diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
index 1142d492160..269cb8f2380 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -684,8 +684,8 @@ pub fn reconstruct_format_args_template_string(pieces: &[FormatArgsPiece]) -> St
     for piece in pieces {
         match piece {
             FormatArgsPiece::Literal(s) => {
-                for c in s.as_str().escape_debug() {
-                    template.push(c);
+                for c in s.as_str().chars() {
+                    template.extend(c.escape_debug());
                     if let '{' | '}' = c {
                         template.push(c);
                     }
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 97ebd42d077..34c28bce5d8 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -314,9 +314,10 @@ fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
 ///     fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
 /// }
 /// ```
-fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
+fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
     // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
     let mut required_bounds_by_item = FxHashMap::default();
+    let associated_items = tcx.associated_items(trait_def_id);
 
     // Loop over all GATs together, because if this lint suggests adding a where-clause bound
     // to one GAT, it might then require us to an additional bound on another GAT.
@@ -325,8 +326,8 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
     // those GATs.
     loop {
         let mut should_continue = false;
-        for gat_item in associated_items {
-            let gat_def_id = gat_item.id.owner_id;
+        for gat_item in associated_items.in_definition_order() {
+            let gat_def_id = gat_item.def_id.expect_local();
             let gat_item = tcx.associated_item(gat_def_id);
             // If this item is not an assoc ty, or has no args, then it's not a GAT
             if gat_item.kind != ty::AssocKind::Type {
@@ -342,8 +343,8 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
             // This is calculated by taking the intersection of the bounds that each item
             // constrains the GAT with individually.
             let mut new_required_bounds: Option<FxHashSet<ty::Clause<'_>>> = None;
-            for item in associated_items {
-                let item_def_id = item.id.owner_id;
+            for item in associated_items.in_definition_order() {
+                let item_def_id = item.def_id.expect_local();
                 // Skip our own GAT, since it does not constrain itself at all.
                 if item_def_id == gat_def_id {
                     continue;
@@ -351,9 +352,9 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
 
                 let param_env = tcx.param_env(item_def_id);
 
-                let item_required_bounds = match item.kind {
+                let item_required_bounds = match tcx.associated_item(item_def_id).kind {
                     // In our example, this corresponds to `into_iter` method
-                    hir::AssocItemKind::Fn { .. } => {
+                    ty::AssocKind::Fn => {
                         // For methods, we check the function signature's return type for any GATs
                         // to constrain. In the `into_iter` case, we see that the return type
                         // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
@@ -369,12 +370,12 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
                             // We also assume that all of the function signature's parameter types
                             // are well formed.
                             &sig.inputs().iter().copied().collect(),
-                            gat_def_id.def_id,
+                            gat_def_id,
                             gat_generics,
                         )
                     }
                     // In our example, this corresponds to the `Iter` and `Item` associated types
-                    hir::AssocItemKind::Type => {
+                    ty::AssocKind::Type => {
                         // If our associated item is a GAT with missing bounds, add them to
                         // the param-env here. This allows this GAT to propagate missing bounds
                         // to other GATs.
@@ -391,11 +392,11 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
                                 .instantiate_identity_iter_copied()
                                 .collect::<Vec<_>>(),
                             &FxIndexSet::default(),
-                            gat_def_id.def_id,
+                            gat_def_id,
                             gat_generics,
                         )
                     }
-                    hir::AssocItemKind::Const => None,
+                    ty::AssocKind::Const => None,
                 };
 
                 if let Some(item_required_bounds) = item_required_bounds {
@@ -431,7 +432,12 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
     }
 
     for (gat_def_id, required_bounds) in required_bounds_by_item {
-        let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id.def_id);
+        // Don't suggest adding `Self: 'a` to a GAT that can't be named
+        if tcx.is_impl_trait_in_trait(gat_def_id.to_def_id()) {
+            continue;
+        }
+
+        let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
         debug!(?required_bounds);
         let param_env = tcx.param_env(gat_def_id);
 
@@ -441,21 +447,16 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
                 ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
                     !region_known_to_outlive(
                         tcx,
-                        gat_def_id.def_id,
+                        gat_def_id,
                         param_env,
                         &FxIndexSet::default(),
                         a,
                         b,
                     )
                 }
-                ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => !ty_known_to_outlive(
-                    tcx,
-                    gat_def_id.def_id,
-                    param_env,
-                    &FxIndexSet::default(),
-                    a,
-                    b,
-                ),
+                ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
+                    !ty_known_to_outlive(tcx, gat_def_id, param_env, &FxIndexSet::default(), a, b)
+                }
                 _ => bug!("Unexpected ClauseKind"),
             })
             .map(|clause| clause.to_string())
@@ -534,7 +535,7 @@ fn augment_param_env<'tcx>(
 fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    item_def_id: hir::OwnerId,
+    item_def_id: LocalDefId,
     to_check: T,
     wf_tys: &FxIndexSet<Ty<'tcx>>,
     gat_def_id: LocalDefId,
@@ -567,7 +568,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
         // reflected in a where clause on the GAT itself.
         for (ty, ty_idx) in &types {
             // In our example, requires that `Self: 'a`
-            if ty_known_to_outlive(tcx, item_def_id.def_id, param_env, &wf_tys, *ty, *region_a) {
+            if ty_known_to_outlive(tcx, item_def_id, param_env, &wf_tys, *ty, *region_a) {
                 debug!(?ty_idx, ?region_a_idx);
                 debug!("required clause: {ty} must outlive {region_a}");
                 // Translate into the generic parameters of the GAT. In
@@ -606,14 +607,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
             if matches!(**region_b, ty::ReStatic | ty::ReError(_)) || region_a == region_b {
                 continue;
             }
-            if region_known_to_outlive(
-                tcx,
-                item_def_id.def_id,
-                param_env,
-                &wf_tys,
-                *region_a,
-                *region_b,
-            ) {
+            if region_known_to_outlive(tcx, item_def_id, param_env, &wf_tys, *region_a, *region_b) {
                 debug!(?region_a_idx, ?region_b_idx);
                 debug!("required clause: {region_a} must outlive {region_b}");
                 // Translate into the generic parameters of the GAT.
@@ -1114,8 +1108,8 @@ fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
     });
 
