Auto merge of #139781 - jhpratt:rollup-qadsjvb, r=jhpratt

Rollup of 9 pull requests

Successful merges:

 - #138336 (Improve `-Z crate-attr` diagnostics)
 - #139636 (Encode dep node edge count as u32 instead of usize)
 - #139666 (cleanup `mir_borrowck`)
 - #139695 (compiletest: consistently use `camino::{Utf8Path,Utf8PathBuf}` throughout)
 - #139699 (Proactively update coroutine drop shim's phase to account for later passes applied during shim query)
 - #139718 (enforce unsafe attributes in pre-2024 editions by default)
 - #139722 (Move some things to rustc_type_ir)
 - #139760 (UI tests: migrate remaining compile time `error-pattern`s to line annotations when possible)
 - #139776 (Switch attrs to `diagnostic::on_unimplemented`)

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

39 files changed, 724 insertions, 692 deletions

diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index 0b65246693d..d656d9b0b8a 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -627,7 +627,7 @@ pub fn mk_doc_comment(
     Attribute { kind: AttrKind::DocComment(comment_kind, data), id: g.mk_attr_id(), style, span }
 }
 
-pub fn mk_attr(
+fn mk_attr(
     g: &AttrIdGenerator,
     style: AttrStyle,
     unsafety: Safety,
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 9a521915667..80dcedea729 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -21,6 +21,7 @@ use std::cell::RefCell;
 use std::marker::PhantomData;
 use std::ops::{ControlFlow, Deref};
 
+use borrow_set::LocalsStateAtExit;
 use root_cx::BorrowCheckRootCtxt;
 use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
@@ -303,33 +304,13 @@ fn do_mir_borrowck<'tcx>(
         root_cx.set_tainted_by_errors(e);
     }
 
-    let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
-    for var_debug_info in &input_body.var_debug_info {
-        if let VarDebugInfoContents::Place(place) = var_debug_info.value {
-            if let Some(local) = place.as_local() {
-                if let Some(prev_name) = local_names[local]
-                    && var_debug_info.name != prev_name
-                {
-                    span_bug!(
-                        var_debug_info.source_info.span,
-                        "local {:?} has many names (`{}` vs `{}`)",
-                        local,
-                        prev_name,
-                        var_debug_info.name
-                    );
-                }
-                local_names[local] = Some(var_debug_info.name);
-            }
-        }
-    }
-
     // Replace all regions with fresh inference variables. This
     // requires first making our own copy of the MIR. This copy will
     // be modified (in place) to contain non-lexical lifetimes. It
     // will have a lifetime tied to the inference context.
     let mut body_owned = input_body.clone();
     let mut promoted = input_promoted.to_owned();
-    let free_regions = nll::replace_regions_in_mir(&infcx, &mut body_owned, &mut promoted);
+    let universal_regions = nll::replace_regions_in_mir(&infcx, &mut body_owned, &mut promoted);
     let body = &body_owned; // no further changes
 
     let location_table = PoloniusLocationTable::new(body);
@@ -354,7 +335,7 @@ fn do_mir_borrowck<'tcx>(
     } = nll::compute_regions(
         root_cx,
         &infcx,
-        free_regions,
+        universal_regions,
         body,
         &promoted,
         &location_table,
@@ -367,24 +348,23 @@ fn do_mir_borrowck<'tcx>(
     // Dump MIR results into a file, if that is enabled. This lets us
     // write unit-tests, as well as helping with debugging.
     nll::dump_nll_mir(&infcx, body, &regioncx, &opt_closure_req, &borrow_set);
+    polonius::dump_polonius_mir(
+        &infcx,
+        body,
+        &regioncx,
+        &opt_closure_req,
+        &borrow_set,
+        polonius_diagnostics.as_ref(),
+    );
 
     // We also have a `#[rustc_regions]` annotation that causes us to dump
     // information.
-    let diags_buffer = &mut BorrowckDiagnosticsBuffer::default();
-    nll::dump_annotation(&infcx, body, &regioncx, &opt_closure_req, diags_buffer);
-
-    let movable_coroutine =
-    // The first argument is the coroutine type passed by value
-    if let Some(local) = body.local_decls.raw.get(1)
-    // Get the interior types and args which typeck computed
-    && let ty::Coroutine(def_id, _) = *local.ty.kind()
-    && tcx.coroutine_movability(def_id) == hir::Movability::Movable
-{
-    true
-} else {
-    false
-};
+    nll::dump_annotation(&infcx, body, &regioncx, &opt_closure_req);
 
+    let movable_coroutine = body.coroutine.is_some()
+        && tcx.coroutine_movability(def.to_def_id()) == hir::Movability::Movable;
+
+    let diags_buffer = &mut BorrowckDiagnosticsBuffer::default();
     // While promoteds should mostly be correct by construction, we need to check them for
     // invalid moves to detect moving out of arrays:`struct S; fn main() { &([S][0]); }`.
     for promoted_body in &promoted {
@@ -402,7 +382,6 @@ fn do_mir_borrowck<'tcx>(
             location_table: &location_table,
             movable_coroutine,
             fn_self_span_reported: Default::default(),
-            locals_are_invalidated_at_exit,
             access_place_error_reported: Default::default(),
             reservation_error_reported: Default::default(),
             uninitialized_error_reported: Default::default(),
@@ -434,6 +413,26 @@ fn do_mir_borrowck<'tcx>(
         promoted_mbcx.report_move_errors();
     }
 
+    let mut local_names = IndexVec::from_elem(None, &body.local_decls);
+    for var_debug_info in &body.var_debug_info {
+        if let VarDebugInfoContents::Place(place) = var_debug_info.value {
+            if let Some(local) = place.as_local() {
+                if let Some(prev_name) = local_names[local]
+                    && var_debug_info.name != prev_name
+                {
+                    span_bug!(
+                        var_debug_info.source_info.span,
+                        "local {:?} has many names (`{}` vs `{}`)",
+                        local,
+                        prev_name,
+                        var_debug_info.name
+                    );
+                }
+                local_names[local] = Some(var_debug_info.name);
+            }
+        }
+    }
+
     let mut mbcx = MirBorrowckCtxt {
         root_cx,
         infcx: &infcx,
@@ -441,7 +440,6 @@ fn do_mir_borrowck<'tcx>(
         move_data: &move_data,
         location_table: &location_table,
         movable_coroutine,
-        locals_are_invalidated_at_exit,
         fn_self_span_reported: Default::default(),
         access_place_error_reported: Default::default(),
         reservation_error_reported: Default::default(),
@@ -454,9 +452,9 @@ fn do_mir_borrowck<'tcx>(
         local_names,
         region_names: RefCell::default(),
         next_region_name: RefCell::new(1),
-        polonius_output,
         move_errors: Vec::new(),
         diags_buffer,
+        polonius_output: polonius_output.as_deref(),
         polonius_diagnostics: polonius_diagnostics.as_ref(),
     };
 
@@ -473,16 +471,6 @@ fn do_mir_borrowck<'tcx>(
 
     mbcx.report_move_errors();
 
-    // If requested, dump polonius MIR.
-    polonius::dump_polonius_mir(
-        &infcx,
-        body,
-        &regioncx,
-        &borrow_set,
-        polonius_diagnostics.as_ref(),
-        &opt_closure_req,
-    );
-
     // For each non-user used mutable variable, check if it's been assigned from
     // a user-declared local. If so, then put that local into the used_mut set.
     // Note that this set is expected to be small - only upvars from closures
@@ -513,7 +501,6 @@ fn do_mir_borrowck<'tcx>(
     };
 
     let body_with_facts = if consumer_options.is_some() {
-        let output_facts = mbcx.polonius_output;
         Some(Box::new(BodyWithBorrowckFacts {
             body: body_owned,
             promoted,
@@ -521,7 +508,7 @@ fn do_mir_borrowck<'tcx>(
             region_inference_context: regioncx,
             location_table: polonius_input.as_ref().map(|_| location_table),
             input_facts: polonius_input,
-            output_facts,
+            output_facts: polonius_output,
         }))
     } else {
         None
@@ -654,13 +641,6 @@ struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
     location_table: &'a PoloniusLocationTable,
 
     movable_coroutine: bool,
-    /// This keeps track of whether local variables are free-ed when the function
-    /// exits even without a `StorageDead`, which appears to be the case for
-    /// constants.
-    ///
-    /// I'm not sure this is the right approach - @eddyb could you try and
-    /// figure this out?
-    locals_are_invalidated_at_exit: bool,
     /// This field keeps track of when borrow errors are reported in the access_place function
     /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
     /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
@@ -708,12 +688,11 @@ struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
     /// The counter for generating new region names.
     next_region_name: RefCell<usize>,
 
-    /// Results of Polonius analysis.
-    polonius_output: Option<Box<PoloniusOutput>>,
-
     diags_buffer: &'a mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>,
     move_errors: Vec<MoveError<'tcx>>,
 
+    /// Results of Polonius analysis.
+    polonius_output: Option<&'a PoloniusOutput>,
     /// When using `-Zpolonius=next`: the data used to compute errors and diagnostics.
     polonius_diagnostics: Option<&'a PoloniusDiagnosticsContext>,
 }
@@ -937,13 +916,20 @@ impl<'a, 'tcx> ResultsVisitor<'a, 'tcx, Borrowck<'a, 'tcx>> for MirBorrowckCtxt<
             | TerminatorKind::Return
             | TerminatorKind::TailCall { .. }
             | TerminatorKind::CoroutineDrop => {
-                // Returning from the function implicitly kills storage for all locals and statics.
-                // Often, the storage will already have been killed by an explicit
-                // StorageDead, but we don't always emit those (notably on unwind paths),
-                // so this "extra check" serves as a kind of backup.
-                for i in state.borrows.iter() {
-                    let borrow = &self.borrow_set[i];
-                    self.check_for_invalidation_at_exit(loc, borrow, span);
+                match self.borrow_set.locals_state_at_exit() {
+                    LocalsStateAtExit::AllAreInvalidated => {
+                        // Returning from the function implicitly kills storage for all locals and statics.
+                        // Often, the storage will already have been killed by an explicit
+                        // StorageDead, but we don't always emit those (notably on unwind paths),
+                        // so this "extra check" serves as a kind of backup.
+                        for i in state.borrows.iter() {
+                            let borrow = &self.borrow_set[i];
+                            self.check_for_invalidation_at_exit(loc, borrow, span);
+                        }
+                    }
+                    // If we do not implicitly invalidate all locals on exit,
+                    // we check for conflicts when dropping or moving this local.
+                    LocalsStateAtExit::SomeAreInvalidated { has_storage_dead_or_moved: _ } => {}
                 }
             }
 
@@ -1715,22 +1701,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         // we'll have a memory leak) and assume that all statics have a destructor.
         //
         // FIXME: allow thread-locals to borrow other thread locals?
-
-        let (might_be_alive, will_be_dropped) =
-            if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
-                // Thread-locals might be dropped after the function exits
-                // We have to dereference the outer reference because
-                // borrows don't conflict behind shared references.
-                root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
-                (true, true)
-            } else {
-                (false, self.locals_are_invalidated_at_exit)
-            };
-
-        if !will_be_dropped {
-            debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
-            return;
-        }
+        let might_be_alive = if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
+            // Thread-locals might be dropped after the function exits
+            // We have to dereference the outer reference because
+            // borrows don't conflict behind shared references.
+            root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
+            true
+        } else {
+            false
+        };
 
         let sd = if might_be_alive { Deep } else { Shallow(None) };
 
