diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 1e4d3ba47f472..3ed342ce48b43 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -2976,7 +2976,7 @@ pub enum ItemKind {
 }
 
 impl ItemKind {
-    pub fn article(&self) -> &str {
+    pub fn article(&self) -> &'static str {
         use ItemKind::*;
         match self {
             Use(..) | Static(..) | Const(..) | Fn(..) | Mod(..) | GlobalAsm(..) | TyAlias(..)
@@ -2985,7 +2985,7 @@ impl ItemKind {
         }
     }
 
-    pub fn descr(&self) -> &str {
+    pub fn descr(&self) -> &'static str {
         match self {
             ItemKind::ExternCrate(..) => "extern crate",
             ItemKind::Use(..) => "`use` import",
diff --git a/compiler/rustc_infer/src/traits/project.rs b/compiler/rustc_infer/src/traits/project.rs
index 8d0af738dd115..e375d611936ea 100644
--- a/compiler/rustc_infer/src/traits/project.rs
+++ b/compiler/rustc_infer/src/traits/project.rs
@@ -20,7 +20,7 @@ pub struct MismatchedProjectionTypes<'tcx> {
     pub err: ty::error::TypeError<'tcx>,
 }
 
-#[derive(Clone, TypeFoldable, TypeVisitable)]
+#[derive(Clone)]
 pub struct Normalized<'tcx, T> {
     pub value: T,
     pub obligations: Vec<PredicateObligation<'tcx>>,
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index a6ba742201a3b..4d0a35368b35d 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -1250,17 +1250,45 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         }
     }
 
-    fn check_foreign_fn(&mut self, def_id: LocalDefId, decl: &hir::FnDecl<'_>) {
+    /// Check if a function's argument types and result type are "ffi-safe".
+    ///
+    /// Argument types and the result type are checked for functions with external ABIs.
+    /// For functions with internal ABIs, argument types and the result type are walked to find
+    /// fn-ptr types that have external ABIs, as these still need checked.
+    fn check_maybe_foreign_fn(
+        &mut self,
+        abi: SpecAbi,
+        def_id: LocalDefId,
+        decl: &'tcx hir::FnDecl<'_>,
+    ) {
         let sig = self.cx.tcx.fn_sig(def_id).subst_identity();
         let sig = self.cx.tcx.erase_late_bound_regions(sig);
 
+        let is_internal_abi = self.is_internal_abi(abi);
+        let check_ty = |this: &mut ImproperCTypesVisitor<'a, 'tcx>,
+                        hir_ty: &'tcx hir::Ty<'_>,
+                        ty: Ty<'tcx>,
+                        is_return_type: bool| {
+            // If this function has an external ABI, then its arguments and return type should be
+            // checked..
+            if !is_internal_abi {
+                this.check_type_for_ffi_and_report_errors(hir_ty.span, ty, false, is_return_type);
+                return;
+            }
+
+            // ..but if this function has an internal ABI, then search the argument or return type
+            // for any fn-ptr types with external ABI, which should be checked..
+            for (fn_ptr_ty, span) in this.find_fn_ptr_ty_with_external_abi(hir_ty, ty) {
+                this.check_type_for_ffi_and_report_errors(span, fn_ptr_ty, false, is_return_type);
+            }
+        };
+
         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
-            self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
+            check_ty(self, input_hir, *input_ty, false);
         }
 
         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
-            let ret_ty = sig.output();
-            self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
+            check_ty(self, ret_hir, sig.output(), true);
         }
     }
 
@@ -1275,28 +1303,134 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
             SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
         )
     }
+
+    /// Find any fn-ptr types with external ABIs in `ty`.
+    ///
+    /// For example, `Option<extern "C" fn()>` returns `extern "C" fn()`
+    fn find_fn_ptr_ty_with_external_abi(
+        &self,
+        hir_ty: &hir::Ty<'tcx>,
+        ty: Ty<'tcx>,
+    ) -> Vec<(Ty<'tcx>, Span)> {
+        struct FnPtrFinder<'parent, 'a, 'tcx> {
+            visitor: &'parent ImproperCTypesVisitor<'a, 'tcx>,
+            spans: Vec<Span>,
+            tys: Vec<Ty<'tcx>>,
+        }
+
+        impl<'parent, 'a, 'tcx> hir::intravisit::Visitor<'_> for FnPtrFinder<'parent, 'a, 'tcx> {
+            fn visit_ty(&mut self, ty: &'_ hir::Ty<'_>) {
+                debug!(?ty);
+                if let hir::TyKind::BareFn(hir::BareFnTy { abi, .. }) = ty.kind
+                    && !self.visitor.is_internal_abi(*abi)
+                {
+                    self.spans.push(ty.span);
+                }
+
+                hir::intravisit::walk_ty(self, ty)
+            }
+        }
+
+        impl<'vis, 'a, 'tcx> ty::visit::TypeVisitor<TyCtxt<'tcx>> for FnPtrFinder<'vis, 'a, 'tcx> {
+            type BreakTy = Ty<'tcx>;
+
+            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
+                if let ty::FnPtr(sig) = ty.kind() && !self.visitor.is_internal_abi(sig.abi()) {
+                    self.tys.push(ty);
+                }
+
+                ty.super_visit_with(self)
+            }
+        }
+
+        let mut visitor = FnPtrFinder { visitor: &*self, spans: Vec::new(), tys: Vec::new() };
+        self.cx
+            .tcx
+            .try_normalize_erasing_regions(self.cx.param_env, ty)
+            .unwrap_or(ty)
+            .visit_with(&mut visitor);
+        hir::intravisit::Visitor::visit_ty(&mut visitor, hir_ty);
+
+        iter::zip(visitor.tys.drain(..), visitor.spans.drain(..)).collect()
+    }
 }
 
 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
-    fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
+    fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, it: &hir::ForeignItem<'tcx>) {
         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
 
-        if !vis.is_internal_abi(abi) {
-            match it.kind {
-                hir::ForeignItemKind::Fn(ref decl, _, _) => {
-                    vis.check_foreign_fn(it.owner_id.def_id, decl);
-                }
-                hir::ForeignItemKind::Static(ref ty, _) => {
-                    vis.check_foreign_static(it.owner_id, ty.span);
-                }
-                hir::ForeignItemKind::Type => (),
+        match it.kind {
+            hir::ForeignItemKind::Fn(ref decl, _, _) => {
+                vis.check_maybe_foreign_fn(abi, it.owner_id.def_id, decl);
             }
+            hir::ForeignItemKind::Static(ref ty, _) if !vis.is_internal_abi(abi) => {
+                vis.check_foreign_static(it.owner_id, ty.span);
+            }
+            hir::ForeignItemKind::Static(..) | hir::ForeignItemKind::Type => (),
         }
     }
 }
 
+impl ImproperCTypesDefinitions {
+    fn check_ty_maybe_containing_foreign_fnptr<'tcx>(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        hir_ty: &'tcx hir::Ty<'_>,
+        ty: Ty<'tcx>,
+    ) {
+        let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
+        for (fn_ptr_ty, span) in vis.find_fn_ptr_ty_with_external_abi(hir_ty, ty) {
+            vis.check_type_for_ffi_and_report_errors(span, fn_ptr_ty, true, false);
+        }
+    }
+}
+
+/// `ImproperCTypesDefinitions` checks items outside of foreign items (e.g. stuff that isn't in
+/// `extern "C" { }` blocks):
+///
+/// - `extern "<abi>" fn` definitions are checked in the same way as the
+///   `ImproperCtypesDeclarations` visitor checks functions if `<abi>` is external (e.g. "C").
+/// - All other items which contain types (e.g. other functions, struct definitions, etc) are
+///   checked for extern fn-ptrs with external ABIs.
 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
+        match item.kind {
+            hir::ItemKind::Static(ty, ..)
+            | hir::ItemKind::Const(ty, ..)
+            | hir::ItemKind::TyAlias(ty, ..) => {
+                self.check_ty_maybe_containing_foreign_fnptr(
+                    cx,
+                    ty,
+                    cx.tcx.type_of(item.owner_id).subst_identity(),
+                );
+            }
+            // See `check_fn`..
+            hir::ItemKind::Fn(..) => {}
+            // See `check_field_def`..
+            hir::ItemKind::Union(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) => {}
+            // Doesn't define something that can contain a external type to be checked.
+            hir::ItemKind::Impl(..)
+            | hir::ItemKind::TraitAlias(..)
+            | hir::ItemKind::Trait(..)
+            | hir::ItemKind::OpaqueTy(..)
+            | hir::ItemKind::GlobalAsm(..)
+            | hir::ItemKind::ForeignMod { .. }
+            | hir::ItemKind::Mod(..)
+            | hir::ItemKind::Macro(..)
+            | hir::ItemKind::Use(..)
+            | hir::ItemKind::ExternCrate(..) => {}
+        }
+    }
+
+    fn check_field_def(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::FieldDef<'tcx>) {
+        self.check_ty_maybe_containing_foreign_fnptr(
+            cx,
+            field.ty,
+            cx.tcx.type_of(field.def_id).subst_identity(),
+        );
+    }
+
     fn check_fn(
         &mut self,
         cx: &LateContext<'tcx>,
@@ -1315,9 +1449,7 @@ impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
         };
 
