typeck: Support multiple expressions getting coerced at the same type.

src/librustc_typeck/check/callee.rs

@@ -82,7 +82,7 @@ pub fn check_call<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         autoderef(fcx,
                   callee_expr.span,
                   original_callee_ty,
-                  Some(callee_expr),
+                  || Some(callee_expr),
                   UnresolvedTypeAction::Error,
                   LvaluePreference::NoPreference,
                   |adj_ty, idx| {

src/librustc_typeck/check/coercion.rs

@@ -87,6 +87,14 @@ struct Coerce<'a, 'tcx: 'a> {
 type CoerceResult<'tcx> = RelateResult<'tcx, Option<AutoAdjustment<'tcx>>>;
 
 impl<'f, 'tcx> Coerce<'f, 'tcx> {
+    fn new(fcx: &'a FnCtxt<'a, 'tcx>, origin: TypeOrigin) -> Self {
+        Coerce {
+            fcx: fcx,
+            origin: origin,
+            unsizing_obligations: RefCell::new(vec![])
+        }
+    }
+
     fn tcx(&self) -> &TyCtxt<'tcx> {
         self.fcx.tcx()
     }
@@ -96,16 +104,17 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         Ok(None) // No coercion required.
     }
 
-    fn coerce(&self,
+    fn coerce<'a, E, I>(&self,
-              expr_a: &hir::Expr,
+                        exprs: &E,
-              a: Ty<'tcx>,
+                        a: Ty<'tcx>,
-              b: Ty<'tcx>)
+                        b: Ty<'tcx>)
-              -> CoerceResult<'tcx> {
+                        -> CoerceResult<'tcx>
-        debug!("Coerce.tys({:?} => {:?})",
+        // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
-               a,
+        where E: Fn() -> I,
-               b);
+              I: IntoIterator<Item=&'a hir::Expr> {
 
         let a = self.fcx.infcx().shallow_resolve(a);
+        debug!("Coerce.tys({:?} => {:?})", a, b);
 
         // Just ignore error types.
         if a.references_error() || b.references_error() {
@@ -156,15 +165,18 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
     /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`.
     /// To match `A` with `B`, autoderef will be performed,
     /// calling `deref`/`deref_mut` where necessary.
-    fn coerce_borrowed_pointer(&self,
+    fn coerce_borrowed_pointer<'a, E, I>(&self,
-                               expr_a: &hir::Expr,
+                                         span: Span,
-                               a: Ty<'tcx>,
+                                         exprs: &E,
-                               b: Ty<'tcx>,
+                                         a: Ty<'tcx>,
-                               mutbl_b: hir::Mutability)
+                                         b: Ty<'tcx>,
-                               -> CoerceResult<'tcx> {
+                                         mutbl_b: hir::Mutability)
-        debug!("coerce_borrowed_pointer(a={:?}, b={:?})",
+                                         -> CoerceResult<'tcx>
-               a,
+        // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
-               b);
+        where E: Fn() -> I,
+              I: IntoIterator<Item=&'a hir::Expr> {
+
+        debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b);
 
         // If we have a parameter of type `&M T_a` and the value
         // provided is `expr`, we will be adding an implicit borrow,
@@ -179,17 +191,15 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             _ => return self.subtype(a, b)
         }
 
-        let coercion = Coercion(self.origin.span());
+        let span = self.origin.span();
+        let coercion = Coercion(span);
         let r_borrow = self.fcx.infcx().next_region_var(coercion);
         let r_borrow = self.tcx().mk_region(r_borrow);
         let autoref = Some(AutoPtr(r_borrow, mutbl_b));
 
         let lvalue_pref = LvaluePreference::from_mutbl(mutbl_b);
         let mut first_error = None;
-        let (_, autoderefs, success) = autoderef(self.fcx,
+        let (_, autoderefs, success) = autoderef(self.fcx, span, a, exprs,
-                                                 expr_a.span,
-                                                 a,
-                                                 Some(expr_a),
                                                  UnresolvedTypeAction::Ignore,
                                                  lvalue_pref,
                                                  |inner_ty, autoderef| {
@@ -323,9 +333,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             }
         }
 
-        let mut obligations = self.unsizing_obligations.borrow_mut();
+        *self.unsizing_obligations.borrow_mut() = leftover_predicates;
-        assert!(obligations.is_empty());
-        *obligations = leftover_predicates;
 
         let adjustment = AutoDerefRef {
             autoderefs: if reborrow.is_some() { 1 } else { 0 },
@@ -425,39 +433,48 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
     }
 }
 
