Borrow checking for overloaded indexing

Closes #15525

9 files changed, 96 insertions, 23 deletions

diff --git a/src/librustc/middle/borrowck/check_loans.rs b/src/librustc/middle/borrowck/check_loans.rs
index db8ab8c83fb..cfec67bf3a3 100644
--- a/src/librustc/middle/borrowck/check_loans.rs
+++ b/src/librustc/middle/borrowck/check_loans.rs
@@ -734,7 +734,8 @@ impl<'a> CheckLoanCtxt<'a> {
                     mc::cat_static_item |
                     mc::cat_copied_upvar(..) |
                     mc::cat_deref(_, _, mc::UnsafePtr(..)) |
-                    mc::cat_deref(_, _, mc::BorrowedPtr(..)) => {
+                    mc::cat_deref(_, _, mc::BorrowedPtr(..)) |
+                    mc::cat_deref(_, _, mc::Implicit(..)) => {
                         assert_eq!(cmt.mutbl, mc::McDeclared);
                         return;
                     }
diff --git a/src/librustc/middle/borrowck/gather_loans/gather_moves.rs b/src/librustc/middle/borrowck/gather_loans/gather_moves.rs
index de77fa602c9..322471f3029 100644
--- a/src/librustc/middle/borrowck/gather_loans/gather_moves.rs
+++ b/src/librustc/middle/borrowck/gather_loans/gather_moves.rs
@@ -131,6 +131,7 @@ fn check_and_get_illegal_move_origin(bccx: &BorrowckCtxt,
                                      cmt: &mc::cmt) -> Option<mc::cmt> {
     match cmt.cat {
         mc::cat_deref(_, _, mc::BorrowedPtr(..)) |
+        mc::cat_deref(_, _, mc::Implicit(..)) |
         mc::cat_deref(_, _, mc::GcPtr) |
         mc::cat_deref(_, _, mc::UnsafePtr(..)) |
         mc::cat_upvar(..) | mc::cat_static_item |
diff --git a/src/librustc/middle/borrowck/gather_loans/lifetime.rs b/src/librustc/middle/borrowck/gather_loans/lifetime.rs
index dc8567af9ed..0785538cc76 100644
--- a/src/librustc/middle/borrowck/gather_loans/lifetime.rs
+++ b/src/librustc/middle/borrowck/gather_loans/lifetime.rs
@@ -72,6 +72,7 @@ impl<'a> GuaranteeLifetimeContext<'a> {
             mc::cat_arg(..) |                           // L-Local
             mc::cat_upvar(..) |
             mc::cat_deref(_, _, mc::BorrowedPtr(..)) |  // L-Deref-Borrowed
+            mc::cat_deref(_, _, mc::Implicit(..)) |
             mc::cat_deref(_, _, mc::UnsafePtr(..)) => {
                 self.check_scope(self.scope(cmt))
             }
@@ -180,7 +181,8 @@ impl<'a> GuaranteeLifetimeContext<'a> {
             mc::cat_deref(_, _, mc::UnsafePtr(..)) => {
                 ty::ReStatic
             }
-            mc::cat_deref(_, _, mc::BorrowedPtr(_, r)) => {
+            mc::cat_deref(_, _, mc::BorrowedPtr(_, r)) |
+            mc::cat_deref(_, _, mc::Implicit(_, r)) => {
                 r
             }
             mc::cat_downcast(ref cmt) |
diff --git a/src/librustc/middle/borrowck/gather_loans/move_error.rs b/src/librustc/middle/borrowck/gather_loans/move_error.rs
index 9876e12d5cc..10f051f004f 100644
--- a/src/librustc/middle/borrowck/gather_loans/move_error.rs
+++ b/src/librustc/middle/borrowck/gather_loans/move_error.rs
@@ -113,6 +113,7 @@ fn group_errors_with_same_origin(errors: &Vec<MoveError>)
 fn report_cannot_move_out_of(bccx: &BorrowckCtxt, move_from: mc::cmt) {
     match move_from.cat {
         mc::cat_deref(_, _, mc::BorrowedPtr(..)) |
+        mc::cat_deref(_, _, mc::Implicit(..)) |
         mc::cat_deref(_, _, mc::GcPtr) |
         mc::cat_deref(_, _, mc::UnsafePtr(..)) |
         mc::cat_upvar(..) | mc::cat_static_item |
diff --git a/src/librustc/middle/borrowck/gather_loans/restrictions.rs b/src/librustc/middle/borrowck/gather_loans/restrictions.rs
index d131b6f7eda..48399cb0b7e 100644
--- a/src/librustc/middle/borrowck/gather_loans/restrictions.rs
+++ b/src/librustc/middle/borrowck/gather_loans/restrictions.rs
@@ -122,7 +122,9 @@ impl<'a> RestrictionsContext<'a> {
             }
 
