Rollup merge of rust-lang#129725 - compiler-errors:predicates-of, r=f…

…mease

Stop using `ty::GenericPredicates` for non-predicates_of queries

`GenericPredicates` is a struct of several parts: A list of of an item's own predicates, and a parent def id (and some effects related stuff, but ignore that since it's kinda irrelevant). When instantiating these generic predicates, it calls `predicates_of` on the parent and instantiates its predicates, and appends the item's own instantiated predicates too:

https://github.com/rust-lang/rust/blob/acb4e8b6251f1d8da36f08e7a70fa23fc581839e/compiler/rustc_middle/src/ty/generics.rs#L407-L413

Notice how this should result in a recursive set of calls to `predicates_of`... However, `GenericPredicates` is *also* misused by a bunch of *other* queries as a convenient way of passing around a list of predicates. For these queries, we don't ever set the parent def id of the `GenericPredicates`, but if we did, then this would be very easy to mistakenly call `predicates_of` instead of some other intended parent query.

Given that footgun, and the fact that we don't ever even *use* the parent def id in the `GenericPredicates` returned from queries like `explicit_super_predicates_of`, It really has no benefit over just returning `&'tcx [(Clause<'tcx>, Span)]`.

This PR additionally opts to wrap the results of `EarlyBinder`, as we've tended to use that in the return type of these kinds of queries to properly convey that the user has params to deal with, and it also gives a convenient way of iterating over a slice of things after instantiating.

compiler/rustc_hir_analysis/src/collect.rs

@@ -420,7 +420,7 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
         span: Span,
         def_id: LocalDefId,
         assoc_name: Ident,
-    ) -> ty::GenericPredicates<'tcx> {
+    ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
         self.tcx.at(span).type_param_predicates((self.item_def_id, def_id, assoc_name))
     }
 

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -580,24 +580,24 @@ pub(super) fn explicit_predicates_of<'tcx>(
 /// Ensures that the super-predicates of the trait with a `DefId`
 /// of `trait_def_id` are lowered and stored. This also ensures that
 /// the transitive super-predicates are lowered.
-pub(super) fn explicit_super_predicates_of(
-    tcx: TyCtxt<'_>,
+pub(super) fn explicit_super_predicates_of<'tcx>(
+    tcx: TyCtxt<'tcx>,
     trait_def_id: LocalDefId,
-) -> ty::GenericPredicates<'_> {
+) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     implied_predicates_with_filter(tcx, trait_def_id.to_def_id(), PredicateFilter::SelfOnly)
 }
 
-pub(super) fn explicit_supertraits_containing_assoc_item(
-    tcx: TyCtxt<'_>,
+pub(super) fn explicit_supertraits_containing_assoc_item<'tcx>(
+    tcx: TyCtxt<'tcx>,
     (trait_def_id, assoc_name): (DefId, Ident),
-) -> ty::GenericPredicates<'_> {
+) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     implied_predicates_with_filter(tcx, trait_def_id, PredicateFilter::SelfThatDefines(assoc_name))
 }
 
-pub(super) fn explicit_implied_predicates_of(
-    tcx: TyCtxt<'_>,
+pub(super) fn explicit_implied_predicates_of<'tcx>(
+    tcx: TyCtxt<'tcx>,
     trait_def_id: LocalDefId,
-) -> ty::GenericPredicates<'_> {
+) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     implied_predicates_with_filter(
         tcx,
         trait_def_id.to_def_id(),
@@ -612,11 +612,11 @@ pub(super) fn explicit_implied_predicates_of(
 /// Ensures that the super-predicates of the trait with a `DefId`
 /// of `trait_def_id` are lowered and stored. This also ensures that
 /// the transitive super-predicates are lowered.
-pub(super) fn implied_predicates_with_filter(
-    tcx: TyCtxt<'_>,
+pub(super) fn implied_predicates_with_filter<'tcx>(
+    tcx: TyCtxt<'tcx>,
     trait_def_id: DefId,
     filter: PredicateFilter,
-) -> ty::GenericPredicates<'_> {
+) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     let Some(trait_def_id) = trait_def_id.as_local() else {
         // if `assoc_name` is None, then the query should've been redirected to an
         // external provider
@@ -679,20 +679,16 @@ pub(super) fn implied_predicates_with_filter(
         _ => {}
     }
 
