Fix multiple mutable autoderefs with `Box`

Closes #26205.

src/librustc/middle/check_match.rs

@@ -664,7 +664,7 @@ fn is_useful(cx: &MatchCheckCtxt,
 
         match real_pat.node {
             hir::PatIdent(hir::BindByRef(..), _, _) => {
-                left_ty.builtin_deref(false).unwrap().ty
+                left_ty.builtin_deref(false, NoPreference).unwrap().ty
             }
             _ => left_ty,
         }

src/librustc/middle/mem_categorization.rs

@@ -400,7 +400,7 @@ fn pat_ty(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
                 // a bind-by-ref means that the base_ty will be the type of the ident itself,
                 // but what we want here is the type of the underlying value being borrowed.
                 // So peel off one-level, turning the &T into T.
-                match base_ty.builtin_deref(false) {
+                match base_ty.builtin_deref(false, ty::NoPreference) {
                     Some(t) => t.ty,
                     None => { return Err(()); }
                 }
@@ -897,7 +897,7 @@ fn cat_deref<N:ast_node>(&self,
             None => base_cmt
         };
         let base_cmt_ty = base_cmt.ty;
-        match base_cmt_ty.builtin_deref(true) {
+        match base_cmt_ty.builtin_deref(true, ty::NoPreference) {
             Some(mt) => {
                 let ret = self.cat_deref_common(node, base_cmt, deref_cnt,
                                               mt.ty,
@@ -1044,7 +1044,7 @@ fn deref_vec<N:ast_node>(&self,
                     span:elt.span(),
                     cat:cat_deref(base_cmt.clone(), 0, ptr),
                     mutbl:m,
-                    ty: match base_cmt.ty.builtin_deref(false) {
+                    ty: match base_cmt.ty.builtin_deref(false, ty::NoPreference) {
                         Some(mt) => mt.ty,
                         None => self.tcx().sess.bug("Found non-derefable type")
                     },

src/librustc/middle/ty.rs

@@ -29,6 +29,7 @@
 pub use self::TypeVariants::*;
 pub use self::IntVarValue::*;
 pub use self::CopyImplementationError::*;
+pub use self::LvaluePreference::*;
 
 pub use self::BuiltinBound::Send as BoundSend;
 pub use self::BuiltinBound::Sized as BoundSized;
@@ -4828,6 +4829,21 @@ fn is_sized_uncached<'a>(&'tcx self, param_env: &ParameterEnvironment<'a,'tcx>,
     }
 }
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum LvaluePreference {
+    PreferMutLvalue,
+    NoPreference
+}
+
+impl LvaluePreference {
+    pub fn from_mutbl(m: hir::Mutability) -> Self {
+        match m {
+            hir::MutMutable => PreferMutLvalue,
+            hir::MutImmutable => NoPreference,
+        }
+    }
+}
+
 /// Describes whether a type is representable. For types that are not
 /// representable, 'SelfRecursive' and 'ContainsRecursive' are used to
 /// distinguish between types that are recursive with themselves and types that
@@ -5073,12 +5089,15 @@ pub fn is_machine(&self) -> bool {
     //
     // The parameter `explicit` indicates if this is an *explicit* dereference.
     // Some types---notably unsafe ptrs---can only be dereferenced explicitly.
-    pub fn builtin_deref(&self, explicit: bool) -> Option<TypeAndMut<'tcx>> {
+    pub fn builtin_deref(&self, explicit: bool, pref: LvaluePreference)
+        -> Option<TypeAndMut<'tcx>>
+    {
         match self.sty {
             TyBox(ty) => {
                 Some(TypeAndMut {
                     ty: ty,
-                    mutbl: hir::MutImmutable,
+                    mutbl:
+                        if pref == PreferMutLvalue { hir::MutMutable } else { hir::MutImmutable },
                 })
             },
             TyRef(_, mt) => Some(mt),
@@ -5183,7 +5202,7 @@ pub fn adjust<F>(&'tcx self, cx: &ctxt<'tcx>,
                                     }
                                     None => {}
                                 }
-                                match adjusted_ty.builtin_deref(true) {
+                                match adjusted_ty.builtin_deref(true, NoPreference) {
                                     Some(mt) => { adjusted_ty = mt.ty; }
                                     None => {
                                         cx.sess.span_bug(

src/librustc_trans/trans/consts.rs

@@ -155,7 +155,7 @@ fn const_deref<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                          v: ValueRef,
                          ty: Ty<'tcx>)
                          -> (ValueRef, Ty<'tcx>) {
-    match ty.builtin_deref(true) {
+    match ty.builtin_deref(true, ty::NoPreference) {
         Some(mt) => {
             if type_is_sized(cx.tcx(), mt.ty) {
                 (const_deref_ptr(cx, v), mt.ty)
@@ -329,7 +329,7 @@ pub fn const_expr<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                                               param_substs,
                                                               &target);
 