+fn apply<'a, 'b, 'tcx, E, I>(coerce: &mut Coerce<'a, 'tcx>,
+                             exprs: &E,
+                             a: Ty<'tcx>,
+                             b: Ty<'tcx>)
+                             -> RelateResult<'tcx, Ty<'tcx>>
+    where E: Fn() -> I,
+          I: IntoIterator<Item=&'b hir::Expr> {
+
+    let (ty, adjustment) = try!(indent(|| coerce.coerce(exprs, a, b)));
+
+    let fcx = coerce.fcx;
+    if let AdjustDerefRef(auto) = adjustment {
+        if auto.unsize.is_some() {
+            for obligation in coerce.unsizing_obligations.borrow_mut().drain() {
+                fcx.register_predicate(obligation);
+            }
+        }
+    }
+
+    if !adjustment.is_identity() {
+        debug!("Success, coerced with {:?}", adjustment);
+        for expr in exprs() {
+            assert!(!fcx.inh.tables.borrow().adjustments.contains(&expr.id));
+            fcx.write_adjustment(expr.id, adjustment);
+        }
+    }
+    Ok(ty)
+}
+
+/// Attempt to coerce an expression from a type (a) to another type (b).
+/// Adjustments are only recorded if the coercion was successful.
+/// The expressions *must not* have any pre-existing adjustments.
 pub fn try<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                      expr: &hir::Expr,
                      a: Ty<'tcx>,
                      b: Ty<'tcx>)
                      -> RelateResult<'tcx, ()> {
     debug!("coercion::try({:?} -> {:?})", a, b);
-    let mut unsizing_obligations = vec![];
+    let mut coerce = Coerce::new(fcx, TypeOrigin::ExprAssignable(expr.span));
-    let adjustment = try!(indent(|| {
+    fcx.infcx().commit_if_ok(|_| {
-        fcx.infcx().commit_if_ok(|_| {
+        apply(&mut coerce, &|| Some(expr), a, b)
-            let coerce = Coerce {
+    }).map(|_| ())
-                fcx: fcx,
-                origin: TypeOrigin::ExprAssignable(expr.span),
-                unsizing_obligations: RefCell::new(vec![])
-            };
-            let adjustment = try!(coerce.coerce(expr, a, b));
-            unsizing_obligations = coerce.unsizing_obligations.into_inner();
-            Ok(adjustment)
-        })
-    }));
-
-    if let Some(AdjustDerefRef(auto)) = adjustment {
-        if auto.unsize.is_some() {
-            for obligation in unsizing_obligations {
-                fcx.register_predicate(obligation);
-            }
-        }
-    }
-
-    if let Some(adjustment) = adjustment {
-        debug!("Success, coerced with {:?}", adjustment);
-        fcx.write_adjustment(expr.id, adjustment);
-    }
-    Ok(())
 }
 
 fn coerce_mutbls<'tcx>(from_mutbl: hir::Mutability,

src/librustc_typeck/check/method/confirm.rs

@@ -158,7 +158,7 @@ impl<'a,'tcx> ConfirmContext<'a,'tcx> {
         let (autoderefd_ty, n, result) = check::autoderef(self.fcx,
                                                           self.span,
                                                           unadjusted_self_ty,
-                                                          Some(self.self_expr),
+                                                          || Some(self.self_expr),
                                                           UnresolvedTypeAction::Error,
                                                           NoPreference,
                                                           |_, n| {
@@ -287,7 +287,7 @@ impl<'a,'tcx> ConfirmContext<'a,'tcx> {
         let (_, _, result) = check::autoderef(self.fcx,
                                               self.span,
                                               self_ty,
-                                              None,
+                                              || None,
                                               UnresolvedTypeAction::Error,
                                               NoPreference,
                                               |ty, _| {
@@ -509,7 +509,7 @@ impl<'a,'tcx> ConfirmContext<'a,'tcx> {
                 check::autoderef(self.fcx,
                                  expr.span,
                                  self.fcx.expr_ty(expr),
-                                 Some(expr),
+                                 || Some(expr),
                                  UnresolvedTypeAction::Error,
                                  PreferMutLvalue,
                                  |_, autoderefs| {
@@ -522,92 +522,94 @@ impl<'a,'tcx> ConfirmContext<'a,'tcx> {
             }
 