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index 8a2a34f207a..fe899bb054f 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -21,7 +21,7 @@ use tracing::{debug, instrument};
 
 use crate::borrow_set::BorrowSet;
 use crate::consumers::ConsumerOptions;
-use crate::diagnostics::{BorrowckDiagnosticsBuffer, RegionErrors};
+use crate::diagnostics::RegionErrors;
 use crate::polonius::PoloniusDiagnosticsContext;
 use crate::polonius::legacy::{
     PoloniusFacts, PoloniusFactsExt, PoloniusLocationTable, PoloniusOutput,
@@ -117,11 +117,6 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         Rc::clone(&location_map),
     );
 
-    // Create the region inference context, taking ownership of the
-    // region inference data that was contained in `infcx`, and the
-    // base constraints generated by the type-check.
-    let var_infos = infcx.get_region_var_infos();
-
     // If requested, emit legacy polonius facts.
     polonius::legacy::emit_facts(
         &mut polonius_facts,
@@ -134,13 +129,8 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         &constraints,
     );
 
-    let mut regioncx = RegionInferenceContext::new(
-        infcx,
-        var_infos,
-        constraints,
-        universal_region_relations,
-        location_map,
-    );
+    let mut regioncx =
+        RegionInferenceContext::new(infcx, constraints, universal_region_relations, location_map);
 
     // If requested for `-Zpolonius=next`, convert NLL constraints to localized outlives constraints
     // and use them to compute loan liveness.
@@ -297,7 +287,6 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
-    diagnostics_buffer: &mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>,
 ) {
     let tcx = infcx.tcx;
     let base_def_id = tcx.typeck_root_def_id(body.source.def_id());
@@ -335,13 +324,11 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     } else {
         let mut err = infcx.dcx().struct_span_note(def_span, "no external requirements");
         regioncx.annotate(tcx, &mut err);
-
         err
     };
 
     // FIXME(@lcnr): We currently don't dump the inferred hidden types here.
-
-    diagnostics_buffer.buffer_non_error(err);
+    err.emit();
 }
 
 fn for_each_region_constraint<'tcx>(
diff --git a/compiler/rustc_borrowck/src/polonius/dump.rs b/compiler/rustc_borrowck/src/polonius/dump.rs
index eb53a98832c..6a943e19208 100644
--- a/compiler/rustc_borrowck/src/polonius/dump.rs
+++ b/compiler/rustc_borrowck/src/polonius/dump.rs
@@ -24,9 +24,9 @@ pub(crate) fn dump_polonius_mir<'tcx>(
     infcx: &BorrowckInferCtxt<'tcx>,
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
+    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
     borrow_set: &BorrowSet<'tcx>,
     polonius_diagnostics: Option<&PoloniusDiagnosticsContext>,
-    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
 ) {
     let tcx = infcx.tcx;
     if !tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index 569c46e6403..c82c7341f02 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -9,7 +9,7 @@ use rustc_errors::Diag;
 use rustc_hir::def_id::CRATE_DEF_ID;
 use rustc_index::IndexVec;
 use rustc_infer::infer::outlives::test_type_match;
-use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound, VerifyIfEq};
+use rustc_infer::infer::region_constraints::{GenericKind, VerifyBound, VerifyIfEq};
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
 use rustc_middle::bug;
 use rustc_middle::mir::{
@@ -145,7 +145,7 @@ pub struct RegionInferenceContext<'tcx> {
     /// variables are identified by their index (`RegionVid`). The
     /// definition contains information about where the region came
     /// from as well as its final inferred value.
-    pub(crate) definitions: IndexVec<RegionVid, RegionDefinition<'tcx>>,
+    pub(crate) definitions: Frozen<IndexVec<RegionVid, RegionDefinition<'tcx>>>,
 
     /// The liveness constraints added to each region. For most
     /// regions, these start out empty and steadily grow, though for
@@ -385,6 +385,26 @@ fn sccs_info<'tcx>(infcx: &BorrowckInferCtxt<'tcx>, sccs: &ConstraintSccs) {
     debug!("SCC edges {:#?}", scc_node_to_edges);
 }
 
+fn create_definitions<'tcx>(
+    infcx: &BorrowckInferCtxt<'tcx>,
+    universal_regions: &UniversalRegions<'tcx>,
+) -> Frozen<IndexVec<RegionVid, RegionDefinition<'tcx>>> {
+    // Create a RegionDefinition for each inference variable.
+    let mut definitions: IndexVec<_, _> = infcx
+        .get_region_var_infos()
+        .iter()
+        .map(|info| RegionDefinition::new(info.universe, info.origin))
+        .collect();
+
+    // Add the external name for all universal regions.
+    for (external_name, variable) in universal_regions.named_universal_regions_iter() {
+        debug!("region {variable:?} has external name {external_name:?}");
+        definitions[variable].external_name = Some(external_name);
+    }
+
+    Frozen::freeze(definitions)
+}
+
 impl<'tcx> RegionInferenceContext<'tcx> {
     /// Creates a new region inference context with a total of
     /// `num_region_variables` valid inference variables; the first N
@@ -395,7 +415,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// of constraints produced by the MIR type check.
     pub(crate) fn new(
         infcx: &BorrowckInferCtxt<'tcx>,
-        var_infos: VarInfos,
         constraints: MirTypeckRegionConstraints<'tcx>,
         universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
         location_map: Rc<DenseLocationMap>,
@@ -426,11 +445,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             infcx.set_tainted_by_errors(guar);
         }
 
-        // Create a RegionDefinition for each inference variable.
-        let definitions: IndexVec<_, _> = var_infos
-            .iter()
-            .map(|info| RegionDefinition::new(info.universe, info.origin))
-            .collect();
+        let definitions = create_definitions(infcx, &universal_regions);
 
         let constraint_sccs =
             outlives_constraints.add_outlives_static(&universal_regions, &definitions);
@@ -526,18 +541,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// means that the `R1: !1` constraint here will cause
     /// `R1` to become `'static`.
     fn init_free_and_bound_regions(&mut self) {
-        // Update the names (if any)
-        // This iterator has unstable order but we collect it all into an IndexVec
-        for (external_name, variable) in
-            self.universal_region_relations.universal_regions.named_universal_regions_iter()
-        {
-            debug!(
-                "init_free_and_bound_regions: region {:?} has external name {:?}",
-                variable, external_name
-            );
-            self.definitions[variable].external_name = Some(external_name);
-        }
-
         for variable in self.definitions.indices() {
             let scc = self.constraint_sccs.scc(variable);
 
diff --git a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
index ccb257ae093..57516565147 100644
--- a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
+++ b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
@@ -21,7 +21,6 @@ use crate::{ClosureOutlivesSubject, ClosureRegionRequirements, ConstraintCategor
 
 pub(crate) struct ConstraintConversion<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
-    tcx: TyCtxt<'tcx>,
     universal_regions: &'a UniversalRegions<'tcx>,
     /// Each RBP `GK: 'a` is assumed to be true. These encode
     /// relationships like `T: 'a` that are added via implicit bounds
@@ -34,7 +33,6 @@ pub(crate) struct ConstraintConversion<'a, 'tcx> {
     /// logic expecting to see (e.g.) `ReStatic`, and if we supplied
     /// our special inference variable there, we would mess that up.
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
-    implicit_region_bound: ty::Region<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     known_type_outlives_obligations: &'a [ty::PolyTypeOutlivesPredicate<'tcx>],
     locations: Locations,
@@ -49,7 +47,6 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         infcx: &'a InferCtxt<'tcx>,
         universal_regions: &'a UniversalRegions<'tcx>,
         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
-        implicit_region_bound: ty::Region<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         known_type_outlives_obligations: &'a [ty::PolyTypeOutlivesPredicate<'tcx>],
         locations: Locations,
@@ -59,10 +56,8 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     ) -> Self {
         Self {
             infcx,
-            tcx: infcx.tcx,
             universal_regions,
             region_bound_pairs,
-            implicit_region_bound,
             param_env,
             known_type_outlives_obligations,
             locations,
@@ -96,7 +91,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         // into a vector. These are the regions that we will be
         // relating to one another.
         let closure_mapping = &UniversalRegions::closure_mapping(
-            self.tcx,
+            self.infcx.tcx,
             closure_args,
             closure_requirements.num_external_vids,
             closure_def_id,
@@ -111,7 +106,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
             let subject = match outlives_requirement.subject {
                 ClosureOutlivesSubject::Region(re) => closure_mapping[re].into(),
                 ClosureOutlivesSubject::Ty(subject_ty) => {
-                    subject_ty.instantiate(self.tcx, |vid| closure_mapping[vid]).into()
+                    subject_ty.instantiate(self.infcx.tcx, |vid| closure_mapping[vid]).into()
                 }
             };
 
@@ -127,14 +122,14 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         predicate: ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
         constraint_category: ConstraintCategory<'tcx>,
     ) {
+        let tcx = self.infcx.tcx;
         debug!("generate: constraints at: {:#?}", self.locations);
 
         // Extract out various useful fields we'll need below.
         let ConstraintConversion {
-            tcx,
             infcx,
+            universal_regions,
             region_bound_pairs,
-            implicit_region_bound,
             known_type_outlives_obligations,
             ..
         } = *self;
@@ -145,7 +140,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                 break;
             }
 
-            if !self.tcx.recursion_limit().value_within_limit(iteration) {
+            if !tcx.recursion_limit().value_within_limit(iteration) {
                 bug!(
                     "FIXME(-Znext-solver): Overflowed when processing region obligations: {outlives_predicates:#?}"
                 );
@@ -170,10 +165,11 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                             );
                         }
 
+                        let implicit_region_bound =
+                            ty::Region::new_var(tcx, universal_regions.implicit_region_bound());
                         // we don't actually use this for anything, but
                         // the `TypeOutlives` code needs an origin.
                         let origin = infer::RelateParamBound(self.span, t1, None);
-
                         TypeOutlives::new(
                             &mut *self,
                             tcx,
@@ -205,7 +201,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     /// are dealt with during trait solving.
     fn replace_placeholders_with_nll<T: TypeFoldable<TyCtxt<'tcx>>>(&mut self, value: T) -> T {
         if value.has_placeholders() {
-            fold_regions(self.tcx, value, |r, _| match r.kind() {
+            fold_regions(self.infcx.tcx, value, |r, _| match r.kind() {
                 ty::RePlaceholder(placeholder) => {
                     self.constraints.placeholder_region(self.infcx, placeholder)
                 }
diff --git a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
index eaac633b512..536a27763d2 100644
--- a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
+++ b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
@@ -49,14 +49,12 @@ pub(crate) struct CreateResult<'tcx> {
 pub(crate) fn create<'tcx>(
     infcx: &InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    implicit_region_bound: ty::Region<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     constraints: &mut MirTypeckRegionConstraints<'tcx>,
 ) -> CreateResult<'tcx> {
     UniversalRegionRelationsBuilder {
         infcx,
         param_env,
-        implicit_region_bound,
         constraints,
         universal_regions,
         region_bound_pairs: Default::default(),
@@ -181,7 +179,6 @@ struct UniversalRegionRelationsBuilder<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
-    implicit_region_bound: ty::Region<'tcx>,
     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 
     // outputs:
@@ -320,7 +317,6 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
                 self.infcx,
                 &self.universal_regions,
                 &self.region_bound_pairs,
-                self.implicit_region_bound,
                 param_env,
                 &known_type_outlives_obligations,
                 Locations::All(span),
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index a17dff5d271..05e0bb3f9f3 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -113,7 +113,6 @@ pub(crate) fn type_check<'a, 'tcx>(
     move_data: &MoveData<'tcx>,
     location_map: Rc<DenseLocationMap>,
 ) -> MirTypeckResults<'tcx> {
-    let implicit_region_bound = ty::Region::new_var(infcx.tcx, universal_regions.fr_fn_body);
     let mut constraints = MirTypeckRegionConstraints {
         placeholder_indices: PlaceholderIndices::default(),
         placeholder_index_to_region: IndexVec::default(),
@@ -129,13 +128,7 @@ pub(crate) fn type_check<'a, 'tcx>(
         region_bound_pairs,
         normalized_inputs_and_output,
         known_type_outlives_obligations,
-    } = free_region_relations::create(
-        infcx,
-        infcx.param_env,
-        implicit_region_bound,
-        universal_regions,
-        &mut constraints,
-    );
+    } = free_region_relations::create(infcx, infcx.param_env, universal_regions, &mut constraints);
 
