Merge #255

255: Fix facet distribution error r=Kerollmops a=Kerollmops

This PR fixes two invalid behaviors and fixes #253:
 - We were ignoring the list of fields for which the user wanted a facet distribution.
 - We were not raising any error for when a non-filterable field was requested a facet distribution.

~For the latter behavior I need the help of @curquiza to help me choose the right error type.~

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

milli/src/error.rs

@@ -1,3 +1,4 @@
+use std::collections::HashSet;
 use std::convert::Infallible;
 use std::error::Error as StdError;
 use std::{fmt, io, str};
@@ -51,13 +52,14 @@ pub enum FieldIdMapMissingEntry {
 pub enum UserError {
     AttributeLimitReached,
     Csv(csv::Error),
-    MaxDatabaseSizeReached,
     DocumentLimitReached,
-    InvalidFilter(pest::error::Error<ParserRule>),
     InvalidCriterionName { name: String },
     InvalidDocumentId { document_id: Value },
+    InvalidFacetsDistribution { invalid_facets_name: HashSet<String> },
+    InvalidFilter(pest::error::Error<ParserRule>),
     InvalidFilterAttribute(pest::error::Error<ParserRule>),
     InvalidStoreFile,
+    MaxDatabaseSizeReached,
     MissingDocumentId { document: Object },
     MissingPrimaryKey,
     NoSpaceLeftOnDevice,
@@ -202,6 +204,15 @@ impl fmt::Display for UserError {
             Self::AttributeLimitReached => f.write_str("maximum number of attributes reached"),
             Self::Csv(error) => error.fmt(f),
             Self::DocumentLimitReached => f.write_str("maximum number of documents reached"),
+            Self::InvalidFacetsDistribution { invalid_facets_name } => {
+                let name_list =
+                    invalid_facets_name.iter().map(AsRef::as_ref).collect::<Vec<_>>().join(", ");
+                write!(
+                    f,
+                    "invalid facet distribution, the fields {} are not set as filterable",
+                    name_list
+                )
+            }
             Self::InvalidFilter(error) => error.fmt(f),
             Self::InvalidCriterionName { name } => write!(f, "invalid criterion {}", name),
             Self::InvalidDocumentId { document_id } => {

milli/src/search/facet/facet_distribution.rs

@@ -6,7 +6,7 @@ use heed::types::{ByteSlice, Unit};
 use heed::{BytesDecode, Database};
 use roaring::RoaringBitmap;
 
-use crate::error::FieldIdMapMissingEntry;
+use crate::error::{FieldIdMapMissingEntry, UserError};
 use crate::facet::FacetType;
 use crate::heed_codec::facet::FacetValueStringCodec;
 use crate::search::facet::{FacetIter, FacetRange};
@@ -174,7 +174,8 @@ impl<'a> FacetDistribution<'a> {
     fn facet_values(&self, field_id: FieldId) -> heed::Result<BTreeMap<String, u64>> {
         use FacetType::{Number, String};
 
-        if let Some(candidates) = self.candidates.as_ref() {
+        match self.candidates {
+            Some(ref candidates) => {
                 // Classic search, candidates were specified, we must return facet values only related
                 // to those candidates. We also enter here for facet strings for performance reasons.
                 let mut distribution = BTreeMap::new();
@@ -206,17 +207,31 @@ impl<'a> FacetDistribution<'a> {
                 }
 
                 Ok(distribution)
-        } else {
+            }
-            self.facet_values_from_raw_facet_database(field_id)
+            None => self.facet_values_from_raw_facet_database(field_id),
         }
     }
 
     pub fn execute(&self) -> Result<BTreeMap<String, BTreeMap<String, u64>>> {
         let fields_ids_map = self.index.fields_ids_map(self.rtxn)?;
         let filterable_fields = self.index.filterable_fields(self.rtxn)?;
+        let fields = match self.facets {
+            Some(ref facets) => {
+                let invalid_fields: HashSet<_> = facets.difference(&filterable_fields).collect();
+                if !invalid_fields.is_empty() {
+                    return Err(UserError::InvalidFacetsDistribution {
+                        invalid_facets_name: invalid_fields.into_iter().cloned().collect(),
+                    }
+                    .into());
+                } else {
+                    facets.clone()
+                }
+            }
+            None => filterable_fields,
+        };
 
         let mut distribution = BTreeMap::new();
-        for name in filterable_fields {
+        for name in fields {
             let fid =
                 fields_ids_map.id(&name).ok_or_else(|| FieldIdMapMissingEntry::FieldName {
                     field_name: name.clone(),