Merging upstream version 1.73.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 251 insertions, 174 deletions

diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index c7d2e4c22..3465759b9 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -12,7 +12,7 @@ pub mod util;
 use crate::infer::canonical::Canonical;
 use crate::mir::ConstraintCategory;
 use crate::ty::abstract_const::NotConstEvaluatable;
-use crate::ty::subst::SubstsRef;
+use crate::ty::GenericArgsRef;
 use crate::ty::{self, AdtKind, Ty, TyCtxt};
 
 use rustc_data_structures::sync::Lrc;
@@ -199,7 +199,7 @@ impl<'tcx> ObligationCause<'tcx> {
 pub struct UnifyReceiverContext<'tcx> {
     pub assoc_item: ty::AssocItem,
     pub param_env: ty::ParamEnv<'tcx>,
-    pub substs: SubstsRef<'tcx>,
+    pub args: GenericArgsRef<'tcx>,
 }
 
 #[derive(Clone, PartialEq, Eq, Lift, Default, HashStable)]
@@ -402,7 +402,7 @@ pub enum ObligationCauseCode<'tcx> {
     OpaqueReturnType(Option<(Ty<'tcx>, Span)>),
 
     /// Block implicit return
-    BlockTailExpression(hir::HirId),
+    BlockTailExpression(hir::HirId, hir::MatchSource),
 
     /// #[feature(trivial_bounds)] is not enabled
     TrivialBound,
@@ -543,7 +543,6 @@ pub struct MatchExpressionArmCause<'tcx> {
     pub scrut_span: Span,
     pub source: hir::MatchSource,
     pub prior_arms: Vec<Span>,
-    pub scrut_hir_id: hir::HirId,
     pub opt_suggest_box_span: Option<Span>,
 }
 
@@ -649,43 +648,31 @@ pub enum ImplSource<'tcx, N> {
     /// for some type parameter. The `Vec<N>` represents the
     /// obligations incurred from normalizing the where-clause (if
     /// any).
-    Param(Vec<N>, ty::BoundConstness),
+    Param(Vec<N>),
 
-    /// Virtual calls through an object.
-    Object(ImplSourceObjectData<N>),
-
-    /// Successful resolution for a builtin trait.
-    Builtin(Vec<N>),
-
-    /// ImplSource for trait upcasting coercion
-    TraitUpcasting(ImplSourceTraitUpcastingData<N>),
+    /// Successful resolution for a builtin impl.
+    Builtin(BuiltinImplSource, Vec<N>),
 }
 
 impl<'tcx, N> ImplSource<'tcx, N> {
     pub fn nested_obligations(self) -> Vec<N> {
         match self {
             ImplSource::UserDefined(i) => i.nested,
-            ImplSource::Param(n, _) | ImplSource::Builtin(n) => n,
-            ImplSource::Object(d) => d.nested,
-            ImplSource::TraitUpcasting(d) => d.nested,
+            ImplSource::Param(n) | ImplSource::Builtin(_, n) => n,
         }
     }
 
     pub fn borrow_nested_obligations(&self) -> &[N] {
         match self {
             ImplSource::UserDefined(i) => &i.nested,
-            ImplSource::Param(n, _) | ImplSource::Builtin(n) => &n,
-            ImplSource::Object(d) => &d.nested,
-            ImplSource::TraitUpcasting(d) => &d.nested,
+            ImplSource::Param(n) | ImplSource::Builtin(_, n) => &n,
         }
     }
 
     pub fn borrow_nested_obligations_mut(&mut self) -> &mut [N] {
         match self {
             ImplSource::UserDefined(i) => &mut i.nested,
-            ImplSource::Param(n, _) | ImplSource::Builtin(n) => n,
-            ImplSource::Object(d) => &mut d.nested,
-            ImplSource::TraitUpcasting(d) => &mut d.nested,
+            ImplSource::Param(n) | ImplSource::Builtin(_, n) => n,
         }
     }
 