     let pre_obligations = infcx.take_registered_region_obligations();
     assert!(
@@ -160,7 +153,6 @@ pub(crate) fn type_check<'a, 'tcx>(
         user_type_annotations: &body.user_type_annotations,
         region_bound_pairs,
         known_type_outlives_obligations,
-        implicit_region_bound,
         reported_errors: Default::default(),
         universal_regions: &universal_region_relations.universal_regions,
         location_table,
@@ -226,7 +218,6 @@ struct TypeChecker<'a, 'tcx> {
     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
     region_bound_pairs: RegionBoundPairs<'tcx>,
     known_type_outlives_obligations: Vec<ty::PolyTypeOutlivesPredicate<'tcx>>,
-    implicit_region_bound: ty::Region<'tcx>,
     reported_errors: FxIndexSet<(Ty<'tcx>, Span)>,
     universal_regions: &'a UniversalRegions<'tcx>,
     location_table: &'a PoloniusLocationTable,
@@ -422,7 +413,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             self.infcx,
             self.universal_regions,
             &self.region_bound_pairs,
-            self.implicit_region_bound,
             self.infcx.param_env,
             &self.known_type_outlives_obligations,
             locations,
@@ -2507,7 +2497,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 self.infcx,
                 self.universal_regions,
                 &self.region_bound_pairs,
-                self.implicit_region_bound,
                 self.infcx.param_env,
                 &self.known_type_outlives_obligations,
                 locations,
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 5c57ab99a85..c11e14d214c 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -438,6 +438,10 @@ impl<'tcx> UniversalRegions<'tcx> {
         }
     }
 
+    pub(crate) fn implicit_region_bound(&self) -> RegionVid {
+        self.fr_fn_body
+    }
+
     pub(crate) fn tainted_by_errors(&self) -> Option<ErrorGuaranteed> {
         self.indices.tainted_by_errors.get()
     }
diff --git a/compiler/rustc_builtin_macros/messages.ftl b/compiler/rustc_builtin_macros/messages.ftl
index 603dc90bafc..5316e90847a 100644
--- a/compiler/rustc_builtin_macros/messages.ftl
+++ b/compiler/rustc_builtin_macros/messages.ftl
@@ -231,8 +231,6 @@ builtin_macros_format_unused_args = multiple unused formatting arguments
 
 builtin_macros_format_use_positional = consider using a positional formatting argument instead
 
-builtin_macros_invalid_crate_attribute = invalid crate attribute
-
 builtin_macros_multiple_default_attrs = multiple `#[default]` attributes
     .note = only one `#[default]` attribute is needed
     .label = `#[default]` used here
diff --git a/compiler/rustc_builtin_macros/src/cmdline_attrs.rs b/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
index 6afd8c4b43b..423b6a15b64 100644
--- a/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
+++ b/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
@@ -1,44 +1,37 @@
 //! Attributes injected into the crate root from command line using `-Z crate-attr`.
 
-use rustc_ast::attr::mk_attr;
-use rustc_ast::{self as ast, AttrItem, AttrStyle, token};
-use rustc_parse::parser::ForceCollect;
-use rustc_parse::{new_parser_from_source_str, unwrap_or_emit_fatal};
+use rustc_ast::{self as ast};
+use rustc_errors::Diag;
+use rustc_parse::parser::attr::InnerAttrPolicy;
+use rustc_parse::{parse_in, source_str_to_stream};
 use rustc_session::parse::ParseSess;
 use rustc_span::FileName;
 
-use crate::errors;
-
 pub fn inject(krate: &mut ast::Crate, psess: &ParseSess, attrs: &[String]) {
     for raw_attr in attrs {
-        let mut parser = unwrap_or_emit_fatal(new_parser_from_source_str(
-            psess,
-            FileName::cli_crate_attr_source_code(raw_attr),
-            raw_attr.clone(),
-        ));
-
-        let start_span = parser.token.span;
-        let AttrItem { unsafety, path, args, tokens: _ } =
-            match parser.parse_attr_item(ForceCollect::No) {
-                Ok(ai) => ai,
-                Err(err) => {
+        let source = format!("#![{raw_attr}]");
+        let parse = || -> Result<ast::Attribute, Vec<Diag<'_>>> {
+            let tokens = source_str_to_stream(
+                psess,
+                FileName::cli_crate_attr_source_code(raw_attr),
+                source,
+                None,
+            )?;
+            parse_in(psess, tokens, "<crate attribute>", |p| {
+                p.parse_attribute(InnerAttrPolicy::Permitted)
+            })
+            .map_err(|e| vec![e])
+        };
+        let meta = match parse() {
+            Ok(meta) => meta,
+            Err(errs) => {
+                for err in errs {
                     err.emit();
-                    continue;
                 }
-            };
-        let end_span = parser.token.span;
-        if parser.token != token::Eof {
-            psess.dcx().emit_err(errors::InvalidCrateAttr { span: start_span.to(end_span) });
-            continue;
-        }
+                continue;
+            }
+        };
 
-        krate.attrs.push(mk_attr(
-            &psess.attr_id_generator,
-            AttrStyle::Inner,
-            unsafety,
-            path,
-            args,
-            start_span.to(end_span),
-        ));
+        krate.attrs.push(meta);
     }
 }
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index 4bbe212f429..c2b1dff4cf1 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -110,13 +110,6 @@ pub(crate) struct ProcMacro {
 }
 
 #[derive(Diagnostic)]
-#[diag(builtin_macros_invalid_crate_attribute)]
-pub(crate) struct InvalidCrateAttr {
-    #[primary_span]
-    pub(crate) span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(builtin_macros_non_abi)]
 pub(crate) struct NonABI {
     #[primary_span]
diff --git a/compiler/rustc_data_structures/src/marker.rs b/compiler/rustc_data_structures/src/marker.rs
index 744ae9b6fe2..5f07cfef133 100644
--- a/compiler/rustc_data_structures/src/marker.rs
+++ b/compiler/rustc_data_structures/src/marker.rs
@@ -1,13 +1,13 @@
 use std::alloc::Allocator;
 
-#[rustc_on_unimplemented(message = "`{Self}` doesn't implement `DynSend`. \
+#[diagnostic::on_unimplemented(message = "`{Self}` doesn't implement `DynSend`. \
             Add it to `rustc_data_structures::marker` or use `IntoDynSyncSend` if it's already `Send`")]
 // This is an auto trait for types which can be sent across threads if `sync::is_dyn_thread_safe()`
 // is true. These types can be wrapped in a `FromDyn` to get a `Send` type. Wrapping a
 // `Send` type in `IntoDynSyncSend` will create a `DynSend` type.
 pub unsafe auto trait DynSend {}
 
-#[rustc_on_unimplemented(message = "`{Self}` doesn't implement `DynSync`. \
+#[diagnostic::on_unimplemented(message = "`{Self}` doesn't implement `DynSync`. \
             Add it to `rustc_data_structures::marker` or use `IntoDynSyncSend` if it's already `Sync`")]
 // This is an auto trait for types which can be shared across threads if `sync::is_dyn_thread_safe()`
 // is true. These types can be wrapped in a `FromDyn` to get a `Sync` type. Wrapping a
diff --git a/compiler/rustc_error_codes/src/error_codes/E0755.md b/compiler/rustc_error_codes/src/error_codes/E0755.md
index 88b7f484969..b67f078c78e 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0755.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0755.md
@@ -5,7 +5,7 @@ Erroneous code example:
 ```compile_fail,E0755
 #![feature(ffi_pure)]
 
-#[ffi_pure] // error!
+#[unsafe(ffi_pure)] // error!
 pub fn foo() {}
 # fn main() {}
 ```
@@ -17,7 +17,7 @@ side effects or infinite loops:
 #![feature(ffi_pure)]
 
 extern "C" {
-    #[ffi_pure] // ok!
+    #[unsafe(ffi_pure)] // ok!
     pub fn strlen(s: *const i8) -> isize;
 }
 # fn main() {}
diff --git a/compiler/rustc_error_codes/src/error_codes/E0756.md b/compiler/rustc_error_codes/src/error_codes/E0756.md
index ffdc421aab5..aadde038d12 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0756.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0756.md
@@ -6,7 +6,7 @@ Erroneous code example:
 ```compile_fail,E0756
 #![feature(ffi_const)]
 
-#[ffi_const] // error!
+#[unsafe(ffi_const)] // error!
 pub fn foo() {}
 # fn main() {}
 ```
@@ -18,7 +18,7 @@ which have no side effects except for their return value:
 #![feature(ffi_const)]
 
 extern "C" {
-    #[ffi_const] // ok!
+    #[unsafe(ffi_const)] // ok!
     pub fn strlen(s: *const i8) -> i32;
 }
 # fn main() {}
diff --git a/compiler/rustc_error_codes/src/error_codes/E0757.md b/compiler/rustc_error_codes/src/error_codes/E0757.md
index 41b06b23c4f..fb75b028f45 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0757.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0757.md
@@ -6,8 +6,9 @@ Erroneous code example:
 #![feature(ffi_const, ffi_pure)]
 
 extern "C" {
-    #[ffi_const]
-    #[ffi_pure] // error: `#[ffi_const]` function cannot be `#[ffi_pure]`
+    #[unsafe(ffi_const)]
+    #[unsafe(ffi_pure)]
+    //~^ ERROR `#[ffi_const]` function cannot be `#[ffi_pure]`
     pub fn square(num: i32) -> i32;
 }
 ```
@@ -19,7 +20,7 @@ As `ffi_const` provides stronger guarantees than `ffi_pure`, remove the
 #![feature(ffi_const)]
 
 extern "C" {
-    #[ffi_const]
+    #[unsafe(ffi_const)]
     pub fn square(num: i32) -> i32;
 }
 ```
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 1e33e2e9393..7615362e1f9 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -6,6 +6,7 @@ use AttributeDuplicates::*;
 use AttributeGate::*;
 use AttributeType::*;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_span::edition::Edition;
 use rustc_span::{Symbol, sym};
 
 use crate::{Features, Stability};
@@ -65,9 +66,12 @@ pub enum AttributeSafety {
     /// Normal attribute that does not need `#[unsafe(...)]`
     Normal,
 
-    /// Unsafe attribute that requires safety obligations
-    /// to be discharged
-    Unsafe,
+    /// Unsafe attribute that requires safety obligations to be discharged.
+    ///
+    /// An error is emitted when `#[unsafe(...)]` is omitted, except when the attribute's edition
+    /// is less than the one stored in `unsafe_since`. This handles attributes that were safe in
+    /// earlier editions, but become unsafe in later ones.
+    Unsafe { unsafe_since: Option<Edition> },
 }
 
