Rebase and use in all in-box preconditions

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Threading.Tasks;
 
 namespace Discord.Commands
@@ -13,6 +13,14 @@ namespace Discord.Commands
         /// </summary>
         public string Group { get; set; } = null;
 
+        /// <summary>
+        /// When overridden in a derived class, uses the supplied string
+        /// as the error message if the precondition doesn't pass.
+        /// Setting this for a class that doesn't override
+        /// this property is a no-op.
+        /// </summary>
+        public virtual string ErrorMessage { get { return null; } set { } }
+
         public abstract Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context, CommandInfo command, IServiceProvider services);
     }
 }

src/Discord.Net.Commands/Attributes/Preconditions/RequireBotPermissionAttribute.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Threading.Tasks;
 
 namespace Discord.Commands
@@ -11,6 +11,7 @@ namespace Discord.Commands
     {
         public GuildPermission? GuildPermission { get; }
         public ChannelPermission? ChannelPermission { get; }
+        public override string ErrorMessage { get; set; }
 
         /// <summary>
         /// Require that the bot account has a specified GuildPermission
@@ -52,7 +53,7 @@ namespace Discord.Commands
                 if (guildUser == null)
                     return PreconditionResult.FromError("Command must be used in a guild channel");
                 if (!guildUser.GuildPermissions.Has(GuildPermission.Value))
-                    return PreconditionResult.FromError($"Bot requires guild permission {GuildPermission.Value}");
+                    return PreconditionResult.FromError(ErrorMessage ?? $"Bot requires guild permission {GuildPermission.Value}");
             }
 
             if (ChannelPermission.HasValue)
@@ -64,7 +65,7 @@ namespace Discord.Commands
                     perms = ChannelPermissions.All(context.Channel);
 
                 if (!perms.Has(ChannelPermission.Value))
-                    return PreconditionResult.FromError($"Bot requires channel permission {ChannelPermission.Value}");
+                    return PreconditionResult.FromError(ErrorMessage ?? $"Bot requires channel permission {ChannelPermission.Value}");
             }
 
             return PreconditionResult.FromSuccess();

src/Discord.Net.Commands/Attributes/Preconditions/RequireContextAttribute.cs

@@ -19,6 +19,7 @@ namespace Discord.Commands
     public class RequireContextAttribute : PreconditionAttribute
     {
         public ContextType Contexts { get; }
+        public override string ErrorMessage { get; set; }
 
         /// <summary>
         /// Require that the command be invoked in a specified context.
@@ -52,7 +53,7 @@ namespace Discord.Commands
             if (isValid)
                 return Task.FromResult(PreconditionResult.FromSuccess());
             else
-                return Task.FromResult(PreconditionResult.FromError($"Invalid context for command; accepted contexts: {Contexts}"));
+                return Task.FromResult(PreconditionResult.FromError(ErrorMessage ?? $"Invalid context for command; accepted contexts: {Contexts}"));
         }
     }
 }

src/Discord.Net.Commands/Attributes/Preconditions/RequireNsfwAttribute.cs

@@ -9,12 +9,14 @@ namespace Discord.Commands
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
     public class RequireNsfwAttribute : PreconditionAttribute
     {
+        public override string ErrorMessage { get; set; }
+
         public override Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context, CommandInfo command, IServiceProvider services)
         {
             if (context.Channel is ITextChannel text && text.IsNsfw)
                 return Task.FromResult(PreconditionResult.FromSuccess());
             else
-                return Task.FromResult(PreconditionResult.FromError("This command may only be invoked in an NSFW channel."));
+                return Task.FromResult(PreconditionResult.FromError(ErrorMessage ?? "This command may only be invoked in an NSFW channel."));
         }
     }
 }

src/Discord.Net.Commands/Attributes/Preconditions/RequireOwnerAttribute.cs

@@ -1,5 +1,7 @@
+#pragma warning disable CS0618
 using System;
 using System.Threading.Tasks;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace Discord.Commands
 {
@@ -10,6 +12,8 @@ namespace Discord.Commands
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
     public class RequireOwnerAttribute : PreconditionAttribute
     {
+        public override string ErrorMessage { get; set; }
+
         public override async Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context, CommandInfo command, IServiceProvider services)
         {
             switch (context.Client.TokenType)
@@ -17,10 +21,10 @@ namespace Discord.Commands
                 case TokenType.Bot:
                     var application = await context.Client.GetApplicationInfoAsync();
                     if (context.User.Id != application.Owner.Id)
-                        return PreconditionResult.FromError("Command can only be run by the owner of the bot");
+                        return PreconditionResult.FromError(ErrorMessage ?? "Command can only be run by the owner of the bot");
                     return PreconditionResult.FromSuccess();
                 default:
-                    return PreconditionResult.FromError($"{nameof(RequireOwnerAttribute)} is not supported by this {nameof(TokenType)}.");                    
+                    return PreconditionResult.FromError($"{nameof(RequireOwnerAttribute)} is not supported by this {nameof(TokenType)}.");
             }
         }
     }

src/Discord.Net.Commands/Attributes/Preconditions/RequireUserPermissionAttribute.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Threading.Tasks;
 
 namespace Discord.Commands
@@ -11,6 +11,7 @@ namespace Discord.Commands
     {
         public GuildPermission? GuildPermission { get; }
         public ChannelPermission? ChannelPermission { get; }
+        public override string ErrorMessage { get; set; }
 
         /// <summary>
         /// Require that the user invoking the command has a specified GuildPermission
@@ -51,7 +52,7 @@ namespace Discord.Commands
                 if (guildUser == null)
                     return Task.FromResult(PreconditionResult.FromError("Command must be used in a guild channel"));                
                 if (!guildUser.GuildPermissions.Has(GuildPermission.Value))
-                    return Task.FromResult(PreconditionResult.FromError($"User requires guild permission {GuildPermission.Value}"));
+                    return Task.FromResult(PreconditionResult.FromError(ErrorMessage ?? $"User requires guild permission {GuildPermission.Value}"));
             }
 
             if (ChannelPermission.HasValue)
@@ -63,7 +64,7 @@ namespace Discord.Commands
                     perms = ChannelPermissions.All(context.Channel);
 
                 if (!perms.Has(ChannelPermission.Value))
-                    return Task.FromResult(PreconditionResult.FromError($"User requires channel permission {ChannelPermission.Value}"));
+                    return Task.FromResult(PreconditionResult.FromError(ErrorMessage ?? $"User requires channel permission {ChannelPermission.Value}"));
             }
 
             return Task.FromResult(PreconditionResult.FromSuccess());