chore: Avoid logging a warning when LOG_LEVEL is unset (docker-mailserver#4497)

Author: polarathene

target/scripts/startup/variables-stack.sh

@@ -4,7 +4,7 @@
 declare -A VARS
 
 function _early_variables_setup() {
-  __environment_variables_log_level
+  __ensure_valid_log_level
   __environment_variables_from_files
   _obtain_hostname_and_domainname
   __environment_variables_backwards_compatibility
@@ -181,21 +181,11 @@ function __environment_variables_general_setup() {
   fi
 }
 
-function __environment_variables_log_level() {
-  if [[ ${LOG_LEVEL} == 'trace' ]] \
-  || [[ ${LOG_LEVEL} == 'debug' ]] \
-  || [[ ${LOG_LEVEL} == 'info' ]]  \
-  || [[ ${LOG_LEVEL} == 'warn' ]]  \
-  || [[ ${LOG_LEVEL} == 'error' ]]
-  then
-    return 0
-  else
-    local DEFAULT_LOG_LEVEL='info'
-    _log 'warn' "Log level '${LOG_LEVEL}' is invalid (falling back to default '${DEFAULT_LOG_LEVEL}')"
-
-    # shellcheck disable=SC2034
-    VARS[LOG_LEVEL]="${DEFAULT_LOG_LEVEL}"
-    LOG_LEVEL="${DEFAULT_LOG_LEVEL}"
+# `LOG_LEVEL` must be set early to correctly filter calls to `scripts/helpers/log.sh:_log()`
+function __ensure_valid_log_level() {
+  if [[ ! ${LOG_LEVEL:-info} =~ ^(trace|debug|info|warn|error)$ ]]; then
+    _log 'warn' "Log level '${LOG_LEVEL}' is invalid (falling back to default: 'info')"
+    LOG_LEVEL='info'
   fi
 }