The old way was way too fragile and had felt like it had more special
cases than normal cases. (see #1874, #1860, #1834, etc) It became very
obvious the old algorithm didn't work when we made the output be
pretty and try to show the user the command they need to run in
5ecc7c7200 for #1746)
The new algorithm is to map the prefs (current and new) back to flags
and then compare flags. This nicely handles the OS-specific flags and
the n:1 and 1:n flag:pref cases.
No change in the existing already-massive test suite, except some ordering
differences (the missing items are now sorted), but some new tests are
added for behavior that was broken before. In particular, it now:
* preserves non-pref boolean flags set to false, and preserves exit
node IPs (mapping them back from the ExitNodeID pref, as well as
ExitNodeIP),
* doesn't ignore --advertise-exit-node when doing an EditPrefs call
(#1880)
* doesn't lose the --operator on the non-EditPrefs paths (e.g. with
--force-reauth, or when the backend was not in state Running).
Fixes#1880
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
5190435d6e