Merge pull request #10131 from intelfx/work/notty

`TERM=dumb` fixes

src/libutil/logging.cc

@@ -52,7 +52,7 @@ public:
         : printBuildLogs(printBuildLogs)
     {
         systemd = getEnv("IN_SYSTEMD") == "1";
-        tty = shouldANSI();
+        tty = isTTY();
     }
 
     bool isVerbose() override {

src/libutil/terminal.cc

@@ -7,11 +7,14 @@
 
 namespace nix {
 
-bool shouldANSI()
+bool isTTY()
 {
-    return isatty(STDERR_FILENO)
+    static const bool tty =
+        isatty(STDERR_FILENO)
         && getEnv("TERM").value_or("dumb") != "dumb"
         && !(getEnv("NO_COLOR").has_value() || getEnv("NOCOLOR").has_value());
+
+    return tty;
 }
 
 std::string filterANSIEscapes(std::string_view s, bool filterAll, unsigned int width)

src/libutil/terminal.hh

@@ -8,7 +8,7 @@ namespace nix {
  * Determine whether ANSI escape sequences are appropriate for the
  * present output.
  */
-bool shouldANSI();
+bool isTTY();
 
 /**
  * Truncate a string to 'width' printable characters. If 'filterAll'