
 
     for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) {
-        let mut files = vec![];
+        let path = module.object.as_ref().map(|path| path.clone());
-
-        if let Some(ref path) = module.object {
-            files.push(path.clone());
-        }
 
         if let Some((id, product)) =
-            copy_cgu_workproducts_to_incr_comp_cache_dir(sess, &module.name, &files)
+            copy_cgu_workproduct_to_incr_comp_cache_dir(sess, &module.name, &path)
         {
             work_products.insert(id, product);
         }
@@ -817,7 +813,7 @@ fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
 ) -> Result<WorkItemResult<B>, FatalError> {
     let incr_comp_session_dir = cgcx.incr_comp_session_dir.as_ref().unwrap();
     let mut object = None;
-    for saved_file in &module.source.saved_files {
+    if let Some(saved_file) = module.source.saved_file {
         let obj_out = cgcx.output_filenames.temp_path(OutputType::Object, Some(&module.name));
         object = Some(obj_out.clone());
         let source_file = in_incr_comp_dir(&incr_comp_session_dir, &saved_file);

src/librustc_error_codes/error_codes.rs

@@ -120,6 +120,7 @@ E0223: include_str!("./error_codes/E0223.md"),
 E0224: include_str!("./error_codes/E0224.md"),
 E0225: include_str!("./error_codes/E0225.md"),
 E0226: include_str!("./error_codes/E0226.md"),
+E0228: include_str!("./error_codes/E0228.md"),
 E0229: include_str!("./error_codes/E0229.md"),
 E0230: include_str!("./error_codes/E0230.md"),
 E0231: include_str!("./error_codes/E0231.md"),
@@ -482,7 +483,6 @@ E0753: include_str!("./error_codes/E0753.md"),
 //  E0218, // no associated type defined
 //  E0219, // associated type defined in higher-ranked supertrait
     E0227, // ambiguous lifetime bound, explicit lifetime bound required
-    E0228, // explicit lifetime bound required
 //  E0233,
 //  E0234,
 //  E0235, // structure constructor specifies a structure of type but

src/librustc_error_codes/error_codes/E0228.md

@@ -0,0 +1,40 @@
+The lifetime bound for this object type cannot be deduced from context and must
+be specified.
+
+Erroneous code example:
+
+```compile_fail,E0228
+trait Trait { }
+
+struct TwoBounds<'a, 'b, T: Sized + 'a + 'b> {
+    x: &'a i32,
+    y: &'b i32,
+    z: T,
+}
+
+type Foo<'a, 'b> = TwoBounds<'a, 'b, dyn Trait>;
+```
+
+When a trait object is used as a type argument of a generic type, Rust will try
+to infer its lifetime if unspecified. However, this isn't possible when the
+containing type has more than one lifetime bound.
+
+The above example can be resolved by either reducing the number of lifetime
+bounds to one or by making the trait object lifetime explicit, like so:
+
+```
+trait Trait { }
+
+struct TwoBounds<'a, 'b, T: Sized + 'a + 'b> {
+    x: &'a i32,
+    y: &'b i32,
+    z: T,
+}
+
+type Foo<'a, 'b> = TwoBounds<'a, 'b, dyn Trait + 'b>;
+```
+
+For more information, see [RFC 599] and its amendment [RFC 1156].
+
+[RFC 599]: https://github.com/rust-lang/rfcs/blob/master/text/0599-default-object-bound.md
+[RFC 1156]: https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md

src/librustc_error_codes/error_codes/E0589.md

@@ -1,6 +1,8 @@
 The value of `N` that was specified for `repr(align(N))` was not a power
 of two, or was greater than 2^29.