     // Only check traits, don't check trait aliases
-    if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
-        check_gat_where_clauses(tcx, items);
+    if let hir::ItemKind::Trait(..) = item.kind {
+        check_gat_where_clauses(tcx, item.owner_id.def_id);
     }
 }
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 506bcea0e39..1d1be8f2492 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -3,7 +3,7 @@
 use rustc_data_structures::graph::WithNumNodes;
 use rustc_index::IndexVec;
 use rustc_middle::mir::{self, AggregateKind, Rvalue, Statement, StatementKind};
-use rustc_span::{BytePos, ExpnKind, MacroKind, Span, Symbol};
+use rustc_span::{BytePos, ExpnKind, MacroKind, Span, Symbol, DUMMY_SP};
 
 use super::graph::{BasicCoverageBlock, CoverageGraph, START_BCB};
 
@@ -215,9 +215,6 @@ struct CoverageSpansGenerator<'a> {
     /// is mutated.
     prev_original_span: Span,
 
-    /// A copy of the expn_span from the prior iteration.
-    prev_expn_span: Option<Span>,
-
     /// One or more `CoverageSpan`s with the same `Span` but different `BasicCoverageBlock`s, and
     /// no `BasicCoverageBlock` in this list dominates another `BasicCoverageBlock` in the list.
     /// If a new `curr` span also fits this criteria (compared to an existing list of
@@ -272,13 +269,12 @@ pub(super) fn generate_coverage_spans(
             body_span,
             basic_coverage_blocks,
             sorted_spans_iter: sorted_spans.into_iter(),
-            refined_spans: Vec::with_capacity(basic_coverage_blocks.num_nodes() * 2),
             some_curr: None,
-            curr_original_span: Span::with_root_ctxt(BytePos(0), BytePos(0)),
+            curr_original_span: DUMMY_SP,
             some_prev: None,
-            prev_original_span: Span::with_root_ctxt(BytePos(0), BytePos(0)),
-            prev_expn_span: None,
+            prev_original_span: DUMMY_SP,
             pending_dups: Vec::new(),
+            refined_spans: Vec::with_capacity(basic_coverage_blocks.num_nodes() * 2),
         };
 
         coverage_spans.to_refined_spans()
@@ -288,43 +284,48 @@ pub(super) fn generate_coverage_spans(
     /// de-duplicated `CoverageSpan`s.
     fn to_refined_spans(mut self) -> Vec<CoverageSpan> {
         while self.next_coverage_span() {
+            // For the first span we don't have `prev` set, so most of the
+            // span-processing steps don't make sense yet.
             if self.some_prev.is_none() {
                 debug!("  initial span");
-                self.check_invoked_macro_name_span();
-            } else if self.curr().is_mergeable(self.prev()) {
-                debug!("  same bcb (and neither is a closure), merge with prev={:?}", self.prev());
+                self.maybe_push_macro_name_span();
+                continue;
+            }
+
+            // The remaining cases assume that `prev` and `curr` are set.
+            let prev = self.prev();
+            let curr = self.curr();
+
+            if curr.is_mergeable(prev) {
+                debug!("  same bcb (and neither is a closure), merge with prev={prev:?}");
                 let prev = self.take_prev();
                 self.curr_mut().merge_from(prev);
-                self.check_invoked_macro_name_span();
+                self.maybe_push_macro_name_span();
             // Note that curr.span may now differ from curr_original_span
-            } else if self.prev_ends_before_curr() {
+            } else if prev.span.hi() <= curr.span.lo() {
                 debug!(
-                    "  different bcbs and disjoint spans, so keep curr for next iter, and add \
-                    prev={:?}",
-                    self.prev()
+                    "  different bcbs and disjoint spans, so keep curr for next iter, and add prev={prev:?}",
                 );
                 let prev = self.take_prev();
                 self.push_refined_span(prev);
-                self.check_invoked_macro_name_span();
-            } else if self.prev().is_closure {
+                self.maybe_push_macro_name_span();
+            } else if prev.is_closure {
                 // drop any equal or overlapping span (`curr`) and keep `prev` to test again in the
                 // next iter
                 debug!(
-                    "  curr overlaps a closure (prev). Drop curr and keep prev for next iter. \
-                    prev={:?}",
-                    self.prev()
+                    "  curr overlaps a closure (prev). Drop curr and keep prev for next iter. prev={prev:?}",
                 );
-                self.take_curr();
-            } else if self.curr().is_closure {
+                self.take_curr(); // Discards curr.
+            } else if curr.is_closure {
                 self.carve_out_span_for_closure();
-            } else if self.prev_original_span == self.curr().span {
+            } else if self.prev_original_span == curr.span {
                 // Note that this compares the new (`curr`) span to `prev_original_span`.
                 // In this branch, the actual span byte range of `prev_original_span` is not
                 // important. What is important is knowing whether the new `curr` span was
                 // **originally** the same as the original span of `prev()`. The original spans
                 // reflect their original sort order, and for equal spans, conveys a partial
                 // ordering based on CFG dominator priority.
-                if self.prev().is_macro_expansion() && self.curr().is_macro_expansion() {
+                if prev.is_macro_expansion() && curr.is_macro_expansion() {
                     // Macros that expand to include branching (such as
                     // `assert_eq!()`, `assert_ne!()`, `info!()`, `debug!()`, or
                     // `trace!()`) typically generate callee spans with identical
@@ -338,23 +339,24 @@ fn to_refined_spans(mut self) -> Vec<CoverageSpan> {
                     debug!(
                         "  curr and prev are part of a macro expansion, and curr has the same span \
                         as prev, but is in a different bcb. Drop curr and keep prev for next iter. \
-                        prev={:?}",
-                        self.prev()
+                        prev={prev:?}",
                     );
-                    self.take_curr();
+                    self.take_curr(); // Discards curr.
                 } else {
-                    self.hold_pending_dups_unless_dominated();
+                    self.update_pending_dups();
                 }
             } else {
                 self.cutoff_prev_at_overlapping_curr();
-                self.check_invoked_macro_name_span();
+                self.maybe_push_macro_name_span();
             }
         }
 
