Re: [Tarantool-patches] [PATCH 07/10] lua/log: use log module settings inside box.cfg

[Oleg Babin <olegrok@tarantool.org>]

Hi! Thanks for your patch! See my comments below.

On 25/05/2020 15:17, Cyrill Gorcunov wrote:
 >
 >   local function log_pid()
 > @@ -197,6 +215,18 @@ return setmetatable({
 >       pid = log_pid;
 >       level = log_level;
 >       log_format = log_format;
 > +    cfg = cfg,
 > +    --
 > +    -- Internal API to box module, not for users,
 > +    -- names can be changed.
 > +    box_api = {
 > +        set_log_level = function()
 > +            log_level(box.cfg.log_level)
 > +        end,
 > +        set_log_format = function()
 > +            log_format(box.cfg.log_format)
 > +        end,
 > +    }
 >   }, {
 >       __index = compat_v16;
 >   })
 >
I think we should hide internal functions from user as it is done e.g. 
in fiber module: 
https://github.com/tarantool/tarantool/blob/master/src/lua/fiber.lua#L89

Also I thinks we shouldn't expose some of functions:
```lua
tarantool> log = require('log')
---
...

tarantool> log
---
- level: 'function: 0x010c087cd8'
   log_format: 'function: 0x010c069d08'
   info: 'function: 0x010c0a3d18'
   pid: 'function: 0x010c09db10'
   error: 'function: 0x010c042410'
   warn: 'function: 0x010c0a2048'
   box_api:
     cfg_update: 'function: 0x010c09e248'
     set_log_level: 'function: 0x010c047818'
     set_log_format: 'function: 0x010c070f78'
   cfg:
     log_level: 5
     log_format: plain
   debug: 'function: 0x010c0a6130'
   init: 'function: 0x010c0762a0'
   rotate: 'function: 0x010c08b7d0'
   verbose: 'function: 0x010c0a4758'
...

tarantool> log.logger_pid() -- shouldn't be exposed if deprecated
logger_pid() is deprecated, please use pid() instead
---
- 0
...
```

And IMO it will be great if an interface that will be similar to 
box.cfg/json.cfg/yaml.cfg... - log.cfg({...}). For that we can add 
__call metamethod for cfg table.