Show a warning prior to opening external links

osu.Game.Tests/Visual/TestCaseChatLink.cs

@@ -23,6 +23,7 @@ namespace osu.Game.Tests.Visual
     public class TestCaseChatLink : OsuTestCase
     {
         private readonly TestChatLineContainer textContainer;
+        private readonly DialogOverlay dialogOverlay;
         private Color4 linkColour;
 
         public override IReadOnlyList<Type> RequiredTypes => new[]
@@ -37,6 +38,7 @@ public class TestCaseChatLink : OsuTestCase
 
         public TestCaseChatLink()
         {
+            Add(dialogOverlay = new DialogOverlay { Depth = float.MinValue });
             Add(textContainer = new TestChatLineContainer
             {
                 Padding = new MarginPadding { Left = 20, Right = 20 },
@@ -50,6 +52,7 @@ public TestCaseChatLink()
         private void load(OsuColour colours)
         {
             linkColour = colours.Blue;
+            Dependencies.Cache(dialogOverlay);
             Dependencies.Cache(new ChatOverlay
             {
                 AvailableChannels =

osu.Game/Graphics/Containers/LinkFlowContainer.cs

@@ -9,6 +9,7 @@
 using System.Collections.Generic;
 using osu.Framework.Platform;
 using osu.Game.Overlays;
+using osu.Game.Overlays.Chat;
 using osu.Game.Overlays.Notifications;
 
 namespace osu.Game.Graphics.Containers
@@ -24,13 +25,15 @@ public LinkFlowContainer(Action<SpriteText> defaultCreationParameters = null)
 
         private Action showNotImplementedError;
         private GameHost host;
+        private DialogOverlay dialogOverlay;
 
         [BackgroundDependencyLoader(true)]
-        private void load(OsuGame game, NotificationOverlay notifications, GameHost host)
+        private void load(OsuGame game, NotificationOverlay notifications, GameHost host, DialogOverlay dialogOverlay)
         {
             // will be null in tests
             this.game = game;
             this.host = host;
+            this.dialogOverlay = dialogOverlay;
 
             showNotImplementedError = () => notifications?.Post(new SimpleNotification
             {
@@ -88,7 +91,7 @@ public void AddLink(string text, string url, LinkAction linkType = LinkAction.Ex
                             showNotImplementedError?.Invoke();
                             break;
                         case LinkAction.External:
-                            host.OpenUrlExternally(url);
+                            dialogOverlay.Push(new ExternalLinkDialog(url, () => host.OpenUrlExternally(url)));
                             break;
                         case LinkAction.OpenUserProfile:
                             if (long.TryParse(linkArgument, out long userId))

osu.Game/Overlays/Chat/ExternalLinkDialog.cs

@@ -0,0 +1,32 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using osu.Game.Graphics;
+using osu.Game.Overlays.Dialog;
+
+namespace osu.Game.Overlays.Chat
+{
+    public class ExternalLinkDialog : PopupDialog
+    {
+        public ExternalLinkDialog(string url, Action openExternalLinkAction)
+        {
+            BodyText = url;
+
+            Icon = FontAwesome.fa_warning;
+            HeaderText = "Confirm opening external link";
+            Buttons = new PopupDialogButton[]
+            {
+                new PopupDialogOkButton
+                {
+                    Text = @"Yes. Go for it.",
+                    Action = openExternalLinkAction
+                },
+                new PopupDialogCancelButton
+                {
+                    Text = @"No! Abort mission!"
+                },
+            };
+        }
+    }
+}