fix(jruby): improve how Node#line is calculated

Note that Java's w3c.dom.Node interface does not have any way to
get (or set) the line number for that node. The original JRuby
implementation counted newlines, but did it poorly -- see #1223.

This commit improves the newline-counting approach. But the solution
itself -- counting newlines! -- is still questionable IMHO and
absolutely inefficient.

I had played around with an approach that I wrote about at #1223,
where the SAX Parser knows what line it's on when `startElement` is
invoked (via the XMLLocator). But I couldn't figure out how to
preserve that information in the final Document or Node.

If you, like me, think this approach is terrible; and if you *also*
understand how to set this metadata on the Node or the Document, then
please help us out.

CHANGELOG.md

@@ -12,6 +12,11 @@ Nokogiri follows [Semantic Versioning](https://semver.org/), please see the [REA
 * [JRuby] `{XML,HTML}::Document.parse` now invokes `#initialize` exactly once. Previously `#initialize` was not called, which was a problem for subclassing such as done by `Loofah`.
 
 
+### Improved
+
+* [JRuby] Update the algorithm used to calculate `Node#line` to be wrong less-often. The underlying parser, Xerces, does not track line numbers, and so we've always used a hacky solution for this method. [[#1223](https://github.com/sparklemotion/nokogiri/issues/1223)]
+
+
 ## v1.11.1 / 2021-01-06
 
 ### Fixed

ext/java/nokogiri/XmlNode.java

@@ -1406,14 +1406,22 @@ private boolean count(Node node, int[] counter) {
         if (node == this.node) {
             return true;
         }
+
         NodeList list = node.getChildNodes();
-        for (int i=0; i<list.getLength(); i++) {
-            Node n = list.item(i);
-            if (n instanceof Text
-                    && ((Text)n).getData().contains("\n")) {
-                counter[0] += 1;
+        for (int jchild=0; jchild<list.getLength(); jchild++) {
+            Node child = list.item(jchild);
+
+            if (child instanceof Text) {
+                String text = ((Text)child).getData();
+                int textLength = text.length();
+                for (int jchar = 0; jchar < textLength; jchar++) {
+                    if (text.charAt(jchar) == '\n') {
+                        counter[0] += 1;
+                    }
+                }
             }
-            if (count(n, counter)) return true;
+
+            if (count(child, counter)) return true;
         }
         return false;
     }

test/xml/test_node.rb

@@ -1055,28 +1055,6 @@ def test_namespace_without_an_href_on_html_node
           assert_nil(node.namespaces['xmlns:o'])
         end
 
-        def test_line
-          xml = Nokogiri::XML(<<~eoxml)
-            <root>
-              <a>
-                Hello world
-              </a>
-            </root>
-          eoxml
-
-          set = xml.search("//a")
-          node = set.first
-          assert_equal(2, node.line)
-        end
-
-        def test_set_line
-          skip("Only supported with libxml2") unless Nokogiri.uses_libxml?
-          document = Nokogiri::XML::Document.new
-          node = document.create_element('a')
-          node.line = 54321
-          assert_equal(54321, node.line)
-        end
-
         def test_xpath_results_have_document_and_are_decorated
           x = Module.new do
             def awesome!; end
@@ -1230,6 +1208,35 @@ def test_wrap
           assert_equal('wrapper', thing.parent.name)
           assert_equal('thing', doc.at_css("wrapper").children.first.name)
         end
+
+        describe "#line" do
+          it "returns a sensible line number for each node" do
+            xml = Nokogiri::XML(<<~eoxml)
+              <a>
+                <b>
+                  Hello world
+                </b>
+                <b>
+                  Goodbye world
+                </b>
+              </root>
+            eoxml
+
+            set = xml.search("//b")
+            assert_equal(2, set[0].line)
+            assert_equal(5, set[1].line)
+          end
+        end
+
+        describe "#line=" do
+          it "overrides the line number of a node" do
+            skip("Xerces does not have line numbers for nodes") unless Nokogiri.uses_libxml?
+            document = Nokogiri::XML::Document.new
+            node = document.create_element('a')
+            node.line = 54321
+            assert_equal(54321, node.line)
+          end
+        end
       end
     end
   end