From 6bac76214d0f5c9276b3eb1cb17857b53537a553 Mon Sep 17 00:00:00 2001
From: Stephen Checkoway <s@pahtak.org>
Date: Tue, 11 Apr 2017 15:34:53 -0500
Subject: [PATCH] Include line numbers from the parser.

Neither libxml2 nor Nokogiri contain an API for setting the line numbers
for a node. When the libxml2 headers are available, the line numbers can
be set directly in the node structure.
---
 ext/nokogumboc/nokogumbo.c | 73 +++++++++++++++++++++++++++++++++++---
 test-nokogumbo.rb          |  9 +++++
 2 files changed, 77 insertions(+), 5 deletions(-)

diff --git a/ext/nokogumboc/nokogumbo.c b/ext/nokogumboc/nokogumbo.c
index a43c34a8..f5f861f7 100644
--- a/ext/nokogumboc/nokogumbo.c
+++ b/ext/nokogumboc/nokogumbo.c
@@ -165,22 +165,85 @@ static xmlNodePtr walk_element(xmlDocPtr document, GumboElement *node) {
 }
 
 static xmlNodePtr walk_tree(xmlDocPtr document, GumboNode *node) {
+  xmlNodePtr output_node = NIL;
+  size_t line = 0;
+
   switch (node->type) {
     case GUMBO_NODE_DOCUMENT:
-      return NIL;
+      output_node = NIL;
+      break;
     case GUMBO_NODE_ELEMENT:
     case GUMBO_NODE_TEMPLATE:
-      return walk_element(document, &node->v.element);
+      output_node = walk_element(document, &node->v.element);
+      line = node->v.element.start_pos.line;
+      break;
     case GUMBO_NODE_TEXT:
     case GUMBO_NODE_WHITESPACE:
-      return xmlNewDocText(document, CONST_CAST node->v.text.text);
+      output_node = xmlNewDocText(document, CONST_CAST node->v.text.text);
+      line = node->v.text.start_pos.line;
+      break;
     case GUMBO_NODE_CDATA:
-      return xmlNewCDataBlock(document,
+      output_node =  xmlNewCDataBlock(document,
         CONST_CAST node->v.text.original_text.data,
         (int) node->v.text.original_text.length);
+      line = node->v.text.start_pos.line;
+      break;
     case GUMBO_NODE_COMMENT:
-      return xmlNewDocComment(document, CONST_CAST node->v.text.text);
+      output_node = xmlNewDocComment(document, CONST_CAST node->v.text.text);
+      line = node->v.text.start_pos.line;
+      break;
+  }
+
+  if (!output_node)
+    return NIL;
+
+#if NGLIB
+  // Set the line number.
+  //
+  // Gumbo uses an unsigned int for a line number. libxml2 uses a long but
+  // internally stores the line number as an unsigned short (which it assumes is
+  // 16-bit. To handle larger documents, complex logic is used to depending on
+  // the type of the element as follows.
+  //
+  // For element, text, comment, and PI nodes, if the line number is less than
+  // 65535, it is stored directly in the xmlNode's line field. Other nodes
+  // don't store the line number directly, but instead look at the previous
+  // node or the parent node.
+  //
+  // If the line number is at least 65535, then line is set to 65535 and
+  //   - text nodes store the real line number in the psvi field;
+  //   - element nodes don't store the real line number, forcing a lookup in
+  //     the element's children or next or previous nodes; and
+  //   - comment and PI nodes look at the next or previous nodes.
+  //
+  //  Note that nodes on line 65535 don't always report their line number
+  //  correctly.
+  //
+  // The lookup alogorithm is tortured and could trivially get into infinite
+  // recursion. To prevent that, libxml2 will only examine 5 nodes before
+  // giving up.
+  //
+  // This function only creates element, text, CDATA, and comment
+  // nodes. libxml2 will ignore CDATA nodes in this look up, but there should
+  // be no harm in setting the line number, assuming it's small enough.
+  // Otherwise, set line to 65535 and, if the node is a text node, set psvi to
+  // the line number.
+
+  if (line < 65535)
+    output_node->line = (unsigned short)line;
+  else {
+    output_node->line = 65535;
+    if (output_node->type == XML_TEXT_NODE)
+      output_node->psvi = (void *)line;
   }
+#else
+  // It'd be great to handle this without the libxml2 headers, but I do not
+  // know a good way to do this since there is no ruby API to set the line
+  // number.
+  (void)line;
+#endif
+
+  return output_node;
 }
 
 // Parse a string using gumbo_parse into a Nokogiri document
diff --git a/test-nokogumbo.rb b/test-nokogumbo.rb
index a8f6eb85..31591261 100644
--- a/test-nokogumbo.rb
+++ b/test-nokogumbo.rb
@@ -137,6 +137,15 @@ def test_parse_fragment_errors
     refute_empty doc.errors
   end
 
+  def test_line_numbers
+    doc = Nokogiri::HTML5(buffer)
+    assert_includes [0, 8], doc.at('h1').line
+    assert_includes [0, 10], doc.at('span').line
+    doc = Nokogiri::HTML5("<!DOCTYPE html>" + "\n"*65535 + buffer)
+    assert_includes [0, 65535+8], doc.at('h1').line
+    assert_includes [0, 65535+10], doc.at('span').line
+  end
+
 private
 
   def buffer