Auto merge of #137848 - matthiaskrgr:rollup-vxtrkis, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #136503 (Tweak output of const panic diagnostic)
 - #137390 (tests: fix up new test for nocapture -> capture(none) change)
 - #137617 (Introduce `feature(generic_const_parameter_types)`)
 - #137719 (Add missing case explanation for doc inlined re-export of doc hidden item)
 - #137763 (Use `mk_ty_from_kind` a bit less, clean up lifetime handling in borrowck)
 - #137769 (Do not yeet `unsafe<>` from type when formatting unsafe binder)
 - #137776 (Some `rustc_transmute` cleanups)
 - #137800 (Remove `ParamEnv::without_caller_bounds`)

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

40 files changed, 251 insertions, 240 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index bd0d98028ae..6d05696e146 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -38,7 +38,7 @@ use rustc_mir_dataflow::move_paths::MoveData;
 use rustc_mir_dataflow::points::DenseLocationMap;
 use rustc_span::def_id::CRATE_DEF_ID;
 use rustc_span::source_map::Spanned;
-use rustc_span::{DUMMY_SP, Span, sym};
+use rustc_span::{Span, sym};
 use rustc_trait_selection::traits::query::type_op::custom::scrape_region_constraints;
 use rustc_trait_selection::traits::query::type_op::{TypeOp, TypeOpOutput};
 use tracing::{debug, instrument, trace};
@@ -51,7 +51,6 @@ use crate::polonius::legacy::{PoloniusFacts, PoloniusLocationTable};
 use crate::polonius::{PoloniusContext, PoloniusLivenessContext};
 use crate::region_infer::TypeTest;
 use crate::region_infer::values::{LivenessValues, PlaceholderIndex, PlaceholderIndices};
-use crate::renumber::RegionCtxt;
 use crate::session_diagnostics::{MoveUnsized, SimdIntrinsicArgConst};
 use crate::type_check::free_region_relations::{CreateResult, UniversalRegionRelations};
 use crate::universal_regions::{DefiningTy, UniversalRegions};
@@ -2121,35 +2120,31 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                 //
                                 // Note that other checks (such as denying `dyn Send` -> `dyn
                                 // Debug`) are in `rustc_hir_typeck`.
-                                if let ty::Dynamic(src_tty, ..) = src_tail.kind()
-                                    && let ty::Dynamic(dst_tty, ..) = dst_tail.kind()
+                                if let ty::Dynamic(src_tty, _src_lt, _) = *src_tail.kind()
+                                    && let ty::Dynamic(dst_tty, dst_lt, _) = *dst_tail.kind()
                                     && src_tty.principal().is_some()
                                     && dst_tty.principal().is_some()
                                 {
                                     // Remove auto traits.
                                     // Auto trait checks are handled in `rustc_hir_typeck` as FCW.
-                                    let src_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                                    let src_obj = Ty::new_dynamic(
+                                        tcx,
                                         tcx.mk_poly_existential_predicates(
                                             &src_tty.without_auto_traits().collect::<Vec<_>>(),
                                         ),
-                                        tcx.lifetimes.re_static,
+                                        // FIXME: Once we disallow casting `*const dyn Trait + 'short`
+                                        // to `*const dyn Trait + 'long`, then this can just be `src_lt`.
+                                        dst_lt,
                                         ty::Dyn,
-                                    ));
-                                    let dst_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                                    );
+                                    let dst_obj = Ty::new_dynamic(
+                                        tcx,
                                         tcx.mk_poly_existential_predicates(
                                             &dst_tty.without_auto_traits().collect::<Vec<_>>(),
                                         ),
-                                        tcx.lifetimes.re_static,
+                                        dst_lt,
                                         ty::Dyn,
-                                    ));
-
-                                    // Replace trait object lifetimes with fresh vars, to allow
-                                    // casts like
-                                    // `*mut dyn FnOnce() + 'a` -> `*mut dyn FnOnce() + 'static`
-                                    let src_obj =
-                                        freshen_single_trait_object_lifetime(self.infcx, src_obj);
-                                    let dst_obj =
-                                        freshen_single_trait_object_lifetime(self.infcx, dst_obj);
+                                    );
 
                                     debug!(?src_tty, ?dst_tty, ?src_obj, ?dst_obj);
 
@@ -2707,16 +2702,3 @@ impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {
         Ok(output)
     }
 }
-
-fn freshen_single_trait_object_lifetime<'tcx>(
-    infcx: &BorrowckInferCtxt<'tcx>,
-    ty: Ty<'tcx>,
-) -> Ty<'tcx> {
-    let &ty::Dynamic(tty, _, dyn_kind @ ty::Dyn) = ty.kind() else { bug!("expected trait object") };
-
-    let fresh = infcx
-        .next_region_var(rustc_infer::infer::RegionVariableOrigin::MiscVariable(DUMMY_SP), || {
-            RegionCtxt::Unknown
-        });
-    infcx.tcx.mk_ty_from_kind(ty::Dynamic(tty, fresh, dyn_kind))
-}
diff --git a/compiler/rustc_const_eval/messages.ftl b/compiler/rustc_const_eval/messages.ftl
index eecc6690f51..ccf9b240d40 100644
--- a/compiler/rustc_const_eval/messages.ftl
+++ b/compiler/rustc_const_eval/messages.ftl
@@ -109,6 +109,8 @@ const_eval_frame_note_inner = inside {$where_ ->
     *[other] {""}
 }
 
+const_eval_frame_note_last = the failure occurred here
+
 const_eval_in_bounds_test = out-of-bounds pointer use
 const_eval_incompatible_calling_conventions =
     calling a function with calling convention {$callee_conv} using calling convention {$caller_conv}
@@ -300,8 +302,7 @@ const_eval_overflow_arith =
 const_eval_overflow_shift =
     overflowing shift by {$shift_amount} in `{$intrinsic}`
 
-const_eval_panic =
-    the evaluated program panicked at '{$msg}', {$file}:{$line}:{$col}
+const_eval_panic = evaluation panicked: {$msg}
 
 const_eval_panic_non_str = argument to `panic!()` in a const context must have type `&str`
 
diff --git a/compiler/rustc_const_eval/src/const_eval/error.rs b/compiler/rustc_const_eval/src/const_eval/error.rs
index 3e32336d8fc..ffb32fa41eb 100644
--- a/compiler/rustc_const_eval/src/const_eval/error.rs
+++ b/compiler/rustc_const_eval/src/const_eval/error.rs
@@ -48,11 +48,8 @@ impl MachineStopType for ConstEvalErrKind {
             | ModifiedGlobal
             | WriteThroughImmutablePointer => {}
             AssertFailure(kind) => kind.add_args(adder),
-            Panic { msg, line, col, file } => {
+            Panic { msg, .. } => {
                 adder("msg".into(), msg.into_diag_arg(&mut None));
-                adder("file".into(), file.into_diag_arg(&mut None));
-                adder("line".into(), line.into_diag_arg(&mut None));
-                adder("col".into(), col.into_diag_arg(&mut None));
             }
         }
     }
@@ -72,7 +69,7 @@ pub fn get_span_and_frames<'tcx>(
     let mut stacktrace = Frame::generate_stacktrace_from_stack(stack);
     // Filter out `requires_caller_location` frames.
     stacktrace.retain(|frame| !frame.instance.def.requires_caller_location(*tcx));
-    let span = stacktrace.first().map(|f| f.span).unwrap_or(tcx.span);
+    let span = stacktrace.last().map(|f| f.span).unwrap_or(tcx.span);
 
     let mut frames = Vec::new();
 
