Auto merge of #41651 - arielb1:missing-adjustment-2, r=eddyb

refactor the handling of lvalue ops

I think I got the code into a "mostly sane" situation.

Fixes #41604.

beta-nominating because fixes regression in #41578. I think I can do a smaller fix, but the previous code is too fragile.

r? @eddyb

src/librustc_typeck/check/autoderef.rs

@@ -10,7 +10,7 @@
 
 use astconv::AstConv;
 
-use super::FnCtxt;
+use super::{FnCtxt, LvalueOp};
 
 use check::coercion::AsCoercionSite;
 use rustc::infer::InferOk;
@@ -18,7 +18,7 @@ use rustc::traits;
 use rustc::ty::{self, Ty, TraitRef};
 use rustc::ty::{ToPredicate, TypeFoldable};
 use rustc::ty::{MethodCall, MethodCallee};
-use rustc::ty::{LvaluePreference, NoPreference, PreferMutLvalue};
+use rustc::ty::{LvaluePreference, NoPreference};
 use rustc::hir;
 
 use syntax_pos::Span;
@@ -213,39 +213,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                 span: Span,
                                 base_expr: Option<&hir::Expr>,
                                 base_ty: Ty<'tcx>,
-                                lvalue_pref: LvaluePreference)
+                                pref: LvaluePreference)
                                 -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
-        debug!("try_overloaded_deref({:?},{:?},{:?},{:?})",
+        let rcvr = base_expr.map(|base_expr| super::AdjustedRcvr {
-               span,
+            rcvr_expr: base_expr, autoderefs: 0, unsize: false
-               base_expr,
+        });
-               base_ty,
-               lvalue_pref);
-        // Try DerefMut first, if preferred.
-        let method = match (lvalue_pref, self.tcx.lang_items.deref_mut_trait()) {
-            (PreferMutLvalue, Some(trait_did)) => {
-                self.lookup_method_in_trait(span,
-                                            base_expr,
-                                            Symbol::intern("deref_mut"),
-                                            trait_did,
-                                            base_ty,
-                                            None)
-            }
-            _ => None,
-        };
 
-        // Otherwise, fall back to Deref.
+        self.try_overloaded_lvalue_op(span, rcvr, base_ty, &[], pref, LvalueOp::Deref)
-        let method = match (method, self.tcx.lang_items.deref_trait()) {
-            (None, Some(trait_did)) => {
-                self.lookup_method_in_trait(span,
-                                            base_expr,
-                                            Symbol::intern("deref"),
-                                            trait_did,
-                                            base_ty,
-                                            None)
-            }
-            (method, _) => method,
-        };
-
-        method
     }
 }

src/librustc_typeck/check/callee.rs

@@ -165,11 +165,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             };
 
             match self.lookup_method_in_trait_adjusted(call_expr.span,
-                                                       Some(&callee_expr),
+                                                       Some(super::AdjustedRcvr {
+                                                           rcvr_expr: callee_expr,
+                                                           autoderefs,
+                                                           unsize: false
+                                                       }),
                                                        method_name,
                                                        trait_def_id,
-                                                       autoderefs,
-                                                       false,
                                                        adjusted_ty,
                                                        None) {
                 None => continue,

src/librustc_typeck/check/method/confirm.rs

@@ -10,7 +10,7 @@
 
 use super::probe;
 
-use check::{FnCtxt, callee};
+use check::{FnCtxt, LvalueOp, callee};
 use hir::def_id::DefId;
 use rustc::ty::subst::Substs;
 use rustc::traits;
@@ -433,11 +433,25 @@ impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
         for (i, &expr) in exprs.iter().rev().enumerate() {
             debug!("convert_lvalue_derefs_to_mutable: i={} expr={:?}", i, expr);
 
