Auto merge of #111984 - matthiaskrgr:rollup-6u7ynyv, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #111384 (Fix linking Mac Catalyst by including LC_BUILD_VERSION in object files)
 - #111899 (CGU cleanups)
 - #111940 (Clarify safety concern of `io::Read::read` is only relevant in unsafe code)
 - #111947 (Add test for RPIT defined with different hidden types with different substs)
 - #111951 (Correct comment on privately uninhabited pattern.)

Failed merges:

 - #111954 (improve error message for calling a method on a raw pointer with an unknown pointee)

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

14 files changed, 424 insertions, 289 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index 8bf84772f08..ad27b854d59 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -188,6 +188,11 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
     };
 
     let mut file = write::Object::new(binary_format, architecture, endianness);
+    if sess.target.is_like_osx {
+        if let Some(build_version) = macho_object_build_version_for_target(&sess.target) {
+            file.set_macho_build_version(build_version)
+        }
+    }
     let e_flags = match architecture {
         Architecture::Mips => {
             let arch = match sess.target.options.cpu.as_ref() {
@@ -258,6 +263,33 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
     Some(file)
 }
 
+/// Apple's LD, when linking for Mac Catalyst, requires object files to
+/// contain information about what they were built for (LC_BUILD_VERSION):
+/// the platform (macOS/watchOS etc), minimum OS version, and SDK version.
+/// This returns a `MachOBuildVersion` if necessary for the target.
+fn macho_object_build_version_for_target(
+    target: &Target,
+) -> Option<object::write::MachOBuildVersion> {
+    if !target.llvm_target.ends_with("-macabi") {
+        return None;
+    }
+    /// The `object` crate demands "X.Y.Z encoded in nibbles as xxxx.yy.zz"
+    /// e.g. minOS 14.0 = 0x000E0000, or SDK 16.2 = 0x00100200
+    fn pack_version((major, minor): (u32, u32)) -> u32 {
+        (major << 16) | (minor << 8)
+    }
+
+    let platform = object::macho::PLATFORM_MACCATALYST;
+    let min_os = (14, 0);
+    let sdk = (16, 2);
+
+    let mut build_version = object::write::MachOBuildVersion::default();
+    build_version.platform = platform;
+    build_version.minos = pack_version(min_os);
+    build_version.sdk = pack_version(sdk);
+    Some(build_version)
+}
+
 pub enum MetadataPosition {
     First,
     Last,
diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs
index ff54ec56a29..f31b343c947 100644
--- a/compiler/rustc_middle/src/mir/mono.rs
+++ b/compiler/rustc_middle/src/mir/mono.rs
@@ -334,10 +334,7 @@ impl<'tcx> CodegenUnit<'tcx> {
     }
 
     pub fn modify_size_estimate(&mut self, delta: usize) {
-        assert!(self.size_estimate.is_some());
-        if let Some(size_estimate) = self.size_estimate {
-            self.size_estimate = Some(size_estimate + delta);
-        }
+        *self.size_estimate.as_mut().unwrap() += delta;
     }
 
     pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index c11a4f7229d..1e51cb9aa96 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -491,8 +491,8 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             AdtDefinedHere { adt_def_span, ty, variants }
         };
 
-        // Emit an extra note if the first uncovered witness is
-        // visibly uninhabited anywhere in the current crate.
+        // Emit an extra note if the first uncovered witness would be uninhabited
+        // if we disregard visibility.
         let witness_1_is_privately_uninhabited =
             if cx.tcx.features().exhaustive_patterns
                 && let Some(witness_1) = witnesses.get(0)
diff --git a/compiler/rustc_monomorphize/src/partitioning/default.rs b/compiler/rustc_monomorphize/src/partitioning/default.rs
index 37b7f6bf8a8..603b3ddc106 100644
--- a/compiler/rustc_monomorphize/src/partitioning/default.rs
+++ b/compiler/rustc_monomorphize/src/partitioning/default.rs
@@ -1,3 +1,4 @@
+use std::cmp;
 use std::collections::hash_map::Entry;
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -14,10 +15,7 @@ use rustc_span::symbol::Symbol;
 
 use super::PartitioningCx;
 use crate::collector::InliningMap;
-use crate::partitioning::merging;
-use crate::partitioning::{
-    MonoItemPlacement, Partition, PostInliningPartitioning, PreInliningPartitioning,
-};
+use crate::partitioning::{MonoItemPlacement, Partition, PlacedRootMonoItems};
 
 pub struct DefaultPartitioning;
 
@@ -26,7 +24,7 @@ impl<'tcx> Partition<'tcx> for DefaultPartitioning {
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
         mono_items: &mut I,
-    ) -> PreInliningPartitioning<'tcx>
+    ) -> PlacedRootMonoItems<'tcx>
     where
         I: Iterator<Item = MonoItem<'tcx>>,
     {
@@ -91,38 +89,120 @@ impl<'tcx> Partition<'tcx> for DefaultPartitioning {
             codegen_units.insert(codegen_unit_name, CodegenUnit::new(codegen_unit_name));
         }
 
-        PreInliningPartitioning {
-            codegen_units: codegen_units.into_values().collect(),
-            roots,
-            internalization_candidates,
-        }
+        let codegen_units = codegen_units.into_values().collect();
+        PlacedRootMonoItems { codegen_units, roots, internalization_candidates }
     }
 
     fn merge_codegen_units(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        initial_partitioning: &mut PreInliningPartitioning<'tcx>,
+        codegen_units: &mut Vec<CodegenUnit<'tcx>>,
     ) {
-        merging::merge_codegen_units(cx, initial_partitioning);
+        assert!(cx.target_cgu_count >= 1);
+
+        // Note that at this point in time the `codegen_units` here may not be
+        // in a deterministic order (but we know they're deterministically the
+        // same set). We want this merging to produce a deterministic ordering
+        // of codegen units from the input.
+        //
+        // Due to basically how we've implemented the merging below (merge the
+        // two smallest into each other) we're sure to start off with a
+        // deterministic order (sorted by name). This'll mean that if two cgus
+        // have the same size the stable sort below will keep everything nice
+        // and deterministic.
+        codegen_units.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str()));
+
+        // This map keeps track of what got merged into what.
+        let mut cgu_contents: FxHashMap<Symbol, Vec<Symbol>> =
+            codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name()])).collect();
+
+        // Merge the two smallest codegen units until the target size is
+        // reached.
+        while codegen_units.len() > cx.target_cgu_count {
+            // Sort small cgus to the back
+            codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
+            let mut smallest = codegen_units.pop().unwrap();
+            let second_smallest = codegen_units.last_mut().unwrap();
+
+            // Move the mono-items from `smallest` to `second_smallest`
+            second_smallest.modify_size_estimate(smallest.size_estimate());
+            for (k, v) in smallest.items_mut().drain() {
+                second_smallest.items_mut().insert(k, v);
+            }
+
+            // Record that `second_smallest` now contains all the stuff that was
+            // in `smallest` before.
+            let mut consumed_cgu_names = cgu_contents.remove(&smallest.name()).unwrap();
+            cgu_contents.get_mut(&second_smallest.name()).unwrap().append(&mut consumed_cgu_names);
+
+            debug!(
+                "CodegenUnit {} merged into CodegenUnit {}",
+                smallest.name(),
+                second_smallest.name()
+            );
+        }
+
+        let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
+
+        if cx.tcx.sess.opts.incremental.is_some() {
+            // If we are doing incremental compilation, we want CGU names to
+            // reflect the path of the source level module they correspond to.
+            // For CGUs that contain the code of multiple modules because of the
+            // merging done above, we use a concatenation of the names of all
+            // contained CGUs.
+            let new_cgu_names: FxHashMap<Symbol, String> = cgu_contents
+                .into_iter()
+                // This `filter` makes sure we only update the name of CGUs that
+                // were actually modified by merging.
+                .filter(|(_, cgu_contents)| cgu_contents.len() > 1)
+                .map(|(current_cgu_name, cgu_contents)| {
+                    let mut cgu_contents: Vec<&str> =
+                        cgu_contents.iter().map(|s| s.as_str()).collect();
+
+                    // Sort the names, so things are deterministic and easy to
+                    // predict. We are sorting primitive `&str`s here so we can
+                    // use unstable sort.
+                    cgu_contents.sort_unstable();
+
+                    (current_cgu_name, cgu_contents.join("--"))
+                })
+                .collect();
+
+            for cgu in codegen_units.iter_mut() {
+                if let Some(new_cgu_name) = new_cgu_names.get(&cgu.name()) {
+                    if cx.tcx.sess.opts.unstable_opts.human_readable_cgu_names {
+                        cgu.set_name(Symbol::intern(&new_cgu_name));
+                    } else {
+                        // If we don't require CGU names to be human-readable,
+                        // we use a fixed length hash of the composite CGU name
+                        // instead.
+                        let new_cgu_name = CodegenUnit::mangle_name(&new_cgu_name);
+                        cgu.set_name(Symbol::intern(&new_cgu_name));
+                    }
+                }
+            }
+        } else {
+            // If we are compiling non-incrementally we just generate simple CGU
+            // names containing an index.
+            for (index, cgu) in codegen_units.iter_mut().enumerate() {
+                let numbered_codegen_unit_name =
+                    cgu_name_builder.build_cgu_name_no_mangle(LOCAL_CRATE, &["cgu"], Some(index));
+                cgu.set_name(numbered_codegen_unit_name);
+            }
+        }
     }
 