@@ -115,6 +112,20 @@ pub fn get_span_and_frames<'tcx>(
         }
     }
 
+    // In `rustc`, we present const-eval errors from the outer-most place first to the inner-most.
+    // So we reverse the frames here. The first frame will be the same as the span from the current
+    // `TyCtxtAt<'_>`, so we remove it as it would be redundant.
+    frames.reverse();
+    if frames.len() > 0 {
+        frames.remove(0);
+    }
+    if let Some(last) = frames.last_mut()
+        // If the span is not going to be printed, we don't want the span label for `is_last`.
+        && tcx.sess.source_map().span_to_snippet(last.span.source_callsite()).is_ok()
+    {
+        last.has_label = true;
+    }
+
     (span, frames)
 }
 
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index ef756e58c5e..b020eeccf71 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -6,6 +6,7 @@ use rustc_abi::WrappingRange;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Diag, DiagArgValue, DiagCtxtHandle, DiagMessage, Diagnostic, EmissionGuarantee, Level,
+    MultiSpan, SubdiagMessageOp, Subdiagnostic,
 };
 use rustc_hir::ConstContext;
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -17,6 +18,7 @@ use rustc_middle::mir::interpret::{
 use rustc_middle::ty::{self, Mutability, Ty};
 use rustc_span::{Span, Symbol};
 
+use crate::fluent_generated as fluent;
 use crate::interpret::InternKind;
 
 #[derive(Diagnostic)]
@@ -278,14 +280,31 @@ pub(crate) struct NonConstImplNote {
     pub span: Span,
 }
 
-#[derive(Subdiagnostic, Clone)]
-#[note(const_eval_frame_note)]
+#[derive(Clone)]
 pub struct FrameNote {
-    #[primary_span]
     pub span: Span,
     pub times: i32,
     pub where_: &'static str,
     pub instance: String,
+    pub has_label: bool,
+}
+
+impl Subdiagnostic for FrameNote {
+    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
+        self,
+        diag: &mut Diag<'_, G>,
+        f: &F,
+    ) {
+        diag.arg("times", self.times);
+        diag.arg("where_", self.where_);
+        diag.arg("instance", self.instance);
+        let mut span: MultiSpan = self.span.into();
+        if self.has_label && !self.span.is_dummy() {
+            span.push_span_label(self.span, fluent::const_eval_frame_note_last);
+        }
+        let msg = f(diag, fluent::const_eval_frame_note.into());
+        diag.span_note(span, msg);
+    }
 }
 
 #[derive(Subdiagnostic)]
diff --git a/compiler/rustc_const_eval/src/interpret/stack.rs b/compiler/rustc_const_eval/src/interpret/stack.rs
index 7d0e0492792..d7b03776bc4 100644
--- a/compiler/rustc_const_eval/src/interpret/stack.rs
+++ b/compiler/rustc_const_eval/src/interpret/stack.rs
@@ -231,13 +231,19 @@ impl<'tcx> FrameInfo<'tcx> {
     pub fn as_note(&self, tcx: TyCtxt<'tcx>) -> errors::FrameNote {
         let span = self.span;
         if tcx.def_key(self.instance.def_id()).disambiguated_data.data == DefPathData::Closure {
-            errors::FrameNote { where_: "closure", span, instance: String::new(), times: 0 }
+            errors::FrameNote {
+                where_: "closure",
+                span,
+                instance: String::new(),
+                times: 0,
+                has_label: false,
+            }
         } else {
             let instance = format!("{}", self.instance);
             // Note: this triggers a `must_produce_diag` state, which means that if we ever get
             // here we must emit a diagnostic. We should never display a `FrameInfo` unless we
             // actually want to emit a warning or error to the user.
-            errors::FrameNote { where_: "instance", span, instance, times: 0 }
+            errors::FrameNote { where_: "instance", span, instance, times: 0, has_label: false }
         }
     }
 }
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 66c26a541f1..0acd3b0f800 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -508,6 +508,8 @@ declare_features! (
     (incomplete, generic_const_exprs, "1.56.0", Some(76560)),
     /// Allows generic parameters and where-clauses on free & associated const items.
     (incomplete, generic_const_items, "1.73.0", Some(113521)),
+    /// Allows the type of const generics to depend on generic parameters
+    (incomplete, generic_const_parameter_types, "CURRENT_RUSTC_VERSION", Some(137626)),
     /// Allows any generic constants being used as pattern type range ends
     (incomplete, generic_pattern_types, "1.86.0", Some(136574)),
     /// Allows registering static items globally, possibly across crates, to iterate over at runtime.
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index e6ea6eddcaa..d72cf00293f 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -966,7 +966,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
             let ty = tcx.type_of(param.def_id).instantiate_identity();
 
             if tcx.features().unsized_const_params() {
-                enter_wf_checking_ctxt(tcx, hir_ty.span, param.def_id, |wfcx| {
+                enter_wf_checking_ctxt(tcx, hir_ty.span, tcx.local_parent(param.def_id), |wfcx| {
                     wfcx.register_bound(
                         ObligationCause::new(
                             hir_ty.span,
@@ -980,7 +980,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
                     Ok(())
                 })
             } else if tcx.features().adt_const_params() {
-                enter_wf_checking_ctxt(tcx, hir_ty.span, param.def_id, |wfcx| {
+                enter_wf_checking_ctxt(tcx, hir_ty.span, tcx.local_parent(param.def_id), |wfcx| {
                     wfcx.register_bound(
                         ObligationCause::new(
                             hir_ty.span,
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 08d63f4349e..027aa5554a4 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -1822,6 +1822,9 @@ fn const_param_default<'tcx>(
         ),
     };
     let icx = ItemCtxt::new(tcx, def_id);
-    let ct = icx.lowerer().lower_const_arg(default_ct, FeedConstTy::Param(def_id.to_def_id()));
+    let identity_args = ty::GenericArgs::identity_for_item(tcx, def_id);
+    let ct = icx
+        .lowerer()
+        .lower_const_arg(default_ct, FeedConstTy::Param(def_id.to_def_id(), identity_args));
     ty::EarlyBinder::bind(ct)
 }
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index 5b511d27074..49549335363 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -223,10 +223,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
             }
             hir::GenericParamKind::Const { .. } => {
                 let param_def_id = param.def_id.to_def_id();
-                let ct_ty = tcx
-                    .type_of(param_def_id)
-                    .no_bound_vars()
-                    .expect("const parameters cannot be generic");
+                let ct_ty = tcx.type_of(param_def_id).instantiate_identity();
                 let ct = icx.lowerer().lower_const_param(param_def_id, param.hir_id);
                 predicates
                     .insert((ty::ClauseKind::ConstArgHasType(ct, ct_ty).upcast(tcx), param.span));
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
index 8d58a3bfbd3..fa58f12c553 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
@@ -273,7 +273,7 @@ pub fn lower_generic_args<'tcx: 'a, 'a>(
 
