diff --git a/Cargo.lock b/Cargo.lock
index a62df06475027..ededa7c2ecfb7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4626,6 +4626,7 @@ dependencies = [
  "rustc_attr",
  "rustc_data_structures",
  "rustc_errors",
+ "rustc_feature",
  "rustc_graphviz",
  "rustc_hir",
  "rustc_hir_pretty",
diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 6e33c261a03b0..97eee56f94807 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -417,6 +417,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 || attr.has_name(sym::stable)
                 || attr.has_name(sym::rustc_const_unstable)
                 || attr.has_name(sym::rustc_const_stable)
+                || attr.has_name(sym::rustc_default_body_unstable)
             {
                 struct_span_err!(
                     self.sess,
diff --git a/compiler/rustc_attr/src/builtin.rs b/compiler/rustc_attr/src/builtin.rs
index 10a9cfb626e63..62ccd734fe720 100644
--- a/compiler/rustc_attr/src/builtin.rs
+++ b/compiler/rustc_attr/src/builtin.rs
@@ -131,6 +131,14 @@ impl ConstStability {
     }
 }
 
+/// Represents the `#[rustc_default_body_unstable]` attribute.
+#[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(HashStable_Generic)]
+pub struct DefaultBodyStability {
+    pub level: StabilityLevel,
+    pub feature: Symbol,
+}
+
 /// The available stability levels.
 #[derive(Encodable, Decodable, PartialEq, Copy, Clone, Debug, Eq, Hash)]
 #[derive(HashStable_Generic)]
@@ -214,7 +222,8 @@ pub fn find_stability(
     sess: &Session,
     attrs: &[Attribute],
     item_sp: Span,
-) -> (Option<(Stability, Span)>, Option<(ConstStability, Span)>) {
+) -> (Option<(Stability, Span)>, Option<(ConstStability, Span)>, Option<(DefaultBodyStability, Span)>)
+{
     find_stability_generic(sess, attrs.iter(), item_sp)
 }
 
@@ -222,7 +231,7 @@ fn find_stability_generic<'a, I>(
     sess: &Session,
     attrs_iter: I,
     item_sp: Span,
-) -> (Option<(Stability, Span)>, Option<(ConstStability, Span)>)
+) -> (Option<(Stability, Span)>, Option<(ConstStability, Span)>, Option<(DefaultBodyStability, Span)>)
 where
     I: Iterator<Item = &'a Attribute>,
 {
@@ -230,6 +239,7 @@ where
 
     let mut stab: Option<(Stability, Span)> = None;
     let mut const_stab: Option<(ConstStability, Span)> = None;
+    let mut body_stab: Option<(DefaultBodyStability, Span)> = None;
     let mut promotable = false;
     let mut allowed_through_unstable_modules = false;
 
@@ -243,6 +253,7 @@ where
             sym::stable,
             sym::rustc_promotable,
             sym::rustc_allowed_through_unstable_modules,
+            sym::rustc_default_body_unstable,
         ]
         .iter()
         .any(|&s| attr.has_name(s))
@@ -280,7 +291,7 @@ where
 
             let meta_name = meta.name_or_empty();
             match meta_name {
-                sym::rustc_const_unstable | sym::unstable => {
+                sym::rustc_const_unstable | sym::rustc_default_body_unstable | sym::unstable => {
                     if meta_name == sym::unstable && stab.is_some() {
                         handle_errors(
                             &sess.parse_sess,
@@ -295,6 +306,13 @@ where
                             AttrError::MultipleStabilityLevels,
                         );
                         break;
+                    } else if meta_name == sym::rustc_default_body_unstable && body_stab.is_some() {
+                        handle_errors(
+                            &sess.parse_sess,
+                            attr.span,
+                            AttrError::MultipleStabilityLevels,
+                        );
+                        break;
                     }
 
                     let mut feature = None;
@@ -405,11 +423,16 @@ where
                             };
                             if sym::unstable == meta_name {
                                 stab = Some((Stability { level, feature }, attr.span));
-                            } else {
+                            } else if sym::rustc_const_unstable == meta_name {
                                 const_stab = Some((
                                     ConstStability { level, feature, promotable: false },
                                     attr.span,
                                 ));
+                            } else if sym::rustc_default_body_unstable == meta_name {
+                                body_stab =
+                                    Some((DefaultBodyStability { level, feature }, attr.span));
+                            } else {
+                                unreachable!("Unknown stability attribute {meta_name}");
                             }
                         }
                         (None, _, _) => {
@@ -542,7 +565,7 @@ where
         }
     }
 
-    (stab, const_stab)
+    (stab, const_stab, body_stab)
 }
 
 pub fn find_crate_name(sess: &Session, attrs: &[Attribute]) -> Option<Symbol> {
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index ed2c4edf9dd72..75528d6140ce5 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -520,6 +520,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     /// Gives raw access to the `Allocation`, without bounds or alignment checks.
     /// The caller is responsible for calling the access hooks!
+    ///
+    /// You almost certainly want to use `get_ptr_alloc`/`get_ptr_alloc_mut` instead.
     fn get_alloc_raw(
         &self,
         id: AllocId,
@@ -589,6 +591,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(&self.get_alloc_raw(id)?.extra)
     }
 
+    /// Return the `mutability` field of the given allocation.
+    pub fn get_alloc_mutability<'a>(&'a self, id: AllocId) -> InterpResult<'tcx, Mutability> {
+        Ok(self.get_alloc_raw(id)?.mutability)
+    }
+
     /// Gives raw mutable access to the `Allocation`, without bounds or alignment checks.
     /// The caller is responsible for calling the access hooks!
     ///
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 6e093811fcf6e..852ea806b20ff 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -772,7 +772,7 @@ impl SyntaxExtension {
                 )
             })
             .unwrap_or_else(|| (None, helper_attrs));
-        let (stability, const_stability) = attr::find_stability(&sess, attrs, span);
+        let (stability, const_stability, body_stability) = attr::find_stability(&sess, attrs, span);
         if let Some((_, sp)) = const_stability {
             sess.parse_sess
                 .span_diagnostic
@@ -784,6 +784,17 @@ impl SyntaxExtension {
                 )
                 .emit();
         }
+        if let Some((_, sp)) = body_stability {
+            sess.parse_sess
+                .span_diagnostic
+                .struct_span_err(sp, "macros cannot have body stability attributes")
+                .span_label(sp, "invalid body stability attribute")
+                .span_label(
+                    sess.source_map().guess_head_span(span),
+                    "body stability attribute affects this macro",
+                )
+                .emit();
+        }
 
         SyntaxExtension {
             kind,
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 0e73d8fd7f600..ee46a364546a9 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -499,6 +499,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     ungated!(rustc_const_unstable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
     ungated!(rustc_const_stable, Normal, template!(List: r#"feature = "name""#), DuplicatesOk),
+    ungated!(
+        rustc_default_body_unstable, Normal,
+        template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk
+    ),
     gated!(
         allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."), DuplicatesOk,
         "allow_internal_unstable side-steps feature gating and stability checks",
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 38ce50e8323b1..61f16be1d6b24 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -207,6 +207,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     def_ident_span => { table }
     lookup_stability => { table }
     lookup_const_stability => { table }
+    lookup_default_body_stability => { table }
     lookup_deprecation_entry => { table }
     visibility => { table }
     unused_generic_params => { table }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 33278367ce32d..f68005c052635 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1029,6 +1029,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             if should_encode_stability(def_kind) {
                 self.encode_stability(def_id);
                 self.encode_const_stability(def_id);
+                self.encode_default_body_stability(def_id);
                 self.encode_deprecation(def_id);
             }
             if should_encode_variances(def_kind) {
@@ -1385,6 +1386,18 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         }
     }
 
