systemd: ignore lack of tty when checking whether colors should be enabled

When started by the kernel, we are connected to the console, and we'll set TERM
properly to some value in fixup_environment(). We'll then enable or disable
colors based on the value of $SYSTEMD_COLORS and $TERM.

When reexecuting, TERM should be already set, so we can use this value.
Effectively, behaviour is the same as before affd7ed1a was reverted, but instead
of reopening the console before configuring color output, we just ignore what
stdout is connected to and decide based on the variables only.

src/basic/terminal-util.c

@@ -1191,12 +1191,9 @@ int open_terminal_in_namespace(pid_t pid, const char *name, int mode) {
         return receive_one_fd(pair[0], 0);
 }
 
-bool terminal_is_dumb(void) {
+static bool getenv_terminal_is_dumb(void) {
         const char *e;
 
-        if (!on_tty())
-                return true;
-
         e = getenv("TERM");
         if (!e)
                 return true;
@@ -1204,6 +1201,13 @@ bool terminal_is_dumb(void) {
         return streq(e, "dumb");
 }
 
+bool terminal_is_dumb(void) {
+        if (!on_tty())
+                return true;
+
+        return getenv_terminal_is_dumb();
+}
+
 bool colors_enabled(void) {
         static int enabled = -1;
 
@@ -1213,6 +1217,9 @@ bool colors_enabled(void) {
                 colors = getenv("SYSTEMD_COLORS");
                 if (colors)
                         enabled = parse_boolean(colors) != 0;
+                else if (getpid() == 1)
+                        /* PID1 outputs to the console without holding it open all the time */
+                        enabled = !getenv_terminal_is_dumb();
                 else
                         enabled = !terminal_is_dumb();
         }