Rollup merge of #112867 - compiler-errors:more-impl-source-nits, r=lcnr

More `ImplSource` nits

Even more clean-ups, I'll put this up in parallel with the `select_in_new_trait_solver` PR.

r? ``@lcnr``

8 files changed, 47 insertions, 106 deletions

diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index f0380204970..a333fbbb506 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -660,9 +660,6 @@ pub enum ImplSource<'tcx, N> {
 
     /// ImplSource for trait upcasting coercion
     TraitUpcasting(ImplSourceTraitUpcastingData<N>),
-
-    /// ImplSource for a trait alias.
-    TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
 }
 
 impl<'tcx, N> ImplSource<'tcx, N> {
@@ -671,7 +668,6 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::UserDefined(i) => i.nested,
             ImplSource::Param(n, _) | ImplSource::Builtin(n) => n,
             ImplSource::Object(d) => d.nested,
-            ImplSource::TraitAlias(d) => d.nested,
             ImplSource::TraitUpcasting(d) => d.nested,
         }
     }
@@ -681,7 +677,6 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::UserDefined(i) => &i.nested,
             ImplSource::Param(n, _) | ImplSource::Builtin(n) => &n,
             ImplSource::Object(d) => &d.nested,
-            ImplSource::TraitAlias(d) => &d.nested,
             ImplSource::TraitUpcasting(d) => &d.nested,
         }
     }
@@ -691,7 +686,6 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::UserDefined(i) => &mut i.nested,
             ImplSource::Param(n, _) | ImplSource::Builtin(n) => n,
             ImplSource::Object(d) => &mut d.nested,
-            ImplSource::TraitAlias(d) => &mut d.nested,
             ImplSource::TraitUpcasting(d) => &mut d.nested,
         }
     }
@@ -709,15 +703,9 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
             ImplSource::Builtin(n) => ImplSource::Builtin(n.into_iter().map(f).collect()),
             ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
-                upcast_trait_def_id: o.upcast_trait_def_id,
                 vtable_base: o.vtable_base,
                 nested: o.nested.into_iter().map(f).collect(),
             }),
-            ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
-                alias_def_id: d.alias_def_id,
-                substs: d.substs,
-                nested: d.nested.into_iter().map(f).collect(),
-            }),
             ImplSource::TraitUpcasting(d) => {
                 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
                     vtable_vptr_slot: d.vtable_vptr_slot,
@@ -761,9 +749,6 @@ pub struct ImplSourceTraitUpcastingData<N> {
 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, Lift)]
 #[derive(TypeFoldable, TypeVisitable)]
 pub struct ImplSourceObjectData<N> {
-    /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
-    pub upcast_trait_def_id: DefId,
-
     /// The vtable is formed by concatenating together the method lists of
     /// the base object trait and all supertraits, pointers to supertrait vtable will
     /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
@@ -773,14 +758,6 @@ pub struct ImplSourceObjectData<N> {
     pub nested: Vec<N>,
 }
 
-#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
-#[derive(TypeFoldable, TypeVisitable)]
-pub struct ImplSourceTraitAliasData<'tcx, N> {
-    pub alias_def_id: DefId,
-    pub substs: SubstsRef<'tcx>,
-    pub nested: Vec<N>,
-}
-
 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 pub enum ObjectSafetyViolation {
     /// `Self: Sized` declared on the trait.
diff --git a/compiler/rustc_middle/src/traits/structural_impls.rs b/compiler/rustc_middle/src/traits/structural_impls.rs
index ac02d6ed62f..a703e3c9562 100644
--- a/compiler/rustc_middle/src/traits/structural_impls.rs
+++ b/compiler/rustc_middle/src/traits/structural_impls.rs
@@ -17,8 +17,6 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSource<'tcx, N> {
                 write!(f, "ImplSourceParamData({:?}, {:?})", n, ct)
             }
 
-            super::ImplSource::TraitAlias(ref d) => write!(f, "{:?}", d),
-
             super::ImplSource::TraitUpcasting(ref d) => write!(f, "{:?}", d),
         }
     }
@@ -48,18 +46,8 @@ impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceObjectData<N> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             f,
-            "ImplSourceObjectData(upcast={:?}, vtable_base={}, nested={:?})",
-            self.upcast_trait_def_id, self.vtable_base, self.nested
-        )
-    }
-}
-
-impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSourceTraitAliasData<'tcx, N> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(
-            f,
-            "ImplSourceTraitAliasData(alias_def_id={:?}, substs={:?}, nested={:?})",
-            self.alias_def_id, self.substs, self.nested
+            "ImplSourceObjectData(vtable_base={}, nested={:?})",
+            self.vtable_base, self.nested
         )
     }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index f93d6b1ce88..c259260c1fa 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -5,7 +5,7 @@ pub mod suggestions;
 use super::{
     FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
     ObligationCauseCode, ObligationCtxt, OutputTypeParameterMismatch, Overflow,
-    PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
+    PredicateObligation, SelectionError, TraitNotObjectSafe,
 };
 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
@@ -2272,55 +2272,40 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     )
                 };
 
