SMLLexer won't terminate on simple input

[bforte]

When the SMLLexer gets fed the string "exception" it seems to loop indefinitely. Here's a simple example:

from pygments import highlight
from pygments.lexers import SMLLexer
from pygments.formatters import HtmlFormatter

code = 'exception'
print(highlight(code, SMLLexer(), HtmlFormatter()))

Tested on both

$ pygmentize -V
Pygments version 2.3.1, (c) 2006-2017 by Georg Brandl.

and

$ pygmentize -V
Pygments version 2.7.3, (c) 2006-2020 by Georg Brandl.

.

[birkenfeld]

Thanks for the report, this will be fixed in the next version (probably 2.7.4).

[legoktm]

For reference, this was assigned CVE-2021-20270.