                             // We lower to an infer even when the feature gate is not enabled
                             // as it is useful for diagnostics to be able to see a `ConstKind::Infer`
-                            args.push(ctx.provided_kind(param, arg));
+                            args.push(ctx.provided_kind(&args, param, arg));
                             args_iter.next();
                             params.next();
                         }
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 750770178ee..a0f848f07c4 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -232,12 +232,15 @@ impl AssocItemQSelf {
 /// Use this enum with `<dyn HirTyLowerer>::lower_const_arg` to instruct it with the
 /// desired behavior.
 #[derive(Debug, Clone, Copy)]
-pub enum FeedConstTy {
+pub enum FeedConstTy<'a, 'tcx> {
     /// Feed the type.
     ///
     /// The `DefId` belongs to the const param that we are supplying
     /// this (anon) const arg to.
-    Param(DefId),
+    ///
+    /// The list of generic args is used to instantiate the parameters
+    /// used by the type of the const param specified by `DefId`.
+    Param(DefId, &'a [ty::GenericArg<'tcx>]),
     /// Don't feed the type.
     No,
 }
@@ -298,6 +301,7 @@ pub trait GenericArgsLowerer<'a, 'tcx> {
 
     fn provided_kind(
         &mut self,
+        preceding_args: &[ty::GenericArg<'tcx>],
         param: &ty::GenericParamDef,
         arg: &GenericArg<'tcx>,
     ) -> ty::GenericArg<'tcx>;
@@ -481,6 +485,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
             fn provided_kind(
                 &mut self,
+                preceding_args: &[ty::GenericArg<'tcx>],
                 param: &ty::GenericParamDef,
                 arg: &GenericArg<'tcx>,
             ) -> ty::GenericArg<'tcx> {
@@ -526,7 +531,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
                         .lowerer
                         // Ambig portions of `ConstArg` are handled in the match arm below
-                        .lower_const_arg(ct.as_unambig_ct(), FeedConstTy::Param(param.def_id))
+                        .lower_const_arg(
+                            ct.as_unambig_ct(),
+                            FeedConstTy::Param(param.def_id, preceding_args),
+                        )
                         .into(),
                     (&GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
                         self.lowerer.ct_infer(Some(param), inf.span).into()
@@ -582,8 +590,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         let ty = tcx
                             .at(self.span)
                             .type_of(param.def_id)
-                            .no_bound_vars()
-                            .expect("const parameter types cannot be generic");
+                            .instantiate(tcx, preceding_args);
                         if let Err(guar) = ty.error_reported() {
                             return ty::Const::new_error(tcx, guar).into();
                         }
@@ -2107,14 +2114,50 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     pub fn lower_const_arg(
         &self,
         const_arg: &hir::ConstArg<'tcx>,
-        feed: FeedConstTy,
+        feed: FeedConstTy<'_, 'tcx>,
     ) -> Const<'tcx> {
         let tcx = self.tcx();
 
-        if let FeedConstTy::Param(param_def_id) = feed
+        if let FeedConstTy::Param(param_def_id, args) = feed
             && let hir::ConstArgKind::Anon(anon) = &const_arg.kind
         {
-            tcx.feed_anon_const_type(anon.def_id, tcx.type_of(param_def_id));
+            let anon_const_type = tcx.type_of(param_def_id).instantiate(tcx, args);
+
+            // We must error if the instantiated type has any inference variables as we will
+            // use this type to feed the `type_of` and query results must not contain inference
+            // variables otherwise we will ICE.
+            //
+            // We also error if the type contains any regions as effectively any region will wind
+            // up as a region variable in mir borrowck. It would also be somewhat concerning if
+            // hir typeck was using equality but mir borrowck wound up using subtyping as that could
+            // result in a non-infer in hir typeck but a region variable in borrowck.
+            //
+            // FIXME(generic_const_parameter_types): Ideally we remove these errors one day when
+            // we have the ability to intermix typeck of anon const const args with the parent
+            // bodies typeck.
+            if tcx.features().generic_const_parameter_types()
+                && (anon_const_type.has_free_regions() || anon_const_type.has_erased_regions())
+            {
+                let e = tcx.dcx().span_err(
+                    const_arg.span(),
+                    "anonymous constants with lifetimes in their type are not yet supported",
+                );
+                tcx.feed_anon_const_type(anon.def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, e)));
+                return ty::Const::new_error(tcx, e);
+            }
+            if anon_const_type.has_non_region_infer() {
+                let e = tcx.dcx().span_err(
+                    const_arg.span(),
+                    "anonymous constants with inferred types are not yet supported",
+                );
+                tcx.feed_anon_const_type(anon.def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, e)));
+                return ty::Const::new_error(tcx, e);
+            }
+
+            tcx.feed_anon_const_type(
+                anon.def_id,
+                ty::EarlyBinder::bind(tcx.type_of(param_def_id).instantiate(tcx, args)),
+            );
         }
 
         let hir_id = const_arg.hir_id;
@@ -2230,10 +2273,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let expr = &tcx.hir_body(anon.body).value;
         debug!(?expr);
 
-        let ty = tcx
-            .type_of(anon.def_id)
-            .no_bound_vars()
-            .expect("const parameter types cannot be generic");
+        // FIXME(generic_const_parameter_types): We should use the proper generic args
+        // here. It's only used as a hint for literals so doesn't matter too much to use the right
+        // generic arguments, just weaker type inference.
+        let ty = tcx.type_of(anon.def_id).instantiate_identity();
 
         match self.try_lower_anon_const_lit(ty, expr) {
             Some(v) => v,
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index bdfbd540e40..cf18bab950a 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -260,7 +260,7 @@ pub fn lower_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
 pub fn lower_const_arg_for_rustdoc<'tcx>(
     tcx: TyCtxt<'tcx>,
     hir_ct: &hir::ConstArg<'tcx>,
-    feed: FeedConstTy,
+    feed: FeedConstTy<'_, 'tcx>,
 ) -> Const<'tcx> {
     let env_def_id = tcx.hir_get_parent_item(hir_ct.hir_id);
     collect::ItemCtxt::new(tcx, env_def_id.def_id).lowerer().lower_const_arg(hir_ct, feed)
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index 462983be88d..ea4ec345ad0 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -895,20 +895,22 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                         // e.g. we want to allow `dyn T -> (dyn T,)`, etc.
                         //
                         // We also need to skip auto traits to emit an FCW and not an error.
-                        let src_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                        let src_obj = Ty::new_dynamic(
+                            tcx,
                             tcx.mk_poly_existential_predicates(
                                 &src_tty.without_auto_traits().collect::<Vec<_>>(),
                             ),
                             tcx.lifetimes.re_erased,
                             ty::Dyn,
-                        ));
-                        let dst_obj = tcx.mk_ty_from_kind(ty::Dynamic(
+                        );
+                        let dst_obj = Ty::new_dynamic(
+                            tcx,
                             tcx.mk_poly_existential_predicates(
                                 &dst_tty.without_auto_traits().collect::<Vec<_>>(),
                             ),
                             tcx.lifetimes.re_erased,
                             ty::Dyn,
-                        ));
+                        );
 