@@ -696,20 +683,12 @@ impl<'tcx, N> ImplSource<'tcx, N> {
         match self {
             ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
                 impl_def_id: i.impl_def_id,
-                substs: i.substs,
+                args: i.args,
                 nested: i.nested.into_iter().map(f).collect(),
             }),
-            ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
-            ImplSource::Builtin(n) => ImplSource::Builtin(n.into_iter().map(f).collect()),
-            ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
-                vtable_base: o.vtable_base,
-                nested: o.nested.into_iter().map(f).collect(),
-            }),
-            ImplSource::TraitUpcasting(d) => {
-                ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
-                    vtable_vptr_slot: d.vtable_vptr_slot,
-                    nested: d.nested.into_iter().map(f).collect(),
-                })
+            ImplSource::Param(n) => ImplSource::Param(n.into_iter().map(f).collect()),
+            ImplSource::Builtin(source, n) => {
+                ImplSource::Builtin(source, n.into_iter().map(f).collect())
             }
         }
     }
@@ -729,33 +708,35 @@ impl<'tcx, N> ImplSource<'tcx, N> {
 #[derive(TypeFoldable, TypeVisitable)]
 pub struct ImplSourceUserDefinedData<'tcx, N> {
     pub impl_def_id: DefId,
-    pub substs: SubstsRef<'tcx>,
+    pub args: GenericArgsRef<'tcx>,
     pub nested: Vec<N>,
 }
 
-#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
-#[derive(TypeFoldable, TypeVisitable)]
-pub struct ImplSourceTraitUpcastingData<N> {
+#[derive(Copy, Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Debug)]
+pub enum BuiltinImplSource {
+    /// Some builtin impl we don't need to differentiate. This should be used
+    /// unless more specific information is necessary.
+    Misc,
+    /// A builtin impl for trait objects.
+    ///
+    /// The vtable is formed by concatenating together the method lists of
+    /// the base object trait and all supertraits, pointers to supertrait vtable will
+    /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
+    /// in that vtable.
+    Object { vtable_base: usize },
     /// The vtable is formed by concatenating together the method lists of
     /// the base object trait and all supertraits, pointers to supertrait vtable will
     /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
     /// within that vtable.
-    pub vtable_vptr_slot: Option<usize>,
-
-    pub nested: Vec<N>,
+    TraitUpcasting { vtable_vptr_slot: Option<usize> },
+    /// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
+    ///
+    /// This needs to be a separate variant as it is still unstable and we need to emit
+    /// a feature error when using it on stable.
+    TupleUnsizing,
 }
 