-    ty::GenericPredicates {
-        parent: None,
-        predicates: implied_bounds,
-        effects_min_tys: ty::List::empty(),
-    }
+    ty::EarlyBinder::bind(implied_bounds)
 }
 
 /// Returns the predicates defined on `item_def_id` of the form
 /// `X: Foo` where `X` is the type parameter `def_id`.
 #[instrument(level = "trace", skip(tcx))]
-pub(super) fn type_param_predicates(
-    tcx: TyCtxt<'_>,
+pub(super) fn type_param_predicates<'tcx>(
+    tcx: TyCtxt<'tcx>,
     (item_def_id, def_id, assoc_name): (LocalDefId, LocalDefId, Ident),
-) -> ty::GenericPredicates<'_> {
+) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     use rustc_hir::*;
     use rustc_middle::ty::Ty;
 
@@ -713,18 +709,20 @@ pub(super) fn type_param_predicates(
         tcx.generics_of(item_def_id).parent.map(|def_id| def_id.expect_local())
     };
 
-    let mut result = parent
-        .map(|parent| {
-            let icx = ItemCtxt::new(tcx, parent);
-            icx.probe_ty_param_bounds(DUMMY_SP, def_id, assoc_name)
-        })
-        .unwrap_or_default();
+    let result = if let Some(parent) = parent {
+        let icx = ItemCtxt::new(tcx, parent);
+        icx.probe_ty_param_bounds(DUMMY_SP, def_id, assoc_name)
+    } else {
+        ty::EarlyBinder::bind(&[] as &[_])
+    };
     let mut extend = None;
 
     let item_hir_id = tcx.local_def_id_to_hir_id(item_def_id);
 
     let hir_node = tcx.hir_node(item_hir_id);
-    let Some(hir_generics) = hir_node.generics() else { return result };
+    let Some(hir_generics) = hir_node.generics() else {
+        return result;
+    };
     if let Node::Item(item) = hir_node
         && let ItemKind::Trait(..) = item.kind
         // Implied `Self: Trait` and supertrait bounds.
@@ -748,9 +746,10 @@ pub(super) fn type_param_predicates(
             _ => false,
         }),
     );
-    result.predicates =
-        tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
-    result
+
+    ty::EarlyBinder::bind(
+        tcx.arena.alloc_from_iter(result.skip_binder().iter().copied().chain(extra_predicates)),
+    )
 }
 
 impl<'tcx> ItemCtxt<'tcx> {

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1761,7 +1761,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                 break Some((bound_vars.into_iter().collect(), assoc_item));
             }
             let predicates = tcx.explicit_supertraits_containing_assoc_item((def_id, assoc_name));
-            let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
+            let obligations = predicates.iter_identity_copied().filter_map(|(pred, _)| {
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {
                     ty::ClauseKind::Trait(data) => {

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -136,7 +136,7 @@ pub trait HirTyLowerer<'tcx> {
         span: Span,
         def_id: LocalDefId,
         assoc_name: Ident,
-    ) -> ty::GenericPredicates<'tcx>;
+    ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]>;
 
     /// Lower an associated type to a projection.
     ///
@@ -831,13 +831,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         debug!(?ty_param_def_id, ?assoc_name, ?span);
         let tcx = self.tcx();
 
-        let predicates = &self.probe_ty_param_bounds(span, ty_param_def_id, assoc_name).predicates;
+        let predicates = &self.probe_ty_param_bounds(span, ty_param_def_id, assoc_name);
         debug!("predicates={:#?}", predicates);
 
         self.probe_single_bound_for_assoc_item(
             || {
                 let trait_refs = predicates
-                    .iter()
+                    .iter_identity_copied()
                     .filter_map(|(p, _)| Some(p.as_trait_clause()?.map_bound(|t| t.trait_ref)));
                 traits::transitive_bounds_that_define_assoc_item(tcx, trait_refs, assoc_name)
             },