+    fn encode_default_body_stability(&mut self, def_id: DefId) {
+        debug!("EncodeContext::encode_default_body_stability({:?})", def_id);
+
+        // The query lookup can take a measurable amount of time in crates with many items. Check if
+        // the stability attributes are even enabled before using their queries.
+        if self.feat.staged_api || self.tcx.sess.opts.unstable_opts.force_unstable_if_unmarked {
+            if let Some(stab) = self.tcx.lookup_default_body_stability(def_id) {
+                record!(self.tables.lookup_default_body_stability[def_id] <- stab)
+            }
+        }
+    }
+
     fn encode_deprecation(&mut self, def_id: DefId) {
         debug!("EncodeContext::encode_deprecation({:?})", def_id);
         if let Some(depr) = self.tcx.lookup_deprecation(def_id) {
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 66bdecc30db85..8efe5051b01cb 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -343,6 +343,7 @@ define_tables! {
     def_ident_span: Table<DefIndex, LazyValue<Span>>,
     lookup_stability: Table<DefIndex, LazyValue<attr::Stability>>,
     lookup_const_stability: Table<DefIndex, LazyValue<attr::ConstStability>>,
+    lookup_default_body_stability: Table<DefIndex, LazyValue<attr::DefaultBodyStability>>,
     lookup_deprecation_entry: Table<DefIndex, LazyValue<attr::Deprecation>>,
     // As an optimization, a missing entry indicates an empty `&[]`.
     explicit_item_bounds: Table<DefIndex, LazyArray<(ty::Predicate<'static>, Span)>>,
diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index 414912dd0f7d8..7a9ad44d1d9ae 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -5,7 +5,7 @@ pub use self::StabilityLevel::*;
 
 use crate::ty::{self, DefIdTree, TyCtxt};
 use rustc_ast::NodeId;
-use rustc_attr::{self as attr, ConstStability, Deprecation, Stability};
+use rustc_attr::{self as attr, ConstStability, DefaultBodyStability, Deprecation, Stability};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{Applicability, Diagnostic};
 use rustc_feature::GateIssue;
@@ -61,6 +61,7 @@ pub struct Index {
     /// are filled by the annotator.
     pub stab_map: FxHashMap<LocalDefId, Stability>,
     pub const_stab_map: FxHashMap<LocalDefId, ConstStability>,
+    pub default_body_stab_map: FxHashMap<LocalDefId, DefaultBodyStability>,
     pub depr_map: FxHashMap<LocalDefId, DeprecationEntry>,
     /// Mapping from feature name to feature name based on the `implied_by` field of `#[unstable]`
     /// attributes. If a `#[unstable(feature = "implier", implied_by = "impliee")]` attribute
@@ -86,6 +87,10 @@ impl Index {
         self.const_stab_map.get(&def_id).copied()
     }
 
+    pub fn local_default_body_stability(&self, def_id: LocalDefId) -> Option<DefaultBodyStability> {
+        self.default_body_stab_map.get(&def_id).copied()
+    }
+
     pub fn local_deprecation_entry(&self, def_id: LocalDefId) -> Option<DeprecationEntry> {
         self.depr_map.get(&def_id).cloned()
     }
@@ -416,6 +421,12 @@ impl<'tcx> TyCtxt<'tcx> {
             return EvalResult::Allow;
         }
 
+        // Only the cross-crate scenario matters when checking unstable APIs
+        let cross_crate = !def_id.is_local();
+        if !cross_crate {
+            return EvalResult::Allow;
+        }
+
         let stability = self.lookup_stability(def_id);
         debug!(
             "stability: \
@@ -423,12 +434,6 @@ impl<'tcx> TyCtxt<'tcx> {
             def_id, span, stability
         );
 
-        // Only the cross-crate scenario matters when checking unstable APIs
-        let cross_crate = !def_id.is_local();
-        if !cross_crate {
-            return EvalResult::Allow;
-        }
-
         // Issue #38412: private items lack stability markers.
         if skip_stability_check_due_to_privacy(self, def_id) {
             return EvalResult::Allow;
@@ -492,6 +497,62 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// Evaluates the default-impl stability of an item.
+    ///
+    /// Returns `EvalResult::Allow` if the item's default implementation is stable, or unstable but the corresponding
+    /// `#![feature]` has been provided. Returns `EvalResult::Deny` which describes the offending
+    /// unstable feature otherwise.
+    pub fn eval_default_body_stability(self, def_id: DefId, span: Span) -> EvalResult {
+        let is_staged_api = self.lookup_stability(def_id.krate.as_def_id()).is_some();
+        if !is_staged_api {
+            return EvalResult::Allow;
+        }
+
+        // Only the cross-crate scenario matters when checking unstable APIs
+        let cross_crate = !def_id.is_local();
+        if !cross_crate {
+            return EvalResult::Allow;
+        }
+
+        let stability = self.lookup_default_body_stability(def_id);
+        debug!(
+            "body stability: inspecting def_id={def_id:?} span={span:?} of stability={stability:?}"
+        );
+
+        // Issue #38412: private items lack stability markers.
+        if skip_stability_check_due_to_privacy(self, def_id) {
+            return EvalResult::Allow;
+        }
+
+        match stability {
+            Some(DefaultBodyStability {
+                level: attr::Unstable { reason, issue, is_soft, .. },
+                feature,
+            }) => {
+                if span.allows_unstable(feature) {
+                    debug!("body stability: skipping span={:?} since it is internal", span);
+                    return EvalResult::Allow;
+                }
+                if self.features().active(feature) {
+                    return EvalResult::Allow;
+                }
+
+                EvalResult::Deny {
+                    feature,
+                    reason: reason.to_opt_reason(),
+                    issue,
+                    suggestion: None,
+                    is_soft,
+                }
+            }
+            Some(_) => {
+                // Stable APIs are always ok to call
+                EvalResult::Allow
+            }
+            None => EvalResult::Unmarked,
+        }
+    }
+
     /// Checks if an item is stable or error out.
     ///
     /// If the item defined by `def_id` is unstable and the corresponding `#![feature]` does not
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index d8483e7e40914..cfc75f673c8f5 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1094,6 +1094,11 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    query lookup_default_body_stability(def_id: DefId) -> Option<attr::DefaultBodyStability> {
+        desc { |tcx| "looking up default body stability of `{}`", tcx.def_path_str(def_id) }
+        separate_provide_extern
+    }
+
     query should_inherit_track_caller(def_id: DefId) -> bool {
         desc { |tcx| "computing should_inherit_track_caller of `{}`", tcx.def_path_str(def_id) }
     }
@@ -1951,6 +1956,14 @@ rustc_queries! {
         }
     }
 
+    query is_impossible_method(key: (DefId, DefId)) -> bool {
+        desc { |tcx|
+            "checking if {} is impossible to call within {}",
+            tcx.def_path_str(key.1),
+            tcx.def_path_str(key.0),
+        }
+    }
+
     query method_autoderef_steps(
         goal: CanonicalTyGoal<'tcx>
     ) -> MethodAutoderefStepsResult<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/parameterized.rs b/compiler/rustc_middle/src/ty/parameterized.rs
index e189ee2fc4db1..ae6e2eecbffb5 100644
--- a/compiler/rustc_middle/src/ty/parameterized.rs
+++ b/compiler/rustc_middle/src/ty/parameterized.rs
@@ -64,6 +64,7 @@ trivially_parameterized_over_tcx! {
     rustc_ast::Attribute,
     rustc_ast::MacArgs,
     rustc_attr::ConstStability,
+    rustc_attr::DefaultBodyStability,
     rustc_attr::Deprecation,
     rustc_attr::Stability,
     rustc_hir::Constness,
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 063c076474e90..69a8c98b27a3d 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -849,22 +849,22 @@ fn non_exhaustive_match<'p, 'tcx>(
             ));
         }
         [.., prev, last] if prev.span.eq_ctxt(last.span) => {
-            if let Ok(snippet) = sm.span_to_snippet(prev.span.between(last.span)) {
-                let comma = if matches!(last.body.kind, hir::ExprKind::Block(..))
-                    && last.span.eq_ctxt(last.body.span)
-                {
-                    ""
-                } else {
-                    ","
-                };
+            let comma = if matches!(last.body.kind, hir::ExprKind::Block(..))
+                && last.span.eq_ctxt(last.body.span)
+            {
+                ""
+            } else {
+                ","
+            };
+            let spacing = if sm.is_multiline(prev.span.between(last.span)) {
+                sm.indentation_before(last.span).map(|indent| format!("\n{indent}"))
+            } else {
+                Some(" ".to_string())
+            };
+            if let Some(spacing) = spacing {
                 suggestion = Some((
                     last.span.shrink_to_hi(),
-                    format!(
-                        "{}{}{} => todo!()",
-                        comma,
-                        snippet.strip_prefix(',').unwrap_or(&snippet),
-                        pattern
-                    ),
+                    format!("{}{}{} => todo!()", comma, spacing, pattern),
                 ));
             }
         }
diff --git a/compiler/rustc_passes/src/lib_features.rs b/compiler/rustc_passes/src/lib_features.rs
index e05994f13e4d9..868887c66cdec 100644
--- a/compiler/rustc_passes/src/lib_features.rs
+++ b/compiler/rustc_passes/src/lib_features.rs
@@ -29,11 +29,16 @@ impl<'tcx> LibFeatureCollector<'tcx> {
     }
 
     fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
-        let stab_attrs =
-            [sym::stable, sym::unstable, sym::rustc_const_stable, sym::rustc_const_unstable];
+        let stab_attrs = [
+            sym::stable,
+            sym::unstable,
+            sym::rustc_const_stable,
+            sym::rustc_const_unstable,
+            sym::rustc_default_body_unstable,
+        ];
 
