Remove some goofy slice logic from the operator path

compiler/rustc_hir_typeck/src/autoderef.rs

@@ -23,7 +23,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         span: Span,
         base_ty: Ty<'tcx>,
     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
-        self.try_overloaded_place_op(span, base_ty, &[], PlaceOp::Deref)
+        self.try_overloaded_place_op(span, base_ty, None, PlaceOp::Deref)
     }
 
     /// Returns the adjustment steps.

compiler/rustc_hir_typeck/src/callee.rs

@@ -1,4 +1,4 @@
-use std::{iter, slice};
+use std::iter;
 
 use rustc_ast::util::parser::PREC_UNAMBIGUOUS;
 use rustc_errors::{Applicability, Diag, ErrorGuaranteed, StashKey};
@@ -300,7 +300,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Ident::with_dummy_span(method_name),
                 trait_def_id,
                 adjusted_ty,
-                opt_input_type.as_ref().map(slice::from_ref),
+                opt_input_type,
             ) {
                 let method = self.register_infer_ok_obligations(ok);
                 let mut autoref = None;

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -336,7 +336,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         m_name: Ident,
         trait_def_id: DefId,
         self_ty: Ty<'tcx>,
-        opt_input_types: Option<&[Ty<'tcx>]>,
+        opt_rhs_ty: Option<Ty<'tcx>>,
     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
         // Construct a trait-reference `self_ty : Trait<input_tys>`
         let args = GenericArgs::for_item(self.tcx, trait_def_id, |param, _| match param.kind {
@@ -346,16 +346,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             GenericParamDefKind::Type { .. } => {
                 if param.index == 0 {
                     self_ty.into()
-                } else if let Some(input_types) = opt_input_types {
+                } else if let Some(rhs_ty) = opt_rhs_ty {
-                    input_types[param.index as usize - 1].into()
+                    assert_eq!(param.index, 1, "did not expect >1 param on operator trait");
+                    rhs_ty.into()
                 } else {
+                    // FIXME: We should stop passing `None` for the failure case
+                    // when probing for call exprs. I.e. `opt_rhs_ty` should always
+                    // be set when it needs to be.
                     self.var_for_def(cause.span, param)
                 }
             }
         });
 
-        let trait_ref = ty::TraitRef::new_from_args(self.tcx, trait_def_id, args);
+        let obligation = traits::Obligation::new(
-        let obligation = traits::Obligation::new(self.tcx, cause, self.param_env, trait_ref);
+            self.tcx,
+            cause,
+            self.param_env,
+            ty::TraitRef::new_from_args(self.tcx, trait_def_id, args),
+        );
 
         // Now we want to know if this can be matched
         if !self.predicate_may_hold(&obligation) {

compiler/rustc_hir_typeck/src/op.rs

@@ -895,7 +895,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let opname = Ident::with_dummy_span(opname);
         let (opt_rhs_expr, opt_rhs_ty) = opt_rhs.unzip();
-        let input_types = opt_rhs_ty.as_slice();
         let cause = self.cause(span, ObligationCauseCode::BinOp {
             lhs_hir_id: lhs_expr.hir_id,
             rhs_hir_id: opt_rhs_expr.map(|expr| expr.hir_id),
@@ -904,13 +903,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             output_ty: expected.only_has_type(self),
         });
 
-        let method = self.lookup_method_in_trait(
+        let method =
-            cause.clone(),
+            self.lookup_method_in_trait(cause.clone(), opname, trait_did, lhs_ty, opt_rhs_ty);
-            opname,
-            trait_did,
-            lhs_ty,
-            Some(input_types),
-        );
         match method {
             Some(ok) => {
                 let method = self.register_infer_ok_obligations(ok);
@@ -942,7 +936,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             if param.index == 0 {
                                 lhs_ty.into()
                             } else {
-                                input_types[param.index as usize - 1].into()
+                                opt_rhs_ty.expect("expected RHS for binop").into()
                             }
                         }
                     });

compiler/rustc_hir_typeck/src/place_op.rs

@@ -149,7 +149,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // If some lookup succeeded, install method in table
             let input_ty = self.next_ty_var(base_expr.span);
             let method =
-                self.try_overloaded_place_op(expr.span, self_ty, &[input_ty], PlaceOp::Index);
+                self.try_overloaded_place_op(expr.span, self_ty, Some(input_ty), PlaceOp::Index);
 
             if let Some(result) = method {
                 debug!("try_index_step: success, using overloaded indexing");
@@ -189,7 +189,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         span: Span,
         base_ty: Ty<'tcx>,
-        arg_tys: &[Ty<'tcx>],
+        opt_rhs_ty: Option<Ty<'tcx>>,
         op: PlaceOp,
     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
         debug!("try_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
@@ -207,7 +207,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Ident::with_dummy_span(imm_op),
             imm_tr,
             base_ty,
-            Some(arg_tys),
+            opt_rhs_ty,
         )
     }
 
@@ -215,7 +215,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         span: Span,
         base_ty: Ty<'tcx>,
-        arg_tys: &[Ty<'tcx>],
+        opt_rhs_ty: Option<Ty<'tcx>>,
         op: PlaceOp,
     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
         debug!("try_mutable_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
@@ -233,7 +233,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Ident::with_dummy_span(mut_op),
             mut_tr,
             base_ty,
-            Some(arg_tys),
+            opt_rhs_ty,
         )
     }
 
@@ -284,7 +284,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         && let Some(ok) = self.try_mutable_overloaded_place_op(
                             expr.span,
                             source,
-                            &[],
+                            None,
                             PlaceOp::Deref,
                         )
                     {
@@ -359,8 +359,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Some(self.typeck_results.borrow().node_args(expr.hir_id).type_at(1))
             }
         };
-        let arg_tys = arg_ty.as_slice();
+        let method = self.try_mutable_overloaded_place_op(expr.span, base_ty, arg_ty, op);
-        let method = self.try_mutable_overloaded_place_op(expr.span, base_ty, arg_tys, op);
         let method = match method {
             Some(ok) => self.register_infer_ok_obligations(ok),
             // Couldn't find the mutable variant of the place op, keep the