Fix for a bug Andrew Reynolds found for iterators that affects empty CDList<> objects that allocate from ContextMemoryAllocator<>. Iterators were broken in that begin() != end() for empty lists (again---only those that allocated space from ContextMemoryAllocator<>). Added a unit test for this, too. Thanks Andy!

2 files changed, 19 insertions, 1 deletions

diff --git a/src/context/cdlist_context_memory.h b/src/context/cdlist_context_memory.h
index 20d672d31..2fd1ceb8c 100644
--- a/src/context/cdlist_context_memory.h
+++ b/src/context/cdlist_context_memory.h
@@ -476,7 +476,11 @@ public:
    * Returns an iterator pointing to the first item in the list.
    */
   const_iterator begin() const {
-    return const_iterator(&d_headSegment, 0);
+    // This looks curious, but we have to make sure that begin() == end()
+    // for an empty list, and begin() == (head,0) for a nonempty one.
+    // Since the segment spill-over is implemented in
+    // iterator::operator++(), let's reuse it. */
+    return ++const_iterator(&d_headSegment, -1);
   }
 
   /**
diff --git a/test/unit/context/cdlist_black.h b/test/unit/context/cdlist_black.h
index aa25ba9eb..6541973bf 100644
--- a/test/unit/context/cdlist_black.h
+++ b/test/unit/context/cdlist_black.h
@@ -25,12 +25,15 @@
 
 #include "memory.h"
 
+#include "util/exception.h"
 #include "context/context.h"
 #include "context/cdlist.h"
+#include "context/cdlist_context_memory.h"
 
 using namespace std;
 using namespace CVC4::context;
 using namespace CVC4::test;
+using namespace CVC4;
 
 struct DtorSensitiveObject {
   bool& d_dtorCalled;
@@ -133,6 +136,17 @@ public:
     TS_ASSERT_EQUALS(aThirdFalse, false);
   }
 
+  void testEmptyIterators() {
+    CDList<int>* list1 = new(true) CDList<int>(d_context);
+    CDList< int, ContextMemoryAllocator<int> >* list2 =
+      new(d_context->getCMM())
+        CDList< int, ContextMemoryAllocator<int> >(true, d_context, false,
+                                                   ContextMemoryAllocator<int>(d_context->getCMM()));
+    TS_ASSERT_EQUALS(list1->begin(), list1->end());
+    TS_ASSERT_EQUALS(list2->begin(), list2->end());
+    list1->deleteSelf();
+  }
+
   /* setrlimit() totally broken on Mac OS X */
   void testOutOfMemory() {
 #ifdef __APPLE__