Auto merge of rust-lang#106235 - compiler-errors:rework-bounds-collection, r=davidtwco

Rework `Bounds` collection

I think it's weird for the `Bounds` struct in astconv to store its predicates *almost* converted into real predicates... so we do this eagerly, instead of lazily.

Author: bors

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -682,7 +682,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             ty::Binder::bind_with_vars(tcx.mk_trait_ref(trait_def_id, substs), bound_vars);
 
         debug!(?poly_trait_ref, ?assoc_bindings);
-        bounds.trait_bounds.push((poly_trait_ref, span, constness));
+        bounds.push_trait_bound(tcx, poly_trait_ref, span, constness);
 
         let mut dup_bindings = FxHashMap::default();
         for binding in &assoc_bindings {
@@ -853,18 +853,19 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     }
 
     /// Sets `implicitly_sized` to true on `Bounds` if necessary
-    pub(crate) fn add_implicitly_sized<'hir>(
+    pub(crate) fn add_implicitly_sized(
         &self,
-        bounds: &mut Bounds<'hir>,
-        ast_bounds: &'hir [hir::GenericBound<'hir>],
-        self_ty_where_predicates: Option<(LocalDefId, &'hir [hir::WherePredicate<'hir>])>,
+        bounds: &mut Bounds<'tcx>,
+        self_ty: Ty<'tcx>,
+        ast_bounds: &'tcx [hir::GenericBound<'tcx>],
+        self_ty_where_predicates: Option<(LocalDefId, &'tcx [hir::WherePredicate<'tcx>])>,
         span: Span,
     ) {
         let tcx = self.tcx();
 
         // Try to find an unbound in bounds.
         let mut unbound = None;
-        let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
+        let mut search_bounds = |ast_bounds: &'tcx [hir::GenericBound<'tcx>]| {
             for ab in ast_bounds {
                 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
                     if unbound.is_none() {
@@ -912,7 +913,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             // No lang item for `Sized`, so we can't add it as a bound.
             return;
         }
-        bounds.implicitly_sized = Some(span);
+        bounds.push_sized(tcx, self_ty, span);
     }
 
     /// This helper takes a *converted* parameter type (`param_ty`)
@@ -963,10 +964,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }
                 hir::GenericBound::Outlives(lifetime) => {
                     let region = self.ast_region_to_region(lifetime, None);
-                    bounds.region_bounds.push((
-                        ty::Binder::bind_with_vars(region, bound_vars),
+                    bounds.push_region_bound(
+                        self.tcx(),
+                        ty::Binder::bind_with_vars(
+                            ty::OutlivesPredicate(param_ty, region),
+                            bound_vars,
+                        ),
                         lifetime.ident.span,
-                    ));
+                    );
                 }
             }
         }
@@ -1234,13 +1239,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         };
                     }
                 }
-                bounds.projection_bounds.push((
-                    projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
-                        projection_ty,
-                        term: term,
-                    }),
+                bounds.push_projection_bound(
+                    tcx,
+                    projection_ty
+                        .map_bound(|projection_ty| ty::ProjectionPredicate { projection_ty, term }),
                     binding.span,
-                ));
+                );
             }
             ConvertedBindingKind::Constraint(ast_bounds) => {
                 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
@@ -1269,7 +1273,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     fn conv_object_ty_poly_trait_ref(
         &self,
         span: Span,
-        trait_bounds: &[hir::PolyTraitRef<'_>],
+        hir_trait_bounds: &[hir::PolyTraitRef<'_>],
         lifetime: &hir::Lifetime,
         borrowed: bool,
         representation: DynKind,
@@ -1279,7 +1283,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let mut bounds = Bounds::default();
         let mut potential_assoc_types = Vec::new();
         let dummy_self = self.tcx().types.trait_object_dummy_self;
-        for trait_bound in trait_bounds.iter().rev() {
+        for trait_bound in hir_trait_bounds.iter().rev() {
             if let GenericArgCountResult {
                 correct:
                     Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
@@ -1296,10 +1300,45 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
 
+        let mut trait_bounds = vec![];
+        let mut projection_bounds = vec![];
+        for (pred, span) in bounds.predicates() {
+            let bound_pred = pred.kind();
+            match bound_pred.skip_binder() {
+                ty::PredicateKind::Clause(clause) => match clause {
+                    ty::Clause::Trait(trait_pred) => {
+                        assert_eq!(trait_pred.polarity, ty::ImplPolarity::Positive);
+                        trait_bounds.push((
+                            bound_pred.rebind(trait_pred.trait_ref),
+                            span,
+                            trait_pred.constness,
+                        ));
+                    }
+                    ty::Clause::Projection(proj) => {
+                        projection_bounds.push((bound_pred.rebind(proj), span));
+                    }
+                    ty::Clause::TypeOutlives(_) => {
+                        // Do nothing, we deal with regions separately
+                    }
+                    ty::Clause::RegionOutlives(_) => bug!(),
+                },
+                ty::PredicateKind::WellFormed(_)
+                | ty::PredicateKind::ObjectSafe(_)
+                | ty::PredicateKind::ClosureKind(_, _, _)
+                | ty::PredicateKind::Subtype(_)
+                | ty::PredicateKind::Coerce(_)
+                | ty::PredicateKind::ConstEvaluatable(_)
+                | ty::PredicateKind::ConstEquate(_, _)
+                | ty::PredicateKind::TypeWellFormedFromEnv(_)
+                | ty::PredicateKind::Ambiguous => bug!(),
+            }
+        }
+
         // Expand trait aliases recursively and check that only one regular (non-auto) trait
         // is used and no 'maybe' bounds are used.
         let expanded_traits =
-            traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
+            traits::expand_trait_aliases(tcx, trait_bounds.iter().map(|&(a, b, _)| (a, b)));
+
         let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
             .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
             .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
@@ -1336,8 +1375,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
 
