introduce the reserved keywords in the filters

milli/src/search/facet/filter_condition.rs

@@ -595,6 +595,18 @@ fn field_id(
 ) -> StdResult<Option<FieldId>, PestError<Rule>> {
     // lexing ensures that we at least have a key
     let key = items.next().unwrap();
+    if key.as_rule() == Rule::reserved {
+        return Err(PestError::new_from_span(
+            ErrorVariant::CustomError {
+                message: format!(
+                    "`{}` is a reserved keyword and thus can't be used as a filter expression. Available filterable attributes are: {}",
+                    key.as_str(),
+                    filterable_fields.iter().join(", "),
+                ),
+            },
+            key.as_span(),
+        ));
+    }
 
     if !filterable_fields.contains(key.as_str()) {
         return Err(PestError::new_from_span(
@@ -671,6 +683,13 @@ mod tests {
         let condition = FilterCondition::from_str(&rtxn, &index, "NOT channel = ponce").unwrap();
         let expected = Operator(0, Operator::NotEqual(None, S("ponce")));
         assert_eq!(condition, expected);
+
+        let result = FilterCondition::from_str(&rtxn, &index, "_geo = France");
+        assert!(result.is_err());
+        let error = result.unwrap_err();
+        assert!(error.to_string().contains(
+            "`_geo` is a reserved keyword and thus can't be used as a filter expression."
+        ));
     }
 
     #[test]

milli/src/search/facet/grammar.pest

@@ -1,4 +1,4 @@
-key = _{quoted | word}
+key = _{reserved | quoted | word }
 value = _{quoted | word }
 quoted = _{ (PUSH("'") | PUSH("\"")) ~ string ~ POP  }
 string = {char*}
@@ -8,6 +8,7 @@ char =  _{ !(PEEK | "\\") ~ ANY
     | "\\" ~ (PEEK | "\\" | "/" | "b" | "f" | "n" | "r" | "t")
     | "\\" ~ ("u" ~ ASCII_HEX_DIGIT{4})}
 
+reserved = { "_geo" | "_geoDistance" | "_geoPoint" | ("_geoPoint" ~ parameters) }
 // we deliberately choose to allow empty parameters to generate more specific error message later
 parameters = {("(" ~ (value ~ ",")* ~ value? ~ ")") | ""}
 condition = _{between | eq | greater | less | geq | leq | neq}