fix: check if it is a Real terminal, not just if it is a terminal

This will stop printing stuff to dumb terminals that they don't support.

I've overall audited usage of isatty and replaced the ones with intent
to mean "is a Real terminal" with checking for that. I've also caught a
case of carelessly assuming "is a tty" means "should be colour" in
nix-env.

Change-Id: I6d83725d9a2d932ac94ff2294f92c0a1100d23c9

1 files changed, 3 insertions, 3 deletions

diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index 0b04a04e6..b99cd5dd0 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -4,11 +4,11 @@
 #include "shared.hh"
 #include "store-api.hh"
 #include "filetransfer.hh"
-#include "finally.hh"
 #include "tarfile.hh"
 #include "attr-path.hh"
-#include "eval-inline.hh"
+#include "eval-inline.hh" // IWYU pragma: keep
 #include "legacy.hh"
+#include "terminal.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -180,7 +180,7 @@ static int main_nix_prefetch_url(int argc, char * * argv)
         if (args.size() > 2)
             throw UsageError("too many arguments");
 
-        if (isatty(STDERR_FILENO))
+        if (isOutputARealTerminal(StandardOutputStream::Stderr))
             setLogFormat(LogFormat::bar);
 
         auto store = openStore();