-                let obligation = obligation.with(self.tcx, trait_ref);
-                let mut selcx = SelectionContext::new(&self);
-                match selcx.select_from_obligation(&obligation) {
-                    Ok(None) => {
-                        let ambiguities =
-                            ambiguity::recompute_applicable_impls(self.infcx, &obligation);
-                        let has_non_region_infer = trait_ref
-                            .skip_binder()
-                            .substs
-                            .types()
-                            .any(|t| !t.is_ty_or_numeric_infer());
-                        // It doesn't make sense to talk about applicable impls if there are more
-                        // than a handful of them.
-                        if ambiguities.len() > 1 && ambiguities.len() < 10 && has_non_region_infer {
-                            if self.tainted_by_errors().is_some() && subst.is_none() {
-                                // If `subst.is_none()`, then this is probably two param-env
-                                // candidates or impl candidates that are equal modulo lifetimes.
-                                // Therefore, if we've already emitted an error, just skip this
-                                // one, since it's not particularly actionable.
-                                err.cancel();
-                                return;
-                            }
-                            self.annotate_source_of_ambiguity(&mut err, &ambiguities, predicate);
-                        } else {
-                            if self.tainted_by_errors().is_some() {
-                                err.cancel();
-                                return;
-                            }
-                            err.note(format!("cannot satisfy `{}`", predicate));
-                            let impl_candidates = self.find_similar_impl_candidates(
-                                predicate.to_opt_poly_trait_pred().unwrap(),
-                            );
-                            if impl_candidates.len() < 10 {
-                                self.report_similar_impl_candidates(
-                                    impl_candidates.as_slice(),
-                                    trait_ref,
-                                    obligation.cause.body_id,
-                                    &mut err,
-                                    false,
-                                );
-                            }
-                        }
+                let ambiguities = ambiguity::recompute_applicable_impls(
+                    self.infcx,
+                    &obligation.with(self.tcx, trait_ref),
+                );
+                let has_non_region_infer =
+                    trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_or_numeric_infer());
+                // It doesn't make sense to talk about applicable impls if there are more
+                // than a handful of them.
+                if ambiguities.len() > 1 && ambiguities.len() < 10 && has_non_region_infer {
+                    if self.tainted_by_errors().is_some() && subst.is_none() {
+                        // If `subst.is_none()`, then this is probably two param-env
+                        // candidates or impl candidates that are equal modulo lifetimes.
+                        // Therefore, if we've already emitted an error, just skip this
+                        // one, since it's not particularly actionable.
+                        err.cancel();
+                        return;
                     }
-                    _ => {
-                        if self.tainted_by_errors().is_some() {
-                            err.cancel();
-                            return;
-                        }
-                        err.note(format!("cannot satisfy `{}`", predicate));
+                    self.annotate_source_of_ambiguity(&mut err, &ambiguities, predicate);
+                } else {
+                    if self.tainted_by_errors().is_some() {
+                        err.cancel();
+                        return;
+                    }
+                    err.note(format!("cannot satisfy `{}`", predicate));
+                    let impl_candidates = self
+                        .find_similar_impl_candidates(predicate.to_opt_poly_trait_pred().unwrap());
+                    if impl_candidates.len() < 10 {
+                        self.report_similar_impl_candidates(
+                            impl_candidates.as_slice(),
+                            trait_ref,
+                            obligation.cause.body_id,
+                            &mut err,
+                            false,
+                        );
                     }
                 }
 
