docs: Replace obsolete Precondition sample with something new (#1230)

* Replace obsolete Precondition sample with something new

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Co-Authored-By: Joe4evr <jii.geugten@gmail.com>

docs/guides/commands/preconditions.md

@@ -76,7 +76,7 @@ necessary.
 
 ### Example - Creating a Custom Precondition
 
-[!code-csharp[Custom Precondition](samples/preconditions/require_owner.cs)]
+[!code-csharp[Custom Precondition](samples/preconditions/require_role.cs)]
 
 [CheckPermissionsAsync]: xref:Discord.Commands.PreconditionAttribute.CheckPermissionsAsync*
 [PreconditionResult.FromSuccess]: xref:Discord.Commands.PreconditionResult.FromSuccess*

docs/guides/commands/samples/preconditions/require_owner.cs

@@ -1,28 +0,0 @@
-// (Note: This precondition is obsolete, it is recommended to use the
-// RequireOwnerAttribute that is bundled with Discord.Commands)
-
-using Discord.Commands;
-using Discord.WebSocket;
-using Microsoft.Extensions.DependencyInjection;
-using System;
-using System.Threading.Tasks;
-
-// Inherit from PreconditionAttribute
-public class RequireOwnerAttribute : PreconditionAttribute
-{
-    // Override the CheckPermissions method
-    public async override Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context, CommandInfo command, IServiceProvider services)
-    {
-        // Get the client via Depedency Injection
-        var client = services.GetRequiredService<DiscordSocketClient>();
-        // Get the ID of the bot's owner
-        var appInfo = await client.GetApplicationInfoAsync().ConfigureAwait(false);
-        var ownerId = appInfo.Owner.Id;
-        // If this command was executed by that user, return a success
-        if (context.User.Id == ownerId)
-            return PreconditionResult.FromSuccess();
-        // Since it wasn't, fail
-        else
-            return PreconditionResult.FromError("You must be the owner of the bot to run this command.");
-    }
-}

docs/guides/commands/samples/preconditions/require_role.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Threading.Tasks;
+using Discord.Commands;
+using Discord.WebSocket;
+
+// Inherit from PreconditionAttribute
+public class RequireRoleAttribute : PreconditionAttribute
+{
+    // Create a field to store the specified name
+    private readonly string _name;
+
+    // Create a constructor so the name can be specified
+    public RequireRoleAttribute(string name) => _name = name;
+
+    // Override the CheckPermissions method
+    public override Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context, CommandInfo command, IServiceProvider services)
+    {
+        // Check if this user is a Guild User, which is the only context where roles exist
+        if (context.User is SocketGuildUser gUser)
+        {
+            // If this command was executed by a user with the appropriate role, return a success
+            if (gUser.Roles.Any(r => r.Name == _name))
+                // Since no async work is done, the result has to be wrapped with `Task.FromResult` to avoid compiler errors
+                return Task.FromResult(PreconditionResult.FromSuccess());
+            // Since it wasn't, fail
+            else
+                return Task.FromResult(PreconditionResult.FromError($"You must have a role named {_name} to run this command."));
+        }
+        else
+            return Task.FromResult(PreconditionResult.FromError("You must be in a guild to run this command."));
+    }
+}