fix: Do not attempt to defrag StringSet as a StringMap (#4283)

That'd be a total waste of time and energy, not to mention you'll crash.

Fixes #4167

Author: chakaz

src/core/compact_object.cc

@@ -215,9 +215,9 @@ pair<void*, bool> DefragSet(unsigned encoding, void* ptr, float ratio) {
       return DefragIntSet((intset*)ptr, ratio);
     }
 
-    // StringMap supports re-allocation of it's internal nodes
     case kEncodingStrMap2: {
-      return DefragStrMap2((StringMap*)ptr, ratio);
+      // Still not implemented
+      return {ptr, false};
     }
 
     default:

src/core/compact_object_test.cc

@@ -16,6 +16,7 @@
 #include "core/detail/bitpacking.h"
 #include "core/flat_set.h"
 #include "core/mi_memory_resource.h"
+#include "core/string_set.h"
 
 extern "C" {
 #include "redis/intset.h"
@@ -575,6 +576,14 @@ TEST_F(CompactObjectTest, DefragHash) {
   }
 }
 
+TEST_F(CompactObjectTest, DefragSet) {
+  // This is still not implemented
+  StringSet* s = new StringSet();
+  s->Add("str");
+  cobj_.InitRobj(OBJ_SET, kEncodingStrMap2, s);
+  ASSERT_FALSE(cobj_.DefragIfNeeded(0.8));
+}
+
 TEST_F(CompactObjectTest, RawInterface) {
   string str(50, 'a'), tmp, owned;
   cobj_.SetString(str);