Add a default catchall case to enum to allow parsing elements with an unknown name

[lovasoa]

Let's say I have an xml document with the following form :

<root>
  <item1 />
  <item2 />
   ...
  <item999 />
</root>

and I am only interested in elements of type item1 and item2.

Currently, there is no good way to parse such a document with serde-xml-rs.

Try 1

I can write the following

struct Root {
   item1: Vec<Item1>,
   item2: Vec<Item2>,
}

Unfortunately, it won't work with documents such as

<root>
  <item1 />
  <item2 />
  <item1 />
</root>

because of #55 which has been a open issue since 2017

Try 2

I can write

struct Root {
    #[serde(rename = "$value")]
    items: Vec<Item>,
}


#[serde(rename_all = "lowercase")]
enum Item {
    Item1(Item1Props),
    Item2(Item2Props),
    Item3,
    ...
    Item999
}

but this requires me to know ahead of time all the possible tags that can occur in addition of <item1> and <item2>, which I don't.

Possible solution

I would like to add a way to parse all unknown tags in a single variant, like this

#[serde(rename_all = "lowercase")]
enum Item {
    Item1(Item1Props),
    Item2(Item2Props),
    #serde(rename = "$other")
    Other
}

This follows the same principle as the existing $value, but allows parsing any incoming tag without error.

For instance

<root> <item1 /> <item999 /> <item1 /> </root>

would be parsed as

Root { items : vec![ Item1{}, Other, Item1{} ] }

Is this issue clear enough ? Would you be interested in a PR implementing that ?

[lovasoa]

Reading more documentation, I see that serde has a #[serde(other)] enum attribute, but it works only on unit enum variants, and this crate refuses to deserialize xml tags with attributes or children to unit variants.

[lovasoa]

The best I found at the moment is

#[derive(Deserialize, Debug)]
#[serde(rename_all = "lowercase")]
enum ItemOrOther {
    Item1,
    Item2,
    #[serde(other, deserialize_with = "deserialize_ignore_any")]
    Other,
}

fn deserialize_ignore_any<'de, D: Deserializer<'de>>(deserializer: D) -> Result<(), D::Error> {
    serde::de::IgnoredAny::deserialize(deserializer)?;
    Ok(())
}

[punkstarman]

Thank you @lovasoa for your detailed info.

I am closing this because :

• I deem that your latest comment is not just a workaround but the proper solution;
• the issue seems to be duplicating Deserializing Vec fails if there's something in between #55.