Fix a regression in displaying diff fragments in comments.

Review Request #12402 — Created June 22, 2022 and submitted — Latest diff uploaded


Review Board


When upgrading to Django 3.2, we converted all of our template tags and
filters to use mark_safe() instead of setting is_safe = True, with
the exception of showextrawhitespace.

This was turning safe HTML into an unsafe string, and the result was
that any comments shown in comments in a review or in e-mails was
turning into big blobs of escaped HTML.

This change fixes it to use mark_safe(), and adds some unit tests to
ensure this never regresses.

Viewed comments in a diff that exhibited this problem. Saw that the
content was correct in all chunks of the diffs I expanded.

Unit tests pass.