         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
-        if !vis.is_internal_abi(abi) {
-            vis.check_foreign_fn(id, decl);
-        }
+        vis.check_maybe_foreign_fn(abi, id, decl);
     }
 }
 
diff --git a/compiler/rustc_middle/src/hir/place.rs b/compiler/rustc_middle/src/hir/place.rs
index 80b4c964ce402..8a22de931c35b 100644
--- a/compiler/rustc_middle/src/hir/place.rs
+++ b/compiler/rustc_middle/src/hir/place.rs
@@ -66,7 +66,6 @@ pub struct Place<'tcx> {
 ///
 /// This is an HIR version of [`rustc_middle::mir::Place`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable)]
-#[derive(TypeFoldable, TypeVisitable)]
 pub struct PlaceWithHirId<'tcx> {
     /// `HirId` of the expression or pattern producing this value.
     pub hir_id: HirId,
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 039194284b80f..2490b17aac09b 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -9,7 +9,7 @@ use crate::mir::visit::MirVisitable;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable};
 use crate::ty::print::{FmtPrinter, Printer};
-use crate::ty::visit::{TypeVisitable, TypeVisitableExt, TypeVisitor};
+use crate::ty::visit::TypeVisitableExt;
 use crate::ty::{self, List, Ty, TyCtxt};
 use crate::ty::{AdtDef, InstanceDef, ScalarInt, UserTypeAnnotationIndex};
 use crate::ty::{GenericArg, InternalSubsts, SubstsRef};
@@ -36,7 +36,7 @@ use either::Either;
 
 use std::borrow::Cow;
 use std::fmt::{self, Debug, Display, Formatter, Write};
-use std::ops::{ControlFlow, Index, IndexMut};
+use std::ops::{Index, IndexMut};
 use std::{iter, mem};
 
 pub use self::query::*;
@@ -2722,6 +2722,7 @@ impl<'tcx> UserTypeProjections {
 ///   `field[0]` (aka `.0`), indicating that the type of `s` is
 ///   determined by finding the type of the `.0` field from `T`.
 #[derive(Clone, Debug, TyEncodable, TyDecodable, Hash, HashStable, PartialEq)]
+#[derive(TypeFoldable, TypeVisitable)]
 pub struct UserTypeProjection {
     pub base: UserTypeAnnotationIndex,
     pub projs: Vec<ProjectionKind>,
@@ -2765,28 +2766,6 @@ impl UserTypeProjection {
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for UserTypeProjection {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(UserTypeProjection {
-            base: self.base.try_fold_with(folder)?,
-            projs: self.projs.try_fold_with(folder)?,
-        })
-    }
-}
-
-impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for UserTypeProjection {
-    fn visit_with<Vs: TypeVisitor<TyCtxt<'tcx>>>(
-        &self,
-        visitor: &mut Vs,
-    ) -> ControlFlow<Vs::BreakTy> {
-        self.base.visit_with(visitor)
-        // Note: there's nothing in `self.proj` to visit.
-    }
-}
-
 rustc_index::newtype_index! {
     #[derive(HashStable)]
     #[debug_format = "promoted[{}]"]
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index da86cfd477229..813e109c41e14 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -234,7 +234,6 @@ pub enum StmtKind<'tcx> {
 }
 
 #[derive(Clone, Debug, Copy, PartialEq, Eq, Hash, HashStable, TyEncodable, TyDecodable)]
-#[derive(TypeFoldable, TypeVisitable)]
 pub struct LocalVarId(pub hir::HirId);
 
 /// A THIR expression.
diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index 6a8ae525069c0..02433026266a3 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -569,7 +569,7 @@ pub struct DerivedObligationCause<'tcx> {
     pub parent_code: InternedObligationCauseCode<'tcx>,
 }
 
-#[derive(Clone, Debug, TypeFoldable, TypeVisitable, Lift)]
+#[derive(Clone, Debug, TypeVisitable, Lift)]
 pub enum SelectionError<'tcx> {
     /// The trait is not implemented.
     Unimplemented,
diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs
index 1cc9fd526b44f..f2dda003b99c5 100644
--- a/compiler/rustc_middle/src/traits/select.rs
+++ b/compiler/rustc_middle/src/traits/select.rs
@@ -103,7 +103,7 @@ pub type EvaluationCache<'tcx> = Cache<
 /// required for associated types to work in default impls, as the bounds
 /// are visible both as projection bounds and as where-clauses from the
 /// parameter environment.
-#[derive(PartialEq, Eq, Debug, Clone, TypeFoldable, TypeVisitable)]
+#[derive(PartialEq, Eq, Debug, Clone, TypeVisitable)]
 pub enum SelectionCandidate<'tcx> {
     /// A builtin implementation for some specific traits, used in cases
     /// where we cannot rely an ordinary library implementations.
diff --git a/compiler/rustc_middle/src/traits/solve.rs b/compiler/rustc_middle/src/traits/solve.rs
index fef2be133e81f..6b7b910a59bf9 100644
--- a/compiler/rustc_middle/src/traits/solve.rs
+++ b/compiler/rustc_middle/src/traits/solve.rs
@@ -120,7 +120,7 @@ impl<'tcx> std::ops::Deref for ExternalConstraints<'tcx> {
 }
 
 /// Additional constraints returned on success.
-#[derive(Debug, PartialEq, Eq, Clone, Hash, Default, TypeFoldable, TypeVisitable)]
+#[derive(Debug, PartialEq, Eq, Clone, Hash, Default)]
 pub struct ExternalConstraintsData<'tcx> {
     // FIXME: implement this.
     pub region_constraints: QueryRegionConstraints<'tcx>,
diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index aff6c77e039af..1be61e16dbed8 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/compiler/rustc_middle/src/ty/error.rs
@@ -28,7 +28,7 @@ impl<T> ExpectedFound<T> {
 }
 
 // Data structures used in type unification
-#[derive(Copy, Clone, Debug, TypeFoldable, TypeVisitable, Lift, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, TypeVisitable, Lift, PartialEq, Eq)]
 #[rustc_pass_by_value]
 pub enum TypeError<'tcx> {
     Mismatch,
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 1c1432ecd5a05..2aced27f7bbdc 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -2690,7 +2690,7 @@ impl<'tcx> ty::PolyTraitPredicate<'tcx> {
     }
 }
 
-#[derive(Debug, Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
+#[derive(Debug, Copy, Clone, Lift)]
 pub struct PrintClosureAsImpl<'tcx> {
     pub closure: ty::ClosureSubsts<'tcx>,
 }
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index b35b514d795dc..29a3bc8bb9756 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -4,7 +4,6 @@
 //! to help with the tedium.
 
 use crate::mir::interpret;
-use crate::mir::ProjectionKind;
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
 use crate::ty::print::{with_no_trimmed_paths, FmtPrinter, Printer};
 use crate::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
@@ -373,16 +372,6 @@ impl<'a, 'tcx> Lift<'tcx> for ty::ParamEnv<'a> {
 ///////////////////////////////////////////////////////////////////////////
 // Traversal implementations.
 
-/// AdtDefs are basically the same as a DefId.
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::AdtDef<'tcx> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        _folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(self)
-    }
-}
-
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ty::AdtDef<'tcx> {
     fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(
         &self,
@@ -445,15 +434,6 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<ty::Const<'tcx>> {
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<ProjectionKind> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_projs(v))
-    }
-}
-
 impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Ty<'tcx> {
     fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
         self,
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 82dec7d98ad5f..7bda20ffe9a32 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -631,7 +631,7 @@ impl<'tcx> UpvarSubsts<'tcx> {
 /// type of the constant. The reason that `R` is represented as an extra type parameter
 /// is the same reason that [`ClosureSubsts`] have `CS` and `U` as type parameters:
 /// inline const can reference lifetimes that are internal to the creating function.
-#[derive(Copy, Clone, Debug, TypeFoldable, TypeVisitable)]
+#[derive(Copy, Clone, Debug)]
 pub struct InlineConstSubsts<'tcx> {
     /// Generic parameters from the enclosing item,
     /// concatenated with the inferred type of the constant.
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index d45fa90a11b08..9c4fac84fc294 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -772,3 +772,75 @@ parse_const_bounds_missing_tilde = const bounds must start with `~`
     .suggestion = add `~`
 
