[rikvanriel]

Render item content when ?regex= is invalid

When an item is viewed with ?regex= containing an invalid regular
expression, highlight.py does re.compile() on user-controlled input
without any exception handling. The re.error is caught by the generic
error handler, so the item body is replaced by an error box and a
traceback is logged for every such request. All it takes is a crafted
query string on any public item: GET /MoinTest?regex=[[[

Wrap the compile in try/except re.error and fall back to a pattern
that never matches ((?!)), so the view renders the content without
highlights. Valid-but-pathological patterns (ReDoS, issue #2234) are
not addressed here.

[UlrichB22]

@rikvanriel, did you see the conflict message? Please rebase with current master and resolve the conflict.

There is also issue #2234 related to this topic.

[rikvanriel]

Rebased on current master and resolved the conflict (append-append in test_frontend.py — kept both the new search regression tests and the highlight test).

Note re #2234: this PR only stops invalid patterns from crashing the view (re.error → match-nothing). Pathological-but-valid patterns (ReDoS) are still unaddressed and left for that issue.