                         // `dyn Src = dyn Dst`, this checks for matching traits/generics/projections
                         // This is `fcx.demand_eqtype`, but inlined to give a better error.
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index c9288b6a9d1..054e3bcb67c 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -522,7 +522,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub(crate) fn lower_const_arg(
         &self,
         const_arg: &'tcx hir::ConstArg<'tcx>,
-        feed: FeedConstTy,
+        feed: FeedConstTy<'_, 'tcx>,
     ) -> ty::Const<'tcx> {
         let ct = self.lowerer().lower_const_arg(const_arg, feed);
         self.register_wf_obligation(
@@ -1138,7 +1138,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .last()
             .is_some_and(|GenericPathSegment(def_id, _)| tcx.generics_of(*def_id).has_self);
 
-        let (res, self_ctor_args) = if let Res::SelfCtor(impl_def_id) = res {
+        let (res, implicit_args) = if let Res::Def(DefKind::ConstParam, def) = res {
+            // types of const parameters are somewhat special as they are part of
+            // the same environment as the const parameter itself. this means that
+            // unlike most paths `type-of(N)` can return a type naming parameters
+            // introduced by the containing item, rather than provided through `N`.
+            //
+            // for example given `<T, const M: usize, const N: [T; M]>` and some
+            // `let a = N;` expression. The path to `N` would wind up with no args
+            // (as it has no args), but instantiating the early binder on `typeof(N)`
+            // requires providing generic arguments for `[T, M, N]`.
+            (res, Some(ty::GenericArgs::identity_for_item(tcx, tcx.parent(def))))
+        } else if let Res::SelfCtor(impl_def_id) = res {
             let ty = LoweredTy::from_raw(
                 self,
                 span,
@@ -1264,6 +1275,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             fn provided_kind(
                 &mut self,
+                preceding_args: &[ty::GenericArg<'tcx>],
                 param: &ty::GenericParamDef,
                 arg: &GenericArg<'tcx>,
             ) -> ty::GenericArg<'tcx> {
@@ -1283,7 +1295,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
                         .fcx
                         // Ambiguous parts of `ConstArg` are handled in the match arms below
-                        .lower_const_arg(ct.as_unambig_ct(), FeedConstTy::Param(param.def_id))
+                        .lower_const_arg(
+                            ct.as_unambig_ct(),
+                            FeedConstTy::Param(param.def_id, preceding_args),
+                        )
                         .into(),
                     (&GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
                         self.fcx.ct_infer(Some(param), inf.span).into()
@@ -1323,7 +1338,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
         }
 
-        let args_raw = self_ctor_args.unwrap_or_else(|| {
+        let args_raw = implicit_args.unwrap_or_else(|| {
             lower_generic_args(
                 self,
                 def_id,
diff --git a/compiler/rustc_hir_typeck/src/method/confirm.rs b/compiler/rustc_hir_typeck/src/method/confirm.rs
index 3b107fbf173..0483164ca03 100644
--- a/compiler/rustc_hir_typeck/src/method/confirm.rs
+++ b/compiler/rustc_hir_typeck/src/method/confirm.rs
@@ -426,6 +426,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
 
             fn provided_kind(
                 &mut self,
+                preceding_args: &[ty::GenericArg<'tcx>],
                 param: &ty::GenericParamDef,
                 arg: &GenericArg<'tcx>,
             ) -> ty::GenericArg<'tcx> {
@@ -446,7 +447,10 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
                         .cfcx
                         // We handle the ambig portions of `ConstArg` in the match arms below
-                        .lower_const_arg(ct.as_unambig_ct(), FeedConstTy::Param(param.def_id))
+                        .lower_const_arg(
+                            ct.as_unambig_ct(),
+                            FeedConstTy::Param(param.def_id, preceding_args),
+                        )
                         .into(),
                     (GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
                         self.cfcx.ct_infer(Some(param), inf.span).into()
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 41958949836..fe42a224d9f 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -224,7 +224,7 @@ impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for Ty<'tcx> {
             })
         } else {
             let tcx = decoder.interner();
-            tcx.mk_ty_from_kind(rustc_type_ir::TyKind::decode(decoder))
+            tcx.mk_ty_from_kind(ty::TyKind::decode(decoder))
         }
     }
 }
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index d926d6cc02a..527509af05f 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -992,12 +992,6 @@ impl<'tcx> ParamEnv<'tcx> {
         ParamEnv { caller_bounds }
     }
 
-    /// Returns this same environment but with no caller bounds.
-    #[inline]
-    pub fn without_caller_bounds(self) -> Self {
-        Self::new(ListWithCachedTypeInfo::empty())
-    }
-
     /// Creates a pair of param-env and value for use in queries.
     pub fn and<T: TypeVisitable<TyCtxt<'tcx>>>(self, value: T) -> ParamEnvAnd<'tcx, T> {
         ParamEnvAnd { param_env: self, value }
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index d5617adf26b..ce563c59251 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -342,6 +342,7 @@ impl ParamConst {
         ParamConst::new(def.index, def.name)
     }
 
+    #[instrument(level = "debug")]
     pub fn find_ty_from_env<'tcx>(self, env: ParamEnv<'tcx>) -> Ty<'tcx> {
         let mut candidates = env.caller_bounds().iter().filter_map(|clause| {
             // `ConstArgHasType` are never desugared to be higher ranked.
@@ -461,7 +462,7 @@ impl<'tcx> Ty<'tcx> {
 
     #[inline]
     pub fn new_param(tcx: TyCtxt<'tcx>, index: u32, name: Symbol) -> Ty<'tcx> {
-        tcx.mk_ty_from_kind(Param(ParamTy { index, name }))
+        Ty::new(tcx, Param(ParamTy { index, name }))
     }
 
     #[inline]
diff --git a/compiler/rustc_next_trait_solver/src/delegate.rs b/compiler/rustc_next_trait_solver/src/delegate.rs
index a64941cce3a..850d86d91e8 100644
--- a/compiler/rustc_next_trait_solver/src/delegate.rs
+++ b/compiler/rustc_next_trait_solver/src/delegate.rs
@@ -102,7 +102,6 @@ pub trait SolverDelegate: Deref<Target = Self::Infcx> + Sized {
 
     fn is_transmutable(
         &self,
-        param_env: <Self::Interner as Interner>::ParamEnv,
         dst: <Self::Interner as Interner>::Ty,
         src: <Self::Interner as Interner>::Ty,
         assume: <Self::Interner as Interner>::Const,
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
index a2719dbd84d..b0bbec48947 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
@@ -1091,12 +1091,11 @@ where
 
     pub(super) fn is_transmutable(
         &mut self,
-        param_env: I::ParamEnv,
         dst: I::Ty,
         src: I::Ty,
         assume: I::Const,
     ) -> Result<Certainty, NoSolution> {
-        self.delegate.is_transmutable(param_env, dst, src, assume)
+        self.delegate.is_transmutable(dst, src, assume)
     }
 }
 