         // Find a stability attribute: one of #[stable(…)], #[unstable(…)],
-        // #[rustc_const_stable(…)], or #[rustc_const_unstable(…)].
+        // #[rustc_const_stable(…)], #[rustc_const_unstable(…)] or #[rustc_default_body_unstable].
         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
             let meta_kind = attr.meta_kind();
             if let Some(MetaItemKind::List(ref metas)) = meta_kind {
@@ -53,8 +58,12 @@ impl<'tcx> LibFeatureCollector<'tcx> {
                     // This additional check for stability is to make sure we
                     // don't emit additional, irrelevant errors for malformed
                     // attributes.
-                    let is_unstable =
-                        matches!(*stab_attr, sym::unstable | sym::rustc_const_unstable);
+                    let is_unstable = matches!(
+                        *stab_attr,
+                        sym::unstable
+                            | sym::rustc_const_unstable
+                            | sym::rustc_default_body_unstable
+                    );
                     if since.is_some() || is_unstable {
                         return Some((feature, since, attr.span));
                     }
diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index ca6a2ac3db34c..be920601ee43f 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -1,8 +1,9 @@
 //! A pass that annotates every item and method with its stability level,
 //! propagating default levels lexically from parent to children ast nodes.
 
-use attr::StabilityLevel;
-use rustc_attr::{self as attr, ConstStability, Stability, Unstable, UnstableReason};
+use rustc_attr::{
+    self as attr, ConstStability, Stability, StabilityLevel, Unstable, UnstableReason,
+};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_errors::{struct_span_err, Applicability};
 use rustc_hir as hir;
@@ -161,7 +162,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             return;
         }
 
-        let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
+        let (stab, const_stab, body_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
         let mut const_span = None;
 
         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
@@ -209,6 +210,13 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             }
         }
 
+        if let Some((body_stab, _span)) = body_stab {
+            // FIXME: check that this item can have body stability
+
+            self.index.default_body_stab_map.insert(def_id, body_stab);
+            debug!(?self.index.default_body_stab_map);
+        }
+
         let stab = stab.map(|(stab, span)| {
             // Error if prohibited, or can't inherit anything from a container.
             if kind == AnnotationKind::Prohibited
@@ -613,6 +621,7 @@ fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
     let mut index = Index {
         stab_map: Default::default(),
         const_stab_map: Default::default(),
+        default_body_stab_map: Default::default(),
         depr_map: Default::default(),
         implications: Default::default(),
     };
@@ -673,6 +682,9 @@ pub(crate) fn provide(providers: &mut Providers) {
         stability_implications: |tcx, _| tcx.stability().implications.clone(),
         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
+        lookup_default_body_stability: |tcx, id| {
+            tcx.stability().local_default_body_stability(id.expect_local())
+        },
         lookup_deprecation_entry: |tcx, id| {
             tcx.stability().local_deprecation_entry(id.expect_local())
         },
@@ -723,7 +735,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                 let features = self.tcx.features();
                 if features.staged_api {
                     let attrs = self.tcx.hir().attrs(item.hir_id());
-                    let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item.span);
+                    let (stab, const_stab, _) =
+                        attr::find_stability(&self.tcx.sess, attrs, item.span);
 
                     // If this impl block has an #[unstable] attribute, give an
                     // error if all involved types and traits are stable, because
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 8839fb1a15120..325b0458638af 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -2544,12 +2544,15 @@ fn show_candidates(
                 Applicability::MaybeIncorrect,
             );
             if let [first, .., last] = &path[..] {
-                err.span_suggestion_verbose(
-                    first.ident.span.until(last.ident.span),
-                    &format!("if you import `{}`, refer to it directly", last.ident),
-                    "",
-                    Applicability::Unspecified,
-                );
+                let sp = first.ident.span.until(last.ident.span);
+                if sp.can_be_used_for_suggestions() {
+                    err.span_suggestion_verbose(
+                        sp,
+                        &format!("if you import `{}`, refer to it directly", last.ident),
+                        "",
+                        Applicability::Unspecified,
+                    );
+                }
             }
         } else {
             msg.push(':');
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index f81a69c1cce0a..2f3519e3edd77 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1218,6 +1218,7 @@ symbols! {
         rustc_conversion_suggestion,
         rustc_deallocator,
         rustc_def_path,
+        rustc_default_body_unstable,
         rustc_diagnostic_item,
         rustc_diagnostic_macros,
         rustc_dirty,
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 2e5400c42d0f8..b6d6df1eec6a1 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -34,7 +34,10 @@ use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
 use rustc_middle::ty::visit::TypeVisitable;
-use rustc_middle::ty::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry};
+use rustc_middle::ty::{
+    self, DefIdTree, GenericParamDefKind, Subst, ToPredicate, Ty, TyCtxt, TypeSuperVisitable,
+    VtblEntry,
+};
 use rustc_span::{sym, Span};
 use smallvec::SmallVec;
 
@@ -503,6 +506,77 @@ fn subst_and_check_impossible_predicates<'tcx>(
     result
 }
 
+/// Checks whether a trait's method is impossible to call on a given impl.
+///
+/// This only considers predicates that reference the impl's generics, and not
+/// those that reference the method's generics.
+fn is_impossible_method<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    (impl_def_id, trait_item_def_id): (DefId, DefId),
+) -> bool {
+    struct ReferencesOnlyParentGenerics<'tcx> {
+        tcx: TyCtxt<'tcx>,
+        generics: &'tcx ty::Generics,
+        trait_item_def_id: DefId,
+    }
+    impl<'tcx> ty::TypeVisitor<'tcx> for ReferencesOnlyParentGenerics<'tcx> {
+        type BreakTy = ();
+        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
+            // If this is a parameter from the trait item's own generics, then bail
+            if let ty::Param(param) = t.kind()
+                && let param_def_id = self.generics.type_param(param, self.tcx).def_id
+                && self.tcx.parent(param_def_id) == self.trait_item_def_id
+            {
+                return ControlFlow::BREAK;
+            }
+            t.super_visit_with(self)
+        }
+        fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
+            if let ty::ReEarlyBound(param) = r.kind()
+                && let param_def_id = self.generics.region_param(&param, self.tcx).def_id
+                && self.tcx.parent(param_def_id) == self.trait_item_def_id
+            {
+                return ControlFlow::BREAK;
+            }
+            r.super_visit_with(self)
+        }
+        fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
+            if let ty::ConstKind::Param(param) = ct.kind()
+                && let param_def_id = self.generics.const_param(&param, self.tcx).def_id
+                && self.tcx.parent(param_def_id) == self.trait_item_def_id
+            {
+                return ControlFlow::BREAK;
+            }
+            ct.super_visit_with(self)
+        }
+    }
+
+    let generics = tcx.generics_of(trait_item_def_id);
+    let predicates = tcx.predicates_of(trait_item_def_id);
+    let impl_trait_ref =
+        tcx.impl_trait_ref(impl_def_id).expect("expected impl to correspond to trait");
+    let param_env = tcx.param_env(impl_def_id);
+
+    let mut visitor = ReferencesOnlyParentGenerics { tcx, generics, trait_item_def_id };
+    let predicates_for_trait = predicates.predicates.iter().filter_map(|(pred, span)| {
+        if pred.visit_with(&mut visitor).is_continue() {
+            Some(Obligation::new(
+                ObligationCause::dummy_with_span(*span),
+                param_env,
+                ty::EarlyBinder(*pred).subst(tcx, impl_trait_ref.substs),
+            ))
+        } else {
+            None
+        }
+    });
+
+    tcx.infer_ctxt().ignoring_regions().enter(|ref infcx| {
+        let mut fulfill_ctxt = <dyn TraitEngine<'_>>::new(tcx);
+        fulfill_ctxt.register_predicate_obligations(infcx, predicates_for_trait);
+        !fulfill_ctxt.select_all_or_error(infcx).is_empty()
+    })
+}
+
 #[derive(Clone, Debug)]
 enum VtblSegment<'tcx> {
     MetadataDSA,
@@ -883,6 +957,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
         vtable_entries,
         vtable_trait_upcasting_coercion_new_vptr_slot,
         subst_and_check_impossible_predicates,
+        is_impossible_method,
         try_unify_abstract_consts: |tcx, param_env_and| {
             let (param_env, (a, b)) = param_env_and.into_parts();
             const_evaluatable::try_unify_abstract_consts(tcx, (a, b), param_env)
diff --git a/compiler/rustc_typeck/Cargo.toml b/compiler/rustc_typeck/Cargo.toml
index faf52e2695a33..cae29c1d3c5f9 100644
--- a/compiler/rustc_typeck/Cargo.toml
+++ b/compiler/rustc_typeck/Cargo.toml
@@ -30,3 +30,4 @@ rustc_ty_utils = { path = "../rustc_ty_utils" }
 rustc_lint = { path = "../rustc_lint" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_type_ir = { path = "../rustc_type_ir" }
+rustc_feature = { path = "../rustc_feature" }
diff --git a/compiler/rustc_typeck/src/check/check.rs b/compiler/rustc_typeck/src/check/check.rs
index c5fa8a5db0312..6e3ef15f88433 100644
--- a/compiler/rustc_typeck/src/check/check.rs
+++ b/compiler/rustc_typeck/src/check/check.rs
@@ -18,6 +18,7 @@ use rustc_infer::infer::{DefiningAnchor, RegionVariableOrigin, TyCtxtInferExt};
 use rustc_infer::traits::Obligation;
 use rustc_lint::builtin::REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS;
 use rustc_middle::hir::nested_filter;
+use rustc_middle::middle::stability::EvalResult;
 use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
 use rustc_middle::ty::subst::GenericArgKind;
 use rustc_middle::ty::util::{Discr, IntTypeExt};
@@ -1103,12 +1104,28 @@ fn check_impl_items_against_trait<'tcx>(
                 missing_items.push(tcx.associated_item(trait_item_id));
             }
 