-#[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, Lift)]
-#[derive(TypeFoldable, TypeVisitable)]
-pub struct ImplSourceObjectData<N> {
-    /// The vtable is formed by concatenating together the method lists of
-    /// the base object trait and all supertraits, pointers to supertrait vtable will
-    /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
-    /// in that vtable.
-    pub vtable_base: usize,
-
-    pub nested: Vec<N>,
-}
+TrivialTypeTraversalAndLiftImpls! { BuiltinImplSource }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 pub enum ObjectSafetyViolation {
@@ -795,49 +776,48 @@ impl ObjectSafetyViolation {
                 "where clause cannot reference non-lifetime `for<...>` variables".into()
             }
             ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
-                format!("associated function `{}` has no `self` parameter", name).into()
+                format!("associated function `{name}` has no `self` parameter").into()
             }
             ObjectSafetyViolation::Method(
                 name,
                 MethodViolationCode::ReferencesSelfInput(_),
                 DUMMY_SP,
-            ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
+            ) => format!("method `{name}` references the `Self` type in its parameters").into(),
             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
-                format!("method `{}` references the `Self` type in this parameter", name).into()
+                format!("method `{name}` references the `Self` type in this parameter").into()
             }
             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
-                format!("method `{}` references the `Self` type in its return type", name).into()
+                format!("method `{name}` references the `Self` type in its return type").into()
             }
             ObjectSafetyViolation::Method(
                 name,
                 MethodViolationCode::ReferencesImplTraitInTrait(_),
                 _,
-            ) => format!("method `{}` references an `impl Trait` type in its return type", name)
-                .into(),
+            ) => {
+                format!("method `{name}` references an `impl Trait` type in its return type").into()
+            }
             ObjectSafetyViolation::Method(name, MethodViolationCode::AsyncFn, _) => {
-                format!("method `{}` is `async`", name).into()
+                format!("method `{name}` is `async`").into()
             }
             ObjectSafetyViolation::Method(
                 name,
                 MethodViolationCode::WhereClauseReferencesSelf,
                 _,
-            ) => {
-                format!("method `{}` references the `Self` type in its `where` clause", name).into()
-            }
+            ) => format!("method `{name}` references the `Self` type in its `where` clause").into(),
             ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
-                format!("method `{}` has generic type parameters", name).into()
+                format!("method `{name}` has generic type parameters").into()
             }
             ObjectSafetyViolation::Method(
                 name,
                 MethodViolationCode::UndispatchableReceiver(_),
                 _,
-            ) => format!("method `{}`'s `self` parameter cannot be dispatched on", name).into(),
+            ) => format!("method `{name}`'s `self` parameter cannot be dispatched on").into(),
             ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
-                format!("it contains associated `const` `{}`", name).into()
+                format!("it contains associated `const` `{name}`").into()
             }
             ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
             ObjectSafetyViolation::GAT(name, _) => {
-                format!("it contains the generic associated type `{}`", name).into()
+                format!("it contains the generic associated type `{name}`").into()
             }
         }
     }
@@ -855,8 +835,7 @@ impl ObjectSafetyViolation {
                 err.span_suggestion(
                     add_self_sugg.1,
                     format!(
-                        "consider turning `{}` into a method by giving it a `&self` argument",
-                        name
+                        "consider turning `{name}` into a method by giving it a `&self` argument"
                     ),
                     add_self_sugg.0.to_string(),
                     Applicability::MaybeIncorrect,
@@ -864,9 +843,8 @@ impl ObjectSafetyViolation {
                 err.span_suggestion(
                     make_sized_sugg.1,
                     format!(
-                        "alternatively, consider constraining `{}` so it does not apply to \
-                             trait objects",
-                        name
+                        "alternatively, consider constraining `{name}` so it does not apply to \
+                             trait objects"
                     ),
                     make_sized_sugg.0.to_string(),
                     Applicability::MaybeIncorrect,
@@ -879,7 +857,7 @@ impl ObjectSafetyViolation {
             ) => {
                 err.span_suggestion(
                     *span,
-                    format!("consider changing method `{}`'s `self` parameter to be `&self`", name),
+                    format!("consider changing method `{name}`'s `self` parameter to be `&self`"),
                     "&Self",
                     Applicability::MachineApplicable,
                 );
@@ -887,7 +865,7 @@ impl ObjectSafetyViolation {
             ObjectSafetyViolation::AssocConst(name, _)
             | ObjectSafetyViolation::GAT(name, _)
             | ObjectSafetyViolation::Method(name, ..) => {
-                err.help(format!("consider moving `{}` to another trait", name));
+                err.help(format!("consider moving `{name}` to another trait"));
             }
         }
     }
diff --git a/compiler/rustc_middle/src/traits/query.rs b/compiler/rustc_middle/src/traits/query.rs
index 60a38747f..950a59e96 100644
--- a/compiler/rustc_middle/src/traits/query.rs
+++ b/compiler/rustc_middle/src/traits/query.rs
@@ -8,7 +8,7 @@
 use crate::error::DropCheckOverflow;
 use crate::infer::canonical::{Canonical, QueryResponse};
 use crate::ty::error::TypeError;
-use crate::ty::subst::GenericArg;
+use crate::ty::GenericArg;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_span::source_map::Span;
 
@@ -132,7 +132,7 @@ impl<'tcx> DropckOutlivesResult<'tcx> {
 pub struct DropckConstraint<'tcx> {
     /// Types that are required to be alive in order for this
     /// type to be valid for destruction.
-    pub outlives: Vec<ty::subst::GenericArg<'tcx>>,
+    pub outlives: Vec<ty::GenericArg<'tcx>>,
 
     /// Types that could not be resolved: projections and params.
     pub dtorck_types: Vec<Ty<'tcx>>,
diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs
index f2dda003b..ffae35798 100644
--- a/compiler/rustc_middle/src/traits/select.rs
+++ b/compiler/rustc_middle/src/traits/select.rs
@@ -127,6 +127,7 @@ pub enum SelectionCandidate<'tcx> {
     /// an applicable bound in the trait definition. The `usize` is an index
     /// into the list returned by `tcx.item_bounds`. The constness is the
     /// constness of the bound in the trait.
+    // FIXME(effects) do we need this constness
     ProjectionCandidate(usize, ty::BoundConstness),
 
