Merge #5258

5258: Unify facet strings by their normalized value r=ManyTheFish a=dureuill

Fixes #5228: the "missing facet keys" issue.

- Before this PR, updating a document such that `"facet": "DUREUILL"` would become `"facet": "dureuill"` could cause the normalized facet value `dureuill` to be removed from `field_id_docid_facet_strings` db.
- This PR makes sure to unify the intermediate representation of the facet strings by their field_id and **normalized** (and truncated) string value.
- The introduced test is testing only one of the two facet distribution algorithms.
- We removed the panic when the facet string was not found, and we instead returned the normalized string.

## Draft status

- [x] target release v1.12.6 branch and milestone
- [ ] ~consider meilitool offline upgrade to fix the corrupted dbs in the wild.~
   workaround: ~remove facets, then add them again... if your facet distribution is right.~ Just use a dump.
- [x] Add unit test demonstrating the issue fixed by this PR.

Co-authored-by: Louis Dureuil <louis@meilisearch.com>
Co-authored-by: Kerollmops <clement@meilisearch.com>

crates/meilisearch/tests/search/mod.rs

@@ -1746,3 +1746,57 @@ async fn change_attributes_settings() {
         )
         .await;
 }
+
+/// Modifying facets with different casing should work correctly
+#[actix_rt::test]
+async fn change_facet_casing() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    let (response, code) = index
+        .update_settings(json!({
+            "filterableAttributes": ["dog"],
+        }))
+        .await;
+    assert_eq!("202", code.as_str(), "{:?}", response);
+    index.wait_task(response.uid()).await;
+
+    let (response, _code) = index
+        .add_documents(
+            json!([
+                {
+                    "id": 1,
+                    "dog": "Bouvier Bernois"
+                }
+            ]),
+            None,
+        )
+        .await;
+    index.wait_task(response.uid()).await;
+
+    let (response, _code) = index
+        .add_documents(
+            json!([
+                {
+                    "id": 1,
+                    "dog": "bouvier bernois"
+                }
+            ]),
+            None,
+        )
+        .await;
+    index.wait_task(response.uid()).await;
+
+    index
+        .search(json!({ "facets": ["dog"] }), |response, code| {
+            meili_snap::snapshot!(code, @"200 OK");
+            meili_snap::snapshot!(meili_snap::json_string!(response["facetDistribution"]), @r###"
+            {
+              "dog": {
+                "bouvier bernois": 1
+              }
+            }
+            "###);
+        })
+        .await;
+}

crates/milli/src/search/facet/facet_distribution.rs

@@ -219,12 +219,19 @@ impl<'a> FacetDistribution<'a> {
                 let facet_key = StrRefCodec::bytes_decode(facet_key).unwrap();
 
                 let key: (FieldId, _, &str) = (field_id, any_docid, facet_key);
-                let original_string = self
-                    .index
-                    .field_id_docid_facet_strings
-                    .get(self.rtxn, &key)?
-                    .unwrap()
-                    .to_owned();
+                let optional_original_string =
+                    self.index.field_id_docid_facet_strings.get(self.rtxn, &key)?;
+
+                let original_string = match optional_original_string {
+                    Some(original_string) => original_string.to_owned(),
+                    None => {
+                        tracing::error!(
+                            "Missing original facet string. Using the normalized facet {} instead",
+                            facet_key
+                        );
+                        facet_key.to_string()
+                    }
+                };
 
                 distribution.insert(original_string, nbr_docids);
                 if distribution.len() == self.max_values_per_facet {

crates/milli/src/update/new/extract/faceted/extract_facets.rs

@@ -283,42 +283,60 @@ impl FacetedDocidsExtractor {
 }
 
 struct DelAddFacetValue<'doc> {
-    strings: HashMap<(FieldId, BVec<'doc, u8>), DelAdd, hashbrown::DefaultHashBuilder, &'doc Bump>,
+    strings: HashMap<
+        (FieldId, &'doc str),
+        Option<BVec<'doc, u8>>,
+        hashbrown::DefaultHashBuilder,
+        &'doc Bump,
+    >,
     f64s: HashMap<(FieldId, BVec<'doc, u8>), DelAdd, hashbrown::DefaultHashBuilder, &'doc Bump>,
+    doc_alloc: &'doc Bump,
 }
 
