config: move role start and stop to _post_apply()

Roles are now started and stopped at the "post_apply" stage rather than
at the "apply" stage. This allows require('config'):get() to correctly
return the configuration that is being applied.

Closes tarantool#9649

NO_DOC=bugfix

(cherry picked from commit ebb170c)

changelogs/unreleased/gh-9649-config-get-in-roles.md

@@ -0,0 +1,4 @@
+## bugfix/config
+
+* Calling `require('config'):get()` in role code now returns the configuration
+  that is currently applied (gh-9649).

src/box/lua/config/applier/roles.lua

@@ -3,6 +3,10 @@ local log = require('internal.config.utils.log')
 local last_loaded = {}
 local last_roles_ordered = {}
 
+local function apply(_config)
+    log.verbose('roles.apply: do nothing')
+end
+
 local function stop_roles(roles_to_skip)
     local roles_to_stop = {}
     for id = #last_roles_ordered, 1, -1 do
@@ -44,7 +48,7 @@ local function stop_roles(roles_to_skip)
         end
     end
     for _, role_name in ipairs(roles_to_stop) do
-        log.verbose('roles.apply: stop role ' .. role_name)
+        log.verbose('roles.post_apply: stop role ' .. role_name)
         local ok, err = pcall(last_loaded[role_name].stop)
         if not ok then
             error(('Error stopping role %s: %s'):format(role_name, err), 0)
@@ -106,7 +110,7 @@ local function resort_roles(original_order, roles)
     return ordered
 end
 
-local function apply(config)
+local function post_apply(config)
     local configdata = config._configdata
     local role_names = configdata:get('roles', {use_default = true})
     if role_names == nil or next(role_names) == nil then
@@ -132,7 +136,7 @@ local function apply(config)
     for _, role_name in ipairs(roles_ordered) do
         local role = last_loaded[role_name]
         if not role then
-            log.verbose('roles.apply: load role ' .. role_name)
+            log.verbose('roles.post_apply: load role ' .. role_name)
             role = require(role_name)
             local funcs = {'validate', 'apply', 'stop'}
             for _, func_name in pairs(funcs) do
@@ -164,7 +168,7 @@ local function apply(config)
 
     -- Apply configs for all roles.
     for _, role_name in ipairs(roles_ordered) do
-        log.verbose('roles.apply: apply config for role ' .. role_name)
+        log.verbose('roles.post_apply: apply config for role ' .. role_name)
         local ok, err = pcall(loaded[role_name].apply, roles_cfg[role_name])
         if not ok then
             error(('Error applying role %s: %s'):format(role_name, err), 0)
@@ -178,4 +182,5 @@ end
 return {
     name = 'roles',
     apply = apply,
+    post_apply = post_apply,
 }

test/config-luatest/roles_test.lua

@@ -572,3 +572,47 @@ g.test_role_dependencies_stop_required_role = function(g)
                   '"one", "two" depend on it'
     })
 end
+
+-- Make sure that role was started after config was fully loaded.
+g.test_role_started_and_stopped_after_config_loaded = function(g)
+    local one = string.dump(function()
+        local function apply()
+            local cfg = require('config')
+            local state = rawget(_G, 'state')
+            table.insert(state, {'start', cfg:info().status, cfg:get('roles')})
+        end
+
+        local function stop()
+            local cfg = require('config')
+            local state = rawget(_G, 'state')
+            table.insert(state, {'stop', cfg:info().status, cfg:get('roles')})
+        end
+
+        rawset(_G, 'state', {})
+
+        return {
+            validate = function() end,
+            apply = apply,
+            stop = stop,
+        }
+    end)
+    local verify = function()
+        local exp = {{'start', 'ready', {'one'}}}
+        t.assert_equals(rawget(_G, 'state'), exp)
+    end
+
+    local verify_2 = function()
+        local exp = {{'start', 'ready', {'one'}}, {'stop', 'ready'}}
+        t.assert_equals(rawget(_G, 'state'), exp)
+    end
+
+    helpers.reload_success_case(g, {
+        roles = {one = one},
+        options = {
+            ['roles'] = {'one'}
+        },
+        options_2 = {},
+        verify = verify,
+        verify_2 = verify_2,
+    })
+end