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index a34a56ae8c8..1b18142c242 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -617,7 +617,6 @@ where
             )?;
 
             let certainty = ecx.is_transmutable(
-                goal.param_env,
                 goal.predicate.trait_ref.args.type_at(0),
                 goal.predicate.trait_ref.args.type_at(1),
                 assume,
diff --git a/compiler/rustc_resolve/messages.ftl b/compiler/rustc_resolve/messages.ftl
index b13de2875bc..9f062b3935f 100644
--- a/compiler/rustc_resolve/messages.ftl
+++ b/compiler/rustc_resolve/messages.ftl
@@ -125,9 +125,6 @@ resolve_const_param_in_enum_discriminant =
 resolve_const_param_in_non_trivial_anon_const =
     const parameters may only be used as standalone arguments, i.e. `{$name}`
 
-resolve_const_param_in_ty_of_const_param =
-    const parameters may not be used in the type of const parameters
-
 resolve_constructor_private_if_any_field_private =
     a constructor is private if any of the fields is private
 
@@ -250,9 +247,6 @@ resolve_lifetime_param_in_enum_discriminant =
 resolve_lifetime_param_in_non_trivial_anon_const =
     lifetime parameters may not be used in const expressions
 
-resolve_lifetime_param_in_ty_of_const_param =
-    lifetime parameters may not be used in the type of const parameters
-
 resolve_lowercase_self =
     attempt to use a non-constant value in a constant
     .suggestion = try using `Self`
@@ -437,9 +431,6 @@ resolve_type_param_in_enum_discriminant =
 resolve_type_param_in_non_trivial_anon_const =
     type parameters may not be used in const expressions
 
-resolve_type_param_in_ty_of_const_param =
-    type parameters may not be used in the type of const parameters
-
 resolve_undeclared_label =
     use of undeclared label `{$name}`
     .label = undeclared label `{$name}`
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 20af56e7ee4..e3405c89b79 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -890,9 +890,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ResolutionError::ForwardDeclaredGenericParam => {
                 self.dcx().create_err(errs::ForwardDeclaredGenericParam { span })
             }
-            ResolutionError::ParamInTyOfConstParam { name, param_kind: is_type } => self
-                .dcx()
-                .create_err(errs::ParamInTyOfConstParam { span, name, param_kind: is_type }),
+            ResolutionError::ParamInTyOfConstParam { name } => {
+                self.dcx().create_err(errs::ParamInTyOfConstParam { span, name })
+            }
             ResolutionError::ParamInNonTrivialAnonConst { name, param_kind: is_type } => {
                 self.dcx().create_err(errs::ParamInNonTrivialAnonConst {
                     span,
diff --git a/compiler/rustc_resolve/src/errors.rs b/compiler/rustc_resolve/src/errors.rs
index 7eb795034b0..b5d3e5ea776 100644
--- a/compiler/rustc_resolve/src/errors.rs
+++ b/compiler/rustc_resolve/src/errors.rs
@@ -347,19 +347,6 @@ pub(crate) struct ParamInTyOfConstParam {
     #[label]
     pub(crate) span: Span,
     pub(crate) name: Symbol,
-    #[subdiagnostic]
-    pub(crate) param_kind: Option<ParamKindInTyOfConstParam>,
-}
-
-#[derive(Debug)]
-#[derive(Subdiagnostic)]
-pub(crate) enum ParamKindInTyOfConstParam {
-    #[note(resolve_type_param_in_ty_of_const_param)]
-    Type,
-    #[note(resolve_const_param_in_ty_of_const_param)]
-    Const,
-    #[note(resolve_lifetime_param_in_ty_of_const_param)]
-    Lifetime,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 499b9bca4d2..d9776be4dd0 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -1131,6 +1131,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             return Res::Err;
         }
 
+        if let RibKind::ConstParamTy = all_ribs[rib_index].kind {
+            if let Some(span) = finalize {
+                self.report_error(
+                    span,
+                    ResolutionError::ParamInTyOfConstParam { name: rib_ident.name },
+                );
+            }
+            assert_eq!(res, Res::Err);
+            return Res::Err;
+        }
+
         match res {
             Res::Local(_) => {
                 use ResolutionError::*;
@@ -1209,10 +1220,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             if let Some(span) = finalize {
                                 self.report_error(
                                     span,
-                                    ParamInTyOfConstParam {
-                                        name: rib_ident.name,
-                                        param_kind: None,
-                                    },
+                                    ParamInTyOfConstParam { name: rib_ident.name },
                                 );
                             }
                             return Res::Err;
@@ -1239,6 +1247,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         | RibKind::MacroDefinition(..)
                         | RibKind::InlineAsmSym
                         | RibKind::AssocItem
+                        | RibKind::ConstParamTy
                         | RibKind::ForwardGenericParamBan => {
                             // Nothing to do. Continue.
                             continue;
@@ -1292,18 +1301,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         RibKind::Item(has_generic_params, def_kind) => {
                             (has_generic_params, def_kind)
                         }
-                        RibKind::ConstParamTy => {
-                            if let Some(span) = finalize {
-                                self.report_error(
-                                    span,
-                                    ResolutionError::ParamInTyOfConstParam {
-                                        name: rib_ident.name,
-                                        param_kind: Some(errors::ParamKindInTyOfConstParam::Type),
-                                    },
-                                );
-                            }
-                            return Res::Err;
-                        }
                     };
 
                     if let Some(span) = finalize {
@@ -1328,6 +1325,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         | RibKind::MacroDefinition(..)
                         | RibKind::InlineAsmSym
                         | RibKind::AssocItem
+                        | RibKind::ConstParamTy
                         | RibKind::ForwardGenericParamBan => continue,
 
                         RibKind::ConstantItem(trivial, _) => {
@@ -1361,18 +1359,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         RibKind::Item(has_generic_params, def_kind) => {
                             (has_generic_params, def_kind)
                         }
-                        RibKind::ConstParamTy => {
-                            if let Some(span) = finalize {
-                                self.report_error(
-                                    span,
-                                    ResolutionError::ParamInTyOfConstParam {
-                                        name: rib_ident.name,
-                                        param_kind: Some(errors::ParamKindInTyOfConstParam::Const),
-                                    },
-                                );
-                            }
-                            return Res::Err;
-                        }
                     };
 
                     // This was an attempt to use a const parameter outside its scope.
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 32ef781631b..f119ed55e7d 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -227,9 +227,11 @@ impl RibKind<'_> {
             | RibKind::ConstantItem(..)
             | RibKind::Module(_)
             | RibKind::MacroDefinition(_)
-            | RibKind::ConstParamTy
             | RibKind::InlineAsmSym => false,
-            RibKind::AssocItem | RibKind::Item(..) | RibKind::ForwardGenericParamBan => true,
+            RibKind::ConstParamTy
+            | RibKind::AssocItem
+            | RibKind::Item(..)
+            | RibKind::ForwardGenericParamBan => true,
         }
     }
 
@@ -1570,6 +1572,17 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             forward_ty_ban_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), Res::Err);
         }
 
