config: introduce droppable alerts

For now it's impossible to drop created alert in any way except
manual searching for _alerts table. However, we need to drop alerts
on missing names, when the names are set.

Let's introduce simple key-value alerts in order to easily drop them
by key.

Needed for tarantool#8978

NO_DOC=internal
NO_TEST=following commit
NO_CHANGELOG=internal

src/box/lua/config/applier/box_cfg.lua

@@ -270,7 +270,8 @@ local function apply(config)
             if v ~= box.cfg[k] then
                 local warning = 'box_cfg.apply: non-dynamic option '..k..
                     ' will not be set until the instance is restarted'
-                config:_alert({type = 'warn', message = warning})
+                config:_alert('box_cfg_apply_non_dynamic',
+                              {type = 'warn', message = warning})
                 box_cfg[k] = nil
             end
         end

src/box/lua/config/applier/credentials.lua

@@ -469,13 +469,15 @@ local privileges_action_f = function(grant_or_revoke, role_or_user, name, privs,
         err = ('credentials.apply: box.schema.%s.%s(%q, %q, %q, %q) failed: %s')
               :format(role_or_user, grant_or_revoke, name, privs, obj_type,
                       obj_name, err)
-        config:_alert({type = 'error', message = err})
+        config:_alert('credentials_grant_or_revoke_err',
+                      {type = 'error', message = err})
     else
         local msg = "credentials.apply: %s %q hasn't been created yet, " ..
                     "'box.schema.%s.%s(%q, %q, %q, %q)' will be applied later"
         msg = msg:format(obj_type, obj_name, role_or_user, grant_or_revoke,
                          name, privs, obj_type, obj_name)
-        config:_alert({type = 'warn', message = msg})
+        config:_alert('credentials_grant_or_revoke_warn',
+                      {type = 'warn', message = msg})
     end
 end
 
@@ -621,9 +623,10 @@ local function set_password(user_name, password)
     end
 
     if user_name == 'guest' then
-        config:_alert({type = 'error',
-            message = 'credentials.apply: setting a password for ' ..
-                      'the guest user is not allowed'})
+        local message = 'credentials.apply: setting a password for ' ..
+                        'the guest user is not allowed'
+        config:_alert('credentials_apply_password',
+                      {type = 'error', message = message})
     end
 
     local auth_def = box.space._user.index.name:get({user_name})[5]
@@ -729,7 +732,8 @@ local function sync_credentials_worker()
                 local msg = 'credentials.apply: Tarantool is in Read Only ' ..
                             'mode, so credentials will be set up in the ' ..
                             'background when it is switched to Read Write mode'
-                config:_alert({type = 'warn', message = msg})
+                config:_alert('credentials_apply_ro',
+                              {type = 'warn', message = msg})
                 box.ctl.wait_rw()
             end
 

src/box/lua/config/init.lua

@@ -95,15 +95,22 @@ local function broadcast(self)
     box.broadcast('config.info', self:info())
 end
 
-function methods._alert(self, alert)
+function methods._alert(self, key, alert)
     assert(alert.type == 'error' or alert.type == 'warn')
     if alert.type == 'error' then
         log.error(alert.message)
     else
         log.warn(alert.message)
     end
     alert.timestamp = datetime.now()
-    table.insert(self._alerts, alert)
+    self._alerts[key] = alert
+end
+
+function methods._alert_drop(self, key)
+    self._alerts[key] = nil
+    if self._status == 'check_warnings' and table.equals(self._alerts, {}) then
+        self._status = 'ready'
+    end
 end
 
 function methods._meta(self, source_name, key, value)
@@ -446,7 +453,7 @@ function methods._reload_noexc(self, opts)
 
     assert(not ok or err == nil)
     if not ok then
-        self:_alert({type = 'error', message = err})
+        self:_alert('reload_error', {type = 'error', message = err})
     end
 
     self:_set_status_based_on_alerts()
@@ -464,8 +471,17 @@ end
 
 function methods.info(self)
     selfcheck(self, 'info')
+    -- Don't return alert keys from config:info().
+    local alerts = {}
+    for _, alert in pairs(self._alerts) do
+        table.insert(alerts, alert)
+    end
+    table.sort(alerts, function(a, b)
+        return a.timestamp < b.timestamp
+    end)
+
     return {
-        alerts = self._alerts,
+        alerts = alerts,
         meta = self._metadata,
         status = self._status,
     }