             // Don't retry the first one or we might infinite loop!
-            if i != 0 {
+            if i == 0 {
-                match expr.node {
+                continue;
-                    hir::ExprIndex(ref base_expr, ref index_expr) => {
+            }
-                        // If this is an overloaded index, the
+            match expr.node {
-                        // adjustment will include an extra layer of
+                hir::ExprIndex(ref base_expr, ref index_expr) => {
-                        // autoref because the method is an &self/&mut
+                    // If this is an overloaded index, the
-                        // self method. We have to peel it off to get
+                    // adjustment will include an extra layer of
-                        // the raw adjustment that `try_index_step`
+                    // autoref because the method is an &self/&mut
-                        // expects. This is annoying and horrible. We
+                    // self method. We have to peel it off to get
-                        // ought to recode this routine so it doesn't
+                    // the raw adjustment that `try_index_step`
-                        // (ab)use the normal type checking paths.
+                    // expects. This is annoying and horrible. We
-                        let adj = self.fcx.inh.tables.borrow().adjustments.get(&base_expr.id)
+                    // ought to recode this routine so it doesn't
-                                                                          .cloned();
+                    // (ab)use the normal type checking paths.
-                        let (autoderefs, unsize) = match adj {
+                    let adj = self.fcx.inh.tables.borrow().adjustments.get(&base_expr.id)
-                            Some(AdjustDerefRef(adr)) => match adr.autoref {
+                                                                        .cloned();
-                                None => {
+                    let (autoderefs, unsize) = match adj {
-                                    assert!(adr.unsize.is_none());
+                        Some(AdjustDerefRef(adr)) => match adr.autoref {
-                                    (adr.autoderefs, None)
+                            None => {
-                                }
+                                assert!(adr.unsize.is_none());
-                                Some(AutoPtr(_, _)) => {
+                                (adr.autoderefs, None)
-                                    (adr.autoderefs, adr.unsize.map(|target| {
+                            }
-                                        target.builtin_deref(false, NoPreference)
+                            Some(AutoPtr(_, _)) => {
-                                              .expect("fixup: AutoPtr is not &T").ty
+                                (adr.autoderefs, adr.unsize.map(|target| {
-                                    }))
+                                    target.builtin_deref(false, NoPreference)
-                                }
+                                            .expect("fixup: AutoPtr is not &T").ty
-                                Some(_) => {
+                                }))
-                                    self.tcx().sess.span_bug(
+                            }
-                                        base_expr.span,
-                                        &format!("unexpected adjustment autoref {:?}",
-                                                adr));
-                                }
-                            },
-                            None => (0, None),
                             Some(_) => {
                                 self.tcx().sess.span_bug(
                                     base_expr.span,
-                                    "unexpected adjustment type");
+                                    &format!("unexpected adjustment autoref {:?}",
+                                            adr));
                             }
-                        };
+                        },
-
+                        None => (0, None),
-                        let (adjusted_base_ty, unsize) = if let Some(target) = unsize {
+                        Some(_) => {
-                            (target, true)
+                            self.tcx().sess.span_bug(
-                        } else {
+                                base_expr.span,
-                            (self.fcx.adjust_expr_ty(base_expr,
+                                "unexpected adjustment type");
-                                Some(&AdjustDerefRef(AutoDerefRef {
-                                    autoderefs: autoderefs,
-                                    autoref: None,
-                                    unsize: None
-                                }))), false)
-                        };
-                        let index_expr_ty = self.fcx.expr_ty(&index_expr);
-
-                        let result = check::try_index_step(
-                            self.fcx,
-                            ty::MethodCall::expr(expr.id),
-                            expr,
-                            &base_expr,
-                            adjusted_base_ty,
-                            autoderefs,
-                            unsize,
-                            PreferMutLvalue,
-                            index_expr_ty);
-
-                        if let Some((input_ty, return_ty)) = result {
-                            demand::suptype(self.fcx, index_expr.span, input_ty, index_expr_ty);
-
-                            let expr_ty = self.fcx.expr_ty(&expr);
-                            demand::suptype(self.fcx, expr.span, expr_ty, return_ty);
                         }
+                    };
+
+                    let (adjusted_base_ty, unsize) = if let Some(target) = unsize {
+                        (target, true)
+                    } else {
+                        (self.fcx.adjust_expr_ty(base_expr,
+                            Some(&AdjustDerefRef(AutoDerefRef {
+                                autoderefs: autoderefs,
+                                autoref: None,
+                                unsize: None
+                            }))), false)
+                    };
+                    let index_expr_ty = self.fcx.expr_ty(&index_expr);
+
+                    let result = check::try_index_step(
+                        self.fcx,
+                        ty::MethodCall::expr(expr.id),
+                        expr,
+                        &base_expr,
+                        adjusted_base_ty,
+                        autoderefs,
+                        unsize,
+                        PreferMutLvalue,
+                        index_expr_ty);
+
+                    if let Some((input_ty, return_ty)) = result {
+                        demand::suptype(self.fcx, index_expr.span, input_ty, index_expr_ty);
+
+                        let expr_ty = self.fcx.expr_ty(&expr);
+                        demand::suptype(self.fcx, expr.span, expr_ty, return_ty);
                     }
-                    hir::ExprUnary(hir::UnDeref, ref base_expr) => {
-                        // if this is an overloaded deref, then re-evaluate with
-                        // a preference for mut
-                        let method_call = ty::MethodCall::expr(expr.id);
-                        if self.fcx.inh.tables.borrow().method_map.contains_key(&method_call) {
-                            check::try_overloaded_deref(
-                                self.fcx,
-                                expr.span,
-                                Some(method_call),
-                                Some(&base_expr),
-                                self.fcx.expr_ty(&base_expr),
-                                PreferMutLvalue);
-                        }
-                    }
-                    _ => {}
                 }
+                hir::ExprUnary(hir::UnDeref, ref base_expr) => {
+                    // if this is an overloaded deref, then re-evaluate with
+                    // a preference for mut
+                    let method_call = ty::MethodCall::expr(expr.id);
+                    if self.fcx.inh.tables.borrow().method_map.contains_key(&method_call) {
+                        let method = check::try_overloaded_deref(
+                            self.fcx,
+                            expr.span,
+                            Some(&base_expr),
+                            self.fcx.expr_ty(&base_expr),
+                            PreferMutLvalue);
+                        let method = method.expect("re-trying deref failed");
+                        self.fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
+                    }
+                }
+                _ => {}
             }
         }
     }

