fix: Bug GEQ range query bug (#4557)

The bug was caused by incorrect handling of corner cases,
when a path that should lead to an item was wrongfully cleared, which lead
to empty results for SortedMap::GetRange query.

This PR:
1. fixes the wrong code in bptree_set.h.
2. Adds unit tests for both bptree_set_test and sorted_map_test.

Related to mastodon/mastodon#33805

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

Author: romange

src/core/bptree_set.h

@@ -489,8 +489,14 @@ template <typename T, typename Policy>
 detail::BPTreePath<T> BPTree<T, Policy>::GEQ(KeyT item) const {
   BPTreePath path;
 
-  if (!Locate(item, &path) && path.Last().second >= path.Last().first->NumItems())
-    path.Clear();
+  bool res = Locate(item, &path);
+
+  // if we did not find the item and the path does not lead to any key in the node,
+  // adjust the path to point to the next key in the tree.
+  // In case we are past all items in the tree, Next() will collapse to the empty path.
+  if (!res && path.Last().second >= path.Last().first->NumItems()) {
+    path.Next();
+  }
 
   return path;
 }

src/core/bptree_set_test.cc

@@ -88,12 +88,16 @@ class BPTreeSetTest : public ::testing::Test {
   static void SetUpTestSuite() {
   }
 
-  void FillTree(unsigned factor = 1) {
-    for (unsigned i = 0; i < kNumElems; ++i) {
+  void FillTree(unsigned start, unsigned factor) {
+    for (unsigned i = start; i < kNumElems; ++i) {
       bptree_.Insert(i * factor);
     }
   }
 
+  void FillTree(unsigned factor = 1) {
+    FillTree(0, factor);
+  }
+
   bool Validate();
 
   MiMemoryResource mi_alloc_;
@@ -277,6 +281,25 @@ TEST_F(BPTreeSetTest, Ranges) {
   EXPECT_TRUE(path.Empty());
 }
 
+TEST_F(BPTreeSetTest, HalfRanges) {
+  FillTree(1, 3);  // 3, 6, 9 ...
+  auto path = bptree_.FromRank(bptree_.Size() - 1);
+  uint64_t val = path.Terminal();
+  for (unsigned i = 0; i <= val; ++i) {
+    path = bptree_.GEQ(i);
+    ASSERT_FALSE(path.Empty()) << i;
+  }
+  path = bptree_.GEQ(val + 1);
+  ASSERT_TRUE(path.Empty());
+
+  for (unsigned i = 3; i <= val + 10; ++i) {
+    path = bptree_.LEQ(i);
+    ASSERT_FALSE(path.Empty()) << i;
+  }
+  path = bptree_.LEQ(2);
+  ASSERT_TRUE(path.Empty());
+}
+
 TEST_F(BPTreeSetTest, MemoryUsage) {
   zskiplist* zsl = zslCreate();
   std::vector<sds> sds_vec;

src/core/sorted_map_test.cc

@@ -246,6 +246,26 @@ TEST_F(SortedMapTest, DeleteRange) {
   EXPECT_EQ(96, sm_.DeleteRangeByLex(lex_range));
 }
 
+TEST_F(SortedMapTest, RangeBug) {
+  constexpr size_t kArrLen = 80;
+  for (unsigned i = 0; i < kArrLen; i++) {
+    sds s = sdsempty();
+
+    s = sdscatfmt(s, "score%u", i);
+    sm_.Insert(i, s);
+  }
+
+  for (unsigned i = 0; i < kArrLen; i++) {
+    zrangespec range;
+    range.max = HUGE_VAL;
+    range.min = i;
+    range.minex = 0;
+    range.maxex = 0;
+    auto arr = sm_.GetRange(range, 0, 5, false);
+    ASSERT_GT(arr.size(), 0) << i;
+  }
+}
+
 // not a real test, just to see how much memory is used by zskiplist.
 TEST_F(SortedMapTest, MemoryUsage) {
   zskiplist* zsl = zslCreate();