-        debug!("    AT END, adding last prev={:?}", self.prev());
         let prev = self.take_prev();
-        let pending_dups = self.pending_dups.split_off(0);
-        for dup in pending_dups {
+        debug!("    AT END, adding last prev={prev:?}");
+
+        // Take `pending_dups` so that we can drain it while calling self methods.
+        // It is never used as a field after this point.
+        for dup in std::mem::take(&mut self.pending_dups) {
             debug!("    ...adding at least one pending dup={:?}", dup);
             self.push_refined_span(dup);
         }
@@ -384,43 +386,40 @@ fn to_refined_spans(mut self) -> Vec<CoverageSpan> {
     }
 
     fn push_refined_span(&mut self, covspan: CoverageSpan) {
-        let len = self.refined_spans.len();
-        if len > 0 {
-            let last = &mut self.refined_spans[len - 1];
-            if last.is_mergeable(&covspan) {
-                debug!(
-                    "merging new refined span with last refined span, last={:?}, covspan={:?}",
-                    last, covspan
-                );
-                last.merge_from(covspan);
-                return;
-            }
+        if let Some(last) = self.refined_spans.last_mut()
+            && last.is_mergeable(&covspan)
+        {
+            // Instead of pushing the new span, merge it with the last refined span.
+            debug!(?last, ?covspan, "merging new refined span with last refined span");
+            last.merge_from(covspan);
+        } else {
+            self.refined_spans.push(covspan);
         }
-        self.refined_spans.push(covspan)
     }
 
-    fn check_invoked_macro_name_span(&mut self) {
-        if let Some(visible_macro) = self.curr().visible_macro(self.body_span) {
-            if !self
-                .prev_expn_span
-                .is_some_and(|prev_expn_span| self.curr().expn_span.ctxt() == prev_expn_span.ctxt())
-            {
-                let merged_prefix_len = self.curr_original_span.lo() - self.curr().span.lo();
-                let after_macro_bang =
-                    merged_prefix_len + BytePos(visible_macro.as_str().len() as u32 + 1);
-                let mut macro_name_cov = self.curr().clone();
-                self.curr_mut().span =
-                    self.curr().span.with_lo(self.curr().span.lo() + after_macro_bang);
-                macro_name_cov.span =
-                    macro_name_cov.span.with_hi(macro_name_cov.span.lo() + after_macro_bang);
-                debug!(
-                    "  and curr starts a new macro expansion, so add a new span just for \
-                            the macro `{}!`, new span={:?}",
-                    visible_macro, macro_name_cov
-                );
-                self.push_refined_span(macro_name_cov);
-            }
+    /// If `curr` is part of a new macro expansion, carve out and push a separate
+    /// span that ends just after the macro name and its subsequent `!`.
+    fn maybe_push_macro_name_span(&mut self) {
+        let curr = self.curr();
+
+        let Some(visible_macro) = curr.visible_macro(self.body_span) else { return };
+        if let Some(prev) = &self.some_prev
+            && prev.expn_span.ctxt() == curr.expn_span.ctxt()
+        {
+            return;
         }
+
+        let merged_prefix_len = self.curr_original_span.lo() - curr.span.lo();
+        let after_macro_bang = merged_prefix_len + BytePos(visible_macro.as_str().len() as u32 + 1);
+        let mut macro_name_cov = curr.clone();
+        self.curr_mut().span = curr.span.with_lo(curr.span.lo() + after_macro_bang);
+        macro_name_cov.span =
+            macro_name_cov.span.with_hi(macro_name_cov.span.lo() + after_macro_bang);
+        debug!(
+            "  and curr starts a new macro expansion, so add a new span just for \
+            the macro `{visible_macro}!`, new span={macro_name_cov:?}",
+        );
+        self.push_refined_span(macro_name_cov);
     }
 
     fn curr(&self) -> &CoverageSpan {
@@ -435,6 +434,12 @@ fn curr_mut(&mut self) -> &mut CoverageSpan {
             .unwrap_or_else(|| bug!("invalid attempt to unwrap a None some_curr"))
     }
 