-            // Count autoderefs. We don't need to fix up the autoref - the parent
+            // Fix up the adjustment.
-            // expression will fix them up for us.
+            let autoderefs = match self.tables.borrow_mut().adjustments.get_mut(&expr.id) {
-            let adjustment = self.tables.borrow().adjustments.get(&expr.id).cloned();
+                Some(&mut Adjustment {
-            match adjustment {
+                    kind: Adjust::DerefRef { autoderefs, ref mut autoref, .. }, ref mut target
-                Some(Adjustment { kind: Adjust::DerefRef { autoderefs, .. }, .. }) => {
+                }) => {
+                    if let &mut Some(AutoBorrow::Ref(_, ref mut mutbl)) = autoref {
+                        *mutbl = hir::Mutability::MutMutable;
+                        *target = match target.sty {
+                            ty::TyRef(r, ty::TypeAndMut { ty, .. }) =>
+                                self.tcx.mk_ref(r, ty::TypeAndMut { ty, mutbl: *mutbl }),
+                            _ => span_bug!(expr.span, "AutoBorrow::Ref resulted in non-ref {:?}",
+                                           target)
+                        };
+                    }
+                    autoderefs
+                }
+                Some(_) | None => 0
+            };
+
             if autoderefs > 0 {
                 let mut autoderef = self.autoderef(expr.span, self.node_ty(expr.id));
                 autoderef.nth(autoderefs).unwrap_or_else(|| {
@@ -447,123 +461,53 @@ impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
                 });
                 autoderef.finalize(PreferMutLvalue, expr);
             }
-                }
-                Some(_) | None => {}
-            }
 
-            // Don't retry the first one or we might infinite loop!
-            if i == 0 {
-                continue;
-            }
             match expr.node {
                 hir::ExprIndex(ref base_expr, ref index_expr) => {
-                    // If this is an overloaded index, the
-                    // adjustment will include an extra layer of
-                    // autoref because the method is an &self/&mut
-                    // self method. We have to peel it off to get
-                    // the raw adjustment that `try_index_step`
-                    // expects. This is annoying and horrible. We
-                    // ought to recode this routine so it doesn't
-                    // (ab)use the normal type checking paths.
-                    let adj = self.tables.borrow_mut().adjustments.remove(&base_expr.id);
-                    let (autoderefs, unsize, adjusted_base_ty) = match adj {
-                        Some(Adjustment {
-                            kind: Adjust::DerefRef { autoderefs, autoref, unsize },
-                            target
-                        }) => {
-                            match autoref {
-                                None => {
-                                    assert!(!unsize);
-                                }
-                                Some(AutoBorrow::Ref(..)) => {}
-                                Some(_) => {
-                                    span_bug!(base_expr.span,
-                                              "unexpected adjustment autoref {:?}",
-                                              adj);
-                                }
-                            }
-
-                            (autoderefs, unsize, if unsize {
-                                target.builtin_deref(false, NoPreference)
-                                      .expect("fixup: AutoBorrow::Ref is not &T")
-                                      .ty
-                            } else {
-                                let ty = self.node_ty(base_expr.id);
-                                let mut ty = self.shallow_resolve(ty);
-                                let mut method_type = |method_call: ty::MethodCall| {
-                                    self.tables.borrow().method_map.get(&method_call).map(|m| {
-                                        self.resolve_type_vars_if_possible(&m.ty)
-                                    })
-                                };
-
-                                if !ty.references_error() {
-                                    for i in 0..autoderefs {
-                                        ty = ty.adjust_for_autoderef(self.tcx,
-                                                                     base_expr.id,
-                                                                     base_expr.span,
-                                                                     i as u32,
-                                                                     &mut method_type);
-                                    }
-                                }
-
-                                ty
-                            })
-                        }
-                        None => (0, false, self.node_ty(base_expr.id)),
-                        Some(_) => {
-                            span_bug!(base_expr.span, "unexpected adjustment type");
-                        }
-                    };
-
                     let index_expr_ty = self.node_ty(index_expr.id);
-                    let adjusted_base_ty = self.resolve_type_vars_if_possible(&adjusted_base_ty);
+                    self.convert_lvalue_op_to_mutable(
-                    let index_expr_ty = self.resolve_type_vars_if_possible(&index_expr_ty);
+                        LvalueOp::Index, expr, base_expr, &[index_expr_ty]);
-
-                    let result = self.try_index_step(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 {
-                        self.demand_suptype(index_expr.span, input_ty, index_expr_ty);
-
-                        let expr_ty = self.node_ty(expr.id);
-                        self.demand_suptype(expr.span, expr_ty, return_ty);
-                    } else {
-                        // We could not perform a mutable index. Re-apply the
-                        // immutable index adjustments - borrowck will detect
-                        // this as an error.
-                        if let Some(adjustment) = adjustment {
-                            self.apply_adjustment(expr.id, adjustment);
-                        }
-                        self.tcx.sess.delay_span_bug(
-                            expr.span, "convert_lvalue_derefs_to_mutable failed");
-                    }
                 }
                 hir::ExprUnary(hir::UnDeref, ref base_expr) => {
-                    // if this is an overloaded deref, then re-evaluate with
+                    self.convert_lvalue_op_to_mutable(
-                    // a preference for mut
+                        LvalueOp::Deref, expr, base_expr, &[]);
-                    let method_call = ty::MethodCall::expr(expr.id);
-                    if self.tables.borrow().method_map.contains_key(&method_call) {
-                        self.tables.borrow_mut().adjustments.remove(&base_expr.id);
-                        let method = self.try_overloaded_deref(expr.span,
-                                                               Some(&base_expr),
-                                                               self.node_ty(base_expr.id),
-                                                               PreferMutLvalue);
-                        let ok = method.expect("re-trying deref failed");
-                        let method = self.register_infer_ok_obligations(ok);
-                        self.tables.borrow_mut().method_map.insert(method_call, method);
-                    }
                 }
                 _ => {}
             }
         }
     }
 