 parse_underscore_literal_suffix = underscore literal suffix is not allowed
+
+parse_expect_label_found_ident = expected a label, found an identifier
+    .suggestion = labels start with a tick
+
+parse_inappropriate_default = {$article} {$descr} cannot be `default`
+    .label = `default` because of this
+    .note = only associated `fn`, `const`, and `type` items can be `default`
+
+parse_recover_import_as_use = expected item, found {$token_name}
+    .suggestion = items are imported using the `use` keyword
+
+parse_single_colon_import_path = expected `::`, found `:`
+    .suggestion = use double colon
+    .note = import paths are delimited using `::`
+
+parse_bad_item_kind = {$descr} is not supported in {$ctx}
+    .help = consider moving the {$descr} out to a nearby module scope
+
+parse_single_colon_struct_type = found single colon in a struct field type path
+    .suggestion = write a path separator here
+
+parse_equals_struct_default = default values on `struct` fields aren't supported
+    .suggestion = remove this unsupported default value
+
+parse_macro_rules_missing_bang = expected `!` after `macro_rules`
+    .suggestion = add a `!`
+
+parse_macro_name_remove_bang = macro names aren't followed by a `!`
+    .suggestion = remove the `!`
+
+parse_macro_rules_visibility = can't qualify macro_rules invocation with `{$vis}`
+    .suggestion = try exporting the macro
+
+parse_macro_invocation_visibility = can't qualify macro invocation with `pub`
+    .suggestion = remove the visibility
+    .help = try adjusting the macro to put `{$vis}` inside the invocation
+
+parse_nested_adt = `{$kw_str}` definition cannot be nested inside `{$keyword}`
+    .suggestion = consider creating a new `{$kw_str}` definition instead of nesting
+
+parse_function_body_equals_expr = function body cannot be `= expression;`
+    .suggestion = surround the expression with `{"{"}` and `{"}"}` instead of `=` and `;`
+
+parse_box_not_pat = expected pattern, found {$descr}
+    .note = `box` is a reserved keyword
+    .suggestion = escape `box` to use it as an identifier
+
+parse_unmatched_angle = unmatched angle {$plural ->
+    [true] brackets
+    *[false] bracket
+    }
+    .suggestion = remove extra angle {$plural ->
+    [true] brackets
+    *[false] bracket
+    }
+
+parse_missing_plus_in_bounds = expected `+` between lifetime and {$sym}
+    .suggestion = add `+`
+
+parse_incorrect_braces_trait_bounds = incorrect braces around trait bounds
+    .suggestion = remove the parentheses
+
+parse_kw_bad_case = keyword `{$kw}` is written in the wrong case
+    .suggestion = write it in the correct case
+
+parse_meta_bad_delim = wrong meta list delimiters
+parse_cfg_attr_bad_delim = wrong `cfg_attr` delimiters
+parse_meta_bad_delim_suggestion = the delimiters should be `(` and `)`
+
+parse_malformed_cfg_attr = malformed `cfg_attr` attribute input
+    .suggestion = missing condition and attribute
+    .note = for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute>
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index b0e1189851a1b..f286707a9c0df 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -2421,3 +2421,227 @@ pub(crate) struct UnderscoreLiteralSuffix {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(parse_expect_label_found_ident)]
+pub(crate) struct ExpectedLabelFoundIdent {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "'", applicability = "machine-applicable", style = "short")]
+    pub start: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_inappropriate_default)]
+#[note]
+pub(crate) struct InappropriateDefault {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub article: &'static str,
+    pub descr: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_recover_import_as_use)]
+pub(crate) struct RecoverImportAsUse {
+    #[primary_span]
+    #[suggestion(code = "use", applicability = "machine-applicable", style = "short")]
+    pub span: Span,
+    pub token_name: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_single_colon_import_path)]
+#[note]
+pub(crate) struct SingleColonImportPath {
+    #[primary_span]
+    #[suggestion(code = "::", applicability = "machine-applicable", style = "short")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_bad_item_kind)]
+#[help]
+pub(crate) struct BadItemKind {
+    #[primary_span]
+    pub span: Span,
+    pub descr: &'static str,
+    pub ctx: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_single_colon_struct_type)]
+pub(crate) struct SingleColonStructType {
+    #[primary_span]
+    #[suggestion(code = "::", applicability = "maybe-incorrect", style = "verbose")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_equals_struct_default)]
+pub(crate) struct EqualsStructDefault {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_rules_missing_bang)]
+pub(crate) struct MacroRulesMissingBang {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "!", applicability = "machine-applicable", style = "verbose")]
+    pub hi: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_name_remove_bang)]
+pub(crate) struct MacroNameRemoveBang {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_rules_visibility)]
+pub(crate) struct MacroRulesVisibility<'a> {
+    #[primary_span]
+    #[suggestion(code = "#[macro_export]", applicability = "maybe-incorrect")]
+    pub span: Span,
+    pub vis: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_invocation_visibility)]
+#[help]
+pub(crate) struct MacroInvocationVisibility<'a> {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    pub vis: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_nested_adt)]
+pub(crate) struct NestedAdt<'a> {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
+    pub item: Span,
+    pub keyword: &'a str,
+    pub kw_str: Cow<'a, str>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_function_body_equals_expr)]
+pub(crate) struct FunctionBodyEqualsExpr {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: FunctionBodyEqualsExprSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
+pub(crate) struct FunctionBodyEqualsExprSugg {
+    #[suggestion_part(code = "{{")]
+    pub eq: Span,
+    #[suggestion_part(code = " }}")]
+    pub semi: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_box_not_pat)]
+pub(crate) struct BoxNotPat {
+    #[primary_span]
+    pub span: Span,
+    #[note]
+    pub kw: Span,
+    #[suggestion(code = "r#", applicability = "maybe-incorrect", style = "verbose")]
+    pub lo: Span,
+    pub descr: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unmatched_angle)]
+pub(crate) struct UnmatchedAngle {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    pub plural: bool,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_missing_plus_in_bounds)]
+pub(crate) struct MissingPlusBounds {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = " +", applicability = "maybe-incorrect", style = "verbose")]
+    pub hi: Span,
+    pub sym: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_incorrect_braces_trait_bounds)]
+pub(crate) struct IncorrectBracesTraitBounds {
+    #[primary_span]
+    pub span: Vec<Span>,
+    #[subdiagnostic]
+    pub sugg: IncorrectBracesTraitBoundsSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
+pub(crate) struct IncorrectBracesTraitBoundsSugg {
+    #[suggestion_part(code = " ")]
+    pub l: Span,
+    #[suggestion_part(code = "")]
+    pub r: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_kw_bad_case)]
+pub(crate) struct KwBadCase<'a> {
+    #[primary_span]
+    #[suggestion(code = "{kw}", applicability = "machine-applicable")]
+    pub span: Span,
+    pub kw: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_meta_bad_delim)]
+pub(crate) struct MetaBadDelim {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: MetaBadDelimSugg,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_cfg_attr_bad_delim)]
+pub(crate) struct CfgAttrBadDelim {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: MetaBadDelimSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_meta_bad_delim_suggestion, applicability = "machine-applicable")]
+pub(crate) struct MetaBadDelimSugg {
+    #[suggestion_part(code = "(")]
+    pub open: Span,
+    #[suggestion_part(code = ")")]
+    pub close: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_malformed_cfg_attr)]
+#[note]
+pub(crate) struct MalformedCfgAttr {
+    #[primary_span]
+    #[suggestion(code = "{sugg}")]
+    pub span: Span,
+    pub sugg: &'static str,
+}
diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
index 507f6e4182eec..61a1cdeb540e9 100644
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@@ -18,7 +18,7 @@ use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{AttrItem, Attribute, MetaItem};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{Applicability, Diagnostic, FatalError, Level, PResult};
+use rustc_errors::{Diagnostic, FatalError, Level, PResult};
 use rustc_errors::{DiagnosticMessage, SubdiagnosticMessage};
 use rustc_fluent_macro::fluent_messages;
 use rustc_session::parse::ParseSess;
@@ -243,8 +243,7 @@ pub fn parse_cfg_attr(
         ast::AttrArgs::Delimited(ast::DelimArgs { dspan, delim, ref tokens })
             if !tokens.is_empty() =>
         {
-            let msg = "wrong `cfg_attr` delimiters";
-            crate::validate_attr::check_meta_bad_delim(parse_sess, dspan, delim, msg);
+            crate::validate_attr::check_cfg_attr_bad_delim(parse_sess, dspan, delim);
             match parse_in(parse_sess, tokens.clone(), "`cfg_attr` input", |p| p.parse_cfg_attr()) {
                 Ok(r) => return Some(r),
                 Err(mut e) => {
@@ -265,15 +264,5 @@ const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
     #the-cfg_attr-attribute>";
 
 fn error_malformed_cfg_attr_missing(span: Span, parse_sess: &ParseSess) {
-    parse_sess
-        .span_diagnostic
-        .struct_span_err(span, "malformed `cfg_attr` attribute input")
-        .span_suggestion(
-            span,
-            "missing condition and attribute",
-            CFG_ATTR_GRAMMAR_HELP,
-            Applicability::HasPlaceholders,
-        )
-        .note(CFG_ATTR_NOTE_REF)
-        .emit();
+    parse_sess.emit_err(errors::MalformedCfgAttr { span, sugg: CFG_ATTR_GRAMMAR_HELP });
 }
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 03c82fbd329fc..27de9bd72685f 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -3151,14 +3151,10 @@ impl<'a> Parser<'a> {
         let label = format!("'{}", ident.name);
         let ident = Ident { name: Symbol::intern(&label), span: ident.span };
 
-        self.struct_span_err(ident.span, "expected a label, found an identifier")
-            .span_suggestion(
-                ident.span,
-                "labels start with a tick",
-                label,
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        self.sess.emit_err(errors::ExpectedLabelFoundIdent {
+            span: ident.span,
+            start: ident.span.shrink_to_lo(),
+        });
 
         Label { ident }
     }
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index f5fef6ad019eb..9e003bfc09747 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -181,11 +181,11 @@ impl<'a> Parser<'a> {
     /// Error in-case `default` was parsed in an in-appropriate context.
     fn error_on_unconsumed_default(&self, def: Defaultness, kind: &ItemKind) {
         if let Defaultness::Default(span) = def {
-            let msg = format!("{} {} cannot be `default`", kind.article(), kind.descr());
-            self.struct_span_err(span, &msg)
-                .span_label(span, "`default` because of this")
-                .note("only associated `fn`, `const`, and `type` items can be `default`")
-                .emit();
+            self.sess.emit_err(errors::InappropriateDefault {
+                span,
+                article: kind.article(),
+                descr: kind.descr(),
+            });
         }
     }
 
@@ -310,14 +310,7 @@ impl<'a> Parser<'a> {
         self.bump();
         match self.parse_use_item() {
             Ok(u) => {
-                self.struct_span_err(span, format!("expected item, found {token_name}"))
-                    .span_suggestion_short(
-                        span,
-                        "items are imported using the `use` keyword",
-                        "use",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(errors::RecoverImportAsUse { span, token_name });
                 Ok(Some(u))
             }
             Err(e) => {
@@ -963,15 +956,8 @@ impl<'a> Parser<'a> {
             } else {
                 // Recover from using a colon as path separator.
                 while self.eat_noexpect(&token::Colon) {
-                    self.struct_span_err(self.prev_token.span, "expected `::`, found `:`")
-                        .span_suggestion_short(
-                            self.prev_token.span,
-                            "use double colon",
-                            "::",
-                            Applicability::MachineApplicable,
-                        )
-                        .note_once("import paths are delimited using `::`")
-                        .emit();
+                    self.sess
+                        .emit_err(errors::SingleColonImportPath { span: self.prev_token.span });
 
                     // We parse the rest of the path and append it to the original prefix.
                     self.parse_path_segments(&mut prefix.segments, PathStyle::Mod, None)?;
@@ -1134,13 +1120,11 @@ impl<'a> Parser<'a> {
         ))
     }
 
-    fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &str) -> Option<T> {
+    fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &'static str) -> Option<T> {
         // FIXME(#100717): needs variant for each `ItemKind` (instead of using `ItemKind::descr()`)
         let span = self.sess.source_map().guess_head_span(span);
         let descr = kind.descr();
-        self.struct_span_err(span, &format!("{descr} is not supported in {ctx}"))
-            .help(&format!("consider moving the {descr} out to a nearby module scope"))
-            .emit();
+        self.sess.emit_err(errors::BadItemKind { span, descr, ctx });
         None
     }
 