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -263,27 +263,24 @@ impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
         _: Span,
         def_id: LocalDefId,
         _: Ident,
-    ) -> ty::GenericPredicates<'tcx> {
+    ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
         let tcx = self.tcx;
         let item_def_id = tcx.hir().ty_param_owner(def_id);
         let generics = tcx.generics_of(item_def_id);
         let index = generics.param_def_id_to_index[&def_id.to_def_id()];
         // HACK(eddyb) should get the original `Span`.
         let span = tcx.def_span(def_id);
-        ty::GenericPredicates {
-            parent: None,
-            predicates: tcx.arena.alloc_from_iter(
-                self.param_env.caller_bounds().iter().filter_map(|predicate| {
-                    match predicate.kind().skip_binder() {
-                        ty::ClauseKind::Trait(data) if data.self_ty().is_param(index) => {
-                            Some((predicate, span))
-                        }
-                        _ => None,
+
+        ty::EarlyBinder::bind(tcx.arena.alloc_from_iter(
+            self.param_env.caller_bounds().iter().filter_map(|predicate| {
+                match predicate.kind().skip_binder() {
+                    ty::ClauseKind::Trait(data) if data.self_ty().is_param(index) => {
+                        Some((predicate, span))
                     }
-                }),
-            ),
-            effects_min_tys: ty::List::empty(),
-        }
+                    _ => None,
+                }
+            }),
+        ))
     }
 
     fn lower_assoc_ty(

compiler/rustc_infer/src/traits/util.rs

@@ -123,7 +123,7 @@ pub fn transitive_bounds_that_define_assoc_item<'tcx>(
 
             stack.extend(
                 tcx.explicit_supertraits_containing_assoc_item((trait_ref.def_id(), assoc_name))
-                    .instantiate_own_identity()
+                    .iter_identity_copied()
                     .map(|(clause, _)| clause.instantiate_supertrait(tcx, trait_ref))
                     .filter_map(|clause| clause.as_trait_clause())
                     // FIXME: Negative supertraits are elaborated here lol

compiler/rustc_lint/src/multiple_supertrait_upcastable.rs

@@ -45,8 +45,7 @@ impl<'tcx> LateLintPass<'tcx> for MultipleSupertraitUpcastable {
             let direct_super_traits_iter = cx
                 .tcx
                 .explicit_super_predicates_of(def_id)
-                .predicates
-                .into_iter()
+                .iter_identity_copied()
                 .filter_map(|(pred, _)| pred.as_trait_clause());
             if direct_super_traits_iter.count() > 1 {
                 cx.emit_span_lint(

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -76,6 +76,24 @@ impl<'a, 'tcx, T: Copy + Decodable<DecodeContext<'a, 'tcx>>> ProcessQueryValue<'
     }
 }
 