     fn place_inlined_mono_items(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        initial_partitioning: PreInliningPartitioning<'tcx>,
-    ) -> PostInliningPartitioning<'tcx> {
-        let mut new_partitioning = Vec::new();
+        codegen_units: &mut [CodegenUnit<'tcx>],
+        roots: FxHashSet<MonoItem<'tcx>>,
+    ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement> {
         let mut mono_item_placements = FxHashMap::default();
 
-        let PreInliningPartitioning {
-            codegen_units: initial_cgus,
-            roots,
-            internalization_candidates,
-        } = initial_partitioning;
-
-        let single_codegen_unit = initial_cgus.len() == 1;
+        let single_codegen_unit = codegen_units.len() == 1;
 
-        for old_codegen_unit in initial_cgus {
+        for old_codegen_unit in codegen_units.iter_mut() {
             // Collect all items that need to be available in this codegen unit.
             let mut reachable = FxHashSet::default();
             for root in old_codegen_unit.items().keys() {
@@ -174,14 +254,10 @@ impl<'tcx> Partition<'tcx> for DefaultPartitioning {
                 }
             }
 
-            new_partitioning.push(new_codegen_unit);
+            *old_codegen_unit = new_codegen_unit;
         }
 
-        return PostInliningPartitioning {
-            codegen_units: new_partitioning,
-            mono_item_placements,
-            internalization_candidates,
-        };
+        return mono_item_placements;
 
         fn follow_inlining<'tcx>(
             mono_item: MonoItem<'tcx>,
@@ -201,14 +277,16 @@ impl<'tcx> Partition<'tcx> for DefaultPartitioning {
     fn internalize_symbols(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        partitioning: &mut PostInliningPartitioning<'tcx>,
+        codegen_units: &mut [CodegenUnit<'tcx>],
+        mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>,
+        internalization_candidates: FxHashSet<MonoItem<'tcx>>,
     ) {
-        if partitioning.codegen_units.len() == 1 {
+        if codegen_units.len() == 1 {
             // Fast path for when there is only one codegen unit. In this case we
             // can internalize all candidates, since there is nowhere else they
             // could be accessed from.
-            for cgu in &mut partitioning.codegen_units {
-                for candidate in &partitioning.internalization_candidates {
+            for cgu in codegen_units {
+                for candidate in &internalization_candidates {
                     cgu.items_mut().insert(*candidate, (Linkage::Internal, Visibility::Default));
                 }
             }
@@ -225,15 +303,13 @@ impl<'tcx> Partition<'tcx> for DefaultPartitioning {
             }
         });
 
-        let mono_item_placements = &partitioning.mono_item_placements;
-
         // For each internalization candidates in each codegen unit, check if it is
         // accessed from outside its defining codegen unit.
-        for cgu in &mut partitioning.codegen_units {
+        for cgu in codegen_units {
             let home_cgu = MonoItemPlacement::SingleCgu { cgu_name: cgu.name() };
 
             for (accessee, linkage_and_visibility) in cgu.items_mut() {
-                if !partitioning.internalization_candidates.contains(accessee) {
+                if !internalization_candidates.contains(accessee) {
                     // This item is no candidate for internalizing, so skip it.
                     continue;
                 }
diff --git a/compiler/rustc_monomorphize/src/partitioning/merging.rs b/compiler/rustc_monomorphize/src/partitioning/merging.rs
deleted file mode 100644
index 5c524a18454..00000000000
--- a/compiler/rustc_monomorphize/src/partitioning/merging.rs
+++ /dev/null
@@ -1,111 +0,0 @@
-use std::cmp;
-
-use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::def_id::LOCAL_CRATE;
-use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder};
-use rustc_span::symbol::Symbol;
-
-use super::PartitioningCx;
-use crate::partitioning::PreInliningPartitioning;
-
-pub fn merge_codegen_units<'tcx>(
-    cx: &PartitioningCx<'_, 'tcx>,
-    initial_partitioning: &mut PreInliningPartitioning<'tcx>,
-) {
-    assert!(cx.target_cgu_count >= 1);
-    let codegen_units = &mut initial_partitioning.codegen_units;
-
-    // Note that at this point in time the `codegen_units` here may not be in a
-    // deterministic order (but we know they're deterministically the same set).
-    // We want this merging to produce a deterministic ordering of codegen units
-    // from the input.
-    //
-    // Due to basically how we've implemented the merging below (merge the two
-    // smallest into each other) we're sure to start off with a deterministic
-    // order (sorted by name). This'll mean that if two cgus have the same size
-    // the stable sort below will keep everything nice and deterministic.
-    codegen_units.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str()));
-
-    // This map keeps track of what got merged into what.
-    let mut cgu_contents: FxHashMap<Symbol, Vec<Symbol>> =
-        codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name()])).collect();
-
-    // Merge the two smallest codegen units until the target size is reached.
-    while codegen_units.len() > cx.target_cgu_count {
-        // Sort small cgus to the back
-        codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
-        let mut smallest = codegen_units.pop().unwrap();
-        let second_smallest = codegen_units.last_mut().unwrap();
-
-        // Move the mono-items from `smallest` to `second_smallest`
-        second_smallest.modify_size_estimate(smallest.size_estimate());
-        for (k, v) in smallest.items_mut().drain() {
-            second_smallest.items_mut().insert(k, v);
-        }
-
-        // Record that `second_smallest` now contains all the stuff that was in
-        // `smallest` before.
-        let mut consumed_cgu_names = cgu_contents.remove(&smallest.name()).unwrap();
-        cgu_contents.get_mut(&second_smallest.name()).unwrap().append(&mut consumed_cgu_names);
-
-        debug!(
-            "CodegenUnit {} merged into CodegenUnit {}",
-            smallest.name(),
-            second_smallest.name()
-        );
-    }
-
-    let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
-
-    if cx.tcx.sess.opts.incremental.is_some() {
-        // If we are doing incremental compilation, we want CGU names to
-        // reflect the path of the source level module they correspond to.
-        // For CGUs that contain the code of multiple modules because of the
-        // merging done above, we use a concatenation of the names of
-        // all contained CGUs.
-        let new_cgu_names: FxHashMap<Symbol, String> = cgu_contents
-            .into_iter()
-            // This `filter` makes sure we only update the name of CGUs that
-            // were actually modified by merging.
-            .filter(|(_, cgu_contents)| cgu_contents.len() > 1)
-            .map(|(current_cgu_name, cgu_contents)| {
-                let mut cgu_contents: Vec<&str> = cgu_contents.iter().map(|s| s.as_str()).collect();
-
-                // Sort the names, so things are deterministic and easy to
-                // predict.
-
-                // We are sorting primitive &strs here so we can use unstable sort
-                cgu_contents.sort_unstable();
-
-                (current_cgu_name, cgu_contents.join("--"))
-            })
-            .collect();
-
-        for cgu in codegen_units.iter_mut() {
-            if let Some(new_cgu_name) = new_cgu_names.get(&cgu.name()) {
-                if cx.tcx.sess.opts.unstable_opts.human_readable_cgu_names {
-                    cgu.set_name(Symbol::intern(&new_cgu_name));
-                } else {
-                    // If we don't require CGU names to be human-readable, we
-                    // use a fixed length hash of the composite CGU name
-                    // instead.
-                    let new_cgu_name = CodegenUnit::mangle_name(&new_cgu_name);
-                    cgu.set_name(Symbol::intern(&new_cgu_name));
-                }
-            }
-        }
-    } else {
-        // If we are compiling non-incrementally we just generate simple CGU
-        // names containing an index.
-        for (index, cgu) in codegen_units.iter_mut().enumerate() {
-            cgu.set_name(numbered_codegen_unit_name(cgu_name_builder, index));
-        }
-    }
-}
-
-fn numbered_codegen_unit_name(
-    name_builder: &mut CodegenUnitNameBuilder<'_>,
-    index: usize,
-) -> Symbol {
-    name_builder.build_cgu_name_no_mangle(LOCAL_CRATE, &["cgu"], Some(index))
-}
diff --git a/compiler/rustc_monomorphize/src/partitioning/mod.rs b/compiler/rustc_monomorphize/src/partitioning/mod.rs
index eafe57a0c02..d0b23ca9ea4 100644
--- a/compiler/rustc_monomorphize/src/partitioning/mod.rs
+++ b/compiler/rustc_monomorphize/src/partitioning/mod.rs
@@ -93,7 +93,6 @@
 //! inlining, even when they are not marked `#[inline]`.
 