 #[derive(Clone, Copy)]
@@ -187,12 +191,23 @@ macro_rules! template {
 }
 
 macro_rules! ungated {
+    (unsafe($edition:ident) $attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $encode_cross_crate:expr $(,)?) => {
+        BuiltinAttribute {
+            name: sym::$attr,
+            encode_cross_crate: $encode_cross_crate,
+            type_: $typ,
+            safety: AttributeSafety::Unsafe { unsafe_since: Some(Edition::$edition) },
+            template: $tpl,
+            gate: Ungated,
+            duplicates: $duplicates,
+        }
+    };
     (unsafe $attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $encode_cross_crate:expr $(,)?) => {
         BuiltinAttribute {
             name: sym::$attr,
             encode_cross_crate: $encode_cross_crate,
             type_: $typ,
-            safety: AttributeSafety::Unsafe,
+            safety: AttributeSafety::Unsafe { unsafe_since: None },
             template: $tpl,
             gate: Ungated,
             duplicates: $duplicates,
@@ -217,7 +232,7 @@ macro_rules! gated {
             name: sym::$attr,
             encode_cross_crate: $encode_cross_crate,
             type_: $typ,
-            safety: AttributeSafety::Unsafe,
+            safety: AttributeSafety::Unsafe { unsafe_since: None },
             template: $tpl,
             duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::$gate, $msg, Features::$gate),
@@ -228,7 +243,7 @@ macro_rules! gated {
             name: sym::$attr,
             encode_cross_crate: $encode_cross_crate,
             type_: $typ,
-            safety: AttributeSafety::Unsafe,
+            safety: AttributeSafety::Unsafe { unsafe_since: None },
             template: $tpl,
             duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::$attr, $msg, Features::$attr),
@@ -423,9 +438,9 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     ungated!(no_link, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(repr, Normal, template!(List: "C"), DuplicatesOk, EncodeCrossCrate::No),
-    ungated!(unsafe export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
-    ungated!(unsafe link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
-    ungated!(unsafe no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
+    ungated!(unsafe(Edition2024) export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
+    ungated!(unsafe(Edition2024) link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
+    ungated!(unsafe(Edition2024) no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing, EncodeCrossCrate::No),
     ungated!(link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding, EncodeCrossCrate::Yes),
 
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 98273a05446..d1bbb0598fe 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -89,7 +89,6 @@ macro_rules! arena_types {
             [] name_set: rustc_data_structures::unord::UnordSet<rustc_span::Symbol>,
             [] autodiff_item: rustc_ast::expand::autodiff_attrs::AutoDiffItem,
             [] ordered_name_set: rustc_data_structures::fx::FxIndexSet<rustc_span::Symbol>,
-            [] pats: rustc_middle::ty::PatternKind<'tcx>,
             [] valtree: rustc_middle::ty::ValTreeKind<'tcx>,
 
             // Note that this deliberately duplicates items in the `rustc_hir::arena`,
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index ae1c6c670cb..dc5fe2d8f8b 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -3,6 +3,7 @@ use std::borrow::Cow;
 use rustc_data_structures::intern::Interned;
 use rustc_error_messages::MultiSpan;
 use rustc_macros::HashStable;
+use rustc_type_ir::walk::TypeWalker;
 use rustc_type_ir::{self as ir, TypeFlags, WithCachedTypeInfo};
 
 use crate::ty::{self, Ty, TyCtxt};
@@ -243,4 +244,18 @@ impl<'tcx> Const<'tcx> {
     pub fn is_ct_infer(self) -> bool {
         matches!(self.kind(), ty::ConstKind::Infer(_))
     }
+
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<TyCtxt<'tcx>> {
+        TypeWalker::new(self.into())
+    }
 }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index abf6cbbcd87..6e5ac13bd2c 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -870,7 +870,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         Ty(Interned::new_unchecked(
             self.type_
                 .intern(kind, |kind| {
-                    let flags = super::flags::FlagComputation::for_kind(&kind);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_kind(&kind);
                     let stable_hash = self.stable_hash(&flags, sess, untracked, &kind);
 
                     InternedInSet(self.arena.alloc(WithCachedTypeInfo {
@@ -896,7 +896,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         Const(Interned::new_unchecked(
             self.const_
                 .intern(kind, |kind: ty::ConstKind<'_>| {
-                    let flags = super::flags::FlagComputation::for_const_kind(&kind);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_const_kind(&kind);
                     let stable_hash = self.stable_hash(&flags, sess, untracked, &kind);
 
                     InternedInSet(self.arena.alloc(WithCachedTypeInfo {
@@ -912,7 +912,7 @@ impl<'tcx> CtxtInterners<'tcx> {
 
     fn stable_hash<'a, T: HashStable<StableHashingContext<'a>>>(
         &self,
-        flags: &ty::flags::FlagComputation,
+        flags: &ty::FlagComputation<TyCtxt<'tcx>>,
         sess: &'a Session,
         untracked: &'a Untracked,
         val: &T,
@@ -940,7 +940,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         Predicate(Interned::new_unchecked(
             self.predicate
                 .intern(kind, |kind| {
-                    let flags = super::flags::FlagComputation::for_predicate(kind);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_predicate(kind);
 
                     let stable_hash = self.stable_hash(&flags, sess, untracked, &kind);
 
@@ -961,7 +961,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         } else {
             self.clauses
                 .intern_ref(clauses, || {
-                    let flags = super::flags::FlagComputation::for_clauses(clauses);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_clauses(clauses);
 