     /// Implementation of a `Fn`-family trait by one of the anonymous types
@@ -304,9 +305,7 @@ impl From<ErrorGuaranteed> for OverflowError {
     }
 }
 
-TrivialTypeTraversalAndLiftImpls! {
-    OverflowError,
-}
+TrivialTypeTraversalAndLiftImpls! { OverflowError }
 
 impl<'tcx> From<OverflowError> for SelectionError<'tcx> {
     fn from(overflow_error: OverflowError) -> SelectionError<'tcx> {
diff --git a/compiler/rustc_middle/src/traits/solve.rs b/compiler/rustc_middle/src/traits/solve.rs
index 73b332fd8..9d63d2918 100644
--- a/compiler/rustc_middle/src/traits/solve.rs
+++ b/compiler/rustc_middle/src/traits/solve.rs
@@ -1,7 +1,6 @@
 use std::ops::ControlFlow;
 
 use rustc_data_structures::intern::Interned;
-use rustc_query_system::cache::Cache;
 
 use crate::infer::canonical::{CanonicalVarValues, QueryRegionConstraints};
 use crate::traits::query::NoSolution;
@@ -11,9 +10,10 @@ use crate::ty::{
     TypeVisitor,
 };
 
+mod cache;
 pub mod inspect;
 
-pub type EvaluationCache<'tcx> = Cache<CanonicalInput<'tcx>, QueryResult<'tcx>>;
+pub use cache::{CacheData, EvaluationCache};
 
 /// A goal is a statement, i.e. `predicate`, we want to prove
 /// given some assumptions, i.e. `param_env`.
@@ -57,6 +57,7 @@ pub enum Certainty {
 
 impl Certainty {
     pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
+    pub const OVERFLOW: Certainty = Certainty::Maybe(MaybeCause::Overflow);
 
     /// Use this function to merge the certainty of multiple nested subgoals.
     ///
@@ -66,7 +67,7 @@ impl Certainty {
     /// success, we merge these two responses. This results in ambiguity.
     ///
     /// If we unify ambiguity with overflow, we return overflow. This doesn't matter
-    /// inside of the solver as we distinguish ambiguity from overflow. It does
+    /// inside of the solver as we do not distinguish ambiguity from overflow. It does
     /// however matter for diagnostics. If `T: Foo` resulted in overflow and `T: Bar`
     /// in ambiguity without changing the inference state, we still want to tell the
     /// user that `T: Baz` results in overflow.
@@ -146,7 +147,7 @@ impl<'tcx> std::ops::Deref for ExternalConstraints<'tcx> {
 }
 
