Change method lookup to require invariance for mutable references

Fixes #17033.
Fixes #15965.

Author: Jakub Wieczorek

src/librustc/middle/typeck/check/method.rs

@@ -348,6 +348,7 @@ struct Candidate {
 pub enum RcvrMatchCondition {
     RcvrMatchesIfObject(ast::DefId),
     RcvrMatchesIfSubtype(ty::t),
+    RcvrMatchesIfEqtype(ty::t)
 }
 
 impl<'a, 'tcx> LookupContext<'a, 'tcx> {
@@ -675,6 +676,14 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                     }
                     _ => {}
                 }
+
+                let condition = match m.explicit_self {
+                    ByReferenceExplicitSelfCategory(_, mt) if mt == MutMutable =>
+                        RcvrMatchesIfEqtype(self_ty),
+                    _ =>
+                        RcvrMatchesIfSubtype(self_ty)
+                };
+
                 debug!("found match: trait_ref={} substs={} m={}",
                        trait_ref.repr(this.tcx()),
                        trait_ref.substs.repr(this.tcx()),
@@ -688,7 +697,7 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                 assert_eq!(m.generics.regions.get_slice(subst::SelfSpace).len(),
                            trait_ref.substs.regions().get_slice(subst::SelfSpace).len());
                 Some(Candidate {
-                    rcvr_match_condition: RcvrMatchesIfSubtype(self_ty),
+                    rcvr_match_condition: condition,
                     rcvr_substs: trait_ref.substs.clone(),
                     method_ty: m,
                     origin: MethodParam(MethodParam {
@@ -822,14 +831,21 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
             ty: impl_ty
         } = impl_self_ty(&vcx, span, impl_did);
 
+        let condition = match method.explicit_self {
+            ByReferenceExplicitSelfCategory(_, mt) if mt == MutMutable =>
+                RcvrMatchesIfEqtype(impl_ty),
+            _ =>
+                RcvrMatchesIfSubtype(impl_ty)
+        };
+
         let candidates = if is_extension {
             &mut self.extension_candidates
         } else {
             &mut self.inherent_candidates
         };
 
         candidates.push(Candidate {
-            rcvr_match_condition: RcvrMatchesIfSubtype(impl_ty),
+            rcvr_match_condition: condition,
             rcvr_substs: impl_substs,
             origin: MethodStatic(method.def_id),
             method_ty: method,
@@ -1525,7 +1541,7 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                 RcvrMatchesIfObject(desired_did) => {
                     self_did == desired_did
                 }
-                RcvrMatchesIfSubtype(_) => {
+                RcvrMatchesIfSubtype(_) | RcvrMatchesIfEqtype(_) => {
                     false
                 }
             }
@@ -1541,6 +1557,9 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                 RcvrMatchesIfSubtype(of_type) => {
                     fcx.can_mk_subty(rcvr_ty, of_type).is_ok()
                 }
+                RcvrMatchesIfEqtype(of_type) => {
+                    fcx.can_mk_eqty(rcvr_ty, of_type).is_ok()
+                }
             }
         }
 
@@ -1656,9 +1675,9 @@ impl Repr for RcvrMatchCondition {
             RcvrMatchesIfSubtype(t) => {
                 format!("RcvrMatchesIfSubtype({})", t.repr(tcx))
             }
+            RcvrMatchesIfEqtype(t) => {
+                format!("RcvrMatchesIfEqtype({})", t.repr(tcx))
+            }
         }
     }
 }
-
-
-

src/librustc/middle/typeck/check/mod.rs

@@ -1740,6 +1740,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         infer::can_mk_subty(self.infcx(), sub, sup)
     }
 
+    pub fn can_mk_eqty(&self, sub: ty::t, sup: ty::t)
+                       -> Result<(), ty::type_err> {
+        infer::can_mk_eqty(self.infcx(), sub, sup)
+    }
+
     pub fn mk_assignty(&self,
                        expr: &ast::Expr,
                        sub: ty::t,

src/librustc/middle/typeck/infer/mod.rs

@@ -362,6 +362,17 @@ pub fn can_mk_subty(cx: &InferCtxt, a: ty::t, b: ty::t) -> ures {
     }).to_ures()
 }
 
+pub fn can_mk_eqty(cx: &InferCtxt, a: ty::t, b: ty::t) -> ures {
+    debug!("can_mk_subty({} <: {})", a.repr(cx.tcx), b.repr(cx.tcx));
+    cx.probe(|| {
+        let trace = TypeTrace {
+            origin: Misc(codemap::DUMMY_SP),
+            values: Types(expected_found(true, a, b))
+        };
+        cx.equate(true, trace).tys(a, b)
+    }).to_ures()
+}
+
 pub fn mk_subr(cx: &InferCtxt,
                origin: SubregionOrigin,
                a: ty::Region,

src/test/compile-fail/issue-15965.rs

@@ -0,0 +1,13 @@
+// Copyright 2014 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.
+
+fn main() {
+    return { return () } (); //~ ERROR expected function, found `!`
+}

src/test/compile-fail/issue-17033.rs

@@ -0,0 +1,15 @@
+// Copyright 2014 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.
+
+fn f<'r>(p: &'r mut fn(p: &mut ())) {
+    p(()) //~ ERROR expected function, found `&'r mut fn(&mut ())`
+}
+
+fn main() {}