src/librustc_typeck/check/method/probe.rs

@@ -200,7 +200,7 @@ fn create_steps<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     let (final_ty, dereferences, _) = check::autoderef(fcx,
                                                        span,
                                                        self_ty,
-                                                       None,
+                                                       || None,
                                                        UnresolvedTypeAction::Error,
                                                        NoPreference,
                                                        |t, d| {

src/librustc_typeck/check/method/suggest.rs

@@ -351,7 +351,7 @@ fn type_derefs_to_local<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         return is_local(fcx.resolve_type_vars_if_possible(rcvr_ty));
     }
 
-    check::autoderef(fcx, span, rcvr_ty, None,
+    check::autoderef(fcx, span, rcvr_ty, || None,
                      check::UnresolvedTypeAction::Ignore, ty::NoPreference,
                      |ty, _| {
         if is_local(ty) {

src/librustc_typeck/check/mod.rs

@@ -2053,20 +2053,21 @@ pub enum UnresolvedTypeAction {
 ///
 /// Note: this method does not modify the adjustments table. The caller is responsible for
 /// inserting an AutoAdjustment record into the `fcx` using one of the suitable methods.
-pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
+pub fn autoderef<'a, 'b, 'tcx, E, I, T, F>(fcx: &FnCtxt<'a, 'tcx>,
-                                 sp: Span,
+                                           sp: Span,
-                                 base_ty: Ty<'tcx>,
+                                           base_ty: Ty<'tcx>,
-                                 opt_expr: Option<&hir::Expr>,
+                                           maybe_exprs: E,
-                                 unresolved_type_action: UnresolvedTypeAction,
+                                           unresolved_type_action: UnresolvedTypeAction,
-                                 mut lvalue_pref: LvaluePreference,
+                                           mut lvalue_pref: LvaluePreference,
-                                 mut should_stop: F)
+                                           mut should_stop: F)
-                                 -> (Ty<'tcx>, usize, Option<T>)
+                                           -> (Ty<'tcx>, usize, Option<T>)
-    where F: FnMut(Ty<'tcx>, usize) -> Option<T>,
+    // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+    where E: Fn() -> I,
+          I: IntoIterator<Item=&'b hir::Expr>,
+          F: FnMut(Ty<'tcx>, usize) -> Option<T>,
 {
-    debug!("autoderef(base_ty={:?}, opt_expr={:?}, lvalue_pref={:?})",
+    debug!("autoderef(base_ty={:?}, lvalue_pref={:?})",
-           base_ty,
+           base_ty, lvalue_pref);
-           opt_expr,
-           lvalue_pref);
 
     let mut t = base_ty;
     for autoderefs in 0..fcx.tcx().sess.recursion_limit.get() {
@@ -2092,34 +2093,34 @@ pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
         }
 