 mod default;
-mod merging;
 
 use std::cmp;
 use std::fs::{self, File};
@@ -129,7 +128,7 @@ impl<'tcx> Partition<'tcx> for Partitioner {
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
         mono_items: &mut I,
-    ) -> PreInliningPartitioning<'tcx>
+    ) -> PlacedRootMonoItems<'tcx>
     where
         I: Iterator<Item = MonoItem<'tcx>>,
     {
@@ -142,12 +141,10 @@ impl<'tcx> Partition<'tcx> for Partitioner {
     fn merge_codegen_units(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        initial_partitioning: &mut PreInliningPartitioning<'tcx>,
+        codegen_units: &mut Vec<CodegenUnit<'tcx>>,
     ) {
         match self {
-            Partitioner::Default(partitioner) => {
-                partitioner.merge_codegen_units(cx, initial_partitioning)
-            }
+            Partitioner::Default(partitioner) => partitioner.merge_codegen_units(cx, codegen_units),
             Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy),
         }
     }
@@ -155,11 +152,12 @@ impl<'tcx> Partition<'tcx> for Partitioner {
     fn place_inlined_mono_items(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        initial_partitioning: PreInliningPartitioning<'tcx>,
-    ) -> PostInliningPartitioning<'tcx> {
+        codegen_units: &mut [CodegenUnit<'tcx>],
+        roots: FxHashSet<MonoItem<'tcx>>,
+    ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement> {
         match self {
             Partitioner::Default(partitioner) => {
-                partitioner.place_inlined_mono_items(cx, initial_partitioning)
+                partitioner.place_inlined_mono_items(cx, codegen_units, roots)
             }
             Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy),
         }
@@ -168,48 +166,62 @@ impl<'tcx> Partition<'tcx> for Partitioner {
     fn internalize_symbols(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        post_inlining_partitioning: &mut PostInliningPartitioning<'tcx>,
+        codegen_units: &mut [CodegenUnit<'tcx>],
+        mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>,
+        internalization_candidates: FxHashSet<MonoItem<'tcx>>,
     ) {
         match self {
-            Partitioner::Default(partitioner) => {
-                partitioner.internalize_symbols(cx, post_inlining_partitioning)
-            }
+            Partitioner::Default(partitioner) => partitioner.internalize_symbols(
+                cx,
+                codegen_units,
+                mono_item_placements,
+                internalization_candidates,
+            ),
             Partitioner::Unknown => cx.tcx.sess.emit_fatal(UnknownPartitionStrategy),
         }
     }
 }
 
-pub struct PartitioningCx<'a, 'tcx> {
+struct PartitioningCx<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
     target_cgu_count: usize,
     inlining_map: &'a InliningMap<'tcx>,
 }
 
+pub struct PlacedRootMonoItems<'tcx> {
+    codegen_units: Vec<CodegenUnit<'tcx>>,
+    roots: FxHashSet<MonoItem<'tcx>>,
+    internalization_candidates: FxHashSet<MonoItem<'tcx>>,
+}
+
 trait Partition<'tcx> {
     fn place_root_mono_items<I>(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
         mono_items: &mut I,
-    ) -> PreInliningPartitioning<'tcx>
+    ) -> PlacedRootMonoItems<'tcx>
     where
         I: Iterator<Item = MonoItem<'tcx>>;
 
     fn merge_codegen_units(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        initial_partitioning: &mut PreInliningPartitioning<'tcx>,
+        codegen_units: &mut Vec<CodegenUnit<'tcx>>,
     );
 
     fn place_inlined_mono_items(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        initial_partitioning: PreInliningPartitioning<'tcx>,
-    ) -> PostInliningPartitioning<'tcx>;
+        codegen_units: &mut [CodegenUnit<'tcx>],
+        roots: FxHashSet<MonoItem<'tcx>>,
+    ) -> FxHashMap<MonoItem<'tcx>, MonoItemPlacement>;
 
     fn internalize_symbols(
         &mut self,
         cx: &PartitioningCx<'_, 'tcx>,
-        partitioning: &mut PostInliningPartitioning<'tcx>,
+        codegen_units: &mut [CodegenUnit<'tcx>],
+        mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>,
+        internalization_candidates: FxHashSet<MonoItem<'tcx>>,
     );
 }
 
@@ -225,7 +237,7 @@ fn get_partitioner(tcx: TyCtxt<'_>) -> Partitioner {
     }
 }
 
-pub fn partition<'tcx, I>(
+fn partition<'tcx, I>(
     tcx: TyCtxt<'tcx>,
     mono_items: &mut I,
     max_cgu_count: usize,
@@ -241,44 +253,51 @@ where
     // In the first step, we place all regular monomorphizations into their
     // respective 'home' codegen unit. Regular monomorphizations are all
     // functions and statics defined in the local crate.
-    let mut initial_partitioning = {
+    let PlacedRootMonoItems { mut codegen_units, roots, internalization_candidates } = {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_roots");
         partitioner.place_root_mono_items(cx, mono_items)
     };
 