 /// Additional constraints returned on success.
-#[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default)]
+#[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default, TypeVisitable, TypeFoldable)]
 pub struct ExternalConstraintsData<'tcx> {
     // FIXME: implement this.
     pub region_constraints: QueryRegionConstraints<'tcx>,
diff --git a/compiler/rustc_middle/src/traits/solve/cache.rs b/compiler/rustc_middle/src/traits/solve/cache.rs
new file mode 100644
index 000000000..9898b0019
--- /dev/null
+++ b/compiler/rustc_middle/src/traits/solve/cache.rs
@@ -0,0 +1,100 @@
+use super::{CanonicalInput, QueryResult};
+use crate::ty::TyCtxt;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::sync::Lock;
+use rustc_query_system::cache::WithDepNode;
+use rustc_query_system::dep_graph::DepNodeIndex;
+use rustc_session::Limit;
+/// The trait solver cache used by `-Ztrait-solver=next`.
+///
+/// FIXME(@lcnr): link to some official documentation of how
+/// this works.
+#[derive(Default)]
+pub struct EvaluationCache<'tcx> {
+    map: Lock<FxHashMap<CanonicalInput<'tcx>, CacheEntry<'tcx>>>,
+}
+
+pub struct CacheData<'tcx> {
+    pub result: QueryResult<'tcx>,
+    pub reached_depth: usize,
+    pub encountered_overflow: bool,
+}
+
+impl<'tcx> EvaluationCache<'tcx> {
+    /// Insert a final result into the global cache.
+    pub fn insert(
+        &self,
+        key: CanonicalInput<'tcx>,
+        reached_depth: usize,
+        did_overflow: bool,
+        cycle_participants: FxHashSet<CanonicalInput<'tcx>>,
+        dep_node: DepNodeIndex,
+        result: QueryResult<'tcx>,
+    ) {
+        let mut map = self.map.borrow_mut();
+        let entry = map.entry(key).or_default();
+        let data = WithDepNode::new(dep_node, result);
+        entry.cycle_participants.extend(cycle_participants);
+        if did_overflow {
+            entry.with_overflow.insert(reached_depth, data);
+        } else {
+            entry.success = Some(Success { data, reached_depth });
+        }
+    }
+
+    /// Try to fetch a cached result, checking the recursion limit
+    /// and handling root goals of coinductive cycles.
+    ///
+    /// If this returns `Some` the cache result can be used.
+    pub fn get(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        key: CanonicalInput<'tcx>,
+        cycle_participant_in_stack: impl FnOnce(&FxHashSet<CanonicalInput<'tcx>>) -> bool,
+        available_depth: Limit,
+    ) -> Option<CacheData<'tcx>> {
+        let map = self.map.borrow();
+        let entry = map.get(&key)?;
+
+        if cycle_participant_in_stack(&entry.cycle_participants) {
+            return None;
+        }
+
+        if let Some(ref success) = entry.success {
+            if available_depth.value_within_limit(success.reached_depth) {
+                return Some(CacheData {
+                    result: success.data.get(tcx),
+                    reached_depth: success.reached_depth,
+                    encountered_overflow: false,
+                });
+            }
+        }
+
+        entry.with_overflow.get(&available_depth.0).map(|e| CacheData {
+            result: e.get(tcx),
+            reached_depth: available_depth.0,
+            encountered_overflow: true,
+        })
+    }
+}
+
+struct Success<'tcx> {
+    data: WithDepNode<QueryResult<'tcx>>,
+    reached_depth: usize,
+}
+
+/// The cache entry for a goal `CanonicalInput`.
+///
+/// This contains results whose computation never hit the
+/// recursion limit in `success`, and all results which hit
+/// the recursion limit in `with_overflow`.
+#[derive(Default)]
+struct CacheEntry<'tcx> {
+    success: Option<Success<'tcx>>,
+    /// We have to be careful when caching roots of cycles.
+    ///
+    /// See the doc comment of `StackEntry::cycle_participants` for more
+    /// details.
+    cycle_participants: FxHashSet<CanonicalInput<'tcx>>,
+    with_overflow: FxHashMap<usize, WithDepNode<QueryResult<'tcx>>>,
+}
diff --git a/compiler/rustc_middle/src/traits/solve/inspect.rs b/compiler/rustc_middle/src/traits/solve/inspect.rs
index 527afa005..4e2af3816 100644
--- a/compiler/rustc_middle/src/traits/solve/inspect.rs
+++ b/compiler/rustc_middle/src/traits/solve/inspect.rs
@@ -32,7 +32,7 @@ pub enum GoalEvaluationKind<'tcx> {
 }
 impl Debug for GoalEvaluation<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter { f, on_newline: true }.format_goal_evaluation(self)
+        ProofTreeFormatter::new(f).format_goal_evaluation(self)
     }
 }
 
@@ -43,7 +43,7 @@ pub struct AddedGoalsEvaluation<'tcx> {
 }
 impl Debug for AddedGoalsEvaluation<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter { f, on_newline: true }.format_nested_goal_evaluation(self)
+        ProofTreeFormatter::new(f).format_nested_goal_evaluation(self)
     }
 }
 
@@ -58,7 +58,7 @@ pub struct GoalEvaluationStep<'tcx> {
 }
 impl Debug for GoalEvaluationStep<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter { f, on_newline: true }.format_evaluation_step(self)
+        ProofTreeFormatter::new(f).format_evaluation_step(self)
     }
 }
 