         // Otherwise, deref if type is derefable:
-        let mt = match resolved_t.builtin_deref(false, lvalue_pref) {
-            Some(mt) => Some(mt),
-            None => {
-                let method_call =
-                    opt_expr.map(|expr| MethodCall::autoderef(expr.id, autoderefs as u32));
 
-                // Super subtle: it might seem as though we should
+        // Super subtle: it might seem as though we should
-                // pass `opt_expr` to `try_overloaded_deref`, so that
+        // pass `opt_expr` to `try_overloaded_deref`, so that
-                // the (implicit) autoref of using an overloaded deref
+        // the (implicit) autoref of using an overloaded deref
-                // would get added to the adjustment table. However we
+        // would get added to the adjustment table. However we
-                // do not do that, because it's kind of a
+        // do not do that, because it's kind of a
-                // "meta-adjustment" -- instead, we just leave it
+        // "meta-adjustment" -- instead, we just leave it
-                // unrecorded and know that there "will be" an
+        // unrecorded and know that there "will be" an
-                // autoref. regionck and other bits of the code base,
+        // autoref. regionck and other bits of the code base,
-                // when they encounter an overloaded autoderef, have
+        // when they encounter an overloaded autoderef, have
-                // to do some reconstructive surgery. This is a pretty
+        // to do some reconstructive surgery. This is a pretty
-                // complex mess that is begging for a proper MIR.
+        // complex mess that is begging for a proper MIR.
-                try_overloaded_deref(fcx, sp, method_call, None, resolved_t, lvalue_pref)
+        let mt = if let Some(mt) = resolved_t.builtin_deref(false, lvalue_pref) {
+            mt
+        } else if let Some(method) = try_overloaded_deref(fcx, sp, None,
+                                                          resolved_t, lvalue_pref) {
+            for expr in maybe_exprs() {
+                let method_call = MethodCall::autoderef(expr.id, autoderefs as u32);
+                fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
             }
+            make_overloaded_lvalue_return_type(fcx.tcx(), method)
+        } else {
+            return (resolved_t, autoderefs, None);
         };
-        match mt {
+
-            Some(mt) => {
+        t = mt.ty;
-                t = mt.ty;
+        if mt.mutbl == hir::MutImmutable {
-                if mt.mutbl == hir::MutImmutable {
+            lvalue_pref = NoPreference;
-                    lvalue_pref = NoPreference;
-                }
-            }
-            None => return (resolved_t, autoderefs, None)
         }
     }
 
@@ -2132,11 +2133,10 @@ pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
 
 fn try_overloaded_deref<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                                   span: Span,
-                                  method_call: Option<MethodCall>,
                                   base_expr: Option<&hir::Expr>,
                                   base_ty: Ty<'tcx>,
                                   lvalue_pref: LvaluePreference)
-                                  -> Option<ty::TypeAndMut<'tcx>>
+                                  -> Option<MethodCallee<'tcx>>
 {
     // Try DerefMut first, if preferred.
     let method = match (lvalue_pref, fcx.tcx().lang_items.deref_mut_trait()) {
@@ -2158,33 +2158,23 @@ fn try_overloaded_deref<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         (method, _) => method
     };
 
-    make_overloaded_lvalue_return_type(fcx, method_call, method)
+    method
 }
 
 /// For the overloaded lvalue expressions (`*x`, `x[3]`), the trait returns a type of `&T`, but the
 /// actual type we assign to the *expression* is `T`. So this function just peels off the return
-/// type by one layer to yield `T`. It also inserts the `method-callee` into the method map.
+/// type by one layer to yield `T`.
-fn make_overloaded_lvalue_return_type<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
+fn make_overloaded_lvalue_return_type<'tcx>(tcx: &ty::ctxt<'tcx>,
-                                                method_call: Option<MethodCall>,
+                                            method: MethodCallee<'tcx>)
-                                                method: Option<MethodCallee<'tcx>>)
+                                            -> ty::TypeAndMut<'tcx>
-                                                -> Option<ty::TypeAndMut<'tcx>>
 {
-    match method {
+    // extract method return type, which will be &T;
-        Some(method) => {
+    // all LB regions should have been instantiated during method lookup
-            // extract method return type, which will be &T;
+    let ret_ty = method.ty.fn_ret();
-            // all LB regions should have been instantiated during method lookup
+    let ret_ty = tcx.no_late_bound_regions(&ret_ty).unwrap().unwrap();
-            let ret_ty = method.ty.fn_ret();
-            let ret_ty = fcx.tcx().no_late_bound_regions(&ret_ty).unwrap().unwrap();
 
