Parse declaration children before building its span

[srawlins]

Declarations with children have an incorrect source span. Take the following SCSS and simple visitor:

a {
  padding: {
    left: 2px;
    top: 2px;
  }
  width: 2px;

  pre {
    color: red;
  }
}

import 'dart:io';

import 'lib/src/ast/sass.dart';
import 'lib/src/value.dart';
import 'lib/src/visitor/interface/statement.dart';

void main(List<String> args) {
  var file = args.first;
  var contents = new File(file).readAsStringSync();
  var sassTree = new Stylesheet.parseScss(contents);
  sassTree.accept(new LittleVisitor());
}

class LittleVisitor implements StatementVisitor<Value> {
  LittleVisitor() {}

  // ## Statements

  void visitStylesheet(Stylesheet node) {
    for (var child in node.children) {
      child.accept(this);
    }
  }

  void visitStyleRule(StyleRule node) {
    stdout.write(node.selector);
    stdout.write('{\n');
    for (var child in node.children) {
      child.accept(this);
    }
    stdout.write('}\n');
  }

  void visitDeclaration(Declaration node) {
    stdout.write(node.span.text);
  }
}

This prints:

// BEFORE THIS PATCH
a {
padding: width: 2pxpre {
color: red}
}

// AFTER THIS PATCH
a {
padding: {
    left: 2px;
    top: 2px;
  }
  width: 2pxpre {
color: red}
}

[nex3]

Thanks!