Add pointer to boolean .present field to opt desc, which (if non-NULL)
will be set to TRUE if the argument in question is present on the
command line. Unchanged otherwise.
Several changes at once, just to not have to change the same lines
several times over:
- Use designated initializers to initialize opt desc arrays.
- Only initialize the needed fields.
- Remove arg_id (short options) as unused.
- Replace opt_type and output_var with several type safe output
variables, where the output variable being non-NULL determines the
type. Introduce checks to ensure only one is set. The downside is
some waste of const space per argument; this could be saved by
retaining opt_type and using a union, but that's still pretty
verbose.
- Fix some variables due to the type safety. Mostly a good thing, but
leads to some enums being changed to ints. This is pedantically
correct, but somewhat annoying. We could also cast, but that defeats
the purpose a bit.
- Terminate the opt desc arrays using {}.
The output variable type safety and the ability to add new fields for
just some output types or arguments are the big wins. For example, if
we wanted to add a variable to set when the argument is present, we
could do so for just the arguments that need it.
Beauty is in the eye of the beholder, but I think this looks nice when
defining the arguments, and reduces some of the verbosity we have
there.
NOTMUCH_OPT_INHERIT expects a notmuch_opt_desc_t * pointer in
output_var.
The "Unrecognized option" message was moved out of parse_option() to
not be emitted twice or when parsing a non-inherited option.
As we noticed when Jani kindly converted things to getopt_long, much
of the work in argument parsing in notmuch is due to the the key-value
style arguments like --format=(raw|json|text).
The framework here provides positional arguments, simple switches,
and --key=value style arguments that can take a value being an integer,
a string, or one of a set of keywords.
