Remove tuple candidate, nothing special about it

compiler/rustc_middle/src/traits/mod.rs

@@ -664,10 +664,6 @@ pub enum ImplSource<'tcx, N> {
 
     /// ImplSource for a `const Drop` implementation.
     ConstDestruct(ImplSourceConstDestructData<N>),
-
-    /// ImplSource for a `std::marker::Tuple` implementation.
-    /// This has no nested predicates ever, so no data.
-    Tuple,
 }
 
 impl<'tcx, N> ImplSource<'tcx, N> {
@@ -682,8 +678,7 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::Object(d) => d.nested,
             ImplSource::FnPointer(d) => d.nested,
             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
-            | ImplSource::Pointee(ImplSourcePointeeData)
-            | ImplSource::Tuple => Vec::new(),
+            | ImplSource::Pointee(ImplSourcePointeeData) => vec![],
             ImplSource::TraitAlias(d) => d.nested,
             ImplSource::TraitUpcasting(d) => d.nested,
             ImplSource::ConstDestruct(i) => i.nested,
@@ -701,8 +696,7 @@ impl<'tcx, N> ImplSource<'tcx, N> {
             ImplSource::Object(d) => &d.nested,
             ImplSource::FnPointer(d) => &d.nested,
             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
-            | ImplSource::Pointee(ImplSourcePointeeData)
-            | ImplSource::Tuple => &[],
+            | ImplSource::Pointee(ImplSourcePointeeData) => &[],
             ImplSource::TraitAlias(d) => &d.nested,
             ImplSource::TraitUpcasting(d) => &d.nested,
             ImplSource::ConstDestruct(i) => &i.nested,
@@ -769,7 +763,6 @@ impl<'tcx, N> ImplSource<'tcx, N> {
                     nested: i.nested.into_iter().map(f).collect(),
                 })
             }
-            ImplSource::Tuple => ImplSource::Tuple,
         }
     }
 }

compiler/rustc_middle/src/traits/select.rs

@@ -161,9 +161,6 @@ pub enum SelectionCandidate<'tcx> {
 
     /// Implementation of `const Destruct`, optionally from a custom `impl const Drop`.
     ConstDestructCandidate(Option<DefId>),
-
-    /// Witnesses the fact that a type is a tuple.
-    TupleCandidate,
 }
 
 /// The result of trait evaluation. The order is important

compiler/rustc_middle/src/traits/structural_impls.rs

@@ -34,8 +34,6 @@ impl<'tcx, N: fmt::Debug> fmt::Debug for traits::ImplSource<'tcx, N> {
             super::ImplSource::TraitUpcasting(ref d) => write!(f, "{:?}", d),
 
             super::ImplSource::ConstDestruct(ref d) => write!(f, "{:?}", d),
-
-            super::ImplSource::Tuple => write!(f, "ImplSource::Tuple"),
         }
     }
 }

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1750,8 +1750,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
             super::ImplSource::AutoImpl(..)
             | super::ImplSource::Builtin(..)
             | super::ImplSource::TraitUpcasting(_)
-            | super::ImplSource::ConstDestruct(_)
-            | super::ImplSource::Tuple => {
+            | super::ImplSource::ConstDestruct(_) => {
                 // These traits have no associated types.
                 selcx.tcx().sess.delay_span_bug(
                     obligation.cause.span,
@@ -1829,8 +1828,7 @@ fn confirm_select_candidate<'cx, 'tcx>(
         | super::ImplSource::Builtin(..)
         | super::ImplSource::TraitUpcasting(_)
         | super::ImplSource::TraitAlias(..)
-        | super::ImplSource::ConstDestruct(_)
-        | super::ImplSource::Tuple => {
+        | super::ImplSource::ConstDestruct(_) => {
             // we don't create Select candidates with this kind of resolution
             span_bug!(
                 obligation.cause.span,

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -1021,7 +1021,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let self_ty = self.infcx().shallow_resolve(obligation.self_ty().skip_binder());
         match self_ty.kind() {
             ty::Tuple(_) => {
-                candidates.vec.push(TupleCandidate);
+                candidates.vec.push(BuiltinCandidate { has_nested: false });
             }
             ty::Infer(ty::TyVar(_)) => {
                 candidates.ambiguous = true;

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -126,8 +126,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let data = self.confirm_const_destruct_candidate(obligation, def_id)?;
                 ImplSource::ConstDestruct(data)
             }
-
-            TupleCandidate => ImplSource::Tuple,
         };
 
         if !obligation.predicate.is_const_if_const() {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1562,7 +1562,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         };
 
         // (*) Prefer `BuiltinCandidate { has_nested: false }`, `PointeeCandidate`,
-        // `DiscriminantKindCandidate`, `ConstDestructCandidate`, and `TupleCandidate`
+        // `DiscriminantKindCandidate`, `ConstDestructCandidate`
         // to anything else.
         //
         // This is a fix for #53123 and prevents winnowing from accidentally extending the
@@ -1583,17 +1583,15 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 BuiltinCandidate { has_nested: false }
                 | DiscriminantKindCandidate
                 | PointeeCandidate
-                | ConstDestructCandidate(_)
-                | TupleCandidate,
+                | ConstDestructCandidate(_),
                 _,
             ) => true,
             (
                 _,
                 BuiltinCandidate { has_nested: false }
                 | DiscriminantKindCandidate
                 | PointeeCandidate
-                | ConstDestructCandidate(_)
-                | TupleCandidate,
+                | ConstDestructCandidate(_),
             ) => false,
 
             (ParamCandidate(other), ParamCandidate(victim)) => {

compiler/rustc_ty_utils/src/instance.rs

@@ -269,8 +269,7 @@ fn resolve_associated_item<'tcx>(
         | traits::ImplSource::DiscriminantKind(..)
         | traits::ImplSource::Pointee(..)
         | traits::ImplSource::TraitUpcasting(_)
-        | traits::ImplSource::ConstDestruct(_)
-        | traits::ImplSource::Tuple => None,
+        | traits::ImplSource::ConstDestruct(_) => None,
     })
 }