Support visitor pattern for tree mutation and multiple files

[Nanonid]

I have an XSD that imports another XSD.

<xs:import namespace="http://www.opengis.net/gml" schemaLocation="gml.xsd"/>

As package:xml exists, attributes, children etc are final and not mutable.

XmlBranch(Iterable<XmlNode> children): children = children.toList(growable: false) 

dart:html DOM is mutable, which is useful for tree transformation.

Ideally, the library could handle an import statement by one or more:

1. natively, somehow support multi-file parsing within the library
2. parse action, exposing a standard means of action augmentation in the base CompositeParser to redefine or add a post action to refine behavior.
3. tree mutation so the xs:import node could have a child XmlDocument, etc.

[Nanonid]

I'm considering forking xml_dart to:

1. Use/extend dart:html DOM nodes in place of local models
2. Add factory and mutation support for tree building
3. Add simple query and visitor support. I already have a xml_visitor project which I'm using, something based on that perhaps.

[Nanonid]

Hah! Some reason I've not perused XmlBuilder and just assumed that the tree was not build-able because XmlElement attributes are not mutable.
Can't figure out the reason for why I didn't read all the code. My fault.
Bounty still stands for tree mutation, actions, and whatever you think might make dart-xml better.

[renggli]

I've just committed 61ba675 that adds a simple node visitor to the library. The change cleans up other parts of the code as well, for example the (pretty) printing is now a visitor and separate to the node classes.

The code also includes a transformation visitor that copies a tree and can be subclassed to perform custom transformations. I believe this allows a rather simple implementation of resolving imports.

The currently committed code is work in progress. Let me know what you think.

[renggli]

04d2629 makes the XmlParser event based, so that subclasses can transform the input while the source file is parsed.

Again, the code is just experimental and work in progress. Let me know what you think.

[Nanonid]

Okay. will do. I just made an xml_visitor so I have something to compare with. Thanks.

[Nanonid]

Looks like in order to mutate a tree, I need to visit and copy. Very FP, but my visitors may be annotating, like adding new namespace elements and state. XmlElement ensures immutable. :-(
Still, I like the new code, and I'll see how far I can get before editing origin.

  @override
  final List<XmlAttribute> attributes;

  /**
   * Create an [XmlElement] with the given `name`, `attributes`, and `children`.
   */
  XmlElement(XmlName name, Iterable<XmlAttribute> attributes, Iterable<XmlNode> children)
      : super(children),
        name = name,
        attributes = attributes.toList(growable: false) {

[Nanonid]

Element 'XmlDocument' from SDK library 'html_dartium.dart' is implicitly hidden by 'xml.dart'
Which means nuisance as xml
I can just make more libraries though. NP

[Nanonid]

Argh! The embedded SVG and dataURI are killing me...
Diagram: 2420642 diagram_export_1.xml

void main(){
  group( "diagram", (){
    test( "parse visit", (){
      String xml = readFileTextSync("diagram_export_1.xml");
      Stopwatch stopwatch = new Stopwatch()..start();
      XmlDocument doc = parse(xml);
      print( "parse time ${stopwatch.elapsed}");
      stopwatch.reset();
      DiaTransformer xform = new DiaTransformer();
      DiaDoc dia = xform.visitDocument(doc);
      print( "visit ${stopwatch.elapsed}");
    });
  });
}

unittest-suite-wait-for-done
parse time 0:00:20.558550
visit 0:00:00.010319
PASS: diagram parse visit

All 1 tests passed.
unittest-suite-success

[Nanonid]

Seems to work OK. Transformer has many name specific specialization.
Difficult to accumulate state across children when everything is passed at constructor.
Can't pass down this if children need parent state for lookup.
Graphs don't work well.

  visitIcon( XmlElement el ) => new Icon(el);
  visitIcons( Iterable<XmlElement> icons ) => icons.map(visitIcon);
  visitDia( XmlElement el ) => new Dia(el, visitIcons(el.findElements("Icon")) );

Have Transformer state variable passed in to constructor?

  DocState state;
  visitIcon( XmlElement el ) => new Icon(el,state);
  visitIcons( Iterable<XmlElement> icons ) => icons.map(visitIcon);
  visitDia( XmlElement el ) => new Dia(el, visitIcons(el.findElements("Icon")), state );

[Nanonid]

I'll close this and just create a new issue if need be.
Thanks! 👍