fix preserve_in_ast for record fields

`from` and `to` was mixed up, and not only it worked incorrectly,
but it was also changing testcase table and passing the test.

Closes #78

Author: Khatskevich

avro_schema/frontend.lua

@@ -350,7 +350,7 @@ copy_schema = function(schema, context, ns, open_rec)
                 for fieldno, xfield in ipairs(xfields) do
                     ptr = fieldno
                     local field = {}
-                    preserve_user_fields(field, xfield, context)
+                    preserve_user_fields(xfield, field, context)
                     res.fields[fieldno] = field
                     if type(xfield) ~= 'table' then
                         copy_schema_error('Record field must be a list')
@@ -1195,9 +1195,9 @@ export_helper = function(node, already_built)
             utils.copy_fields(node, res, {exclude={"fields"}})
             for i, field in ipairs(node.fields) do
                 local xfield = {
-                    name = field.name,
                     type = export_helper(field.type, already_built)
                 }
+                utils.copy_fields(field, xfield, {exclude={"type"}})
                 res.fields[i] = xfield
             end
             pack_nullable_to_type(res)

test/api_tests/export.lua

@@ -237,8 +237,8 @@ res = {schema.create(
             preserve_in_fingerprint={"extra_field"}})}
 fingerprint = schema.fingerprint(res[2], "sha256", 32)
 test:is(string.lower(string.tohex(fingerprint)),
-        "70bd295335daafff0a4512cadc39a4298cd81c460defec530c7372bdd1ec6f44",
-        "Fingerprint extra fields 2")
+    "ed1e8b275fe8c436839bdb2962f7595bbef6bc364dfdcd47d3d1334888350711",
+    "Fingerprint extra fields 2")
 
 res = {schema.create(
         {