Auto merge of rust-lang#133397 - compiler-errors:fix-dyn-incompleteness, r=<try>

Fix dyn incompleteness with multiple supertraits with different substitutions

So much to write about this.

Fixes rust-lang#133361

r? `@ghost`

Author: bors

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -3,15 +3,14 @@ use rustc_errors::codes::*;
 use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::DefId;
 use rustc_lint_defs::builtin::UNUSED_ASSOCIATED_TYPE_BOUNDS;
 use rustc_middle::span_bug;
 use rustc_middle::ty::fold::BottomUpFolder;
 use rustc_middle::ty::{
     self, DynKind, ExistentialPredicateStableCmpExt as _, Ty, TyCtxt, TypeFoldable,
     TypeVisitableExt, Upcast,
 };
-use rustc_span::{ErrorGuaranteed, Span};
+use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
 use rustc_trait_selection::error_reporting::traits::report_dyn_incompatibility;
 use rustc_trait_selection::traits::{self, hir_ty_lowering_dyn_compatibility_violations};
 use rustc_type_ir::elaborate::ClauseWithSupertraitSpan;
@@ -62,7 +61,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }
 
         let mut trait_bounds = vec![];
-        let mut projection_bounds = vec![];
+        let mut projection_bounds = FxIndexMap::default();
         for (pred, span) in bounds.clauses() {
             let bound_pred = pred.kind();
             match bound_pred.skip_binder() {
@@ -71,7 +70,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     trait_bounds.push((bound_pred.rebind(trait_pred.trait_ref), span));
                 }
                 ty::ClauseKind::Projection(proj) => {
-                    projection_bounds.push((bound_pred.rebind(proj), span));
+                    let anon = tcx.anonymize_bound_vars(bound_pred.rebind(proj));
+                    projection_bounds.insert(anon, (bound_pred.rebind(proj), span));
                 }
                 ty::ClauseKind::TypeOutlives(_) => {
                     // Do nothing, we deal with regions separately
@@ -88,8 +88,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         // 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, trait_bounds.iter().map(|&(a, b)| (a, b)));
+        let mut trait_alias_projection_bounds = FxIndexSet::default();
+        let expanded_traits = traits::expand_trait_aliases(
+            tcx,
+            &mut trait_alias_projection_bounds,
+            trait_bounds.iter().map(|&(a, b)| (a, b)),
+        );
 
         let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
             expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
@@ -128,12 +132,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
         }
 
-        let mut associated_types: FxIndexMap<Span, FxIndexSet<DefId>> = FxIndexMap::default();
+        let mut needed_associated_types = FxIndexSet::default();
 
+        let principal_span = regular_traits.first().map_or(DUMMY_SP, |info| info.bottom().1);
         let regular_traits_refs_spans = trait_bounds
             .into_iter()
             .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()));
 
+        let mut implied_projection_bounds = vec![];
         for (base_trait_ref, original_span) in regular_traits_refs_spans {
             let base_pred: ty::Predicate<'tcx> = base_trait_ref.upcast(tcx);
             for ClauseWithSupertraitSpan { pred, supertrait_span } in
@@ -145,17 +151,28 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {
                     ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
-                        let pred = bound_predicate.rebind(pred);
-                        associated_types.entry(original_span).or_default().extend(
-                            tcx.associated_items(pred.def_id())
+                        // FIXME(negative_bounds): Handle this correctly...
+                        let trait_ref =
+                            tcx.anonymize_bound_vars(bound_predicate.rebind(pred.trait_ref));
+                        needed_associated_types.extend(
+                            tcx.associated_items(trait_ref.def_id())
                                 .in_definition_order()
                                 .filter(|item| item.kind == ty::AssocKind::Type)
                                 .filter(|item| !item.is_impl_trait_in_trait())
-                                .map(|item| item.def_id),
+                                // If the associated type has a `where Self: Sized` bound,
+                                // we do not need to constrain the associated type.
+                                .filter(|item| !tcx.generics_require_sized_self(item.def_id))
+                                .map(|item| (item.def_id, trait_ref)),
                         );
                     }
                     ty::PredicateKind::Clause(ty::ClauseKind::Projection(pred)) => {
                         let pred = bound_predicate.rebind(pred);
+
+                        let pred_key = tcx.anonymize_bound_vars(pred);
+                        if !trait_alias_projection_bounds.contains(&pred_key) {
+                            projection_bounds.shift_remove(&pred_key);
+                        }
+
                         // A `Self` within the original bound will be instantiated with a
                         // `trait_object_dummy_self`, so check for that.
                         let references_self = match pred.skip_binder().term.unpack() {
@@ -182,8 +199,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
                         // the discussion in #56288 for alternatives.
                         if !references_self {
-                            // Include projections defined on supertraits.
-                            projection_bounds.push((pred, original_span));
+                            if trait_alias_projection_bounds.contains(&pred_key) {
+                                // Include projections defined on supertraits.
+                                projection_bounds.insert(pred_key, (pred, supertrait_span));
+                            } else {
+                                // Include projections defined on supertraits.
+                                implied_projection_bounds.push(pred);
+                            }
                         }
 
                         self.check_elaborated_projection_mentions_input_lifetimes(
@@ -201,26 +223,32 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // So every `Projection` clause is an `Assoc = Foo` bound. `associated_types` contains all associated
         // types's `DefId`, so the following loop removes all the `DefIds` of the associated types that have a
         // corresponding `Projection` clause
-        for def_ids in associated_types.values_mut() {
-            for (projection_bound, span) in &projection_bounds {
-                let def_id = projection_bound.projection_def_id();
-                def_ids.swap_remove(&def_id);
-                if tcx.generics_require_sized_self(def_id) {
-                    tcx.emit_node_span_lint(
-                        UNUSED_ASSOCIATED_TYPE_BOUNDS,
-                        hir_id,
-                        *span,
-                        crate::errors::UnusedAssociatedTypeBounds { span: *span },
-                    );
-                }
+        for (projection_bound, span) in projection_bounds.values() {
+            let def_id = projection_bound.projection_def_id();
+            let trait_ref = tcx.anonymize_bound_vars(
+                projection_bound.map_bound(|p| p.projection_term.trait_ref(tcx)),
+            );
+            needed_associated_types.swap_remove(&(def_id, trait_ref));
+            if tcx.generics_require_sized_self(def_id) {
+                tcx.emit_node_span_lint(
+                    UNUSED_ASSOCIATED_TYPE_BOUNDS,
+                    hir_id,
+                    *span,
+                    crate::errors::UnusedAssociatedTypeBounds { span: *span },
+                );
             }
-            // If the associated type has a `where Self: Sized` bound, we do not need to constrain the associated
-            // type in the `dyn Trait`.
-            def_ids.retain(|def_id| !tcx.generics_require_sized_self(def_id));
+        }
+        for projection_bound in &implied_projection_bounds {
+            let def_id = projection_bound.projection_def_id();
+            let trait_ref = tcx.anonymize_bound_vars(
+                projection_bound.map_bound(|p| p.projection_term.trait_ref(tcx)),
+            );
+            needed_associated_types.swap_remove(&(def_id, trait_ref));
         }
 
         self.complain_about_missing_assoc_tys(
-            associated_types,
+            principal_span,
+            needed_associated_types,
             potential_assoc_types,
             hir_trait_bounds,
         );
@@ -302,7 +330,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             })
         });
 
-        let existential_projections = projection_bounds.iter().map(|(bound, _)| {
+        let existential_projections = projection_bounds.values().map(|(bound, _)| {
             bound.map_bound(|mut b| {
                 assert_eq!(b.projection_term.self_ty(), dummy_self);