Avoid rewinding previous inline when auto-linking

When a bit like "_foo_1@bar.com" is processed, first the emphasis is
rendered, then the 1 is output verbatim. When the `@` is encountered,
Redcarpet tries to find the "local part" of the address and stops when
it encounters an invalid char (i.e. here the `!`).

The problem is that when it searches for the local part, Redcarpet
rewinds the characters but here, the emphasis is already rendered so
the previous HTML tag is rewinded as well and is not correctly closed.

Author: danlec

CHANGELOG.md

@@ -38,6 +38,13 @@
 * Non-alphanumeric chars are now stripped out from generated anchors
   (along the lines of Active Support's `#parameterize` method).
 
+## Version 3.2.3
+
+* Avoid rewinding content of a previous inline when autolinking is
+  enabled.
+
+  *Daniel LeCheminant*
+
 ## Version 3.2.2
 
 * Consider `script` as a block-level element so it doesn't get included

ext/redcarpet/markdown.c

@@ -461,7 +461,7 @@ tag_length(uint8_t *data, size_t size, enum mkd_autolink *autolink)
 static void
 parse_inline(struct buf *ob, struct sd_markdown *rndr, uint8_t *data, size_t size)
 {
-	size_t i = 0, end = 0;
+	size_t i = 0, end = 0, consumed = 0;
 	uint8_t action = 0;
 	struct buf work = { 0, 0, 0, 0 };
 
@@ -486,12 +486,13 @@ parse_inline(struct buf *ob, struct sd_markdown *rndr, uint8_t *data, size_t siz
 		if (end >= size) break;
 		i = end;
 
-		end = markdown_char_ptrs[(int)action](ob, rndr, data + i, i, size - i);
+		end = markdown_char_ptrs[(int)action](ob, rndr, data + i, i - consumed, size - i);
 		if (!end) /* no action from the callback */
 			end = i + 1;
 		else {
 			i += end;
 			end = i;
+			consumed = i;
 		}
 	}
 }

test/markdown_test.rb

@@ -344,4 +344,16 @@ def test_superscript_enclosed_in_parenthesis
     markdown = render_with({:superscript => true}, "this is the 2^(nd) time")
     assert_equal "<p>this is the 2<sup>nd</sup> time</p>\n", markdown
   end
+
+  def test_no_rewind_into_previous_inline
+    result = "<p><em>!dl</em><a href=\"mailto:1@danlec.com\">1@danlec.com</a></p>\n"
+    output = render("_!dl_1@danlec.com", with: [:autolink])
+
+    assert_equal result, output
+
+    result = "<p>abc123<em><a href=\"http://www.foo.com\">www.foo.com</a></em>@foo.com</p>\n"
+    output = render("abc123_www.foo.com_@foo.com", with: [:autolink])
+
+    assert_equal result, output
+  end
 end