make find_similar_impl_candidates even fuzzier

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -26,7 +26,7 @@ use rustc_middle::mir::interpret;
 use rustc_middle::thir;
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::codec::TyEncoder;
-use rustc_middle::ty::fast_reject::{self, SimplifiedType, SimplifyParams, StripReferences};
+use rustc_middle::ty::fast_reject::{self, SimplifiedType, SimplifyParams};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, SymbolName, Ty, TyCtxt};
 use rustc_serialize::{opaque, Encodable, Encoder};
@@ -2066,7 +2066,6 @@ impl<'tcx, 'v> ItemLikeVisitor<'v> for ImplsVisitor<'tcx> {
                         self.tcx,
                         trait_ref.self_ty(),
                         SimplifyParams::No,
-                        StripReferences::No,
                     );
 
                     self.impls

compiler/rustc_middle/src/ty/fast_reject.rs

@@ -54,12 +54,6 @@ pub enum SimplifyParams {
     No,
 }
 
-#[derive(PartialEq, Eq, Debug, Clone, Copy)]
-pub enum StripReferences {
-    Yes,
-    No,
-}
-
 /// Tries to simplify a type by only returning the outermost injective¹ layer, if one exists.
 ///
 /// The idea is to get something simple that we can use to quickly decide if two types could unify,
@@ -73,8 +67,6 @@ pub enum StripReferences {
 /// When using `SimplifyParams::Yes`, we still return a simplified type for params and projections²,
 /// the reasoning for this can be seen at the places doing this.
 ///
-/// For diagnostics we strip references with `StripReferences::Yes`. This is currently the best
-/// way to skip some unhelpful suggestions.
 ///
 /// ¹ meaning that if two outermost layers are different, then the whole types are also different.
 /// ² FIXME(@lcnr): this seems like it can actually end up being unsound with the way it's used during
@@ -87,7 +79,6 @@ pub fn simplify_type(
     tcx: TyCtxt<'_>,
     ty: Ty<'_>,
     can_simplify_params: SimplifyParams,
-    strip_references: StripReferences,
 ) -> Option<SimplifiedType> {
     match *ty.kind() {
         ty::Bool => Some(BoolSimplifiedType),
@@ -106,16 +97,7 @@ pub fn simplify_type(
             }
             _ => Some(MarkerTraitObjectSimplifiedType),
         },
-        ty::Ref(_, ty, mutbl) => {
-            if strip_references == StripReferences::Yes {
-                // For diagnostics, when recommending similar impls we want to
-                // recommend impls even when there is a reference mismatch,
-                // so we treat &T and T equivalently in that case.
-                simplify_type(tcx, ty, can_simplify_params, strip_references)
-            } else {
-                Some(RefSimplifiedType(mutbl))
-            }
-        }
+        ty::Ref(_, _, mutbl) => Some(RefSimplifiedType(mutbl)),
         ty::FnDef(def_id, _) | ty::Closure(def_id, _) => Some(ClosureSimplifiedType(def_id)),
         ty::Generator(def_id, _, _) => Some(GeneratorSimplifiedType(def_id)),
         ty::GeneratorWitness(ref tys) => {

compiler/rustc_middle/src/ty/trait_def.rs

@@ -1,5 +1,5 @@
 use crate::traits::specialization_graph;
-use crate::ty::fast_reject::{self, SimplifiedType, SimplifyParams, StripReferences};
+use crate::ty::fast_reject::{self, SimplifiedType, SimplifyParams};
 use crate::ty::fold::TypeFoldable;
 use crate::ty::{Ident, Ty, TyCtxt};
 use rustc_hir as hir;
@@ -150,9 +150,7 @@ impl<'tcx> TyCtxt<'tcx> {
         self_ty: Ty<'tcx>,
     ) -> impl Iterator<Item = DefId> + 'tcx {
         let impls = self.trait_impls_of(def_id);
-        if let Some(simp) =
-            fast_reject::simplify_type(self, self_ty, SimplifyParams::No, StripReferences::No)
-        {
+        if let Some(simp) = fast_reject::simplify_type(self, self_ty, SimplifyParams::No) {
             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
                 return impls.iter().copied();
             }
@@ -189,9 +187,7 @@ impl<'tcx> TyCtxt<'tcx> {
         // whose outer level is not a parameter or projection. Especially for things like
         // `T: Clone` this is incredibly useful as we would otherwise look at all the impls
         // of `Clone` for `Option<T>`, `Vec<T>`, `ConcreteType` and so on.
-        if let Some(simp) =
-            fast_reject::simplify_type(self, self_ty, SimplifyParams::Yes, StripReferences::No)
-        {
+        if let Some(simp) = fast_reject::simplify_type(self, self_ty, SimplifyParams::Yes) {
             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
                 for &impl_def_id in impls {
                     if let result @ Some(_) = f(impl_def_id) {
@@ -251,7 +247,7 @@ pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> Trait
         }
 
         if let Some(simplified_self_ty) =
-            fast_reject::simplify_type(tcx, impl_self_ty, SimplifyParams::No, StripReferences::No)
+            fast_reject::simplify_type(tcx, impl_self_ty, SimplifyParams::No)
         {
             impls.non_blanket_impls.entry(simplified_self_ty).or_default().push(impl_def_id);
         } else {

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -15,7 +15,7 @@ use crate::traits::{
 };
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::traits::specialization_graph::OverlapMode;
-use rustc_middle::ty::fast_reject::{self, SimplifyParams, StripReferences};
+use rustc_middle::ty::fast_reject::{self, SimplifyParams};
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -82,8 +82,8 @@ where
         impl2_ref.iter().flat_map(|tref| tref.substs.types()),
     )
     .any(|(ty1, ty2)| {
-        let t1 = fast_reject::simplify_type(tcx, ty1, SimplifyParams::No, StripReferences::No);
-        let t2 = fast_reject::simplify_type(tcx, ty2, SimplifyParams::No, StripReferences::No);
+        let t1 = fast_reject::simplify_type(tcx, ty1, SimplifyParams::No);
+        let t2 = fast_reject::simplify_type(tcx, ty2, SimplifyParams::No);
 
         if let (Some(t1), Some(t2)) = (t1, t2) {
             // Simplified successfully