Issue #2633: remove last_use entries that are subject to a loan

Author: nikomatsakis

src/rustc/driver/driver.rs

@@ -203,7 +203,8 @@ fn compile_upto(sess: session, cfg: ast::crate_cfg,
          bind middle::tstate::ck::check_crate(ty_cx, crate));
     let (root_map, mutbl_map) = time(
         time_passes, "borrow checking",
-        bind middle::borrowck::check_crate(ty_cx, method_map, crate));
+        bind middle::borrowck::check_crate(ty_cx, method_map,
+                                           last_use_map, crate));
     time(time_passes, "kind checking",
          bind kind::check_crate(ty_cx, method_map, last_use_map, crate));
     time(time_passes, "lint checking",

src/rustc/middle/borrowck.rs

@@ -170,9 +170,11 @@ export check_crate, root_map, mutbl_map;
 
 fn check_crate(tcx: ty::ctxt,
                method_map: typeck::method_map,
+               last_use_map: liveness::last_use_map,
                crate: @ast::crate) -> (root_map, mutbl_map) {
     let bccx = @{tcx: tcx,
                  method_map: method_map,
+                 last_use_map: last_use_map,
                  root_map: root_map(),
                  mutbl_map: int_hash()};
 
@@ -186,6 +188,7 @@ fn check_crate(tcx: ty::ctxt,
 
 type borrowck_ctxt = @{tcx: ty::ctxt,
                        method_map: typeck::method_map,
+                       last_use_map: liveness::last_use_map,
                        root_map: root_map,
                        mutbl_map: mutbl_map};
 

src/rustc/middle/borrowck/check_loans.rs

@@ -448,6 +448,23 @@ impl methods for check_loan_ctxt {
         }
     }
 
+    // Very subtle (#2633): liveness can mark options as last_use even
+    // when there is an outstanding loan.  In that case, it is not
+    // safe to consider the use a last_use.
+    fn check_last_use(expr: @ast::expr) {
+        let cmt = self.bccx.cat_expr(expr);
+        let lp = alt cmt.lp {
+          none { ret; }
+          some(lp) { lp }
+        };
+        for self.walk_loans_of(cmt.id, lp) { |_loan|
+            #debug["Removing last use entry %? due to outstanding loan",
+                   expr.id];
+            self.bccx.last_use_map.remove(expr.id);
+            ret;
+        }
+    }
+
     fn check_call(expr: @ast::expr,
                   callee: option<@ast::expr>,
                   callee_id: ast::node_id,
@@ -531,6 +548,10 @@ fn check_loans_in_expr(expr: @ast::expr,
     self.check_for_conflicting_loans(expr.id);
 
     alt expr.node {
+      ast::expr_path(*) if self.bccx.last_use_map.contains_key(expr.id) {
+        self.check_last_use(expr);
+      }
+
       ast::expr_swap(l, r) {
         self.check_assignment(at_swap, l);
         self.check_assignment(at_swap, r);

src/rustc/middle/liveness.rs

@@ -63,6 +63,9 @@ export last_use_map;
 // the local/argument/etc that the path refers to.  However, it also
 // possible for the expr to be a closure, in which case the list is a
 // list of closed over variables that can be moved into the closure.
+//
+// Very subtle (#2633): borrowck will remove entries from this table
+// if it detects an outstanding loan (that is, the addr is taken).
 type last_use_map = hashmap<node_id, @dvec<node_id>>;
 
 enum variable = uint;

src/test/run-pass/issue-2633-2.rs

@@ -0,0 +1,8 @@
+fn a_val(&&x: ~int, +y: ~int) -> int {
+    *x + *y
+}
+
+fn main() {
+    let z = ~22;
+    a_val(z, z);
+}

src/test/run-pass/issue-2633.rs

@@ -1,5 +1,3 @@
-// Currently segfaults
-// xfail-test
 class cat {
     let mut meow: fn@();
     new() { self.meow = fn@() { #error("meow"); };}
@@ -15,4 +13,4 @@ fn nyan(kitty: cat, _kitty_info: kitty_info) {
 fn main() {
     let mut kitty = cat();
     nyan(kitty, {kitty: kitty});
-}
+}