+impl<'a, 'tcx, T: Copy + Decodable<DecodeContext<'a, 'tcx>>>
+    ProcessQueryValue<'tcx, ty::EarlyBinder<'tcx, &'tcx [T]>>
+    for Option<DecodeIterator<'a, 'tcx, T>>
+{
+    #[inline(always)]
+    fn process_decoded(
+        self,
+        tcx: TyCtxt<'tcx>,
+        _err: impl Fn() -> !,
+    ) -> ty::EarlyBinder<'tcx, &'tcx [T]> {
+        ty::EarlyBinder::bind(if let Some(iter) = self {
+            tcx.arena.alloc_from_iter(iter)
+        } else {
+            &[]
+        })
+    }
+}
+
 impl<'a, 'tcx, T: Copy + Decodable<DecodeContext<'a, 'tcx>>>
     ProcessQueryValue<'tcx, Option<&'tcx [T]>> for Option<DecodeIterator<'a, 'tcx, T>>
 {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1446,17 +1446,21 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             }
             if let DefKind::Trait = def_kind {
                 record!(self.tables.trait_def[def_id] <- self.tcx.trait_def(def_id));
-                record!(self.tables.explicit_super_predicates_of[def_id] <- self.tcx.explicit_super_predicates_of(def_id));
-                record!(self.tables.explicit_implied_predicates_of[def_id] <- self.tcx.explicit_implied_predicates_of(def_id));
+                record_array!(self.tables.explicit_super_predicates_of[def_id] <-
+                    self.tcx.explicit_super_predicates_of(def_id).skip_binder());
+                record_array!(self.tables.explicit_implied_predicates_of[def_id] <-
+                    self.tcx.explicit_implied_predicates_of(def_id).skip_binder());
 
                 let module_children = self.tcx.module_children_local(local_id);
                 record_array!(self.tables.module_children_non_reexports[def_id] <-
                     module_children.iter().map(|child| child.res.def_id().index));
             }
             if let DefKind::TraitAlias = def_kind {
                 record!(self.tables.trait_def[def_id] <- self.tcx.trait_def(def_id));
-                record!(self.tables.explicit_super_predicates_of[def_id] <- self.tcx.explicit_super_predicates_of(def_id));
-                record!(self.tables.explicit_implied_predicates_of[def_id] <- self.tcx.explicit_implied_predicates_of(def_id));
+                record_array!(self.tables.explicit_super_predicates_of[def_id] <-
+                    self.tcx.explicit_super_predicates_of(def_id).skip_binder());
+                record_array!(self.tables.explicit_implied_predicates_of[def_id] <-
+                    self.tcx.explicit_implied_predicates_of(def_id).skip_binder());
             }
             if let DefKind::Trait | DefKind::Impl { .. } = def_kind {
                 let associated_item_def_ids = self.tcx.associated_item_def_ids(def_id);

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -419,10 +419,10 @@ define_tables! {
     lookup_deprecation_entry: Table<DefIndex, LazyValue<attr::Deprecation>>,
     explicit_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
     generics_of: Table<DefIndex, LazyValue<ty::Generics>>,
-    explicit_super_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
+    explicit_super_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
     // As an optimization, we only store this for trait aliases,
     // since it's identical to explicit_super_predicates_of for traits.
-    explicit_implied_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
+    explicit_implied_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
     type_of: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, Ty<'static>>>>,
     variances_of: Table<DefIndex, LazyArray<ty::Variance>>,
     fn_sig: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, ty::PolyFnSig<'static>>>>,

compiler/rustc_middle/src/query/mod.rs

@@ -651,7 +651,7 @@ rustc_queries! {
     /// is a subset of the full list of predicates. We store these in a separate map
     /// because we must evaluate them even during type conversion, often before the full
     /// predicates are available (note that super-predicates must not be cyclic).
-    query explicit_super_predicates_of(key: DefId) -> ty::GenericPredicates<'tcx> {
+    query explicit_super_predicates_of(key: DefId) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
         desc { |tcx| "computing the super predicates of `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
@@ -662,7 +662,7 @@ rustc_queries! {
     /// of the trait. For regular traits, this includes all super-predicates and their
     /// associated type bounds. For trait aliases, currently, this includes all of the
     /// predicates of the trait alias.
-    query explicit_implied_predicates_of(key: DefId) -> ty::GenericPredicates<'tcx> {
+    query explicit_implied_predicates_of(key: DefId) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
         desc { |tcx| "computing the implied predicates of `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
@@ -671,7 +671,9 @@ rustc_queries! {
     /// The Ident is the name of an associated type.The query returns only the subset
     /// of supertraits that define the given associated type. This is used to avoid
     /// cycles in resolving type-dependent associated item paths like `T::Item`.
-    query explicit_supertraits_containing_assoc_item(key: (DefId, rustc_span::symbol::Ident)) -> ty::GenericPredicates<'tcx> {
+    query explicit_supertraits_containing_assoc_item(
+        key: (DefId, rustc_span::symbol::Ident)
+    ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
         desc { |tcx| "computing the super traits of `{}` with associated type name `{}`",
             tcx.def_path_str(key.0),
             key.1
@@ -680,7 +682,9 @@ rustc_queries! {
 
