[WIP] Support param bounds on non-lifetime binders

compiler/rustc_ast_lowering/src/item.rs

@@ -1818,6 +1818,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     bounded_ty: self.arena.alloc(bounded_ty),
                     bounds,
                     bound_generic_params: &[],
+                    bound_assumptions: &[],
                     origin,
                 })
             }
@@ -1846,6 +1847,20 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }) => hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate {
                 bound_generic_params: self
                     .lower_generic_params(bound_generic_params, hir::GenericParamSource::Binder),
+                bound_assumptions: self.arena.alloc_from_iter(
+                    bound_generic_params.iter().filter_map(|param| {
+                        self.lower_generic_bound_predicate(
+                            param.ident,
+                            param.id,
+                            &param.kind,
+                            &param.bounds,
+                            param.colon_span,
+                            span,
+                            ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
+                            PredicateOrigin::GenericParam,
+                        )
+                    }),
+                ),
                 bounded_ty: self
                     .lower_ty(bounded_ty, ImplTraitContext::Disallowed(ImplTraitPosition::Bound)),
                 bounds: self.lower_param_bounds(

compiler/rustc_ast_lowering/src/lib.rs

@@ -56,7 +56,7 @@ use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId};
 use rustc_hir::{
     self as hir, ConstArg, GenericArg, HirId, IsAnonInPath, ItemLocalMap, LangItem, ParamName,
-    TraitCandidate,
+    PredicateOrigin, TraitCandidate,
 };
 use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_macros::extension;
@@ -1728,6 +1728,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         hir::GenericBound::Trait(hir::PolyTraitRef {
             bound_generic_params: &[],
+            bound_assumptions: &[],
             modifiers: hir::TraitBoundModifiers::NONE,
             trait_ref: hir::TraitRef {
                 path: self.make_lang_item_path(trait_lang_item, opaque_ty_span, Some(bound_args)),
@@ -1948,12 +1949,26 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         p: &PolyTraitRef,
         itctx: ImplTraitContext,
     ) -> hir::PolyTraitRef<'hir> {
+        let bound_assumptions =
+            self.arena.alloc_from_iter(p.bound_generic_params.iter().filter_map(|param| {
+                self.lower_generic_bound_predicate(
+                    param.ident,
+                    param.id,
+                    &param.kind,
+                    &param.bounds,
+                    param.colon_span,
+                    p.span,
+                    ImplTraitContext::Disallowed(ImplTraitPosition::Bound),
+                    PredicateOrigin::GenericParam,
+                )
+            }));
         let bound_generic_params =
             self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params);
         let trait_ref = self.lower_trait_ref(p.modifiers, &p.trait_ref, itctx);
         let modifiers = self.lower_trait_bound_modifiers(p.modifiers);
         hir::PolyTraitRef {
             bound_generic_params,
+            bound_assumptions,
             modifiers,
             trait_ref,
             span: self.lower_span(p.span),
@@ -2362,6 +2377,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
                         let principal = hir::PolyTraitRef {
                             bound_generic_params: &[],
+                            bound_assumptions: &[],
                             modifiers: hir::TraitBoundModifiers::NONE,
                             trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
                             span: self.lower_span(span),

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -140,10 +140,12 @@ impl<'a> PostExpansionVisitor<'a> {
             }
         }
 
-        for param in params {
-            if !param.bounds.is_empty() {
-                let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
-                self.sess.dcx().emit_err(errors::ForbiddenBound { spans });
+        if !self.features.non_lifetime_binders() {
+            for param in params {
+                if !param.bounds.is_empty() {
+                    let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
+                    self.sess.dcx().emit_err(errors::ForbiddenBound { spans });
+                }
             }
         }
     }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1641,7 +1641,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 let expected_ty = self.infcx.instantiate_binder_with_fresh_vars(
                     self.body().source_info(location).span,
                     BoundRegionConversionTime::HigherRankedType,
-                    binder_ty.into(),
+                    *binder_ty,
                 );
                 self.sub_types(
                     operand_ty,
@@ -1891,7 +1891,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 let found_ty = self.infcx.instantiate_binder_with_fresh_vars(
                     self.body.source_info(location).span,
                     BoundRegionConversionTime::HigherRankedType,
-                    binder_ty.into(),
+                    *binder_ty,
                 );
                 self.relate_types(
                     ty,