+        let mut forward_ty_ban_rib_const_param_ty = Rib {
+            bindings: forward_ty_ban_rib.bindings.clone(),
+            patterns_with_skipped_bindings: FxHashMap::default(),
+            kind: RibKind::ConstParamTy,
+        };
+        let mut forward_const_ban_rib_const_param_ty = Rib {
+            bindings: forward_const_ban_rib.bindings.clone(),
+            patterns_with_skipped_bindings: FxHashMap::default(),
+            kind: RibKind::ConstParamTy,
+        };
+
         self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
             for param in params {
                 match param.kind {
@@ -1592,21 +1605,27 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                         }
 
                         // Allow all following defaults to refer to this type parameter.
-                        forward_ty_ban_rib
-                            .bindings
-                            .remove(&Ident::with_dummy_span(param.ident.name));
+                        let i = &Ident::with_dummy_span(param.ident.name);
+                        forward_ty_ban_rib.bindings.remove(i);
+                        if this.r.tcx.features().generic_const_parameter_types() {
+                            forward_ty_ban_rib_const_param_ty.bindings.remove(i);
+                        }
                     }
                     GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
                         // Const parameters can't have param bounds.
                         assert!(param.bounds.is_empty());
 
-                        this.ribs[TypeNS].push(Rib::new(RibKind::ConstParamTy));
-                        this.ribs[ValueNS].push(Rib::new(RibKind::ConstParamTy));
-                        this.with_lifetime_rib(LifetimeRibKind::ConstParamTy, |this| {
+                        this.ribs[TypeNS].push(forward_ty_ban_rib_const_param_ty);
+                        this.ribs[ValueNS].push(forward_const_ban_rib_const_param_ty);
+                        if this.r.tcx.features().generic_const_parameter_types() {
                             this.visit_ty(ty)
-                        });
-                        this.ribs[TypeNS].pop().unwrap();
-                        this.ribs[ValueNS].pop().unwrap();
+                        } else {
+                            this.with_lifetime_rib(LifetimeRibKind::ConstParamTy, |this| {
+                                this.visit_ty(ty)
+                            });
+                        }
+                        forward_const_ban_rib_const_param_ty = this.ribs[ValueNS].pop().unwrap();
+                        forward_ty_ban_rib_const_param_ty = this.ribs[TypeNS].pop().unwrap();
 
                         if let Some(expr) = default {
                             this.ribs[TypeNS].push(forward_ty_ban_rib);
@@ -1620,9 +1639,11 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                         }
 
                         // Allow all following defaults to refer to this const parameter.
-                        forward_const_ban_rib
-                            .bindings
-                            .remove(&Ident::with_dummy_span(param.ident.name));
+                        let i = &Ident::with_dummy_span(param.ident.name);
+                        forward_const_ban_rib.bindings.remove(i);
+                        if this.r.tcx.features().generic_const_parameter_types() {
+                            forward_const_ban_rib_const_param_ty.bindings.remove(i);
+                        }
                     }
                 }
             }
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index fa9c42e3593..0e14e7671b1 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -3052,7 +3052,6 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
             .create_err(errors::ParamInTyOfConstParam {
                 span: lifetime_ref.ident.span,
                 name: lifetime_ref.ident.name,
-                param_kind: Some(errors::ParamKindInTyOfConstParam::Lifetime),
             })
             .emit();
     }
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index ea48d0cad74..4c5d4041022 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -30,9 +30,7 @@ use std::sync::Arc;
 
 use diagnostics::{ImportSuggestion, LabelSuggestion, Suggestion};
 use effective_visibilities::EffectiveVisibilitiesVisitor;
-use errors::{
-    ParamKindInEnumDiscriminant, ParamKindInNonTrivialAnonConst, ParamKindInTyOfConstParam,
-};
+use errors::{ParamKindInEnumDiscriminant, ParamKindInNonTrivialAnonConst};
 use imports::{Import, ImportData, ImportKind, NameResolution};
 use late::{HasGenericParams, PathSource, PatternSource, UnnecessaryQualification};
 use macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};
@@ -276,8 +274,10 @@ enum ResolutionError<'ra> {
     },
     /// Error E0128: generic parameters with a default cannot use forward-declared identifiers.
     ForwardDeclaredGenericParam,
+    // FIXME(generic_const_parameter_types): This should give custom output specifying it's only
+    // problematic to use *forward declared* parameters when the feature is enabled.
     /// ERROR E0770: the type of const parameters must not depend on other generic parameters.
-    ParamInTyOfConstParam { name: Symbol, param_kind: Option<ParamKindInTyOfConstParam> },
+    ParamInTyOfConstParam { name: Symbol },
     /// generic parameters must not be used inside const evaluations.
     ///
     /// This error is only emitted when using `min_const_generics`.
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 501c9039f2d..2a709b07255 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1037,6 +1037,7 @@ symbols! {
         generic_associated_types_extended,
         generic_const_exprs,
         generic_const_items,
+        generic_const_parameter_types,
         generic_param_attrs,
         generic_pattern_types,
         get_context,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 5c489a55aec..d270b4cf96b 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -1189,9 +1189,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let span = obligation.cause.span;
 
         let mut diag = match ty.kind() {
-            _ if ty.has_param() => {
-                span_bug!(span, "const param tys cannot mention other generic parameters");
-            }
             ty::Float(_) => {
                 struct_span_code_err!(
                     self.dcx(),
@@ -2536,9 +2533,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 return GetSafeTransmuteErrorAndReason::Silent;
             };
 
-            let Some(assume) =
-                rustc_transmute::Assume::from_const(self.infcx.tcx, obligation.param_env, assume)
-            else {
+            let Some(assume) = rustc_transmute::Assume::from_const(self.infcx.tcx, assume) else {
                 self.dcx().span_delayed_bug(
                     span,
                     "Unable to construct rustc_transmute::Assume where it was previously possible",
@@ -2550,11 +2545,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             let src = trait_pred.trait_ref.args.type_at(1);
             let err_msg = format!("`{src}` cannot be safely transmuted into `{dst}`");
 
-            match rustc_transmute::TransmuteTypeEnv::new(self.infcx).is_transmutable(
-                obligation.cause,
-                src_and_dst,
-                assume,
-            ) {
+            match rustc_transmute::TransmuteTypeEnv::new(self.infcx.tcx)
+                .is_transmutable(src_and_dst, assume)
+            {
                 Answer::No(reason) => {
                     let safe_transmute_explanation = match reason {
                         rustc_transmute::Reason::SrcIsNotYetSupported => {
diff --git a/compiler/rustc_trait_selection/src/solve/delegate.rs b/compiler/rustc_trait_selection/src/solve/delegate.rs
index 58d8a3a6254..e69bad095e3 100644
--- a/compiler/rustc_trait_selection/src/solve/delegate.rs
+++ b/compiler/rustc_trait_selection/src/solve/delegate.rs
@@ -7,7 +7,6 @@ use rustc_infer::infer::canonical::{
     Canonical, CanonicalExt as _, CanonicalQueryInput, CanonicalVarInfo, CanonicalVarValues,
 };
 use rustc_infer::infer::{InferCtxt, RegionVariableOrigin, TyCtxtInferExt};
-use rustc_infer::traits::ObligationCause;
 use rustc_infer::traits::solve::Goal;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt as _};
@@ -222,7 +221,6 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
     // register candidates. We probably need to register >1 since we may have an OR of ANDs.
     fn is_transmutable(
         &self,
-        param_env: ty::ParamEnv<'tcx>,
         dst: Ty<'tcx>,
         src: Ty<'tcx>,
         assume: ty::Const<'tcx>,
@@ -231,16 +229,14 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
         // which will ICE for region vars.
         let (dst, src) = self.tcx.erase_regions((dst, src));
 