+    fn convert_lvalue_op_to_mutable(&self,
+                                    op: LvalueOp,
+                                    expr: &hir::Expr,
+                                    base_expr: &hir::Expr,
+                                    arg_tys: &[Ty<'tcx>])
+    {
+        debug!("convert_lvalue_op_to_mutable({:?}, {:?}, {:?}, {:?})",
+               op, expr, base_expr, arg_tys);
+        let method_call = ty::MethodCall::expr(expr.id);
+        if !self.tables.borrow().method_map.contains_key(&method_call) {
+            debug!("convert_lvalue_op_to_mutable - builtin, nothing to do");
+            return
+        }
+
+        let base_ty = self.tables.borrow().adjustments.get(&base_expr.id)
+            .map_or_else(|| self.node_ty(expr.id), |adj| adj.target);
+        let base_ty = self.resolve_type_vars_if_possible(&base_ty);
+
+        // Need to deref because overloaded lvalue ops take self by-reference.
+        let base_ty = base_ty.builtin_deref(false, NoPreference)
+            .expect("lvalue op takes something that is not a ref")
+            .ty;
+
+        let method = self.try_overloaded_lvalue_op(
+            expr.span, None, base_ty, arg_tys, PreferMutLvalue, op);
+        let ok = method.expect("re-trying op failed");
+        let method = self.register_infer_ok_obligations(ok);
+        debug!("convert_lvalue_op_to_mutable: method={:?}", method);
+        self.tables.borrow_mut().method_map.insert(method_call, method);
+    }
+
     ///////////////////////////////////////////////////////////////////////////
     // MISCELLANY
 

src/librustc_typeck/check/method/mod.rs

@@ -10,7 +10,7 @@
 
 //! Method lookup: the secret sauce of Rust. See `README.md`.
 