@@ -1713,27 +1697,13 @@ impl<'a> Parser<'a> {
         self.expect_field_ty_separator()?;
         let ty = self.parse_ty()?;
         if self.token.kind == token::Colon && self.look_ahead(1, |tok| tok.kind != token::Colon) {
-            self.struct_span_err(self.token.span, "found single colon in a struct field type path")
-                .span_suggestion_verbose(
-                    self.token.span,
-                    "write a path separator here",
-                    "::",
-                    Applicability::MaybeIncorrect,
-                )
-                .emit();
+            self.sess.emit_err(errors::SingleColonStructType { span: self.token.span });
         }
         if self.token.kind == token::Eq {
             self.bump();
             let const_expr = self.parse_expr_anon_const()?;
             let sp = ty.span.shrink_to_hi().to(const_expr.value.span);
-            self.struct_span_err(sp, "default values on `struct` fields aren't supported")
-                .span_suggestion(
-                    sp,
-                    "remove this unsupported default value",
-                    "",
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(errors::EqualsStructDefault { span: sp });
         }
         Ok(FieldDef {
             span: lo.to(self.prev_token.span),
@@ -1871,14 +1841,10 @@ impl<'a> Parser<'a> {
                 return IsMacroRulesItem::Yes { has_bang: true };
             } else if self.look_ahead(1, |t| (t.is_ident())) {
                 // macro_rules foo
-                self.struct_span_err(macro_rules_span, "expected `!` after `macro_rules`")
-                    .span_suggestion(
-                        macro_rules_span,
-                        "add a `!`",
-                        "macro_rules!",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(errors::MacroRulesMissingBang {
+                    span: macro_rules_span,
+                    hi: macro_rules_span.shrink_to_hi(),
+                });
 
                 return IsMacroRulesItem::Yes { has_bang: false };
             }
@@ -1903,9 +1869,7 @@ impl<'a> Parser<'a> {
         if self.eat(&token::Not) {
             // Handle macro_rules! foo!
             let span = self.prev_token.span;
-            self.struct_span_err(span, "macro names aren't followed by a `!`")
-                .span_suggestion(span, "remove the `!`", "", Applicability::MachineApplicable)
-                .emit();
+            self.sess.emit_err(errors::MacroNameRemoveBang { span });
         }
 
         let body = self.parse_delim_args()?;
@@ -1925,25 +1889,9 @@ impl<'a> Parser<'a> {
         let vstr = pprust::vis_to_string(vis);
         let vstr = vstr.trim_end();
         if macro_rules {
-            let msg = format!("can't qualify macro_rules invocation with `{vstr}`");
-            self.struct_span_err(vis.span, &msg)
-                .span_suggestion(
-                    vis.span,
-                    "try exporting the macro",
-                    "#[macro_export]",
-                    Applicability::MaybeIncorrect, // speculative
-                )
-                .emit();
+            self.sess.emit_err(errors::MacroRulesVisibility { span: vis.span, vis: vstr });
         } else {
-            self.struct_span_err(vis.span, "can't qualify macro invocation with `pub`")
-                .span_suggestion(
-                    vis.span,
-                    "remove the visibility",
-                    "",
-                    Applicability::MachineApplicable,
-                )
-                .help(&format!("try adjusting the macro to put `{vstr}` inside the invocation"))
-                .emit();
+            self.sess.emit_err(errors::MacroInvocationVisibility { span: vis.span, vis: vstr });
         }
     }
 
@@ -1989,18 +1937,12 @@ impl<'a> Parser<'a> {
             let kw_token = self.token.clone();
             let kw_str = pprust::token_to_string(&kw_token);
             let item = self.parse_item(ForceCollect::No)?;
-
-            self.struct_span_err(
-                kw_token.span,
-                &format!("`{kw_str}` definition cannot be nested inside `{keyword}`"),
-            )
-            .span_suggestion(
-                item.unwrap().span,
-                &format!("consider creating a new `{kw_str}` definition instead of nesting"),
-                "",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
+            self.sess.emit_err(errors::NestedAdt {
+                span: kw_token.span,
+                item: item.unwrap().span,
+                kw_str,
+                keyword: keyword.as_str(),
+            });
             // We successfully parsed the item but we must inform the caller about nested problem.
             return Ok(false);
         }
@@ -2139,13 +2081,10 @@ impl<'a> Parser<'a> {
             let _ = self.parse_expr()?;
             self.expect_semi()?; // `;`
             let span = eq_sp.to(self.prev_token.span);
-            self.struct_span_err(span, "function body cannot be `= expression;`")
-                .multipart_suggestion(
-                    "surround the expression with `{` and `}` instead of `=` and `;`",
-                    vec![(eq_sp, "{".to_string()), (self.prev_token.span, " }".to_string())],
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(errors::FunctionBodyEqualsExpr {
+                span,
+                sugg: errors::FunctionBodyEqualsExprSugg { eq: eq_sp, semi: self.prev_token.span },
+            });
             (AttrVec::new(), Some(self.mk_block_err(span)))
         } else {
             let expected = if req_body {
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index aa57b804779b0..1c34e491f210e 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -43,7 +43,7 @@ use thin_vec::ThinVec;
 use tracing::debug;
 
 use crate::errors::{
-    IncorrectVisibilityRestriction, MismatchedClosingDelimiter, NonStringAbiLiteral,
+    self, IncorrectVisibilityRestriction, MismatchedClosingDelimiter, NonStringAbiLiteral,
 };
 
 bitflags::bitflags! {
@@ -663,15 +663,10 @@ impl<'a> Parser<'a> {
         if case == Case::Insensitive
         && let Some((ident, /* is_raw */ false)) = self.token.ident()
         && ident.as_str().to_lowercase() == kw.as_str().to_lowercase() {
-            self
-                .struct_span_err(ident.span, format!("keyword `{kw}` is written in a wrong case"))
-                .span_suggestion(
-                    ident.span,
-                    "write it in the correct case",
-                    kw,
-                    Applicability::MachineApplicable
-                ).emit();
-
+            self.sess.emit_err(errors::KwBadCase {
+                span: ident.span,
+                kw: kw.as_str()
+            });
             self.bump();
             return true;
         }
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 2246002f5d32a..f2422fe307c5f 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1,6 +1,6 @@
 use super::{ForceCollect, Parser, PathStyle, TrailingToken};
 use crate::errors::{
-    AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
+    self, AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
     DotDotDotRestPattern, EnumPatternInsteadOfIdentifier, ExpectedBindingLeftOfAt,
     ExpectedCommaAfterPatternField, InclusiveRangeExtraEquals, InclusiveRangeMatchArrow,
     InclusiveRangeNoEnd, InvalidMutInPattern, PatternOnWrongSideOfAt, RefMutOrderIncorrect,
@@ -908,18 +908,13 @@ impl<'a> Parser<'a> {
         let box_span = self.prev_token.span;
 
         if self.isnt_pattern_start() {
-            self.struct_span_err(
-                self.token.span,
-                format!("expected pattern, found {}", super::token_descr(&self.token)),
-            )
-            .span_note(box_span, "`box` is a reserved keyword")
-            .span_suggestion_verbose(
-                box_span.shrink_to_lo(),
-                "escape `box` to use it as an identifier",
-                "r#",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
+            let descr = super::token_descr(&self.token);
+            self.sess.emit_err(errors::BoxNotPat {
+                span: self.token.span,
+                kw: box_span,
+                lo: box_span.shrink_to_lo(),
+                descr,
+            });
 
             // We cannot use `parse_pat_ident()` since it will complain `box`
             // is not an identifier.
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 6cceb47ff8384..ae73760bd8cab 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -8,7 +8,7 @@ use rustc_ast::{
     AssocConstraintKind, BlockCheckMode, GenericArg, GenericArgs, Generics, ParenthesizedArgs,
     Path, PathSegment, QSelf,
 };
-use rustc_errors::{pluralize, Applicability, PResult};
+use rustc_errors::{Applicability, PResult};
 use rustc_span::source_map::{BytePos, Span};
 use rustc_span::symbol::{kw, sym, Ident};
 use std::mem;
@@ -464,23 +464,10 @@ impl<'a> Parser<'a> {
                     // i.e. no multibyte characters, in this range.
                     let span =
                         lo.with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count));
-                    self.struct_span_err(
+                    self.sess.emit_err(errors::UnmatchedAngle {
                         span,
-                        &format!(
-                            "unmatched angle bracket{}",
-                            pluralize!(snapshot.unmatched_angle_bracket_count)
-                        ),
-                    )
-                    .span_suggestion(
-                        span,
-                        &format!(
-                            "remove extra angle bracket{}",
-                            pluralize!(snapshot.unmatched_angle_bracket_count)
-                        ),
-                        "",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                        plural: snapshot.unmatched_angle_bracket_count > 1,
+                    });
 
                     // Try again without unmatched angle bracket characters.
                     self.parse_angle_args(ty_generics)
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index f5f6788362ba9..3ceb3a2bef16e 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -588,20 +588,14 @@ impl<'a> Parser<'a> {
         // Always parse bounds greedily for better error recovery.
         if self.token.is_lifetime() {
             self.look_ahead(1, |t| {
-                if let token::Ident(symname, _) = t.kind {
+                if let token::Ident(sym, _) = t.kind {
                     // parse pattern with "'a Sized" we're supposed to give suggestion like
                     // "'a + Sized"
-                    self.struct_span_err(
-                        self.token.span,
-                        &format!("expected `+` between lifetime and {}", symname),
-                    )
-                    .span_suggestion_verbose(
-                        self.token.span.shrink_to_hi(),
-                        "add `+`",
-                        " +",
-                        Applicability::MaybeIncorrect,
-                    )
-                    .emit();
+                    self.sess.emit_err(errors::MissingPlusBounds {
+                        span: self.token.span,
+                        hi: self.token.span.shrink_to_hi(),
+                        sym,
+                    });
                 }
             })
         }
@@ -926,14 +920,10 @@ impl<'a> Parser<'a> {
                 self.parse_remaining_bounds(bounds, true)?;
                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
                 let sp = vec![lo, self.prev_token.span];
-                let sugg = vec![(lo, String::from(" ")), (self.prev_token.span, String::new())];
-                self.struct_span_err(sp, "incorrect braces around trait bounds")
-                    .multipart_suggestion(
-                        "remove the parentheses",
-                        sugg,
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(errors::IncorrectBracesTraitBounds {
+                    span: sp,
+                    sugg: errors::IncorrectBracesTraitBoundsSugg { l: lo, r: self.prev_token.span },
+                });
             } else {
                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
             }
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 2f397e303e508..815b7c8567918 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -1,6 +1,6 @@
 //! Meta-syntax validation logic of attributes for post-expansion.
 