         if regular_traits.is_empty() && auto_traits.is_empty() {
-            let trait_alias_span = bounds
-                .trait_bounds
+            let trait_alias_span = trait_bounds
                 .iter()
                 .map(|&(trait_ref, _, _)| trait_ref.def_id())
                 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
@@ -1368,8 +1406,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         // Use a `BTreeSet` to keep output in a more consistent order.
         let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
 
-        let regular_traits_refs_spans = bounds
-            .trait_bounds
+        let regular_traits_refs_spans = trait_bounds
             .into_iter()
             .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
 
@@ -1423,15 +1460,15 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         // the discussion in #56288 for alternatives.
                         if !references_self {
                             // Include projections defined on supertraits.
-                            bounds.projection_bounds.push((pred, span));
+                            projection_bounds.push((pred, span));
                         }
                     }
                     _ => (),
                 }
             }
         }
 
-        for (projection_bound, _) in &bounds.projection_bounds {
+        for (projection_bound, _) in &projection_bounds {
             for def_ids in associated_types.values_mut() {
                 def_ids.remove(&projection_bound.projection_def_id());
             }
@@ -1440,7 +1477,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self.complain_about_missing_associated_types(
             associated_types,
             potential_assoc_types,
-            trait_bounds,
+            hir_trait_bounds,
         );
 
         // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
@@ -1482,7 +1519,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let substs = tcx.intern_substs(&substs[..]);
 
                 let span = i.bottom().1;
-                let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
+                let empty_generic_args = hir_trait_bounds.iter().any(|hir_bound| {
                     hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
                         && hir_bound.span.contains(span)
                 });
@@ -1514,7 +1551,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             })
         });
 
-        let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
+        let existential_projections = projection_bounds.iter().map(|(bound, _)| {
             bound.map_bound(|mut b| {
                 assert_eq!(b.projection_ty.self_ty(), dummy_self);
 

compiler/rustc_hir_analysis/src/bounds.rs

@@ -1,6 +1,7 @@
 //! Bounds are restrictions applied to some types after they've been converted into the
 //! `ty` form from the HIR.
 
+use rustc_hir::LangItem;
 use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use rustc_span::Span;
 
@@ -15,73 +16,53 @@ use rustc_span::Span;
 ///           ^^^^^^^^^ bounding the type parameter `T`
 ///
 /// impl dyn Bar + Baz
-///          ^^^^^^^^^ bounding the forgotten dynamic type
+///          ^^^^^^^^^ bounding the type-erased dynamic type
 /// ```
 ///
 /// Our representation is a bit mixed here -- in some cases, we
 /// include the self type (e.g., `trait_bounds`) but in others we do not
 #[derive(Default, PartialEq, Eq, Clone, Debug)]
 pub struct Bounds<'tcx> {
-    /// A list of region bounds on the (implicit) self type. So if you
-    /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
-    /// the `T` is not explicitly included).
-    pub region_bounds: Vec<(ty::Binder<'tcx, ty::Region<'tcx>>, Span)>,
-
-    /// A list of trait bounds. So if you had `T: Debug` this would be
-    /// `T: Debug`. Note that the self-type is explicit here.
-    pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, ty::BoundConstness)>,
-
-    /// A list of projection equality bounds. So if you had `T:
-    /// Iterator<Item = u32>` this would include `<T as
-    /// Iterator>::Item => u32`. Note that the self-type is explicit
-    /// here.
-    pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
-
-    /// `Some` if there is *no* `?Sized` predicate. The `span`
-    /// is the location in the source of the `T` declaration which can
-    /// be cited as the source of the `T: Sized` requirement.
-    pub implicitly_sized: Option<Span>,
+    pub predicates: Vec<(ty::Predicate<'tcx>, Span)>,
 }
 
