added comments

include/spdlog/logger.h

@@ -109,7 +109,8 @@ public:
         }
     }
 
-#ifdef SPDLOG_SOURCE_LOCATION
+#ifdef SPDLOG_SOURCE_LOCATION  // off by default. define SPDLOG_SOURCE_LOCATION before including
+                               // spdlog to enable.
     template <typename... Args>
     void trace(loc_with_fmt fmt, Args &&...args) {
         log(fmt.loc, level::trace, fmt.fmt_string, std::forward<Args>(args)...);
@@ -165,7 +166,7 @@ public:
     void critical(string_view_t msg, source_loc loc = source_loc::current()) {
         log(loc, level::critical, msg);
     }
-#else
+#else   // without source location
     template <typename... Args>
     void trace(format_string_t<Args...> fmt, Args &&...args) {
         log(level::trace, fmt, std::forward<Args>(args)...);
@@ -198,17 +199,12 @@ public:
 
     // log functions with no format string, just string
     void trace(string_view_t msg) { log(level::trace, msg); }
-
     void debug(string_view_t msg) { log(level::debug, msg); }
-
     void info(string_view_t msg) { log(level::info, msg); }
-
+    void warn(string_view_t msg) { log(level::warn, msg); }
-    inline void warn(string_view_t msg) { log(level::warn, msg); }
-
     void error(string_view_t msg) { log(level::err, msg); }
-
     void critical(string_view_t msg) { log(level::critical, msg); }
-#endif
+#endif  // SPDLOG_SOURCE_LOCATION
 
     // return true if logging is enabled for the given level.
     [[nodiscard]] bool should_log(level msg_level) const {
@@ -241,7 +237,6 @@ public:
 
     // sinks
     [[nodiscard]] const std::vector<sink_ptr> &sinks() const;
-
     [[nodiscard]] std::vector<sink_ptr> &sinks();
 
     // error handler