Add error logging to slash command handlers

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

Boyfriend.cs

@@ -69,6 +69,7 @@ public class Boyfriend {
                     services.AddTransient<IConfigurationBuilder, ConfigurationBuilder>()
                         .AddDiscordCaching()
                         .AddDiscordCommands(true)
+                        .AddPostExecutionEvent<ErrorLoggingPostExecutionEvent>()
                         .AddInteractivity()
                         .AddInteractionGroup<InteractionResponders>()
                         .AddSingleton<GuildDataService>()

Commands/ErrorLoggingPostExecutionEvent.cs

@@ -0,0 +1,24 @@
+using Microsoft.Extensions.Logging;
+using Remora.Discord.Commands.Contexts;
+using Remora.Discord.Commands.Services;
+using Remora.Results;
+
+// ReSharper disable ClassNeverInstantiated.Global
+
+namespace Boyfriend.Commands;
+
+public class ErrorLoggingPostExecutionEvent : IPostExecutionEvent {
+    private readonly ILogger<ErrorLoggingPostExecutionEvent> _logger;
+
+    public ErrorLoggingPostExecutionEvent(ILogger<ErrorLoggingPostExecutionEvent> logger) {
+        _logger = logger;
+    }
+
+    public Task<Result> AfterExecutionAsync(
+        ICommandContext context, IResult commandResult, CancellationToken ct = default) {
+        if (!commandResult.IsSuccess)
+            _logger.LogWarning("Error in slash command handler.\n{ErrorMessage}", commandResult.Error.Message);
+
+        return Task.FromResult(Result.FromSuccess());
+    }
+}