Add a session timestamp prefix to log files (and retain 7 days of logs)

[peppy]

Will be useful for diagnosing user issues where they already restarted the game and as a consequence, nuked previous logs.

[Susko3]

Just noting this: changing the logger storage when the game is running will no longer write the logger header to the new log files.

Changing the logger storage during runtime is dubious, and the old code is incorrect since it wasn't locking flush_sync_lock when accessing a thread-shared resource (static_loggers).

So I'm not against this change. Maybe change the setter to internal to reflect that we don't support changing the storage.

[peppy]

Unfortunately the setter is used osu! side:

I actually removed this because it was writing the headers more than once to the same file location. I guess I'll add it back and fix that part instead..

[peppy]

On second thoughts, I guess this depends on what we consider the log header to be. Should it signal the start of a session and therefore not be present on a partial log? I could imagine this being one correct way of looking at it.

Here's a diff to make the log header output correctly after storage changes only, in case that is the preferred direction:

diff --git a/osu.Framework/Logging/Logger.cs b/osu.Framework/Logging/Logger.cs
index fb7301901..ea492be99 100644
--- a/osu.Framework/Logging/Logger.cs
+++ b/osu.Framework/Logging/Logger.cs
@@ -63,6 +63,8 @@ public class Logger
 
         private static Storage storage;
 
+        private static string storageFullPath = string.Empty;
+
         /// <summary>
         /// The storage to place logs inside.
         /// </summary>
@@ -71,8 +73,20 @@ public static Storage Storage
             private get => storage;
             set
             {
+                if (storage == value)
+                    return;
+
                 storage = value ?? throw new ArgumentNullException(nameof(value));
 
+                string newPath = storage.GetFullPath(string.Empty);
+
+                // If the full path has changed, recreate loggers to correctly purge and
+                // repopulate the log's header.
+                if (newPath == storageFullPath)
+                    static_loggers.Clear();
+
+                storageFullPath = newPath;
+
                 cycleLogs();
             }
         }

[smoogipoo]

I consider it as the start of a session, but I wouldn't mind it being output every time.

[peppy]

I think I'd rather it didn't output every time so we know that some logs might be missing from the start.

[smoogipoo]

A bit worried about this, in-case storage is set incorrectly it could nuke unrelated files.

How about doing additional checks against the filename? Something like making sure it matches *.{Name}.log?

[smoogipoo]

I consider it as the start of a session, but I wouldn't mind it being output every time.