 
+Erroneous code example:
+
 ```compile_fail,E0589
 #[repr(align(15))] // error: invalid `repr(align)` attribute: not a power of two
 enum Foo {

src/librustc_incremental/lib.rs

@@ -15,7 +15,7 @@ pub mod assert_module_sources;
 mod persist;
 
 pub use assert_dep_graph::assert_dep_graph;
-pub use persist::copy_cgu_workproducts_to_incr_comp_cache_dir;
+pub use persist::copy_cgu_workproduct_to_incr_comp_cache_dir;
 pub use persist::delete_workproduct_files;
 pub use persist::dep_graph_tcx_init;
 pub use persist::finalize_session_directory;

src/librustc_incremental/persist/load.rs

@@ -134,7 +134,7 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture {
 
             for swp in work_products {
                 let mut all_files_exist = true;
-                for file_name in swp.work_product.saved_files.iter() {
+                if let Some(ref file_name) = swp.work_product.saved_file {
                     let path = in_incr_comp_dir_sess(sess, file_name);
                     if !path.exists() {
                         all_files_exist = false;

src/librustc_incremental/persist/mod.rs

@@ -21,5 +21,5 @@ pub use load::LoadResult;
 pub use load::{load_dep_graph, DepGraphFuture};
 pub use save::save_dep_graph;
 pub use save::save_work_product_index;
-pub use work_product::copy_cgu_workproducts_to_incr_comp_cache_dir;
+pub use work_product::copy_cgu_workproduct_to_incr_comp_cache_dir;
 pub use work_product::delete_workproduct_files;

src/librustc_incremental/persist/save.rs

@@ -74,9 +74,9 @@ pub fn save_work_product_index(
         if !new_work_products.contains_key(id) {
             work_product::delete_workproduct_files(sess, wp);
             debug_assert!(
-                wp.saved_files
+                wp.saved_file.as_ref().map_or(true, |file_name| {
-                    .iter()
+                    !in_incr_comp_dir_sess(sess, &file_name).exists()
-                    .all(|file_name| { !in_incr_comp_dir_sess(sess, file_name).exists() })
+                })
             );
         }
     }
@@ -85,7 +85,7 @@ pub fn save_work_product_index(
     debug_assert!({
         new_work_products
             .iter()
-            .flat_map(|(_, wp)| wp.saved_files.iter())
+            .flat_map(|(_, wp)| wp.saved_file.iter())
             .map(|name| in_incr_comp_dir_sess(sess, name))
             .all(|path| path.exists())
     });

src/librustc_incremental/persist/work_product.rs

@@ -7,43 +7,41 @@ use rustc_session::Session;
 use std::fs as std_fs;
 use std::path::PathBuf;
 
-pub fn copy_cgu_workproducts_to_incr_comp_cache_dir(
+pub fn copy_cgu_workproduct_to_incr_comp_cache_dir(
     sess: &Session,
     cgu_name: &str,
-    files: &[PathBuf],
+    path: &Option<PathBuf>,
 ) -> Option<(WorkProductId, WorkProduct)> {
-    debug!("copy_cgu_workproducts_to_incr_comp_cache_dir({:?},{:?})", cgu_name, files);
+    debug!("copy_cgu_workproduct_to_incr_comp_cache_dir({:?},{:?})", cgu_name, path);
     sess.opts.incremental.as_ref()?;
 
-    let saved_files = files
+    let saved_file = if let Some(path) = path {
-        .iter()
+        let file_name = format!("{}.o", cgu_name);
-        .map(|path| {
+        let path_in_incr_dir = in_incr_comp_dir_sess(sess, &file_name);
-            let file_name = format!("{}.o", cgu_name);
+        match link_or_copy(path, &path_in_incr_dir) {
-            let path_in_incr_dir = in_incr_comp_dir_sess(sess, &file_name);
+            Ok(_) => Some(file_name),
-            match link_or_copy(path, &path_in_incr_dir) {
+            Err(err) => {
-                Ok(_) => Some(file_name),
+                sess.warn(&format!(
-                Err(err) => {
+                    "error copying object file `{}` to incremental directory as `{}`: {}",
-                    sess.warn(&format!(
+                    path.display(),
-                        "error copying object file `{}` \