-use crate::parse_in;
+use crate::{errors, parse_in};
 
 use rustc_ast::tokenstream::DelimSpan;
 use rustc_ast::MetaItemKind;
@@ -45,7 +45,7 @@ pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, Meta
         kind: match &item.args {
             AttrArgs::Empty => MetaItemKind::Word,
             AttrArgs::Delimited(DelimArgs { dspan, delim, tokens }) => {
-                check_meta_bad_delim(sess, *dspan, *delim, "wrong meta list delimiters");
+                check_meta_bad_delim(sess, *dspan, *delim);
                 let nmis = parse_in(sess, tokens.clone(), "meta list", |p| p.parse_meta_seq_top())?;
                 MetaItemKind::List(nmis)
             }
@@ -84,19 +84,24 @@ pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, Meta
     })
 }
 
-pub fn check_meta_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter, msg: &str) {
+pub fn check_meta_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter) {
     if let ast::MacDelimiter::Parenthesis = delim {
         return;
     }
+    sess.emit_err(errors::MetaBadDelim {
+        span: span.entire(),
+        sugg: errors::MetaBadDelimSugg { open: span.open, close: span.close },
+    });
+}
 
-    sess.span_diagnostic
-        .struct_span_err(span.entire(), msg)
-        .multipart_suggestion(
-            "the delimiters should be `(` and `)`",
-            vec![(span.open, "(".to_string()), (span.close, ")".to_string())],
-            Applicability::MachineApplicable,
-        )
-        .emit();
+pub fn check_cfg_attr_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter) {
+    if let ast::MacDelimiter::Parenthesis = delim {
+        return;
+    }
+    sess.emit_err(errors::CfgAttrBadDelim {
+        span: span.entire(),
+        sugg: errors::MetaBadDelimSugg { open: span.open, close: span.close },
+    });
 }
 
 /// Checks that the given meta-item is compatible with this `AttributeTemplate`.
diff --git a/compiler/rustc_target/src/abi/call/x86_64.rs b/compiler/rustc_target/src/abi/call/x86_64.rs
index 9427f27d1b7bb..2470cdfebe225 100644
--- a/compiler/rustc_target/src/abi/call/x86_64.rs
+++ b/compiler/rustc_target/src/abi/call/x86_64.rs
@@ -153,9 +153,9 @@ fn reg_component(cls: &[Option<Class>], i: &mut usize, size: Size) -> Option<Reg
     }
 }
 
-fn cast_target(cls: &[Option<Class>], size: Size) -> CastTarget {
+fn cast_target(cls: &[Option<Class>], size: Size) -> Option<CastTarget> {
     let mut i = 0;
-    let lo = reg_component(cls, &mut i, size).unwrap();
+    let lo = reg_component(cls, &mut i, size)?;
     let offset = Size::from_bytes(8) * (i as u64);
     let mut target = CastTarget::from(lo);
     if size > offset {
@@ -164,7 +164,7 @@ fn cast_target(cls: &[Option<Class>], size: Size) -> CastTarget {
         }
     }
     assert_eq!(reg_component(cls, &mut i, Size::ZERO), None);
-    target
+    Some(target)
 }
 
 const MAX_INT_REGS: usize = 6; // RDI, RSI, RDX, RCX, R8, R9
@@ -227,7 +227,9 @@ where
                 // split into sized chunks passed individually
                 if arg.layout.is_aggregate() {
                     let size = arg.layout.size;
-                    arg.cast_to(cast_target(cls, size))
+                    if let Some(cast_target) = cast_target(cls, size) {
+                        arg.cast_to(cast_target);
+                    }
                 } else {
                     arg.extend_integer_width_to(32);
                 }
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
index bd52957d162f2..63a73f8d50d93 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
@@ -3,7 +3,8 @@ use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::CanonicalVarValues;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::{
-    DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, TyCtxtInferExt,
+    DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, RegionVariableOrigin,
+    TyCtxtInferExt,
 };
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::ObligationCause;
@@ -223,18 +224,20 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         {
             debug!("rerunning goal to check result is stable");
             let (_orig_values, canonical_goal) = self.canonicalize_goal(goal);
-            let canonical_response =
+            let new_canonical_response =
                 EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?;
-            if !canonical_response.value.var_values.is_identity() {
+            if !new_canonical_response.value.var_values.is_identity() {
                 bug!(
                     "unstable result: re-canonicalized goal={canonical_goal:#?} \
-                     response={canonical_response:#?}"
+                    first_response={canonical_response:#?} \
+                    second_response={new_canonical_response:#?}"
                 );
             }
-            if certainty != canonical_response.value.certainty {
+            if certainty != new_canonical_response.value.certainty {
                 bug!(
                     "unstable certainty: {certainty:#?} re-canonicalized goal={canonical_goal:#?} \
-                     response={canonical_response:#?}"
+                     first_response={canonical_response:#?} \
+                     second_response={new_canonical_response:#?}"
                 );
             }
         }
@@ -434,6 +437,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         })
     }
 
+    pub(super) fn next_region_infer(&self) -> ty::Region<'tcx> {
+        self.infcx.next_region_var(RegionVariableOrigin::MiscVariable(DUMMY_SP))
+    }
+
     pub(super) fn next_const_infer(&self, ty: Ty<'tcx>) -> ty::Const<'tcx> {
         self.infcx.next_const_var(
             ty,
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
index 226d29687e3a8..67ad7fb4bd21d 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
@@ -16,7 +16,7 @@ use rustc_infer::infer::canonical::query_response::make_query_region_constraints
 use rustc_infer::infer::canonical::CanonicalVarValues;
 use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints};
 use rustc_middle::traits::query::NoSolution;
-use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData};
+use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData, MaybeCause};
 use rustc_middle::ty::{self, BoundVar, GenericArgKind};
 use rustc_span::DUMMY_SP;
 use std::iter;
@@ -60,9 +60,27 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
 
         let certainty = certainty.unify_with(goals_certainty);
 
-        let external_constraints = self.compute_external_query_constraints()?;
+        let response = match certainty {
+            Certainty::Yes | Certainty::Maybe(MaybeCause::Ambiguity) => {
+                let external_constraints = self.compute_external_query_constraints()?;
+                Response { var_values: self.var_values, external_constraints, certainty }
+            }
+            Certainty::Maybe(MaybeCause::Overflow) => {
+                // If we have overflow, it's probable that we're substituting a type
+                // into itself infinitely and any partial substitutions in the query
+                // response are probably not useful anyways, so just return an empty
+                // query response.
+                //
+                // This may prevent us from potentially useful inference, e.g.
+                // 2 candidates, one ambiguous and one overflow, which both
+                // have the same inference constraints.
+                //
+                // Changing this to retain some constraints in the future
+                // won't be a breaking change, so this is good enough for now.
+                return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow));
+            }
+        };
 
-        let response = Response { var_values: self.var_values, external_constraints, certainty };
         let canonical = Canonicalizer::canonicalize(
             self.infcx,
             CanonicalizeMode::Response { max_input_universe: self.max_input_universe },
@@ -72,6 +90,40 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         Ok(canonical)
     }
 
+    /// Constructs a totally unconstrained, ambiguous response to a goal.
+    ///
+    /// Take care when using this, since often it's useful to respond with
+    /// ambiguity but return constrained variables to guide inference.
+    pub(in crate::solve) fn make_ambiguous_response_no_constraints(
+        &self,
+        maybe_cause: MaybeCause,
+    ) -> CanonicalResponse<'tcx> {
+        let unconstrained_response = Response {
+            var_values: CanonicalVarValues {
+                var_values: self.tcx().mk_substs_from_iter(self.var_values.var_values.iter().map(
+                    |arg| -> ty::GenericArg<'tcx> {
+                        match arg.unpack() {
+                            GenericArgKind::Lifetime(_) => self.next_region_infer().into(),
+                            GenericArgKind::Type(_) => self.next_ty_infer().into(),
+                            GenericArgKind::Const(ct) => self.next_const_infer(ct.ty()).into(),
+                        }
+                    },
+                )),
+            },
+            external_constraints: self
+                .tcx()
+                .mk_external_constraints(ExternalConstraintsData::default()),
+            certainty: Certainty::Maybe(maybe_cause),
+        };
+
+        Canonicalizer::canonicalize(
+            self.infcx,
+            CanonicalizeMode::Response { max_input_universe: self.max_input_universe },
+            &mut Default::default(),
+            unconstrained_response,
+        )
+    }
+
     #[instrument(level = "debug", skip(self), ret)]
     fn compute_external_query_constraints(&self) -> Result<ExternalConstraints<'tcx>, NoSolution> {
         // Cannot use `take_registered_region_obligations` as we may compute the response
diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs
index 19bcbd461447d..d94679fef2833 100644
--- a/compiler/rustc_trait_selection/src/solve/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/mod.rs
@@ -340,17 +340,17 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         if responses.is_empty() {
             return Err(NoSolution);
         }
-        let certainty = responses.iter().fold(Certainty::AMBIGUOUS, |certainty, response| {
-            certainty.unify_with(response.value.certainty)
-        });
-
-        let response = self.evaluate_added_goals_and_make_canonical_response(certainty);
-        if let Ok(response) = response {
-            assert!(response.has_no_inference_or_external_constraints());
-            Ok(response)
-        } else {
-            bug!("failed to make floundered response: {responses:?}");
-        }
+
+        let Certainty::Maybe(maybe_cause) = responses.iter().fold(
+            Certainty::AMBIGUOUS,
+            |certainty, response| {
+                certainty.unify_with(response.value.certainty)
+            },
+        ) else {
+            bug!("expected flounder response to be ambiguous")
+        };
+
+        Ok(self.make_ambiguous_response_no_constraints(maybe_cause))
     }
 }
 
diff --git a/compiler/rustc_transmute/src/lib.rs b/compiler/rustc_transmute/src/lib.rs
index 8be02c1d9888a..77c0526e3aabe 100644
--- a/compiler/rustc_transmute/src/lib.rs
+++ b/compiler/rustc_transmute/src/lib.rs
@@ -62,7 +62,7 @@ mod rustc {
 
     use rustc_hir::lang_items::LangItem;
     use rustc_infer::infer::InferCtxt;
-    use rustc_macros::{TypeFoldable, TypeVisitable};
+    use rustc_macros::TypeVisitable;
     use rustc_middle::traits::ObligationCause;
     use rustc_middle::ty::Const;
     use rustc_middle::ty::ParamEnv;
@@ -70,7 +70,7 @@ mod rustc {
     use rustc_middle::ty::TyCtxt;
 