-                let pointee_ty = ty.builtin_deref(true)
+                let pointee_ty = ty.builtin_deref(true, ty::NoPreference)
                     .expect("consts: unsizing got non-pointer type").ty;
                 let (base, old_info) = if !type_is_sized(cx.tcx(), pointee_ty) {
                     // Normally, the source is a thin pointer and we are
@@ -344,7 +344,7 @@ pub fn const_expr<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                     (llconst, None)
                 };
 
-                let unsized_ty = target.builtin_deref(true)
+                let unsized_ty = target.builtin_deref(true, ty::NoPreference)
                     .expect("consts: unsizing got non-pointer target type").ty;
                 let ptr_ty = type_of::in_memory_type_of(cx, unsized_ty).ptr_to();
                 let base = ptrcast(base, ptr_ty);
@@ -642,7 +642,8 @@ fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
             }
             if type_is_fat_ptr(cx.tcx(), t_expr) {
                 // Fat pointer casts.
-                let t_cast_inner = t_cast.builtin_deref(true).expect("cast to non-pointer").ty;
+                let t_cast_inner =
+                    t_cast.builtin_deref(true, ty::NoPreference).expect("cast to non-pointer").ty;
                 let ptr_ty = type_of::in_memory_type_of(cx, t_cast_inner).ptr_to();
                 let addr = ptrcast(const_get_elt(cx, v, &[abi::FAT_PTR_ADDR as u32]),
                                    ptr_ty);

src/librustc_trans/trans/expr.rs

@@ -780,7 +780,7 @@ fn trans_index<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 
             let ref_ty = // invoked methods have LB regions instantiated:
                 bcx.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap().unwrap();
-            let elt_ty = match ref_ty.builtin_deref(true) {
+            let elt_ty = match ref_ty.builtin_deref(true, ty::NoPreference) {
                 None => {
                     bcx.tcx().sess.span_bug(index_expr.span,
                                             "index method didn't return a \
@@ -1971,7 +1971,8 @@ pub fn cast_is_noop<'tcx>(tcx: &ty::ctxt<'tcx>,
         return true;
     }
 
-    match (t_in.builtin_deref(true), t_out.builtin_deref(true)) {
+    match (t_in.builtin_deref(true, ty::NoPreference),
+           t_out.builtin_deref(true, ty::NoPreference)) {
         (Some(ty::TypeAndMut{ ty: t_in, .. }), Some(ty::TypeAndMut{ ty: t_out, .. })) => {
             t_in == t_out
         }

src/librustc_typeck/check/_match.rs

@@ -15,10 +15,10 @@
 use middle::pat_util::pat_is_resolved_const;
 use middle::privacy::{AllPublic, LastMod};
 use middle::subst::Substs;
-use middle::ty::{self, Ty, HasTypeFlags};
+use middle::ty::{self, Ty, HasTypeFlags, LvaluePreference};
 use check::{check_expr, check_expr_has_type, check_expr_with_expectation};
 use check::{check_expr_coercable_to_type, demand, FnCtxt, Expectation};
-use check::{check_expr_with_lvalue_pref, LvaluePreference};
+use check::{check_expr_with_lvalue_pref};
 use check::{instantiate_path, resolve_ty_and_def_ufcs, structurally_resolved_type};
 use require_same_types;
 use util::nodemap::FnvHashMap;
@@ -292,7 +292,7 @@ pub fn check_pat<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
                     let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
                     tcx.mk_ref(tcx.mk_region(region), ty::TypeAndMut {
                         ty: tcx.mk_slice(inner_ty),
-                        mutbl: expected_ty.builtin_deref(true).map(|mt| mt.mutbl)
+                        mutbl: expected_ty.builtin_deref(true, ty::NoPreference).map(|mt| mt.mutbl)
                                                               .unwrap_or(hir::MutImmutable)
                     })
                 }
@@ -310,7 +310,7 @@ pub fn check_pat<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
             }
             if let Some(ref slice) = *slice {
                 let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
-                let mutbl = expected_ty.builtin_deref(true)
+                let mutbl = expected_ty.builtin_deref(true, ty::NoPreference)
                     .map_or(hir::MutImmutable, |mt| mt.mutbl);
 
