From fb88c7bd147221f7a64f7ffad018b4f4ec02eac5 Mon Sep 17 00:00:00 2001
From: Antony Peacock <ant.peacock@gmail.com>
Date: Wed, 12 Oct 2022 11:42:56 +0100
Subject: [PATCH] Test failure path for allocated objects

---
 polymorphic_value.h        |  3 ++-
 polymorphic_value_test.cpp | 46 +++++++++++++++++++++++++++-----------
 2 files changed, 35 insertions(+), 14 deletions(-)

diff --git a/polymorphic_value.h b/polymorphic_value.h
index bd33c37..d290a1b 100644
--- a/polymorphic_value.h
+++ b/polymorphic_value.h
@@ -52,9 +52,10 @@ struct copier_traits_deleter_base<U* (*)(V)> {
 class control_block_deleter {
  public:
   template <class T>
-  void operator()(T* t) const noexcept {
+  void operator()(T*& t) const noexcept {
     if (t != nullptr) {
       t->destroy();
+      t = nullptr;
     }
   }
 };
diff --git a/polymorphic_value_test.cpp b/polymorphic_value_test.cpp
index 02cf14c..a0f0fc6 100644
--- a/polymorphic_value_test.cpp
+++ b/polymorphic_value_test.cpp
@@ -856,18 +856,38 @@ TEST_CASE("Copying object with allocator allocates") {
 }
 
 TEST_CASE("Allocator used to construct with make_polymorphic") {
-  unsigned allocs = 0;
-  unsigned deallocs = 0;
-
-  tracking_allocator<DerivedType> alloc(&allocs, &deallocs);
-
-  {
-    unsigned const value = 99;
-    polymorphic_value<DerivedType> p = make_polymorphic_value<DerivedType>(
-        std::allocator_arg_t{}, alloc, value);
-    CHECK(allocs == 2);
-    CHECK(deallocs == 0);
+  GIVEN("an alloator which tracks allocations") {
+    unsigned allocs = 0;
+    unsigned deallocs = 0;
+
+    tracking_allocator<int> alloc(&allocs, &deallocs);
+    WHEN("Constructing a type from the allocator") {
+      unsigned const value = 99;
+      auto p = make_polymorphic_value<DerivedType>(std::allocator_arg_t{},
+                                                   alloc, value);
+      THEN("Expect the allocation to be tracked") {
+        CHECK(allocs == 2);
+        CHECK(deallocs == 0);
+      }
+      AND_THEN("Expect the deallocation to be tracked") {
+        p.~polymorphic_value();
+        CHECK(allocs == 2);
+        CHECK(deallocs == 2);
+      }
+    }
+    WHEN("Constructing a type that throws on construction from the allocator") {
+      struct ThrowOnConstruction : DerivedType {
+        ThrowOnConstruction() { throw "I throw in my default constructor"; }
+      };
+
+      CHECK_THROWS(make_polymorphic_value<ThrowOnConstruction>(
+          std::allocator_arg_t{}, alloc));
+      THEN(
+          "Expect allocation and subsequent deallocation of the intial T to be "
+          "tracked after the throw (but not the control block's allocation)") {
+        CHECK(allocs == 1);
+        CHECK(deallocs == 1);
+      }
+    }
   }
-  CHECK(allocs == 2);
-  CHECK(deallocs == 2);
 }