 impl<'doc> DelAddFacetValue<'doc> {
     fn new(doc_alloc: &'doc Bump) -> Self {
-        Self { strings: HashMap::new_in(doc_alloc), f64s: HashMap::new_in(doc_alloc) }
+        Self { strings: HashMap::new_in(doc_alloc), f64s: HashMap::new_in(doc_alloc), doc_alloc }
     }
 
     fn insert_add(&mut self, fid: FieldId, value: BVec<'doc, u8>, kind: FacetKind) {
-        let cache = match kind {
-            FacetKind::String => &mut self.strings,
-            FacetKind::Number => &mut self.f64s,
-            _ => return,
-        };
-
-        let key = (fid, value);
-        if let Some(DelAdd::Deletion) = cache.get(&key) {
-            cache.remove(&key);
-        } else {
-            cache.insert(key, DelAdd::Addition);
+        match kind {
+            FacetKind::Number => {
+                let key = (fid, value);
+                if let Some(DelAdd::Deletion) = self.f64s.get(&key) {
+                    self.f64s.remove(&key);
+                } else {
+                    self.f64s.insert(key, DelAdd::Addition);
+                }
+            }
+            FacetKind::String => {
+                if let Ok(s) = std::str::from_utf8(&value) {
+                    let normalized = crate::normalize_facet(s);
+                    let truncated = self.doc_alloc.alloc_str(truncate_str(&normalized));
+                    self.strings.insert((fid, truncated), Some(value));
+                }
+            }
+            _ => (),
         }
     }
 
     fn insert_del(&mut self, fid: FieldId, value: BVec<'doc, u8>, kind: FacetKind) {
-        let cache = match kind {
-            FacetKind::String => &mut self.strings,
-            FacetKind::Number => &mut self.f64s,
-            _ => return,
-        };
-
-        let key = (fid, value);
-        if let Some(DelAdd::Addition) = cache.get(&key) {
-            cache.remove(&key);
-        } else {
-            cache.insert(key, DelAdd::Deletion);
+        match kind {
+            FacetKind::Number => {
+                let key = (fid, value);
+                if let Some(DelAdd::Addition) = self.f64s.get(&key) {
+                    self.f64s.remove(&key);
+                } else {
+                    self.f64s.insert(key, DelAdd::Deletion);
+                }
+            }
+            FacetKind::String => {
+                if let Ok(s) = std::str::from_utf8(&value) {
+                    let normalized = crate::normalize_facet(s);
+                    let truncated = self.doc_alloc.alloc_str(truncate_str(&normalized));
+                    self.strings.insert((fid, truncated), None);
+                }
+            }
+            _ => (),
         }
     }
 
@@ -329,18 +347,14 @@ impl<'doc> DelAddFacetValue<'doc> {
         doc_alloc: &Bump,
     ) -> crate::Result<()> {
         let mut buffer = bumpalo::collections::Vec::new_in(doc_alloc);
-        for ((fid, value), deladd) in self.strings {
-            if let Ok(s) = std::str::from_utf8(&value) {
-                buffer.clear();
-                buffer.extend_from_slice(&fid.to_be_bytes());
-                buffer.extend_from_slice(&docid.to_be_bytes());
-                let normalized = crate::normalize_facet(s);
-                let truncated = truncate_str(&normalized);
-                buffer.extend_from_slice(truncated.as_bytes());
-                match deladd {
-                    DelAdd::Deletion => sender.delete_facet_string(&buffer)?,
-                    DelAdd::Addition => sender.write_facet_string(&buffer, &value)?,
-                }
+        for ((fid, truncated), value) in self.strings {
+            buffer.clear();
+            buffer.extend_from_slice(&fid.to_be_bytes());
+            buffer.extend_from_slice(&docid.to_be_bytes());
+            buffer.extend_from_slice(truncated.as_bytes());
+            match &value {
+                Some(value) => sender.write_facet_string(&buffer, value)?,
+                None => sender.delete_facet_string(&buffer)?,
             }
         }