             mc::cat_deref(cmt_base, _, mc::BorrowedPtr(ty::ImmBorrow, lt)) |
-            mc::cat_deref(cmt_base, _, mc::BorrowedPtr(ty::UniqueImmBorrow, lt)) => {
+            mc::cat_deref(cmt_base, _, mc::BorrowedPtr(ty::UniqueImmBorrow, lt)) |
+            mc::cat_deref(cmt_base, _, mc::Implicit(ty::ImmBorrow, lt)) |
+            mc::cat_deref(cmt_base, _, mc::Implicit(ty::UniqueImmBorrow, lt)) => {
                 // R-Deref-Imm-Borrowed
                 if !self.bccx.is_subregion_of(self.loan_region, lt) {
                     self.bccx.report(
@@ -137,7 +139,8 @@ impl<'a> RestrictionsContext<'a> {
                 Safe
             }
 
-            mc::cat_deref(cmt_base, _, pk @ mc::BorrowedPtr(ty::MutBorrow, lt)) => {
+            mc::cat_deref(cmt_base, _, pk @ mc::BorrowedPtr(ty::MutBorrow, lt)) |
+            mc::cat_deref(cmt_base, _, pk @ mc::Implicit(ty::MutBorrow, lt)) => {
                 // R-Deref-Mut-Borrowed
                 if !self.bccx.is_subregion_of(self.loan_region, lt) {
                     self.bccx.report(
diff --git a/src/librustc/middle/mem_categorization.rs b/src/librustc/middle/mem_categorization.rs
index 33ab2ed3632..e928704b0cc 100644
--- a/src/librustc/middle/mem_categorization.rs
+++ b/src/librustc/middle/mem_categorization.rs
@@ -106,7 +106,8 @@ pub enum PointerKind {
     OwnedPtr,
     GcPtr,
     BorrowedPtr(ty::BorrowKind, ty::Region),
-    UnsafePtr(ast::Mutability),
+    Implicit(ty::BorrowKind, ty::Region),     // Implicit deref of a borrowed ptr.
+    UnsafePtr(ast::Mutability)
 }
 
 // We use the term "interior" to mean "something reachable from the
@@ -293,7 +294,7 @@ impl MutabilityCategory {
             OwnedPtr => {
                 base_mutbl.inherit()
             }
-            BorrowedPtr(borrow_kind, _) => {
+            BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
                 MutabilityCategory::from_borrow_kind(borrow_kind)
             }
             GcPtr => {
@@ -422,7 +423,7 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
                                -> McResult<cmt> {
         let mut cmt = if_ok!(self.cat_expr_unadjusted(expr));
         for deref in range(1u, autoderefs + 1) {
-            cmt = self.cat_deref(expr, cmt, deref);
+            cmt = self.cat_deref(expr, cmt, deref, false);
         }
         return Ok(cmt);
     }
@@ -434,7 +435,7 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
         match expr.node {
           ast::ExprUnary(ast::UnDeref, ref e_base) => {
             let base_cmt = if_ok!(self.cat_expr(&**e_base));
-            Ok(self.cat_deref(expr, base_cmt, 0))
+            Ok(self.cat_deref(expr, base_cmt, 0, false))
           }
 
           ast::ExprField(ref base, f_name, _) => {
@@ -443,8 +444,22 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
           }
 
           ast::ExprIndex(ref base, _) => {
-            let base_cmt = if_ok!(self.cat_expr(&**base));
-            Ok(self.cat_index(expr, base_cmt, 0))
+            let method_call = typeck::MethodCall::expr(expr.id());
+            match self.typer.node_method_ty(method_call) {
+                Some(method_ty) => {
+                    // If this is an index implemented by a method call, then it will
+                    // include an implicit deref of the result.
+                    let ret_ty = ty::ty_fn_ret(method_ty);
+                    Ok(self.cat_deref(expr,
+                                      self.cat_rvalue_node(expr.id(),
+                                                           expr.span(),
+                                                           ret_ty), 1, true))
+                }
+                None => {
+                    let base_cmt = if_ok!(self.cat_expr(&**base));
+                    Ok(self.cat_index(expr, base_cmt, 0))
+                }
+            }
           }
 