-    for cgu in &mut initial_partitioning.codegen_units {
+    for cgu in &mut codegen_units {
         cgu.create_size_estimate(tcx);
     }
 
-    debug_dump(tcx, "INITIAL PARTITIONING", &initial_partitioning.codegen_units);
+    debug_dump(tcx, "INITIAL PARTITIONING", &codegen_units);
 
     // Merge until we have at most `max_cgu_count` codegen units.
+    // `merge_codegen_units` is responsible for updating the CGU size
+    // estimates.
     {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_merge_cgus");
-        partitioner.merge_codegen_units(cx, &mut initial_partitioning);
-        debug_dump(tcx, "POST MERGING", &initial_partitioning.codegen_units);
+        partitioner.merge_codegen_units(cx, &mut codegen_units);
+        debug_dump(tcx, "POST MERGING", &codegen_units);
     }
 
     // In the next step, we use the inlining map to determine which additional
     // monomorphizations have to go into each codegen unit. These additional
     // monomorphizations can be drop-glue, functions from external crates, and
     // local functions the definition of which is marked with `#[inline]`.
-    let mut post_inlining = {
+    let mono_item_placements = {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_inline_items");
-        partitioner.place_inlined_mono_items(cx, initial_partitioning)
+        partitioner.place_inlined_mono_items(cx, &mut codegen_units, roots)
     };
 
-    for cgu in &mut post_inlining.codegen_units {
+    for cgu in &mut codegen_units {
         cgu.create_size_estimate(tcx);
     }
 
-    debug_dump(tcx, "POST INLINING", &post_inlining.codegen_units);
+    debug_dump(tcx, "POST INLINING", &codegen_units);
 
     // Next we try to make as many symbols "internal" as possible, so LLVM has
     // more freedom to optimize.
     if !tcx.sess.link_dead_code() {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols");
-        partitioner.internalize_symbols(cx, &mut post_inlining);
+        partitioner.internalize_symbols(
+            cx,
+            &mut codegen_units,
+            mono_item_placements,
+            internalization_candidates,
+        );
     }
 
     let instrument_dead_code =
@@ -286,7 +305,7 @@ where
 
     if instrument_dead_code {
         assert!(
-            post_inlining.codegen_units.len() > 0,
+            codegen_units.len() > 0,
             "There must be at least one CGU that code coverage data can be generated in."
         );
 
@@ -297,7 +316,7 @@ where
         // the object file (CGU) containing the dead function stubs is included
         // in the final binary. This will probably require forcing these
         // function symbols to be included via `-u` or `/include` linker args.
-        let mut cgus: Vec<_> = post_inlining.codegen_units.iter_mut().collect();
+        let mut cgus: Vec<_> = codegen_units.iter_mut().collect();
         cgus.sort_by_key(|cgu| cgu.size_estimate());
 
         let dead_code_cgu =
@@ -308,29 +327,17 @@ where
             } else {
                 // If there are no CGUs that have externally linked items,
                 // then we just pick the first CGU as a fallback.
-                &mut post_inlining.codegen_units[0]
+                &mut codegen_units[0]
             };
         dead_code_cgu.make_code_coverage_dead_code_cgu();
     }
 
     // Finally, sort by codegen unit name, so that we get deterministic results.
-    let PostInliningPartitioning {
-        codegen_units: mut result,
-        mono_item_placements: _,
-        internalization_candidates: _,
-    } = post_inlining;
+    codegen_units.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str()));
 
-    result.sort_by(|a, b| a.name().as_str().cmp(b.name().as_str()));
+    debug_dump(tcx, "FINAL", &codegen_units);
 
-    debug_dump(tcx, "FINAL", &result);
-
-    result
-}
-
-pub struct PreInliningPartitioning<'tcx> {
-    codegen_units: Vec<CodegenUnit<'tcx>>,
-    roots: FxHashSet<MonoItem<'tcx>>,
-    internalization_candidates: FxHashSet<MonoItem<'tcx>>,
+    codegen_units
 }
 
 /// For symbol internalization, we need to know whether a symbol/mono-item is
@@ -342,12 +349,6 @@ enum MonoItemPlacement {
     MultipleCgus,
 }
 
-struct PostInliningPartitioning<'tcx> {
-    codegen_units: Vec<CodegenUnit<'tcx>>,
-    mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>,
-    internalization_candidates: FxHashSet<MonoItem<'tcx>>,
-}
-
 fn debug_dump<'a, 'tcx: 'a>(tcx: TyCtxt<'tcx>, label: &str, cgus: &[CodegenUnit<'tcx>]) {
     let dump = move || {
         use std::fmt::Write;
diff --git a/compiler/rustc_target/src/spec/aarch64_apple_ios_macabi.rs b/compiler/rustc_target/src/spec/aarch64_apple_ios_macabi.rs
index 2b135b67034..e2df7e0bdcc 100644
--- a/compiler/rustc_target/src/spec/aarch64_apple_ios_macabi.rs
+++ b/compiler/rustc_target/src/spec/aarch64_apple_ios_macabi.rs
@@ -2,7 +2,7 @@ use super::apple_base::{opts, Arch};
 use crate::spec::{Cc, FramePointer, LinkerFlavor, Lld, Target, TargetOptions};
 
 pub fn target() -> Target {
-    let llvm_target = "arm64-apple-ios-macabi";
+    let llvm_target = "arm64-apple-ios14.0-macabi";
 
     let arch = Arch::Arm64_macabi;
     let mut base = opts("ios", arch);
diff --git a/compiler/rustc_target/src/spec/x86_64_apple_ios_macabi.rs b/compiler/rustc_target/src/spec/x86_64_apple_ios_macabi.rs
index 5a3e2a79bb9..9f3b0fab697 100644
--- a/compiler/rustc_target/src/spec/x86_64_apple_ios_macabi.rs
+++ b/compiler/rustc_target/src/spec/x86_64_apple_ios_macabi.rs
@@ -2,7 +2,7 @@ use super::apple_base::{opts, Arch};
 use crate::spec::{Cc, LinkerFlavor, Lld, StackProbeType, Target, TargetOptions};
 
 pub fn target() -> Target {
-    let llvm_target = "x86_64-apple-ios-macabi";
+    let llvm_target = "x86_64-apple-ios14.0-macabi";
 