@@ -75,9 +75,16 @@ pub enum CandidateKind<'tcx> {
     NormalizedSelfTyAssembly,
     /// A normal candidate for proving a goal
     Candidate { name: String, result: QueryResult<'tcx> },
+    /// Used in the probe that wraps normalizing the non-self type for the unsize
+    /// trait, which is also structurally matched on.
+    UnsizeAssembly,
+    /// During upcasting from some source object to target object type, used to
+    /// do a probe to find out what projection type(s) may be used to prove that
+    /// the source type upholds all of the target type's object bounds.
+    UpcastProbe,
 }
 impl Debug for GoalCandidate<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter { f, on_newline: true }.format_candidate(self)
+        ProofTreeFormatter::new(f).format_candidate(self)
     }
 }
diff --git a/compiler/rustc_middle/src/traits/solve/inspect/format.rs b/compiler/rustc_middle/src/traits/solve/inspect/format.rs
index 2ee625674..8759fecb0 100644
--- a/compiler/rustc_middle/src/traits/solve/inspect/format.rs
+++ b/compiler/rustc_middle/src/traits/solve/inspect/format.rs
@@ -1,17 +1,25 @@
 use super::*;
 
 pub(super) struct ProofTreeFormatter<'a, 'b> {
-    pub(super) f: &'a mut (dyn Write + 'b),
-    pub(super) on_newline: bool,
+    f: &'a mut (dyn Write + 'b),
 }
 
-impl Write for ProofTreeFormatter<'_, '_> {
+/// A formatter which adds 4 spaces of indentation to its input before
+/// passing it on to its nested formatter.
+///
+/// We can use this for arbitrary levels of indentation by nesting it.
+struct Indentor<'a, 'b> {
+    f: &'a mut (dyn Write + 'b),
+    on_newline: bool,
+}
+
+impl Write for Indentor<'_, '_> {
     fn write_str(&mut self, s: &str) -> std::fmt::Result {
-        for line in s.split_inclusive("\n") {
+        for line in s.split_inclusive('\n') {
             if self.on_newline {
                 self.f.write_str("    ")?;
             }
-            self.on_newline = line.ends_with("\n");
+            self.on_newline = line.ends_with('\n');
             self.f.write_str(line)?;
         }
 
@@ -19,49 +27,52 @@ impl Write for ProofTreeFormatter<'_, '_> {
     }
 }
 
-impl ProofTreeFormatter<'_, '_> {
-    fn nested(&mut self) -> ProofTreeFormatter<'_, '_> {
-        ProofTreeFormatter { f: self, on_newline: true }
+impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
+    pub(super) fn new(f: &'a mut (dyn Write + 'b)) -> Self {
+        ProofTreeFormatter { f }
     }
 
-    pub(super) fn format_goal_evaluation(&mut self, goal: &GoalEvaluation<'_>) -> std::fmt::Result {
-        let f = &mut *self.f;
+    fn nested<F, R>(&mut self, func: F) -> R
+    where
+        F: FnOnce(&mut ProofTreeFormatter<'_, '_>) -> R,
+    {
+        func(&mut ProofTreeFormatter { f: &mut Indentor { f: self.f, on_newline: true } })
+    }
 
+    pub(super) fn format_goal_evaluation(&mut self, goal: &GoalEvaluation<'_>) -> std::fmt::Result {
         let goal_text = match goal.is_normalizes_to_hack {
             IsNormalizesToHack::Yes => "NORMALIZES-TO HACK GOAL",
             IsNormalizesToHack::No => "GOAL",
         };
 
-        writeln!(f, "{}: {:?}", goal_text, goal.uncanonicalized_goal,)?;
-        writeln!(f, "CANONICALIZED: {:?}", goal.canonicalized_goal)?;
+        writeln!(self.f, "{}: {:?}", goal_text, goal.uncanonicalized_goal)?;
+        writeln!(self.f, "CANONICALIZED: {:?}", goal.canonicalized_goal)?;
 
         match &goal.kind {
             GoalEvaluationKind::CacheHit(CacheHit::Global) => {
-                writeln!(f, "GLOBAL CACHE HIT: {:?}", goal.result)
+                writeln!(self.f, "GLOBAL CACHE HIT: {:?}", goal.result)
             }
             GoalEvaluationKind::CacheHit(CacheHit::Provisional) => {
-                writeln!(f, "PROVISIONAL CACHE HIT: {:?}", goal.result)
+                writeln!(self.f, "PROVISIONAL CACHE HIT: {:?}", goal.result)
             }
             GoalEvaluationKind::Uncached { revisions } => {
                 for (n, step) in revisions.iter().enumerate() {
-                    let f = &mut *self.f;
-                    writeln!(f, "REVISION {n}: {:?}", step.result)?;
-                    let mut f = self.nested();
-                    f.format_evaluation_step(step)?;
+                    writeln!(self.f, "REVISION {n}: {:?}", step.result)?;
+                    self.nested(|this| this.format_evaluation_step(step))?;
                 }
-
-                let f = &mut *self.f;
-                writeln!(f, "RESULT: {:?}", goal.result)
+                writeln!(self.f, "RESULT: {:?}", goal.result)
             }
         }?;
 
