libutil: drop Pool resources on exceptional free

if a scope owning a resource does not gracefully drop that resource
while handling exceptions from deeper down the call stack we should
assume the resource is invalid state and drop it. currently it *is*
true that such cases do not cause resources to be freed, but thanks
to validator misuses this has so far not caused any larger problem.

Change-Id: Ie4f91bcd60a64d05c5ff9d22cc97954816d13b97

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/unit/libutil/pool.cc b/tests/unit/libutil/pool.cc
index 127e42dda..a3743e601 100644
--- a/tests/unit/libutil/pool.cc
+++ b/tests/unit/libutil/pool.cc
@@ -124,4 +124,19 @@ namespace nix {
             ASSERT_NE(h->num, counter);
         }
     }
+
+    TEST(Pool, throwingOperationDropsResource)
+    {
+        auto createResource = []() { return make_ref<TestResource>(); };
+
+        Pool<TestResource> pool = Pool<TestResource>((size_t)1, createResource);
+
+        ASSERT_THROW({
+            auto _r = pool.get();
+            ASSERT_EQ(pool.count(), 1);
+            throw 1;
+        }, int);
+
+        ASSERT_EQ(pool.count(), 0);
+    }
 }