feature: support interval type

Support interval type checks [1] (added in Tarantool 2.10.0).

1. tarantool/tarantool#5941

Part of tarantool/tarantool#7726

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - "error" type supported.
 - "datetime" type supported.
+- "interval" type supported.
 
 ### Fixed
 

checks.lua

@@ -354,4 +354,6 @@ if has_datetime then
     checkers.datetime = datetime.is_datetime
 end
 
+add_ffi_type_checker('interval', 'struct interval')
+
 return checks

test.lua

@@ -633,6 +633,12 @@ if has_datetime then
     testdata.datetime = datetime
 end
 
+function testdata.fn_interval(arg) -- luacheck: no unused args
+    checks('interval')
+end
+
+local has_interval = has_datetime and datetime.interval ~= nil
+
 local ret_cases = {
     -- fn_int64
     {
@@ -1037,6 +1043,36 @@ local ret_cases = {
         code = 'fn_datetime({year=2023, month=1, day=11})',
         ok = false,
     },
+
+    -- fn_interval
+    {
+        skip = not has_interval,
+        code = 'fn_interval(datetime.interval.new())',
+        ok = true,
+        additional_data = {'datetime'},
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval(datetime.interval.new{day=1})',
+        ok = true,
+        additional_data = {'datetime'},
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval(datetime.interval.new{month=1, adjust="last"})',
+        ok = true,
+        additional_data = {'datetime'},
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval()',
+        ok = false,
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval({month=1, adjust="last"})',
+        ok = false,
+    },
 }
 
 for _, case in pairs(ret_cases) do