add error on search with empty facets

meilisearch-core/src/error.rs

@@ -183,6 +183,7 @@ pub enum FacetError {
     AttributeNotFound(String),
     AttributeNotSet { expected: Vec<String>, found: String },
     InvalidDocumentAttribute(String),
+    NoAttributesForFaceting,
 }
 
 impl FacetError {
@@ -207,6 +208,7 @@ impl fmt::Display for FacetError {
             AttributeNotFound(attr) => write!(f, "unknown {:?} attribute", attr),
             AttributeNotSet { found, expected } => write!(f, "`{}` is not set as a faceted attribute. available facet attributes: {}", found, expected.join(", ")),
             InvalidDocumentAttribute(attr) => write!(f, "invalid document attribute {}, accepted types: String and [String]", attr),
+            NoAttributesForFaceting => write!(f, "impossible to perform faceted search, no attributes for faceting are set"),
         }
     }
 }

meilisearch-core/src/facets.rs

@@ -35,6 +35,9 @@ impl FacetFilter {
         schema: &Schema,
         attributes_for_faceting: &[FieldId],
     ) -> MResult<FacetFilter> {
+        if attributes_for_faceting.is_empty() {
+            return Err(FacetError::NoAttributesForFaceting.into());
+        }
         let parsed = serde_json::from_str::<Value>(s).map_err(|e| FacetError::ParsingError(e.to_string()))?;
         let mut filter = Vec::new();
         match parsed {