fix(jruby): Node#line returns position in the final DOM

- document this difference from CRuby/libxml2
- add 1 to account for the prolog
- update tests to explicitly specify this difference

CHANGELOG.md

@@ -39,6 +39,7 @@ A related discussion about Trust exists at [#2357](https://github.com/sparklemot
 * [CRuby] Handle abruptly-closed HTML comments as WHATWG recommends for browsers. (Thanks to HackerOne user [tehryanx](https://hackerone.com/tehryanx?type=user) for reporting this!)
 * [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)]
+* [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

@@ -1580,14 +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

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/xml/test_node.rb

@@ -1242,19 +1242,33 @@ def test_wrap
         end
 
         describe "#line" do
-          it "properly numbers lines with documents containing XML prolog" do
+          it "counts lines" do
             xml = Nokogiri::XML(<<~XML)
-              <?xml version="1.0" ?>
               <a>
                 <b>Test</b>
               </a>
             XML
 
-            pending_if("https://github.com/sparklemotion/nokogiri/issues/2380", Nokogiri.jruby?) do
+            if Nokogiri.jruby?
+              # in the output
               assert_equal(3, xml.at_css("b").line)
+            else
+              # in the input
+              assert_equal(2, xml.at_css("b").line)
             end
           end
 
+          it "properly numbers lines with documents containing XML prolog" do
+            xml = Nokogiri::XML(<<~XML)
+              <?xml version="1.0" ?>
+              <a>
+                <b>Test</b>
+              </a>
+            XML
+
+            assert_equal(3, xml.at_css("b").line)
+          end
+
           it "properly numbers lines with documents containing XML comments" do
             xml = Nokogiri::XML(<<~XML)
               <a>
@@ -1265,7 +1279,11 @@ def test_wrap
               </a>
             XML
 
-            assert_equal(4, xml.at_css("c").line)
+            if Nokogiri.jruby?
+              assert_equal(5, xml.at_css("c").line)
+            else
+              assert_equal(4, xml.at_css("c").line)
+            end
           end
 
           it "properly numbers lines with documents containing XML multiline comments" do
@@ -1282,7 +1300,11 @@ def test_wrap
               </a>
             XML
 
-            assert_equal(6, xml.at_css("c").line)
+            if Nokogiri.jruby?
+              assert_equal(7, xml.at_css("c").line)
+            else
+              assert_equal(6, xml.at_css("c").line)
+            end
           end
 
           it "returns a sensible line number for each node" do
@@ -1298,8 +1320,13 @@ def test_wrap
             XML
 
             set = xml.css("b")
-            assert_equal(2, set[0].line)
-            assert_equal(5, set[1].line)
+            if Nokogiri.jruby?
+              assert_equal(3, set[0].line)
+              assert_equal(6, set[1].line)
+            else
+              assert_equal(2, set[0].line)
+              assert_equal(5, set[1].line)
+            end
           end
 
           it "supports a line number greater than a short int" do