+                    path_in_incr_dir.display(),
-                                             to incremental directory as `{}`: {}",
+                    err
-                        path.display(),
+                ));
-                        path_in_incr_dir.display(),
+                return None;
-                        err
-                    ));
-                    None
-                }
             }
-        })
+        }
-        .collect::<Option<Vec<_>>>()?;
+    } else {
+        None
+    };
 
-    let work_product = WorkProduct { cgu_name: cgu_name.to_string(), saved_files };
+    let work_product = WorkProduct { cgu_name: cgu_name.to_string(), saved_file };
 
     let work_product_id = WorkProductId::from_cgu_name(cgu_name);
     Some((work_product_id, work_product))
 }
 
 pub fn delete_workproduct_files(sess: &Session, work_product: &WorkProduct) {
-    for file_name in &work_product.saved_files {
+    if let Some(ref file_name) = work_product.saved_file {
         let path = in_incr_comp_dir_sess(sess, file_name);
         match std_fs::remove_file(&path) {
             Ok(()) => {}

src/librustc_infer/infer/lexical_region_resolve/mod.rs

@@ -325,8 +325,21 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
             }
         }
 
-        debug!("enforce_member_constraint: final least choice = {:?}", least_choice);
+        // (#72087) Different `ty::Regions` can be known to be equal, for
-        if least_choice != member_lower_bound {
+        // example, we know that `'a` and `'static` are equal in a function
+        // with a parameter of type `&'static &'a ()`.
+        //
+        // When we have two equal regions like this `expansion` will use
+        // `lub_concrete_regions` to pick a canonical representative. The same
+        // choice is needed here so that we don't end up in a cycle of
+        // `expansion` changing the region one way and the code here changing
+        // it back.
+        let lub = self.lub_concrete_regions(least_choice, member_lower_bound);
+        debug!(
+            "enforce_member_constraint: final least choice = {:?}\nlub = {:?}",
+            least_choice, lub
+        );
+        if lub != member_lower_bound {
             *var_values.value_mut(member_vid) = VarValue::Value(least_choice);
             true
         } else {
@@ -578,8 +591,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 self.tcx().mk_region(ReScope(lub))
             }
 
-            (&ReEarlyBound(_), &ReEarlyBound(_) | &ReFree(_))
+            (&ReEarlyBound(_) | &ReFree(_), &ReEarlyBound(_) | &ReFree(_)) => {
-            | (&ReFree(_), &ReEarlyBound(_) | &ReFree(_)) => {
                 self.region_rels.lub_free_regions(a, b)
             }
 

src/librustc_lint/unused.rs

@@ -380,11 +380,27 @@ trait UnusedDelimLint {
     );
 
     fn is_expr_delims_necessary(inner: &ast::Expr, followed_by_block: bool) -> bool {
-        followed_by_block
+        // Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`
-            && match inner.kind {
+        let lhs_needs_parens = {
-                ExprKind::Ret(_) | ExprKind::Break(..) => true,
+            let mut innermost = inner;
-                _ => parser::contains_exterior_struct_lit(&inner),
+            loop {
+                if let ExprKind::Binary(_, lhs, _rhs) = &innermost.kind {
+                    innermost = lhs;
+                    if !rustc_ast::util::classify::expr_requires_semi_to_be_stmt(innermost) {
+                        break true;
+                    }
+                } else {
+                    break false;
+                }
             }
+        };
+
+        lhs_needs_parens
+            || (followed_by_block
+                && match inner.kind {
+                    ExprKind::Ret(_) | ExprKind::Break(..) => true,
+                    _ => parser::contains_exterior_struct_lit(&inner),
+                })