-use check::FnCtxt;
+use check::{FnCtxt, AdjustedRcvr};
 use hir::def::Def;
 use hir::def_id::DefId;
 use rustc::ty::subst::Substs;
@@ -153,24 +153,6 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                supplied_method_types))
     }
 
-    pub fn lookup_method_in_trait(&self,
-                                  span: Span,
-                                  self_expr: Option<&hir::Expr>,
-                                  m_name: ast::Name,
-                                  trait_def_id: DefId,
-                                  self_ty: ty::Ty<'tcx>,
-                                  opt_input_types: Option<Vec<ty::Ty<'tcx>>>)
-                                  -> Option<InferOk<'tcx, ty::MethodCallee<'tcx>>> {
-        self.lookup_method_in_trait_adjusted(span,
-                                             self_expr,
-                                             m_name,
-                                             trait_def_id,
-                                             0,
-                                             false,
-                                             self_ty,
-                                             opt_input_types)
-    }
-
     /// `lookup_in_trait_adjusted` is used for overloaded operators.
     /// It does a very narrow slice of what the normal probe/confirm path does.
     /// In particular, it doesn't really do any probing: it simply constructs
@@ -184,18 +166,16 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     /// this method is basically the same as confirmation.
     pub fn lookup_method_in_trait_adjusted(&self,
                                            span: Span,
-                                           self_expr: Option<&hir::Expr>,
+                                           self_info: Option<AdjustedRcvr>,
                                            m_name: ast::Name,
                                            trait_def_id: DefId,
-                                           autoderefs: usize,
-                                           unsize: bool,
                                            self_ty: ty::Ty<'tcx>,
                                            opt_input_types: Option<Vec<ty::Ty<'tcx>>>)
                                            -> Option<InferOk<'tcx, ty::MethodCallee<'tcx>>> {
-        debug!("lookup_in_trait_adjusted(self_ty={:?}, self_expr={:?}, \
+        debug!("lookup_in_trait_adjusted(self_ty={:?}, self_info={:?}, \
                 m_name={}, trait_def_id={:?})",
                self_ty,
-               self_expr,
+               self_info,
                m_name,
                trait_def_id);
 
@@ -288,10 +268,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         obligations.push(traits::Obligation::new(cause, ty::Predicate::WellFormed(method_ty)));
 
         // Insert any adjustments needed (always an autoref of some mutability).
-        if let Some(self_expr) = self_expr {
+        if let Some(AdjustedRcvr { rcvr_expr, autoderefs, unsize }) = self_info {
             debug!("lookup_in_trait_adjusted: inserting adjustment if needed \
                     (self-id={}, autoderefs={}, unsize={}, fty={:?})",
-                    self_expr.id, autoderefs, unsize, original_method_ty);
+                    rcvr_expr.id, autoderefs, unsize, original_method_ty);
 
             let original_sig = original_method_ty.fn_sig();
             let autoref = match (&original_sig.input(0).skip_binder().sty,
@@ -308,7 +288,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
             };
 
-            self.apply_adjustment(self_expr.id, Adjustment {
+            self.apply_adjustment(rcvr_expr.id, Adjustment {
                 kind: Adjust::DerefRef {
                     autoderefs: autoderefs,
                     autoref: autoref,

