XML improvements

[rossabaker]

• Split scala-xml dependency from core. It's no longer stdlib in Scala 2.11, and it won't be transitively inherited in Scalaz 7.2.
• Decode to XMLEvents for streaming parsing.
• Consider aalto-xml for incremental parsing. It looks like a great fit for scalaz-stream

[rossabaker]

The overload of xml is nice from a DSL perspective, but shady. Namely, it will quietly ignore the implicit SAX parser.

[rossabaker]

Started in 0.6. Let's finish it in 0.7.

[ChristopherDavenport]

So this was on milestones for a very long time but hasn't been referenced in over a year, we should probably invest or close until there is renewed interest.

[rossabaker]

I guess the question is whether the streaming support could be added later without breaking compatibility. I think the answer is yes?

[jmcardon]

Isnt' this now a module?

[rossabaker]

It is a module. It does not support streaming. aalto-xml could, in a way similar to jawn.

[rossabaker]

Nobody is clamoring for Aalto, and that would be a separate module. XMLEvents is still interesting enough.

[tovbinm]

FYI, scala-xml dependency is blocking us from upgrading to scala-xml 2.0.0

[error] (app / update) found version conflict(s) in library dependencies; some are suspected to be binary incompatible:
[error] 	* org.scala-lang.modules:scala-xml_2.13:2.0.0 (early-semver) is selected over 1.3.0
[error] 	    +- org.http4s:http4s-scala-xml_2.13:0.21.23           (depends on 1.3.0)

[rossabaker]

scala-xml-2.0 is a breaking change, so we can't really adopt that in 0.21. We are targeting that release in 0.22, which will be released ASAP.

If you can't upgrade http4s right now, you can try overriding that semver warning (it probably works?) or just copy the XML module, which isn't that large.