snap-server: commandLineConfig does not allow overriding some default settings

[j3h]

This is with snap-server 0.4.1. For instance, providing --hostname=foo does not change the hostname that gets used.

I think I traced this down to the mappend implementation for OptionData in Snap.Http.Server.Config:

a `mappend` b = OptionData
    { config       = (config       b) `mappend` (config       a)
    , bind         = (bind         b) `mplus`   (bind         a)
    , port         = (port         b) `mplus`   (port         a)
    , sslbind      = (sslbind      b) `mplus`   (sslbind      a)
    , sslport      = (sslport      b) `mplus`   (sslport      a)
    , sslcert      = (sslcert      b) `mplus`   (sslcert      a)
    , sslkey       = (sslkey       b) `mplus`   (sslkey       a)
    , tout         = (tout         b) `mplus`   (tout         a)
    }

In particular, the Monoid instance for Config prefers options from the second argument to mappend, so:

(config b) `mappend` (config a)

prefers options from config a, which is defaultConfig in the commandLineConfig case. I think the a and b need to be swapped in this expression.

[dop]

I should have created an issue for this one before pull request... Also, found two more bugs in handling of command line arguments and fixed them in my forked repository of snap-server dop/snap-server@6123d9076723c608fb455660f8a513c2f88c0953

[gregorycollins]

Should be fixed as of snap 0.5.0. Please re-open if not.