+    /// If called, then the next call to `next_coverage_span()` will *not* update `prev` with the
+    /// `curr` coverage span.
+    fn take_curr(&mut self) -> CoverageSpan {
+        self.some_curr.take().unwrap_or_else(|| bug!("invalid attempt to unwrap a None some_curr"))
+    }
+
     fn prev(&self) -> &CoverageSpan {
         self.some_prev
             .as_ref()
@@ -460,84 +465,78 @@ fn take_prev(&mut self) -> CoverageSpan {
     ///     `pending_dups` could have as few as one span)
     /// In either case, no more spans will match the span of `pending_dups`, so
     /// add the `pending_dups` if they don't overlap `curr`, and clear the list.
-    fn check_pending_dups(&mut self) {
-        if let Some(dup) = self.pending_dups.last()
-            && dup.span != self.prev().span
-        {
-            debug!(
-                "    SAME spans, but pending_dups are NOT THE SAME, so BCBs matched on \
-                previous iteration, or prev started a new disjoint span"
-            );
-            if dup.span.hi() <= self.curr().span.lo() {
-                let pending_dups = self.pending_dups.split_off(0);
-                for dup in pending_dups.into_iter() {
-                    debug!("    ...adding at least one pending={:?}", dup);
-                    self.push_refined_span(dup);
-                }
-            } else {
-                self.pending_dups.clear();
+    fn maybe_flush_pending_dups(&mut self) {
+        let Some(last_dup) = self.pending_dups.last() else { return };
+        if last_dup.span == self.prev().span {
+            return;
+        }
+
+        debug!(
+            "    SAME spans, but pending_dups are NOT THE SAME, so BCBs matched on \
+            previous iteration, or prev started a new disjoint span"
+        );
+        if last_dup.span.hi() <= self.curr().span.lo() {
+            // Temporarily steal `pending_dups` into a local, so that we can
+            // drain it while calling other self methods.
+            let mut pending_dups = std::mem::take(&mut self.pending_dups);
+            for dup in pending_dups.drain(..) {
+                debug!("    ...adding at least one pending={:?}", dup);
+                self.push_refined_span(dup);
             }
+            // The list of dups is now empty, but we can recycle its capacity.
+            assert!(pending_dups.is_empty() && self.pending_dups.is_empty());
+            self.pending_dups = pending_dups;
+        } else {
+            self.pending_dups.clear();
         }
     }
 
     /// Advance `prev` to `curr` (if any), and `curr` to the next `CoverageSpan` in sorted order.
     fn next_coverage_span(&mut self) -> bool {
         if let Some(curr) = self.some_curr.take() {
-            self.prev_expn_span = Some(curr.expn_span);
             self.some_prev = Some(curr);
             self.prev_original_span = self.curr_original_span;
         }
         while let Some(curr) = self.sorted_spans_iter.next() {
             debug!("FOR curr={:?}", curr);
-            if self.some_prev.is_some() && self.prev_starts_after_next(&curr) {
+            if let Some(prev) = &self.some_prev && prev.span.lo() > curr.span.lo() {
+                // Skip curr because prev has already advanced beyond the end of curr.
+                // This can only happen if a prior iteration updated `prev` to skip past
+                // a region of code, such as skipping past a closure.
                 debug!(
                     "  prev.span starts after curr.span, so curr will be dropped (skipping past \
-                    closure?); prev={:?}",
-                    self.prev()
+                    closure?); prev={prev:?}",
                 );
             } else {
                 // Save a copy of the original span for `curr` in case the `CoverageSpan` is changed
                 // by `self.curr_mut().merge_from(prev)`.
                 self.curr_original_span = curr.span;
                 self.some_curr.replace(curr);
-                self.check_pending_dups();
+                self.maybe_flush_pending_dups();
                 return true;
             }
         }
         false
     }
 