     let arch = Arch::X86_64_macabi;
     let mut base = opts("ios", arch);
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 9e09ce337bc..8a007d095d5 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -593,7 +593,8 @@ pub trait Read {
     /// This may happen for example because fewer bytes are actually available right now
     /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
     ///
-    /// As this trait is safe to implement, callers cannot rely on `n <= buf.len()` for safety.
+    /// As this trait is safe to implement, callers in unsafe code cannot rely on
+    /// `n <= buf.len()` for safety.
     /// Extra care needs to be taken when `unsafe` functions are used to access the read bytes.
     /// Callers have to ensure that no unchecked out-of-bounds accesses are possible even if
     /// `n > buf.len()`.
@@ -603,8 +604,8 @@ pub trait Read {
     /// contents of `buf` being true. It is recommended that *implementations*
     /// only write data to `buf` instead of reading its contents.
     ///
-    /// Correspondingly, however, *callers* of this method must not assume any guarantees
-    /// about how the implementation uses `buf`. The trait is safe to implement,
+    /// Correspondingly, however, *callers* of this method in unsafe code must not assume
+    /// any guarantees about how the implementation uses `buf`. The trait is safe to implement,
     /// so it is possible that the code that's supposed to write to the buffer might also read
     /// from it. It is your responsibility to make sure that `buf` is initialized
     /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
diff --git a/tests/ui/impl-trait/multiple-defining-usages-in-body.rs b/tests/ui/impl-trait/multiple-defining-usages-in-body.rs
new file mode 100644
index 00000000000..c3a6f09f86d
--- /dev/null
+++ b/tests/ui/impl-trait/multiple-defining-usages-in-body.rs
@@ -0,0 +1,12 @@
+trait Trait {}
+impl Trait for () {}
+
+fn foo<T: Trait, U: Trait>() -> impl Trait {
+    //~^ WARN function cannot return without recursing [unconditional_recursion]
+    let a: T = foo::<T, U>();
+    //~^ ERROR concrete type differs from previous defining opaque type use
+    loop {}
+    let _: T = foo::<U, T>();
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/multiple-defining-usages-in-body.stderr b/tests/ui/impl-trait/multiple-defining-usages-in-body.stderr
new file mode 100644
index 00000000000..06991749bfa
--- /dev/null
+++ b/tests/ui/impl-trait/multiple-defining-usages-in-body.stderr
@@ -0,0 +1,26 @@
+warning: function cannot return without recursing
+  --> $DIR/multiple-defining-usages-in-body.rs:4:1
+   |
+LL | fn foo<T: Trait, U: Trait>() -> impl Trait {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+LL |
+LL |     let a: T = foo::<T, U>();
+   |                ------------- recursive call site
+   |
+   = help: a `loop` may express intention better if this is on purpose
+   = note: `#[warn(unconditional_recursion)]` on by default
+
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/multiple-defining-usages-in-body.rs:6:16
+   |
+LL |     let a: T = foo::<T, U>();
+   |                ^^^^^^^^^^^^^ expected `U`, got `T`
+   |
+note: previous use here
+  --> $DIR/multiple-defining-usages-in-body.rs:9:16
+   |
+LL |     let _: T = foo::<U, T>();
+   |                ^^^^^^^^^^^^^
+
+error: aborting due to previous error; 1 warning emitted
+
diff --git a/tests/ui/pattern/usefulness/empty-match.exhaustive_patterns.stderr b/tests/ui/pattern/usefulness/empty-match.exhaustive_patterns.stderr
index 5a145efce94..49b6dfca62e 100644
--- a/tests/ui/pattern/usefulness/empty-match.exhaustive_patterns.stderr
+++ b/tests/ui/pattern/usefulness/empty-match.exhaustive_patterns.stderr
@@ -1,5 +1,5 @@
 error: unreachable pattern
-  --> $DIR/empty-match.rs:37:9
+  --> $DIR/empty-match.rs:58:9
    |
 LL |         _ => {},
    |         ^
@@ -11,37 +11,52 @@ LL | #![deny(unreachable_patterns)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:40:9
+  --> $DIR/empty-match.rs:61:9
    |
 LL |         _ if false => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:47:9
+  --> $DIR/empty-match.rs:68:9
    |
 LL |         _ => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:50:9
+  --> $DIR/empty-match.rs:71:9
    |
 LL |         _ if false => {},
    |         ^
 
+error[E0005]: refutable pattern in local binding
+  --> $DIR/empty-match.rs:76:9
+   |
+LL |     let None = x;
+   |         ^^^^ pattern `Some(_)` not covered
+   |
+   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
+   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+   = note: pattern `Some(_)` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
+   = note: the matched value is of type `Option<SecretlyUninhabitedForeignStruct>`
+help: you might want to use `if let` to ignore the variant that isn't matched
+   |
+LL |     if let None = x { todo!() };
+   |     ++              +++++++++++
+
 error: unreachable pattern
-  --> $DIR/empty-match.rs:57:9
+  --> $DIR/empty-match.rs:88:9
    |
 LL |         _ => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:60:9
+  --> $DIR/empty-match.rs:91:9
    |
 LL |         _ if false => {},
    |         ^
 
 error[E0004]: non-exhaustive patterns: type `u8` is non-empty
-  --> $DIR/empty-match.rs:78:20
+  --> $DIR/empty-match.rs:109:20
    |
 LL |     match_no_arms!(0u8);
    |                    ^^^
@@ -50,13 +65,13 @@ LL |     match_no_arms!(0u8);
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyStruct1` is non-empty
-  --> $DIR/empty-match.rs:79:20
+  --> $DIR/empty-match.rs:111:20
    |
 LL |     match_no_arms!(NonEmptyStruct1);
    |                    ^^^^^^^^^^^^^^^
    |
 note: `NonEmptyStruct1` defined here
-  --> $DIR/empty-match.rs:14:8
+  --> $DIR/empty-match.rs:15:8
    |
 LL | struct NonEmptyStruct1;
    |        ^^^^^^^^^^^^^^^
@@ -64,13 +79,13 @@ LL | struct NonEmptyStruct1;
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyStruct2` is non-empty
-  --> $DIR/empty-match.rs:80:20
+  --> $DIR/empty-match.rs:113:20
    |
 LL |     match_no_arms!(NonEmptyStruct2(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyStruct2` defined here
-  --> $DIR/empty-match.rs:15:8
+  --> $DIR/empty-match.rs:18:8
    |
 LL | struct NonEmptyStruct2(bool);
    |        ^^^^^^^^^^^^^^^
@@ -78,13 +93,13 @@ LL | struct NonEmptyStruct2(bool);
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyUnion1` is non-empty
-  --> $DIR/empty-match.rs:81:20
+  --> $DIR/empty-match.rs:115:20
    |
 LL |     match_no_arms!((NonEmptyUnion1 { foo: () }));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyUnion1` defined here
-  --> $DIR/empty-match.rs:16:7
+  --> $DIR/empty-match.rs:21:7
    |
 LL | union NonEmptyUnion1 {
    |       ^^^^^^^^^^^^^^
@@ -92,13 +107,13 @@ LL | union NonEmptyUnion1 {
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyUnion2` is non-empty
-  --> $DIR/empty-match.rs:82:20
+  --> $DIR/empty-match.rs:117:20
    |
 LL |     match_no_arms!((NonEmptyUnion2 { foo: () }));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyUnion2` defined here
-  --> $DIR/empty-match.rs:19:7
+  --> $DIR/empty-match.rs:26:7
    |
 LL | union NonEmptyUnion2 {
    |       ^^^^^^^^^^^^^^
@@ -106,13 +121,13 @@ LL | union NonEmptyUnion2 {
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum1::Foo(_)` not covered
-  --> $DIR/empty-match.rs:83:20
+  --> $DIR/empty-match.rs:119:20
    |
 LL |     match_no_arms!(NonEmptyEnum1::Foo(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyEnum1::Foo(_)` not covered
    |
 note: `NonEmptyEnum1` defined here
-  --> $DIR/empty-match.rs:24:5
+  --> $DIR/empty-match.rs:33:5
    |
 LL | enum NonEmptyEnum1 {
    |      -------------
@@ -122,31 +137,32 @@ LL |     Foo(bool),
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
-  --> $DIR/empty-match.rs:84:20
+  --> $DIR/empty-match.rs:122:20
    |
 LL |     match_no_arms!(NonEmptyEnum2::Foo(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
    |
 note: `NonEmptyEnum2` defined here
-  --> $DIR/empty-match.rs:27:5
+  --> $DIR/empty-match.rs:40:5
    |
 LL | enum NonEmptyEnum2 {
    |      -------------
 LL |     Foo(bool),
    |     ^^^ not covered
+...
 LL |     Bar,
    |     ^^^ not covered
    = note: the matched value is of type `NonEmptyEnum2`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or multiple match arms
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
-  --> $DIR/empty-match.rs:85:20
+  --> $DIR/empty-match.rs:125:20
    |
 LL |     match_no_arms!(NonEmptyEnum5::V1);
    |                    ^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
    |
 note: `NonEmptyEnum5` defined here
-  --> $DIR/empty-match.rs:30:6
+  --> $DIR/empty-match.rs:49:6
    |
 LL | enum NonEmptyEnum5 {
    |      ^^^^^^^^^^^^^
@@ -154,7 +170,7 @@ LL | enum NonEmptyEnum5 {
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or multiple match arms
 
