feat(v2): contextual search, dynamic Algolia facetFilters

[slorber]

Motivation

Algolia search engine should create its filter dynamically according to the browsed page, instead of hardcoding the facetFilters in config file.

See also #3396

In practice, this allows:

• to search in the version you are currently browsing (so the filter query adapts to the current page)
• to search in standalone pages and blog posts (not possible before)
• to search in sites with multiple docs plugins (we have 2 "docs" and "community" on Docusaurus)

Design choice: make the page tagging system decoupled from Algolia, so that maybe we could support another search engine plugin in the future ( like docusaurus-theme-search-elastic) or enable the community to provide its own search system, and still be able to use the contextual search feature.

Enable contextual search

Documentation: https://deploy-preview-3550--docusaurus-2.netlify.app/classic/docs/search#contextual-search

The contextualSearch is for now opt-in, for retrocompatibility.

Algolia crawler should run on your upgraded site, so you'd rather turn this on in 2 phases (ie not upgrade + contextualSearch: true in the same PR/commit). You should rather get this working locally before publishing a site with contextualSearch: true.

If it does not work, check that the Algolia DocSearch team has added the docusaurus_tag value in your config attributesForFaceting , like here: algolia/docsearch-configs#2546

Note: the Algolia team should normally add this to your config automatically before the 23 October, in the meantime you can submit a PR to your own config.

Breaking change:

• the facet version:latest has been removed, as it was introduced recently, was not widely used, and is a bit hacky

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Preview + dogfooding + tests

[docusaurus-bot]

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[slorber]

Note

• we keep the version: meta tags for retrocompatibility.
• the algolia search page will need updates, handled separately through Algolia search results page: handle docs multi-instance + contextual search #3590