Fix anchor generation on titles with ampersands

Fixes #696.

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+* Fix anchor generation on titles with ampersands.
+
+  Fixes #696.
+
 ## Version 3.5.1 (Security)
 
 * Fix a security vulnerability using `:quote` in combination with the

ext/redcarpet/html.c

@@ -277,6 +277,22 @@ rndr_linebreak(struct buf *ob, void *opaque)
 	return 1;
 }
 
+static int html_entity_ahead(const uint8_t *text, size_t start, size_t size) {
+	size_t i = start;
+
+	if (text[i] != '&')
+		return 0;
+
+	for (; i < size; ++i) {
+		if (text[i] == ' ')
+			return 0;
+		else if (text[i] == ';')
+			return 1;
+	}
+
+	return 0;
+}
+
 static void
 rndr_header_anchor(struct buf *out, const struct buf *anchor)
 {
@@ -293,10 +309,11 @@ rndr_header_anchor(struct buf *out, const struct buf *anchor)
 			while (i < size && a[i] != '>')
 				i++;
 		// skip html entities
-		} else if (a[i] == '&') {
+		} else if (a[i] == '&' && html_entity_ahead(a, i, size)) {
 			while (i < size && a[i] != ';')
 				i++;
 		}
+
 		// replace non-ascii or invalid characters with dashes
 		else if (!isascii(a[i]) || strchr(STRIPPED, a[i])) {
 			if (inserted && !stripped)

test/html_toc_render_test.rb

@@ -66,14 +66,17 @@ def test_toc_heading_with_hyphen_and_equal
   end
 
   def test_anchor_generation_with_edge_cases
-    # Imported from ActiveSupport::Inflector#parameterize's tests
+    # Mostly imported from ActiveSupport::Inflector#parameterize's tests
     titles = {
       "Donald E. Knuth"                     => "donald-e-knuth",
       "Random text with *(bad)* characters" => "random-text-with-bad-characters",
       "!@#Surrounding bad characters!@#"    => "surrounding-bad-characters",
       "Squeeze   separators"                => "squeeze-separators",
       "Test with + sign"                    => "test-with-sign",
-      "Test with a Namespaced::Class"       => "test-with-a-namespaced-class"
+      "Test with a Namespaced::Class"       => "test-with-a-namespaced-class",
+      "Foo & Bar"                           => "foo-bar",
+      "Foo&Bar"                             => "foo-bar",
+      "Foo & Bar"                       => "foo-bar"
     }
 
     titles.each do |title, anchor|