 error[E0004]: non-exhaustive patterns: `_` not covered
-  --> $DIR/empty-match.rs:87:24
+  --> $DIR/empty-match.rs:129:24
    |
 LL |     match_guarded_arm!(0u8);
    |                        ^^^ pattern `_` not covered
@@ -167,13 +183,13 @@ LL +             _ => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyStruct1` not covered
-  --> $DIR/empty-match.rs:88:24
+  --> $DIR/empty-match.rs:133:24
    |
 LL |     match_guarded_arm!(NonEmptyStruct1);
    |                        ^^^^^^^^^^^^^^^ pattern `NonEmptyStruct1` not covered
    |
 note: `NonEmptyStruct1` defined here
-  --> $DIR/empty-match.rs:14:8
+  --> $DIR/empty-match.rs:15:8
    |
 LL | struct NonEmptyStruct1;
    |        ^^^^^^^^^^^^^^^
@@ -185,13 +201,13 @@ LL +             NonEmptyStruct1 => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyStruct2(_)` not covered
-  --> $DIR/empty-match.rs:89:24
+  --> $DIR/empty-match.rs:137:24
    |
 LL |     match_guarded_arm!(NonEmptyStruct2(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyStruct2(_)` not covered
    |
 note: `NonEmptyStruct2` defined here
-  --> $DIR/empty-match.rs:15:8
+  --> $DIR/empty-match.rs:18:8
    |
 LL | struct NonEmptyStruct2(bool);
    |        ^^^^^^^^^^^^^^^
@@ -203,13 +219,13 @@ LL +             NonEmptyStruct2(_) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyUnion1 { .. }` not covered
-  --> $DIR/empty-match.rs:90:24
+  --> $DIR/empty-match.rs:141:24
    |
 LL |     match_guarded_arm!((NonEmptyUnion1 { foo: () }));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyUnion1 { .. }` not covered
    |
 note: `NonEmptyUnion1` defined here
-  --> $DIR/empty-match.rs:16:7
+  --> $DIR/empty-match.rs:21:7
    |
 LL | union NonEmptyUnion1 {
    |       ^^^^^^^^^^^^^^
@@ -221,13 +237,13 @@ LL +             NonEmptyUnion1 { .. } => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyUnion2 { .. }` not covered
-  --> $DIR/empty-match.rs:91:24
+  --> $DIR/empty-match.rs:145:24
    |
 LL |     match_guarded_arm!((NonEmptyUnion2 { foo: () }));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyUnion2 { .. }` not covered
    |
 note: `NonEmptyUnion2` defined here
-  --> $DIR/empty-match.rs:19:7
+  --> $DIR/empty-match.rs:26:7
    |
 LL | union NonEmptyUnion2 {
    |       ^^^^^^^^^^^^^^
@@ -239,13 +255,13 @@ LL +             NonEmptyUnion2 { .. } => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum1::Foo(_)` not covered
-  --> $DIR/empty-match.rs:92:24
+  --> $DIR/empty-match.rs:149:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum1::Foo(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyEnum1::Foo(_)` not covered
    |
 note: `NonEmptyEnum1` defined here
-  --> $DIR/empty-match.rs:24:5
+  --> $DIR/empty-match.rs:33:5
    |
 LL | enum NonEmptyEnum1 {
    |      -------------
@@ -259,18 +275,19 @@ LL +             NonEmptyEnum1::Foo(_) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
-  --> $DIR/empty-match.rs:93:24
+  --> $DIR/empty-match.rs:153:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum2::Foo(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
    |
 note: `NonEmptyEnum2` defined here
-  --> $DIR/empty-match.rs:27:5
+  --> $DIR/empty-match.rs:40:5
    |
 LL | enum NonEmptyEnum2 {
    |      -------------
 LL |     Foo(bool),
    |     ^^^ not covered
+...
 LL |     Bar,
    |     ^^^ not covered
    = note: the matched value is of type `NonEmptyEnum2`
@@ -281,13 +298,13 @@ LL +             NonEmptyEnum2::Foo(_) | NonEmptyEnum2::Bar => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
-  --> $DIR/empty-match.rs:94:24
+  --> $DIR/empty-match.rs:157:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum5::V1);
    |                        ^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
    |
 note: `NonEmptyEnum5` defined here
-  --> $DIR/empty-match.rs:30:6
+  --> $DIR/empty-match.rs:49:6
    |
 LL | enum NonEmptyEnum5 {
    |      ^^^^^^^^^^^^^
@@ -298,6 +315,7 @@ LL ~             _ if false => {},
 LL +             _ => todo!()
    |
 
-error: aborting due to 22 previous errors
+error: aborting due to 23 previous errors
 
-For more information about this error, try `rustc --explain E0004`.
+Some errors have detailed explanations: E0004, E0005.
+For more information about an error, try `rustc --explain E0004`.
diff --git a/tests/ui/pattern/usefulness/empty-match.normal.stderr b/tests/ui/pattern/usefulness/empty-match.normal.stderr
index 5a145efce94..f54a3f3364f 100644
--- a/tests/ui/pattern/usefulness/empty-match.normal.stderr
+++ b/tests/ui/pattern/usefulness/empty-match.normal.stderr
@@ -1,5 +1,5 @@
 error: unreachable pattern
-  --> $DIR/empty-match.rs:37:9
+  --> $DIR/empty-match.rs:58:9
    |
 LL |         _ => {},
    |         ^
@@ -11,37 +11,51 @@ LL | #![deny(unreachable_patterns)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:40:9
+  --> $DIR/empty-match.rs:61:9
    |
 LL |         _ if false => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:47:9
+  --> $DIR/empty-match.rs:68:9
    |
 LL |         _ => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:50:9
+  --> $DIR/empty-match.rs:71:9
    |
 LL |         _ if false => {},
    |         ^
 
+error[E0005]: refutable pattern in local binding
+  --> $DIR/empty-match.rs:76:9
+   |
+LL |     let None = x;
+   |         ^^^^ pattern `Some(_)` not covered
+   |
+   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
+   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+   = note: the matched value is of type `Option<SecretlyUninhabitedForeignStruct>`
+help: you might want to use `if let` to ignore the variant that isn't matched
+   |
+LL |     if let None = x { todo!() };
+   |     ++              +++++++++++
+
 error: unreachable pattern
-  --> $DIR/empty-match.rs:57:9
+  --> $DIR/empty-match.rs:88:9
    |
 LL |         _ => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:60:9
+  --> $DIR/empty-match.rs:91:9
    |
 LL |         _ if false => {},
    |         ^
 