-            if let Some(required_items) = &must_implement_one_of {
-                // true if this item is specifically implemented in this impl
-                let is_implemented_here = ancestors
-                    .leaf_def(tcx, trait_item_id)
-                    .map_or(false, |node_item| !node_item.defining_node.is_from_trait());
+            // true if this item is specifically implemented in this impl
+            let is_implemented_here = ancestors
+                .leaf_def(tcx, trait_item_id)
+                .map_or(false, |node_item| !node_item.defining_node.is_from_trait());
+
+            if !is_implemented_here {
+                match tcx.eval_default_body_stability(trait_item_id, full_impl_span) {
+                    EvalResult::Deny { feature, reason, issue, .. } => default_body_is_unstable(
+                        tcx,
+                        full_impl_span,
+                        trait_item_id,
+                        feature,
+                        reason,
+                        issue,
+                    ),
 
+                    // Unmarked default bodies are considered stable (at least for now).
+                    EvalResult::Allow | EvalResult::Unmarked => {}
+                }
+            }
+
+            if let Some(required_items) = &must_implement_one_of {
                 if is_implemented_here {
                     let trait_item = tcx.associated_item(trait_item_id);
                     if required_items.contains(&trait_item.ident(tcx)) {
diff --git a/compiler/rustc_typeck/src/check/coercion.rs b/compiler/rustc_typeck/src/check/coercion.rs
index 21d0a7869d68e..540a8c3a83d95 100644
--- a/compiler/rustc_typeck/src/check/coercion.rs
+++ b/compiler/rustc_typeck/src/check/coercion.rs
@@ -1589,11 +1589,11 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
     ) {
         let hir::ExprKind::Loop(_, _, _, loop_span) = expr.kind else { return;};
         let mut span: MultiSpan = vec![loop_span].into();
-        span.push_span_label(loop_span, "this might have zero elements to iterate on".to_string());
+        span.push_span_label(loop_span, "this might have zero elements to iterate on");
         for ret_expr in ret_exprs {
             span.push_span_label(
                 ret_expr.span,
-                "if the loop doesn't execute, this value would never get returned".to_string(),
+                "if the loop doesn't execute, this value would never get returned",
             );
         }
         err.span_note(
diff --git a/compiler/rustc_typeck/src/check/mod.rs b/compiler/rustc_typeck/src/check/mod.rs
index 199277abbc484..b73d9a9eb7599 100644
--- a/compiler/rustc_typeck/src/check/mod.rs
+++ b/compiler/rustc_typeck/src/check/mod.rs
@@ -121,13 +121,14 @@ use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::source_map::DUMMY_SP;
 use rustc_span::symbol::{kw, Ident};
-use rustc_span::{self, BytePos, Span};
+use rustc_span::{self, BytePos, Span, Symbol};
 use rustc_target::abi::VariantIdx;
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits;
 use rustc_trait_selection::traits::error_reporting::recursive_type_with_infinite_size_error;
 use rustc_trait_selection::traits::error_reporting::suggestions::ReturnsVisitor;
 use std::cell::RefCell;
+use std::num::NonZeroU32;
 
 use crate::require_c_abi_if_c_variadic;
 use crate::util::common::indenter;
@@ -661,6 +662,37 @@ fn missing_items_must_implement_one_of_err(
     err.emit();
 }
 
+fn default_body_is_unstable(
+    tcx: TyCtxt<'_>,
+    impl_span: Span,
+    item_did: DefId,
+    feature: Symbol,
+    reason: Option<Symbol>,
+    issue: Option<NonZeroU32>,
+) {
+    let missing_item_name = &tcx.associated_item(item_did).name;
+    let use_of_unstable_library_feature_note = match reason {
+        Some(r) => format!("use of unstable library feature '{feature}': {r}"),
+        None => format!("use of unstable library feature '{feature}'"),
+    };
+
+    let mut err = struct_span_err!(
+        tcx.sess,
+        impl_span,
+        E0046,
+        "not all trait items implemented, missing: `{missing_item_name}`",
+    );
+    err.note(format!("default implementation of `{missing_item_name}` is unstable"));
+    err.note(use_of_unstable_library_feature_note);
+    rustc_session::parse::add_feature_diagnostics_for_issue(
+        &mut err,
+        &tcx.sess.parse_sess,
+        feature,
+        rustc_feature::GateIssue::Library(issue),
+    );
+    err.emit();
+}
+
 /// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
 fn bounds_from_generic_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 197821f034f89..ed1d883d0dca6 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -628,6 +628,10 @@ impl Step for Miri {
             cargo.env("MIRI_HOST_SYSROOT", sysroot);
             cargo.env("RUSTC_LIB_PATH", builder.rustc_libdir(compiler));
             cargo.env("MIRI", miri);
+            // propagate --bless
+            if builder.config.cmd.bless() {
+                cargo.env("MIRI_BLESS", "Gesundheit");
+            }
 
             cargo.arg("--").args(builder.config.cmd.test_args());
 
diff --git a/src/etc/check_missing_items.py b/src/etc/check_missing_items.py
index 343dd0387f479..a705e2384959f 100644
--- a/src/etc/check_missing_items.py
+++ b/src/etc/check_missing_items.py
@@ -88,8 +88,8 @@ def check_type(ty):
                         for bound in binding["binding"]["constraint"]:
                             check_generic_bound(bound)
             elif "parenthesized" in args:
-                for ty in args["parenthesized"]["inputs"]:
-                    check_type(ty)
+                for input_ty in args["parenthesized"]["inputs"]:
+                    check_type(input_ty)
                 if args["parenthesized"]["output"]:
                     check_type(args["parenthesized"]["output"])
         if not valid_id(ty["inner"]["id"]):
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index a262c8f7d1948..ae7d8c108d3ee 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -1550,6 +1550,15 @@ fn render_impl(
         rendering_params: ImplRenderingParameters,
     ) {
         for trait_item in &t.items {
+            // Skip over any default trait items that are impossible to call
+            // (e.g. if it has a `Self: Sized` bound on an unsized type).
+            if let Some(impl_def_id) = parent.item_id.as_def_id()
+                && let Some(trait_item_def_id) = trait_item.item_id.as_def_id()
+                && cx.tcx().is_impossible_method((impl_def_id, trait_item_def_id))
+            {
+                continue;
+            }
+
             let n = trait_item.name;
             if i.items.iter().any(|m| m.name == n) {
                 continue;
diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
index 716a4c9ea4319..8caba8cb9029c 100644
--- a/src/librustdoc/json/conversions.rs
+++ b/src/librustdoc/json/conversions.rs
@@ -119,6 +119,16 @@ where
     }
 }
 
