Merge #4476

4476: Make the `/facet-search` route use the `sortFacetValuesBy` setting r=irevoire a=Kerollmops

This PR fixes #4423 by ensuring that the `/facet-search` route uses the `sortFacetValuesBy` setting.

Note for the documentation team (to be moved in the tracking issue): Using the new `sortFacetValuesBy` setting can slow down the facet-search requests as Meilisearch iterates over the whole list of facet values and computes the count of documents on every entry. That is hardly or even impossible to optimize correctly.

### TODO
 - [x] Create a custom HashMap wrapper for the facet `OrderBy` settings.
         This wrapper will return the `OrderBy` setting of the facet, if not defined will use the default `*` one, and if not there either (strange) will fall back on the lexicographic one.
- [x] Create a `ValuesCollection` wrapper that implements the logic for the lexicographic and count order by.
  - [x] Use it when there is no search query.
  - [x] Use it when there is a search query with and without allowed typos.
  - [x] Do not change the original logic, only use a wrapper.
- [x] Add tests

Co-authored-by: Clément Renault <clement@meilisearch.com>

meilisearch/src/search.rs

@@ -671,27 +671,16 @@ pub fn perform_search(
 
             let sort_facet_values_by =
                 index.sort_facet_values_by(&rtxn).map_err(milli::Error::from)?;
-            let default_sort_facet_values_by =
-                sort_facet_values_by.get("*").copied().unwrap_or_default();
 
             if fields.iter().all(|f| f != "*") {
-                let fields: Vec<_> = fields
-                    .iter()
-                    .map(|n| {
-                        (
-                            n,
-                            sort_facet_values_by
-                                .get(n)
-                                .copied()
-                                .unwrap_or(default_sort_facet_values_by),
-                        )
-                    })
-                    .collect();
+                let fields: Vec<_> =
+                    fields.iter().map(|n| (n, sort_facet_values_by.get(n))).collect();
                 facet_distribution.facets(fields);
             }
+
             let distribution = facet_distribution
                 .candidates(candidates)
-                .default_order_by(default_sort_facet_values_by)
+                .default_order_by(sort_facet_values_by.get("*"))
                 .execute()?;
             let stats = facet_distribution.compute_stats()?;
             (Some(distribution), Some(stats))

meilisearch/tests/search/facet_search.rs

@@ -123,6 +123,28 @@ async fn simple_facet_search_with_max_values() {
     assert_eq!(dbg!(response)["facetHits"].as_array().unwrap().len(), 1);
 }
 
+#[actix_rt::test]
+async fn simple_facet_search_by_count_with_max_values() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    let documents = DOCUMENTS.clone();
+    index
+        .update_settings_faceting(
+            json!({ "maxValuesPerFacet": 1, "sortFacetValuesBy": { "*": "count" } }),
+        )
+        .await;
+    index.update_settings_filterable_attributes(json!(["genres"])).await;
+    index.add_documents(documents, None).await;
+    index.wait_task(2).await;
+
+    let (response, code) =
+        index.facet_search(json!({"facetName": "genres", "facetQuery": "a"})).await;
+
+    assert_eq!(code, 200, "{}", response);
+    assert_eq!(dbg!(response)["facetHits"].as_array().unwrap().len(), 1);
+}
+
 #[actix_rt::test]
 async fn non_filterable_facet_search_error() {
     let server = Server::new().await;
@@ -157,3 +179,24 @@ async fn facet_search_dont_support_words() {
     assert_eq!(code, 200, "{}", response);
     assert_eq!(response["facetHits"].as_array().unwrap().len(), 0);
 }
+
+#[actix_rt::test]
+async fn simple_facet_search_with_sort_by_count() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    let documents = DOCUMENTS.clone();
+    index.update_settings_faceting(json!({ "sortFacetValuesBy": { "*": "count" } })).await;
+    index.update_settings_filterable_attributes(json!(["genres"])).await;
+    index.add_documents(documents, None).await;
+    index.wait_task(2).await;
+
+    let (response, code) =
+        index.facet_search(json!({"facetName": "genres", "facetQuery": "a"})).await;
+
+    assert_eq!(code, 200, "{}", response);
+    let hits = response["facetHits"].as_array().unwrap();
+    assert_eq!(hits.len(), 2);
+    assert_eq!(hits[0], json!({ "value": "Action", "count": 3 }));
+    assert_eq!(hits[1], json!({ "value": "Adventure", "count": 2 }));
+}