makeTeeLogger(): Distinguish between main and extra loggers

src/libutil/logging.cc

@@ -344,15 +344,16 @@ std::unique_ptr<Logger> makeJSONLogger(const std::filesystem::path & path, bool
 void applyJSONLogger()
 {
     if (!loggerSettings.jsonLogPath.get().empty()) {
-        std::vector<std::unique_ptr<Logger>> loggers;
         try {
-            loggers.push_back(std::move(logger));
+            std::vector<std::unique_ptr<Logger>> loggers;
             loggers.push_back(makeJSONLogger(std::filesystem::path(loggerSettings.jsonLogPath.get()), false));
-            logger = makeTeeLogger(std::move(loggers));
+            // Note: this had better not throw, otherwise `logger` is
+            // left unset.
+            logger = makeTeeLogger(std::move(logger), std::move(loggers));
         } catch (...) {
-            logger = std::move(loggers[0]);
             ignoreExceptionExceptInterrupt();
         }
+
     }
 }
 

src/libutil/logging.hh

@@ -215,7 +215,14 @@ extern std::unique_ptr<Logger> logger;
 
 std::unique_ptr<Logger> makeSimpleLogger(bool printBuildLogs = true);
 
-std::unique_ptr<Logger> makeTeeLogger(std::vector<std::unique_ptr<Logger>> && loggers);
+/**
+ * Create a logger that sends log messages to `mainLogger` and the
+ * list of loggers in `extraLoggers`. Only `mainLogger` is used for
+ * writing to stdout and getting user input.
+ */
+std::unique_ptr<Logger> makeTeeLogger(
+    std::unique_ptr<Logger> mainLogger,
+    std::vector<std::unique_ptr<Logger>> && extraLoggers);
 
 std::unique_ptr<Logger> makeJSONLogger(Descriptor fd, bool includeNixPrefix = true);
 

src/libutil/tee-logger.cc

@@ -100,9 +100,14 @@ struct TeeLogger : Logger
     }
 };
 
-std::unique_ptr<Logger> makeTeeLogger(std::vector<std::unique_ptr<Logger>> && loggers)
+std::unique_ptr<Logger>
+makeTeeLogger(std::unique_ptr<Logger> mainLogger, std::vector<std::unique_ptr<Logger>> && extraLoggers)
 {
-    return std::make_unique<TeeLogger>(std::move(loggers));
+    std::vector<std::unique_ptr<Logger>> allLoggers;
+    allLoggers.push_back(std::move(mainLogger));
+    for (auto & l : extraLoggers)
+        allLoggers.push_back(std::move(l));
+    return std::make_unique<TeeLogger>(std::move(allLoggers));
 }
 
 }