     }
 
     fn emit_unused_delims_expr(

src/librustc_middle/ty/adjustment.rs

@@ -2,6 +2,7 @@ use crate::ty::subst::SubstsRef;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::{DerefMutTraitLangItem, DerefTraitLangItem};
 use rustc_macros::HashStable;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
@@ -117,11 +118,11 @@ pub struct OverloadedDeref<'tcx> {
 impl<'tcx> OverloadedDeref<'tcx> {
     pub fn method_call(&self, tcx: TyCtxt<'tcx>, source: Ty<'tcx>) -> (DefId, SubstsRef<'tcx>) {
         let trait_def_id = match self.mutbl {
-            hir::Mutability::Not => tcx.lang_items().deref_trait(),
+            hir::Mutability::Not => tcx.require_lang_item(DerefTraitLangItem, None),
-            hir::Mutability::Mut => tcx.lang_items().deref_mut_trait(),
+            hir::Mutability::Mut => tcx.require_lang_item(DerefMutTraitLangItem, None),
         };
         let method_def_id = tcx
-            .associated_items(trait_def_id.unwrap())
+            .associated_items(trait_def_id)
             .in_definition_order()
             .find(|m| m.kind == ty::AssocKind::Fn)
             .unwrap()

src/librustc_middle/ty/instance.rs

@@ -4,7 +4,7 @@ use crate::ty::{self, SubstsRef, Ty, TyCtxt, TypeFoldable};
 use rustc_errors::ErrorReported;
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::{CrateNum, DefId};
-use rustc_hir::lang_items::DropInPlaceFnLangItem;
+use rustc_hir::lang_items::{DropInPlaceFnLangItem, FnOnceTraitLangItem};
 use rustc_macros::HashStable;
 
 use std::fmt;
@@ -375,7 +375,7 @@ impl<'tcx> Instance<'tcx> {
         substs: ty::SubstsRef<'tcx>,
     ) -> Instance<'tcx> {
         debug!("fn_once_adapter_shim({:?}, {:?})", closure_did, substs);
-        let fn_once = tcx.lang_items().fn_once_trait().unwrap();
+        let fn_once = tcx.require_lang_item(FnOnceTraitLangItem, None);
         let call_once = tcx
             .associated_items(fn_once)
             .in_definition_order()

src/librustc_middle/ty/layout.rs

@@ -8,6 +8,7 @@ use rustc_ast::ast::{self, IntTy, UintTy};
 use rustc_attr as attr;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hir as hir;
+use rustc_hir::lang_items::{GeneratorStateLangItem, PinTypeLangItem};
 use rustc_index::bit_set::BitSet;
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_session::{DataTypeKind, FieldInfo, SizeKind, VariantInfo};
@@ -2314,13 +2315,13 @@ impl<'tcx> ty::Instance<'tcx> {
                 let env_region = ty::ReLateBound(ty::INNERMOST, ty::BrEnv);
                 let env_ty = tcx.mk_mut_ref(tcx.mk_region(env_region), ty);
 
-                let pin_did = tcx.lang_items().pin_type().unwrap();
+                let pin_did = tcx.require_lang_item(PinTypeLangItem, None);
                 let pin_adt_ref = tcx.adt_def(pin_did);
                 let pin_substs = tcx.intern_substs(&[env_ty.into()]);
                 let env_ty = tcx.mk_adt(pin_adt_ref, pin_substs);
 
                 sig.map_bound(|sig| {
-                    let state_did = tcx.lang_items().gen_state().unwrap();
+                    let state_did = tcx.require_lang_item(GeneratorStateLangItem, None);
                     let state_adt_ref = tcx.adt_def(state_did);
                     let state_substs = tcx.intern_substs(&[
                         sig.yield_ty.into(),

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -10,6 +10,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_hir::lang_items::{CoerceUnsizedTraitLangItem, CopyTraitLangItem, SizedTraitLangItem};
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_infer::infer::outlives::env::RegionBoundPairs;
@@ -502,7 +503,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
         if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
             let tcx = self.tcx();
             let trait_ref = ty::TraitRef {
-                def_id: tcx.lang_items().copy_trait().unwrap(),