                     InternedInSet(ListWithCachedTypeInfo::from_arena(
                         &*self.arena,
diff --git a/compiler/rustc_middle/src/ty/flags.rs b/compiler/rustc_middle/src/ty/flags.rs
deleted file mode 100644
index 2424923fb78..00000000000
--- a/compiler/rustc_middle/src/ty/flags.rs
+++ /dev/null
@@ -1,359 +0,0 @@
-use std::slice;
-
-use crate::ty::{self, GenericArg, GenericArgKind, InferConst, Ty, TypeFlags};
-
-#[derive(Debug)]
-pub struct FlagComputation {
-    pub flags: TypeFlags,
-
-    /// see `Ty::outer_exclusive_binder` for details
-    pub outer_exclusive_binder: ty::DebruijnIndex,
-}
-
-impl FlagComputation {
-    fn new() -> FlagComputation {
-        FlagComputation { flags: TypeFlags::empty(), outer_exclusive_binder: ty::INNERMOST }
-    }
-
-    #[allow(rustc::usage_of_ty_tykind)]
-    pub fn for_kind(kind: &ty::TyKind<'_>) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        result.add_kind(kind);
-        result
-    }
-
-    pub fn for_predicate(binder: ty::Binder<'_, ty::PredicateKind<'_>>) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        result.add_predicate(binder);
-        result
-    }
-
-    pub fn for_const_kind(kind: &ty::ConstKind<'_>) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        result.add_const_kind(kind);
-        result
-    }
-
-    pub fn for_clauses(clauses: &[ty::Clause<'_>]) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        for c in clauses {
-            result.add_flags(c.as_predicate().flags());
-            result.add_exclusive_binder(c.as_predicate().outer_exclusive_binder());
-        }
-        result
-    }
-
-    fn add_flags(&mut self, flags: TypeFlags) {
-        self.flags = self.flags | flags;
-    }
-
-    /// indicates that `self` refers to something at binding level `binder`
-    fn add_bound_var(&mut self, binder: ty::DebruijnIndex) {
-        let exclusive_binder = binder.shifted_in(1);
-        self.add_exclusive_binder(exclusive_binder);
-    }
-
-    /// indicates that `self` refers to something *inside* binding
-    /// level `binder` -- not bound by `binder`, but bound by the next
-    /// binder internal to it
-    fn add_exclusive_binder(&mut self, exclusive_binder: ty::DebruijnIndex) {
-        self.outer_exclusive_binder = self.outer_exclusive_binder.max(exclusive_binder);
-    }
-
-    /// Adds the flags/depth from a set of types that appear within the current type, but within a
-    /// region binder.
-    fn bound_computation<T, F>(&mut self, value: ty::Binder<'_, T>, f: F)
-    where
-        F: FnOnce(&mut Self, T),
-    {
-        let mut computation = FlagComputation::new();
-
-        if !value.bound_vars().is_empty() {
-            computation.add_flags(TypeFlags::HAS_BINDER_VARS);
-        }
-
-        f(&mut computation, value.skip_binder());
-
-        self.add_flags(computation.flags);
-
-        // The types that contributed to `computation` occurred within
-        // a region binder, so subtract one from the region depth
-        // within when adding the depth to `self`.
-        let outer_exclusive_binder = computation.outer_exclusive_binder;
-        if outer_exclusive_binder > ty::INNERMOST {
-            self.add_exclusive_binder(outer_exclusive_binder.shifted_out(1));
-        } // otherwise, this binder captures nothing
-    }
-
-    #[allow(rustc::usage_of_ty_tykind)]
-    fn add_kind(&mut self, kind: &ty::TyKind<'_>) {
-        match kind {
-            &ty::Bool
-            | &ty::Char
-            | &ty::Int(_)
-            | &ty::Float(_)
-            | &ty::Uint(_)
-            | &ty::Never
-            | &ty::Str
-            | &ty::Foreign(..) => {}
-
-            &ty::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
-
-            &ty::Param(_) => {
-                self.add_flags(TypeFlags::HAS_TY_PARAM);
-            }
-
-            &ty::Closure(_, args)
-            | &ty::Coroutine(_, args)
-            | &ty::CoroutineClosure(_, args)
-            | &ty::CoroutineWitness(_, args) => {
-                self.add_args(args);
-            }
-
-            &ty::Bound(debruijn, _) => {
-                self.add_bound_var(debruijn);
-                self.add_flags(TypeFlags::HAS_TY_BOUND);
-            }
-
-            &ty::Placeholder(..) => {
-                self.add_flags(TypeFlags::HAS_TY_PLACEHOLDER);
-            }
-
-            &ty::Infer(infer) => match infer {
-                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
-                    self.add_flags(TypeFlags::HAS_TY_FRESH)
-                }
-
-                ty::TyVar(_) | ty::IntVar(_) | ty::FloatVar(_) => {
-                    self.add_flags(TypeFlags::HAS_TY_INFER)
-                }
-            },
-
-            &ty::Adt(_, args) => {
-                self.add_args(args);
-            }
-
-            &ty::Alias(kind, data) => {
-                self.add_flags(match kind {
-                    ty::Projection => TypeFlags::HAS_TY_PROJECTION,
-                    ty::Weak => TypeFlags::HAS_TY_WEAK,
-                    ty::Opaque => TypeFlags::HAS_TY_OPAQUE,
-                    ty::Inherent => TypeFlags::HAS_TY_INHERENT,
-                });
-
-                self.add_alias_ty(data);
-            }
-
-            &ty::Dynamic(obj, r, _) => {
-                for predicate in obj.iter() {
-                    self.bound_computation(predicate, |computation, predicate| match predicate {
-                        ty::ExistentialPredicate::Trait(tr) => computation.add_args(tr.args),
-                        ty::ExistentialPredicate::Projection(p) => {
-                            computation.add_existential_projection(&p);
-                        }
-                        ty::ExistentialPredicate::AutoTrait(_) => {}
-                    });
-                }
-
-                self.add_region(r);
-            }
-
-            &ty::Array(tt, len) => {
-                self.add_ty(tt);
-                self.add_const(len);
-            }
-
-            &ty::Pat(ty, pat) => {
-                self.add_ty(ty);
-                match *pat {
-                    ty::PatternKind::Range { start, end } => {
-                        self.add_const(start);
-                        self.add_const(end);
-                    }
-                }
-            }
-
-            &ty::Slice(tt) => self.add_ty(tt),
-
-            &ty::RawPtr(ty, _) => {
-                self.add_ty(ty);
-            }
-
-            &ty::Ref(r, ty, _) => {
-                self.add_region(r);
-                self.add_ty(ty);
-            }
-
-            &ty::Tuple(types) => {
-                self.add_tys(types);
-            }
-
-            &ty::FnDef(_, args) => {
-                self.add_args(args);
-            }
-
-            &ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
-                computation.add_tys(sig_tys.inputs_and_output);
-            }),
-
-            &ty::UnsafeBinder(bound_ty) => {
-                self.bound_computation(bound_ty.into(), |computation, ty| {
-                    computation.add_ty(ty);
-                })
-            }
-        }
-    }
-
-    fn add_predicate(&mut self, binder: ty::Binder<'_, ty::PredicateKind<'_>>) {
-        self.bound_computation(binder, |computation, atom| computation.add_predicate_atom(atom));
-    }
-
-    fn add_predicate_atom(&mut self, atom: ty::PredicateKind<'_>) {
-        match atom {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) => {
-                self.add_args(trait_pred.trait_ref.args);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(ty::HostEffectPredicate {
-                trait_ref,
-                constness: _,
-            })) => {
-                self.add_args(trait_ref.args);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
-                a,
-                b,
-            ))) => {
-                self.add_region(a);
-                self.add_region(b);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
-                ty,
-                region,
-            ))) => {
-                self.add_ty(ty);
-                self.add_region(region);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
-                self.add_const(ct);
-                self.add_ty(ty);
-            }
-            ty::PredicateKind::Subtype(ty::SubtypePredicate { a_is_expected: _, a, b }) => {
-                self.add_ty(a);
-                self.add_ty(b);
-            }
-            ty::PredicateKind::Coerce(ty::CoercePredicate { a, b }) => {
-                self.add_ty(a);
-                self.add_ty(b);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(ty::ProjectionPredicate {
-                projection_term,
-                term,
-            })) => {
-                self.add_alias_term(projection_term);
-                self.add_term(term);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
-                self.add_args(slice::from_ref(&arg));
-            }
-            ty::PredicateKind::DynCompatible(_def_id) => {}
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
-                self.add_const(uv);
-            }
-            ty::PredicateKind::ConstEquate(expected, found) => {
-                self.add_const(expected);
-                self.add_const(found);
-            }
-            ty::PredicateKind::Ambiguous => {}
-            ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term }) => {
-                self.add_alias_term(alias);
-                self.add_term(term);
-            }
-            ty::PredicateKind::AliasRelate(t1, t2, _) => {
-                self.add_term(t1);
-                self.add_term(t2);
-            }
-        }
-    }
-
-    fn add_ty(&mut self, ty: Ty<'_>) {
-        self.add_flags(ty.flags());
-        self.add_exclusive_binder(ty.outer_exclusive_binder());
-    }
-
-    fn add_tys(&mut self, tys: &[Ty<'_>]) {
-        for &ty in tys {
-            self.add_ty(ty);
-        }
-    }
-
-    fn add_region(&mut self, r: ty::Region<'_>) {
-        self.add_flags(r.type_flags());
-        if let ty::ReBound(debruijn, _) = r.kind() {
-            self.add_bound_var(debruijn);
-        }
-    }
-
-    fn add_const(&mut self, c: ty::Const<'_>) {
-        self.add_flags(c.flags());
-        self.add_exclusive_binder(c.outer_exclusive_binder());
-    }
-
-    fn add_const_kind(&mut self, c: &ty::ConstKind<'_>) {
-        match *c {
-            ty::ConstKind::Unevaluated(uv) => {
-                self.add_args(uv.args);
-                self.add_flags(TypeFlags::HAS_CT_PROJECTION);
-            }
-            ty::ConstKind::Infer(infer) => match infer {
-                InferConst::Fresh(_) => self.add_flags(TypeFlags::HAS_CT_FRESH),
-                InferConst::Var(_) => self.add_flags(TypeFlags::HAS_CT_INFER),
-            },
-            ty::ConstKind::Bound(debruijn, _) => {
-                self.add_bound_var(debruijn);
-                self.add_flags(TypeFlags::HAS_CT_BOUND);
-            }
-            ty::ConstKind::Param(_) => {
-                self.add_flags(TypeFlags::HAS_CT_PARAM);
-            }
-            ty::ConstKind::Placeholder(_) => {
-                self.add_flags(TypeFlags::HAS_CT_PLACEHOLDER);
-            }
-            ty::ConstKind::Value(cv) => self.add_ty(cv.ty),
-            ty::ConstKind::Expr(e) => self.add_args(e.args()),
-            ty::ConstKind::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
-        }
-    }
-
-    fn add_existential_projection(&mut self, projection: &ty::ExistentialProjection<'_>) {
-        self.add_args(projection.args);
-        match projection.term.unpack() {
-            ty::TermKind::Ty(ty) => self.add_ty(ty),
-            ty::TermKind::Const(ct) => self.add_const(ct),
-        }
-    }
-
-    fn add_alias_ty(&mut self, alias_ty: ty::AliasTy<'_>) {
-        self.add_args(alias_ty.args);
-    }
-
-    fn add_alias_term(&mut self, alias_term: ty::AliasTerm<'_>) {
-        self.add_args(alias_term.args);
-    }
-
-    fn add_args(&mut self, args: &[GenericArg<'_>]) {
-        for kind in args {
-            match kind.unpack() {
-                GenericArgKind::Type(ty) => self.add_ty(ty),
-                GenericArgKind::Lifetime(lt) => self.add_region(lt),
-                GenericArgKind::Const(ct) => self.add_const(ct),
-            }
-        }
-    }
-
-    fn add_term(&mut self, term: ty::Term<'_>) {
-        match term.unpack() {
-            ty::TermKind::Ty(ty) => self.add_ty(ty),
-            ty::TermKind::Const(ct) => self.add_const(ct),
-        }
-    }
-}
diff --git a/compiler/rustc_middle/src/ty/generic_args.rs b/compiler/rustc_middle/src/ty/generic_args.rs
index 9c1ff134f0f..1f04937232d 100644
--- a/compiler/rustc_middle/src/ty/generic_args.rs
+++ b/compiler/rustc_middle/src/ty/generic_args.rs
@@ -11,6 +11,7 @@ use rustc_hir::def_id::DefId;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, extension};
 use rustc_serialize::{Decodable, Encodable};
 use rustc_type_ir::WithCachedTypeInfo;
+use rustc_type_ir::walk::TypeWalker;
 use smallvec::SmallVec;
 
 use crate::ty::codec::{TyDecoder, TyEncoder};
@@ -297,6 +298,20 @@ impl<'tcx> GenericArg<'tcx> {
             GenericArgKind::Const(ct) => ct.is_ct_infer(),
         }
     }
+
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<TyCtxt<'tcx>> {
+        TypeWalker::new(self)
+    }
 }
 
 impl<'a, 'tcx> Lift<TyCtxt<'tcx>> for GenericArg<'a> {
diff --git a/compiler/rustc_middle/src/ty/list.rs b/compiler/rustc_middle/src/ty/list.rs
index 0fd370a5619..0cf5820959e 100644
--- a/compiler/rustc_middle/src/ty/list.rs
+++ b/compiler/rustc_middle/src/ty/list.rs
@@ -7,9 +7,9 @@ use std::{fmt, iter, mem, ptr, slice};
 use rustc_data_structures::aligned::{Aligned, align_of};
 use rustc_data_structures::sync::DynSync;
 use rustc_serialize::{Encodable, Encoder};
+use rustc_type_ir::FlagComputation;
 
-use super::flags::FlagComputation;
-use super::{DebruijnIndex, TypeFlags};
+use super::{DebruijnIndex, TyCtxt, TypeFlags};
 use crate::arena::Arena;
 
 /// `List<T>` is a bit like `&[T]`, but with some critical differences.
@@ -299,8 +299,8 @@ impl TypeInfo {
     }
 }
 
-impl From<FlagComputation> for TypeInfo {
-    fn from(computation: FlagComputation) -> TypeInfo {
+impl<'tcx> From<FlagComputation<TyCtxt<'tcx>>> for TypeInfo {
+    fn from(computation: FlagComputation<TyCtxt<'tcx>>) -> TypeInfo {
         TypeInfo {
             flags: computation.flags,
             outer_exclusive_binder: computation.outer_exclusive_binder,
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index a2b3acac3f2..61e869f5de4 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -117,7 +117,6 @@ pub mod cast;
 pub mod codec;
 pub mod error;
 pub mod fast_reject;
-pub mod flags;
 pub mod inhabitedness;
 pub mod layout;
 pub mod normalize_erasing_regions;
@@ -128,7 +127,6 @@ pub mod significant_drop_order;
 pub mod trait_def;
 pub mod util;
 pub mod vtable;
-pub mod walk;
 
 mod adt;
 mod assoc;
diff --git a/compiler/rustc_middle/src/ty/pattern.rs b/compiler/rustc_middle/src/ty/pattern.rs
index 4cad1ab2099..758adc42e3e 100644
--- a/compiler/rustc_middle/src/ty/pattern.rs
+++ b/compiler/rustc_middle/src/ty/pattern.rs
@@ -1,14 +1,40 @@
 use std::fmt;
 
 use rustc_data_structures::intern::Interned;
-use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
+use rustc_macros::HashStable;
+use rustc_type_ir::ir_print::IrPrint;
+use rustc_type_ir::{
+    FlagComputation, Flags, {self as ir},
+};
 
+use super::TyCtxt;
 use crate::ty;
 
+pub type PatternKind<'tcx> = ir::PatternKind<TyCtxt<'tcx>>;
+
 #[derive(Copy, Clone, PartialEq, Eq, Hash, HashStable)]
 #[rustc_pass_by_value]
 pub struct Pattern<'tcx>(pub Interned<'tcx, PatternKind<'tcx>>);
 
+impl<'tcx> Flags for Pattern<'tcx> {
+    fn flags(&self) -> rustc_type_ir::TypeFlags {
+        match &**self {
+            ty::PatternKind::Range { start, end } => {
+                FlagComputation::for_const_kind(&start.kind()).flags
+                    | FlagComputation::for_const_kind(&end.kind()).flags
+            }
+        }
+    }
+
+    fn outer_exclusive_binder(&self) -> rustc_type_ir::DebruijnIndex {
+        match &**self {
+            ty::PatternKind::Range { start, end } => {
+                start.outer_exclusive_binder().max(end.outer_exclusive_binder())
+            }
+        }
+    }
+}
+
 impl<'tcx> std::ops::Deref for Pattern<'tcx> {
     type Target = PatternKind<'tcx>;
 
@@ -23,9 +49,9 @@ impl<'tcx> fmt::Debug for Pattern<'tcx> {
     }
 }
 
-impl<'tcx> fmt::Debug for PatternKind<'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
+impl<'tcx> IrPrint<PatternKind<'tcx>> for TyCtxt<'tcx> {
+    fn print(t: &PatternKind<'tcx>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *t {
             PatternKind::Range { start, end } => {
                 write!(f, "{start}")?;
 
@@ -53,10 +79,15 @@ impl<'tcx> fmt::Debug for PatternKind<'tcx> {
             }
         }
     }
+
+    fn print_debug(t: &PatternKind<'tcx>, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Self::print(t, fmt)
+    }
 }
 