-        let Some(assume) = rustc_transmute::Assume::from_const(self.tcx, param_env, assume) else {
+        let Some(assume) = rustc_transmute::Assume::from_const(self.tcx, assume) else {
             return Err(NoSolution);
         };
 
         // FIXME(transmutability): This really should be returning nested goals for `Answer::If*`
-        match rustc_transmute::TransmuteTypeEnv::new(&self.0).is_transmutable(
-            ObligationCause::dummy(),
-            rustc_transmute::Types { src, dst },
-            assume,
-        ) {
+        match rustc_transmute::TransmuteTypeEnv::new(self.0.tcx)
+            .is_transmutable(rustc_transmute::Types { src, dst }, assume)
+        {
             rustc_transmute::Answer::Yes => Ok(Certainty::Yes),
             rustc_transmute::Answer::No(_) | rustc_transmute::Answer::If(_) => Err(NoSolution),
         }
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 32cbb97e314..a58317dd56d 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -414,9 +414,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         if self.tcx().features().generic_const_exprs() {
             assume = crate::traits::evaluate_const(self.infcx, assume, obligation.param_env)
         }
-        let Some(assume) =
-            rustc_transmute::Assume::from_const(self.infcx.tcx, obligation.param_env, assume)
-        else {
+        let Some(assume) = rustc_transmute::Assume::from_const(self.infcx.tcx, assume) else {
             return Err(Unimplemented);
         };
 
@@ -424,12 +422,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let src = predicate.trait_ref.args.type_at(1);
 
         debug!(?src, ?dst);
-        let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx);
-        let maybe_transmutable = transmute_env.is_transmutable(
-            obligation.cause.clone(),
-            rustc_transmute::Types { dst, src },
-            assume,
-        );
+        let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx.tcx);
+        let maybe_transmutable =
+            transmute_env.is_transmutable(rustc_transmute::Types { dst, src }, assume);
 
         let fully_flattened = match maybe_transmutable {
             Answer::No(_) => Err(Unimplemented)?,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 120e6f6e2ce..77dbb43465e 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1007,7 +1007,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // depend on its particular value in order to work, so we can clear
             // out the param env and get better caching.
             debug!("in global");
-            obligation.param_env = obligation.param_env.without_caller_bounds();
+            obligation.param_env = ty::ParamEnv::empty();
         }
 
         let stack = self.push_stack(previous_stack, &obligation);
diff --git a/compiler/rustc_transmute/Cargo.toml b/compiler/rustc_transmute/Cargo.toml
index e9daf6b0c38..f0c783b3002 100644
--- a/compiler/rustc_transmute/Cargo.toml
+++ b/compiler/rustc_transmute/Cargo.toml
@@ -8,8 +8,6 @@ edition = "2024"
 rustc_abi = { path = "../rustc_abi", optional = true }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_hir = { path = "../rustc_hir", optional = true }
-rustc_infer = { path = "../rustc_infer", optional = true }
-rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_middle = { path = "../rustc_middle", optional = true }
 rustc_span = { path = "../rustc_span", optional = true }
 tracing = "0.1"
@@ -19,8 +17,6 @@ tracing = "0.1"
 rustc = [
     "dep:rustc_abi",
     "dep:rustc_hir",
-    "dep:rustc_infer",
-    "dep:rustc_macros",
     "dep:rustc_middle",
     "dep:rustc_span",
 ]
diff --git a/compiler/rustc_transmute/src/layout/dfa.rs b/compiler/rustc_transmute/src/layout/dfa.rs
index a70dc034e63..a29baade42f 100644
--- a/compiler/rustc_transmute/src/layout/dfa.rs
+++ b/compiler/rustc_transmute/src/layout/dfa.rs
@@ -38,7 +38,7 @@ impl<R> Transitions<R>
 where
     R: Ref,
 {
-    #[allow(dead_code)]
+    #[cfg(test)]
     fn insert(&mut self, transition: Transition<R>, state: State) {
         match transition {
             Transition::Byte(b) => {
@@ -86,15 +86,6 @@ impl<R> Dfa<R>
 where
     R: Ref,
 {
-    #[allow(dead_code)]
-    pub(crate) fn unit() -> Self {
-        let transitions: Map<State, Transitions<R>> = Map::default();
-        let start = State::new();
-        let accepting = start;
-
-        Self { transitions, start, accepting }
-    }
-
     #[cfg(test)]
     pub(crate) fn bool() -> Self {
         let mut transitions: Map<State, Transitions<R>> = Map::default();
diff --git a/compiler/rustc_transmute/src/layout/nfa.rs b/compiler/rustc_transmute/src/layout/nfa.rs
index 3b49c59fa68..9c21fd94f03 100644
--- a/compiler/rustc_transmute/src/layout/nfa.rs
+++ b/compiler/rustc_transmute/src/layout/nfa.rs
@@ -159,11 +159,6 @@ where
         }
         Self { transitions, start, accepting }
     }
-
-    #[allow(dead_code)]
-    pub(crate) fn edges_from(&self, start: State) -> Option<&Map<Transition<R>, Set<State>>> {
-        self.transitions.get(&start)
-    }
 }
 
 impl State {
diff --git a/compiler/rustc_transmute/src/layout/tree.rs b/compiler/rustc_transmute/src/layout/tree.rs
index b00585d2922..a21be5dda4e 100644
--- a/compiler/rustc_transmute/src/layout/tree.rs
+++ b/compiler/rustc_transmute/src/layout/tree.rs
@@ -237,7 +237,7 @@ pub(crate) mod rustc {
 
                 ty::Tuple(members) => Self::from_tuple((ty, layout), members, cx),
 
-                ty::Array(inner_ty, len) => {
+                ty::Array(inner_ty, _len) => {
                     let FieldsShape::Array { stride, count } = &layout.fields else {
                         return Err(Err::NotYetSupported);
                     };
@@ -282,7 +282,6 @@ pub(crate) mod rustc {
                 FieldsShape::Primitive => {
                     assert_eq!(members.len(), 1);
                     let inner_ty = members[0];
-                    let inner_layout = layout_of(cx, inner_ty)?;
                     Self::from_ty(inner_ty, cx)
                 }
                 FieldsShape::Arbitrary { offsets, .. } => {
@@ -345,7 +344,7 @@ pub(crate) mod rustc {
                     // the enum delegates its layout to the variant at `index`.
                     layout_of_variant(*index, None)
                 }
-                Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
+                Variants::Multiple { tag: _, tag_encoding, tag_field, .. } => {
                     // `Variants::Multiple` denotes an enum with multiple
                     // variants. The layout of such an enum is the disjunction
                     // of the layouts of its tagged variants.
@@ -356,7 +355,7 @@ pub(crate) mod rustc {
 
                     let variants = def.discriminants(cx.tcx()).try_fold(
                         Self::uninhabited(),
-                        |variants, (idx, ref discriminant)| {
+                        |variants, (idx, _discriminant)| {
                             let variant = layout_of_variant(idx, Some(tag_encoding.clone()))?;
                             Result::<Self, Err>::Ok(variants.or(variant))
                         },
@@ -414,7 +413,7 @@ pub(crate) mod rustc {
 
