Avoid string index upgrade

src/realm/index_string.cpp

@@ -1075,7 +1075,7 @@ bool StringIndex::leaf_insert(ObjKey obj_key, key_type key, size_t offset, Strin
             if (index_data == index_data_2 || suboffset > s_max_offset) {
                 // These strings have the same prefix up to this point but we
                 // don't want to recurse further, create a list in sorted order.
-                bool row_ndx_first = value < v2;
+                bool row_ndx_first = value.compare_signed(v2) < 0;
                 Array row_list(alloc);
                 row_list.create(Array::type_Normal); // Throws
                 row_list.add(row_ndx_first ? obj_key.value : obj_key2.value);
@@ -1629,7 +1629,7 @@ bool SortedListComparator::operator()(int64_t key_value, Mixed needle) // used i
 
     // We need to be consistent with using the same compare method as how these strings
     // were they were put into this ordered column in the first place.
-    return a < needle;
+    return a.compare_signed(needle) < 0;
 }
 
 
@@ -1693,7 +1693,7 @@ void StringIndex::verify() const
                     while (it != it_end) {
                         Mixed it_data = get(ObjKey(*it));
                         size_t it_row = to_size_t(*it);
-                        REALM_ASSERT(previous <= it_data);
+                        REALM_ASSERT(previous.compare_signed(it_data) <= 0);
                         if (it != sub.cbegin() && previous == it_data) {
                             REALM_ASSERT_EX(it_row > last_row, it_row, last_row);
                         }

src/realm/mixed.cpp

@@ -351,6 +351,21 @@ int Mixed::compare(const Mixed& b) const noexcept
     // Observe! Changing this function breaks the file format for Set<Mixed> and the StringIndex
 }
 
+int Mixed::compare_signed(const Mixed& b) const noexcept
+{
+    if (is_type(type_String) && b.is_type(type_String)) {
+        auto a_val = get_string();
+        auto b_val = b.get_string();
+        if (a_val == b_val)
+            return 0;
+        if (std::lexicographical_compare(a_val.data(), a_val.data() + a_val.size(), b_val.data(),
+                                         b_val.data() + b_val.size()))
+            return -1;
+        return 1;
+    }
+    return compare(b);
+}
+
 template <>
 int64_t Mixed::export_to_type() const noexcept
 {

src/realm/mixed.hpp

@@ -230,6 +230,8 @@ class Mixed {
     bool is_same_type(const Mixed& b) const noexcept;
     // Will use unsigned lexicographical comparison for strings
     int compare(const Mixed& b) const noexcept;
+    // Will compare strings as arrays of signed chars
+    int compare_signed(const Mixed& b) const noexcept;
     friend bool operator==(const Mixed& a, const Mixed& b) noexcept
     {
         return a.compare(b) == 0;

src/realm/transaction.cpp

@@ -562,28 +562,6 @@ void Transaction::upgrade_file_format(int target_file_format_version)
         for (auto k : table_keys) {
             auto t = get_table(k);
             t->migrate_string_sets(); // rewrite sets to use the new string order
-            t->for_each_public_column([&](ColKey col) {
-                if (col.get_type() != col_type_String) {
-                    return IteratorControl::AdvanceToNext;
-                }
-                switch (t->search_index_type(col)) {
-                    case IndexType::General: {
-                        if (current_file_format_version < 22 && t->get_primary_key_column() == col) {
-                            break; // this index was just added by a previous upgrade step above
-                        }
-                        t->remove_search_index(col);
-                        t->add_search_index(col, IndexType::General);
-                        break;
-                    }
-                    case IndexType::Fulltext:
-                        t->remove_search_index(col);
-                        t->add_search_index(col, IndexType::Fulltext);
-                        break;
-                    case IndexType::None:
-                        break;
-                }
-                return IteratorControl::AdvanceToNext;
-            });
         }
     }
     // NOTE: Additional future upgrade steps go here.