Allow moving out of temporary values

This will probably need more work, as moving doesn't appear to do
quite the right thing yet in general, and we should also check
somewhere that we're not, for example, moving out the content out of
an immutable field (probably moving out of fields is not okay in
general).

Author: marijnh

src/comp/front/ast.rs

@@ -301,6 +301,13 @@ tag lit_ {
     lit_bool(bool);
 }
 
+fn is_path(&@expr e) -> bool {
+    ret alt (e.node) {
+        case (expr_path(_)) { true }
+        case (_) { false }
+    };
+}
+
 
 // NB: If you change this, you'll probably want to change the corresponding
 // type structure in middle/ty.rs as well.

src/comp/middle/tstate/pre_post_conditions.rs

@@ -367,11 +367,12 @@ fn find_pre_post_expr(&fn_ctxt fcx, @expr e) {
                 }
                 case (_) { find_pre_post_exprs(fcx, [lhs, rhs], e.id); }
             }
-            forget_in_postcond(fcx, e.id, rhs.id);
+            if (is_path(rhs)) {
+                forget_in_postcond(fcx, e.id, rhs.id);
+            }
         }
         case (expr_swap(?lhs, ?rhs)) {
             // Both sides must already be initialized
-            
             find_pre_post_exprs(fcx, [lhs, rhs], e.id);
             forget_in_postcond_still_init(fcx, e.id, lhs.id);
             forget_in_postcond_still_init(fcx, e.id, rhs.id);
@@ -591,14 +592,10 @@ fn find_pre_post_stmt(&fn_ctxt fcx, &stmt s) {
                                 rec(id=alocal.node.id, 
                                     c=ninit(alocal.node.ident)));
 
-                            alt (an_init.op) {
-                                case (init_move) {
-                                    forget_in_postcond(fcx, id,
-                                                       an_init.expr.id);
-                                }
-                                case (_) { /* nothing gets deinitialized */ } 
+                            if (an_init.op == init_move &&
+                                is_path(an_init.expr)) {
+                                forget_in_postcond(fcx, id, an_init.expr.id);
                             }
-
                         }
                         case (none) {
                             clear_pp(node_id_to_ts_ann(fcx.ccx,

src/comp/middle/tstate/states.rs

@@ -633,12 +633,9 @@ fn find_pre_post_state_stmt(&fn_ctxt fcx, &prestate pres, @stmt s) -> bool {
 
                             auto post = tritv_clone(expr_poststate(fcx.ccx,
                                                       an_init.expr));
-                            alt (an_init.op) {
-                                case (init_move) {
-                                    clear_in_poststate_expr(fcx, an_init.expr,
-                                                            post);
-                                }
-                                case (_) { /* nothing gets deinitialized */ } 
+                            if (an_init.op == init_move) {
+                                clear_in_poststate_expr(fcx, an_init.expr,
+                                                        post);
                             }
 
                             set_in_poststate_ident(fcx, alocal.node.id,