Exercise copyChildrenAndKeyFrom for Node{48,256} to itself

CMakeLists.txt

@@ -263,6 +263,10 @@ if(BUILD_TESTING)
   # find.
   if(NOT CMAKE_CROSSCOMPILING)
     find_package(Python3 REQUIRED COMPONENTS Interpreter)
+    set_property(
+      DIRECTORY
+      APPEND
+      PROPERTY CMAKE_CONFIGURE_DEPENDS ${CMAKE_SOURCE_DIR}/test_conflict_set.py)
     execute_process(
       COMMAND ${Python3_EXECUTABLE} ${CMAKE_SOURCE_DIR}/test_conflict_set.py
               list OUTPUT_VARIABLE SCRIPT_TESTS)

ConflictSet.cpp

@@ -1146,8 +1146,14 @@ void freeAndMakeCapacityAtLeast(Node *&self, int capacity,
 // capacity.
 void maybeDecreaseCapacity(Node *&self, NodeAllocators *allocators,
                            ConflictSet::Impl *impl) {
+
   const int maxCapacity =
       (self->numChildren + int(self->entryPresent)) * (self->partialKeyLen + 1);
+#if DEBUG_VERBOSE && !defined(NDEBUG)
+  fprintf(stderr, "maybeDecreaseCapacity: current: %d, max: %d, key: %s\n",
+          self->getCapacity(), maxCapacity,
+          getSearchPathPrintable(self).c_str());
+#endif
   if (self->getCapacity() <= maxCapacity) {
     return;
   }

test_conflict_set.py

@@ -66,6 +66,21 @@ def test_inner_full_words():
         cs.check(read(1, b"\x21", b"\xc2"))
 
 
+def test_decrease_capacity():
+    # make a Node48, then a Node256
+    for count in (17, 49):
+        with DebugConflictSet() as cs:
+            for i in range(count):
+                cs.addWrites(1, write(bytes(([0] * 99) + [i])))
+            # lower its partial key length
+            cs.addWrites(2, write(bytes([0] * 98)))
+            # create work for setOldestVersion
+            for i in range(3, 1000):
+                cs.addWrites(i)
+            # setOldestVersion should decrease the capacity
+            cs.setOldestVersion(1)
+
+
 if __name__ == "__main__":
     # budget "pytest" for ctest integration without pulling in a dependency. You can of course still use pytest in local development.
     import argparse