Introduce a new InvalidFacetsDistribution user error

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};
@@ -219,7 +219,10 @@ impl<'a> FacetDistribution<'a> {
             Some(ref facets) => {
                 let invalid_fields: HashSet<_> = facets.difference(&filterable_fields).collect();
                 if !invalid_fields.is_empty() {
-                    todo!("return an error specifying that these fields are not filterable");
+                    return Err(UserError::InvalidFacetsDistribution {
+                        invalid_facets_name: invalid_fields.into_iter().cloned().collect(),
+                    }
+                    .into());
                 } else {
                     facets.clone()
                 }