     /// The source and destination types of a transmutation.
-    #[derive(TypeFoldable, TypeVisitable, Debug, Clone, Copy)]
+    #[derive(TypeVisitable, Debug, Clone, Copy)]
     pub struct Types<'tcx> {
         /// The source type.
         pub src: Ty<'tcx>,
diff --git a/compiler/rustc_type_ir/src/structural_impls.rs b/compiler/rustc_type_ir/src/structural_impls.rs
index 54c1ab5a275ef..c9675f93f9564 100644
--- a/compiler/rustc_type_ir/src/structural_impls.rs
+++ b/compiler/rustc_type_ir/src/structural_impls.rs
@@ -6,11 +6,10 @@ use crate::fold::{FallibleTypeFolder, TypeFoldable};
 use crate::visit::{TypeVisitable, TypeVisitor};
 use crate::Interner;
 use rustc_data_structures::functor::IdFunctor;
+use rustc_data_structures::sync::Lrc;
 use rustc_index::{Idx, IndexVec};
 
 use std::ops::ControlFlow;
-use std::rc::Rc;
-use std::sync::Arc;
 
 ///////////////////////////////////////////////////////////////////////////
 // Atomic structs
@@ -106,25 +105,13 @@ impl<I: Interner, T: TypeVisitable<I>, E: TypeVisitable<I>> TypeVisitable<I> for
     }
 }
 
-impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Rc<T> {
+impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Lrc<T> {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         self.try_map_id(|value| value.try_fold_with(folder))
     }
 }
 
-impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Rc<T> {
-    fn visit_with<V: TypeVisitor<I>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
-        (**self).visit_with(visitor)
-    }
-}
-
-impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Arc<T> {
-    fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
-        self.try_map_id(|value| value.try_fold_with(folder))
-    }
-}
-
-impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Arc<T> {
+impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Lrc<T> {
     fn visit_with<V: TypeVisitor<I>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         (**self).visit_with(visitor)
     }
@@ -154,19 +141,11 @@ impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Vec<T> {
     }
 }
 
-impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for &[T] {
-    fn visit_with<V: TypeVisitor<I>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
-        self.iter().try_for_each(|t| t.visit_with(visitor))
-    }
-}
-
-impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Box<[T]> {
-    fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
-        self.try_map_id(|t| t.try_fold_with(folder))
-    }
-}
+// `TypeFoldable` isn't impl'd for `&[T]`. It doesn't make sense in the general
+// case, because we can't return a new slice. But note that there are a couple
+// of trivial impls of `TypeFoldable` for specific slice types elsewhere.
 
-impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Box<[T]> {
+impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for &[T] {
     fn visit_with<V: TypeVisitor<I>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
diff --git a/library/std/src/alloc.rs b/library/std/src/alloc.rs
index c5a5991cc81c4..ec774e62debbf 100644
--- a/library/std/src/alloc.rs
+++ b/library/std/src/alloc.rs
@@ -93,7 +93,7 @@ pub use alloc_crate::alloc::*;
 ///
 /// ```rust
 /// use std::alloc::{System, GlobalAlloc, Layout};
-/// use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
+/// use std::sync::atomic::{AtomicUsize, Ordering::Relaxed};
 ///
 /// struct Counter;
 ///
@@ -103,14 +103,14 @@ pub use alloc_crate::alloc::*;
 ///     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
 ///         let ret = System.alloc(layout);
 ///         if !ret.is_null() {
-///             ALLOCATED.fetch_add(layout.size(), SeqCst);
+///             ALLOCATED.fetch_add(layout.size(), Relaxed);
 ///         }
 ///         ret
 ///     }
 ///
 ///     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
 ///         System.dealloc(ptr, layout);
-///         ALLOCATED.fetch_sub(layout.size(), SeqCst);
+///         ALLOCATED.fetch_sub(layout.size(), Relaxed);
 ///     }
 /// }
 ///
@@ -118,7 +118,7 @@ pub use alloc_crate::alloc::*;
 /// static A: Counter = Counter;
 ///
 /// fn main() {
-///     println!("allocated bytes before main: {}", ALLOCATED.load(SeqCst));
+///     println!("allocated bytes before main: {}", ALLOCATED.load(Relaxed));
 /// }
 /// ```
 ///
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 42a68496fc491..30e553f285b98 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -2284,6 +2284,11 @@ pub fn remove_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
 ///
 /// See [`fs::remove_file`] and [`fs::remove_dir`].
 ///
+/// `remove_dir_all` will fail if `remove_dir` or `remove_file` fail on any constituent paths, including the root path.
+/// As a result, the directory you are deleting must exist, meaning that this function is not idempotent.
+///
+/// Consider ignoring the error if validating the removal is not required for your use case.
+///
 /// [`fs::remove_file`]: remove_file
 /// [`fs::remove_dir`]: remove_dir
 ///
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index f6597c729387e..f5b34f8395205 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -2332,7 +2332,7 @@ impl<'test> TestCx<'test> {
                 // No extra flags needed.
             }
 
-            Some(_) => self.fatal("unknown 'assembly-output' header"),
+            Some(header) => self.fatal(&format!("unknown 'assembly-output' header: {header}")),
             None => self.fatal("missing 'assembly-output' header"),
         }
 
diff --git a/tests/ui/abi/foreign/foreign-fn-with-byval.rs b/tests/ui/abi/foreign/foreign-fn-with-byval.rs
index f366b6ee1bdd5..e20ee0da45d9d 100644
--- a/tests/ui/abi/foreign/foreign-fn-with-byval.rs
+++ b/tests/ui/abi/foreign/foreign-fn-with-byval.rs
@@ -1,5 +1,5 @@
 // run-pass
-#![allow(improper_ctypes)]
+#![allow(improper_ctypes, improper_ctypes_definitions)]
 
 // ignore-wasm32-bare no libc to test ffi with
 
diff --git a/tests/ui/abi/issue-94223.rs b/tests/ui/abi/issue-94223.rs
new file mode 100644
index 0000000000000..79d6b94031bc2
--- /dev/null
+++ b/tests/ui/abi/issue-94223.rs
@@ -0,0 +1,8 @@
+// check-pass
+#![allow(improper_ctypes_definitions)]
+#![crate_type = "lib"]
+
+// Check that computing the fn abi for `bad`, with a external ABI fn ptr that is not FFI-safe, does
+// not ICE.
+
+pub fn bad(f: extern "C" fn([u8])) {}
diff --git a/tests/ui/coherence/coherence-overlap-negative-impls.rs b/tests/ui/coherence/coherence-overlap-negative-impls.rs
new file mode 100644
index 0000000000000..cd1df53a52889
--- /dev/null
+++ b/tests/ui/coherence/coherence-overlap-negative-impls.rs
@@ -0,0 +1,41 @@
+// check-pass
+// known-bug: #74629
+
+// Should fail. The `0` and `1` impls overlap, violating coherence. Eg, with
+// `T = Test, F = ()`, all bounds are true, making both impls applicable.
+// `Test: Fold<Nil>`, `Test: Fold<()>` are true because of `2`.
+// `Is<Test>: NotNil` is true because of `auto trait` and lack of negative impl.
+
+#![feature(negative_impls)]
+#![feature(auto_traits)]
+
+struct Nil;
+struct Cons<H>(H);
+struct Test;
+
+trait Fold<F> {}
+
+impl<T, F> Fold<F> for Cons<T> // 0
+where
+    T: Fold<Nil>,
+{}
+
+impl<T, F> Fold<F> for Cons<T> // 1
+where
+    T: Fold<F>,
+    private::Is<T>: private::NotNil,
+{}
+
+impl<F> Fold<F> for Test {} // 2
+
+mod private {
+    use crate::Nil;
+
+    pub struct Is<T>(T);
+    pub auto trait NotNil {}
+
+    #[allow(suspicious_auto_trait_impls)]
+    impl !NotNil for Is<Nil> {}
+}
+
+fn main() {}
diff --git a/tests/ui/hashmap/hashmap-memory.rs b/tests/ui/hashmap/hashmap-memory.rs
index 87f8b6ad5730b..bd364b349e263 100644
--- a/tests/ui/hashmap/hashmap-memory.rs
+++ b/tests/ui/hashmap/hashmap-memory.rs
@@ -1,5 +1,6 @@
 // run-pass
 