+                def_id: tcx.require_lang_item(CopyTraitLangItem, Some(self.last_span)),
                 substs: tcx.mk_substs_trait(place_ty.ty, &[]),
             };
 
@@ -1468,7 +1469,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 self.check_rvalue(body, rv, location);
                 if !self.tcx().features().unsized_locals {
                     let trait_ref = ty::TraitRef {
-                        def_id: tcx.lang_items().sized_trait().unwrap(),
+                        def_id: tcx.require_lang_item(SizedTraitLangItem, Some(self.last_span)),
                         substs: tcx.mk_substs_trait(place_ty, &[]),
                     };
                     self.prove_trait_ref(
@@ -2013,7 +2014,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                     ty::Predicate::Trait(
                                         ty::Binder::bind(ty::TraitPredicate {
                                             trait_ref: ty::TraitRef::new(
-                                                self.tcx().lang_items().copy_trait().unwrap(),
+                                                self.tcx().require_lang_item(
+                                                    CopyTraitLangItem,
+                                                    Some(self.last_span),
+                                                ),
                                                 tcx.mk_substs_trait(ty, &[]),
                                             ),
                                         }),
@@ -2037,7 +2041,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
 
                 let trait_ref = ty::TraitRef {
-                    def_id: tcx.lang_items().sized_trait().unwrap(),
+                    def_id: tcx.require_lang_item(SizedTraitLangItem, Some(self.last_span)),
                     substs: tcx.mk_substs_trait(ty, &[]),
                 };
 
@@ -2135,7 +2139,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     CastKind::Pointer(PointerCast::Unsize) => {
                         let &ty = ty;
                         let trait_ref = ty::TraitRef {
-                            def_id: tcx.lang_items().coerce_unsized_trait().unwrap(),
+                            def_id: tcx.require_lang_item(
+                                CoerceUnsizedTraitLangItem,
+                                Some(self.last_span),
+                            ),
                             substs: tcx.mk_substs_trait(op.ty(body, tcx), &[ty.into()]),
                         };
 

src/librustc_mir/monomorphize/collector.rs

@@ -580,10 +580,8 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
             }
             mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
                 let tcx = self.tcx;
-                let exchange_malloc_fn_def_id = tcx
+                let exchange_malloc_fn_def_id =
-                    .lang_items()
+                    tcx.require_lang_item(ExchangeMallocFnLangItem, None);
-                    .require(ExchangeMallocFnLangItem)
-                    .unwrap_or_else(|e| tcx.sess.fatal(&e));
                 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
                 if should_monomorphize_locally(tcx, &instance) {
                     self.output.push(create_fn_mono_item(instance));

src/librustc_mir/shim.rs

@@ -1,5 +1,6 @@
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::FnMutTraitLangItem;
 use rustc_middle::mir::*;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::subst::{InternalSubsts, Subst};
@@ -70,7 +71,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
             build_call_shim(tcx, instance, None, CallKind::Direct(def_id), None)
         }
         ty::InstanceDef::ClosureOnceShim { call_once: _ } => {
-            let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
+            let fn_mut = tcx.require_lang_item(FnMutTraitLangItem, None);
             let call_mut = tcx