-#[derive(Clone, PartialEq, Eq, Hash)]
-#[derive(HashStable, TyEncodable, TyDecodable, TypeVisitable, TypeFoldable)]
-pub enum PatternKind<'tcx> {
-    Range { start: ty::Const<'tcx>, end: ty::Const<'tcx> },
+impl<'tcx> rustc_type_ir::inherent::IntoKind for Pattern<'tcx> {
+    type Kind = PatternKind<'tcx>;
+    fn kind(self) -> Self::Kind {
+        *self
+    }
 }
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 27ee363f1c1..d9a65ae57a0 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -16,6 +16,7 @@ use rustc_hir::def_id::DefId;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, extension};
 use rustc_span::{DUMMY_SP, Span, Symbol, sym};
 use rustc_type_ir::TyKind::*;
+use rustc_type_ir::walk::TypeWalker;
 use rustc_type_ir::{self as ir, BoundVar, CollectAndApply, DynKind, TypeVisitableExt, elaborate};
 use tracing::instrument;
 use ty::util::{AsyncDropGlueMorphology, IntTypeExt};
@@ -2029,6 +2030,20 @@ impl<'tcx> Ty<'tcx> {
     pub fn is_known_rigid(self) -> bool {
         self.kind().is_known_rigid()
     }
+
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<TyCtxt<'tcx>> {
+        TypeWalker::new(self.into())
+    }
 }
 
 impl<'tcx> rustc_type_ir::inherent::Tys<TyCtxt<'tcx>> for &'tcx ty::List<Ty<'tcx>> {
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index 80c729d66b1..4405bd82410 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -1169,6 +1169,13 @@ fn create_coroutine_drop_shim<'tcx>(
     dump_mir(tcx, false, "coroutine_drop", &0, &body, |_, _| Ok(()));
     body.source.instance = drop_instance;
 
+    // Creating a coroutine drop shim happens on `Analysis(PostCleanup) -> Runtime(Initial)`
+    // but the pass manager doesn't update the phase of the coroutine drop shim. Update the
+    // phase of the drop shim so that later on when we run the pass manager on the shim, in
+    // the `mir_shims` query, we don't ICE on the intra-pass validation before we've updated
+    // the phase of the body from analysis.
+    body.phase = MirPhase::Runtime(RuntimePhase::Initial);
+
     body
 }
 
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 6bbd650dcdf..6a1c2af48ed 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -157,7 +157,7 @@ fn is_attr_template_compatible(template: &AttributeTemplate, meta: &ast::MetaIte
 pub fn check_attribute_safety(psess: &ParseSess, safety: AttributeSafety, attr: &Attribute) {
     let attr_item = attr.get_normal_item();
 
-    if safety == AttributeSafety::Unsafe {
+    if let AttributeSafety::Unsafe { unsafe_since } = safety {
         if let ast::Safety::Default = attr_item.unsafety {
             let path_span = attr_item.path.span;
 
@@ -167,7 +167,13 @@ pub fn check_attribute_safety(psess: &ParseSess, safety: AttributeSafety, attr:
             // square bracket respectively.
             let diag_span = attr_item.span();
 
-            if attr.span.at_least_rust_2024() {
+            // Attributes can be safe in earlier editions, and become unsafe in later ones.
+            let emit_error = match unsafe_since {
+                None => true,
+                Some(unsafe_since) => attr.span.edition() >= unsafe_since,
+            };
+
+            if emit_error {
                 psess.dcx().emit_err(errors::UnsafeAttrOutsideUnsafe {
                     span: path_span,
                     suggestion: errors::UnsafeAttrOutsideUnsafeSuggestion {
diff --git a/compiler/rustc_query_system/src/dep_graph/serialized.rs b/compiler/rustc_query_system/src/dep_graph/serialized.rs
index 7556a2456aa..471ac8ff2ed 100644
--- a/compiler/rustc_query_system/src/dep_graph/serialized.rs
+++ b/compiler/rustc_query_system/src/dep_graph/serialized.rs
@@ -226,12 +226,12 @@ impl SerializedDepGraph {
 
             // If the length of this node's edge list is small, the length is stored in the header.
             // If it is not, we fall back to another decoder call.
-            let num_edges = node_header.len().unwrap_or_else(|| d.read_usize());
+            let num_edges = node_header.len().unwrap_or_else(|| d.read_u32());
 
             // The edges index list uses the same varint strategy as rmeta tables; we select the
             // number of byte elements per-array not per-element. This lets us read the whole edge
             // list for a node with one decoder call and also use the on-disk format in memory.
-            let edges_len_bytes = node_header.bytes_per_index() * num_edges;
+            let edges_len_bytes = node_header.bytes_per_index() * (num_edges as usize);
             // The in-memory structure for the edges list stores the byte width of the edges on
             // this node with the offset into the global edge data array.
             let edges_header = node_header.edges_header(&edge_list_data);
@@ -296,7 +296,7 @@ struct SerializedNodeHeader<D> {
 // The fields of a `SerializedNodeHeader`, this struct is an implementation detail and exists only
 // to make the implementation of `SerializedNodeHeader` simpler.
 struct Unpacked {
-    len: Option<usize>,
+    len: Option<u32>,
     bytes_per_index: usize,
     kind: DepKind,
     hash: PackedFingerprint,
@@ -352,7 +352,7 @@ impl<D: Deps> SerializedNodeHeader<D> {
             assert_eq!(fingerprint, res.fingerprint());
             assert_eq!(node, res.node());
             if let Some(len) = res.len() {
-                assert_eq!(edge_count, len);
+                assert_eq!(edge_count, len as usize);
             }
         }
         Self { bytes, _marker: PhantomData }
@@ -366,7 +366,7 @@ impl<D: Deps> SerializedNodeHeader<D> {
 
         let kind = head & mask(Self::KIND_BITS) as u16;
         let bytes_per_index = (head >> Self::KIND_BITS) & mask(Self::WIDTH_BITS) as u16;
-        let len = (head as usize) >> (Self::WIDTH_BITS + Self::KIND_BITS);
+        let len = (head as u32) >> (Self::WIDTH_BITS + Self::KIND_BITS);
 
         Unpacked {
             len: len.checked_sub(1),
@@ -378,7 +378,7 @@ impl<D: Deps> SerializedNodeHeader<D> {
     }
 
     #[inline]
-    fn len(&self) -> Option<usize> {
+    fn len(&self) -> Option<u32> {
         self.unpack().len
     }
 
@@ -421,7 +421,8 @@ impl NodeInfo {
         e.write_array(header.bytes);
 
         if header.len().is_none() {
-            e.emit_usize(edges.len());
+            // The edges are all unique and the number of unique indices is less than u32::MAX.
+            e.emit_u32(edges.len().try_into().unwrap());
         }
 
         let bytes_per_index = header.bytes_per_index();
@@ -456,7 +457,8 @@ impl NodeInfo {
         e.write_array(header.bytes);
 
         if header.len().is_none() {
-            e.emit_usize(edge_count);
+            // The edges are all unique and the number of unique indices is less than u32::MAX.
+            e.emit_u32(edge_count.try_into().unwrap());
         }
 
         let bytes_per_index = header.bytes_per_index();
diff --git a/compiler/rustc_trait_selection/messages.ftl b/compiler/rustc_trait_selection/messages.ftl
index 05bbb42fb7c..74e38f525c8 100644
--- a/compiler/rustc_trait_selection/messages.ftl
+++ b/compiler/rustc_trait_selection/messages.ftl
@@ -268,8 +268,8 @@ trait_selection_oc_type_compat = type not compatible with trait
 trait_selection_opaque_captures_lifetime = hidden type for `{$opaque_ty}` captures lifetime that does not appear in bounds
     .label = opaque type defined here
 trait_selection_opaque_type_non_generic_param =
-    expected generic {$kind} parameter, found `{$ty}`
-    .label = {STREQ($ty, "'static") ->
+    expected generic {$kind} parameter, found `{$arg}`
+    .label = {STREQ($arg, "'static") ->
         [true] cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
         *[other] this generic parameter must be used with a generic {$kind} parameter
     }
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index bb4aba9d29e..4e5581fb1da 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -1926,7 +1926,7 @@ impl Subdiagnostic for AddPreciseCapturingForOvercapture {
 #[derive(Diagnostic)]
 #[diag(trait_selection_opaque_type_non_generic_param, code = E0792)]
 pub(crate) struct NonGenericOpaqueTypeParam<'a, 'tcx> {
-    pub ty: GenericArg<'tcx>,
+    pub arg: GenericArg<'tcx>,
     pub kind: &'a str,
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_trait_selection/src/opaque_types.rs b/compiler/rustc_trait_selection/src/opaque_types.rs
index 309bf4dda3d..cce67b066dd 100644
--- a/compiler/rustc_trait_selection/src/opaque_types.rs
+++ b/compiler/rustc_trait_selection/src/opaque_types.rs
@@ -70,7 +70,7 @@ pub fn check_opaque_type_parameter_valid<'tcx>(
             opaque_env.param_is_error(i)?;
 
