Bug Description

When modifying the searchableAttributes setting through the settings API, the order of attributes was not being preserved. The system would incorrectly detect that no changes had occurred when only the order was modified, causing the update to be skipped.

Example:

• Set searchableAttributes: ["title", "overview"]
• Modify to searchableAttributes: ["overview", "title"]
• The system would not detect this as a change and keep the original order

Root Cause

The bug was in the change detection logic within update_user_defined_searchable_attributes() in crates/milli/src/update/settings.rs. The method was comparing the new user-defined order against the computed searchable_fields instead of the user_defined_searchable_fields.

// BUGGY: Comparing against computed fields
let old_fields = self.index.searchable_fields(self.wtxn)?;
let did_change = new_fields != old_fields;

Since searchable_fields returns computed fields that may have a different order than the user-defined ones, order changes were not being detected.

Fix

Changed the comparison to use user_defined_searchable_fields instead:

// FIXED: Compare against user-defined fields
let old_fields = self.index.user_defined_searchable_fields(self.wtxn)?;
let did_change = old_fields.map(|old| new_fields != old).unwrap_or(true);

This ensures that any change in the user-defined order is properly detected and applied.