Add method to filesinks to return filename

include/spdlog/sinks/basic_file_sink.h

@@ -30,6 +30,11 @@ public:
         file_helper_.open(filename, truncate);
     }
 
+    const filename_t &filename() const
+    {
+        return file_helper_.filename();
+    }
+
 protected:
     void sink_it_(const details::log_msg &msg) override
     {

include/spdlog/sinks/daily_file_sink.h

@@ -63,6 +63,11 @@ public:
         rotation_tp_ = next_rotation_tp_();
     }
 
+    const filename_t &filename() const
+    {
+        return file_helper_.filename();
+    }
+
 protected:
     void sink_it_(const details::log_msg &msg) override
     {

include/spdlog/sinks/rotating_file_sink.h

@@ -58,6 +58,11 @@ public:
         return fmt::to_string(w);
     }
 
+    const filename_t &filename() const
+    {
+        return file_helper_.filename();
+    }
+
 protected:
     void sink_it_(const details::log_msg &msg) override
     {