Make a struct or enum parseable from XML

This derives the [FromXml] trait on a struct or enum. It is the counterpart to [macro@IntoXml].

Example

# use xso::FromXml;
static MY_NAMESPACE: &str = "urn:example";

#[derive(FromXml, Debug, PartialEq)]
#[xml(namespace = MY_NAMESPACE, name = "foo")]
struct Foo;

let foo: Foo = xso::from_bytes(b"<foo xmlns='urn:example'/>").unwrap();
assert_eq!(foo, Foo);

Attributes

The derive macros need to know which XML namespace and name the elements it is supposed have. This must be specified via key-value pairs on the type the derive macro is invoked on. These are specified as Rust attributes. In order to disambiguate between XML attributes and Rust attributes, we are going to refer to Rust attributes using the term meta instead, which is consistent with the Rust language reference calling that syntax construct meta.

All key-value pairs interpreted by these derive macros must be wrapped in a #[xml( ... )] meta. The following keys are defined on structs:

Limitations

Supports only empty structs currently. For example, the following will not work:

# use xso::FromXml;
# static MY_NAMESPACE: &str = "urn:example";
#[derive(FromXml, Debug, PartialEq)]
#[xml(namespace = MY_NAMESPACE, name = "foo")]
struct Foo {
    some_field: String,
}