Distinguish tuple elements by index in mem_categorization. Fixes rust…

…-lang#5362.

src/librustc/middle/borrowck/check_loans.rs

@@ -400,6 +400,7 @@ pub impl<'self> CheckLoanCtxt<'self> {
                         cmt = b;
                     }
 
+                    mc::cat_downcast(b) |
                     mc::cat_interior(b, _) => {
                         if cmt.mutbl == mc::McInherited {
                             cmt = b;

src/librustc/middle/borrowck/gather_loans/lifetime.rs

@@ -105,6 +105,7 @@ impl GuaranteeLifetimeContext {
                 }
             }
 
+            mc::cat_downcast(base) |
             mc::cat_deref(base, _, mc::uniq_ptr(*)) |
             mc::cat_interior(base, _) => {
                 self.check(base, discr_scope)
@@ -303,6 +304,7 @@ impl GuaranteeLifetimeContext {
             mc::cat_deref(*) => {
                 false
             }
+            r @ mc::cat_downcast(*) |
             r @ mc::cat_interior(*) |
             r @ mc::cat_stack_upvar(*) |
             r @ mc::cat_discr(*) => {
@@ -340,6 +342,7 @@ impl GuaranteeLifetimeContext {
             mc::cat_deref(_, _, mc::region_ptr(_, r)) => {
                 r
             }
+            mc::cat_downcast(cmt) |
             mc::cat_deref(cmt, _, mc::uniq_ptr(*)) |
             mc::cat_deref(cmt, _, mc::gc_ptr(*)) |
             mc::cat_interior(cmt, _) |

src/librustc/middle/borrowck/gather_loans/restrictions.rs

@@ -80,24 +80,17 @@ impl RestrictionsContext {
                                           set: restrictions}])
             }
 
-            mc::cat_interior(cmt_base, i @ mc::interior_variant(_)) => {
+            mc::cat_downcast(cmt_base) => {
                 // When we borrow the interior of an enum, we have to
                 // ensure the enum itself is not mutated, because that
                 // could cause the type of the memory to change.
-                let result = self.compute(cmt_base, restrictions | RESTR_MUTATE);
-                self.extend(result, cmt.mutbl, LpInterior(i), restrictions)
+                self.compute(cmt_base, restrictions | RESTR_MUTATE)
             }
 
-            mc::cat_interior(cmt_base, i @ mc::interior_tuple) |
-            mc::cat_interior(cmt_base, i @ mc::interior_anon_field) |
-            mc::cat_interior(cmt_base, i @ mc::interior_field(*)) |
-            mc::cat_interior(cmt_base, i @ mc::interior_index(*)) => {
-                // For all of these cases, overwriting the base would
-                // not change the type of the memory, so no additional
-                // restrictions are needed.
-                //
-                // FIXME(#5397) --- Mut fields are not treated soundly
-                //                  (hopefully they will just get phased out)
+            mc::cat_interior(cmt_base, i) => {
+                // Overwriting the base would not change the type of
+                // the memory, so no additional restrictions are
+                // needed.
                 let result = self.compute(cmt_base, restrictions);
                 self.extend(result, cmt.mutbl, LpInterior(i), restrictions)
             }

src/librustc/middle/borrowck/mod.rs

@@ -236,8 +236,8 @@ pub enum LoanPath {
 
 #[deriving(Eq)]
 pub enum LoanPathElem {
-    LpDeref,                      // `*LV` in doc.rs
-    LpInterior(mc::interior_kind) // `LV.f` in doc.rs
+    LpDeref,                     // `*LV` in doc.rs
+    LpInterior(mc::InteriorKind) // `LV.f` in doc.rs
 }
 
 pub impl LoanPath {
@@ -280,6 +280,7 @@ pub fn opt_loan_path(cmt: mc::cmt) -> Option<@LoanPath> {
                 |&lp| @LpExtend(lp, cmt.mutbl, LpInterior(ik)))
         }
 
+        mc::cat_downcast(cmt_base) |
         mc::cat_stack_upvar(cmt_base) |
         mc::cat_discr(cmt_base, _) => {
             opt_loan_path(cmt_base)
@@ -616,24 +617,25 @@ pub impl BorrowckCtxt {
                 }
             }
 
-            LpExtend(lp_base, _, LpInterior(mc::interior_field(fld))) => {
+            LpExtend(lp_base, _, LpInterior(mc::InteriorField(fname))) => {
                 self.append_loan_path_to_str_from_interior(lp_base, out);
-                str::push_char(out, '.');
-                str::push_str(out, *self.tcx.sess.intr().get(fld));
+                match fname {
+                    mc::NamedField(fname) => {
+                        str::push_char(out, '.');
+                        str::push_str(out, *self.tcx.sess.intr().get(fname));
+                    }
+                    mc::PositionalField(idx) => {
+                        str::push_char(out, '#'); // invent a notation here
+                        str::push_str(out, idx.to_str());
+                    }
+                }
             }
 
-            LpExtend(lp_base, _, LpInterior(mc::interior_index(*))) => {
+            LpExtend(lp_base, _, LpInterior(mc::InteriorElement(_))) => {
                 self.append_loan_path_to_str_from_interior(lp_base, out);
                 str::push_str(out, "[]");
             }
 
-            LpExtend(lp_base, _, LpInterior(mc::interior_tuple)) |
-            LpExtend(lp_base, _, LpInterior(mc::interior_anon_field)) |
-            LpExtend(lp_base, _, LpInterior(mc::interior_variant(_))) => {
-                self.append_loan_path_to_str_from_interior(lp_base, out);
-                str::push_str(out, ".(tuple)");
-            }
-
             LpExtend(lp_base, _, LpDeref) => {
                 str::push_char(out, '*');
                 self.append_loan_path_to_str(lp_base, out);