Fix resetting the terminal with '-L'

Using '-L' caused another call to setLogFormat(), which caused another
ProgressBar to be created. But the ProgressBar should be a singleton.

To do: remove LogFormat::barWithLogs. '-L' should be a setting of the
ProgressBar, not a different log format.

src/libmain/progress-bar.cc

@@ -143,7 +143,7 @@ private:
         bool helpShown = false;
     };
 
-    bool isTTY;
+    const bool isTTY;
 
     Sync<State> state_;
 
@@ -173,14 +173,9 @@ public:
                 draw(*state);
                 state.wait_for(quitCV, std::chrono::milliseconds(50));
             }
-
-            if (savedTermAttrs) {
-                tcsetattr(STDIN_FILENO, TCSANOW, &*savedTermAttrs);
-                savedTermAttrs.reset();
-            }
         });
 
-        if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO) && isatty(STDERR_FILENO)) {
+        if (isTTY) {
 
             struct termios term;
             if (tcgetattr(STDIN_FILENO, &term))
@@ -291,6 +286,11 @@ public:
             state->active = false;
             updateCV.notify_one();
             quitCV.notify_one();
+
+            if (savedTermAttrs) {
+                tcsetattr(STDIN_FILENO, TCSANOW, &*savedTermAttrs);
+                savedTermAttrs.reset();
+            }
         }
 
         updateThread.join();

src/nix/main.cc

@@ -88,11 +88,12 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
             }},
         });
 
+        // FIXME: make this a setting, remove LogFormat::barWithLogs.
         addFlag({
             .longName = "print-build-logs",
             .shortName = 'L',
             .description = "print full build logs on stderr",
-            .handler = {[&]() {setLogFormat(LogFormat::barWithLogs); }},
+            .handler = {[&]() { printBuildLogs = true; }},
         });
 
         addFlag({
@@ -254,10 +255,6 @@ void mainWrapped(int argc, char * * argv)
     settings.verboseBuild = false;
     evalSettings.pureEval = true;
 
-    setLogFormat("bar");
-
-    Finally f([] { logger->stop(); });
-
     NixArgs args;
 
     if (argc == 2 && std::string(argv[1]) == "__dump-args") {
@@ -301,6 +298,10 @@ void mainWrapped(int argc, char * * argv)
 
     if (completions) return;
 
+    setLogFormat(args.printBuildLogs ? LogFormat::bar : LogFormat::barWithLogs);
+
+    Finally f([] { logger->stop(); });
+
     initPlugins();
 
     if (!args.command) args.showHelpAndExit();