handle collection array for mixed types

src/realm/cluster.cpp

@@ -1646,12 +1646,14 @@ ref_type Cluster::typed_write(ref_type ref, _impl::ArrayWriterBase& out, const T
                 written_leaf.set_as_ref(1, Array::write(rot1.get_as_ref(), m_alloc, out, only_modified, true));
             }
             else if (col_type == col_type_Mixed) {
-                // REALM_ASSERT(leaf.size() == 4);
-                for (size_t i = 0; i < leaf.size(); ++i) {
+                const auto sz = leaf.size();
+                REALM_ASSERT(sz == 6);
+                for (size_t i = 0; i < sz; ++i) {
                     auto rot = leaf.get_as_ref_or_tagged(i);
                     if (rot.is_ref() && rot.get_as_ref()) {
                         // entries 0-2 are integral and can be compressed, entry 3 is strings and not compressed (yet)
-                        bool do_compress = compress && i < 3;
+                        // collections in mixed are stored at position 4.
+                        bool do_compress = (i < 3 || i == 4) ? true : false;
                         written_leaf.set_as_ref(
                             i, Array::write(rot.get_as_ref(), m_alloc, out, only_modified, do_compress));
                     }

src/realm/spec.cpp

@@ -339,15 +339,8 @@ bool Spec::operator==(const Spec& spec) const noexcept
 
 ColKey Spec::get_key(size_t column_ndx) const
 {
-    auto val = m_keys.get(column_ndx);
-
-    auto key = ColKey(val);
-    // when type is not valid ... val == -128
-    auto type = key.get_type();
-    // type is 0x20 ObjectId | TypeLink ... in the test we are setting a backlink
-    if (!type.is_valid())
-        REALM_ASSERT(m_keys.is_encoded());
-    REALM_ASSERT(type.is_valid());
+    const auto val = m_keys.get(column_ndx);
+    const auto key = ColKey(val);
     return key;
 }