Use $TZ for local time if it is set

libstdc++ doesn't.

include/modules/clock.hpp

@@ -52,6 +52,9 @@ class Clock final : public ALabel {
   auto get_calendar(const year_month_day& today, const year_month_day& ymd, const time_zone* tz)
       -> const std::string;
 
+  // get local time zone
+  auto local_zone() -> const time_zone*;
+
   // time zoned time in tooltip
   const bool tzInTooltip_;                // if need to print time zones text
   std::vector<const time_zone*> tzList_;  // time zones list

src/modules/clock.cpp

@@ -87,7 +87,7 @@ waybar::modules::Clock::Clock(const std::string& id, const Json::Value& config)
       fmtMap_.insert({3, config_[kCldPlaceholder]["format"]["today"].asString()});
       cldBaseDay_ =
           year_month_day{
-              floor<days>(zoned_time{current_zone(), system_clock::now()}.get_local_time())}
+              floor<days>(zoned_time{local_zone(), system_clock::now()}.get_local_time())}
               .day();
     } else
       fmtMap_.insert({3, "{}"});
@@ -131,7 +131,7 @@ waybar::modules::Clock::Clock(const std::string& id, const Json::Value& config)
 }
 
 auto waybar::modules::Clock::update() -> void {
-  const auto* tz = tzList_[tzCurrIdx_] != nullptr ? tzList_[tzCurrIdx_] : current_zone();
+  const auto* tz = tzList_[tzCurrIdx_] != nullptr ? tzList_[tzCurrIdx_] : local_zone();
   const zoned_time now{tz, floor<seconds>(system_clock::now())};
 
   label_.set_markup(fmt_lib::vformat(locale_, format_, fmt_lib::make_format_args(now)));
@@ -168,7 +168,7 @@ auto waybar::modules::Clock::getTZtext(sys_seconds now) -> std::string {
   std::stringstream os;
   for (size_t tz_idx{0}; tz_idx < tzList_.size(); ++tz_idx) {
     if (static_cast<int>(tz_idx) == tzCurrIdx_) continue;
-    const auto* tz = tzList_[tz_idx] != nullptr ? tzList_[tz_idx] : current_zone();
+    const auto* tz = tzList_[tz_idx] != nullptr ? tzList_[tz_idx] : local_zone();
     auto zt{zoned_time{tz, now}};
     os << fmt_lib::vformat(locale_, format_, fmt_lib::make_format_args(zt)) << '\n';
   }
@@ -393,6 +393,18 @@ auto waybar::modules::Clock::get_calendar(const year_month_day& today, const yea
   return os.str();
 }
 
+auto waybar::modules::Clock::local_zone() -> const time_zone* {
+  const char* tz_name = getenv("TZ");
+  if (tz_name) {
+    try {
+      return locate_zone(tz_name);
+    } catch (const std::runtime_error& e) {
+      spdlog::warn("Timezone: {0}. {1}", tz_name, e.what());
+    }
+  }
+  return current_zone();
+}
+
 // Actions handler
 auto waybar::modules::Clock::doAction(const std::string& name) -> void {
   if (actionMap_[name]) {