         if goal.returned_goals.len() > 0 {
-            let f = &mut *self.f;
-            writeln!(f, "NESTED GOALS ADDED TO CALLER: [")?;
-            let mut f = self.nested();
-            for goal in goal.returned_goals.iter() {
-                writeln!(f, "ADDED GOAL: {:?},", goal)?;
-            }
+            writeln!(self.f, "NESTED GOALS ADDED TO CALLER: [")?;
+            self.nested(|this| {
+                for goal in goal.returned_goals.iter() {
+                    writeln!(this.f, "ADDED GOAL: {goal:?},")?;
+                }
+                Ok(())
+            })?;
+
             writeln!(self.f, "]")?;
         }
 
@@ -72,58 +83,59 @@ impl ProofTreeFormatter<'_, '_> {
         &mut self,
         evaluation_step: &GoalEvaluationStep<'_>,
     ) -> std::fmt::Result {
-        let f = &mut *self.f;
-        writeln!(f, "INSTANTIATED: {:?}", evaluation_step.instantiated_goal)?;
+        writeln!(self.f, "INSTANTIATED: {:?}", evaluation_step.instantiated_goal)?;
 
         for candidate in &evaluation_step.candidates {
-            let mut f = self.nested();
-            f.format_candidate(candidate)?;
+            self.nested(|this| this.format_candidate(candidate))?;
         }
-        for nested_goal_evaluation in &evaluation_step.nested_goal_evaluations {
-            let mut f = self.nested();
-            f.format_nested_goal_evaluation(nested_goal_evaluation)?;
+        for nested in &evaluation_step.nested_goal_evaluations {
+            self.nested(|this| this.format_nested_goal_evaluation(nested))?;
         }
 
         Ok(())
     }
 
     pub(super) fn format_candidate(&mut self, candidate: &GoalCandidate<'_>) -> std::fmt::Result {
-        let f = &mut *self.f;
-
         match &candidate.kind {
             CandidateKind::NormalizedSelfTyAssembly => {
-                writeln!(f, "NORMALIZING SELF TY FOR ASSEMBLY:")
+                writeln!(self.f, "NORMALIZING SELF TY FOR ASSEMBLY:")
+            }
+            CandidateKind::UnsizeAssembly => {
+                writeln!(self.f, "ASSEMBLING CANDIDATES FOR UNSIZING:")
+            }
+            CandidateKind::UpcastProbe => {
+                writeln!(self.f, "PROBING FOR PROJECTION COMPATIBILITY FOR UPCASTING:")
             }
             CandidateKind::Candidate { name, result } => {
-                writeln!(f, "CANDIDATE {}: {:?}", name, result)
+                writeln!(self.f, "CANDIDATE {name}: {result:?}")
             }
         }?;
 
-        let mut f = self.nested();
-        for candidate in &candidate.candidates {
-            f.format_candidate(candidate)?;
-        }
-        for nested_evaluations in &candidate.nested_goal_evaluations {
-            f.format_nested_goal_evaluation(nested_evaluations)?;
-        }
-
-        Ok(())
+        self.nested(|this| {
+            for candidate in &candidate.candidates {
+                this.format_candidate(candidate)?;
+            }
+            for nested in &candidate.nested_goal_evaluations {
+                this.format_nested_goal_evaluation(nested)?;
+            }
+            Ok(())
+        })
     }
 
     pub(super) fn format_nested_goal_evaluation(
         &mut self,
         nested_goal_evaluation: &AddedGoalsEvaluation<'_>,
     ) -> std::fmt::Result {
-        let f = &mut *self.f;
-        writeln!(f, "TRY_EVALUATE_ADDED_GOALS: {:?}", nested_goal_evaluation.result)?;
+        writeln!(self.f, "TRY_EVALUATE_ADDED_GOALS: {:?}", nested_goal_evaluation.result)?;
 
