Make the logger customisable

Add a new `--log-format` cli argument to change the format of the logs.
The possible values are
- raw (the default one for old-style commands)
- bar (the default one for new-style commands)
- bar-with-logs (equivalent to `--print-build-logs`)
- internal-json (the internal machine-readable json format)

src/libmain/common-args.cc

@@ -1,5 +1,6 @@
 #include "common-args.hh"
 #include "globals.hh"
+#include "loggers.hh"
 
 namespace nix {
 
@@ -38,6 +39,14 @@ MixCommonArgs::MixCommonArgs(const string & programName)
         }},
     });
 
+    addFlag({
+        .longName = "log-format",
+        .description = "Format of the logs. One of \"raw\", \"internal-json\", \"bar\" "
+                        "or \"bar-with-logs\".",
+        .labels = {"format"},
+        .handler = {[](std::string format) { setLogFormat(format); }},
+    });
+
     addFlag({
         .longName = "max-jobs",
         .shortName = 'j',

src/libmain/loggers.cc

@@ -0,0 +1,47 @@
+#include "loggers.hh"
+#include "../nix/progress-bar.hh"
+
+namespace nix {
+
+LogFormat defaultLogFormat = LogFormat::raw;
+
+LogFormat parseLogFormat(const string &logFormatStr) {
+    if (logFormatStr == "raw")
+        return LogFormat::raw;
+    else if (logFormatStr == "internal-json")
+        return LogFormat::internalJson;
+    else if (logFormatStr == "bar")
+        return LogFormat::bar;
+    else if (logFormatStr == "bar-with-logs")
+        return LogFormat::barWithLogs;
+    throw Error(format("option 'log-format' has an invalid value '%s'") %
+                logFormatStr);
+}
+
+Logger *makeDefaultLogger() {
+    switch (defaultLogFormat) {
+    case LogFormat::raw:
+        return makeSimpleLogger();
+    case LogFormat::internalJson:
+        return makeJSONLogger(*makeSimpleLogger());
+    case LogFormat::bar:
+        return makeProgressBar();
+    case LogFormat::barWithLogs:
+        return makeProgressBar(true);
+    }
+}
+
+void setLogFormat(const string &logFormatStr) {
+    setLogFormat(parseLogFormat(logFormatStr));
+}
+
+void setLogFormat(const LogFormat &logFormat) {
+    defaultLogFormat = logFormat;
+    createDefaultLogger();
+}
+
+void createDefaultLogger() {
+    logger = makeDefaultLogger();
+}
+
+}

src/libmain/loggers.hh

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "types.hh"
+
+namespace nix {
+
+enum class LogFormat {
+  raw,
+  internalJson,
+  bar,
+  barWithLogs,
+};
+
+void setLogFormat(const string &logFormatStr);
+void setLogFormat(const LogFormat &logFormat);
+
+void createDefaultLogger();
+
+}

src/libutil/logging.cc

@@ -18,7 +18,7 @@ void setCurActivity(const ActivityId activityId)
     curActivity = activityId;
 }
 
-Logger * logger = makeDefaultLogger();
+Logger * logger = makeSimpleLogger();
 
 void Logger::warn(const std::string & msg)
 {
@@ -94,7 +94,7 @@ void writeToStderr(const string & s)
     }
 }
 
-Logger * makeDefaultLogger()
+Logger * makeSimpleLogger()
 {
     return new SimpleLogger();
 }

src/libutil/logging.hh

@@ -63,6 +63,8 @@ public:
 
     virtual ~Logger() { }
 
+    virtual void stop() { };
+
     virtual void log(Verbosity lvl, const FormatOrString & fs) = 0;
 
     void log(const FormatOrString & fs)
@@ -141,7 +143,7 @@ struct PushActivity
 
 extern Logger * logger;
 
-Logger * makeDefaultLogger();
+Logger * makeSimpleLogger();
 
 Logger * makeJSONLogger(Logger & prevLogger);
 

src/libutil/util.cc

@@ -989,7 +989,7 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
 {
     auto wrapper = [&]() {
         if (!options.allowVfork)
-            logger = makeDefaultLogger();
+            logger = makeSimpleLogger();
         try {
 #if __linux__
             if (options.dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1)

src/nix-build/nix-build.cc

@@ -472,6 +472,8 @@ static void _main(int argc, char * * argv)
 
         restoreSignals();
 
+        logger->stop();
+
         execvp(shell->c_str(), argPtrs.data());
 
         throw SysError("executing shell '%s'", *shell);
@@ -521,6 +523,8 @@ static void _main(int argc, char * * argv)
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
                 store2->addPermRoot(store->parseStorePath(symlink.second), absPath(symlink.first), true);
 
+        logger->stop();
+
         for (auto & path : outPaths)
             std::cout << path << '\n';
     }

src/nix-env/nix-env.cc

@@ -1446,6 +1446,8 @@ static int _main(int argc, char * * argv)
 
         globals.state->printStats();
 
+        logger->stop();
+
         return 0;
     }
 }

src/nix-store/nix-store.cc

@@ -1098,6 +1098,8 @@ static int _main(int argc, char * * argv)
 
         op(opFlags, opArgs);
 
+        logger->stop();
+
         return 0;
     }
 }

src/nix/main.cc

@@ -10,6 +10,7 @@
 #include "progress-bar.hh"
 #include "filetransfer.hh"
 #include "finally.hh"
+#include "loggers.hh"
 
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -90,7 +91,7 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
             .longName = "print-build-logs",
             .shortName = 'L',
             .description = "print full build logs on stderr",
-            .handler = {&printBuildLogs, true},
+            .handler = {[&]() {setLogFormat(LogFormat::barWithLogs); }},
         });
 
         addFlag({
@@ -165,6 +166,10 @@ void mainWrapped(int argc, char * * argv)
     verbosity = lvlWarn;
     settings.verboseBuild = false;
 
+    setLogFormat("bar");
+
+    Finally f([] { logger->stop(); });
+
     NixArgs args;
 
     args.parseCmdline(argvToStrings(argc, argv));
@@ -178,10 +183,6 @@ void mainWrapped(int argc, char * * argv)
         && args.command->first != "upgrade-nix")
         settings.requireExperimentalFeature("nix-command");
 
-    Finally f([]() { stopProgressBar(); });
-
-    startProgressBar(args.printBuildLogs);
-
     if (args.useNet && !haveInternet()) {
         warn("you don't have Internet access; disabling some network-dependent features");
         args.useNet = false;

src/nix/progress-bar.cc

@@ -106,7 +106,7 @@ public:
         updateThread.join();
     }
 
-    void stop()
+    void stop() override
     {
         auto state(state_.lock());
         if (!state->active) return;
@@ -457,11 +457,17 @@ public:
     }
 };
 
+Logger *makeProgressBar(bool printBuildLogs)
+{
+    return new ProgressBar(
+        printBuildLogs,
+        isatty(STDERR_FILENO) && getEnv("TERM").value_or("dumb") != "dumb"
+    );
+}
+
 void startProgressBar(bool printBuildLogs)
 {
-    logger = new ProgressBar(
+    logger = makeProgressBar(printBuildLogs);
-        printBuildLogs,
-        isatty(STDERR_FILENO) && getEnv("TERM").value_or("dumb") != "dumb");
 }
 
 void stopProgressBar()

src/nix/progress-bar.hh

@@ -4,6 +4,8 @@
 
 namespace nix {
 
+Logger* makeProgressBar(bool printBuildLogs = false);
+
 void startProgressBar(bool printBuildLogs = false);
 
 void stopProgressBar();