                 let slice_ty = tcx.mk_ref(tcx.mk_region(region), ty::TypeAndMut {
@@ -399,7 +399,7 @@ pub fn check_dereferencable<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
     let tcx = pcx.fcx.ccx.tcx;
     if pat_is_binding(&tcx.def_map, inner) {
         let expected = fcx.infcx().shallow_resolve(expected);
-        expected.builtin_deref(true).map_or(true, |mt| match mt.ty.sty {
+        expected.builtin_deref(true, ty::NoPreference).map_or(true, |mt| match mt.ty.sty {
             ty::TyTrait(_) => {
                 // This is "x = SomeTrait" being reduced from
                 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.

src/librustc_typeck/check/callee.rs

@@ -18,7 +18,6 @@
 use super::Expectation;
 use super::expected_types_for_fn_args;
 use super::FnCtxt;
-use super::LvaluePreference;
 use super::method;
 use super::structurally_resolved_type;
 use super::TupleArgumentsFlag;
@@ -28,7 +27,7 @@
 use CrateCtxt;
 use middle::def_id::{DefId, LOCAL_CRATE};
 use middle::infer;
-use middle::ty::{self, Ty};
+use middle::ty::{self, LvaluePreference, Ty};
 use syntax::codemap::Span;
 use syntax::parse::token;
 use syntax::ptr::P;

src/librustc_typeck/check/coercion.rs

@@ -60,13 +60,13 @@
 //! sort of a minor point so I've opted to leave it for later---after all
 //! we may want to adjust precisely when coercions occur.
 
-use check::{autoderef, FnCtxt, LvaluePreference, UnresolvedTypeAction};
+use check::{autoderef, FnCtxt, UnresolvedTypeAction};
 
 use middle::infer::{self, Coercion};
 use middle::traits::{self, ObligationCause};
 use middle::traits::{predicate_for_trait_def, report_selection_error};
 use middle::ty::{AutoDerefRef, AdjustDerefRef};
-use middle::ty::{self, TypeAndMut, Ty, TypeError};
+use middle::ty::{self, LvaluePreference, TypeAndMut, Ty, TypeError};
 use middle::ty_relate::RelateResult;
 use util::common::indent;
 

src/librustc_typeck/check/method/confirm.rs

@@ -10,12 +10,12 @@
 
 use super::probe;
 
-use check::{self, FnCtxt, NoPreference, PreferMutLvalue, callee, demand};
+use check::{self, FnCtxt, callee, demand};
 use check::UnresolvedTypeAction;
 use middle::def_id::DefId;
 use middle::subst::{self};
 use middle::traits;
-use middle::ty::{self, Ty};
+use middle::ty::{self, NoPreference, PreferMutLvalue, Ty};
 use middle::ty_fold::TypeFoldable;
 use middle::infer;
 use middle::infer::InferCtxt;
@@ -534,7 +534,7 @@ fn fixup_derefs_on_method_receiver_if_necessary(&self,
                                 }
                                 Some(ty::AutoPtr(_, _)) => {
                                     (adr.autoderefs, adr.unsize.map(|target| {
-                                        target.builtin_deref(false)
+                                        target.builtin_deref(false, NoPreference)
                                               .expect("fixup: AutoPtr is not &T").ty
                                     }))
                                 }

src/librustc_typeck/check/method/probe.rs

@@ -14,13 +14,13 @@
 use super::suggest;
 
 use check;
-use check::{FnCtxt, NoPreference, UnresolvedTypeAction};
+use check::{FnCtxt, UnresolvedTypeAction};
 use middle::def_id::DefId;
 use middle::fast_reject;
 use middle::subst;
 use middle::subst::Subst;
 use middle::traits;
-use middle::ty::{self, RegionEscape, Ty, ToPolyTraitRef, TraitRef};
+use middle::ty::{self, NoPreference, RegionEscape, Ty, ToPolyTraitRef, TraitRef};
 use middle::ty::HasTypeFlags;
 use middle::ty_fold::TypeFoldable;
 use middle::infer;

