Merge #4539

4539: Don't optimize reindexing when fields contain dots r=Kerollmops a=dureuill

# Pull Request

## Related issue
Fixes https://github.com/meilisearch/meilisearch/issues/4525

## What does this PR do?
- Don't try to optimize the amount of reindexing operation when nested fields are used anywhere in:
    - the field distribution (e.g. a key actually contains a `.`)
    - the old faceted fields
    - the new faceted fields

This is because the facet distribution is not reporting on existing nested fields.



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

milli/src/update/settings.rs

@@ -1032,13 +1032,14 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
     {
         self.index.set_updated_at(self.wtxn, &OffsetDateTime::now_utc())?;
 
+        // Note: this MUST be before `update_sortable` so that we can get the old value to compare with the updated value afterwards
+
         let existing_fields: HashSet<_> = self
             .index
             .field_distribution(self.wtxn)?
             .into_iter()
             .filter_map(|(field, count)| (count != 0).then_some(field))
             .collect();
-
         let old_faceted_fields = self.index.user_defined_faceted_fields(self.wtxn)?;
         let old_fields_ids_map = self.index.fields_ids_map(self.wtxn)?;
 
@@ -1055,13 +1056,7 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
         self.update_sort_facet_values_by()?;
         self.update_pagination_max_total_hits()?;
 
-        // If there is new faceted fields we indicate that we must reindex as we must
+        let faceted_updated = self.update_faceted(existing_fields, old_faceted_fields)?;
-        // index new fields as facets. It means that the distinct attribute,
-        // an Asc/Desc criterion or a filtered attribute as be added or removed.
-        let new_faceted_fields = self.index.user_defined_faceted_fields(self.wtxn)?;
-        let faceted_updated =
-            (&existing_fields - &old_faceted_fields) != (&existing_fields - &new_faceted_fields);
-
         let stop_words_updated = self.update_stop_words()?;
         let non_separator_tokens_updated = self.update_non_separator_tokens()?;
         let separator_tokens_updated = self.update_separator_tokens()?;
@@ -1094,6 +1089,34 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
 
         Ok(())
     }
+
+    fn update_faceted(
+        &self,
+        existing_fields: HashSet<String>,
+        old_faceted_fields: HashSet<String>,
+    ) -> Result<bool> {
+        if existing_fields.iter().any(|field| field.contains('.')) {
+            return Ok(true);
+        }
+
+        if old_faceted_fields.iter().any(|field| field.contains('.')) {
+            return Ok(true);
+        }
+
+        // If there is new faceted fields we indicate that we must reindex as we must
+        // index new fields as facets. It means that the distinct attribute,
+        // an Asc/Desc criterion or a filtered attribute as be added or removed.
+        let new_faceted_fields = self.index.user_defined_faceted_fields(self.wtxn)?;
+
+        if new_faceted_fields.iter().any(|field| field.contains('.')) {
+            return Ok(true);
+        }
+
+        let faceted_updated =
+            (&existing_fields - &old_faceted_fields) != (&existing_fields - &new_faceted_fields);
+
+        Ok(faceted_updated)
+    }
 }
 
 fn validate_prompt(