Terminal: Display current tab's icon as the taskbar icon

[dstaley]

Description of the new feature/enhancement

I'd love to have the ability to select a custom Terminal icon from a limited set of icons packaged with the application by Microsoft. Particularly, I'd love the ability to use this icon from @cinnamon-msft.

Proposed technical implementation details (optional)

This isn't asking for completely arbitrary icons; the scope would be limited to a set of included icons. I also believe that means it's not in scope of #4000.

As for a potential solution, I'm not sure which of the Windows APIs Terminal has access to. If Win32 APIs can be called, I think WM_SETICON could be a good place to start.

[WSLUser]

Let's keep Windows Terminal from being political. You could technically change your icon yourself by replacing the existing icon with the one of your choice. However I can see a feature request for this in general (you can already set an icon inside Terminal in settings.json as a background, this would just be near duplicate code that changes the main icon instead.)

I would still rather see this particular feature request as an extension.

[zadjii-msft]

I'm gonna keep this discussion _strictly_ technical.

There's no way I'm aware of to dynamically change the tile in the Start Menu. I'm pretty sure that's something that the platform hasn't provided any sort of API for, so that's out of the question.

The next idea would be setting the icon in the taskbar. #1871 covers _some_ of that discussion, but that's mostly just "show the profile's icon as a badge on the taskbar". I'm not really sure if it's possible to generically replace the entire icon for an application at runtime, and if we could, I'd bet that it would revert to the default when the app was closed. Since #1871 seems specific to using the icon as a _badge_, I'm gonna convert this issue into "use the profile icon _as the taskbar icon_". I don't know if WM_SETICON would work, or how we'd convert a image into an HICON, but that's probably the hardest bit of work.

Then of course, as the _least_ visible solution, you can already set the icon for the tab itself. Since that's already a possible solution, I'm not gonna discuss that too much more.

[dstaley]

I'm not really sure if it's possible to generically replace the entire icon for an application at runtime, and if we could, I'd bet that it would revert to the default when the app was closed.

I'm totally fine with that solution! It makes sense that a user-choice would only be reflected at runtime.

Since #1871 seems specific to using the icon as a _badge_, I'm gonna convert this issue into "use the profile icon _as the taskbar icon_".

My only worry here is if we default to using the profile icon in all instances, you could find yourself in a situation where you're running both Command Prompt and Windows Terminal at the same time, and they both have the same taskbar icon (since the profile icon for Command Prompt is the Command Prompt icon). I think it would make the most sense to support specifically declaring a taskbar icon for a profile, with the ability to set that property at a global level as well. That way, you can opt-in to having the taskbar icon change, and have a way to say "I don't care which profile is running, just use this icon".

I don't know if WM_SETICON would work, or how we'd convert a image into an HICON, but that's probably the hardest bit of work.

The original intent of the request was to have icons embedded as ICO resources, not arbitrary images, so I believe you could just use LoadIcon with the identifier from the resource definition file. The idea was to only support Microsoft-provided images. If we can find a solution that works with arbitrary images, that's awesome, but if that proves to be difficult I'd rather have just included icons than not have the functionality at all.

[electronic-dk]

@dstaley regarding your second concern about the same taskbar icon for different profiles and the terminal: the proposal there is to have it as a small overlay over the default terminal icon not to replace it entirely, so that you wouldn't confuse it with the actual prompt if it's running alongside the terminal, so I don't really think this should be an issue.

[dstaley]

@electronic-dk #1871 covers the badge use case, this issue is for replacing the entire icon.