         for (n, revision) in nested_goal_evaluation.evaluations.iter().enumerate() {
-            let f = &mut *self.f;
-            writeln!(f, "REVISION {n}")?;
-            let mut f = self.nested();
-            for goal_evaluation in revision {
-                f.format_goal_evaluation(goal_evaluation)?;
-            }
+            writeln!(self.f, "REVISION {n}")?;
+            self.nested(|this| {
+                for goal_evaluation in revision {
+                    this.format_goal_evaluation(goal_evaluation)?;
+                }
+                Ok(())
+            })?;
         }
 
         Ok(())
diff --git a/compiler/rustc_middle/src/traits/specialization_graph.rs b/compiler/rustc_middle/src/traits/specialization_graph.rs
index dc2cd2035..e48b46d12 100644
--- a/compiler/rustc_middle/src/traits/specialization_graph.rs
+++ b/compiler/rustc_middle/src/traits/specialization_graph.rs
@@ -43,7 +43,7 @@ impl Graph {
     /// The parent of a given impl, which is the `DefId` of the trait when the
     /// impl is a "specialization root".
     pub fn parent(&self, child: DefId) -> DefId {
-        *self.parent.get(&child).unwrap_or_else(|| panic!("Failed to get parent for {:?}", child))
+        *self.parent.get(&child).unwrap_or_else(|| panic!("Failed to get parent for {child:?}"))
     }
 }
 
@@ -259,7 +259,9 @@ pub fn ancestors(
 
     if let Some(reported) = specialization_graph.has_errored {
         Err(reported)
-    } else if let Err(reported) = tcx.type_of(start_from_impl).subst_identity().error_reported() {
+    } else if let Err(reported) =
+        tcx.type_of(start_from_impl).instantiate_identity().error_reported()
+    {
         Err(reported)
     } else {
         Ok(Ancestors {
diff --git a/compiler/rustc_middle/src/traits/structural_impls.rs b/compiler/rustc_middle/src/traits/structural_impls.rs
index a703e3c95..ec450cf55 100644
--- a/compiler/rustc_middle/src/traits/structural_impls.rs
+++ b/compiler/rustc_middle/src/traits/structural_impls.rs
@@ -6,18 +6,16 @@ use std::fmt;
 
 impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSource<'tcx, N> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            super::ImplSource::UserDefined(ref v) => write!(f, "{:?}", v),
+        match self {
+            super::ImplSource::UserDefined(v) => write!(f, "{v:?}"),
 
-            super::ImplSource::Builtin(ref d) => write!(f, "{:?}", d),
-
-            super::ImplSource::Object(ref d) => write!(f, "{:?}", d),
-
-            super::ImplSource::Param(ref n, ct) => {
-                write!(f, "ImplSourceParamData({:?}, {:?})", n, ct)
+            super::ImplSource::Builtin(source, d) => {
+                write!(f, "Builtin({source:?}, {d:?})")
             }
 
-            super::ImplSource::TraitUpcasting(ref d) => write!(f, "{:?}", d),
+            super::ImplSource::Param(n) => {
+                write!(f, "ImplSourceParamData({n:?})")
+            }
         }
     }
 }
@@ -26,28 +24,8 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSourceUserDefinedData<'tcx,
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             f,
-            "ImplSourceUserDefinedData(impl_def_id={:?}, substs={:?}, nested={:?})",
-            self.impl_def_id, self.substs, self.nested
-        )
-    }
-}
-
-impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceTraitUpcastingData<N> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(
-            f,
-            "ImplSourceTraitUpcastingData(vtable_vptr_slot={:?}, nested={:?})",
-            self.vtable_vptr_slot, self.nested
-        )
-    }
-}
-
-impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceObjectData<N> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(
-            f,
-            "ImplSourceObjectData(vtable_base={}, nested={:?})",
-            self.vtable_base, self.nested
+            "ImplSourceUserDefinedData(impl_def_id={:?}, args={:?}, nested={:?})",
+            self.impl_def_id, self.args, self.nested
         )
     }
 }