Show build and substitution information when not connected to a TTY

When stderr is not connected to a tty, show "building" and
"substituting" messages, a-la nix-build et al.

Closes https://github.com/NixOS/nix/issues/4402

Co-authored-by: Théophane Hufschmitt <7226587+thufschmitt@users.noreply.github.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/nix/main.cc b/src/nix/main.cc
index fe7469be4..5158c3902 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -270,11 +270,15 @@ void mainWrapped(int argc, char * * argv)
         if (legacy) return legacy(argc, argv);
     }
 
-    verbosity = lvlNotice;
-    settings.verboseBuild = false;
     evalSettings.pureEval = true;
 
     setLogFormat("bar");
+    settings.verboseBuild = false;
+    if (isatty(STDERR_FILENO)) {
+        verbosity = lvlNotice;
+    } else {
+        verbosity = lvlInfo;
+    }
 
     Finally f([] { logger->stop(); });