                 .associated_items(fn_mut)
                 .in_definition_order()

src/librustc_mir/transform/generator.rs

@@ -61,6 +61,7 @@ use crate::util::storage;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::{GeneratorStateLangItem, PinTypeLangItem};
 use rustc_index::bit_set::{BitMatrix, BitSet};
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_middle::mir::visit::{MutVisitor, PlaceContext};
@@ -381,7 +382,7 @@ fn make_generator_state_argument_indirect<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Bo
 fn make_generator_state_argument_pinned<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let ref_gen_ty = body.local_decls.raw[1].ty;
 
-    let pin_did = tcx.lang_items().pin_type().unwrap();
+    let pin_did = tcx.require_lang_item(PinTypeLangItem, Some(body.span));
     let pin_adt_ref = tcx.adt_def(pin_did);
     let substs = tcx.intern_substs(&[ref_gen_ty.into()]);
     let pin_ref_gen_ty = tcx.mk_adt(pin_adt_ref, substs);
@@ -1207,7 +1208,7 @@ impl<'tcx> MirPass<'tcx> for StateTransform {
         };
 
         // Compute GeneratorState<yield_ty, return_ty>
-        let state_did = tcx.lang_items().gen_state().unwrap();
+        let state_did = tcx.require_lang_item(GeneratorStateLangItem, None);
         let state_adt_ref = tcx.adt_def(state_did);
         let state_substs = tcx.intern_substs(&[yield_ty.into(), body.return_ty().into()]);
         let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);

src/librustc_mir/util/elaborate_drops.rs

@@ -1,6 +1,6 @@
 use crate::util::patch::MirPatch;
 use rustc_hir as hir;
-use rustc_hir::lang_items;
+use rustc_hir::lang_items::{BoxFreeFnLangItem, DropTraitLangItem};
 use rustc_index::vec::Idx;
 use rustc_middle::mir::*;
 use rustc_middle::traits::Reveal;
@@ -535,7 +535,7 @@ where
     fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
         debug!("destructor_call_block({:?}, {:?})", self, succ);
         let tcx = self.tcx();
-        let drop_trait = tcx.lang_items().drop_trait().unwrap();
+        let drop_trait = tcx.require_lang_item(DropTraitLangItem, None);
         let drop_fn = tcx.associated_items(drop_trait).in_definition_order().next().unwrap();
         let ty = self.place_ty(self.place);
         let substs = tcx.mk_substs_trait(ty, &[]);
@@ -877,8 +877,7 @@ where
     ) -> BasicBlock {
         let tcx = self.tcx();
         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
-        let free_func =
+        let free_func = tcx.require_lang_item(BoxFreeFnLangItem, Some(self.source_info.span));
-            tcx.require_lang_item(lang_items::BoxFreeFnLangItem, Some(self.source_info.span));
         let args = adt.variants[VariantIdx::new(0)]
             .fields
             .iter()

src/librustc_mir_build/hair/pattern/const_to_pat.rs

@@ -1,4 +1,5 @@
 use rustc_hir as hir;
+use rustc_hir::lang_items::EqTraitLangItem;
 use rustc_index::vec::Idx;
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_middle::mir::Field;
@@ -140,7 +141,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                 // code at the moment, because types like `for <'a> fn(&'a ())` do
                 // not *yet* implement `PartialEq`. So for now we leave this here.
                 let ty_is_partial_eq: bool = {
-                    let partial_eq_trait_id = self.tcx().lang_items().eq_trait().unwrap();
+                    let partial_eq_trait_id = self.tcx().require_lang_item(EqTraitLangItem, None);
                     let obligation: PredicateObligation<'_> = predicate_for_trait_def(
                         self.tcx(),
                         self.param_env,

src/librustc_query_system/dep_graph/graph.rs

@@ -860,8 +860,8 @@ impl<K: DepKind> DepGraph<K> {
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub struct WorkProduct {
     pub cgu_name: String,
-    /// Saved files associated with this CGU.
+    /// Saved file associated with this CGU.
