Fold vtable_trait_upcasting_coercion_new_vptr_slot logic into obligation processing.

compiler/rustc_middle/src/query/mod.rs

@@ -987,9 +987,9 @@ rustc_queries! {
         desc { |tcx| "finding all vtable entries for trait {}", tcx.def_path_str(key.def_id()) }
     }
 
-    query vtable_trait_upcasting_coercion_new_vptr_slot(key: (ty::PolyTraitRef<'tcx>, ty::PolyTraitRef<'tcx>)) -> Option<usize> {
-        desc { |tcx| "finding the slot within vtable for trait {} vtable ptr during trait upcasting coercion from {} vtable",
-            tcx.def_path_str(key.1.def_id()), tcx.def_path_str(key.0.def_id()) }
+    query vtable_trait_upcasting_coercion_new_vptr_slot(key: (ty::Ty<'tcx>, ty::Ty<'tcx>)) -> Option<usize> {
+        desc { |tcx| "finding the slot within vtable for trait object {} vtable ptr during trait upcasting coercion from {} vtable",
+            key.1, key.0 }
     }
 
     query codegen_fulfill_obligation(

compiler/rustc_middle/src/traits/mod.rs

@@ -503,6 +503,9 @@ pub enum ImplSource<'tcx, N> {
     /// Successful resolution for a builtin trait.
     Builtin(ImplSourceBuiltinData<N>),
 
+    /// ImplSource for trait upcasting coercion
+    TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
+
     /// ImplSource automatically generated for a closure. The `DefId` is the ID
     /// of the closure expression. This is a `ImplSource::UserDefined` in spirit, but the
     /// impl is generated by the compiler and does not appear in the source.
@@ -538,6 +541,7 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
             | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
             ImplSource::TraitAlias(d) => d.nested,
+            ImplSource::TraitUpcasting(d) => d.nested,
         }
     }
 
@@ -554,6 +558,7 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
             | ImplSource::Pointee(ImplSourcePointeeData) => &[],
             ImplSource::TraitAlias(d) => &d.nested[..],
+            ImplSource::TraitUpcasting(d) => &d.nested[..],
         }
     }
 
@@ -605,6 +610,13 @@ impl<'tcx, N> ImplSource<'tcx, N> {
                 substs: d.substs,
                 nested: d.nested.into_iter().map(f).collect(),
             }),
+            ImplSource::TraitUpcasting(d) => {
+                ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
+                    upcast_trait_ref: d.upcast_trait_ref,
+                    vtable_vptr_slot: d.vtable_vptr_slot,
+                    nested: d.nested.into_iter().map(f).collect(),
+                })
+            }
         }
     }
 }
@@ -650,6 +662,20 @@ pub struct ImplSourceAutoImplData<N> {
     pub nested: Vec<N>,
 }
 
+#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
+pub struct ImplSourceTraitUpcastingData<'tcx, N> {
+    /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
+    pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
+
+    /// 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 position of `upcast_trait_ref`'s vtable
+    /// within that vtable.
+    pub vtable_vptr_slot: Option<usize>,
+
+    pub nested: Vec<N>,
+}
+
 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 pub struct ImplSourceBuiltinData<N> {
     pub nested: Vec<N>,
@@ -661,8 +687,9 @@ pub struct ImplSourceObjectData<'tcx, N> {
     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 
     /// The vtable is formed by concatenating together the method lists of
-    /// the base object trait and all supertraits; this is the start of
-    /// `upcast_trait_ref`'s methods in that vtable.
+    /// 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
+    /// in that vtable.
     pub vtable_base: usize,
 
     pub nested: Vec<N>,

compiler/rustc_middle/src/traits/structural_impls.rs

@@ -30,6 +30,8 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSource<'tcx, N> {
             super::ImplSource::Builtin(ref d) => write!(f, "{:?}", d),
 
             super::ImplSource::TraitAlias(ref d) => write!(f, "{:?}", d),
+
+            super::ImplSource::TraitUpcasting(ref d) => write!(f, "{:?}", d),
         }
     }
 }
@@ -70,6 +72,16 @@ impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceBuiltinData<N> {
     }
 }
 
+impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceTraitUpcastingData<'tcx, N> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "ImplSourceTraitUpcastingData(upcast={:?}, vtable_vptr_slot={:?}, nested={:?})",
+            self.upcast_trait_ref, self.vtable_vptr_slot, self.nested
+        )
+    }
+}
+
 impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceAutoImplData<N> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(