From 29a9e638c1bf70eb5f57bf8c6b78de71293cdedf Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 13 Mar 2025 13:37:38 +0100
Subject: [PATCH] Remove "@nix" prefix from json-log-path output

---
 src/libutil/logging.cc | 22 ++++++++++++++--------
 src/libutil/logging.hh |  4 ++--
 src/nix/main.cc        |  5 +++--
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 0bffe40e3..fcbc61d5e 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -168,8 +168,12 @@ void to_json(nlohmann::json & json, std::shared_ptr<Pos> pos)
 
 struct JSONLogger : Logger {
     Descriptor fd;
+    bool includeNixPrefix;
 
-    JSONLogger(Descriptor fd) : fd(fd) { }
+    JSONLogger(Descriptor fd, bool includeNixPrefix)
+        : fd(fd)
+        , includeNixPrefix(includeNixPrefix)
+    { }
 
     bool isVerbose() override {
         return true;
@@ -190,7 +194,9 @@ struct JSONLogger : Logger {
 
     void write(const nlohmann::json & json)
     {
-        writeLine(fd, "@nix " + json.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace));
+        writeLine(fd,
+            (includeNixPrefix ? "@nix " : "") +
+            json.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace));
     }
 
     void log(Verbosity lvl, std::string_view s) override
@@ -262,18 +268,18 @@ struct JSONLogger : Logger {
     }
 };
 
-Logger * makeJSONLogger(Descriptor fd)
+Logger * makeJSONLogger(Descriptor fd, bool includeNixPrefix)
 {
-    return new JSONLogger(fd);
+    return new JSONLogger(fd, includeNixPrefix);
 }
 
-Logger * makeJSONLogger(const std::filesystem::path & path)
+Logger * makeJSONLogger(const std::filesystem::path & path, bool includeNixPrefix)
 {
     struct JSONFileLogger : JSONLogger {
         AutoCloseFD fd;
 
-        JSONFileLogger(AutoCloseFD && fd)
-            : JSONLogger(fd.get())
+        JSONFileLogger(AutoCloseFD && fd, bool includeNixPrefix)
+            : JSONLogger(fd.get(), includeNixPrefix)
             , fd(std::move(fd))
         { }
     };
@@ -282,7 +288,7 @@ Logger * makeJSONLogger(const std::filesystem::path & path)
     if (!fd)
         throw SysError("opening log file '%1%'", path);
 
-    return new JSONFileLogger(std::move(fd));
+    return new JSONFileLogger(std::move(fd), includeNixPrefix);
 }
 
 static Logger::Fields getFields(nlohmann::json & json)
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index cadeafea4..ef449d03e 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -189,9 +189,9 @@ Logger * makeSimpleLogger(bool printBuildLogs = true);
 
 Logger * makeTeeLogger(std::vector<Logger *> loggers);
 
-Logger * makeJSONLogger(Descriptor fd);
+Logger * makeJSONLogger(Descriptor fd, bool includeNixPrefix = true);
 
-Logger * makeJSONLogger(const std::filesystem::path & path);
+Logger * makeJSONLogger(const std::filesystem::path & path, bool includeNixPrefix = true);
 
 /**
  * @param source A noun phrase describing the source of the message, e.g. "the builder".
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 10a02fe3f..68137a216 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -354,7 +354,8 @@ struct ExtLoggerSettings : Config
         this, "", "json-log-path",
         R"(
           A path to which JSON records of Nix's log output will be
-          written, in the same format as `--log-format internal-json`.
+          written, in the same format as `--log-format internal-json`
+          (without the `@nix ` prefixes on each line).
         )"};
 };
 
@@ -501,7 +502,7 @@ void mainWrapped(int argc, char * * argv)
     }
 
     if (!extLoggerSettings.jsonLogPath.get().empty()) {
-        logger = makeTeeLogger({logger, makeJSONLogger(std::filesystem::path(extLoggerSettings.jsonLogPath.get()))});
+        logger = makeTeeLogger({logger, makeJSONLogger(std::filesystem::path(extLoggerSettings.jsonLogPath.get()), false)});
     }
 
     if (args.helpRequested) {