-    /// If called, then the next call to `next_coverage_span()` will *not* update `prev` with the
-    /// `curr` coverage span.
-    fn take_curr(&mut self) -> CoverageSpan {
-        self.some_curr.take().unwrap_or_else(|| bug!("invalid attempt to unwrap a None some_curr"))
-    }
-
-    /// Returns true if the curr span should be skipped because prev has already advanced beyond the
-    /// end of curr. This can only happen if a prior iteration updated `prev` to skip past a region
-    /// of code, such as skipping past a closure.
-    fn prev_starts_after_next(&self, next_curr: &CoverageSpan) -> bool {
-        self.prev().span.lo() > next_curr.span.lo()
-    }
-
-    /// Returns true if the curr span starts past the end of the prev span, which means they don't
-    /// overlap, so we now know the prev can be added to the refined coverage spans.
-    fn prev_ends_before_curr(&self) -> bool {
-        self.prev().span.hi() <= self.curr().span.lo()
-    }
-
     /// If `prev`s span extends left of the closure (`curr`), carve out the closure's span from
     /// `prev`'s span. (The closure's coverage counters will be injected when processing the
     /// closure's own MIR.) Add the portion of the span to the left of the closure; and if the span
     /// extends to the right of the closure, update `prev` to that portion of the span. For any
     /// `pending_dups`, repeat the same process.
     fn carve_out_span_for_closure(&mut self) {
-        let curr_span = self.curr().span;
-        let left_cutoff = curr_span.lo();
-        let right_cutoff = curr_span.hi();
-        let has_pre_closure_span = self.prev().span.lo() < right_cutoff;
-        let has_post_closure_span = self.prev().span.hi() > right_cutoff;
-        let mut pending_dups = self.pending_dups.split_off(0);
+        let prev = self.prev();
+        let curr = self.curr();
+
+        let left_cutoff = curr.span.lo();
+        let right_cutoff = curr.span.hi();
+        let has_pre_closure_span = prev.span.lo() < right_cutoff;
+        let has_post_closure_span = prev.span.hi() > right_cutoff;
+
+        // Temporarily steal `pending_dups` into a local, so that we can
+        // mutate and/or drain it while calling other self methods.
+        let mut pending_dups = std::mem::take(&mut self.pending_dups);
+
         if has_pre_closure_span {
             let mut pre_closure = self.prev().clone();
             pre_closure.span = pre_closure.span.with_hi(left_cutoff);
@@ -551,6 +550,7 @@ fn carve_out_span_for_closure(&mut self) {
             }
             self.push_refined_span(pre_closure);
         }
+
         if has_post_closure_span {
             // Mutate `prev.span()` to start after the closure (and discard curr).
             // (**NEVER** update `prev_original_span` because it affects the assumptions
@@ -561,12 +561,15 @@ fn carve_out_span_for_closure(&mut self) {
                 debug!("    ...and at least one overlapping dup={:?}", dup);
                 dup.span = dup.span.with_lo(right_cutoff);
             }
-            self.pending_dups.append(&mut pending_dups);
-            let closure_covspan = self.take_curr();
+            let closure_covspan = self.take_curr(); // Prevent this curr from becoming prev.
             self.push_refined_span(closure_covspan); // since self.prev() was already updated
         } else {
             pending_dups.clear();
         }
+
+        // Restore the modified post-closure spans, or the empty vector's capacity.
+        assert!(self.pending_dups.is_empty());
+        self.pending_dups = pending_dups;
     }
 
     /// Called if `curr.span` equals `prev_original_span` (and potentially equal to all
@@ -583,26 +586,28 @@ fn carve_out_span_for_closure(&mut self) {
     /// neither `CoverageSpan` dominates the other, both (or possibly more than two) are held,
     /// until their disposition is determined. In this latter case, the `prev` dup is moved into
     /// `pending_dups` so the new `curr` dup can be moved to `prev` for the next iteration.
-    fn hold_pending_dups_unless_dominated(&mut self) {
+    fn update_pending_dups(&mut self) {
+        let prev_bcb = self.prev().bcb;
+        let curr_bcb = self.curr().bcb;
+
         // Equal coverage spans are ordered by dominators before dominated (if any), so it should be
         // impossible for `curr` to dominate any previous `CoverageSpan`.
-        debug_assert!(!self.span_bcb_dominates(self.curr(), self.prev()));
+        debug_assert!(!self.basic_coverage_blocks.dominates(curr_bcb, prev_bcb));
 
         let initial_pending_count = self.pending_dups.len();
         if initial_pending_count > 0 {
-            let mut pending_dups = self.pending_dups.split_off(0);
-            pending_dups.retain(|dup| !self.span_bcb_dominates(dup, self.curr()));
-            self.pending_dups.append(&mut pending_dups);
-            if self.pending_dups.len() < initial_pending_count {
+            self.pending_dups
+                .retain(|dup| !self.basic_coverage_blocks.dominates(dup.bcb, curr_bcb));
+
+            let n_discarded = initial_pending_count - self.pending_dups.len();
+            if n_discarded > 0 {
                 debug!(
-                    "  discarded {} of {} pending_dups that dominated curr",
-                    initial_pending_count - self.pending_dups.len(),
-                    initial_pending_count
+                    "  discarded {n_discarded} of {initial_pending_count} pending_dups that dominated curr",
                 );
             }
         }
 
-        if self.span_bcb_dominates(self.prev(), self.curr()) {
+        if self.basic_coverage_blocks.dominates(prev_bcb, curr_bcb) {
             debug!(
                 "  different bcbs but SAME spans, and prev dominates curr. Discard prev={:?}",
                 self.prev()
@@ -667,8 +672,4 @@ fn cutoff_prev_at_overlapping_curr(&mut self) {
             self.pending_dups.clear();
         }
     }
-
-    fn span_bcb_dominates(&self, dom_covspan: &CoverageSpan, covspan: &CoverageSpan) -> bool {
-        self.basic_coverage_blocks.dominates(dom_covspan.bcb, covspan.bcb)
-    }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index cbfb06eac7b..9c9b78f4152 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -180,8 +180,9 @@ fn on_unimplemented_note(
             flags.push((sym::cause, Some("MainFunctionType".to_string())));
         }
 