 error[E0004]: non-exhaustive patterns: type `u8` is non-empty
-  --> $DIR/empty-match.rs:78:20
+  --> $DIR/empty-match.rs:109:20
    |
 LL |     match_no_arms!(0u8);
    |                    ^^^
@@ -50,13 +64,13 @@ LL |     match_no_arms!(0u8);
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyStruct1` is non-empty
-  --> $DIR/empty-match.rs:79:20
+  --> $DIR/empty-match.rs:111:20
    |
 LL |     match_no_arms!(NonEmptyStruct1);
    |                    ^^^^^^^^^^^^^^^
    |
 note: `NonEmptyStruct1` defined here
-  --> $DIR/empty-match.rs:14:8
+  --> $DIR/empty-match.rs:15:8
    |
 LL | struct NonEmptyStruct1;
    |        ^^^^^^^^^^^^^^^
@@ -64,13 +78,13 @@ LL | struct NonEmptyStruct1;
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyStruct2` is non-empty
-  --> $DIR/empty-match.rs:80:20
+  --> $DIR/empty-match.rs:113:20
    |
 LL |     match_no_arms!(NonEmptyStruct2(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyStruct2` defined here
-  --> $DIR/empty-match.rs:15:8
+  --> $DIR/empty-match.rs:18:8
    |
 LL | struct NonEmptyStruct2(bool);
    |        ^^^^^^^^^^^^^^^
@@ -78,13 +92,13 @@ LL | struct NonEmptyStruct2(bool);
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyUnion1` is non-empty
-  --> $DIR/empty-match.rs:81:20
+  --> $DIR/empty-match.rs:115:20
    |
 LL |     match_no_arms!((NonEmptyUnion1 { foo: () }));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyUnion1` defined here
-  --> $DIR/empty-match.rs:16:7
+  --> $DIR/empty-match.rs:21:7
    |
 LL | union NonEmptyUnion1 {
    |       ^^^^^^^^^^^^^^
@@ -92,13 +106,13 @@ LL | union NonEmptyUnion1 {
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyUnion2` is non-empty
-  --> $DIR/empty-match.rs:82:20
+  --> $DIR/empty-match.rs:117:20
    |
 LL |     match_no_arms!((NonEmptyUnion2 { foo: () }));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyUnion2` defined here
-  --> $DIR/empty-match.rs:19:7
+  --> $DIR/empty-match.rs:26:7
    |
 LL | union NonEmptyUnion2 {
    |       ^^^^^^^^^^^^^^
@@ -106,13 +120,13 @@ LL | union NonEmptyUnion2 {
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum1::Foo(_)` not covered
-  --> $DIR/empty-match.rs:83:20
+  --> $DIR/empty-match.rs:119:20
    |
 LL |     match_no_arms!(NonEmptyEnum1::Foo(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyEnum1::Foo(_)` not covered
    |
 note: `NonEmptyEnum1` defined here
-  --> $DIR/empty-match.rs:24:5
+  --> $DIR/empty-match.rs:33:5
    |
 LL | enum NonEmptyEnum1 {
    |      -------------
@@ -122,31 +136,32 @@ LL |     Foo(bool),
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
-  --> $DIR/empty-match.rs:84:20
+  --> $DIR/empty-match.rs:122:20
    |
 LL |     match_no_arms!(NonEmptyEnum2::Foo(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
    |
 note: `NonEmptyEnum2` defined here
-  --> $DIR/empty-match.rs:27:5
+  --> $DIR/empty-match.rs:40:5
    |
 LL | enum NonEmptyEnum2 {
    |      -------------
 LL |     Foo(bool),
    |     ^^^ not covered
+...
 LL |     Bar,
    |     ^^^ not covered
    = note: the matched value is of type `NonEmptyEnum2`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or multiple match arms
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
-  --> $DIR/empty-match.rs:85:20
+  --> $DIR/empty-match.rs:125:20
    |
 LL |     match_no_arms!(NonEmptyEnum5::V1);
    |                    ^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
    |
 note: `NonEmptyEnum5` defined here
-  --> $DIR/empty-match.rs:30:6
+  --> $DIR/empty-match.rs:49:6
    |
 LL | enum NonEmptyEnum5 {
    |      ^^^^^^^^^^^^^
@@ -154,7 +169,7 @@ LL | enum NonEmptyEnum5 {
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or multiple match arms
 
 error[E0004]: non-exhaustive patterns: `_` not covered
-  --> $DIR/empty-match.rs:87:24
+  --> $DIR/empty-match.rs:129:24
    |
 LL |     match_guarded_arm!(0u8);
    |                        ^^^ pattern `_` not covered
@@ -167,13 +182,13 @@ LL +             _ => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyStruct1` not covered
-  --> $DIR/empty-match.rs:88:24
+  --> $DIR/empty-match.rs:133:24
    |
 LL |     match_guarded_arm!(NonEmptyStruct1);
    |                        ^^^^^^^^^^^^^^^ pattern `NonEmptyStruct1` not covered
    |
 note: `NonEmptyStruct1` defined here
-  --> $DIR/empty-match.rs:14:8
+  --> $DIR/empty-match.rs:15:8
    |
 LL | struct NonEmptyStruct1;
    |        ^^^^^^^^^^^^^^^
@@ -185,13 +200,13 @@ LL +             NonEmptyStruct1 => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyStruct2(_)` not covered
-  --> $DIR/empty-match.rs:89:24
+  --> $DIR/empty-match.rs:137:24
    |
 LL |     match_guarded_arm!(NonEmptyStruct2(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyStruct2(_)` not covered
    |
 note: `NonEmptyStruct2` defined here
-  --> $DIR/empty-match.rs:15:8
+  --> $DIR/empty-match.rs:18:8
    |
 LL | struct NonEmptyStruct2(bool);
    |        ^^^^^^^^^^^^^^^
@@ -203,13 +218,13 @@ LL +             NonEmptyStruct2(_) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyUnion1 { .. }` not covered
-  --> $DIR/empty-match.rs:90:24
+  --> $DIR/empty-match.rs:141:24
    |
 LL |     match_guarded_arm!((NonEmptyUnion1 { foo: () }));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyUnion1 { .. }` not covered
    |
 note: `NonEmptyUnion1` defined here
-  --> $DIR/empty-match.rs:16:7
+  --> $DIR/empty-match.rs:21:7
    |
 LL | union NonEmptyUnion1 {
    |       ^^^^^^^^^^^^^^
@@ -221,13 +236,13 @@ LL +             NonEmptyUnion1 { .. } => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyUnion2 { .. }` not covered
-  --> $DIR/empty-match.rs:91:24
+  --> $DIR/empty-match.rs:145:24
    |
 LL |     match_guarded_arm!((NonEmptyUnion2 { foo: () }));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyUnion2 { .. }` not covered
    |
 note: `NonEmptyUnion2` defined here
-  --> $DIR/empty-match.rs:19:7
+  --> $DIR/empty-match.rs:26:7
    |
 LL | union NonEmptyUnion2 {
    |       ^^^^^^^^^^^^^^
@@ -239,13 +254,13 @@ LL +             NonEmptyUnion2 { .. } => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum1::Foo(_)` not covered
-  --> $DIR/empty-match.rs:92:24
+  --> $DIR/empty-match.rs:149:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum1::Foo(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyEnum1::Foo(_)` not covered
    |
 note: `NonEmptyEnum1` defined here
-  --> $DIR/empty-match.rs:24:5
+  --> $DIR/empty-match.rs:33:5
    |
 LL | enum NonEmptyEnum1 {
    |      -------------
@@ -259,18 +274,19 @@ LL +             NonEmptyEnum1::Foo(_) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
-  --> $DIR/empty-match.rs:93:24
+  --> $DIR/empty-match.rs:153:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum2::Foo(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
    |
 note: `NonEmptyEnum2` defined here
-  --> $DIR/empty-match.rs:27:5
+  --> $DIR/empty-match.rs:40:5
    |
 LL | enum NonEmptyEnum2 {
    |      -------------
 LL |     Foo(bool),
    |     ^^^ not covered
+...
 LL |     Bar,
    |     ^^^ not covered
    = note: the matched value is of type `NonEmptyEnum2`
@@ -281,13 +297,13 @@ LL +             NonEmptyEnum2::Foo(_) | NonEmptyEnum2::Bar => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
-  --> $DIR/empty-match.rs:94:24
+  --> $DIR/empty-match.rs:157:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum5::V1);
    |                        ^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
    |
 note: `NonEmptyEnum5` defined here
-  --> $DIR/empty-match.rs:30:6
+  --> $DIR/empty-match.rs:49:6
    |
 LL | enum NonEmptyEnum5 {
    |      ^^^^^^^^^^^^^
@@ -298,6 +314,7 @@ LL ~             _ if false => {},
 LL +             _ => todo!()
    |
 
