Disable hot reload profile/release mode

[johnpryan]

The hot reload and hot restart buttons should be disabled when you run in profile or release mode, since they won't work. See flutter/flutter#37987.

[DanTup]

I think the Hot Reload button used to use the presence of the service extension to be enabled, but maybe when adding support for hot-reloading Dart (non-Flutter) the condition was removed. I guess it should be "(is Flutter and service extension is available) || is not Flutter".

As for Restart, we can't actually disable that button, it's not a "Hot Restart" button but rather just a "Restart Debugging session" button that in the case of Flutter works by doing a Hot Restart (since it's faster). However, it should work because it should just stop the existing session (closing the app) and then restart it (a new instance of flutter run). I think the problem is that at the time when we need to tell VS Code whether we're handling the restart or not (during initialisation), we haven't been told whether it's preview/release mode. I'll look for some way to improve this.

[johnpryan]

Sounds good to me 👍

[DanTup]

I've pushed a change that hides/disabled Hot Reload for Flutter apps when the reloadSources extension is not available (it remains enabled/visible for Dart projects since they don't require this service and work via a standard VM Service API).

However, restart is more complicated. We can't hide the "restart" button (which we usually use for Hot Restart) because VS Code doesn't allow it (restart should always be possible, even if it's not a Hot Restart, because it should just be the same as stopping the session and starting it again). We also can't currently tell VS Code to handle the restart because we only know about profile/release flags in launchRequest (not during startup when capabilities are exchanged).

So there are a few options:

1. Do nothing. This means the restart button on the debug toolbar will not work, and instead prints an error to the console in profile/release mode:

   Failed to Hot Restart: DebugAdapterException: Exception: Restart is not supported in profile mode

2. Handle restartRequest in the DAP and terminate the flutter run process, clean up all state, and then restart it (this is probably the best solution, but also complex)
3. Pass an additional flag for profile/release mode to the flutter debug_adapter process so it's known before launchRequest, and use that to set the supportsRestartRequest capability.

1 is ofc easiest, but I think we should probably do 2.

(on a related note, we should ensure Hot Restart commands are disabled/hidden from the palette etc., since we're just implementing a standard restart here, and having Hot Restart commands show up may be confusing where it's not supporting and we will do a cold restart).

[DanTup]

Since the restart change above requires DAP changes, but the Hot Reload change will ship in the next VS Code release, I'm splitting this into two issues. This one can be for the Hot Reload change, and #4281 tracks handling Restart for profile/release.

(so I'm closing this one as done by ecad283)