We already know about one regex limitation, which is that they cannot
segment words in e.g. Japanese, Chinese, or Thai. It may also end up
that regex matching is too slow compared to other methods.
However, the regex is an implementation detail. We still want the
ability to switch between "occurs anywhere" and "match whole word", and
caching the matcher result is likely to still be important (since the
matcher itself won't change nearly as often as status ingress rate).
Therefore, we ought to be able to change the cache keys to reflect a
change of data structure.
(Old cache keys expire within minutes, so they shouldn't be too big of
an issue. Old cache keys could also be explicitly removed by an
instance administrator.)
It is reasonable to expect someone to enter #foo to mute hashtag #foo.
However, tags are recorded on statuses without the preceding #.
To adjust for this, we build a separate tag matcher and use
Tag::HASHTAG_RE to extract a hashtag from the hashtag syntax.
When given two regexps, Regexp.union preserves the options set (or not
set) on each regex; this meant that none of the multiline (m),
case-insensitivity (i), or extended syntax (x) options were set. Our
regexps are written expecting the m, i, and x options were set on all of
them, so we need to make sure that we preserve that behavior.
Note that this will only hide/show *future* reblogs by a user, and does
nothing to remove/add reblogs that are already in the timeline. I don't
think that's a particularly confusing behavior, and it's a lot easier
to implement (similar to mutes, I believe).
Glitch::KeywordMute's name is inferred as glitch_keyword_mutes, and in
templates this turns into e.g. settings/glitch/keyword_mutes. Going
along with this convention means a lot of file movement, though, and for
a UI that's as temporary and awkward as this one I think it's less
effort to slap a bunch of as: options everywhere.
We'll do the Right Thing when we build out the API and frontend UI.
Also make the keyword-building methods private: they always probably
should have been private, but now I have encoded enough fun and games
into them that it now seems wrong for them to *not* be private.
It is possible to cache a Regexp object, but I'm not sure what happens
if e.g. that object remains in cache across two different Ruby versions.
Caching a string seems to raise fewer questions.
Ditto for ending with \b.
Consider muting the phrase "(hot take)". I stipulate it is reasonable
to enter this with the default "match whole word" behavior. Under the
old behavior, this would be encoded as
\b\(hot\ take\)\b
However, if \b is before the first character in the string and the first
character in the string is not a word character, then the match will
fail. Ditto for after. In our example, "(" is not a word character, so
this will not match statuses containing "(hot take)", and that's a very
surprising behavior.
To address this, we only add leading and trailing \b to keywords that
start or end with word characters.
There are two motivations for this:
1. It looks like we're going to add other features that require
server-side storage (e.g. user notes).
2. Namespacing glitchsoc modifications is a good idea anyway: even if we
do not end up doing (1), if upstream introduces a keyword-mute feature
that also uses a "KeywordMute" model, we can avoid some merge
conflicts this way and work on the more interesting task of
choosing which implementation to use.
Word-boundary matching only works as intended in English and languages
that use similar word-breaking characters; it doesn't work so well in
(say) Japanese, Chinese, or Thai. It's unacceptable to have a feature
that doesn't work as intended for some languages. (Moreso especially
considering that it's likely that the largest contingent on the Mastodon
bit of the fediverse speaks Japanese.)
There are rules specified in Unicode TR29[1] for word-breaking across
all languages supported by Unicode, but the rules deliberately do not
cover all cases. In fact, TR29 states
For example, reliable detection of word boundaries in languages such
as Thai, Lao, Chinese, or Japanese requires the use of dictionary
lookup, analogous to English hyphenation.
So we aren't going to be able to make word detection work with regexes
within Mastodon (or glitchsoc). However, for a first pass (even if it's
kind of punting) we can allow the user to choose whether they want word
or substring detection and warn about the limitations of this
implementation in, say, docs.
[1]: https://unicode.org/reports/tr29/https://web.archive.org/web/20171001005125/https://unicode.org/reports/tr29/
This should eventually be accessible via the API and the web frontend,
but I find it easier to set up an editing interface using Rails
templates and the like. We can always take it out if it turns out we
don't need it.