-    pub saved_files: Vec<String>,
+    pub saved_file: Option<String>,
 }
 
 #[derive(Clone)]

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -283,6 +283,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             .unwrap_or(false);
                         let is_from = format!("{}", trait_ref.print_only_trait_path())
                             .starts_with("std::convert::From<");
+                        let is_unsize =
+                            { Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait() };
                         let (message, note) = if is_try && is_from {
                             (
                                 Some(format!(
@@ -405,6 +407,17 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             return;
                         }
 
+                        if is_unsize {
+                            // If the obligation failed due to a missing implementation of the
+                            // `Unsize` trait, give a pointer to why that might be the case
+                            err.note(
+                                "all implementations of `Unsize` are provided \
+                                automatically by the compiler, see \
+                                <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
+                                for more information",
+                            );
+                        }
+
                         // Try to report a help message
                         if !trait_ref.has_infer_types_or_consts()
                             && self.predicate_can_apply(obligation.param_env, trait_ref)
@@ -427,12 +440,16 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                                 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
                                 self.report_similar_impl_candidates(impl_candidates, &mut err);
                             }
-                            self.suggest_change_mut(
+                            // Changing mutability doesn't make a difference to whether we have
-                                &obligation,
+                            // an `Unsize` impl (Fixes ICE in #71036)
-                                &mut err,
+                            if !is_unsize {
-                                &trait_ref,
+                                self.suggest_change_mut(
-                                points_at_arg,
+                                    &obligation,
-                            );
+                                    &mut err,
+                                    &trait_ref,
+                                    points_at_arg,
+                                );
+                            }
                         }
 
                         // If this error is due to `!: Trait` not implemented but `(): Trait` is

src/librustc_trait_selection/traits/project.rs

@@ -20,6 +20,7 @@ use crate::traits::error_reporting::InferCtxtExt;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::ErrorReported;
 use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::{FnOnceTraitLangItem, GeneratorTraitLangItem};
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::subst::{InternalSubsts, Subst};
 use rustc_middle::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, WithConstness};
@@ -1222,7 +1223,7 @@ fn confirm_generator_candidate<'cx, 'tcx>(
 
     let tcx = selcx.tcx();
 
-    let gen_def_id = tcx.lang_items().gen_trait().unwrap();
+    let gen_def_id = tcx.require_lang_item(GeneratorTraitLangItem, None);
 
     let predicate = super::util::generator_trait_ref_and_outputs(
         tcx,
@@ -1309,7 +1310,7 @@ fn confirm_callable_candidate<'cx, 'tcx>(
     debug!("confirm_callable_candidate({:?},{:?})", obligation, fn_sig);
 
     // the `Output` associated type is declared on `FnOnce`
-    let fn_once_def_id = tcx.lang_items().fn_once_trait().unwrap();
+    let fn_once_def_id = tcx.require_lang_item(FnOnceTraitLangItem, None);
 
     let predicate = super::util::closure_trait_ref_and_return_type(
         tcx,

src/librustc_typeck/check/demand.rs

@@ -7,6 +7,7 @@ use rustc_trait_selection::traits::{self, ObligationCause};
 use rustc_ast::util::parser::PREC_POSTFIX;
 use rustc_errors::{Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
+use rustc_hir::lang_items::DerefTraitLangItem;
 use rustc_hir::{is_range_literal, Node};
 use rustc_middle::ty::adjustment::AllowTwoPhase;
 use rustc_middle::ty::{self, AssocItem, Ty, TypeAndMut};
@@ -634,7 +635,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ if sp == expr.span && !is_macro => {
                 // Check for `Deref` implementations by constructing a predicate to
                 // prove: `<T as Deref>::Output == U`
-                let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
+                let deref_trait = self.tcx.require_lang_item(DerefTraitLangItem, Some(expr.span));
                 let item_def_id = self
                     .tcx
                     .associated_items(deref_trait)

src/libstd/thread/mod.rs

@@ -737,6 +737,8 @@ pub fn panicking() -> bool {
 /// The thread may sleep longer than the duration specified due to scheduling
 /// specifics or platform-dependent functionality. It will never sleep less.
 ///
+/// This function is blocking, and should not be used in `async` functions.
+///
 /// # Platform-specific behavior
 ///
 /// On Unix platforms, the underlying syscall may be interrupted by a
@@ -763,6 +765,8 @@ pub fn sleep_ms(ms: u32) {
 /// The thread may sleep longer than the duration specified due to scheduling
 /// specifics or platform-dependent functionality. It will never sleep less.
 ///
+/// This function is blocking, and should not be used in `async` functions.
