Analogous to the already existing `IntoXml` implementation helpers
based on an `Into<Element>` implementation on a type, this provides
the utilities for `AsXml`.
This is of course exceptionally inefficient, but it is only needed
transitionally until we have everything migrated to derive macros or
otherwise rewritten in terms of AsXml/FromXml.
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.
This adds shims which provide FromXml and IntoXml implementations to
*all* macro-generated types in `xmpp_parsers`. Mind that this does not
cover all types in `xmpp_parsers`, but a good share of them.
This is another first step toward real, fully streamed parsing.
This library provides the traits to parse structs from XML and
serialise them into XML without having to buffer the document object
model in memory.
The only implementations it provides are for minidom, basically
providing a lower-level interface to `minidom::Element::from_reader` and
`minidom::Element::to_writer`.
This is the first stepping stone into a world where `xmpp_parsers` can
parse the structs directly from XML.
