Implement XML configuration loader

[lucko]

Implements #57

[lucko]

This is no longer WIP.

I'd welcome any feedback / comments.

[FerusGrim]

I had given up hope. I'm in love with you @lucko <3

[lucko]

Bump - any update on the status of this?

[kashike]

I'd want to see this merged after #92.

[parlough]

Can you update this with the other changes, as well as style changes you previously made?

[lucko]

I've rebased this against master and updated the style to match the other changes.

I've also fixed an issue with the way lists were serialised, and added a few more tests. Should be good to be reviewed/merged now. :)

[parlough]

I will give this a look soon, but I'd also like to see @zml2008's feedback as this is a fairly large change, adding a completely new loader.

[XakepSDK]

map/list types are made wrong, they re must be namespaced and must have schema.

Every xml file(since xml 1.1) must start with xml header.
https://www.w3.org/TR/2006/REC-xml11-20060816/#sec-prolog-dtd
Also, attributes may be not just strings, but enums or sets of tokenized types.
https://www.w3.org/TR/xml11/#attdecls

Also, you don't handle XML comments system.
https://github.com/SpongePowered/configurate/pull/90/files#diff-121eb04ce2db1e49a56ba506f61ebd66R221
This is wrong, XML doesn't allow comments with # or //, they are must be in <!-- COMMENT HERE -->
Also, XML restricts usage of -- inside a comment.
https://www.w3.org/TR/2006/REC-xml11-20060816/#sec-comments

https://www.w3.org/XML/Core/#Publications

[lucko]

Thanks for your feedback.

map/list types are made wrong, they re must be namespaced and must have schema.

Could you elaborate a bit more on exactly what you mean by this? I don't really understand what you're talking about.

Every xml file(since xml 1.1) must start with xml header.

The loader already had the option to include the header, I've now set it to be enabled by default. Thanks :)

Also, attributes may be not just strings, but enums or sets of tokenized types.

The page you linked doesn't make much sense to me. The native Java library being used for parsing doesn't seem to support anything other than String-String pairs for attributes.

https://docs.oracle.com/javase/7/docs/api/org/w3c/dom/Attr.html

Also, you don't handle XML comments system.

I've implemented an appropriate comment handler now and added a test.

[XakepSDK]

1. Ok, just skip it
2. Does your comments impl. allow me to write multi-line comments like this:

<!--
My multiline
comment here
-->

If no, impl is wrong.

[lucko]

No, the comment handler forms comments like this

<!--
 ~ My multiline
 ~ comment here
 -->

It will still correctly parse your example

[FerusGrim]

@lucko Still looking forward to this being merged! Are there any concerns besides the issues brought forth by @XakepSDK ?

Additionally, it looks as if the project has been switched over to Gradle, causing some issues as this PR was started when it was still using Maven. <3

[lucko]

Yea, will need to be rebased.

I'm not sure what the status is, I would prefer to gather more feedback / approval from people before this is merged though.

[lucko]

It's rebased now, so can be merged when ready.

I've also added a few more tests.

[bloodmc]

@Meronat Please review so we can get this merged.

[kashike]

Thanks, @lucko.