-        // Add all types without trimmed paths.
-        ty::print::with_no_trimmed_paths!({
+        // Add all types without trimmed paths or visible paths, ensuring they end up with
+        // their "canonical" def path.
+        ty::print::with_no_trimmed_paths!(ty::print::with_no_visible_paths!({
             let generics = self.tcx.generics_of(def_id);
             let self_ty = trait_ref.self_ty();
             // This is also included through the generics list as `Self`,
@@ -296,7 +297,7 @@ fn on_unimplemented_note(
             {
                 flags.push((sym::_Self, Some("&[{integral}]".to_owned())));
             }
-        });
+        }));
 
         if let Ok(Some(command)) = OnUnimplementedDirective::of_item(self.tcx, def_id) {
             command.evaluate(self.tcx, trait_ref, &flags)
@@ -578,7 +579,9 @@ pub fn evaluate(
                     Some(tcx.features()),
                     &mut |cfg| {
                         let value = cfg.value.map(|v| {
-                            OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map)
+                            // `with_no_visible_paths` is also used when generating the options,
+                            // so we need to match it here.
+                            ty::print::with_no_visible_paths!(OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map))
                         });
 
                         options.contains(&(cfg.name, value))
diff --git a/library/core/src/convert/mod.rs b/library/core/src/convert/mod.rs
index 9407c1609c2..89125b7955e 100644
--- a/library/core/src/convert/mod.rs
+++ b/library/core/src/convert/mod.rs
@@ -573,7 +573,7 @@ pub trait Into<T>: Sized {
 #[rustc_diagnostic_item = "From"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(on(
-    all(_Self = "&str", any(T = "alloc::string::String", T = "std::string::String")),
+    all(_Self = "&str", T = "alloc::string::String"),
     note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
 ))]
 pub trait From<T>: Sized {
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index ac1fc26a1ef..c7ace58afa8 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -27,13 +27,13 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
     on(
-        any(_Self = "core::ops::RangeTo<Idx>", _Self = "std::ops::RangeTo<Idx>"),
+        _Self = "core::ops::range::RangeTo<Idx>",
         label = "if you meant to iterate until a value, add a starting value",
         note = "`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \
               bounded `Range`: `0..end`"
     ),
     on(
-        any(_Self = "core::ops::RangeToInclusive<Idx>", _Self = "std::ops::RangeToInclusive<Idx>"),
+        _Self = "core::ops::range::RangeToInclusive<Idx>",
         label = "if you meant to iterate until a value (including it), add a starting value",
         note = "`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \
               to have a bounded `RangeInclusive`: `0..=end`"
@@ -44,7 +44,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
     ),
     on(_Self = "&[]", label = "`{Self}` is not an iterator; try calling `.iter()`"),
     on(
-        any(_Self = "alloc::vec::Vec<T, A>", _Self = "std::vec::Vec<T, A>"),
+        _Self = "alloc::vec::Vec<T, A>",
         label = "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`"
     ),
     on(
@@ -52,7 +52,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
         label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
     ),
     on(
-        any(_Self = "alloc::string::String", _Self = "std::string::String"),
+        _Self = "alloc::string::String",
         label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
     ),
     on(
diff --git a/library/core/src/marker.rs b/library/core/src/marker.rs
index 5ed82e26a0a..f1594501d40 100644
--- a/library/core/src/marker.rs
+++ b/library/core/src/marker.rs
@@ -573,59 +573,59 @@ impl<T: ?Sized> Copy for &T {}
 #[lang = "sync"]
 #[rustc_on_unimplemented(
     on(
-        any(_Self = "core::cell:OnceCell<T>", _Self = "std::cell::OnceCell<T>"),
+        _Self = "core::cell::once::OnceCell<T>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::OnceLock` instead"
     ),
     on(
-        any(_Self = "core::cell::Cell<u8>", _Self = "std::cell::Cell<u8>"),
+        _Self = "core::cell::Cell<u8>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU8` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<u16>", _Self = "std::cell::Cell<u16>"),
+        _Self = "core::cell::Cell<u16>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU16` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<u32>", _Self = "std::cell::Cell<u32>"),
+        _Self = "core::cell::Cell<u32>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU32` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<u64>", _Self = "std::cell::Cell<u64>"),
+        _Self = "core::cell::Cell<u64>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU64` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<usize>", _Self = "std::cell::Cell<usize>"),
+        _Self = "core::cell::Cell<usize>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicUsize` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<i8>", _Self = "std::cell::Cell<i8>"),
+        _Self = "core::cell::Cell<i8>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI8` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<i16>", _Self = "std::cell::Cell<i16>"),
+        _Self = "core::cell::Cell<i16>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI16` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<i32>", _Self = "std::cell::Cell<i32>"),
+        _Self = "core::cell::Cell<i32>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI32` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<i64>", _Self = "std::cell::Cell<i64>"),
+        _Self = "core::cell::Cell<i64>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI64` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<isize>", _Self = "std::cell::Cell<isize>"),
+        _Self = "core::cell::Cell<isize>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicIsize` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<bool>", _Self = "std::cell::Cell<bool>"),