 impl<'tcx> Bounds<'tcx> {
-    /// Converts a bounds list into a flat set of predicates (like
-    /// where-clauses). Because some of our bounds listings (e.g.,
-    /// regions) don't include the self-type, you must supply the
-    /// self-type here (the `param_ty` parameter).
-    pub fn predicates<'out, 's>(
-        &'s self,
+    pub fn push_region_bound(
+        &mut self,
         tcx: TyCtxt<'tcx>,
-        param_ty: Ty<'tcx>,
-        // the output must live shorter than the duration of the borrow of self and 'tcx.
-    ) -> impl Iterator<Item = (ty::Predicate<'tcx>, Span)> + 'out
-    where
-        'tcx: 'out,
-        's: 'out,
-    {
-        // If it could be sized, and is, add the `Sized` predicate.
-        let sized_predicate = self.implicitly_sized.and_then(|span| {
-            // FIXME: use tcx.at(span).mk_trait_ref(LangItem::Sized) here? This may make no-core code harder to write.
-            let sized = tcx.lang_items().sized_trait()?;
-            let trait_ref = ty::Binder::dummy(tcx.mk_trait_ref(sized, [param_ty]));
-            Some((trait_ref.without_const().to_predicate(tcx), span))
-        });
+        region: ty::PolyTypeOutlivesPredicate<'tcx>,
+        span: Span,
+    ) {
+        self.predicates.push((region.to_predicate(tcx), span));
+    }
 
-        let region_preds = self.region_bounds.iter().map(move |&(region_bound, span)| {
-            let pred = region_bound
-                .map_bound(|region_bound| ty::OutlivesPredicate(param_ty, region_bound))
-                .to_predicate(tcx);
-            (pred, span)
-        });
-        let trait_bounds =
-            self.trait_bounds.iter().map(move |&(bound_trait_ref, span, constness)| {
-                let predicate = bound_trait_ref.with_constness(constness).to_predicate(tcx);
-                (predicate, span)
-            });
-        let projection_bounds = self
-            .projection_bounds
-            .iter()
-            .map(move |&(projection, span)| (projection.to_predicate(tcx), span));
+    pub fn push_trait_bound(
+        &mut self,
+        tcx: TyCtxt<'tcx>,
+        trait_ref: ty::PolyTraitRef<'tcx>,
+        span: Span,
+        constness: ty::BoundConstness,
+    ) {
+        self.predicates.push((trait_ref.with_constness(constness).to_predicate(tcx), span));
+    }
+
+    pub fn push_projection_bound(
+        &mut self,
+        tcx: TyCtxt<'tcx>,
+        projection: ty::PolyProjectionPredicate<'tcx>,
+        span: Span,
+    ) {
+        self.predicates.push((projection.to_predicate(tcx), span));
+    }
+
+    pub fn push_sized(&mut self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span) {
+        let sized_def_id = tcx.require_lang_item(LangItem::Sized, Some(span));
+        let trait_ref = ty::Binder::dummy(tcx.mk_trait_ref(sized_def_id, [ty]));
+        // Preferrable to put this obligation first, since we report better errors for sized ambiguity.
+        self.predicates.insert(0, (trait_ref.without_const().to_predicate(tcx), span));
+    }
 
-        sized_predicate.into_iter().chain(region_preds).chain(trait_bounds).chain(projection_bounds)
+    pub fn predicates(&self) -> impl Iterator<Item = (ty::Predicate<'tcx>, Span)> + '_ {
+        self.predicates.iter().cloned()
     }
 }

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -28,7 +28,7 @@ fn associated_type_bounds<'tcx>(
     let icx = ItemCtxt::new(tcx, assoc_item_def_id);
     let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, item_ty, ast_bounds);
     // Associated types are implicitly sized unless a `?Sized` bound is found
-    <dyn AstConv<'_>>::add_implicitly_sized(&icx, &mut bounds, ast_bounds, None, span);
+    <dyn AstConv<'_>>::add_implicitly_sized(&icx, &mut bounds, item_ty, ast_bounds, None, span);
 
     let trait_def_id = tcx.parent(assoc_item_def_id);
     let trait_predicates = tcx.trait_explicit_predicates_and_bounds(trait_def_id.expect_local());
@@ -44,9 +44,7 @@ fn associated_type_bounds<'tcx>(
         }
     });
 
-    let all_bounds = tcx
-        .arena
-        .alloc_from_iter(bounds.predicates(tcx, item_ty).into_iter().chain(bounds_from_parent));
+    let all_bounds = tcx.arena.alloc_from_iter(bounds.predicates().chain(bounds_from_parent));
     debug!("associated_type_bounds({}) = {:?}", tcx.def_path_str(assoc_item_def_id), all_bounds);
     all_bounds
 }
@@ -74,10 +72,10 @@ fn opaque_type_bounds<'tcx>(
         let icx = ItemCtxt::new(tcx, opaque_def_id);
         let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, item_ty, ast_bounds);
         // Opaque types are implicitly sized unless a `?Sized` bound is found
-        <dyn AstConv<'_>>::add_implicitly_sized(&icx, &mut bounds, ast_bounds, None, span);
+        <dyn AstConv<'_>>::add_implicitly_sized(&icx, &mut bounds, item_ty, ast_bounds, None, span);
         debug!(?bounds);
 
-        tcx.arena.alloc_from_iter(bounds.predicates(tcx, item_ty))
+        tcx.arena.alloc_from_iter(bounds.predicates())
     })
 }