     /// To avoid cycles within the predicates of a single item we compute
     /// per-type-parameter predicates for resolving `T::AssocTy`.
-    query type_param_predicates(key: (LocalDefId, LocalDefId, rustc_span::symbol::Ident)) -> ty::GenericPredicates<'tcx> {
+    query type_param_predicates(
+        key: (LocalDefId, LocalDefId, rustc_span::symbol::Ident)
+    ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
         desc { |tcx| "computing the bounds for type parameter `{}`", tcx.hir().ty_param_name(key.1) }
     }
 

compiler/rustc_middle/src/ty/context.rs

@@ -349,16 +349,14 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self,
         def_id: DefId,
     ) -> ty::EarlyBinder<'tcx, impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>> {
-        ty::EarlyBinder::bind(self.explicit_super_predicates_of(def_id).instantiate_identity(self))
+        self.explicit_super_predicates_of(def_id).map_bound(|preds| preds.into_iter().copied())
     }
 
     fn explicit_implied_predicates_of(
         self,
         def_id: DefId,
     ) -> ty::EarlyBinder<'tcx, impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>> {
-        ty::EarlyBinder::bind(
-            self.explicit_implied_predicates_of(def_id).instantiate_identity(self),
-        )
+        self.explicit_implied_predicates_of(def_id).map_bound(|preds| preds.into_iter().copied())
     }
 
     fn has_target_features(self, def_id: DefId) -> bool {

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -185,12 +185,11 @@ fn predicates_reference_self(
 ) -> SmallVec<[Span; 1]> {
     let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_def_id));
     let predicates = if supertraits_only {
-        tcx.explicit_super_predicates_of(trait_def_id)
+        tcx.explicit_super_predicates_of(trait_def_id).skip_binder()
     } else {
-        tcx.predicates_of(trait_def_id)
+        tcx.predicates_of(trait_def_id).predicates
     };
     predicates
-        .predicates
         .iter()
         .map(|&(predicate, sp)| (predicate.instantiate_supertrait(tcx, trait_ref), sp))
         .filter_map(|(clause, sp)| {
@@ -266,9 +265,8 @@ fn super_predicates_have_non_lifetime_binders(
         return SmallVec::new();
     }
     tcx.explicit_super_predicates_of(trait_def_id)
-        .predicates
-        .iter()
-        .filter_map(|(pred, span)| pred.has_non_region_bound_vars().then_some(*span))
+        .iter_identity_copied()
+        .filter_map(|(pred, span)| pred.has_non_region_bound_vars().then_some(span))
         .collect()
 }
 

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -600,21 +600,19 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         // Check supertraits hold. This is so that their associated type bounds
         // will be checked in the code below.
-        for super_trait in tcx
+        for (supertrait, _) in tcx
             .explicit_super_predicates_of(trait_predicate.def_id())
-            .instantiate(tcx, trait_predicate.trait_ref.args)
-            .predicates
-            .into_iter()
+            .iter_instantiated_copied(tcx, trait_predicate.trait_ref.args)
         {
-            let normalized_super_trait = normalize_with_depth_to(
+            let normalized_supertrait = normalize_with_depth_to(
                 self,
                 obligation.param_env,
                 obligation.cause.clone(),
                 obligation.recursion_depth + 1,
-                super_trait,
+                supertrait,
                 &mut nested,
             );
-            nested.push(obligation.with(tcx, normalized_super_trait));
+            nested.push(obligation.with(tcx, normalized_supertrait));
         }
 
         let assoc_types: Vec<_> = tcx