+        _Self = "core::cell::Cell<bool>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicBool` instead",
     ),
     on(
-        any(_Self = "core::cell::Cell<T>", _Self = "std::cell::Cell<T>"),
+        _Self = "core::cell::Cell<T>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`",
     ),
     on(
-        any(_Self = "core::cell::RefCell<T>", _Self = "std::cell::RefCell<T>"),
+        _Self = "core::cell::RefCell<T>",
         note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` instead",
     ),
     message = "`{Self}` cannot be shared between threads safely",
diff --git a/library/core/src/ops/index.rs b/library/core/src/ops/index.rs
index f4649be54d5..6ceee463729 100644
--- a/library/core/src/ops/index.rs
+++ b/library/core/src/ops/index.rs
@@ -153,7 +153,7 @@ pub trait Index<Idx: ?Sized> {
 see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
     ),
     on(
-        any(_Self = "alloc::string::String", _Self = "std::string::String"),
+        _Self = "alloc::string::String",
         note = "you can use `.chars().nth()` or `.bytes().nth()`
 see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
     ),
diff --git a/library/core/src/ops/try_trait.rs b/library/core/src/ops/try_trait.rs
index 17625daccbc..3f8c8efd416 100644
--- a/library/core/src/ops/try_trait.rs
+++ b/library/core/src/ops/try_trait.rs
@@ -226,14 +226,8 @@ pub trait Try: FromResidual {
     on(
         all(
             from_desugaring = "QuestionMark",
-            any(
-                _Self = "core::result::Result<T, E>",
-                _Self = "std::result::Result<T, E>",
-            ),
-            any(
-                R = "core::option::Option<core::convert::Infallible>",
-                R = "std::option::Option<std::convert::Infallible>",
-            )
+            _Self = "core::result::Result<T, E>",
+            R = "core::option::Option<core::convert::Infallible>",
         ),
         message = "the `?` operator can only be used on `Result`s, not `Option`s, \
             in {ItemContext} that returns `Result`",
@@ -243,10 +237,7 @@ pub trait Try: FromResidual {
     on(
         all(
             from_desugaring = "QuestionMark",
-            any(
-                _Self = "core::result::Result<T, E>",
-                _Self = "std::result::Result<T, E>",
-            )
+            _Self = "core::result::Result<T, E>",
         ),
         // There's a special error message in the trait selection code for
         // `From` in `?`, so this is not shown for result-in-result errors,
@@ -259,14 +250,8 @@ pub trait Try: FromResidual {
     on(
         all(
             from_desugaring = "QuestionMark",
-            any(
-                _Self = "core::option::Option<T>",
-                _Self = "std::option::Option<T>",
-            ),
-            any(
-                R = "core::result::Result<T, E>",
-                R = "std::result::Result<T, E>",
-            )
+            _Self = "core::option::Option<T>",
+            R = "core::result::Result<T, E>",
         ),
         message = "the `?` operator can only be used on `Option`s, not `Result`s, \
             in {ItemContext} that returns `Option`",
@@ -276,10 +261,7 @@ pub trait Try: FromResidual {
     on(
         all(
             from_desugaring = "QuestionMark",
-            any(
-                _Self = "core::option::Option<T>",
-                _Self = "std::option::Option<T>",
-            )
+            _Self = "core::option::Option<T>",
         ),
         // `Option`-in-`Option` always works, as there's only one possible
         // residual, so this can also be phrased strongly.
@@ -291,14 +273,8 @@ pub trait Try: FromResidual {
     on(
         all(
             from_desugaring = "QuestionMark",
-            any(
-                _Self = "core::ops::ControlFlow<B, C>",
-                _Self = "std::ops::ControlFlow<B, C>",
-            ),
-            any(
-                R = "core::ops::ControlFlow<B, C>",
-                R = "std::ops::ControlFlow<B, C>",
-            )
+            _Self = "core::ops::control_flow::ControlFlow<B, C>",
+            R = "core::ops::control_flow::ControlFlow<B, C>",
         ),
         message = "the `?` operator in {ItemContext} that returns `ControlFlow<B, _>` \
             can only be used on other `ControlFlow<B, _>`s (with the same Break type)",
@@ -309,10 +285,7 @@ pub trait Try: FromResidual {
     on(
         all(
             from_desugaring = "QuestionMark",
-            any(
-                _Self = "core::ops::ControlFlow<B, C>",
-                _Self = "std::ops::ControlFlow<B, C>",
-            )
+            _Self = "core::ops::control_flow::ControlFlow<B, C>",
             // `R` is not a `ControlFlow`, as that case was matched previously
         ),
         message = "the `?` operator can only be used on `ControlFlow`s \
diff --git a/library/core/src/slice/index.rs b/library/core/src/slice/index.rs
index d313e8e012f..1da3a87e117 100644
--- a/library/core/src/slice/index.rs
+++ b/library/core/src/slice/index.rs
@@ -152,10 +152,7 @@ impl Sealed for ops::IndexRange {}
 #[rustc_on_unimplemented(
     on(T = "str", label = "string indices are ranges of `usize`",),
     on(
-        all(
-            any(T = "str", T = "&str", T = "alloc::string::String", T = "std::string::String"),
-            _Self = "{integer}"
-        ),
+        all(any(T = "str", T = "&str", T = "alloc::string::String"), _Self = "{integer}"),
         note = "you can use `.chars().nth()` or `.bytes().nth()`\n\
                 for more information, see chapter 8 in The Book: \
                 <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
diff --git a/src/tools/rustdoc-gui/tester.js b/src/tools/rustdoc-gui/tester.js
index af1bc05ddb2..8f6626f6296 100644
--- a/src/tools/rustdoc-gui/tester.js
+++ b/src/tools/rustdoc-gui/tester.js
@@ -249,12 +249,17 @@ async function main(argv) {
         console.log("`--no-headless` option is active, disabling concurrency for running tests.");
     }
 
