Merge #915

915: Beta: Multi index search and disjunctive facet search r=bidoubiwa a=bidoubiwa

see #888 


Body of the release:

## ⚠️ Breaking change

- Facets behavior changed and uses `disjunctive facet search` see  #884 added in #888

## 🚀 Enchancement

- The `Index` widget is now compatible with instant-meilisearch #888

Thanks again to `@bidoubiwa!` 🎉



Co-authored-by: Charlotte Vermandel <[email protected]>
Co-authored-by: cvermand <[email protected]>

Author: meili-bors[bot]

.changeset/fresh-tables-clap.md

@@ -0,0 +1,77 @@
+---
+"@meilisearch/instant-meilisearch": minor
+---
+
+- Change the behavior of the `or` operator parameter on the [`RefinmentList`](https://www.algolia.com/doc/api-reference/widgets/refinement-list/js/) widget.
+
+⚠️ This impacts the facet distribution number
+
+## Drawback
+
+Currently, for each `facet value` selected in a different `facet` a separate request is made to Meilisearch. Plus, an additional one containing all the facets filters. It results in tedious search requests and a high bandwidth cost.
+For example, if I select `Adventure` on genres and `Multiplayer` on players, one request is made with both facet filters, one with only `genres=Adventure` and one with only `players=Multiplayer`
+
+In the next release of Meilisearch, a new `multi-search` API route is planned to be released (see [PR](https://github.com/meilisearch/meilisearch/pull/3417)). When it is released, the work-around will be removed and only one HTTP request will be done in all cases!
+
+
+## Explanation
+
+The way the `facetDistribution` is calculated changed. The `facetDistribution` shows the numbers of hits for each facet. For example:
+
+Given the following facet:
+
+```
+Genres
+- [ ] Adventure 7
+```
+
+The `facetDistribution` provides the information that there are `7` hits containing the adventure genre.
+
+For the example, let's take the following facets:
+
+```
+Genres
+- [ ] Adventure 7
+- [ ] Action 5
+- [ ] Science Fiction 5
+Players
+- [ ] Multiplayer 11
+- [ ] Single player 7
+```
+
+Before, when selecting a facet value in a certain facet, the distribution of that facet was impacted.
+
+```
+- [x] Adventure 7
+- [ ] Action 3 // <- number changed from 5 to 3
+- [ ] Science Fiction 1 // <- number changed from 5 to 1
+Players
+- [ ] Multiplayer 6
+- [ ] Single player 3
+```
+
+With the new behavior, the distributed number are not changed when facet values are selected inside the same facet because a facet distribution is computed with a dedicated search request.
+
+```
+Genres
+- [x] Adventure 7
+- [ ] Action 5 // <- number did not change
+- [ ] Science Fiction 5 // <- number did not change
+Players
+- [ ] Multiplayer 6
+- [ ] Single player 3
+```
+
+```
+Genres
+- [x] Adventure 7 // changed because of Multiplayer
+- [ ] Action 4
+- [ ] Science Fiction 3
+Players
+- [x] Multiplayer 6
+- [ ] Single player 3
+```
+
+This is the conventional way of calculating the facet distribution. Similar to Algolia's behavior. If you prefer the old behavior, please consider opening an issue.
+
+See [complete explanation here](https://github.com/meilisearch/instant-meilisearch/issues/884)

.changeset/pre.json

@@ -0,0 +1,11 @@
+---
+"@meilisearch/instant-meilisearch": minor
+---
+
+- Compatibility with the `Index` widget is added.
+
+## Drawback
+
+Currently, for each index a request is made on, a separated request is made to Meilisearch. For example, if you have two indexes on which to search, two http requests are made.
+
+In the next release of Meilisearch, a new `multi-search` API route is planned to be released (see [PR](https://github.com/meilisearch/meilisearch/pull/3417)). When it is released, the work-around will be removed and only one HTTP request will be done in all cases!

.changeset/rich-wasps-tell.md

@@ -275,7 +275,7 @@ List of all the components that are available in [instantSearch](https://github.
 ### Table Of Widgets
 
 - ✅ [InstantSearch](#-instantsearch)
-- ❌ [index](#-index)
+- ✅ [index](#-index)
 - ✅ [SearchBox](#-searchbox)
 - ✅ [Configure](#-configure)
 - ❌ [ConfigureRelatedItems](#-configure-related-items)
@@ -344,15 +344,13 @@ const search = instantsearch({
 })
 ```
 
-### ❌ Index
+### ✅ Index
 
 [Index references](https://www.algolia.com/doc/api-reference/widgets/index-widget/js/)
 
 `Index` is the component that lets you apply widgets to a dedicated index. It’s useful if you want to build an interface that targets multiple indices.
 
-Not compatible as Meilisearch does not support federated search on multiple indexes.
-
-If you'd like to see federated search implemented please vote for it in the [roadmap](https://roadmap.meilisearch.com/c/74-multi-index-search?utm_medium=social&utm_source=portal_share).
+Using this component, instant-meilisearch does an http-request for each different `Index` widget added. More http requests are made when using the [`RefinementList`](#✅-refinementlist) widget.
 
 ### ✅ SearchBox
 
@@ -677,6 +675,9 @@ The `refinementList` widget is one of the most common widgets you can find in a
 - ✅ templates: The templates to use for the widget.
 - ✅ cssClasses: The CSS classes to override.
 
+The `RefinementList` widget uses the `disjunctive facet search` principle when using the `or` operator. For each different facet category used, an additional http call is made.
+For example, if I ask for `color=green` and `size=2`, three http requests are made. One for the hits, one for the `color` facet distribution, and one for the `size` facet distribution. To provide feedback on the subject, refer to [this discussion](https://github.com/meilisearch/product/issues/54).
+
 The following example will create a UI component with the a list of genres on which you will be able to facet.
 
 ```js