             return Err(infcx.dcx().emit_err(NonGenericOpaqueTypeParam {
-                ty: arg,
+                arg,
                 kind,
                 span,
                 param_span: tcx.def_span(opaque_param.def_id),
diff --git a/compiler/rustc_type_ir/src/flags.rs b/compiler/rustc_type_ir/src/flags.rs
index 6a2498242fe..e9d3a149a73 100644
--- a/compiler/rustc_type_ir/src/flags.rs
+++ b/compiler/rustc_type_ir/src/flags.rs
@@ -1,3 +1,9 @@
+use std::slice;
+
+use crate::inherent::*;
+use crate::visit::Flags;
+use crate::{self as ty, Interner};
+
 bitflags::bitflags! {
     /// Flags that we track on types. These flags are propagated upwards
     /// through the type during type construction, so that we can quickly check
@@ -128,3 +134,362 @@ bitflags::bitflags! {
         const HAS_BINDER_VARS             = 1 << 23;
     }
 }
+
+#[derive(Debug)]
+pub struct FlagComputation<I> {
+    pub flags: TypeFlags,
+
+    /// see `Ty::outer_exclusive_binder` for details
+    pub outer_exclusive_binder: ty::DebruijnIndex,
+
+    interner: std::marker::PhantomData<I>,
+}
+
+impl<I: Interner> FlagComputation<I> {
+    fn new() -> FlagComputation<I> {
+        FlagComputation {
+            flags: TypeFlags::empty(),
+            outer_exclusive_binder: ty::INNERMOST,
+            interner: std::marker::PhantomData,
+        }
+    }
+
+    #[allow(rustc::usage_of_ty_tykind)]
+    pub fn for_kind(kind: &ty::TyKind<I>) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        result.add_kind(kind);
+        result
+    }
+
+    pub fn for_predicate(binder: ty::Binder<I, ty::PredicateKind<I>>) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        result.add_predicate(binder);
+        result
+    }
+
+    pub fn for_const_kind(kind: &ty::ConstKind<I>) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        result.add_const_kind(kind);
+        result
+    }
+
+    pub fn for_clauses(clauses: &[I::Clause]) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        for c in clauses {
+            result.add_flags(c.as_predicate().flags());
+            result.add_exclusive_binder(c.as_predicate().outer_exclusive_binder());
+        }
+        result
+    }
+
+    fn add_flags(&mut self, flags: TypeFlags) {
+        self.flags = self.flags | flags;
+    }
+
+    /// indicates that `self` refers to something at binding level `binder`
+    fn add_bound_var(&mut self, binder: ty::DebruijnIndex) {
+        let exclusive_binder = binder.shifted_in(1);
+        self.add_exclusive_binder(exclusive_binder);
+    }
+
+    /// indicates that `self` refers to something *inside* binding
+    /// level `binder` -- not bound by `binder`, but bound by the next
+    /// binder internal to it
+    fn add_exclusive_binder(&mut self, exclusive_binder: ty::DebruijnIndex) {
+        self.outer_exclusive_binder = self.outer_exclusive_binder.max(exclusive_binder);
+    }
+
+    /// Adds the flags/depth from a set of types that appear within the current type, but within a
+    /// region binder.
+    fn bound_computation<T, F>(&mut self, value: ty::Binder<I, T>, f: F)
+    where
+        F: FnOnce(&mut Self, T),
+    {
+        let mut computation = FlagComputation::new();
+
+        if !value.bound_vars().is_empty() {
+            computation.add_flags(TypeFlags::HAS_BINDER_VARS);
+        }
+
+        f(&mut computation, value.skip_binder());
+
+        self.add_flags(computation.flags);
+
+        // The types that contributed to `computation` occurred within
+        // a region binder, so subtract one from the region depth
+        // within when adding the depth to `self`.
+        let outer_exclusive_binder = computation.outer_exclusive_binder;
+        if outer_exclusive_binder > ty::INNERMOST {
+            self.add_exclusive_binder(outer_exclusive_binder.shifted_out(1));
+        } // otherwise, this binder captures nothing
+    }
+
+    #[allow(rustc::usage_of_ty_tykind)]
+    fn add_kind(&mut self, kind: &ty::TyKind<I>) {
+        match *kind {
+            ty::Bool
+            | ty::Char
+            | ty::Int(_)
+            | ty::Float(_)
+            | ty::Uint(_)
+            | ty::Never
+            | ty::Str
+            | ty::Foreign(..) => {}
+
+            ty::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
+
+            ty::Param(_) => {
+                self.add_flags(TypeFlags::HAS_TY_PARAM);
+            }
+
+            ty::Closure(_, args)
+            | ty::Coroutine(_, args)
+            | ty::CoroutineClosure(_, args)
+            | ty::CoroutineWitness(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::Bound(debruijn, _) => {
+                self.add_bound_var(debruijn);
+                self.add_flags(TypeFlags::HAS_TY_BOUND);
+            }
+
+            ty::Placeholder(..) => {
+                self.add_flags(TypeFlags::HAS_TY_PLACEHOLDER);
+            }
+
+            ty::Infer(infer) => match infer {
+                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
+                    self.add_flags(TypeFlags::HAS_TY_FRESH)
+                }
+
+                ty::TyVar(_) | ty::IntVar(_) | ty::FloatVar(_) => {
+                    self.add_flags(TypeFlags::HAS_TY_INFER)
+                }
+            },
+
+            ty::Adt(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::Alias(kind, data) => {
+                self.add_flags(match kind {
+                    ty::Projection => TypeFlags::HAS_TY_PROJECTION,
+                    ty::Weak => TypeFlags::HAS_TY_WEAK,
+                    ty::Opaque => TypeFlags::HAS_TY_OPAQUE,
+                    ty::Inherent => TypeFlags::HAS_TY_INHERENT,
+                });
+
+                self.add_alias_ty(data);
+            }
+
+            ty::Dynamic(obj, r, _) => {
+                for predicate in obj.iter() {
+                    self.bound_computation(predicate, |computation, predicate| match predicate {
+                        ty::ExistentialPredicate::Trait(tr) => {
+                            computation.add_args(tr.args.as_slice())
+                        }
+                        ty::ExistentialPredicate::Projection(p) => {
+                            computation.add_existential_projection(&p);
+                        }
+                        ty::ExistentialPredicate::AutoTrait(_) => {}
+                    });
+                }
+
+                self.add_region(r);
+            }
+
+            ty::Array(tt, len) => {
+                self.add_ty(tt);
+                self.add_const(len);
+            }
+
+            ty::Pat(ty, pat) => {
+                self.add_ty(ty);
+                self.add_flags(pat.flags());
+            }
+
+            ty::Slice(tt) => self.add_ty(tt),
+
+            ty::RawPtr(ty, _) => {
+                self.add_ty(ty);
+            }
+
+            ty::Ref(r, ty, _) => {
+                self.add_region(r);
+                self.add_ty(ty);
+            }
+
+            ty::Tuple(types) => {
+                self.add_tys(types);
+            }
+
+            ty::FnDef(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
+                computation.add_tys(sig_tys.inputs_and_output);
+            }),
+
+            ty::UnsafeBinder(bound_ty) => {
+                self.bound_computation(bound_ty.into(), |computation, ty| {
+                    computation.add_ty(ty);
+                })
+            }
+        }
+    }
+
+    fn add_predicate(&mut self, binder: ty::Binder<I, ty::PredicateKind<I>>) {
+        self.bound_computation(binder, |computation, atom| computation.add_predicate_atom(atom));
+    }
+
+    fn add_predicate_atom(&mut self, atom: ty::PredicateKind<I>) {
+        match atom {
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) => {
+                self.add_args(trait_pred.trait_ref.args.as_slice());
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(ty::HostEffectPredicate {
+                trait_ref,
+                constness: _,
+            })) => {
+                self.add_args(trait_ref.args.as_slice());
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
+                a,
+                b,
+            ))) => {
+                self.add_region(a);
+                self.add_region(b);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
+                ty,
+                region,
+            ))) => {
+                self.add_ty(ty);
+                self.add_region(region);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
+                self.add_const(ct);
+                self.add_ty(ty);
+            }
+            ty::PredicateKind::Subtype(ty::SubtypePredicate { a_is_expected: _, a, b }) => {
+                self.add_ty(a);
+                self.add_ty(b);
+            }
+            ty::PredicateKind::Coerce(ty::CoercePredicate { a, b }) => {
+                self.add_ty(a);
+                self.add_ty(b);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::Projection(ty::ProjectionPredicate {
+                projection_term,
+                term,
+            })) => {
+                self.add_alias_term(projection_term);
+                self.add_term(term);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
+                self.add_args(slice::from_ref(&arg));
+            }
+            ty::PredicateKind::DynCompatible(_def_id) => {}
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
+                self.add_const(uv);
+            }
+            ty::PredicateKind::ConstEquate(expected, found) => {
+                self.add_const(expected);
+                self.add_const(found);
+            }
+            ty::PredicateKind::Ambiguous => {}
+            ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term }) => {
+                self.add_alias_term(alias);
+                self.add_term(term);
+            }
+            ty::PredicateKind::AliasRelate(t1, t2, _) => {
+                self.add_term(t1);
+                self.add_term(t2);
+            }
+        }
+    }
+
+    fn add_ty(&mut self, ty: I::Ty) {
+        self.add_flags(ty.flags());
+        self.add_exclusive_binder(ty.outer_exclusive_binder());
+    }
+
+    fn add_tys(&mut self, tys: I::Tys) {
+        for ty in tys.iter() {
+            self.add_ty(ty);
+        }
+    }
+
+    fn add_region(&mut self, r: I::Region) {
+        self.add_flags(r.flags());
+        if let ty::ReBound(debruijn, _) = r.kind() {
+            self.add_bound_var(debruijn);
+        }
+    }
+
+    fn add_const(&mut self, c: I::Const) {
+        self.add_flags(c.flags());
+        self.add_exclusive_binder(c.outer_exclusive_binder());
+    }
+
+    fn add_const_kind(&mut self, c: &ty::ConstKind<I>) {
+        match *c {
+            ty::ConstKind::Unevaluated(uv) => {
+                self.add_args(uv.args.as_slice());
+                self.add_flags(TypeFlags::HAS_CT_PROJECTION);
+            }
+            ty::ConstKind::Infer(infer) => match infer {
+                ty::InferConst::Fresh(_) => self.add_flags(TypeFlags::HAS_CT_FRESH),
+                ty::InferConst::Var(_) => self.add_flags(TypeFlags::HAS_CT_INFER),
+            },
+            ty::ConstKind::Bound(debruijn, _) => {
+                self.add_bound_var(debruijn);
+                self.add_flags(TypeFlags::HAS_CT_BOUND);
+            }
+            ty::ConstKind::Param(_) => {
+                self.add_flags(TypeFlags::HAS_CT_PARAM);
+            }
+            ty::ConstKind::Placeholder(_) => {
+                self.add_flags(TypeFlags::HAS_CT_PLACEHOLDER);
+            }
+            ty::ConstKind::Value(cv) => self.add_ty(cv.ty()),
+            ty::ConstKind::Expr(e) => self.add_args(e.args().as_slice()),
+            ty::ConstKind::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
+        }
+    }
+
+    fn add_existential_projection(&mut self, projection: &ty::ExistentialProjection<I>) {
+        self.add_args(projection.args.as_slice());
+        match projection.term.kind() {
+            ty::TermKind::Ty(ty) => self.add_ty(ty),
+            ty::TermKind::Const(ct) => self.add_const(ct),
+        }
+    }
+
+    fn add_alias_ty(&mut self, alias_ty: ty::AliasTy<I>) {
+        self.add_args(alias_ty.args.as_slice());
+    }
+
+    fn add_alias_term(&mut self, alias_term: ty::AliasTerm<I>) {
+        self.add_args(alias_term.args.as_slice());
+    }
+
+    fn add_args(&mut self, args: &[I::GenericArg]) {
+        for kind in args {
+            match kind.kind() {
+                ty::GenericArgKind::Type(ty) => self.add_ty(ty),
+                ty::GenericArgKind::Lifetime(lt) => self.add_region(lt),
+                ty::GenericArgKind::Const(ct) => self.add_const(ct),
+            }
+        }
+    }
+
+    fn add_term(&mut self, term: I::Term) {
+        match term.kind() {
+            ty::TermKind::Ty(ty) => self.add_ty(ty),
+            ty::TermKind::Const(ct) => self.add_const(ct),
+        }
+    }
+}
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 6e6c40580d8..417803e75ea 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -583,7 +583,7 @@ pub trait Span<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
 
 pub trait SliceLike: Sized + Copy {
     type Item: Copy;
-    type IntoIter: Iterator<Item = Self::Item>;
+    type IntoIter: Iterator<Item = Self::Item> + DoubleEndedIterator;
 
     fn iter(self) -> Self::IntoIter;
 