-    console.log(`Running ${files.length} rustdoc-gui (${opts["jobs"]} concurrently) ...`);
-
     if (opts["jobs"] < 1) {
+        const len = files.length;
+        console.log(
+            `Running ${len} rustdoc-gui (UNBOUNDED concurrency; use "-j#" for a limit) ...`,
+        );
         process.setMaxListeners(files.length + 1);
     } else if (headless) {
+        console.log(`Running ${files.length} rustdoc-gui (${opts["jobs"]} concurrently) ...`);
         process.setMaxListeners(opts["jobs"] + 1);
+    } else {
+        console.log(`Running ${files.length} rustdoc-gui ...`);
     }
 
     // We catch this "event" to display a nicer message in case of unexpected exit (because of a
diff --git a/tests/pretty/format-args-str-escape.pp b/tests/pretty/format-args-str-escape.pp
new file mode 100644
index 00000000000..b84bc2303b7
--- /dev/null
+++ b/tests/pretty/format-args-str-escape.pp
@@ -0,0 +1,21 @@
+#![feature(prelude_import)]
+#![no_std]
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+#[macro_use]
+extern crate std;
+// pretty-compare-only
+// pretty-mode:expanded
+// pp-exact:format-args-str-escape.pp
+
+fn main() {
+    { ::std::io::_print(format_args!("\u{1b}[1mHello, world!\u{1b}[0m\n")); };
+    { ::std::io::_print(format_args!("\u{1b}[1mHello, world!\u{1b}[0m\n")); };
+    {
+        ::std::io::_print(format_args!("Not an escape sequence: \\u{{1B}}[1mbold\\x1B[0m\n"));
+    };
+    {
+        ::std::io::_print(format_args!("{0}\n",
+                "\x1B[1mHello, world!\x1B[0m"));
+    };
+}
diff --git a/tests/pretty/format-args-str-escape.rs b/tests/pretty/format-args-str-escape.rs
new file mode 100644
index 00000000000..e596fcfd8bc
--- /dev/null
+++ b/tests/pretty/format-args-str-escape.rs
@@ -0,0 +1,10 @@
+// pretty-compare-only
+// pretty-mode:expanded
+// pp-exact:format-args-str-escape.pp
+
+fn main() {
+    println!("\x1B[1mHello, world!\x1B[0m");
+    println!("\u{1B}[1mHello, world!\u{1B}[0m");
+    println!("Not an escape sequence: \\u{{1B}}[1mbold\\x1B[0m");
+    println!("{}", "\x1B[1mHello, world!\x1B[0m");
+}
diff --git a/tests/ui/impl-trait/in-trait/gat-outlives.rs b/tests/ui/impl-trait/in-trait/gat-outlives.rs
new file mode 100644
index 00000000000..83dd6cfce53
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/gat-outlives.rs
@@ -0,0 +1,17 @@
+// edition: 2021
+
+use std::future::Future;
+
+trait Trait {
+    type Gat<'a>;
+    //~^ ERROR missing required bound on `Gat`
+    async fn foo(&self) -> Self::Gat<'_>;
+}
+
+trait Trait2 {
+    type Gat<'a>;
+    //~^ ERROR missing required bound on `Gat`
+    async fn foo(&self) -> impl Future<Output = Self::Gat<'_>>;
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/in-trait/gat-outlives.stderr b/tests/ui/impl-trait/in-trait/gat-outlives.stderr
new file mode 100644
index 00000000000..8ec4b0ab2ee
--- /dev/null
+++ b/tests/ui/impl-trait/in-trait/gat-outlives.stderr
@@ -0,0 +1,24 @@
+error: missing required bound on `Gat`
+  --> $DIR/gat-outlives.rs:6:5
+   |
+LL |     type Gat<'a>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clause: `where Self: 'a`
+   |
+   = note: this bound is currently required to ensure that impls have maximum flexibility
+   = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
+
+error: missing required bound on `Gat`
+  --> $DIR/gat-outlives.rs:12:5
+   |
+LL |     type Gat<'a>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clause: `where Self: 'a`
+   |
+   = note: this bound is currently required to ensure that impls have maximum flexibility
+   = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
+
+error: aborting due to 2 previous errors
+
diff --git a/triagebot.toml b/triagebot.toml
index b17b415c0ff..fbdc28787ff 100644
--- a/triagebot.toml
+++ b/triagebot.toml
@@ -556,7 +556,7 @@ cc = ["@davidtwco", "@compiler-errors", "@JohnTitor", "@TaKO8Ki"]
 
 [mentions."compiler/rustc_smir"]
 message = "This PR changes Stable MIR"
-cc = ["@oli-obk", "@celinval", "@spastorino"]
+cc = ["@oli-obk", "@celinval", "@spastorino", "@ouz-a"]
 
 [mentions."compiler/stable_mir"]
 message = "This PR changes Stable MIR"