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index c84c75cecdf..60712ad05f1 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -1720,7 +1720,6 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
         };
 
         let eligible = match &impl_source {
-            super::ImplSource::TraitAlias(_) => true,
             super::ImplSource::UserDefined(impl_data) => {
                 // We have to be careful when projecting out of an
                 // impl because of specialization. If we are not in
@@ -2012,8 +2011,7 @@ fn confirm_select_candidate<'cx, 'tcx>(
         }
         super::ImplSource::Object(_)
         | super::ImplSource::Param(..)
-        | super::ImplSource::TraitUpcasting(_)
-        | super::ImplSource::TraitAlias(..) => {
+        | super::ImplSource::TraitUpcasting(_) => {
             // we don't create Select candidates with this kind of resolution
             span_bug!(
                 obligation.cause.span,
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index c94fddc124f..cc6521f3b50 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -27,10 +27,9 @@ use crate::traits::vtable::{
 };
 use crate::traits::{
     BuiltinDerivedObligation, ImplDerivedObligation, ImplDerivedObligationCause, ImplSource,
-    ImplSourceObjectData, ImplSourceTraitAliasData, ImplSourceTraitUpcastingData,
-    ImplSourceUserDefinedData, Normalized, Obligation, ObligationCause,
-    OutputTypeParameterMismatch, PredicateObligation, Selection, SelectionError,
-    TraitNotObjectSafe, TraitObligation, Unimplemented,
+    ImplSourceObjectData, ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized,
+    Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection,
+    SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented,
 };
 
 use super::BuiltinImplConditions;
@@ -105,7 +104,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             TraitAliasCandidate => {
                 let data = self.confirm_trait_alias_candidate(obligation);
-                ImplSource::TraitAlias(data)
+                ImplSource::Builtin(data)
             }
 
             BuiltinObjectCandidate => {
@@ -652,11 +651,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             (unnormalized_upcast_trait_ref, ty::Binder::dummy(object_trait_ref)),
         );
 
-        Ok(ImplSourceObjectData {
-            upcast_trait_def_id: upcast_trait_ref.def_id(),
-            vtable_base,
-            nested,
-        })
+        Ok(ImplSourceObjectData { vtable_base, nested })
     }
 
     fn confirm_fn_pointer_candidate(
@@ -721,10 +716,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     fn confirm_trait_alias_candidate(
         &mut self,
         obligation: &TraitObligation<'tcx>,
-    ) -> ImplSourceTraitAliasData<'tcx, PredicateObligation<'tcx>> {
+    ) -> Vec<PredicateObligation<'tcx>> {
         debug!(?obligation, "confirm_trait_alias_candidate");
 
-        let alias_def_id = obligation.predicate.def_id();
         let predicate = self.infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let trait_ref = predicate.trait_ref;
         let trait_def_id = trait_ref.def_id;
@@ -741,7 +735,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         debug!(?trait_def_id, ?trait_obligations, "trait alias obligations");
 
-        ImplSourceTraitAliasData { alias_def_id, substs, nested: trait_obligations }
+        trait_obligations
     }
 
     fn confirm_generator_candidate(
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 72adf3106ab..b6c64c0196a 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -248,7 +248,7 @@ pub fn get_vtable_index_of_object_method<'tcx, N>(
 ) -> Option<usize> {
     // Count number of methods preceding the one we are selecting and
     // add them to the total offset.
-    tcx.own_existential_vtable_entries(object.upcast_trait_def_id)
+    tcx.own_existential_vtable_entries(tcx.parent(method_def_id))
         .iter()
         .copied()
         .position(|def_id| def_id == method_def_id)
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 45b1075b602..2d75862014d 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -293,9 +293,7 @@ fn resolve_associated_item<'tcx>(
                 None
             }
         }
-        traits::ImplSource::Param(..)
-        | traits::ImplSource::TraitAlias(..)
-        | traits::ImplSource::TraitUpcasting(_) => None,
+        traits::ImplSource::Param(..) | traits::ImplSource::TraitUpcasting(_) => None,
     })
 }
 
diff --git a/tests/ui/traits/new-solver/two-projection-param-candidates-are-ambiguous.stderr b/tests/ui/traits/new-solver/two-projection-param-candidates-are-ambiguous.stderr
index fa5e780ee5e..83a0452b088 100644
--- a/tests/ui/traits/new-solver/two-projection-param-candidates-are-ambiguous.stderr
+++ b/tests/ui/traits/new-solver/two-projection-param-candidates-are-ambiguous.stderr
@@ -5,6 +5,7 @@ LL |     needs_bar::<T>();
    |     ^^^^^^^^^^^^^^
    |
    = note: cannot satisfy `T: Bar`
+   = help: the trait `Bar` is implemented for `T`
 note: required by a bound in `needs_bar`
   --> $DIR/two-projection-param-candidates-are-ambiguous.rs:23:17
    |