           ast::ExprPath(_) => {
@@ -687,13 +702,14 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
     }
 
     pub fn cat_deref_obj<N:ast_node>(&self, node: &N, base_cmt: cmt) -> cmt {
-        self.cat_deref_common(node, base_cmt, 0, ty::mk_nil())
+        self.cat_deref_common(node, base_cmt, 0, ty::mk_nil(), false)
     }
 
     fn cat_deref<N:ast_node>(&self,
                              node: &N,
                              base_cmt: cmt,
-                             deref_cnt: uint)
+                             deref_cnt: uint,
+                             implicit: bool)
                              -> cmt {
         let adjustment = match self.typer.adjustments().borrow().find(&node.id()) {
             Some(&ty::AutoObject(..)) => typeck::AutoObject,
@@ -717,7 +733,7 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
             None => base_cmt
         };
         match ty::deref(base_cmt.ty, true) {
-            Some(mt) => self.cat_deref_common(node, base_cmt, deref_cnt, mt.ty),
+            Some(mt) => self.cat_deref_common(node, base_cmt, deref_cnt, mt.ty, implicit),
             None => {
                 self.tcx().sess.span_bug(
                     node.span(),
@@ -731,10 +747,20 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
                                     node: &N,
                                     base_cmt: cmt,
                                     deref_cnt: uint,
-                                    deref_ty: ty::t)
+                                    deref_ty: ty::t,
+                                    implicit: bool)
                                     -> cmt {
         let (m, cat) = match deref_kind(self.tcx(), base_cmt.ty) {
             deref_ptr(ptr) => {
+                let ptr = if implicit {
+                    match ptr {
+                        BorrowedPtr(bk, r) => Implicit(bk, r),
+                        _ => self.tcx().sess.span_bug(node.span(),
+                            "Implicit deref of non-borrowed pointer")
+                    }
+                } else {
+                    ptr
+                };
                 // for unique ptrs, we inherit mutability from the
                 // owning reference.
                 (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
@@ -1073,7 +1099,7 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
 
           ast::PatBox(ref subpat) | ast::PatRegion(ref subpat) => {
             // @p1, ~p1
-            let subcmt = self.cat_deref(pat, cmt, 0);
+            let subcmt = self.cat_deref(pat, cmt, 0, false);
             if_ok!(self.cat_pattern(subcmt, &**subpat, op));
           }
 
@@ -1129,6 +1155,9 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
                   }
                   _ => {
                       match pk {
+                          Implicit(..) => {
+                            "dereference (dereference is implicit, due to indexing)".to_string()
+                          }
                           OwnedPtr | GcPtr => format!("dereference of `{}`", ptr_sigil(pk)),
                           _ => format!("dereference of `{}`-pointer", ptr_sigil(pk))
                       }
@@ -1188,6 +1217,7 @@ impl cmt_ {
             cat_deref(_, _, UnsafePtr(..)) |
             cat_deref(_, _, GcPtr(..)) |
             cat_deref(_, _, BorrowedPtr(..)) |
+            cat_deref(_, _, Implicit(..)) |
             cat_upvar(..) => {
                 Rc::new((*self).clone())
             }
@@ -1212,7 +1242,9 @@ impl cmt_ {
 
         match self.cat {
             cat_deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) |
+            cat_deref(ref b, _, Implicit(ty::MutBorrow, _)) |
             cat_deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
+            cat_deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
             cat_downcast(ref b) |
             cat_deref(ref b, _, OwnedPtr) |
             cat_interior(ref b, _) |
@@ -1252,7 +1284,8 @@ impl cmt_ {
                 Some(AliasableManaged)
             }
 
