Add tests to cover line numbering edge cases with JRuby

CHANGELOG.md

@@ -41,6 +41,7 @@ A related discussion about Trust exists at [#2357](https://github.com/sparklemot
 * [CRuby] `Node#line` is no longer capped at 65535. libxml v2.9.0 and later support a new parse option, exposed as `Nokogiri::XML::ParseOptions::PARSE_BIG_LINES` and set in `ParseOptions::DEFAULT_XML`, `::DEFAULT_XSLT`, `::DEFAULT_HTML`, and `::DEFAULT_SCHEMA`. (Note that JRuby never had this problem.) [[#1764](https://github.com/sparklemotion/nokogiri/issues/1764), [#1493](https://github.com/sparklemotion/nokogiri/issues/1493), [#1617](https://github.com/sparklemotion/nokogiri/issues/1617), [#1505](https://github.com/sparklemotion/nokogiri/issues/1505), [#1003](https://github.com/sparklemotion/nokogiri/issues/1003), [#533](https://github.com/sparklemotion/nokogiri/issues/533)]
 * [CRuby] If a cycle is introduced when reparenting a node (i.e., the node becomes its own ancestor), a `RuntimeError` is raised. libxml2 does no checking for this, which means cycles would otherwise result in infinite loops on subsequent operations. (Note: JRuby/Xerces already does this.) [[#1912](https://github.com/sparklemotion/nokogiri/issues/1912)]
 * [CRuby] Source builds will download zlib and libiconv via HTTPS. [[#2391](https://github.com/sparklemotion/nokogiri/issues/2391)] (Thanks, [@jmartin-r7](https://github.com/jmartin-r7)!)
+* [JRuby] `Node#line` behavior has been modified to return the line number of the node in the _final DOM structure_ (the value returned in JRuby is increased by 1 to count the XML prolog). This behavior is different from CRuby, which returns the node's position in the _input string_. This difference is not ideal, but at least is now officially documented and tested. The real-world impact of this change is that the value returned in JRuby is greater by 1 to account for the XML prolog in the output. [[#2380](https://github.com/sparklemotion/nokogiri/issues/2380)] (Thanks, [@dabdine](https://github.com/dabdine)!)
 
 
 ## 1.12.5 / 2021-09-27

ext/java/nokogiri/XmlNode.java

@@ -36,6 +36,7 @@
 import org.w3c.dom.Node;
 import org.w3c.dom.NodeList;
 import org.w3c.dom.Text;
+import org.w3c.dom.Comment;
 
 import nokogiri.internals.HtmlDomParserContext;
 import nokogiri.internals.NokogiriHelpers;
@@ -1579,14 +1580,21 @@ public class XmlNode extends RubyObject
     return getNokogiriClass(context.runtime, "Nokogiri::XML::Node").getConstant(type);
   }
 
+  /*
+   * NOTE that the behavior of this function is very difference from the CRuby implementation, see
+   * the docstring in ext/nokogiri/xml_node.c for details.
+   */
   @JRubyMethod
   public IRubyObject
   line(ThreadContext context)
   {
     Node root = getOwnerDocument();
     int[] counter = new int[1];
     count(root, counter);
-    return RubyFixnum.newFixnum(context.runtime, counter[0] + 1);
+    // offset of 2:
+    // - one because humans start counting at 1 not zero
+    // - one to account for the XML declaration present in the output
+    return RubyFixnum.newFixnum(context.runtime, counter[0] + 2);
   }
 
   private boolean
@@ -1599,9 +1607,14 @@ public class XmlNode extends RubyObject
     NodeList list = node.getChildNodes();
     for (int jchild = 0; jchild < list.getLength(); jchild++) {
       Node child = list.item(jchild);
+      String text = null;
 
       if (child instanceof Text) {
-        String text = ((Text)child).getData();
+        text = ((Text)child).getData();
+      } else if (child instanceof Comment) {
+        text = ((Comment)child).getData();
+      }
+      if (text != null) {
         int textLength = text.length();
         for (int jchar = 0; jchar < textLength; jchar++) {
           if (text.charAt(jchar) == '\n') {

ext/nokogiri/xml_node.c

@@ -1698,10 +1698,31 @@ native_write_to(
 }
 
 /*
- * call-seq:
- *  line
+ * :call-seq:
+ *   line() → Integer
+ *
+ * [Returns] The line number of this Node.
+ *
+ * ---
+ *
+ * <b> ⚠ The CRuby and JRuby implementations differ in important ways! </b>
+ *
+ * Semantic differences:
+ * - The CRuby method reflects the node's line number <i>in the parsed string</i>
+ * - The JRuby method reflects the node's line number <i>in the final DOM structure</i> after
+ *   corrections have been applied
+ *
+ * Performance differences:
+ * - The CRuby method is {O(1)}[https://en.wikipedia.org/wiki/Time_complexity#Constant_time]
+ *   (constant time)
+ * - The JRuby method is {O(n)}[https://en.wikipedia.org/wiki/Time_complexity#Linear_time] (linear
+ *   time, where n is the number of nodes before/above the element in the DOM)
  *
- * Returns the line for this Node
+ * If you'd like to help improve the JRuby implementation, please review these issues and reach out
+ * to the maintainers:
+ * - https://github.com/sparklemotion/nokogiri/issues/1223
+ * - https://github.com/sparklemotion/nokogiri/pull/2177
+ * - https://github.com/sparklemotion/nokogiri/issues/2380
  */
 static VALUE
 rb_xml_node_line(VALUE rb_node)

test/helper.rb

@@ -196,6 +196,20 @@ def assert_not_send(send_ary, m = nil)
       refute(recv.__send__(msg, *args), m)
     end unless method_defined?(:assert_not_send)
 
+    def pending(msg)
+      begin
+        yield
+      rescue MiniTest::Assertion
+        skip("pending #{msg}")
+      end
+      flunk("pending test unexpectedly passed: #{msg}")
+    end
+
+    def pending_if(msg, pend_eh, &block)
+      return yield unless pend_eh
+      pending(msg, &block)
+    end
+
     def i_am_ruby_matching(gem_version_requirement_string)
       Gem::Requirement.new(gem_version_requirement_string).satisfied_by?(Gem::Version.new(RUBY_VERSION))
     end