Check const Drop impls considering ConstIfConst bounds

compiler/rustc_middle/src/traits/mod.rs

@@ -566,7 +566,7 @@ pub enum ImplSource<'tcx, N> {
     TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
 
     /// ImplSource for a `const Drop` implementation.
-    ConstDrop(ImplSourceConstDropData),
+    ConstDrop(ImplSourceConstDropData<N>),
 }
 
 impl<'tcx, N> ImplSource<'tcx, N> {
@@ -581,10 +581,10 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::Object(d) => d.nested,
             ImplSource::FnPointer(d) => d.nested,
             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
-            | ImplSource::Pointee(ImplSourcePointeeData)
-            | ImplSource::ConstDrop(ImplSourceConstDropData) => Vec::new(),
+            | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
             ImplSource::TraitAlias(d) => d.nested,
             ImplSource::TraitUpcasting(d) => d.nested,
+            ImplSource::ConstDrop(i) => i.nested,
         }
     }
 
@@ -599,10 +599,10 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::Object(d) => &d.nested,
             ImplSource::FnPointer(d) => &d.nested,
             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
-            | ImplSource::Pointee(ImplSourcePointeeData)
-            | ImplSource::ConstDrop(ImplSourceConstDropData) => &[],
+            | ImplSource::Pointee(ImplSourcePointeeData) => &[],
             ImplSource::TraitAlias(d) => &d.nested,
             ImplSource::TraitUpcasting(d) => &d.nested,
+            ImplSource::ConstDrop(i) => &i.nested,
         }
     }
 
@@ -661,9 +661,9 @@ impl<'tcx, N> ImplSource<'tcx, N> {
                     nested: d.nested.into_iter().map(f).collect(),
                 })
             }
-            ImplSource::ConstDrop(ImplSourceConstDropData) => {
-                ImplSource::ConstDrop(ImplSourceConstDropData)
-            }
+            ImplSource::ConstDrop(i) => ImplSource::ConstDrop(ImplSourceConstDropData {
+                nested: i.nested.into_iter().map(f).collect(),
+            }),
         }
     }
 }
@@ -755,8 +755,10 @@ pub struct ImplSourceDiscriminantKindData;
 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
 pub struct ImplSourcePointeeData;
 
-#[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
-pub struct ImplSourceConstDropData;
+#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
+pub struct ImplSourceConstDropData<N> {
+    pub nested: Vec<N>,
+}
 
 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 pub struct ImplSourceTraitAliasData<'tcx, N> {

compiler/rustc_middle/src/traits/select.rs

@@ -146,8 +146,8 @@ pub enum SelectionCandidate<'tcx> {
 
     BuiltinUnsizeCandidate,
 
-    /// Implementation of `const Drop`.
-    ConstDropCandidate,
+    /// Implementation of `const Drop`, optionally from a custom `impl const Drop`.
+    ConstDropCandidate(Option<DefId>),
 }
 
 /// The result of trait evaluation. The order is important

compiler/rustc_middle/src/traits/structural_impls.rs

@@ -120,6 +120,12 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSourceTraitAliasData<'tcx,
     }
 }
 
+impl<N: fmt::Debug> fmt::Debug for traits::ImplSourceConstDropData<N> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "ImplSourceConstDropData(nested={:?})", self.nested)
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // Lift implementations
 
@@ -127,5 +133,4 @@ TrivialTypeFoldableAndLiftImpls! {
     super::IfExpressionCause,
     super::ImplSourceDiscriminantKindData,
     super::ImplSourcePointeeData,
-    super::ImplSourceConstDropData,
 }