-error: aborting due to 22 previous errors
+error: aborting due to 23 previous errors
 
-For more information about this error, try `rustc --explain E0004`.
+Some errors have detailed explanations: E0004, E0005.
+For more information about an error, try `rustc --explain E0004`.
diff --git a/tests/ui/pattern/usefulness/empty-match.rs b/tests/ui/pattern/usefulness/empty-match.rs
index 9cdc0413ba1..062241faa4c 100644
--- a/tests/ui/pattern/usefulness/empty-match.rs
+++ b/tests/ui/pattern/usefulness/empty-match.rs
@@ -6,28 +6,49 @@
 #![feature(never_type_fallback)]
 #![cfg_attr(exhaustive_patterns, feature(exhaustive_patterns))]
 #![deny(unreachable_patterns)]
+//~^ NOTE the lint level is defined here
 
 extern crate empty;
 
 enum EmptyEnum {}
 
 struct NonEmptyStruct1;
+//~^ NOTE `NonEmptyStruct1` defined here
+//~| NOTE `NonEmptyStruct1` defined here
 struct NonEmptyStruct2(bool);
+//~^ NOTE `NonEmptyStruct2` defined here
+//~| NOTE `NonEmptyStruct2` defined here
 union NonEmptyUnion1 {
+    //~^ NOTE `NonEmptyUnion1` defined here
+    //~| NOTE `NonEmptyUnion1` defined here
     foo: (),
 }
 union NonEmptyUnion2 {
+    //~^ NOTE `NonEmptyUnion2` defined here
+    //~| NOTE `NonEmptyUnion2` defined here
     foo: (),
     bar: (),
 }
 enum NonEmptyEnum1 {
     Foo(bool),
+    //~^ NOTE `NonEmptyEnum1` defined here
+    //~| NOTE `NonEmptyEnum1` defined here
+    //~| NOTE not covered
+    //~| NOTE not covered
 }
 enum NonEmptyEnum2 {
     Foo(bool),
+    //~^ NOTE `NonEmptyEnum2` defined here
+    //~| NOTE `NonEmptyEnum2` defined here
+    //~| NOTE not covered
+    //~| NOTE not covered
     Bar,
+    //~^ NOTE not covered
+    //~| NOTE not covered
 }
 enum NonEmptyEnum5 {
+    //~^ NOTE `NonEmptyEnum5` defined here
+    //~| NOTE `NonEmptyEnum5` defined here
     V1, V2, V3, V4, V5,
 }
 
@@ -51,6 +72,16 @@ fn empty_foreign_enum(x: empty::EmptyForeignEnum) {
     }
 }
 
+fn empty_foreign_enum_private(x: Option<empty::SecretlyUninhabitedForeignStruct>) {
+    let None = x;
+    //~^ ERROR refutable pattern in local binding
+    //~| NOTE `let` bindings require an "irrefutable pattern"
+    //~| NOTE for more information, visit
+    //~| NOTE the matched value is of type
+    //~| NOTE pattern `Some(_)` not covered
+    //[exhaustive_patterns]~| NOTE currently uninhabited, but this variant contains private fields
+}
+
 fn never(x: !) {
     match x {} // ok
     match x {
@@ -76,20 +107,55 @@ macro_rules! match_guarded_arm {
 
 fn main() {
     match_no_arms!(0u8); //~ ERROR type `u8` is non-empty
+                         //~| NOTE the matched value is of type
     match_no_arms!(NonEmptyStruct1); //~ ERROR type `NonEmptyStruct1` is non-empty
+                                     //~| NOTE the matched value is of type
     match_no_arms!(NonEmptyStruct2(true)); //~ ERROR type `NonEmptyStruct2` is non-empty
+                                           //~| NOTE the matched value is of type
     match_no_arms!((NonEmptyUnion1 { foo: () })); //~ ERROR type `NonEmptyUnion1` is non-empty
+                                                  //~| NOTE the matched value is of type
     match_no_arms!((NonEmptyUnion2 { foo: () })); //~ ERROR type `NonEmptyUnion2` is non-empty
+                                                  //~| NOTE the matched value is of type
     match_no_arms!(NonEmptyEnum1::Foo(true)); //~ ERROR `NonEmptyEnum1::Foo(_)` not covered
+                                              //~| NOTE pattern `NonEmptyEnum1::Foo(_)` not covered
+                                              //~| NOTE the matched value is of type
     match_no_arms!(NonEmptyEnum2::Foo(true)); //~ ERROR `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
+                                              //~| NOTE patterns `NonEmptyEnum2::Foo(_)` and
+                                              //~| NOTE the matched value is of type
     match_no_arms!(NonEmptyEnum5::V1); //~ ERROR `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
+                                       //~| NOTE patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`
+                                       //~| NOTE the matched value is of type
 
     match_guarded_arm!(0u8); //~ ERROR `_` not covered
+                             //~| NOTE the matched value is of type
+                             //~| NOTE pattern `_` not covered
+                             //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!(NonEmptyStruct1); //~ ERROR `NonEmptyStruct1` not covered
+                                         //~| NOTE pattern `NonEmptyStruct1` not covered
+                                         //~| NOTE the matched value is of type
+                                         //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!(NonEmptyStruct2(true)); //~ ERROR `NonEmptyStruct2(_)` not covered
+                                               //~| NOTE the matched value is of type
+                                               //~| NOTE pattern `NonEmptyStruct2(_)` not covered
+                                               //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!((NonEmptyUnion1 { foo: () })); //~ ERROR `NonEmptyUnion1 { .. }` not covered
+                                                      //~| NOTE the matched value is of type
+                                                      //~| NOTE pattern `NonEmptyUnion1 { .. }` not covered
+                                                      //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!((NonEmptyUnion2 { foo: () })); //~ ERROR `NonEmptyUnion2 { .. }` not covered
+                                                      //~| NOTE the matched value is of type
+                                                      //~| NOTE pattern `NonEmptyUnion2 { .. }` not covered
+                                                      //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!(NonEmptyEnum1::Foo(true)); //~ ERROR `NonEmptyEnum1::Foo(_)` not covered
+                                                  //~| NOTE the matched value is of type
+                                                  //~| NOTE pattern `NonEmptyEnum1::Foo(_)` not covered
+                                                  //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!(NonEmptyEnum2::Foo(true)); //~ ERROR `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
+                                                  //~| NOTE the matched value is of type
+                                                  //~| NOTE patterns `NonEmptyEnum2::Foo(_)` and
+                                                  //~| NOTE in this expansion of match_guarded_arm!
     match_guarded_arm!(NonEmptyEnum5::V1); //~ ERROR `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
+                                           //~| NOTE the matched value is of type
+                                           //~| NOTE patterns `NonEmptyEnum5::V1`,
+                                           //~| NOTE in this expansion of match_guarded_arm!
 }