Merge #766

766: Indicate filterable attributes when the user sets a non filterable attribute in facet distributions r=irevoire a=dureuill

# Pull Request

## Related issue
Related to https://github.com/meilisearch/meilisearch/issues/3390

## What does this PR do?
- Title

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


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

milli/src/error.rs

@@ -1,5 +1,6 @@
 use std::collections::BTreeSet;
 use std::convert::Infallible;
+use std::fmt::Write;
 use std::{io, str};
 
 use heed::{Error as HeedError, MdbError};
@@ -100,10 +101,11 @@ A document identifier can be of type integer or string, \
 only composed of alphanumeric characters (a-z A-Z 0-9), hyphens (-) and underscores (_).", .document_id.to_string()
     )]
     InvalidDocumentId { document_id: Value },
-    #[error("Invalid facet distribution, the fields `{}` are not set as filterable.",
+    #[error("Invalid facet distribution, {}", format_invalid_filter_distribution(.invalid_facets_name, .valid_facets_name))]
-        .invalid_facets_name.iter().map(AsRef::as_ref).collect::<Vec<&str>>().join(", ")
+    InvalidFacetsDistribution {
-     )]
+        invalid_facets_name: BTreeSet<String>,
-    InvalidFacetsDistribution { invalid_facets_name: BTreeSet<String> },
+        valid_facets_name: BTreeSet<String>,
+    },
     #[error(transparent)]
     InvalidGeoField(#[from] GeoError),
     #[error("{0}")]
@@ -166,6 +168,50 @@ pub enum GeoError {
     BadLongitude { document_id: Value, value: Value },
 }
 
+fn format_invalid_filter_distribution(
+    invalid_facets_name: &BTreeSet<String>,
+    valid_facets_name: &BTreeSet<String>,
+) -> String {
+    if valid_facets_name.is_empty() {
+        return "this index does not have configured filterable attributes.".into();
+    }
+
+    let mut result = String::new();
+
+    match invalid_facets_name.len() {
+        0 => (),
+        1 => write!(
+            result,
+            "attribute `{}` is not filterable.",
+            invalid_facets_name.first().unwrap()
+        )
+        .unwrap(),
+        _ => write!(
+            result,
+            "attributes `{}` are not filterable.",
+            invalid_facets_name.iter().map(AsRef::as_ref).collect::<Vec<&str>>().join(", ")
+        )
+        .unwrap(),
+    };
+
+    match valid_facets_name.len() {
+        1 => write!(
+            result,
+            " The available filterable attribute is `{}`.",
+            valid_facets_name.first().unwrap()
+        )
+        .unwrap(),
+        _ => write!(
+            result,
+            " The available filterable attributes are `{}`.",
+            valid_facets_name.iter().map(AsRef::as_ref).collect::<Vec<&str>>().join(", ")
+        )
+        .unwrap(),
+    }
+
+    result
+}
+
 /// A little macro helper to autogenerate From implementation that needs two `Into`.
 /// Given the following parameters: `error_from_sub_error!(FieldIdMapMissingEntry => InternalError)`
 /// the macro will create the following code:

milli/src/search/facet/facet_distribution.rs

@@ -291,6 +291,7 @@ impl<'a> FacetDistribution<'a> {
                 if !invalid_fields.is_empty() {
                     return Err(UserError::InvalidFacetsDistribution {
                         invalid_facets_name: invalid_fields.into_iter().cloned().collect(),
+                        valid_facets_name: filterable_fields.into_iter().collect(),
                     }
                     .into());
                 } else {