-            if let Some(method_call) = method_call {
+    // method returns &T, but the type as visible to user is T, so deref
-                fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
+    ret_ty.builtin_deref(true, NoPreference).unwrap()
-            }
-
-            // method returns &T, but the type as visible to user is T, so deref
-            ret_ty.builtin_deref(true, NoPreference)
-        }
-        None => None,
-    }
 }
 
 fn lookup_indexing<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
@@ -2202,7 +2192,7 @@ fn lookup_indexing<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     let (ty, autoderefs, final_mt) = autoderef(fcx,
                                                base_expr.span,
                                                base_ty,
-                                               Some(base_expr),
+                                               || Some(base_expr),
                                                UnresolvedTypeAction::Error,
                                                lvalue_pref,
                                                |adj_ty, idx| {
@@ -2299,10 +2289,10 @@ fn try_index_step<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     // If some lookup succeeds, write callee into table and extract index/element
     // type from the method signature.
     // If some lookup succeeded, install method in table
-    method.and_then(|method| {
+    method.map(|method| {
         debug!("try_index_step: success, using overloaded indexing");
-        make_overloaded_lvalue_return_type(fcx, Some(method_call), Some(method)).
+        fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
-            map(|ret| (input_ty, ret.ty))
+        (input_ty, make_overloaded_lvalue_return_type(fcx.tcx(), method).ty)
     })
 }
 
@@ -2907,7 +2897,7 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
         let (_, autoderefs, field_ty) = autoderef(fcx,
                                                   expr.span,
                                                   expr_t,
-                                                  Some(base),
+                                                  || Some(base),
                                                   UnresolvedTypeAction::Error,
                                                   lvalue_pref,
                                                   |base_t, _| {
@@ -3005,7 +2995,7 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
         let (_, autoderefs, field_ty) = autoderef(fcx,
                                                   expr.span,
                                                   expr_t,
-                                                  Some(base),
+                                                  || Some(base),
                                                   UnresolvedTypeAction::Error,
                                                   lvalue_pref,
                                                   |base_t, _| {
@@ -3253,21 +3243,21 @@ fn check_expr_with_unifier<'a, 'tcx, F>(fcx: &FnCtxt<'a, 'tcx>,
             match unop {
                 hir::UnDeref => {
                     oprnd_t = structurally_resolved_type(fcx, expr.span, oprnd_t);
-                    oprnd_t = match oprnd_t.builtin_deref(true, NoPreference) {
+
-                        Some(mt) => mt.ty,
+                    if let Some(mt) = oprnd_t.builtin_deref(true, NoPreference) {
-                        None => match try_overloaded_deref(fcx, expr.span,
+                        oprnd_t = mt.ty;
-                                                           Some(MethodCall::expr(expr.id)),
+                    } else if let Some(method) = try_overloaded_deref(
-                                                           Some(&oprnd), oprnd_t, lvalue_pref) {
+                            fcx, expr.span, Some(&oprnd), oprnd_t, lvalue_pref) {
-                            Some(mt) => mt.ty,
+                        oprnd_t = make_overloaded_lvalue_return_type(tcx, method).ty;
-                            None => {
+                        fcx.inh.tables.borrow_mut().method_map.insert(MethodCall::expr(expr.id),
-                                fcx.type_error_message(expr.span, |actual| {
+                                                                      method);
-                                    format!("type `{}` cannot be \
+                    } else {
-                                            dereferenced", actual)
+                        fcx.type_error_message(expr.span, |actual| {
-                                }, oprnd_t, None);
+                            format!("type `{}` cannot be \
-                                tcx.types.err
+                                    dereferenced", actual)
-                            }
+                        }, oprnd_t, None);
-                        }
+                        oprnd_t = tcx.types.err;
-                    };
+                    }
                 }
                 hir::UnNot => {
                     oprnd_t = structurally_resolved_type(fcx, oprnd.span,