XML parser reverses attribute order

[cogpp]

This issue is copied across from https://issues.scala-lang.org/browse/SI-6341

The original person who raised the issue attached a patch to add a failing test case.

When parsing XML and then writing it out again, the order of attributes is reversed.

This prevents certain use cases where one wants to modify an XML file and have a minimal amount of changes. E.g. adding a new element to a file causes all existing attributes to get reversed.

The cause is here:

https://github.com/scala/scala/blob/81e3121eb09010375783d13e8c4c853686a34ffd/src/library/scala/xml/parsing/MarkupParser.scala#L302

aMap: MetaData is built by prepending new attributes to the linked list, causing the reversal.

The attached patch adds a failing test case. (It failed when I wrote it originally, now I can't test it because the build fails).

commit 272ed40345c9f8f4af878f15299155cecfd8db2e
Author: Robin Stocker robin@nibor.org
Date: Sat Sep 8 19:11:50 2012 +0200

Add failing test for scala.xml attribute order problem

diff --git a/test/files/run/xml-attribute-order-parse.check b/test/files/run/xml-attribute-order-parse.check
new file mode 100644
index 0000000..6637a4f
--- /dev/null
+++ b/test/files/run/xml-attribute-order-parse.check
@@ -0,0 +1 @@
+
diff --git a/test/files/run/xml-attribute-order-parse.scala b/test/files/run/xml-attribute-order-parse.scala
new file mode 100644
index 0000000..3be386c
--- /dev/null
+++ b/test/files/run/xml-attribute-order-parse.scala
@@ -0,0 +1,9 @@
+import xml.XML
+
+object Test {

• def main(args: Array[String]): Unit = {
• val input = """"""
• val doc = XML.loadString(input)
• println(doc)
• }
  +}

[biswanaths]

Thanks Graeme for taking time to re-reporting this issue from scala JIRA. We are in the process of migrating all the open issues from JIRA to github. I have left my test work on the migration as comment so that community can review it. ( #62)

Thanks again.

[nikhilsinha]

If no one's picked this up yet, I'd be happy to take a wack at it.

[biswanaths]

Glad that you would like to help. We will be more than happy if we can get some help from you. Please let me know if you need any help from me.

Good luck.

[mbeckerle]

I wanted to comment on this issue.

Technically, order of attributes is not significant in XML. A proper equality comparison of two XML objects would find them equal even if the attributes are in different orders.

However, I understand the motivation for wanting to reduce deltas. The library shouldn't change things that don't need to be changed.

A related issue is changes of namespace prefixes for attributes or elements. The actual prefixes used are part of the XML Infoset, so techically <a:b xmlns:a="urn:foo"/> is not always equal to <c:b xmlns:c="urn:foo"/> because their infoset contents are different. XML is allowed to be sensitive to the specific characters used in the prefixes of the QNames.

This suggests that there are really several different levels of equality and correspondingly preservation (which is what this issue is about).

• preserve order of attributes (and do comparison/equality where order of attributes matters)
• preserve XML infoset (and equality where everything about XML infoset is compared, and only that - so attribute order doesn't matter, but specific prefix characters do matter)
• preserve XML namespace-aware infoset (and equality where namespace prefixes are interpreted as their namespaces and the specific characters of the prefix are disregarded, and attribute order doesn't matter)

[ashawley]

@biswanaths Do I need to make a pull request out of my branch, or can the commit (only the 2nd one, sorry) get pulled in here as a first-class citizen by you (as the admin)?

[hhimanshu]

any updates on this pull request?

[SethTisue]

What if you use ConstructingParser, is the order still scrambled?

[hhimanshu]

hey @SethTisue
I guess I am not able to load my document using ConsructingParser

My file

 $cat /tmp/person.xml
 <root xmlns="http://www.nyorg.com/metadata/config" xmlns:core="http://www.myorg.com/metadata/commonschematypes" xmlns:xi="http://www.w3.org/2001/XInclude" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../xschema/AppConfig.xsd">
    <!-- This is important comment about person-->
    <person>
      <firstName>John</firstName>
      <lastName>Doe</lastName>
      <email>john.doe@noone.com</email>
      <city>SomeWhere</city>
      <property name="myName" value="someValue" />
    </person>
  </root>

This is how I am using it

val source = io.Source.fromURL(new java.io.File("/tmp/person.xml").toURL)
val d = scala.xml.parsing.ConstructingParser.fromSource(source, preserveWS = true)
val doc = d.document()
println(doc)

What I get back?

:1:1: < expected<root xmlns="http://www.nyorg.com/metadata/config" xmlns:core="http://www.myorg.com/metadata/commonschematypes" xmlns:xi="http://www.w3.org/2001/XInclude" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../xschema/AppConfig.xsd">^
doc: scala.xml.Document = null
null

On this other hand when I load the same file using XML.loadFile as

val doc = XML.loadFile("/tmp/person.xml")
println(doc)

It seems to load it correctly

<root xsi:noNamespaceSchemaLocation="../xschema/AppConfig.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xi="http://www.w3.org/2001/XInclude" xmlns:core="http://www.myorg.com/metadata/commonschematypes" xmlns="http://www.nyorg.com/metadata/config">
    
    <person>
      <firstName>John</firstName>
      <lastName>Doe</lastName>
      <email>john.doe@noone.com</email>
      <city>SomeWhere</city>
      <property value="someValue" name="myName"/>
    </person>
  </root>

but semantically has different orders and removed comments as documented http://stackoverflow.com/questions/40941628/scala-loadfile-xml-reorders-original-xml-and-removes-comments

any help resolving this is appreciated

[SethTisue]

@hhimanshu I'm sorry but this is an issue tracker, not a support forum. if you have a question about ConstructingParser, ask on Stack Overflow. if you become convinced there is a bug in ConstructingParser, you can open a new issue here.

[ashawley]

Looks like Constructing Parser has the same issue. I'll add tests to the previous tests and make them in to a PR.

[hhimanshu]

I added the question on Stackoverflow. http://stackoverflow.com/questions/40942075/constructingparser-could-not-load-valid-xml-document-from-file

Thanks

[hhimanshu]

I was able to use ConstructingParser, but I can prove that even ConstructingParser reorders attributes. For details, see http://stackoverflow.com/a/40942534/379235

[SethTisue]

good to know, thanks @hhimanshu