+impl<I, T, U> FromWithTcx<I> for Vec<U>
+where
+    I: IntoIterator<Item = T>,
+    U: FromWithTcx<T>,
+{
+    fn from_tcx(f: I, tcx: TyCtxt<'_>) -> Vec<U> {
+        f.into_iter().map(|x| x.into_tcx(tcx)).collect()
+    }
+}
+
 pub(crate) fn from_deprecation(deprecation: rustc_attr::Deprecation) -> Deprecation {
     #[rustfmt::skip]
     let rustc_attr::Deprecation { since, note, is_since_rustc_version: _, suggestion: _ } = deprecation;
@@ -130,11 +140,11 @@ impl FromWithTcx<clean::GenericArgs> for GenericArgs {
         use clean::GenericArgs::*;
         match args {
             AngleBracketed { args, bindings } => GenericArgs::AngleBracketed {
-                args: args.into_vec().into_iter().map(|a| a.into_tcx(tcx)).collect(),
-                bindings: bindings.into_iter().map(|a| a.into_tcx(tcx)).collect(),
+                args: args.into_vec().into_tcx(tcx),
+                bindings: bindings.into_tcx(tcx),
             },
             Parenthesized { inputs, output } => GenericArgs::Parenthesized {
-                inputs: inputs.into_vec().into_iter().map(|a| a.into_tcx(tcx)).collect(),
+                inputs: inputs.into_vec().into_tcx(tcx),
                 output: output.map(|a| (*a).into_tcx(tcx)),
             },
         }
@@ -145,7 +155,7 @@ impl FromWithTcx<clean::GenericArg> for GenericArg {
     fn from_tcx(arg: clean::GenericArg, tcx: TyCtxt<'_>) -> Self {
         use clean::GenericArg::*;
         match arg {
-            Lifetime(l) => GenericArg::Lifetime(l.0.to_string()),
+            Lifetime(l) => GenericArg::Lifetime(convert_lifetime(l)),
             Type(t) => GenericArg::Type(t.into_tcx(tcx)),
             Const(box c) => GenericArg::Const(c.into_tcx(tcx)),
             Infer => GenericArg::Infer,
@@ -177,9 +187,7 @@ impl FromWithTcx<clean::TypeBindingKind> for TypeBindingKind {
         use clean::TypeBindingKind::*;
         match kind {
             Equality { term } => TypeBindingKind::Equality(term.into_tcx(tcx)),
-            Constraint { bounds } => {
-                TypeBindingKind::Constraint(bounds.into_iter().map(|a| a.into_tcx(tcx)).collect())
-            }
+            Constraint { bounds } => TypeBindingKind::Constraint(bounds.into_tcx(tcx)),
         }
     }
 }
@@ -244,7 +252,7 @@ fn from_clean_item(item: clean::Item, tcx: TyCtxt<'_>) -> ItemEnum {
         TraitAliasItem(t) => ItemEnum::TraitAlias(t.into_tcx(tcx)),
         MethodItem(m, _) => ItemEnum::Method(from_function_method(m, true, header.unwrap(), tcx)),
         TyMethodItem(m) => ItemEnum::Method(from_function_method(m, false, header.unwrap(), tcx)),
-        ImplItem(i) => ItemEnum::Impl(i.into_tcx(tcx)),
+        ImplItem(i) => ItemEnum::Impl((*i).into_tcx(tcx)),
         StaticItem(s) => ItemEnum::Static(s.into_tcx(tcx)),
         ForeignStaticItem(s) => ItemEnum::Static(s.into_tcx(tcx)),
         ForeignTypeItem => ItemEnum::ForeignType,
@@ -260,12 +268,12 @@ fn from_clean_item(item: clean::Item, tcx: TyCtxt<'_>) -> ItemEnum {
         }
         TyAssocTypeItem(g, b) => ItemEnum::AssocType {
             generics: (*g).into_tcx(tcx),
-            bounds: b.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+            bounds: b.into_tcx(tcx),
             default: None,
         },
         AssocTypeItem(t, b) => ItemEnum::AssocType {
             generics: t.generics.into_tcx(tcx),
-            bounds: b.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+            bounds: b.into_tcx(tcx),
             default: Some(t.item_type.unwrap_or(t.type_).into_tcx(tcx)),
         },
         // `convert_item` early returns `None` for stripped items and keywords.
@@ -347,15 +355,15 @@ fn convert_abi(a: RustcAbi) -> Abi {
     }
 }
 
+fn convert_lifetime(l: clean::Lifetime) -> String {
+    l.0.to_string()
+}
+
 impl FromWithTcx<clean::Generics> for Generics {
     fn from_tcx(generics: clean::Generics, tcx: TyCtxt<'_>) -> Self {
         Generics {
-            params: generics.params.into_iter().map(|x| x.into_tcx(tcx)).collect(),
-            where_predicates: generics
-                .where_predicates
-                .into_iter()
-                .map(|x| x.into_tcx(tcx))
-                .collect(),
+            params: generics.params.into_tcx(tcx),
+            where_predicates: generics.where_predicates.into_tcx(tcx),
         }
     }
 }
@@ -374,10 +382,10 @@ impl FromWithTcx<clean::GenericParamDefKind> for GenericParamDefKind {
         use clean::GenericParamDefKind::*;
         match kind {
             Lifetime { outlives } => GenericParamDefKind::Lifetime {
-                outlives: outlives.into_iter().map(|lt| lt.0.to_string()).collect(),
+                outlives: outlives.into_iter().map(convert_lifetime).collect(),
             },
             Type { did: _, bounds, default, synthetic } => GenericParamDefKind::Type {
-                bounds: bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+                bounds: bounds.into_tcx(tcx),
                 default: default.map(|x| (*x).into_tcx(tcx)),
                 synthetic,
             },
@@ -395,7 +403,7 @@ impl FromWithTcx<clean::WherePredicate> for WherePredicate {
         match predicate {
             BoundPredicate { ty, bounds, bound_params } => WherePredicate::BoundPredicate {
                 type_: ty.into_tcx(tcx),
-                bounds: bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+                bounds: bounds.into_tcx(tcx),
                 generic_params: bound_params
                     .into_iter()
                     .map(|x| GenericParamDef {
@@ -405,8 +413,8 @@ impl FromWithTcx<clean::WherePredicate> for WherePredicate {
                     .collect(),
             },
             RegionPredicate { lifetime, bounds } => WherePredicate::RegionPredicate {
-                lifetime: lifetime.0.to_string(),
-                bounds: bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+                lifetime: convert_lifetime(lifetime),
+                bounds: bounds.into_tcx(tcx),
             },
             EqPredicate { lhs, rhs } => {
                 WherePredicate::EqPredicate { lhs: lhs.into_tcx(tcx), rhs: rhs.into_tcx(tcx) }
@@ -424,11 +432,11 @@ impl FromWithTcx<clean::GenericBound> for GenericBound {
                 let trait_ = clean::Type::Path { path: trait_ }.into_tcx(tcx);
                 GenericBound::TraitBound {
                     trait_,
-                    generic_params: generic_params.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+                    generic_params: generic_params.into_tcx(tcx),
                     modifier: from_trait_bound_modifier(modifier),
                 }
             }
-            Outlives(lifetime) => GenericBound::Outlives(lifetime.0.to_string()),
+            Outlives(lifetime) => GenericBound::Outlives(convert_lifetime(lifetime)),
         }
     }
 }
@@ -447,8 +455,8 @@ pub(crate) fn from_trait_bound_modifier(
 impl FromWithTcx<clean::Type> for Type {
     fn from_tcx(ty: clean::Type, tcx: TyCtxt<'_>) -> Self {
         use clean::Type::{
-            Array, BareFunction, BorrowedRef, DynTrait, Generic, ImplTrait, Infer, Primitive,
-            QPath, RawPointer, Slice, Tuple,
+            Array, BareFunction, BorrowedRef, Generic, ImplTrait, Infer, Primitive, QPath,
+            RawPointer, Slice, Tuple,
         };
 
