Add grouping of preconditions to allow for flexible precondition logic.

src/Discord.Net.Commands/Attributes/PreconditionAttribute.cs

@@ -6,6 +6,16 @@ namespace Discord.Commands
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
     public abstract class PreconditionAttribute : Attribute
     {
+        /// <summary>
+        /// Specify a group that this precondition belongs to.
+        /// Preconditions of the same group require only one
+        /// of the preconditions to pass in order to be
+        /// successful (A || B). Specifying <see cref="Group"/> = 0
+        /// or not at all will require *all* preconditions
+        /// to pass, just like normal (A && B).
+        /// </summary>
+        public int Group { get; set; } = 0;
+
         public abstract Task<PreconditionResult> CheckPermissions(ICommandContext context, CommandInfo command, IServiceProvider services);
     }
 }

src/Discord.Net.Commands/Info/CommandInfo.cs

@@ -68,18 +68,48 @@ namespace Discord.Commands
         {
             services = services ?? EmptyServiceProvider.Instance;
 
-            foreach (PreconditionAttribute precondition in Module.Preconditions)
+            foreach (IGrouping<int, PreconditionAttribute> preconditionGroup in Module.Preconditions.GroupBy(p => p.Group))
             {
-                var result = await precondition.CheckPermissions(context, this, services).ConfigureAwait(false);
-                if (!result.IsSuccess)
-                    return result;
+                if (preconditionGroup.Key == 0)
+                {
+                    foreach (PreconditionAttribute precondition in preconditionGroup)
+                    {
+                        var result = await precondition.CheckPermissions(context, this, services).ConfigureAwait(false);
+                        if (!result.IsSuccess)
+                            return result;
+                    }
+                }
+                else
+                {
+                    var results = new List<PreconditionResult>();
+                    foreach (PreconditionAttribute precondition in preconditionGroup)
+                        results.Add(await precondition.CheckPermissions(context, this, services).ConfigureAwait(false));
+
+                    if (!results.Any(p => p.IsSuccess))
+                        return results[0];
+                }
             }
 
-            foreach (PreconditionAttribute precondition in Preconditions)
+            foreach (IGrouping<int, PreconditionAttribute> preconditionGroup in Module.Preconditions.GroupBy(p => p.Group))
             {
-                var result = await precondition.CheckPermissions(context, this, services).ConfigureAwait(false);
-                if (!result.IsSuccess)
-                    return result;
+                if (preconditionGroup.Key == 0)
+                {
+                    foreach (PreconditionAttribute precondition in Preconditions)
+                    {
+                        var result = await precondition.CheckPermissions(context, this, services).ConfigureAwait(false);
+                        if (!result.IsSuccess)
+                            return result;
+                    }
+                }
+                else
+                {
+                    var results = new List<PreconditionResult>();
+                    foreach (PreconditionAttribute precondition in preconditionGroup)
+                        results.Add(await precondition.CheckPermissions(context, this, services).ConfigureAwait(false));
+
+                    if (!results.Any(p => p.IsSuccess))
+                        return results[0];
+                }
             }
 
             return PreconditionResult.FromSuccess();