flatpak: Disable progress escape sequence by default

And add the FLATPAK_TTY_PROGRESS env var to re-enable it.

This seems to only be supported by recent versions of terminal emulators
which will cause problems with shipping Flatpak on older distros.

Closes https://github.com/flatpak/flatpak/issues/6052

app/flatpak-tty-utils.c

@@ -522,14 +522,37 @@ flatpak_print_escaped_string (const char        *s,
   g_print ("%s", escaped);
 }
 
+static gboolean
+use_progress_escape_sequence (void)
+{
+  static gsize tty_progress_once = 0;
+  enum {
+    TTY_PROGRESS_ENABLED = 1,
+    TTY_PROGRESS_DISABLED = 2
+  };
+
+  if (g_once_init_enter (&tty_progress_once))
+    {
+      // FIXME: make this opt-out for Flatpak 1.18
+      if (g_strcmp0 (g_getenv ("FLATPAK_TTY_PROGRESS"), "1") == 0)
+        g_once_init_leave (&tty_progress_once, TTY_PROGRESS_ENABLED);
+      else
+        g_once_init_leave (&tty_progress_once, TTY_PROGRESS_DISABLED);
+    }
+
+  return tty_progress_once == TTY_PROGRESS_ENABLED;
+}
+
 void
 flatpak_pty_clear_progress (void)
 {
-  g_print ("\033]9;4;0\007");
+  if (use_progress_escape_sequence ())
+    g_print ("\033]9;4;0\007");
 }
 
 void
 flatpak_pty_set_progress (guint percent)
 {
-  g_print ("\033]9;4;1;%d\007", MIN (percent, 100));
+  if (use_progress_escape_sequence ())
+    g_print ("\033]9;4;1;%d\007", MIN (percent, 100));
 }

doc/flatpak.xml

@@ -617,6 +617,14 @@
                         or when <envar>G_MESSAGES_DEBUG</envar> is set.
                     </para></listitem>
                 </varlistentry>
+                <varlistentry>
+                    <term><envar>FLATPAK_TTY_PROGRESS</envar></term>
+
+                    <listitem><para>
+                        May be set to <literal>1</literal> to enable emitting
+                        the progress escape character.
+                    </para></listitem>
+                </varlistentry>
                 <varlistentry>
                     <term><envar>FLATPAK_USER_DIR</envar></term>