fix(set_family): Transfer TTL flag from DenseLink object in delete (#4947)

fix(set_family): Transfer TTL flag from link to object in delete

When extracting DensePtr from LinkObject we need to transfer TTL flag
before this DensePtr is assigned.

Fixes #3915

Signed-off-by: mkaruza <mario@dragonflydb.io>

Author: mkaruza

src/core/dense_set.cc

@@ -633,6 +633,8 @@ void DenseSet::Delete(DensePtr* prev, DensePtr* ptr) {
 
       DenseLinkKey* plink = prev->AsLink();
       DensePtr tmp = DensePtr::From(plink);
+      // Transfer TTL flag
+      tmp.SetTtl(prev->HasTtl());
       DCHECK(ObjectAllocSize(tmp.GetObject()));
 
       FreeLink(plink);

src/core/string_set_test.cc

@@ -706,4 +706,16 @@ TEST_F(StringSetTest, ReallocIfNeeded) {
     EXPECT_EQ(*ss_->Find(build_str(i * 10)), build_str(i * 10));
 }
 
+TEST_F(StringSetTest, TransferTTLFlagLinkToObjectOnDelete) {
+  for (size_t i = 0; i < 10; i++) {
+    EXPECT_TRUE(ss_->Add(absl::StrCat(i), 1));
+  }
+  for (size_t i = 0; i < 9; i++) {
+    EXPECT_TRUE(ss_->Erase(absl::StrCat(i)));
+  }
+  auto it = ss_->Find("9"sv);
+  EXPECT_TRUE(it.HasExpiry());
+  EXPECT_EQ(1u, it.ExpiryTime());
+}
+
 }  // namespace dfly

src/server/set_family_test.cc

@@ -412,4 +412,17 @@ TEST_F(SetFamilyTest, SAddEx) {
   EXPECT_THAT(Run({"saddex", "key", "KEEPTTL", "2"}), ErrArg("wrong number of arguments"));
 }
 
+TEST_F(SetFamilyTest, CheckSetLinkExpiryTransfer) {
+  for (int i = 0; i < 10; i++) {
+    EXPECT_THAT(Run({"SADDEX", "key", "5", absl::StrCat(i)}), IntArg(1));
+  }
+  for (int i = 0; i < 9; i++) {
+    Run({"SREM", "key", absl::StrCat(i)});
+  }
+  EXPECT_THAT(Run({"SCARD", "key"}), IntArg(1));
+  AdvanceTime(6000);
+  Run({"SMEMBERS", "key"});
+  EXPECT_THAT(Run({"SCARD", "key"}), IntArg(0));
+}
+
 }  // namespace dfly