compiler/rustc_hir/src/hir.rs

@@ -990,6 +990,8 @@ pub struct WhereBoundPredicate<'hir> {
     pub origin: PredicateOrigin,
     /// Any generics from a `for` binding.
     pub bound_generic_params: &'hir [GenericParam<'hir>],
+    /// The `'a + Trait` in `for<T: 'a + Trait> ...`
+    pub bound_assumptions: &'hir [WherePredicate<'hir>],
     /// The type being bounded.
     pub bounded_ty: &'hir Ty<'hir>,
     /// Trait and lifetime bounds (e.g., `Clone + Send + 'static`).
@@ -3840,6 +3842,9 @@ pub struct PolyTraitRef<'hir> {
     /// The `'a` in `for<'a> Foo<&'a T>`.
     pub bound_generic_params: &'hir [GenericParam<'hir>],
 
+    /// The `'a + Trait` in `for<T: 'a + Trait> ...`
+    pub bound_assumptions: &'hir [WherePredicate<'hir>],
+
     /// The constness and polarity of the trait ref.
     ///
     /// The `async` modifier is lowered directly into a different trait for now.
@@ -4843,7 +4848,7 @@ mod size_asserts {
     static_assert_size!(ForeignItem<'_>, 88);
     static_assert_size!(ForeignItemKind<'_>, 56);
     static_assert_size!(GenericArg<'_>, 16);
-    static_assert_size!(GenericBound<'_>, 64);
+    static_assert_size!(GenericBound<'_>, 80);
     static_assert_size!(Generics<'_>, 56);
     static_assert_size!(Impl<'_>, 80);
     static_assert_size!(ImplItem<'_>, 88);

compiler/rustc_hir/src/intravisit.rs

@@ -1082,10 +1082,12 @@ pub fn walk_where_predicate<'v, V: Visitor<'v>>(
             ref bounded_ty,
             bounds,
             bound_generic_params,
+            bound_assumptions,
             origin: _,
         }) => {
             try_visit!(visitor.visit_ty_unambig(bounded_ty));
             walk_list!(visitor, visit_param_bound, bounds);
+            walk_list!(visitor, visit_where_predicate, bound_assumptions);
             walk_list!(visitor, visit_generic_param, bound_generic_params);
         }
         WherePredicateKind::RegionPredicate(WhereRegionPredicate {
@@ -1296,6 +1298,7 @@ pub fn walk_poly_trait_ref<'v, V: Visitor<'v>>(
     trait_ref: &'v PolyTraitRef<'v>,
 ) -> V::Result {
     walk_list!(visitor, visit_generic_param, trait_ref.bound_generic_params);
+    walk_list!(visitor, visit_where_predicate, trait_ref.bound_assumptions);
     visitor.visit_trait_ref(&trait_ref.trait_ref)
 }
 

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -37,7 +37,14 @@ fn associated_type_bounds<'tcx>(
 
         let icx = ItemCtxt::new(tcx, assoc_item_def_id);
         let mut bounds = Vec::new();
-        icx.lowerer().lower_bounds(item_ty, hir_bounds, &mut bounds, ty::List::empty(), filter);
+        icx.lowerer().lower_bounds(
+            item_ty,
+            hir_bounds,
+            &mut bounds,
+            ty::List::empty(),
+            ty::ListWithCachedTypeInfo::empty(),
+            filter,
+        );
         // Associated types are implicitly sized unless a `?Sized` bound is found
         match filter {
             PredicateFilter::All
@@ -326,7 +333,14 @@ fn opaque_type_bounds<'tcx>(
     ty::print::with_reduced_queries!({
         let icx = ItemCtxt::new(tcx, opaque_def_id);
         let mut bounds = Vec::new();
-        icx.lowerer().lower_bounds(item_ty, hir_bounds, &mut bounds, ty::List::empty(), filter);
+        icx.lowerer().lower_bounds(
+            item_ty,
+            hir_bounds,
+            &mut bounds,
+            ty::List::empty(),
+            ty::ListWithCachedTypeInfo::empty(),
+            filter,
+        );
         // Opaque types are implicitly sized unless a `?Sized` bound is found
         match filter {
             PredicateFilter::All