Let’s continue reexporting jid and minidom, but not their inner pub
items, users of this crate can go one level deeper if they need that.
Only xso::error::Error is still useful to reexport, as this is part of
the public API of all of our parsers.
This is a large change and as such, it needs good motivation. Let me
remind you of the ultimate goal: we want a derive macro which allows us
to FromXml/IntoXml, and that derive macro should be usable from
`xmpp_parsers` and other crates.
For that, any code generated by the derive macro mustn't depend on any
code in the `xmpp_parsers` crate, because you cannot name the crate you
are in portably (`xmpp_parsers::..` wouldn't resolve within
`xmpp_parsers`, and `crate::..` would point at other crates if the macro
was used in other crates).
We also want to interoperate with code already implementing
`TryFrom<Element>` and `Into<Element>` on structs. This ultimately
requires that we have an error type which is shared by the two
implementations and that error type must be declared in the `xso` crate
to be usable by the macros.
Thus, we port the error type over to use the type declared in `xso`.
This changes the structure of the error type greatly; I do not think
that `xso` should have to know about all the different types we are
parsing there and they don't deserve special treatment. Wrapping them in
a `Box<dyn ..>` seems more appropriate.
From [XEP-0004: Data Forms](https://xmpp.org/extensions/xep-0004.html#protocol-field):
> ...
> The <field/> element MAY contain any of the following child elements:
>
> <desc/>
> The XML character data of this element provides a natural-language
> description of the field, intended for presentation in a
> user-agent (e.g., as a "tool-tip", help button, or explanatory text
> provided near the field). The <desc/> element SHOULD NOT contain
> newlines (the \n and \r characters), since layout is the
> responsibility of a user agent, and any handling of
> newlines (e.g., presentation in a user interface) is unspecified
> herein. (Note: To provide a description of a field, it
> is RECOMMENDED to use a <desc/> element rather than
> a separate <field/> element of type "fixed".)
> ...
Looking at [the spec](https://xmpp.org/extensions/xep-0004.html#protocol-field)
it seems valid not to have a `var` attribute set, at least for fields of type
`fixed` that is:
> If the element type is anything other than "fixed" (see below), it MUST
> possess a 'var' attribute that uniquely identifies the field in the context
> of the form (if it is "fixed", it MAY possess a 'var' attribute). The element
> MAY possess a 'label' attribute that defines a human-readable name for the field.
This moves InnerJid into Jid and reformulates BareJid and FullJid in
terms of Jid.
Doing this has the key advantage that FullJid and BareJid can deref to
and borrow as Jid. This, in turn, has the advantage that they can be
used much more flexibly in HashMaps. However, this is (as we say in
Germany) future music; this commit only does the internal reworking.
Oh and also, it saves 20% memory on Jid objects.
Fixes#122 more thoroughly, or rather the original intent behind it.