+///
 /// # Platform-specific behavior
 ///
 /// On Unix platforms, the underlying syscall may be interrupted by a

src/test/ui/issues/issue-71036.rs

@@ -0,0 +1,17 @@
+#![feature(unsize, dispatch_from_dyn)]
+
+use std::marker::Unsize;
+use std::ops::DispatchFromDyn;
+
+#[allow(unused)]
+struct Foo<'a, T: ?Sized> {
+    _inner: &'a &'a T,
+}
+
+impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
+//~^ ERROR the trait bound `&'a T: std::marker::Unsize<&'a U>` is not satisfied
+//~| NOTE the trait `std::marker::Unsize<&'a U>` is not implemented for `&'a T`
+//~| NOTE all implementations of `Unsize` are provided automatically by the compiler
+//~| NOTE required because of the requirements on the impl
+
+fn main() {}

src/test/ui/issues/issue-71036.stderr

@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `&'a T: std::marker::Unsize<&'a U>` is not satisfied
+  --> $DIR/issue-71036.rs:11:1
+   |
+LL | impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Unsize<&'a U>` is not implemented for `&'a T`
+   |
+   = note: all implementations of `Unsize` are provided automatically by the compiler, see <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> for more information
+   = note: required because of the requirements on the impl of `std::ops::DispatchFromDyn<&'a &'a U>` for `&'a &'a T`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/lint/issue-71290-unused-paren-binop.rs

@@ -0,0 +1,23 @@
+// check-pass
+// Make sure unused parens lint doesn't emit a false positive.
+// See https://github.com/rust-lang/rust/issues/71290 for details.
+#![deny(unused_parens)]
+
+fn x() -> u8 {
+    ({ 0 }) + 1
+}
+
+fn y() -> u8 {
+    ({ 0 } + 1)
+}
+
+pub fn foo(a: bool, b: bool) -> u8 {
+    (if a { 1 } else { 0 } + if b { 1 } else { 0 })
+}
+
+pub fn bar() -> u8 {
+    // Make sure nested expressions are handled correctly as well
+    ({ 0 } + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9)
+}
+
+fn main() {}

src/test/ui/object-lifetime/object-lifetime-default-ambiguous.stderr

@@ -18,3 +18,4 @@ LL | fn f(t: &Ref2<dyn Test>) {
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0228`.

src/test/ui/object-lifetime/object-lifetime-default-dyn-binding-nonstatic1.stderr

@@ -6,3 +6,4 @@ LL | fn bar<'a>(x: &'a str) -> &'a dyn Foo<'a, Item = dyn Bar> { &() }
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0228`.

src/test/ui/object-lifetime/object-lifetime-default-dyn-binding-nonstatic2.stderr

@@ -6,3 +6,4 @@ LL | fn bar<'a>(x: &'a str) -> &'a dyn Foo<'a, Item = dyn Bar> { &() }
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0228`.

src/test/ui/object-lifetime/object-lifetime-default-dyn-binding-nonstatic3.stderr

@@ -6,3 +6,4 @@ LL | fn bar(x: &str) -> &dyn Foo<Item = dyn Bar> { &() }
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0228`.

src/test/ui/regions/issue-72051-member-region-hang.rs

@@ -0,0 +1,7 @@
+// Regression test for #72051, hang when resolving regions.
+
+// check-pass
+// edition:2018
+
+pub async fn query<'a>(_: &(), _: &(), _: (&(dyn std::any::Any + 'a),) ) {}
+fn main() {}

src/test/ui/suggestions/missing-lifetime-specifier.stderr

@@ -252,5 +252,5 @@ LL |     static f: RefCell<HashMap<i32, Vec<Vec<&Tar<'static, i32>>>>> = RefCell
 
 error: aborting due to 28 previous errors
 
-Some errors have detailed explanations: E0106, E0107.
+Some errors have detailed explanations: E0106, E0107, E0228.
 For more information about an error, try `rustc --explain E0106`.

src/test/ui/underscore-lifetime/dyn-trait-underscore-in-struct.stderr

@@ -18,4 +18,5 @@ LL |     x: Box<dyn Debug + '_>,
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0106`.
+Some errors have detailed explanations: E0106, E0228.
+For more information about an error, try `rustc --explain E0106`.