src/librustc_typeck/check/method/suggest.rs

@@ -324,7 +324,7 @@ fn is_local(ty: Ty) -> bool {
     }
 
     check::autoderef(fcx, span, rcvr_ty, None,
-                     check::UnresolvedTypeAction::Ignore, check::NoPreference,
+                     check::UnresolvedTypeAction::Ignore, ty::NoPreference,
                      |ty, _| {
         if is_local(ty) {
             Some(())

src/librustc_typeck/check/mod.rs

@@ -76,7 +76,6 @@
 
 */
 
-pub use self::LvaluePreference::*;
 pub use self::Expectation::*;
 pub use self::compare_method::{compare_impl_method, compare_const_impl};
 use self::TupleArgumentsFlag::*;
@@ -95,6 +94,7 @@
 use middle::traits::{self, report_fulfillment_errors};
 use middle::ty::{FnSig, GenericPredicates, TypeScheme};
 use middle::ty::{Disr, ParamTy, ParameterEnvironment};
+use middle::ty::{LvaluePreference, NoPreference, PreferMutLvalue};
 use middle::ty::{self, HasTypeFlags, RegionEscape, ToPolyTraitRef, Ty};
 use middle::ty::{MethodCall, MethodCallee};
 use middle::ty_fold::{TypeFolder, TypeFoldable};
@@ -2086,21 +2086,6 @@ fn anon_regions(&self, span: Span, count: usize)
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum LvaluePreference {
-    PreferMutLvalue,
-    NoPreference
-}
-
-impl LvaluePreference {
-    pub fn from_mutbl(m: hir::Mutability) -> Self {
-        match m {
-            hir::MutMutable => PreferMutLvalue,
-            hir::MutImmutable => NoPreference,
-        }
-    }
-}
-
 /// Whether `autoderef` requires types to resolve.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum UnresolvedTypeAction {
@@ -2156,7 +2141,7 @@ 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) {
+        let mt = match resolved_t.builtin_deref(false, lvalue_pref) {
             Some(mt) => Some(mt),
             None => {
                 let method_call =
@@ -2245,7 +2230,7 @@ fn make_overloaded_lvalue_return_type<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
             }
 
             // method returns &T, but the type as visible to user is T, so deref
-            ret_ty.builtin_deref(true)
+            ret_ty.builtin_deref(true, NoPreference)
         }
         None => None,
     }
@@ -3293,7 +3278,7 @@ fn check_expr_struct<'a, 'tcx>(fcx: &FnCtxt<'a,'tcx>,
                 }
                 hir::UnDeref => {
                     oprnd_t = structurally_resolved_type(fcx, expr.span, oprnd_t);
-                    oprnd_t = match oprnd_t.builtin_deref(true) {
+                    oprnd_t = match oprnd_t.builtin_deref(true, NoPreference) {
                         Some(mt) => mt.ty,
                         None => match try_overloaded_deref(fcx, expr.span,
                                                            Some(MethodCall::expr(expr.id)),

src/librustc_typeck/check/op.rs

@@ -17,12 +17,11 @@
     demand,
     method,
     FnCtxt,
-    PreferMutLvalue,
     structurally_resolved_type,
 };
 use middle::def_id::DefId;
 use middle::traits;
-use middle::ty::{Ty, HasTypeFlags};
+use middle::ty::{Ty, HasTypeFlags, PreferMutLvalue};
 use syntax::ast;
 use syntax::parse::token;
 use rustc_front::hir;

src/librustc_typeck/check/regionck.rs

@@ -1031,7 +1031,7 @@ fn constrain_autoderefs<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
                                             r_deref_expr, *r_ptr);
         }
 
-        match derefd_ty.builtin_deref(true) {
+        match derefd_ty.builtin_deref(true, ty::NoPreference) {
             Some(mt) => derefd_ty = mt.ty,
             /* if this type can't be dereferenced, then there's already an error
                in the session saying so. Just bail out for now */

src/test/run-pass/issue-26205.rs

+// Copyright 2015 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.
+
+use std::ops::{Deref, DerefMut};
+
+struct Foo;
+
+impl Foo {
+    fn foo_mut(&mut self) {}
+}
+
+struct Bar(Foo);
+
+impl Deref for Bar {
+    type Target = Foo;
+
+    fn deref(&self) -> &Foo {
+        &self.0
+    }
+}
+
+impl DerefMut for Bar {
+    fn deref_mut(&mut self) -> &mut Foo {
+        &mut self.0
+    }
+}
+
+fn test(mut bar: Box<Bar>) {
+    bar.foo_mut();
+}
+
+fn main() {}