+#![allow(improper_ctypes_definitions)]
 #![allow(non_camel_case_types)]
 #![allow(dead_code)]
 #![allow(unused_mut)]
diff --git a/tests/ui/lint/lint-ctypes-94223.rs b/tests/ui/lint/lint-ctypes-94223.rs
new file mode 100644
index 0000000000000..70dd2a71f2675
--- /dev/null
+++ b/tests/ui/lint/lint-ctypes-94223.rs
@@ -0,0 +1,42 @@
+#![crate_type = "lib"]
+#![deny(improper_ctypes_definitions)]
+
+pub fn bad(f: extern "C" fn([u8])) {}
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+pub fn bad_twice(f: Result<extern "C" fn([u8]), extern "C" fn([u8])>) {}
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+//~^^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+struct BadStruct(extern "C" fn([u8]));
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+enum BadEnum {
+    A(extern "C" fn([u8])),
+    //~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+}
+
+enum BadUnion {
+    A(extern "C" fn([u8])),
+    //~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+}
+
+type Foo = extern "C" fn([u8]);
+//~^ ERROR `extern` fn uses type `[u8]`, which is not FFI-safe
+
+pub struct FfiUnsafe;
+
+#[allow(improper_ctypes_definitions)]
+extern "C" fn f(_: FfiUnsafe) {
+    unimplemented!()
+}
+
+pub static BAD: extern "C" fn(FfiUnsafe) = f;
+//~^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+
+pub static BAD_TWICE: Result<extern "C" fn(FfiUnsafe), extern "C" fn(FfiUnsafe)> = Ok(f);
+//~^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+//~^^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+
+pub const BAD_CONST: extern "C" fn(FfiUnsafe) = f;
+//~^ ERROR `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
diff --git a/tests/ui/lint/lint-ctypes-94223.stderr b/tests/ui/lint/lint-ctypes-94223.stderr
new file mode 100644
index 0000000000000..49e64ed5140c2
--- /dev/null
+++ b/tests/ui/lint/lint-ctypes-94223.stderr
@@ -0,0 +1,126 @@
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:4:15
+   |
+LL | pub fn bad(f: extern "C" fn([u8])) {}
+   |               ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+note: the lint level is defined here
+  --> $DIR/lint-ctypes-94223.rs:2:9
+   |
+LL | #![deny(improper_ctypes_definitions)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:7:28
+   |
+LL | pub fn bad_twice(f: Result<extern "C" fn([u8]), extern "C" fn([u8])>) {}
+   |                            ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:7:49
+   |
+LL | pub fn bad_twice(f: Result<extern "C" fn([u8]), extern "C" fn([u8])>) {}
+   |                                                 ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:11:18
+   |
+LL | struct BadStruct(extern "C" fn([u8]));
+   |                  ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:15:7
+   |
+LL |     A(extern "C" fn([u8])),
+   |       ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:20:7
+   |
+LL |     A(extern "C" fn([u8])),
+   |       ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `[u8]`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:24:12
+   |
+LL | type Foo = extern "C" fn([u8]);
+   |            ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider using a raw pointer instead
+   = note: slices have no C equivalent
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:34:17
+   |
+LL | pub static BAD: extern "C" fn(FfiUnsafe) = f;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
+   = note: this struct has unspecified layout
+note: the type is defined here
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:37:30
+   |
+LL | pub static BAD_TWICE: Result<extern "C" fn(FfiUnsafe), extern "C" fn(FfiUnsafe)> = Ok(f);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
+   = note: this struct has unspecified layout
+note: the type is defined here
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:37:56
+   |
+LL | pub static BAD_TWICE: Result<extern "C" fn(FfiUnsafe), extern "C" fn(FfiUnsafe)> = Ok(f);
+   |                                                        ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
+   = note: this struct has unspecified layout
+note: the type is defined here
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: `extern` fn uses type `FfiUnsafe`, which is not FFI-safe
+  --> $DIR/lint-ctypes-94223.rs:41:22
+   |
+LL | pub const BAD_CONST: extern "C" fn(FfiUnsafe) = f;
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
+   = note: this struct has unspecified layout
+note: the type is defined here
+  --> $DIR/lint-ctypes-94223.rs:27:1
+   |
+LL | pub struct FfiUnsafe;
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 11 previous errors
+
diff --git a/tests/ui/macros/missing-bang-in-decl.stderr b/tests/ui/macros/missing-bang-in-decl.stderr
index dfabafb0a7ab8..aa78c9a690643 100644
--- a/tests/ui/macros/missing-bang-in-decl.stderr
+++ b/tests/ui/macros/missing-bang-in-decl.stderr
@@ -2,13 +2,23 @@ error: expected `!` after `macro_rules`
   --> $DIR/missing-bang-in-decl.rs:5:1
    |
 LL | macro_rules foo {
-   | ^^^^^^^^^^^ help: add a `!`: `macro_rules!`
+   | ^^^^^^^^^^^
+   |
+help: add a `!`
+   |
+LL | macro_rules! foo {
+   |            +
 
 error: expected `!` after `macro_rules`
   --> $DIR/missing-bang-in-decl.rs:10:1
    |
 LL | macro_rules bar! {
-   | ^^^^^^^^^^^ help: add a `!`: `macro_rules!`
+   | ^^^^^^^^^^^
+   |
+help: add a `!`
+   |
+LL | macro_rules! bar! {
+   |            +
 
 error: macro names aren't followed by a `!`
   --> $DIR/missing-bang-in-decl.rs:10:16
diff --git a/tests/ui/parser/item-kw-case-mismatch.fixed b/tests/ui/parser/item-kw-case-mismatch.fixed
index 1794268f260e1..4b99537fbf7f4 100644
--- a/tests/ui/parser/item-kw-case-mismatch.fixed
+++ b/tests/ui/parser/item-kw-case-mismatch.fixed
@@ -4,31 +4,31 @@
 
 fn main() {}
 
-use std::ptr::read;  //~ ERROR keyword `use` is written in a wrong case
-use std::ptr::write; //~ ERROR keyword `use` is written in a wrong case
+use std::ptr::read;  //~ ERROR keyword `use` is written in the wrong case
+use std::ptr::write; //~ ERROR keyword `use` is written in the wrong case
 
 async fn _a() {}
-//~^ ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `fn` is written in the wrong case
 
 fn _b() {}
-//~^ ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `fn` is written in the wrong case
 
 async fn _c() {}
-//~^ ERROR keyword `async` is written in a wrong case
-//~| ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `async` is written in the wrong case
+//~| ERROR keyword `fn` is written in the wrong case
 
 async fn _d() {}
-//~^ ERROR keyword `async` is written in a wrong case
+//~^ ERROR keyword `async` is written in the wrong case
 
 const unsafe fn _e() {}
-//~^ ERROR keyword `const` is written in a wrong case
-//~| ERROR keyword `unsafe` is written in a wrong case
-//~| ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `const` is written in the wrong case
+//~| ERROR keyword `unsafe` is written in the wrong case
+//~| ERROR keyword `fn` is written in the wrong case
 
 unsafe extern fn _f() {}
-//~^ ERROR keyword `unsafe` is written in a wrong case
-//~| ERROR keyword `extern` is written in a wrong case
+//~^ ERROR keyword `unsafe` is written in the wrong case
+//~| ERROR keyword `extern` is written in the wrong case
 
 extern "C" fn _g() {}
-//~^ ERROR keyword `extern` is written in a wrong case
-//~| ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `extern` is written in the wrong case
+//~| ERROR keyword `fn` is written in the wrong case
diff --git a/tests/ui/parser/item-kw-case-mismatch.rs b/tests/ui/parser/item-kw-case-mismatch.rs
index ac8390efdb9a3..b11ec93754fc5 100644
--- a/tests/ui/parser/item-kw-case-mismatch.rs
+++ b/tests/ui/parser/item-kw-case-mismatch.rs
@@ -4,31 +4,31 @@
 
 fn main() {}
 
-Use std::ptr::read;  //~ ERROR keyword `use` is written in a wrong case
-USE std::ptr::write; //~ ERROR keyword `use` is written in a wrong case
+Use std::ptr::read;  //~ ERROR keyword `use` is written in the wrong case
+USE std::ptr::write; //~ ERROR keyword `use` is written in the wrong case
 
 async Fn _a() {}
-//~^ ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `fn` is written in the wrong case
 
 Fn _b() {}
-//~^ ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `fn` is written in the wrong case
 
 aSYNC fN _c() {}
-//~^ ERROR keyword `async` is written in a wrong case
-//~| ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `async` is written in the wrong case
+//~| ERROR keyword `fn` is written in the wrong case
 
 Async fn _d() {}
-//~^ ERROR keyword `async` is written in a wrong case
+//~^ ERROR keyword `async` is written in the wrong case
 
 CONST UNSAFE FN _e() {}
-//~^ ERROR keyword `const` is written in a wrong case
-//~| ERROR keyword `unsafe` is written in a wrong case
-//~| ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `const` is written in the wrong case
+//~| ERROR keyword `unsafe` is written in the wrong case
+//~| ERROR keyword `fn` is written in the wrong case
 
 unSAFE EXTern fn _f() {}
-//~^ ERROR keyword `unsafe` is written in a wrong case
-//~| ERROR keyword `extern` is written in a wrong case
+//~^ ERROR keyword `unsafe` is written in the wrong case
+//~| ERROR keyword `extern` is written in the wrong case
 
 EXTERN "C" FN _g() {}
-//~^ ERROR keyword `extern` is written in a wrong case
-//~| ERROR keyword `fn` is written in a wrong case
+//~^ ERROR keyword `extern` is written in the wrong case
+//~| ERROR keyword `fn` is written in the wrong case
diff --git a/tests/ui/parser/item-kw-case-mismatch.stderr b/tests/ui/parser/item-kw-case-mismatch.stderr
index e66dae825f9c4..ba59ea8536338 100644
--- a/tests/ui/parser/item-kw-case-mismatch.stderr
+++ b/tests/ui/parser/item-kw-case-mismatch.stderr
@@ -1,82 +1,82 @@
-error: keyword `use` is written in a wrong case
+error: keyword `use` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:7:1
    |
 LL | Use std::ptr::read;
    | ^^^ help: write it in the correct case (notice the capitalization): `use`
 
-error: keyword `use` is written in a wrong case
+error: keyword `use` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:8:1
    |
 LL | USE std::ptr::write;
    | ^^^ help: write it in the correct case: `use`
 
-error: keyword `fn` is written in a wrong case
+error: keyword `fn` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:10:7
    |
 LL | async Fn _a() {}
    |       ^^ help: write it in the correct case (notice the capitalization): `fn`
 
