Convert --log-format CLI argument to setting

src/libmain/common-args.cc

@@ -55,14 +55,6 @@ MixCommonArgs::MixCommonArgs(const std::string & programName)
         }
     });
 
-    addFlag({
-        .longName = "log-format",
-        .description = "Set the format of log output; one of `raw`, `internal-json`, `bar` or `bar-with-logs`.",
-        .category = loggingCategory,
-        .labels = {"format"},
-        .handler = {[](std::string format) { setLogFormat(format); }},
-    });
-
     addFlag({
         .longName = "max-jobs",
         .shortName = 'j',

src/libmain/shared.cc

@@ -182,7 +182,7 @@ LegacyArgs::LegacyArgs(const std::string & programName,
         .longName = "no-build-output",
         .shortName = 'Q',
         .description = "Do not show build output.",
-        .handler = {[&]() {setLogFormat(LogFormat::raw); }},
+        .handler = {[&]() {loggerSettings.logFormat.assign(LogFormat::raw); }},
     });
 
     addFlag({

src/libutil/args.cc

@@ -359,6 +359,8 @@ void RootArgs::parseCmdline(const Strings & _cmdline, bool allowShebang)
      */
     for (auto d : deferredCompletions)
         d.completer(*completions, d.n, d.prefix);
+
+    setLogFormat(loggerSettings.logFormat);
 }
 
 Path Args::getCommandBaseDir() const

src/libutil/config-impl.hh

@@ -13,6 +13,7 @@
  */
 
 #include "config.hh"
+#include "logging.hh"
 
 namespace nix {
 
@@ -130,4 +131,60 @@ std::string BaseSetting<T>::to_string() const
     return std::to_string(value);
 }
 
+template<>
+LogFormat BaseSetting<LogFormat>::parse(const std::string & str) const
+{
+    auto format = parseLogFormat(str);
+    if (format.has_value()) {
+        return format.value();
+    } else {
+        throw UsageError("setting '%s' has invalid value '%s'", name, str);
+    }
+}
+
+template<>
+std::string BaseSetting<LogFormat>::to_string() const
+{
+    return logFormatToString(value);
+}
+
+template<>
+void BaseSetting<LogFormat>::convertToArg(Args &args, const std::string &category)
+{
+    args.addFlag({
+        .longName = name,
+        .description = fmt("Set the `%s` setting.", name),
+        .category = category,
+        .labels = {"format"},
+        .handler = {[this](std::string format) { override(parse(format)); }},
+        .experimentalFeature = experimentalFeature,
+    });
+}
+
+template<>
+std::optional<LogFormat> BaseSetting<std::optional<LogFormat>>::parse(const std::string & str) const
+{
+    if (str.empty()) {
+        return std::nullopt;
+    }
+
+    auto format = parseLogFormat(str);
+    if (format.has_value()) {
+        return format.value();
+    } else {
+        throw UsageError("setting '%s' has invalid value '%s'", name, str);
+    }
+}
+
+template<>
+std::string BaseSetting<std::optional<LogFormat>>::to_string() const
+{
+    if (value.has_value()) {
+        return logFormatToString(value.value());
+    } else {
+        // TODO: Will returning the empty string here cause problems?
+        return "";
+    }
+}
+
 }

src/libutil/config.cc

@@ -392,6 +392,8 @@ template class BaseSetting<Strings>;
 template class BaseSetting<StringSet>;
 template class BaseSetting<StringMap>;
 template class BaseSetting<std::set<ExperimentalFeature>>;
+template class BaseSetting<LogFormat>;
+template class BaseSetting<std::optional<LogFormat>>;
 
 static Path parsePath(const AbstractSetting & s, const std::string & str)
 {

src/libutil/json-utils.hh

@@ -64,6 +64,10 @@ struct json_avoids_null<std::list<T>> : std::true_type {};
 template<typename K, typename V>
 struct json_avoids_null<std::map<K, V>> : std::true_type {};
 
+enum class LogFormat;
+template<>
+struct json_avoids_null<LogFormat> : std::true_type {};
+
 }
 
 namespace nlohmann {

src/libutil/logging.hh

@@ -83,6 +83,20 @@ struct LoggerSettings : Config
           Whether Nix should print out a stack trace in case of Nix
           expression evaluation errors.
         )"};
+
+    Setting<LogFormat> logFormat{
+        this, LogFormat::raw, "log-format",
+        R"(
+            The log format to use.
+            One of `raw`, `raw-with-logs`, `internal-json`, `bar`, or `bar-with-logs`.
+        )"};
+
+    Setting<std::optional<LogFormat>> logFormatLegacy{
+        this, std::nullopt, "log-format-legacy",
+        R"(
+            The log format to use for legacy commands like `nix-build` and `nix-shell`.
+            One of `raw`, `raw-with-logs`, `internal-json`, `bar`, or `bar-with-logs`.
+        )"};
 };
 
 extern LoggerSettings loggerSettings;

src/nix/main.cc

@@ -322,6 +322,22 @@ void mainWrapped(int argc, char * * argv)
         return;
     }
 
+    programPath = argv[0];
+    auto programName = std::string(baseNameOf(programPath));
+    auto legacy = (*RegisterLegacyCommand::commands)[programName];
+
+    if (!legacy) {
+        // New-style commands default to `bar` logs.
+        // `initNix()` reads configuration files and will override this setting
+        // if it's set.
+        loggerSettings.logFormat.assign(LogFormat::bar);
+    }
+
+    if (argc > 1 && std::string_view(argv[1]) == "__build-remote") {
+        programName = "build-remote";
+        argv++; argc--;
+    }
+
     initNix();
     initGC();
 
@@ -337,22 +353,24 @@ void mainWrapped(int argc, char * * argv)
 
     Finally f([] { logger->stop(); });
 
-    programPath = argv[0];
-    auto programName = std::string(baseNameOf(programPath));
-
-    if (argc > 1 && std::string_view(argv[1]) == "__build-remote") {
-        programName = "build-remote";
-        argv++; argc--;
+    if (legacy) {
+        // If we're in a legacy command and `logFormatLegacy` has a value, use
+        // that for the log format setting.
+        if (loggerSettings.logFormatLegacy.get().has_value()) {
+            loggerSettings.logFormat.assign(
+                loggerSettings.logFormatLegacy.get().value()
+            );
+        }
     }
 
-    {
-        auto legacy = (*RegisterLegacyCommand::commands)[programName];
-        if (legacy) return legacy(argc, argv);
+    setLogFormat(loggerSettings.logFormat);
+
+    if (legacy) {
+        return legacy(argc, argv);
     }
 
     evalSettings.pureEval = true;
 
-    setLogFormat("bar");
     settings.verboseBuild = false;
     if (isatty(STDERR_FILENO)) {
         verbosity = lvlNotice;