         match ty {
@@ -458,40 +466,24 @@ impl FromWithTcx<clean::Type> for Type {
                 args: path.segments.last().map(|args| Box::new(args.clone().args.into_tcx(tcx))),
                 param_names: Vec::new(),
             },
-            DynTrait(mut bounds, lt) => {
-                let first_trait = bounds.remove(0).trait_;
-
-                Type::ResolvedPath {
-                    name: first_trait.whole_name(),
-                    id: from_item_id(first_trait.def_id().into(), tcx),
-                    args: first_trait
-                        .segments
-                        .last()
-                        .map(|args| Box::new(args.clone().args.into_tcx(tcx))),
-                    param_names: bounds
-                        .into_iter()
-                        .map(|t| {
-                            clean::GenericBound::TraitBound(t, rustc_hir::TraitBoundModifier::None)
-                        })
-                        .chain(lt.map(clean::GenericBound::Outlives))
-                        .map(|bound| bound.into_tcx(tcx))
-                        .collect(),
-                }
-            }
+            clean::Type::DynTrait(bounds, lt) => Type::DynTrait(DynTrait {
+                lifetime: lt.map(convert_lifetime),
+                traits: bounds.into_tcx(tcx),
+            }),
             Generic(s) => Type::Generic(s.to_string()),
             Primitive(p) => Type::Primitive(p.as_sym().to_string()),
             BareFunction(f) => Type::FunctionPointer(Box::new((*f).into_tcx(tcx))),
-            Tuple(t) => Type::Tuple(t.into_iter().map(|x| x.into_tcx(tcx)).collect()),
+            Tuple(t) => Type::Tuple(t.into_tcx(tcx)),
             Slice(t) => Type::Slice(Box::new((*t).into_tcx(tcx))),
             Array(t, s) => Type::Array { type_: Box::new((*t).into_tcx(tcx)), len: s },
-            ImplTrait(g) => Type::ImplTrait(g.into_iter().map(|x| x.into_tcx(tcx)).collect()),
+            ImplTrait(g) => Type::ImplTrait(g.into_tcx(tcx)),
             Infer => Type::Infer,
             RawPointer(mutability, type_) => Type::RawPointer {
                 mutable: mutability == ast::Mutability::Mut,
                 type_: Box::new((*type_).into_tcx(tcx)),
             },
             BorrowedRef { lifetime, mutability, type_ } => Type::BorrowedRef {
-                lifetime: lifetime.map(|l| l.0.to_string()),
+                lifetime: lifetime.map(convert_lifetime),
                 mutable: mutability == ast::Mutability::Mut,
                 type_: Box::new((*type_).into_tcx(tcx)),
             },
@@ -528,7 +520,7 @@ impl FromWithTcx<clean::BareFunctionDecl> for FunctionPointer {
                 async_: false,
                 abi: convert_abi(abi),
             },
-            generic_params: generic_params.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+            generic_params: generic_params.into_tcx(tcx),
             decl: decl.into_tcx(tcx),
         }
     }
@@ -562,16 +554,28 @@ impl FromWithTcx<clean::Trait> for Trait {
             is_unsafe,
             items: ids(items, tcx),
             generics: generics.into_tcx(tcx),
-            bounds: bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
+            bounds: bounds.into_tcx(tcx),
             implementations: Vec::new(), // Added in JsonRenderer::item
         }
     }
 }
 
-impl FromWithTcx<Box<clean::Impl>> for Impl {
-    fn from_tcx(impl_: Box<clean::Impl>, tcx: TyCtxt<'_>) -> Self {
+impl FromWithTcx<clean::PolyTrait> for PolyTrait {
+    fn from_tcx(
+        clean::PolyTrait { trait_, generic_params }: clean::PolyTrait,
+        tcx: TyCtxt<'_>,
+    ) -> Self {
+        PolyTrait {
+            trait_: clean::Type::Path { path: trait_ }.into_tcx(tcx),
+            generic_params: generic_params.into_tcx(tcx),
+        }
+    }
+}
+
+impl FromWithTcx<clean::Impl> for Impl {
+    fn from_tcx(impl_: clean::Impl, tcx: TyCtxt<'_>) -> Self {
         let provided_trait_methods = impl_.provided_trait_methods(tcx);
-        let clean::Impl { unsafety, generics, trait_, for_, items, polarity, kind } = *impl_;
+        let clean::Impl { unsafety, generics, trait_, for_, items, polarity, kind } = impl_;
         // FIXME: should `trait_` be a clean::Path equivalent in JSON?
         let trait_ = trait_.map(|path| clean::Type::Path { path }.into_tcx(tcx));
         // FIXME: use something like ImplKind in JSON?
@@ -730,10 +734,7 @@ impl FromWithTcx<Box<clean::Typedef>> for Typedef {
 
 impl FromWithTcx<clean::OpaqueTy> for OpaqueTy {
     fn from_tcx(opaque: clean::OpaqueTy, tcx: TyCtxt<'_>) -> Self {
-        OpaqueTy {
-            bounds: opaque.bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
-            generics: opaque.generics.into_tcx(tcx),
-        }
+        OpaqueTy { bounds: opaque.bounds.into_tcx(tcx), generics: opaque.generics.into_tcx(tcx) }
     }
 }
 
@@ -749,10 +750,7 @@ impl FromWithTcx<clean::Static> for Static {
 
 impl FromWithTcx<clean::TraitAlias> for TraitAlias {
     fn from_tcx(alias: clean::TraitAlias, tcx: TyCtxt<'_>) -> Self {
-        TraitAlias {
-            generics: alias.generics.into_tcx(tcx),
-            params: alias.bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
-        }
+        TraitAlias { generics: alias.generics.into_tcx(tcx), params: alias.bounds.into_tcx(tcx) }
     }
 }
 
diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
index 761e94c7ebbc4..bd4ea98441d66 100644
--- a/src/rustdoc-json-types/lib.rs
+++ b/src/rustdoc-json-types/lib.rs
@@ -9,7 +9,7 @@ use std::path::PathBuf;
 use serde::{Deserialize, Serialize};
 
 /// rustdoc format-version.
-pub const FORMAT_VERSION: u32 = 16;
+pub const FORMAT_VERSION: u32 = 17;
 
 /// A `Crate` is the root of the emitted JSON blob. It contains all type/documentation information
 /// about the language items in the local crate, as well as info about external items to allow
@@ -115,6 +115,35 @@ pub enum Visibility {
     },
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct DynTrait {
+    /// All the traits implemented. One of them is the vtable, and the rest must be auto traits.
+    pub traits: Vec<PolyTrait>,
+    /// The lifetime of the whole dyn object
+    /// ```text
+    /// dyn Debug + 'static
+    ///             ^^^^^^^
+    ///             |
+    ///             this part
+    /// ```
+    pub lifetime: Option<String>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+/// A trait and potential HRTBs
+pub struct PolyTrait {
+    #[serde(rename = "trait")]
+    pub trait_: Type,
+    /// Used for Higher-Rank Trait Bounds (HRTBs)
+    /// ```text
+    /// dyn for<'a> Fn() -> &'a i32"
+    ///     ^^^^^^^
+    ///       |
+    ///       this part
+    /// ```
+    pub generic_params: Vec<GenericParamDef>,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum GenericArgs {
@@ -395,7 +424,7 @@ pub enum WherePredicate {
         type_: Type,
         bounds: Vec<GenericBound>,
         /// Used for Higher-Rank Trait Bounds (HRTBs)
-        /// ```plain
+        /// ```text
         /// where for<'a> &'a T: Iterator,"
         ///       ^^^^^^^
         ///       |
@@ -420,7 +449,7 @@ pub enum GenericBound {
         #[serde(rename = "trait")]
         trait_: Type,
         /// Used for Higher-Rank Trait Bounds (HRTBs)
-        /// ```plain
+        /// ```text
         /// where F: for<'a, 'b> Fn(&'a u8, &'b u8)
         ///          ^^^^^^^^^^^
         ///          |
@@ -458,6 +487,7 @@ pub enum Type {
         args: Option<Box<GenericArgs>>,
         param_names: Vec<GenericBound>,
     },
+    DynTrait(DynTrait),
     /// Parameterized types
     Generic(String),
     /// Fixed-size numeric types (plus int/usize/float), char, arrays, slices, and tuples
@@ -505,7 +535,7 @@ pub enum Type {
 pub struct FunctionPointer {
     pub decl: FnDecl,
     /// Used for Higher-Rank Trait Bounds (HRTBs)
-    /// ```plain
+    /// ```text
     /// for<'c> fn(val: &'c i32) -> i32
     /// ^^^^^^^
     ///       |
diff --git a/src/test/rustdoc-json/type/dyn.rs b/src/test/rustdoc-json/type/dyn.rs
index f53dc03f4b47f..c18b54d1fdf0e 100644
--- a/src/test/rustdoc-json/type/dyn.rs
+++ b/src/test/rustdoc-json/type/dyn.rs
@@ -1,8 +1,13 @@
 // ignore-tidy-linelength
+use std::fmt::Debug;
 