             // Append the fields, in memory order, to the layout.
             let inverse_memory_index = memory_index.invert_bijective_mapping();
-            for (memory_idx, &field_idx) in inverse_memory_index.iter_enumerated() {
+            for &field_idx in inverse_memory_index.iter() {
                 // Add interfield padding.
                 let padding_needed = offsets[field_idx] - size;
                 let padding = Self::padding(padding_needed.bytes_usize());
@@ -468,15 +467,14 @@ pub(crate) mod rustc {
 
             // This constructor does not support non-`FieldsShape::Union`
             // layouts. Fields of this shape are all placed at offset 0.
-            let FieldsShape::Union(fields) = layout.fields() else {
+            let FieldsShape::Union(_fields) = layout.fields() else {
                 return Err(Err::NotYetSupported);
             };
 
             let fields = &def.non_enum_variant().fields;
             let fields = fields.iter_enumerated().try_fold(
                 Self::uninhabited(),
-                |fields, (idx, field_def)| {
-                    let field_def = Def::Field(field_def);
+                |fields, (idx, _field_def)| {
                     let field_ty = ty_field(cx, (ty, layout), idx);
                     let field_layout = layout_of(cx, field_ty)?;
                     let field = Self::from_ty(field_ty, cx)?;
diff --git a/compiler/rustc_transmute/src/lib.rs b/compiler/rustc_transmute/src/lib.rs
index f9537f708ef..81a11f7cfb2 100644
--- a/compiler/rustc_transmute/src/lib.rs
+++ b/compiler/rustc_transmute/src/lib.rs
@@ -1,6 +1,4 @@
 // tidy-alphabetical-start
-#![allow(unused_variables)]
-#![feature(alloc_layout_extra)]
 #![feature(never_type)]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end
@@ -81,15 +79,12 @@ pub enum Reason<T> {
 #[cfg(feature = "rustc")]
 mod rustc {
     use rustc_hir::lang_items::LangItem;
-    use rustc_infer::infer::InferCtxt;
-    use rustc_macros::TypeVisitable;
-    use rustc_middle::traits::ObligationCause;
-    use rustc_middle::ty::{Const, ParamEnv, Ty, TyCtxt};
+    use rustc_middle::ty::{Const, Ty, TyCtxt};
 
     use super::*;
 
     /// The source and destination types of a transmutation.
-    #[derive(TypeVisitable, Debug, Clone, Copy)]
+    #[derive(Debug, Clone, Copy)]
     pub struct Types<'tcx> {
         /// The source type.
         pub src: Ty<'tcx>,
@@ -97,27 +92,22 @@ mod rustc {
         pub dst: Ty<'tcx>,
     }
 
-    pub struct TransmuteTypeEnv<'cx, 'tcx> {
-        infcx: &'cx InferCtxt<'tcx>,
+    pub struct TransmuteTypeEnv<'tcx> {
+        tcx: TyCtxt<'tcx>,
     }
 
-    impl<'cx, 'tcx> TransmuteTypeEnv<'cx, 'tcx> {
-        pub fn new(infcx: &'cx InferCtxt<'tcx>) -> Self {
-            Self { infcx }
+    impl<'tcx> TransmuteTypeEnv<'tcx> {
+        pub fn new(tcx: TyCtxt<'tcx>) -> Self {
+            Self { tcx }
         }
 
-        #[allow(unused)]
         pub fn is_transmutable(
             &mut self,
-            cause: ObligationCause<'tcx>,
             types: Types<'tcx>,
             assume: crate::Assume,
         ) -> crate::Answer<crate::layout::rustc::Ref<'tcx>> {
             crate::maybe_transmutable::MaybeTransmutableQuery::new(
-                types.src,
-                types.dst,
-                assume,
-                self.infcx.tcx,
+                types.src, types.dst, assume, self.tcx,
             )
             .answer()
         }
@@ -125,11 +115,7 @@ mod rustc {
 
     impl Assume {
         /// Constructs an `Assume` from a given const-`Assume`.
-        pub fn from_const<'tcx>(
-            tcx: TyCtxt<'tcx>,
-            param_env: ParamEnv<'tcx>,
-            ct: Const<'tcx>,
-        ) -> Option<Self> {
+        pub fn from_const<'tcx>(tcx: TyCtxt<'tcx>, ct: Const<'tcx>) -> Option<Self> {
             use rustc_middle::ty::ScalarInt;
             use rustc_span::sym;
 
diff --git a/compiler/rustc_transmute/src/maybe_transmutable/mod.rs b/compiler/rustc_transmute/src/maybe_transmutable/mod.rs
index 023c8fad781..63fabc9c83d 100644
--- a/compiler/rustc_transmute/src/maybe_transmutable/mod.rs
+++ b/compiler/rustc_transmute/src/maybe_transmutable/mod.rs
@@ -79,12 +79,12 @@ where
     pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
         let Self { src, dst, assume, context } = self;
 
-        // Unconditionally all `Def` nodes from `src`, without pruning away the
+        // Unconditionally remove all `Def` nodes from `src`, without pruning away the
         // branches they appear in. This is valid to do for value-to-value
         // transmutations, but not for `&mut T` to `&mut U`; we will need to be
         // more sophisticated to handle transmutations between mutable
         // references.
-        let src = src.prune(&|def| false);
+        let src = src.prune(&|_def| false);
 
         if src.is_inhabited() && !dst.is_inhabited() {
             return Answer::No(Reason::DstUninhabited);
@@ -96,7 +96,7 @@ where
         let dst = if assume.safety {
             // ...if safety is assumed, don't check if they carry safety
             // invariants; retain all paths.
-            dst.prune(&|def| false)
+            dst.prune(&|_def| false)
         } else {
             // ...otherwise, prune away all paths with safety invariants from
             // the `Dst` layout.
diff --git a/compiler/rustc_transmute/src/maybe_transmutable/tests.rs b/compiler/rustc_transmute/src/maybe_transmutable/tests.rs
index 84af20c773e..4d81382eba0 100644
--- a/compiler/rustc_transmute/src/maybe_transmutable/tests.rs
+++ b/compiler/rustc_transmute/src/maybe_transmutable/tests.rs
@@ -92,7 +92,6 @@ mod bool {
 
     #[test]
     fn should_permit_validity_expansion_and_reject_contraction() {
-        let un = layout::Tree::<Def, !>::uninhabited();
         let b0 = layout::Tree::<Def, !>::from_bits(0);
         let b1 = layout::Tree::<Def, !>::from_bits(1);
         let b2 = layout::Tree::<Def, !>::from_bits(2);