Test multi-ref'ed vec growth more seriously than before.

src/lib/_vec.rs

@@ -29,6 +29,11 @@ fn alloc[T](uint n_elts) -> vec[T] {
   ret rustrt.vec_alloc[vec[T], T](n_elts);
 }
 
+fn refcount[T](vec[T] v) -> uint {
+  // -1 because calling this function incremented the refcount.
+  ret rustrt.refcount[T](v) - 1u;
+}
+
 type init_op[T] = fn(uint i) -> T;
 
 fn init_fn[T](&init_op[T] op, uint n_elts) -> vec[T] {

src/test/run-pass/vec-append.rs

@@ -1,5 +1,9 @@
 // -*- rust -*-
 
+use std;
+import std._str;
+import std._vec;
+
 fn fast_growth() {
   let vec[int] v = vec(1,2,3,4,5);
   v += vec(6,7,8,9,0);
@@ -19,7 +23,66 @@ fn slow_growth() {
   check (v.(0) == 17);
 }
 
+fn slow_growth2_helper(str s) {   // ref up: s
+
+  obj acc(vec[str] v) {
+    fn add(&str s) { v += vec(s); }
+  }
+
+  let str ss = s;                 // ref up: s
+  let str mumble = "mrghrm";      // ref up: mumble
+
+  {
+    /**
+     * Within this block, mumble goes into a vec that is referenced
+     * both by the local slot v and the acc's v data field.  When we
+     * add(s) on the acc, its v undergoes a slow append (allocate a
+     * new vec, copy over existing elements).  Here we're testing to
+     * see that this slow path goes over well.  In particular, the
+     * copy of existing elements should increment the ref count of
+     * mumble, the existing str in the originally- shared vec.
+     */
+    let vec[str] v = vec(mumble); // ref up: v, mumble
+    let acc a = acc(v);           // ref up: a, v
+
+    log _vec.refcount[str](v);
+    check (_vec.refcount[str](v) == 2u);
+
+    a.add(s);                     // ref up: mumble, s.  ref down: v
+
+    log _vec.refcount[str](v);
+    log _str.refcount(s);
+    log _str.refcount(mumble);
+
+    check (_vec.refcount[str](v) == 1u);
+    check (_str.refcount(s) == 4u);
+    check (_str.refcount(mumble) == 3u);
+
+    log v.(0);
+    log _vec.len[str](v);
+    check (_str.eq(v.(0), mumble));
+    check (_vec.len[str](v) == 1u);
+  }                               // ref down: a, mumble, s, v
+
+  log _str.refcount(s);
+  log _str.refcount(mumble);
+
+  check (_str.refcount(s) == 3u);
+  check (_str.refcount(mumble) == 1u);
+
+  log mumble;
+  log ss;
+}                                 // ref down
+
+fn slow_growth2() {
+  let str s = "hi";               // ref up: s
+  slow_growth2_helper(s);
+  log _str.refcount(s);
+  check (_str.refcount(s) == 1u);
+}
+
 fn main() {
   fast_growth();
   slow_growth();
+  slow_growth2();
 }