-// @count dyn.json "$.index[*][?(@.name=='dyn')].inner.items" 1
+// @count dyn.json "$.index[*][?(@.name=='dyn')].inner.items[*]" 3
 // @set sync_int_gen = - "$.index[*][?(@.name=='SyncIntGen')].id"
-// @is - "$.index[*][?(@.name=='dyn')].inner.items[0]" $sync_int_gen
+// @set ref_fn       = - "$.index[*][?(@.name=='RefFn')].id"
+// @set weird_order  = - "$.index[*][?(@.name=='WeirdOrder')].id"
+// @has - "$.index[*][?(@.name=='dyn')].inner.items[*]" $sync_int_gen
+// @has - "$.index[*][?(@.name=='dyn')].inner.items[*]" $ref_fn
+// @has - "$.index[*][?(@.name=='dyn')].inner.items[*]" $weird_order
 
 // @is    - "$.index[*][?(@.name=='SyncIntGen')].kind" \"typedef\"
 // @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.generics" '{"params": [], "where_predicates": []}'
@@ -10,12 +15,35 @@
 // @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.name" \"Box\"
 // @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.bindings" []
 // @count - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args" 1
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.kind" \"resolved_path\"
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.kind" \"resolved_path\"
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.name" \"Fn\"
-// @count - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.param_names[*]" 3
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.param_names[0].trait_bound.trait.inner.name" \"Send\"
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.param_names[1].trait_bound.trait.inner.name" \"Sync\"
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.param_names[2]" "{\"outlives\": \"'static\"}"
-// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.args" '{"parenthesized": {"inputs": [],"output": {"inner": "i32","kind": "primitive"}}}'
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.kind" \"dyn_trait\"
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.lifetime" \"\'static\"
+// @count - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[*]" 3
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[0].generic_params" []
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[1].generic_params" []
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[2].generic_params" []
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[0].trait.inner.name" '"Fn"'
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[1].trait.inner.name" '"Send"'
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[2].trait.inner.name" '"Sync"'
+// @is    - "$.index[*][?(@.name=='SyncIntGen')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[0].trait.inner.args" '{"parenthesized": {"inputs": [],"output": {"inner": "i32","kind": "primitive"}}}'
 pub type SyncIntGen = Box<dyn Fn() -> i32 + Send + Sync + 'static>;
+
+// @is - "$.index[*][?(@.name=='RefFn')].kind" \"typedef\"
+// @is - "$.index[*][?(@.name=='RefFn')].inner.generics" '{"params": [{"kind": {"lifetime": {"outlives": []}},"name": "'\''a"}],"where_predicates": []}'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.kind" '"borrowed_ref"'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.mutable" 'false'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.lifetime" "\"'a\""
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.kind" '"dyn_trait"'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.lifetime" null
+// @count - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[*]" 1
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].generic_params" '[{"kind": {"lifetime": {"outlives": []}},"name": "'\''b"}]'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].trait.kind" '"resolved_path"'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].trait.inner.name" '"Fn"'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].trait.inner.args.parenthesized.inputs[0].kind" '"borrowed_ref"'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].trait.inner.args.parenthesized.inputs[0].inner.lifetime" "\"'b\""
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].trait.inner.args.parenthesized.output.kind" '"borrowed_ref"'
+// @is - "$.index[*][?(@.name=='RefFn')].inner.type.inner.type.inner.traits[0].trait.inner.args.parenthesized.output.inner.lifetime" "\"'b\""
+pub type RefFn<'a> = &'a dyn for<'b> Fn(&'b i32) -> &'b i32;
+
+// @is    - "$.index[*][?(@.name=='WeirdOrder')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[0].trait.inner.name" '"Send"'
+// @is    - "$.index[*][?(@.name=='WeirdOrder')].inner.type.inner.args.angle_bracketed.args[0].type.inner.traits[1].trait.inner.name" '"Debug"'
+pub type WeirdOrder = Box<dyn Send + Debug>;
diff --git a/src/test/rustdoc-json/type/hrtb.rs b/src/test/rustdoc-json/type/hrtb.rs
new file mode 100644
index 0000000000000..9311737be0fec
--- /dev/null
+++ b/src/test/rustdoc-json/type/hrtb.rs
@@ -0,0 +1,26 @@
+// ignore-tidy-linelength
+
+// @has hrtb.json
+
+// @is - "$.index[*][?(@.name=='genfn')].inner.generics.where_predicates[0].bound_predicate.type" '{"inner": "F","kind": "generic"}'
+// @is - "$.index[*][?(@.name=='genfn')].inner.generics.where_predicates[0].bound_predicate.generic_params" '[{"kind": {"lifetime": {"outlives": []}},"name": "'\''a"},{"kind": {"lifetime": {"outlives": []}},"name": "'\''b"}]'
+pub fn genfn<F>(f: F)
+where
+    for<'a, 'b> F: Fn(&'a i32, &'b i32),
+{
+    let zero = 0;
+    f(&zero, &zero);
+}
+
+// @is - "$.index[*][?(@.name=='dynfn')].inner.generics" '{"params": [], "where_predicates": []}'
+// @is - "$.index[*][?(@.name=='dynfn')].inner.generics" '{"params": [], "where_predicates": []}'
+// @is - "$.index[*][?(@.name=='dynfn')].inner.decl.inputs[0][1].kind" '"borrowed_ref"'
+// @is - "$.index[*][?(@.name=='dynfn')].inner.decl.inputs[0][1].inner.type.kind" '"dyn_trait"'
+// @is - "$.index[*][?(@.name=='dynfn')].inner.decl.inputs[0][1].inner.type.inner.lifetime" null
+// @count - "$.index[*][?(@.name=='dynfn')].inner.decl.inputs[0][1].inner.type.inner.traits[*]" 1
+// @is - "$.index[*][?(@.name=='dynfn')].inner.decl.inputs[0][1].inner.type.inner.traits[0].generic_params" '[{"kind": {"lifetime": {"outlives": []}},"name": "'\''a"},{"kind": {"lifetime": {"outlives": []}},"name": "'\''b"}]'
+// @is - "$.index[*][?(@.name=='dynfn')].inner.decl.inputs[0][1].inner.type.inner.traits[0].trait.inner.name" '"Fn"'
+pub fn dynfn(f: &dyn for<'a, 'b> Fn(&'a i32, &'b i32)) {
+    let zero = 0;
+    f(&zero, &zero);
+}
diff --git a/src/test/rustdoc/impossible-default.rs b/src/test/rustdoc/impossible-default.rs
new file mode 100644
index 0000000000000..24d6e3bdac1bd
--- /dev/null
+++ b/src/test/rustdoc/impossible-default.rs
@@ -0,0 +1,20 @@
+#![crate_name = "foo"]
+
+// Check that default trait items that are impossible to satisfy
+
+pub trait Foo {
+    fn needs_sized(&self)
+    where
+        Self: Sized,
+    {}
+
+    fn no_needs_sized(&self) {}
+}
+
+// @!has foo/struct.Bar.html '//*[@id="method.needs_sized"]//h4[@class="code-header"]' \
+// "fn needs_sized"
+// @has foo/struct.Bar.html '//*[@id="method.no_needs_sized"]//h4[@class="code-header"]' \
+// "fn no_needs_sized"
+pub struct Bar([u8]);
+
+impl Foo for Bar {}
diff --git a/src/test/ui/macros/auxiliary/issue-100199.rs b/src/test/ui/macros/auxiliary/issue-100199.rs
new file mode 100644
index 0000000000000..9e190b542db49
--- /dev/null
+++ b/src/test/ui/macros/auxiliary/issue-100199.rs
@@ -0,0 +1,18 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro_quote)]
+
+extern crate proc_macro;
+
+use proc_macro::{quote, Ident, Span, TokenStream, TokenTree};
+
+#[proc_macro_attribute]
+pub fn struct_with_bound(_: TokenStream, _: TokenStream) -> TokenStream {
+    let crate_ident = TokenTree::Ident(Ident::new("crate", Span::call_site()));
+    let trait_ident = TokenTree::Ident(Ident::new("MyTrait", Span::call_site()));
+    quote!(
+        struct Foo<T: $crate_ident::$trait_ident> {}
+    )
+}
diff --git a/src/test/ui/macros/issue-100199.rs b/src/test/ui/macros/issue-100199.rs
new file mode 100644
index 0000000000000..6e50afa075984
--- /dev/null
+++ b/src/test/ui/macros/issue-100199.rs
@@ -0,0 +1,16 @@