-error: keyword `fn` is written in a wrong case
+error: keyword `fn` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:13:1
    |
 LL | Fn _b() {}
    | ^^ help: write it in the correct case (notice the capitalization): `fn`
 
-error: keyword `async` is written in a wrong case
+error: keyword `async` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:16:1
    |
 LL | aSYNC fN _c() {}
    | ^^^^^ help: write it in the correct case: `async`
 
-error: keyword `fn` is written in a wrong case
+error: keyword `fn` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:16:7
    |
 LL | aSYNC fN _c() {}
    |       ^^ help: write it in the correct case: `fn`
 
-error: keyword `async` is written in a wrong case
+error: keyword `async` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:20:1
    |
 LL | Async fn _d() {}
    | ^^^^^ help: write it in the correct case: `async`
 
-error: keyword `const` is written in a wrong case
+error: keyword `const` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:23:1
    |
 LL | CONST UNSAFE FN _e() {}
    | ^^^^^ help: write it in the correct case: `const`
 
-error: keyword `unsafe` is written in a wrong case
+error: keyword `unsafe` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:23:7
    |
 LL | CONST UNSAFE FN _e() {}
    |       ^^^^^^ help: write it in the correct case: `unsafe`
 
-error: keyword `fn` is written in a wrong case
+error: keyword `fn` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:23:14
    |
 LL | CONST UNSAFE FN _e() {}
    |              ^^ help: write it in the correct case: `fn`
 
-error: keyword `unsafe` is written in a wrong case
+error: keyword `unsafe` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:28:1
    |
 LL | unSAFE EXTern fn _f() {}
    | ^^^^^^ help: write it in the correct case: `unsafe`
 
-error: keyword `extern` is written in a wrong case
+error: keyword `extern` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:28:8
    |
 LL | unSAFE EXTern fn _f() {}
    |        ^^^^^^ help: write it in the correct case: `extern`
 
-error: keyword `extern` is written in a wrong case
+error: keyword `extern` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:32:1
    |
 LL | EXTERN "C" FN _g() {}
    | ^^^^^^ help: write it in the correct case: `extern`
 
-error: keyword `fn` is written in a wrong case
+error: keyword `fn` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:32:12
    |
 LL | EXTERN "C" FN _g() {}
diff --git a/tests/ui/parser/recover-unticked-labels.stderr b/tests/ui/parser/recover-unticked-labels.stderr
index c115dffb10e9c..fbd108ca613c7 100644
--- a/tests/ui/parser/recover-unticked-labels.stderr
+++ b/tests/ui/parser/recover-unticked-labels.stderr
@@ -2,13 +2,17 @@ error: expected a label, found an identifier
   --> $DIR/recover-unticked-labels.rs:5:26
    |
 LL |     'label: loop { break label 0 };
-   |                          ^^^^^ help: labels start with a tick: `'label`
+   |                          -^^^^
+   |                          |
+   |                          help: labels start with a tick
 
 error: expected a label, found an identifier
   --> $DIR/recover-unticked-labels.rs:6:29
    |
 LL |     'label: loop { continue label };
-   |                             ^^^^^ help: labels start with a tick: `'label`
+   |                             -^^^^
+   |                             |
+   |                             help: labels start with a tick
 
 error[E0425]: cannot find value `label` in this scope
   --> $DIR/recover-unticked-labels.rs:4:26
diff --git a/tests/ui/parser/use-colon-as-mod-sep.stderr b/tests/ui/parser/use-colon-as-mod-sep.stderr
index e825dfed11192..bfc5374ef9d2d 100644
--- a/tests/ui/parser/use-colon-as-mod-sep.stderr
+++ b/tests/ui/parser/use-colon-as-mod-sep.stderr
@@ -11,18 +11,24 @@ error: expected `::`, found `:`
    |
 LL | use std:fs::File;
    |        ^ help: use double colon
+   |
+   = note: import paths are delimited using `::`
 
 error: expected `::`, found `:`
   --> $DIR/use-colon-as-mod-sep.rs:7:8
    |
 LL | use std:collections:HashMap;
    |        ^ help: use double colon
+   |
+   = note: import paths are delimited using `::`
 
 error: expected `::`, found `:`
   --> $DIR/use-colon-as-mod-sep.rs:7:20
    |
 LL | use std:collections:HashMap;
    |                    ^ help: use double colon
+   |
+   = note: import paths are delimited using `::`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/specialization/issue-40582.rs b/tests/ui/specialization/issue-40582.rs
new file mode 100644
index 0000000000000..9805933553dd7
--- /dev/null
+++ b/tests/ui/specialization/issue-40582.rs
@@ -0,0 +1,35 @@
+// check-pass
+// known-bug: #40582
+
+// Should fail. Should not be possible to implement `make_static`.
+
+#![feature(specialization)]
+#![allow(incomplete_features)]
+
+trait FromRef<'a, T: ?Sized> {
+    fn from_ref(r: &'a T) -> Self;
+}
+
+impl<'a, T: ?Sized> FromRef<'a, T> for &'a T {
+    fn from_ref(r: &'a T) -> Self {
+        r
+    }
+}
+
+impl<'a, T: ?Sized, R> FromRef<'a, T> for R {
+    default fn from_ref(_: &'a T) -> Self {
+        unimplemented!()
+    }
+}
+
+fn make_static<T: ?Sized>(data: &T) -> &'static T {
+    fn helper<T: ?Sized, R>(data: &T) -> R {
+        R::from_ref(data)
+    }
+    helper(data)
+}
+
+fn main() {
+    let s = "specialization".to_owned();
+    println!("{:?}", make_static(s.as_str()));
+}
diff --git a/tests/ui/specialization/specialization-default-items-drop-coherence.rs b/tests/ui/specialization/specialization-default-items-drop-coherence.rs
new file mode 100644
index 0000000000000..16ad942d5ab95
--- /dev/null
+++ b/tests/ui/specialization/specialization-default-items-drop-coherence.rs
@@ -0,0 +1,30 @@
+// check-pass
+// known-bug: #105782
+
+// Should fail. Default items completely drop candidates instead of ambiguity,
+// which is unsound during coherence, since coherence requires completeness.
+
+#![feature(specialization)]
+#![allow(incomplete_features)]
+
+trait Default {
+   type Id;
+}
+
+impl<T> Default for T {
+   default type Id = T;
+}
+
+trait Overlap {
+   type Assoc;
+}
+
+impl Overlap for u32 {
+   type Assoc = usize;
+}
+
+impl Overlap for <u32 as Default>::Id {
+   type Assoc = Box<usize>;
+}
+
+fn main() {}
diff --git a/tests/ui/thread-local/thread-local-static-ref-use-after-free.rs b/tests/ui/thread-local/thread-local-static-ref-use-after-free.rs
new file mode 100644
index 0000000000000..c282e2185bca2
--- /dev/null
+++ b/tests/ui/thread-local/thread-local-static-ref-use-after-free.rs
@@ -0,0 +1,46 @@
+// check-pass
+// known-bug: #49682
+// edition:2021
+
+// Should fail. Keeping references to thread local statics can result in a
+// use-after-free.
+
+#![feature(thread_local)]
+
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::thread;
+
+#[allow(dead_code)]
+#[thread_local]
+static FOO: AtomicUsize = AtomicUsize::new(0);
+
+#[allow(dead_code)]
+async fn bar() {}
+
+#[allow(dead_code)]
+async fn foo() {
+    let r = &FOO;
+    bar().await;
+    r.load(Ordering::SeqCst);
+}
+
+fn main() {
+    // &FOO = 0x7fd1e9cbf6d0
+    _ = thread::spawn(|| {
+        let g = foo();
+        println!("&FOO = {:p}", &FOO);
+        g
+    })
+    .join()
+    .unwrap();
+
+    // &FOO = 0x7fd1e9cc0f50
+    println!("&FOO = {:p}", &FOO);
+
+    // &FOO = 0x7fd1e9cbf6d0
+    thread::spawn(move || {
+        println!("&FOO = {:p}", &FOO);
+    })
+    .join()
+    .unwrap();
+}
diff --git a/tests/ui/traits/new-solver/exponential-trait-goals.rs b/tests/ui/traits/new-solver/exponential-trait-goals.rs
new file mode 100644
index 0000000000000..b37f09ee185e9
--- /dev/null
+++ b/tests/ui/traits/new-solver/exponential-trait-goals.rs
@@ -0,0 +1,20 @@
+// compile-flags: -Ztrait-solver=next
+
+trait Trait {}
+
+struct W<T>(T);
+
+impl<T, U> Trait for W<(W<T>, W<U>)>
+where
+    W<T>: Trait,
+    W<U>: Trait,
+{
+}
+
+fn impls<T: Trait>() {}
+
+fn main() {
+    impls::<W<_>>();
+    //~^ ERROR type annotations needed
+    //~| ERROR overflow evaluating the requirement `W<_>: Trait`
+}
diff --git a/tests/ui/traits/new-solver/exponential-trait-goals.stderr b/tests/ui/traits/new-solver/exponential-trait-goals.stderr
new file mode 100644
index 0000000000000..28a99cbbca6a1
--- /dev/null
+++ b/tests/ui/traits/new-solver/exponential-trait-goals.stderr
@@ -0,0 +1,23 @@
+error[E0282]: type annotations needed
+  --> $DIR/exponential-trait-goals.rs:17:5
+   |
+LL |     impls::<W<_>>();
+   |     ^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `impls`
+
+error[E0275]: overflow evaluating the requirement `W<_>: Trait`
+  --> $DIR/exponential-trait-goals.rs:17:5
+   |
+LL |     impls::<W<_>>();
+   |     ^^^^^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`exponential_trait_goals`)
+note: required by a bound in `impls`
+  --> $DIR/exponential-trait-goals.rs:14:13
+   |
+LL | fn impls<T: Trait>() {}
+   |             ^^^^^ required by this bound in `impls`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0275, E0282.
+For more information about an error, try `rustc --explain E0275`.