-            cat_deref(_, _, BorrowedPtr(ty::ImmBorrow, _)) => {
+            cat_deref(_, _, BorrowedPtr(ty::ImmBorrow, _)) |
+            cat_deref(_, _, Implicit(ty::ImmBorrow, _)) => {
                 Some(AliasableBorrowed)
             }
         }
@@ -1300,9 +1333,12 @@ pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
     match ptr {
         OwnedPtr => "Box",
         GcPtr => "Gc",
-        BorrowedPtr(ty::ImmBorrow, _) => "&",
-        BorrowedPtr(ty::MutBorrow, _) => "&mut",
-        BorrowedPtr(ty::UniqueImmBorrow, _) => "&unique",
+        BorrowedPtr(ty::ImmBorrow, _) |
+        Implicit(ty::ImmBorrow, _) => "&",
+        BorrowedPtr(ty::MutBorrow, _) |
+        Implicit(ty::MutBorrow, _) => "&mut",
+        BorrowedPtr(ty::UniqueImmBorrow, _) |
+        Implicit(ty::UniqueImmBorrow, _) => "&unique",
         UnsafePtr(_) => "*"
     }
 }
diff --git a/src/librustc/middle/typeck/check/regionck.rs b/src/librustc/middle/typeck/check/regionck.rs
index 924934e4bcd..180dac53828 100644
--- a/src/librustc/middle/typeck/check/regionck.rs
+++ b/src/librustc/middle/typeck/check/regionck.rs
@@ -1219,7 +1219,8 @@ fn link_region(rcx: &Rcx,
                kind.repr(rcx.tcx()),
                cmt_borrowed.repr(rcx.tcx()));
         match cmt_borrowed.cat.clone() {
-            mc::cat_deref(base, _, mc::BorrowedPtr(_, r_borrowed)) => {
+            mc::cat_deref(base, _, mc::BorrowedPtr(_, r_borrowed)) |
+            mc::cat_deref(base, _, mc::Implicit(_, r_borrowed)) => {
                 // References to an upvar `x` are translated to
                 // `*x`, since that is what happens in the
                 // underlying machine.  We detect such references
@@ -1340,7 +1341,8 @@ fn adjust_upvar_borrow_kind_for_mut(rcx: &Rcx,
                 continue;
             }
 
-            mc::cat_deref(base, _, mc::BorrowedPtr(..)) => {
+            mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
+            mc::cat_deref(base, _, mc::Implicit(..)) => {
                 match base.cat {
                     mc::cat_upvar(ref upvar_id, _) => {
                         // if this is an implicit deref of an
@@ -1394,7 +1396,8 @@ fn adjust_upvar_borrow_kind_for_unique(rcx: &Rcx, cmt: mc::cmt) {
                 continue;
             }
 
-            mc::cat_deref(base, _, mc::BorrowedPtr(..)) => {
+            mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
+            mc::cat_deref(base, _, mc::Implicit(..)) => {
                 match base.cat {
                     mc::cat_upvar(ref upvar_id, _) => {
                         // if this is an implicit deref of an
diff --git a/src/test/compile-fail/borrowck-overloaded-index-2.rs b/src/test/compile-fail/borrowck-overloaded-index-2.rs
new file mode 100644
index 00000000000..1e3144a931f
--- /dev/null
+++ b/src/test/compile-fail/borrowck-overloaded-index-2.rs
@@ -0,0 +1,26 @@
+// 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.
+
+struct MyVec<T> {
+    data: Vec<T>,
+}
+
+impl<T> Index<uint, T> for MyVec<T> {
+    fn index<'a>(&'a self, &i: &uint) -> &'a T {
+        self.data.get(i)
+    }
+}
+
+fn main() {
+    let v = MyVec { data: vec!(box 1i, box 2, box 3) };
+    let good = &v[0]; // Shouldn't fail here
+    let bad = v[0];
+    //~^ ERROR cannot move out of dereference (dereference is implicit, due to indexing)
+}
diff --git a/src/test/compile-fail/borrowck-overloaded-index.rs b/src/test/compile-fail/borrowck-overloaded-index.rs
index d34aa1cd9cb..0422f6381dc 100644
--- a/src/test/compile-fail/borrowck-overloaded-index.rs
+++ b/src/test/compile-fail/borrowck-overloaded-index.rs
@@ -58,7 +58,7 @@ fn main() {
         x: 1,
     };
     s[2] = 20;
-    //~^ ERROR cannot assign to immutable indexed content
+    //~^ ERROR cannot assign to immutable dereference (dereference is implicit, due to indexing)
 }