+#[issue_100199::struct_with_bound] //~ ERROR cannot find trait `MyTrait` in the crate root
+struct Foo {}
+// The above must be on the first line so that it's span points to pos 0.
+// This used to trigger an ICE because the diagnostic emitter would get
+// an unexpected dummy span (lo == 0 == hi) while attempting to print a
+// suggestion.
+
+// aux-build: issue-100199.rs
+
+extern crate issue_100199;
+
+mod traits {
+    pub trait MyTrait {}
+}
+
+fn main() {}
diff --git a/src/test/ui/macros/issue-100199.stderr b/src/test/ui/macros/issue-100199.stderr
new file mode 100644
index 0000000000000..2cb45dc12473e
--- /dev/null
+++ b/src/test/ui/macros/issue-100199.stderr
@@ -0,0 +1,15 @@
+error[E0405]: cannot find trait `MyTrait` in the crate root
+  --> $DIR/issue-100199.rs:1:1
+   |
+LL | #[issue_100199::struct_with_bound]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in the crate root
+   |
+   = note: this error originates in the attribute macro `issue_100199::struct_with_bound` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider importing this trait
+   |
+LL | use traits::MyTrait;
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0405`.
diff --git a/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.fixed b/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.fixed
new file mode 100644
index 0000000000000..b28dce8810593
--- /dev/null
+++ b/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.fixed
@@ -0,0 +1,10 @@
+// run-rustfix
+
+fn main() {
+    match Some(1) { //~ ERROR non-exhaustive patterns: `None` not covered
+        Some(1) => {}
+        // hello
+        Some(_) => {}
+        None => todo!()
+    }
+}
diff --git a/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.rs b/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.rs
new file mode 100644
index 0000000000000..42493a6327173
--- /dev/null
+++ b/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.rs
@@ -0,0 +1,9 @@
+// run-rustfix
+
+fn main() {
+    match Some(1) { //~ ERROR non-exhaustive patterns: `None` not covered
+        Some(1) => {}
+        // hello
+        Some(_) => {}
+    }
+}
diff --git a/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.stderr b/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.stderr
new file mode 100644
index 0000000000000..f3dca9bcb07d1
--- /dev/null
+++ b/src/test/ui/pattern/suggest-adding-appropriate-missing-pattern-excluding-comments.stderr
@@ -0,0 +1,24 @@
+error[E0004]: non-exhaustive patterns: `None` not covered
+  --> $DIR/suggest-adding-appropriate-missing-pattern-excluding-comments.rs:4:11
+   |
+LL |     match Some(1) {
+   |           ^^^^^^^ pattern `None` not covered
+   |
+note: `Option<i32>` defined here
+  --> $SRC_DIR/core/src/option.rs:LL:COL
+   |
+LL | pub enum Option<T> {
+   | ------------------
+...
+LL |     None,
+   |     ^^^^ not covered
+   = note: the matched value is of type `Option<i32>`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         Some(_) => {}
+LL +         None => todo!()
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0004`.
diff --git a/src/test/ui/stability-attribute/auxiliary/default_body.rs b/src/test/ui/stability-attribute/auxiliary/default_body.rs
new file mode 100644
index 0000000000000..3a177419d666d
--- /dev/null
+++ b/src/test/ui/stability-attribute/auxiliary/default_body.rs
@@ -0,0 +1,29 @@
+#![crate_type = "lib"]
+#![feature(staged_api, rustc_attrs)]
+#![stable(feature = "stable_feature", since = "1.0.0")]
+
+#[stable(feature = "stable_feature", since = "1.0.0")]
+pub trait JustTrait {
+    #[stable(feature = "stable_feature", since = "1.0.0")]
+    #[rustc_default_body_unstable(feature = "constant_default_body", issue = "none")]
+    const CONSTANT: usize = 0;
+
+    #[rustc_default_body_unstable(feature = "fun_default_body", issue = "none")]
+    #[stable(feature = "stable_feature", since = "1.0.0")]
+    fn fun() {}
+}
+
+#[rustc_must_implement_one_of(eq, neq)]
+#[stable(feature = "stable_feature", since = "1.0.0")]
+pub trait Equal {
+    #[rustc_default_body_unstable(feature = "eq_default_body", issue = "none")]
+    #[stable(feature = "stable_feature", since = "1.0.0")]
+    fn eq(&self, other: &Self) -> bool {
+        !self.neq(other)
+    }
+
+    #[stable(feature = "stable_feature", since = "1.0.0")]
+    fn neq(&self, other: &Self) -> bool {
+        !self.eq(other)
+    }
+}
diff --git a/src/test/ui/stability-attribute/default-body-stability-err.rs b/src/test/ui/stability-attribute/default-body-stability-err.rs
new file mode 100644
index 0000000000000..ecb281bccf604
--- /dev/null
+++ b/src/test/ui/stability-attribute/default-body-stability-err.rs
@@ -0,0 +1,19 @@
+// aux-build:default_body.rs
+#![crate_type = "lib"]
+
+extern crate default_body;
+
+use default_body::{Equal, JustTrait};
+
+struct Type;
+
+impl JustTrait for Type {}
+//~^ ERROR not all trait items implemented, missing: `CONSTANT` [E0046]
+//~| ERROR not all trait items implemented, missing: `fun` [E0046]
+
+impl Equal for Type {
+    //~^ ERROR not all trait items implemented, missing: `eq` [E0046]
+    fn neq(&self, other: &Self) -> bool {
+        false
+    }
+}
diff --git a/src/test/ui/stability-attribute/default-body-stability-err.stderr b/src/test/ui/stability-attribute/default-body-stability-err.stderr
new file mode 100644
index 0000000000000..ef666f30fc2a2
--- /dev/null
+++ b/src/test/ui/stability-attribute/default-body-stability-err.stderr
@@ -0,0 +1,38 @@
+error[E0046]: not all trait items implemented, missing: `CONSTANT`
+  --> $DIR/default-body-stability-err.rs:10:1
+   |
+LL | impl JustTrait for Type {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: default implementation of `CONSTANT` is unstable
+   = note: use of unstable library feature 'constant_default_body'
+   = help: add `#![feature(constant_default_body)]` to the crate attributes to enable
+
+error[E0046]: not all trait items implemented, missing: `fun`
+  --> $DIR/default-body-stability-err.rs:10:1
+   |
+LL | impl JustTrait for Type {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: default implementation of `fun` is unstable
+   = note: use of unstable library feature 'fun_default_body'
+   = help: add `#![feature(fun_default_body)]` to the crate attributes to enable
+
+error[E0046]: not all trait items implemented, missing: `eq`
+  --> $DIR/default-body-stability-err.rs:14:1
+   |
+LL | / impl Equal for Type {
+LL | |
+LL | |     fn neq(&self, other: &Self) -> bool {
+LL | |         false
+LL | |     }
+LL | | }
+   | |_^
+   |
+   = note: default implementation of `eq` is unstable
+   = note: use of unstable library feature 'eq_default_body'
+   = help: add `#![feature(eq_default_body)]` to the crate attributes to enable
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0046`.
diff --git a/src/test/ui/stability-attribute/default-body-stability-ok-enables.rs b/src/test/ui/stability-attribute/default-body-stability-ok-enables.rs
new file mode 100644
index 0000000000000..bdc7522f48dde
--- /dev/null
+++ b/src/test/ui/stability-attribute/default-body-stability-ok-enables.rs
@@ -0,0 +1,18 @@
+// check-pass
+// aux-build:default_body.rs
+#![crate_type = "lib"]
+#![feature(fun_default_body, eq_default_body, constant_default_body)]
+
+extern crate default_body;
+
+use default_body::{Equal, JustTrait};
+
+struct Type;
+
+impl JustTrait for Type {}
+
+impl Equal for Type {
+    fn neq(&self, other: &Self) -> bool {
+        false
+    }
+}
diff --git a/src/test/ui/stability-attribute/default-body-stability-ok-impls.rs b/src/test/ui/stability-attribute/default-body-stability-ok-impls.rs
new file mode 100644
index 0000000000000..e1f5c017096ab
--- /dev/null
+++ b/src/test/ui/stability-attribute/default-body-stability-ok-impls.rs
@@ -0,0 +1,21 @@
+// check-pass
+// aux-build:default_body.rs
+#![crate_type = "lib"]
+
+extern crate default_body;
+
+use default_body::{Equal, JustTrait};
+
+struct Type;
+
+impl JustTrait for Type {
+    const CONSTANT: usize = 1;
+
+    fn fun() {}
+}
+
+impl Equal for Type {
+    fn eq(&self, other: &Self) -> bool {
+        false
+    }
+}