lua/log: accept symbolic logging levels

Currently `log` module accepts only numeric values of
logging levels. I turn `box.cfg` interface supports
symbolic names (such as 'fatal', 'crit' and etc).

Thus we should support the same in `log` module.

Closes tarantool#5882

Reported-by: Alexander Turenko <[email protected]>
Acked-by: Alexander Turenko <[email protected]>
Acked-by: Serge Petrenko <[email protected]>
Signed-off-by: Cyrill Gorcunov <[email protected]>

Author: cyrillos

changelogs/unreleased/gh-5882-log-levels.md

@@ -0,0 +1,13 @@
+## feature/lua/log
+
+ * Implemented support of symbolic log levels representation
+   in `log` module (gh-5882). Now it is possible to specify
+   levels the same way as in `box.cfg{}` call. For example
+   instead of
+   ``` Lua
+   require('log').cfg{level = 6}
+   ```
+   One can use
+   ``` Lua
+   require('log').cfg{level = 'verbose'}
+   ```

src/lua/log.lua

@@ -499,6 +499,12 @@ local function load_cfg(self, cfg)
             local m = "log.cfg: \'%s\' %s"
             error(m:format('level', msg))
         end
+        -- Convert level to a numeric value since
+        -- low level api operates with numbers only.
+        if type(cfg.level) == 'string' then
+            assert(log_level_keys[cfg.level] ~= nil)
+            cfg.level = log_level_keys[cfg.level]
+        end
     end
 
     if cfg.nonblock ~= nil then

test/app-tap/logmod.test.lua

@@ -0,0 +1,36 @@
+#!/usr/bin/env tarantool
+
+local test = require('tap').test('log')
+local log = require('log')
+
+test:plan(8)
+
+log.log_format('plain')
+
+-- Test symbolic names for loglevels
+local _, err = pcall(log.cfg, {level='fatal'})
+test:ok(err == nil and log.cfg.level == 0, 'both got fatal')
+
+_, err = pcall(log.cfg, {level='syserror'})
+test:ok(err == nil and log.cfg.level == 1, 'got syserror')
+
+_, err = pcall(log.cfg, {level='error'})
+test:ok(err == nil and log.cfg.level == 2, 'got error')
+
+_, err = pcall(log.cfg, {level='crit'})
+test:ok(err == nil and log.cfg.level == 3, 'got crit')
+
+_, err = pcall(log.cfg, {level='warn'})
+test:ok(err == nil and log.cfg.level == 4, 'got warn')
+
+_, err = pcall(log.cfg, {level='info'})
+test:ok(err == nil and log.cfg.level == 5, 'got info')
+
+_, err = pcall(log.cfg, {level='verbose'})
+test:ok(err == nil and log.cfg.level == 6, 'got verbose')
+
+_, err = pcall(log.cfg, {level='debug'})
+test:ok(err == nil and log.cfg.level == 7, 'got debug')
+
+test:check()
+os.exit()