Tag extraction from packages

[tchoutri]

We can extract tags from packages using RAKE.
This will require tuning, filtering and more automated filtering. The datalog can be useful.

This requires the following:

• Pre-compute some tags from categories, such as the "phantom types" category and the "yesod" category.
• Store more information about the source repo (service, url, description, topics)

In terms of normalisation, we can learn a great deal from lib.rs:

I normalize keywords to kebab-case, except CJK and a few exceptions like "iOS" which looks silly.
I had to manage synonyms mostly manually: https://gitlab.com/crates.rs/crates.rs/-/blob/main/data/tag-synonyms.csv
Joining adjacent keywords into pairs helps ["data", "structures"] => ["data-structures"].
Each keyword has a weight, and for similarity search I add hidden keywords: https://gitlab.com/crates.rs/crates.rs/-/blob/main/crate_db/src/lib_crate_db.rs#L306
For keyword extraction I take markdown sections into account: https://gitlab.com/crates.rs/crates.rs/-/blob/main/feat_extractor/src/lib.rs#L44
and use only never-seen-before sentences.

https://mastodon.social/@kornel/109508654611639728

[tchoutri]

@qw04 will take this