parsers: use Error type from xso

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.

parsers/src/blocking.rs

@@ -6,9 +6,9 @@
 
 use crate::iq::{IqGetPayload, IqResultPayload, IqSetPayload};
 use crate::ns;
-use crate::util::error::Error;
 use crate::Element;
 use jid::Jid;
+use xso::error::FromElementError;
 
 generate_empty_element!(
     /// The element requesting the blocklist, the result iq will contain a
@@ -30,9 +30,9 @@ macro_rules! generate_blocking_element {
         }
 
         impl TryFrom<Element> for $elem {
-            type Error = Error;
+            type Error = FromElementError;
 
-            fn try_from(elem: Element) -> Result<$elem, Error> {
+            fn try_from(elem: Element) -> Result<$elem, FromElementError> {
                 check_self!(elem, $name, BLOCKING);
                 check_no_attributes!(elem, $name);
                 let mut items = vec!();
@@ -96,6 +96,8 @@ generate_empty_element!(
 
 #[cfg(test)]
 mod tests {
+    use xso::error::Error;
+
     use super::*;
 
     #[cfg(target_pointer_width = "32")]
@@ -165,7 +167,7 @@ mod tests {
         let request_elem = elem.clone();
         let error = BlocklistRequest::try_from(request_elem).unwrap_err();
         let message = match error {
-            Error::ParseError(string) => string,
+            FromElementError::Invalid(Error::Other(string)) => string,
             _ => panic!(),
         };
         assert_eq!(message, "Unknown attribute in blocklist element.");
@@ -173,7 +175,7 @@ mod tests {
         let result_elem = elem.clone();
         let error = BlocklistResult::try_from(result_elem).unwrap_err();
         let message = match error {
-            Error::ParseError(string) => string,
+            FromElementError::Invalid(Error::Other(string)) => string,
             _ => panic!(),
         };
         assert_eq!(message, "Unknown attribute in blocklist element.");
@@ -183,7 +185,7 @@ mod tests {
             .unwrap();
         let error = Block::try_from(elem).unwrap_err();
         let message = match error {
-            Error::ParseError(string) => string,
+            FromElementError::Invalid(Error::Other(string)) => string,
             _ => panic!(),
         };
         assert_eq!(message, "Unknown attribute in block element.");
@@ -193,7 +195,7 @@ mod tests {
             .unwrap();
         let error = Unblock::try_from(elem).unwrap_err();
         let message = match error {
-            Error::ParseError(string) => string,
+            FromElementError::Invalid(Error::Other(string)) => string,
             _ => panic!(),
         };
         assert_eq!(message, "Unknown attribute in unblock element.");
@@ -205,7 +207,7 @@ mod tests {
         let elem: Element = "<blocklist xmlns='urn:xmpp:blocking'><item jid='coucou@coucou'/><item jid='domain'/></blocklist>".parse().unwrap();
         let error = BlocklistRequest::try_from(elem).unwrap_err();
         let message = match error {
-            Error::ParseError(string) => string,
+            FromElementError::Invalid(Error::Other(string)) => string,
             _ => panic!(),
         };
         assert_eq!(message, "Unknown child in blocklist element.");