src/librustc_typeck/check/mod.rs

@@ -361,6 +361,19 @@ impl UnsafetyState {
     }
 }
 
+#[derive(Debug, Copy, Clone)]
+pub enum LvalueOp {
+    Deref,
+    Index
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct AdjustedRcvr<'a> {
+    pub rcvr_expr: &'a hir::Expr,
+    pub autoderefs: usize,
+    pub unsize: bool
+}
+
 /// Tracks whether executing a node may exit normally (versus
 /// return/break/panic, which "diverge", leaving dead code in their
 /// wake). Tracked semi-automatically (through type variables marked
@@ -2156,9 +2169,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         while let Some((adj_ty, autoderefs)) = autoderef.next() {
             if let Some(final_mt) = self.try_index_step(
-                MethodCall::expr(expr.id),
+                MethodCall::expr(expr.id), expr, Some(AdjustedRcvr {
-                expr, base_expr, adj_ty, autoderefs,
+                    rcvr_expr: base_expr,
-                false, lvalue_pref, idx_ty)
+                    autoderefs,
+                    unsize: false
+                }), base_expr.span, adj_ty, lvalue_pref, idx_ty)
             {
                 autoderef.finalize(lvalue_pref, base_expr);
                 return Some(final_mt);
@@ -2166,10 +2181,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
             if let ty::TyArray(element_ty, _) = adj_ty.sty {
                 autoderef.finalize(lvalue_pref, base_expr);
-                let adjusted_ty = self.tcx.mk_slice(element_ty);
+                let adj_ty = self.tcx.mk_slice(element_ty);
                 return self.try_index_step(
-                    MethodCall::expr(expr.id), expr, base_expr,
+                    MethodCall::expr(expr.id), expr, Some(AdjustedRcvr {
-                    adjusted_ty, autoderefs, true, lvalue_pref, idx_ty);
+                        rcvr_expr: base_expr,
+                        autoderefs,
+                        unsize: true
+                    }), base_expr.span, adj_ty, lvalue_pref, idx_ty)
             }
         }
         autoderef.unambiguous_final_ty();
@@ -2184,71 +2202,44 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     fn try_index_step(&self,
                       method_call: MethodCall,
                       expr: &hir::Expr,
-                      base_expr: &'gcx hir::Expr,
+                      base_expr: Option<AdjustedRcvr>,
+                      base_span: Span,
                       adjusted_ty: Ty<'tcx>,
-                      autoderefs: usize,
-                      unsize: bool,
                       lvalue_pref: LvaluePreference,
                       index_ty: Ty<'tcx>)
                       -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)>
     {
         let tcx = self.tcx;
-        debug!("try_index_step(expr={:?}, base_expr.id={:?}, adjusted_ty={:?}, \
+        debug!("try_index_step(expr={:?}, base_expr={:?}, adjusted_ty={:?}, \
-                               autoderefs={}, unsize={}, index_ty={:?})",
+                               index_ty={:?})",
                expr,
                base_expr,
                adjusted_ty,
-               autoderefs,
-               unsize,
                index_ty);
 
-        let input_ty = self.next_ty_var(TypeVariableOrigin::AutoDeref(base_expr.span));
+        let input_ty = self.next_ty_var(TypeVariableOrigin::AutoDeref(base_span));
 
         // First, try built-in indexing.
         match (adjusted_ty.builtin_index(), &index_ty.sty) {
             (Some(ty), &ty::TyUint(ast::UintTy::Us)) | (Some(ty), &ty::TyInfer(ty::IntVar(_))) => {
                 debug!("try_index_step: success, using built-in indexing");
                 // If we had `[T; N]`, we should've caught it before unsizing to `[T]`.
-                assert!(!unsize);
+                if let Some(base_expr) = base_expr {
-                self.apply_autoderef_adjustment(base_expr.id, autoderefs, adjusted_ty);
+                    assert!(!base_expr.unsize);
+                    self.apply_autoderef_adjustment(
+                        base_expr.rcvr_expr.id, base_expr.autoderefs, adjusted_ty);
+                }
                 return Some((tcx.types.usize, ty));
             }
             _ => {}
         }
 
-        // Try `IndexMut` first, if preferred.
-        let method = match (lvalue_pref, tcx.lang_items.index_mut_trait()) {
-            (PreferMutLvalue, Some(trait_did)) => {
-                self.lookup_method_in_trait_adjusted(expr.span,
-                                                     Some(&base_expr),
-                                                     Symbol::intern("index_mut"),
-                                                     trait_did,
-                                                     autoderefs,
-                                                     unsize,
-                                                     adjusted_ty,
-                                                     Some(vec![input_ty]))
-            }
-            _ => None,
-        };
-
-        // Otherwise, fall back to `Index`.
-        let method = match (method, tcx.lang_items.index_trait()) {
-            (None, Some(trait_did)) => {
-                self.lookup_method_in_trait_adjusted(expr.span,
-                                                     Some(&base_expr),
-                                                     Symbol::intern("index"),
-                                                     trait_did,
-                                                     autoderefs,
-                                                     unsize,
-                                                     adjusted_ty,
-                                                     Some(vec![input_ty]))
-            }
-            (method, _) => method,
-        };
-
         // 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
+        let method = self.try_overloaded_lvalue_op(
+            expr.span, base_expr, adjusted_ty, &[input_ty], lvalue_pref, LvalueOp::Index);
+
         method.map(|ok| {
             debug!("try_index_step: success, using overloaded indexing");
             let method = self.register_infer_ok_obligations(ok);
@@ -2257,6 +2248,67 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         })
     }
 
