Add ability to search for difficulty names

osu.Game/Screens/Select/Carousel/CarouselBeatmap.cs

@@ -64,6 +64,8 @@ namespace osu.Game.Screens.Select.Carousel
 
             if (!match) return false;
 
+            match &= criteria.DifficultySearchTerms.All(term => term.Matches(BeatmapInfo.DifficultyName));
+
             if (criteria.SearchTerms.Length > 0)
             {
                 var searchableTerms = BeatmapInfo.GetSearchableTerms();

osu.Game/Screens/Select/FilterCriteria.cs

@@ -46,6 +46,7 @@ namespace osu.Game.Screens.Select
         };
 
         public OptionalTextFilter[] SearchTerms = Array.Empty<OptionalTextFilter>();
+        public OptionalTextFilter[] DifficultySearchTerms = Array.Empty<OptionalTextFilter>();
 
         public RulesetInfo? Ruleset;
         public bool AllowConvertedBeatmaps;
@@ -64,24 +65,7 @@ namespace osu.Game.Screens.Select
             {
                 searchText = value;
 
-                List<OptionalTextFilter> terms = new List<OptionalTextFilter>();
+                SearchTerms = getTermsFromSearchText(value);
-
-                string remainingText = value;
-
-                // First handle quoted segments to ensure we keep inline spaces in exact matches.
-                foreach (Match quotedSegment in Regex.Matches(searchText, "(\"[^\"]+\"[!]?)"))
-                {
-                    terms.Add(new OptionalTextFilter { SearchTerm = quotedSegment.Value });
-                    remainingText = remainingText.Replace(quotedSegment.Value, string.Empty);
-                }
-
-                // Then handle the rest splitting on any spaces.
-                terms.AddRange(remainingText.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s => new OptionalTextFilter
-                {
-                    SearchTerm = s
-                }));
-
-                SearchTerms = terms.ToArray();
 
                 SearchNumber = null;
 
@@ -90,6 +74,11 @@ namespace osu.Game.Screens.Select
             }
         }
 
+        public string DifficultySearchText
+        {
+            set => DifficultySearchTerms = getTermsFromSearchText(value);
+        }
+
         /// <summary>
         /// Hashes from the <see cref="BeatmapCollection"/> to filter to.
         /// </summary>
@@ -97,6 +86,28 @@ namespace osu.Game.Screens.Select
 
         public IRulesetFilterCriteria? RulesetCriteria { get; set; }
 
+        private static OptionalTextFilter[] getTermsFromSearchText(string searchText)
+        {
+            List<OptionalTextFilter> terms = new List<OptionalTextFilter>();
+
+            string remainingText = searchText;
+
+            // First handle quoted segments to ensure we keep inline spaces in exact matches.
+            foreach (Match quotedSegment in Regex.Matches(searchText, "(\"[^\"]+\"[!]?)"))
+            {
+                terms.Add(new OptionalTextFilter { SearchTerm = quotedSegment.Value });
+                remainingText = remainingText.Replace(quotedSegment.Value, string.Empty);
+            }
+
+            // Then handle the rest splitting on any spaces.
+            terms.AddRange(remainingText.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s => new OptionalTextFilter
+            {
+                SearchTerm = s
+            }));
+
+            return terms.ToArray();
+        }
+
         public struct OptionalRange<T> : IEquatable<OptionalRange<T>>
             where T : struct
         {

osu.Game/Screens/Select/FilterQueryParser.cs

@@ -19,8 +19,27 @@ namespace osu.Game.Screens.Select
             @"\b(?<key>\w+)(?<op>(:|=|(>|<)(:|=)?))(?<value>("".*""[!]?)|(\S*))",
             RegexOptions.Compiled | RegexOptions.IgnoreCase);
 
+        private static readonly Regex difficulty_query_syntax_regex = new Regex(
+            @"(\s|^)((\[(?>\[(?<level>)|[^[\]]+|\](?<-level>))*(?(level)(?!))\](\s|$))|(\[.*))",
+            RegexOptions.Compiled);
+
         internal static void ApplyQueries(FilterCriteria criteria, string query)
         {
+            foreach (Match match in difficulty_query_syntax_regex.Matches(query))
+            {
+                // Trim the first character because it's always '[' (ignoring spaces)
+                string cleanDifficultyQuery = match.Value.Trim(' ')[1..];
+
+                if (cleanDifficultyQuery.EndsWith(']'))
+                    cleanDifficultyQuery = cleanDifficultyQuery[..^1];
+
+                criteria.DifficultySearchText = cleanDifficultyQuery;
+
+                // Insert whitespace if necessary so that the words before and after the difficulty query aren't joined together.
+                bool insertWhitespace = match.Value.StartsWith(' ') && match.Value.EndsWith(' ');
+                query = query.Replace(match.Value, insertWhitespace ? " " : "");
+            }
+
             foreach (Match match in query_syntax_regex.Matches(query))
             {
                 string key = match.Groups["key"].Value.ToLowerInvariant();