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index a9e6764e218..71bfeabfda8 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -31,6 +31,7 @@ pub trait Interner:
     + IrPrint<ty::SubtypePredicate<Self>>
     + IrPrint<ty::CoercePredicate<Self>>
     + IrPrint<ty::FnSig<Self>>
+    + IrPrint<ty::PatternKind<Self>>
 {
     type DefId: DefId<Self>;
     type LocalDefId: Copy + Debug + Hash + Eq + Into<Self::DefId> + TypeFoldable<Self>;
@@ -104,7 +105,14 @@ pub trait Interner:
     type ErrorGuaranteed: Copy + Debug + Hash + Eq;
     type BoundExistentialPredicates: BoundExistentialPredicates<Self>;
     type AllocId: Copy + Debug + Hash + Eq;
-    type Pat: Copy + Debug + Hash + Eq + Debug + Relate<Self>;
+    type Pat: Copy
+        + Debug
+        + Hash
+        + Eq
+        + Debug
+        + Relate<Self>
+        + Flags
+        + IntoKind<Kind = ty::PatternKind<Self>>;
     type Safety: Safety<Self>;
     type Abi: Abi<Self>;
 
diff --git a/compiler/rustc_type_ir/src/ir_print.rs b/compiler/rustc_type_ir/src/ir_print.rs
index 0c71f3a3df2..c259a9747f0 100644
--- a/compiler/rustc_type_ir/src/ir_print.rs
+++ b/compiler/rustc_type_ir/src/ir_print.rs
@@ -2,8 +2,8 @@ use std::fmt;
 
 use crate::{
     AliasTerm, AliasTy, Binder, CoercePredicate, ExistentialProjection, ExistentialTraitRef, FnSig,
-    HostEffectPredicate, Interner, NormalizesTo, OutlivesPredicate, ProjectionPredicate,
-    SubtypePredicate, TraitPredicate, TraitRef,
+    HostEffectPredicate, Interner, NormalizesTo, OutlivesPredicate, PatternKind,
+    ProjectionPredicate, SubtypePredicate, TraitPredicate, TraitRef,
 };
 
 pub trait IrPrint<T> {
@@ -57,9 +57,10 @@ define_display_via_print!(
     AliasTy,
     AliasTerm,
     FnSig,
+    PatternKind,
 );
 
-define_debug_via_print!(TraitRef, ExistentialTraitRef, ExistentialProjection);
+define_debug_via_print!(TraitRef, ExistentialTraitRef, ExistentialProjection, PatternKind);
 
 impl<I: Interner, T> fmt::Display for OutlivesPredicate<I, T>
 where
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index bdc61e956f8..792090effcf 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -31,6 +31,7 @@ pub mod outlives;
 pub mod relate;
 pub mod search_graph;
 pub mod solve;
+pub mod walk;
 
 // These modules are not `pub` since they are glob-imported.
 #[macro_use]
@@ -44,6 +45,7 @@ mod generic_arg;
 mod infer_ctxt;
 mod interner;
 mod opaque_ty;
+mod pattern;
 mod predicate;
 mod predicate_kind;
 mod region_kind;
@@ -67,6 +69,7 @@ pub use generic_arg::*;
 pub use infer_ctxt::*;
 pub use interner::*;
 pub use opaque_ty::*;
+pub use pattern::*;
 pub use predicate::*;
 pub use predicate_kind::*;
 pub use region_kind::*;
diff --git a/compiler/rustc_type_ir/src/pattern.rs b/compiler/rustc_type_ir/src/pattern.rs
new file mode 100644
index 00000000000..d74a82da1f9
--- /dev/null
+++ b/compiler/rustc_type_ir/src/pattern.rs
@@ -0,0 +1,16 @@
+use derive_where::derive_where;
+#[cfg(feature = "nightly")]
+use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
+use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
+
+use crate::Interner;
+
+#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+#[cfg_attr(
+    feature = "nightly",
+    derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
+)]
+pub enum PatternKind<I: Interner> {
+    Range { start: I::Const, end: I::Const },
+}
diff --git a/compiler/rustc_middle/src/ty/walk.rs b/compiler/rustc_type_ir/src/walk.rs
index a23316ae6fc..5683e1f1712 100644
--- a/compiler/rustc_middle/src/ty/walk.rs
+++ b/compiler/rustc_type_ir/src/walk.rs
@@ -1,20 +1,21 @@
 //! An iterator over the type substructure.
 //! WARNING: this does not keep track of the region depth.
 
-use rustc_data_structures::sso::SsoHashSet;
 use smallvec::{SmallVec, smallvec};
 use tracing::debug;
 
-use crate::ty::{self, GenericArg, GenericArgKind, Ty};
+use crate::data_structures::SsoHashSet;
+use crate::inherent::*;
+use crate::{self as ty, Interner};
 
 // The TypeWalker's stack is hot enough that it's worth going to some effort to
 // avoid heap allocations.
-type TypeWalkerStack<'tcx> = SmallVec<[GenericArg<'tcx>; 8]>;
+type TypeWalkerStack<I> = SmallVec<[<I as Interner>::GenericArg; 8]>;
 
-pub struct TypeWalker<'tcx> {
-    stack: TypeWalkerStack<'tcx>,
+pub struct TypeWalker<I: Interner> {
+    stack: TypeWalkerStack<I>,
     last_subtree: usize,
-    pub visited: SsoHashSet<GenericArg<'tcx>>,
+    pub visited: SsoHashSet<I::GenericArg>,
 }
 
 /// An iterator for walking the type tree.
@@ -25,8 +26,8 @@ pub struct TypeWalker<'tcx> {
 /// in this situation walker only visits each type once.
 /// It maintains a set of visited types and
 /// skips any types that are already there.
-impl<'tcx> TypeWalker<'tcx> {
-    pub fn new(root: GenericArg<'tcx>) -> Self {
+impl<I: Interner> TypeWalker<I> {
+    pub fn new(root: I::GenericArg) -> Self {
         Self { stack: smallvec![root], last_subtree: 1, visited: SsoHashSet::new() }
     }
 
@@ -47,16 +48,16 @@ impl<'tcx> TypeWalker<'tcx> {
     }
 }
 
-impl<'tcx> Iterator for TypeWalker<'tcx> {
-    type Item = GenericArg<'tcx>;
+impl<I: Interner> Iterator for TypeWalker<I> {
+    type Item = I::GenericArg;
 
-    fn next(&mut self) -> Option<GenericArg<'tcx>> {
+    fn next(&mut self) -> Option<I::GenericArg> {
         debug!("next(): stack={:?}", self.stack);
         loop {
             let next = self.stack.pop()?;
             self.last_subtree = self.stack.len();
             if self.visited.insert(next) {
-                push_inner(&mut self.stack, next);
+                push_inner::<I>(&mut self.stack, next);
                 debug!("next: stack={:?}", self.stack);
                 return Some(next);
             }
@@ -64,63 +65,15 @@ impl<'tcx> Iterator for TypeWalker<'tcx> {
     }
 }
 
-impl<'tcx> GenericArg<'tcx> {
-    /// Iterator that walks `self` and any types reachable from
-    /// `self`, in depth-first order. Note that just walks the types
-    /// that appear in `self`, it does not descend into the fields of
-    /// structs or variants. For example:
-    ///
-    /// ```text
-    /// isize => { isize }
-    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
-    /// [isize] => { [isize], isize }
-    /// ```
-    pub fn walk(self) -> TypeWalker<'tcx> {
-        TypeWalker::new(self)
-    }
-}
-
-impl<'tcx> Ty<'tcx> {
-    /// Iterator that walks `self` and any types reachable from
-    /// `self`, in depth-first order. Note that just walks the types
-    /// that appear in `self`, it does not descend into the fields of
-    /// structs or variants. For example:
-    ///
-    /// ```text
-    /// isize => { isize }
-    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
-    /// [isize] => { [isize], isize }
-    /// ```
-    pub fn walk(self) -> TypeWalker<'tcx> {
-        TypeWalker::new(self.into())
-    }
-}
-
-impl<'tcx> ty::Const<'tcx> {
-    /// Iterator that walks `self` and any types reachable from
-    /// `self`, in depth-first order. Note that just walks the types
-    /// that appear in `self`, it does not descend into the fields of
-    /// structs or variants. For example:
-    ///
-    /// ```text
-    /// isize => { isize }
-    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
-    /// [isize] => { [isize], isize }
-    /// ```
-    pub fn walk(self) -> TypeWalker<'tcx> {
-        TypeWalker::new(self.into())
-    }
-}
-
 /// We push `GenericArg`s on the stack in reverse order so as to
 /// maintain a pre-order traversal. As of the time of this
 /// writing, the fact that the traversal is pre-order is not
 /// known to be significant to any code, but it seems like the
 /// natural order one would expect (basically, the order of the
 /// types as they are written).
-fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>) {
-    match parent.unpack() {
-        GenericArgKind::Type(parent_ty) => match *parent_ty.kind() {
+fn push_inner<I: Interner>(stack: &mut TypeWalkerStack<I>, parent: I::GenericArg) {
+    match parent.kind() {
+        ty::GenericArgKind::Type(parent_ty) => match parent_ty.kind() {
             ty::Bool
             | ty::Char
             | ty::Int(_)
@@ -136,7 +89,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             | ty::Foreign(..) => {}
 
             ty::Pat(ty, pat) => {
-                match *pat {
+                match pat.kind() {
                     ty::PatternKind::Range { start, end } => {
                         stack.push(end.into());
                         stack.push(start.into());
@@ -163,22 +116,25 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             }
             ty::Dynamic(obj, lt, _) => {
                 stack.push(lt.into());
-                stack.extend(obj.iter().rev().flat_map(|predicate| {
-                    let (args, opt_ty) = match predicate.skip_binder() {
-                        ty::ExistentialPredicate::Trait(tr) => (tr.args, None),
-                        ty::ExistentialPredicate::Projection(p) => (p.args, Some(p.term)),
-                        ty::ExistentialPredicate::AutoTrait(_) =>
-                        // Empty iterator
-                        {
-                            (ty::GenericArgs::empty(), None)
-                        }
-                    };
-
-                    args.iter().rev().chain(opt_ty.map(|term| match term.unpack() {
-                        ty::TermKind::Ty(ty) => ty.into(),
-                        ty::TermKind::Const(ct) => ct.into(),
-                    }))
-                }));
+                stack.extend(
+                    obj.iter()
+                        .rev()
+                        .filter_map(|predicate| {
+                            let (args, opt_ty) = match predicate.skip_binder() {
+                                ty::ExistentialPredicate::Trait(tr) => (tr.args, None),
+                                ty::ExistentialPredicate::Projection(p) => (p.args, Some(p.term)),
+                                ty::ExistentialPredicate::AutoTrait(_) => {
+                                    return None;
+                                }
+                            };
+
+                            Some(args.iter().rev().chain(opt_ty.map(|term| match term.kind() {
+                                ty::TermKind::Ty(ty) => ty.into(),
+                                ty::TermKind::Const(ct) => ct.into(),
+                            })))
+                        })
+                        .flatten(),
+                );
             }
             ty::Adt(_, args)
             | ty::Closure(_, args)
@@ -188,7 +144,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             | ty::FnDef(_, args) => {
                 stack.extend(args.iter().rev());
             }
-            ty::Tuple(ts) => stack.extend(ts.iter().rev().map(GenericArg::from)),
+            ty::Tuple(ts) => stack.extend(ts.iter().rev().map(|ty| ty.into())),
             ty::FnPtr(sig_tys, _hdr) => {
                 stack.extend(
                     sig_tys.skip_binder().inputs_and_output.iter().rev().map(|ty| ty.into()),
@@ -198,15 +154,15 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
                 stack.push(bound_ty.skip_binder().into());
             }
         },
-        GenericArgKind::Lifetime(_) => {}
-        GenericArgKind::Const(parent_ct) => match parent_ct.kind() {
+        ty::GenericArgKind::Lifetime(_) => {}
+        ty::GenericArgKind::Const(parent_ct) => match parent_ct.kind() {
             ty::ConstKind::Infer(_)
             | ty::ConstKind::Param(_)
             | ty::ConstKind::Placeholder(_)
             | ty::ConstKind::Bound(..)
             | ty::ConstKind::Error(_) => {}
 
-            ty::ConstKind::Value(cv) => stack.push(cv.ty.into()),
+            ty::ConstKind::Value(cv) => stack.push(cv.ty().into()),
 
             ty::ConstKind::Expr(expr) => stack.extend(expr.args().iter().rev()),
             ty::ConstKind::Unevaluated(ct) => {