Bug in markdown parser - Horizontal line parser

Question

Symptoms

The following input causes stackexchange page to freeze (give it a try :P)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - a

Cause

This is caused by a Catastrophic Backtracking in the horizontal lines regexes. The responsible code should be something like this:

var replacement = "<hr />\n";
text = text.replace(/^[ ]{0,2}([ ]?\*[ ]?){3,}[ \t]*$/gm, replacement);
text = text.replace(/^[ ]{0,2}([ ]?-[ ]?){3,}[ \t]*$/gm, replacement);
text = text.replace(/^[ ]{0,2}([ ]?_[ ]?){3,}[ \t]*$/gm, replacement);

Fix

In order to fix this, the regexes can be simplified:

/^( ?-){3,}[ \t]*$/gm

Related post

Regex to parse horizontal rules in Markdown

Answer 1

Good thing I tested this out in a separate browser. :)

Used your regex with a small modification to preserve leading spaces that we currently allow in front of horizontal rules. The fix will go out with the next prod build. Thanks!