Fuzzed regex causes assertion-failure

[lukaslueg]

AFL found this regex which causes an assertion failure !ranges.is_empty() in regex-0.1.71/src/compile.rs:421 while Regex::new() using rustc-1.11.0-dev 2016-06-13. In release-mode it causes an index 18446744073709551615 out of range for slice of length 0.

/=(?-u:\?(?:\[\[:\[\[[^|\]]*(?:\|(?-u:\?[\[[]*(?:\|(?:[^|\]]*))2:[^|\]]*))25[σף]]*(?:\|(?:[^|\]]*)0?:[^|\]]*))25[0])�+

Beware the special characters. In Base64 it's Lz0oPy11Olw/KD86XFtcWzpcW1xbW158XF1dKig/Olx8KD8tdTpcP1tcW1tdKig/Olx8KD86W158
XF1dKikpMjpbXnxcXV0qKSkyNVvPg9ejXV0qKD86XHwoPzpbXnxcXV0qKTA/OltefFxdXSopKTI1
WzBdKX8r

[BurntSushi]

Nice. This is a bug because Unicode literals should be disallowed in character classes when Unicode mode is disabled, but they weren't. A smaller reproducible example is (?-u)[☃].