box: fix shared lang between connected clients

Fixed the implementation of the box console.
Before this fix, result of `\set language` is shared between clients
via `console.connect`, despite the fact that clients have different
`box.session.id`. Now the parameter of the selected language is stored
by each client in his own `box.session.storage`.

Fixes #8817

NO_DOC=bugfix

(cherry picked from commit e4fda4b7)

changelogs/unreleased/gh-8817-bug-fix-set-language-shared-between-conn-clients.md

+## bugfix/box
+
+* Fixed a bug in the box console implementation because of
+  which the `language` parameter was shared between connected
+  clients (gh-8817).

src/box/lua/console.lua

@@ -426,7 +426,7 @@ local function local_eval(storage, line)
 end
 
 local function eval(line)
-    return local_eval(box.session, line)
+    return local_eval(box.session.storage, line)
 end
 
 local text_connection_mt = {

test/box-luatest/gh_8817_bug_set_language_shared_test.lua

+local fio = require('fio')
+local t = require('luatest')
+local server = require('luatest.server')
+local it = require('test.interactive_tarantool')
+
+local g = t.group()
+
+-- Create test instances and open connections.
+g.before_all(function()
+    g.server = server:new({alias = 'test-gh-8817-server'})
+    g.server:start()
+
+    local socket_path = fio.pathjoin(g.server.workdir, 'admin.socket')
+    local listen_command  = "require('console').listen('%s')"
+    local connect_command = "require('console').connect('%s')"
+
+    listen_command  = listen_command:format(socket_path)
+    connect_command = connect_command:format(socket_path)
+
+    -- Listen on the server.
+    g.server:eval(listen_command)
+
+    g.first_client = it:new()
+    g.second_client = it:new()
+
+    -- Create first connection to the server.
+    g.first_client:execute_command(connect_command)
+    t.assert_equals(
+        g.first_client:read_response(),
+        true
+    )
+    g.first_client:set_prompt(('unix/:%s> '):format(socket_path))
+
+    -- Create second connection to the server.
+    g.second_client:execute_command(connect_command)
+    t.assert_equals(
+        g.second_client:read_response(),
+        true
+    )
+    g.second_client:set_prompt(('unix/:%s> '):format(socket_path))
+
+    -- Make sure that box.session.id are different on test clients.
+    g.first_client:execute_command("box.session.id()")
+    local first_client_session_id = g.first_client:read_response()
+    g.second_client:execute_command("box.session.id()")
+    local second_client_session_id = g.second_client:read_response()
+    t.assert_not_equals(
+        first_client_session_id,
+        second_client_session_id
+    )
+end)
+
+-- Stop test instances.
+g.after_all(function()
+    g.server:stop()
+    g.first_client:close()
+    g.second_client:close()
+end)
+
+-- Checks that the language setting is not shared between clients.
+g.test_set_language_not_shared_between_clients = function()
+    -- Check initial language on clients.
+    g.first_client:execute_command("\\set language")
+    t.assert_equals(
+        g.first_client:read_response(),
+        {language = "lua"}
+    )
+    g.second_client:execute_command("\\set language")
+    t.assert_equals(
+        g.second_client:read_response(),
+        {language = "lua"}
+    )
+
+    -- Set new language on first client.
+    g.first_client:execute_command("\\set language sql")
+    t.assert_equals(
+        g.first_client:read_response(),
+        true
+    )
+
+    -- Check that language changes on the first client
+    -- did not spread to the second.
+    g.second_client:execute_command("\\set language")
+    t.assert_equals(
+        g.second_client:read_response(),
+        {language = "lua"}
+    )
+end