select: fix result order with negative first

crud.select reverses order of the results from the cluster in case
of negative first. It is necessary because the pagination results
should be in the same order when moving in both directions. The reverse
function did not work correctly.

Author: oleg-jukovec

CHANGELOG.md

@@ -52,6 +52,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
     - [6, 1064, 'Alexey', 'Sidorov', 31]
   ...
 
+* `crud.select()` results order with negative `first`.
+
 ## [0.11.2] - 23-05-22
 
 ### Added

crud/common/utils.lua

@@ -455,7 +455,7 @@ function utils.invert_tarantool_iter(iter)
 end
 
 function utils.reverse_inplace(t)
-    for i = 1,#t - 1 do
+    for i = 1,math.floor(#t / 2) do
         t[i], t[#t - i + 1] = t[#t - i + 1], t[i]
     end
     return t

test/integration/select_test.lua

@@ -206,15 +206,15 @@ pgroup.test_negative_first = function(g)
     table.sort(customers, function(obj1, obj2) return obj1.id < obj2.id end)
 
     -- no conditions
-    -- first -3 after 5
-    local first = -3
-    local after = crud_utils.flatten(customers[5], g.space_format)
+    -- first -4 after 6
+    local first = -4
+    local after = crud_utils.flatten(customers[6], g.space_format)
     local result, err = g.cluster.main_server.net_box:call(
        'crud.select', {'customers', nil, {first=first, after=after}})
 
     t.assert_equals(err, nil)
     local objects = crud.unflatten_rows(result.rows, result.metadata)
-    t.assert_equals(objects, helpers.get_objects_by_idxs(customers, {2, 3, 4}))
+    t.assert_equals(objects, helpers.get_objects_by_idxs(customers, {2, 3, 4, 5}))
 
     -- id >= 2
     -- first -2 after 5

test/unit/reverse_inplace_test.lua

@@ -0,0 +1,24 @@
+local t = require('luatest')
+local g = t.group('utils')
+
+local utils = require('crud.common.utils')
+
+local reverse_inplace_cases = {
+    single_value = {1},
+    two_values = {1, 2},
+    three_values = {1, 2, 3},
+    four_values = {1, 2, 3, 4},
+    uneven_values = {1, 2, 3, 4, 5, 6, 7, 8, 9},
+    even_values = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+}
+
+for case_name, case in pairs(reverse_inplace_cases) do
+    g["test_reverse_inplace_" .. case_name] = function()
+        local case_reversed = {}
+        for i=#case,1,-1 do
+            table.insert(case_reversed, case[i])
+        end
+        case = utils.reverse_inplace(case)
+        t.assert_equals(case, case_reversed)
+    end
+end