+    fn resolve_lvalue_op(&self, op: LvalueOp, is_mut: bool) -> (Option<DefId>, Symbol) {
+        let (tr, name) = match (op, is_mut) {
+            (LvalueOp::Deref, false) =>
+                (self.tcx.lang_items.deref_trait(), "deref"),
+            (LvalueOp::Deref, true) =>
+                (self.tcx.lang_items.deref_mut_trait(), "deref_mut"),
+            (LvalueOp::Index, false) =>
+                (self.tcx.lang_items.index_trait(), "index"),
+            (LvalueOp::Index, true) =>
+                (self.tcx.lang_items.index_mut_trait(), "index_mut"),
+        };
+        (tr, Symbol::intern(name))
+    }
+
+    fn try_overloaded_lvalue_op(&self,
+                                span: Span,
+                                base_expr: Option<AdjustedRcvr>,
+                                base_ty: Ty<'tcx>,
+                                arg_tys: &[Ty<'tcx>],
+                                lvalue_pref: LvaluePreference,
+                                op: LvalueOp)
+                                -> Option<InferOk<'tcx, MethodCallee<'tcx>>>
+    {
+        debug!("try_overloaded_lvalue_op({:?},{:?},{:?},{:?},{:?})",
+               span,
+               base_expr,
+               base_ty,
+               lvalue_pref,
+               op);
+
+        // Try Mut first, if preferred.
+        let (mut_tr, mut_op) = self.resolve_lvalue_op(op, true);
+        let method = match (lvalue_pref, mut_tr) {
+            (PreferMutLvalue, Some(trait_did)) => {
+                self.lookup_method_in_trait_adjusted(span,
+                                                     base_expr,
+                                                     mut_op,
+                                                     trait_did,
+                                                     base_ty,
+                                                     Some(arg_tys.to_owned()))
+            }
+            _ => None,
+        };
+
+        // Otherwise, fall back to the immutable version.
+        let (imm_tr, imm_op) = self.resolve_lvalue_op(op, false);
+        let method = match (method, imm_tr) {
+            (None, Some(trait_did)) => {
+                self.lookup_method_in_trait_adjusted(span,
+                                                     base_expr,
+                                                     imm_op,
+                                                     trait_did,
+                                                     base_ty,
+                                                     Some(arg_tys.to_owned()))
+            }
+            (method, _) => method,
+        };
+
+        method
+    }
+
     fn check_method_argument_types(&self,
                                    sp: Span,
                                    method_fn_ty: Ty<'tcx>,

src/librustc_typeck/check/op.rs

@@ -398,8 +398,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         let method = match trait_did {
             Some(trait_did) => {
-                self.lookup_method_in_trait(expr.span,
+                let lhs_expr = Some(super::AdjustedRcvr {
-                                            Some(lhs_expr),
+                    rcvr_expr: lhs_expr, autoderefs: 0, unsize: false
+                });
+                self.lookup_method_in_trait_adjusted(expr.span,
+                                                     lhs_expr,
                                                      opname,
                                                      trait_did,
                                                      lhs_ty,

src/test/run-pass/issue-41604.rs

@@ -0,0 +1,20 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct B;
+
+impl B {
+    fn init(&mut self) {}
+}
+
+fn main() {
+    let mut b = [B];
+    b[1-1].init();
+}