feature: support error type

Support error type checks for box.error objects [1] (can be explicitly
created in Tarantool Lua scripts since 2.4.1).

1. tarantool/tarantool#4398

Part of tarantool/tarantool#7726

Author: DifferentialOrange

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+- "error" type supported.
+
 ### Fixed
 
 - Fixed compatibility with LuaJIT.

checks.lua

@@ -342,4 +342,6 @@ function checkers.uuid_bin(arg)
     end
 end
 
+add_ffi_type_checker('error', 'struct error')
+
 return checks

test.lua

@@ -618,6 +618,12 @@ if has_decimal then
     testdata.decimal = decimal
 end
 
+function testdata.fn_error(arg) -- luacheck: no unused args
+    checks('error')
+end
+
+local has_error = (box.error ~= nil) and (box.error.new ~= nil)
+
 local ret_cases = {
     -- fn_int64
     {
@@ -937,6 +943,33 @@ local ret_cases = {
         code = 'fn_decimal(1)',
         ok = false,
     },
+
+    -- fn_error
+    {
+        skip = not has_error,
+        code = 'fn_error(box.error.new(box.error.UNKNOWN))',
+        ok = true,
+    },
+    {
+        skip = not has_error,
+        code = 'fn_error(box.error.UNKNOWN)', -- It's an error code, not an error object.
+        ok = false,
+    },
+    {
+        skip = not has_error,
+        code = 'fn_error(select(2, pcall(error, "my error")))',
+        ok = false,
+    },
+    {
+        skip = not has_error,
+        code = 'fn_error()',
+        ok = false,
+    },
+    {
+        skip = not has_error,
+        code = 'fn_error(1)',
+        ok = false,
+    },
 }
 
 for _, case in pairs(ret_cases) do