Bring back matching by filename when performing online metadata lookups

osu.Game/Beatmaps/APIBeatmapMetadataSource.cs

@@ -33,7 +33,7 @@ namespace osu.Game.Beatmaps
 
             Debug.Assert(beatmapInfo.BeatmapSet != null);
 
-            var req = new GetBeatmapRequest(beatmapInfo.MD5Hash);
+            var req = new GetBeatmapRequest(md5Hash: beatmapInfo.MD5Hash, filename: beatmapInfo.Path);
 
             try
             {

osu.Game/Beatmaps/BeatmapUpdaterMetadataLookup.cs

@@ -43,10 +43,15 @@ namespace osu.Game.Beatmaps
 
             foreach (var beatmapInfo in beatmapSet.Beatmaps)
             {
-                // note that it is KEY that the lookup here only uses MD5 inside
+                // note that these lookups DO NOT ACTUALLY FULLY GUARANTEE that the beatmap is what it claims it is,
-                // (see implementations of underlying `IOnlineBeatmapMetadataSource`s).
+                // i.e. the correctness of this lookup should be treated as APPROXIMATE AT WORST.
-                // anything else like online ID or filename can be manipulated, thus being inherently unreliable,
+                // this is because the beatmap filename is used as a fallback in some scenarios where the MD5 of the beatmap may mismatch.
-                // thus being unusable here for any purpose.
+                // this is considered to be an acceptable casualty so that things can continue to work as expected for users in some rare scenarios
+                // (stale beatmap files in beatmap packs, beatmap mirror desyncs).
+                // however, all this means that other places such as score submission ARE EXPECTED TO VERIFY THE MD5 OF THE BEATMAP AGAINST THE ONLINE ONE EXPLICITLY AGAIN.
+                //
+                // additionally note that the online ID stored to the map is EXPLICITLY NOT USED because some users in a silly attempt to "fix" things for themselves on stable
+                // would reuse online IDs of already submitted beatmaps, which means that information is pretty much expected to be bogus in a nonzero number of beatmapsets.
                 if (!tryLookup(beatmapInfo, preferOnlineFetch, out var res))
                     continue;
 

osu.Game/Beatmaps/LocalCachedBeatmapMetadataSource.cs

@@ -89,7 +89,8 @@ namespace osu.Game.Beatmaps
                 return false;
             }
 
-            if (string.IsNullOrEmpty(beatmapInfo.MD5Hash))
+            if (string.IsNullOrEmpty(beatmapInfo.MD5Hash)
+                && string.IsNullOrEmpty(beatmapInfo.Path))
             {
                 onlineMetadata = null;
                 return false;
@@ -238,9 +239,10 @@ namespace osu.Game.Beatmaps
             using var cmd = db.CreateCommand();
 
             cmd.CommandText =
-                @"SELECT beatmapset_id, beatmap_id, approved, user_id, checksum, last_update FROM osu_beatmaps WHERE checksum = @MD5Hash";
+                @"SELECT beatmapset_id, beatmap_id, approved, user_id, checksum, last_update FROM osu_beatmaps WHERE checksum = @MD5Hash OR filename = @Path";
 
             cmd.Parameters.Add(new SqliteParameter(@"@MD5Hash", beatmapInfo.MD5Hash));
+            cmd.Parameters.Add(new SqliteParameter(@"@Path", beatmapInfo.Path));
 
             using var reader = cmd.ExecuteReader();
 
@@ -277,10 +279,11 @@ namespace osu.Game.Beatmaps
                 SELECT `b`.`beatmapset_id`, `b`.`beatmap_id`, `b`.`approved`, `b`.`user_id`, `b`.`checksum`, `b`.`last_update`, `s`.`submit_date`, `s`.`approved_date`
                 FROM `osu_beatmaps` AS `b`
                 JOIN `osu_beatmapsets` AS `s` ON `s`.`beatmapset_id` = `b`.`beatmapset_id`
-                WHERE `b`.`checksum` = @MD5Hash
+                WHERE `b`.`checksum` = @MD5Hash OR `b`.`filename` = @Path
                 """;
 
             cmd.Parameters.Add(new SqliteParameter(@"@MD5Hash", beatmapInfo.MD5Hash));
+            cmd.Parameters.Add(new SqliteParameter(@"@Path", beatmapInfo.Path));
 
             using var reader = cmd.ExecuteReader();
 

osu.Game/Online/API/Requests/GetBeatmapRequest.cs

@@ -10,20 +10,20 @@ namespace osu.Game.Online.API.Requests
 {
     public class GetBeatmapRequest : APIRequest<APIBeatmap>
     {
-        public readonly int OnlineID = -1;
+        public readonly int OnlineID;
         public readonly string? MD5Hash;
         public readonly string? Filename;
 
         public GetBeatmapRequest(IBeatmapInfo beatmapInfo)
+            : this(onlineId: beatmapInfo.OnlineID, md5Hash: beatmapInfo.MD5Hash, filename: (beatmapInfo as BeatmapInfo)?.Path)
         {
-            OnlineID = beatmapInfo.OnlineID;
-            MD5Hash = beatmapInfo.MD5Hash;
-            Filename = (beatmapInfo as BeatmapInfo)?.Path ?? string.Empty;
         }
 
-        public GetBeatmapRequest(string md5Hash)
+        public GetBeatmapRequest(int onlineId = -1, string? md5Hash = null, string? filename = null)
         {
+            OnlineID = onlineId;
             MD5Hash = md5Hash;
+            Filename = filename;
         }
 
         protected override WebRequest CreateWebRequest()