Time Travel Debugging

[hecrj]

Introducing Comet

I never properly introduced comet, so please let me.

comet is a new companion debugging tool that can be summoned by pressing F12 when the debug feature is enabled—replacing the old (and hideous) debug overlay.

comet_1080.mp4

When the debug feature is enabled, an iced application will send performance metrics through a socket to any server implementing the iced_beacon protocol.

comet is one of such servers. It is built with iced itself and you can find the code over here: https://github.com/iced-rs/comet

Of course, this all means you could build your own custom debugger if you wanted to! It should all be reusable enough.

Custom Performance Metrics

As I introduced in #2891, you can decorate any piece of code with debug::time and debug::time_with to time and visualize different parts of your app.

comet-custom_timings-720p.mp4

Time Traveling

As you know, iced uses the Elm Architecture. One of the advantages of this architecture is that application state can only be mutated in a single place: update—and only in response of a Message. Furthermore, impure side effects are encouraged to happen inside Task and Subscription which are run indirectly by the runtime.

Effectively, this means that if we have an initial state and a list of messages, then we should be able to replicate any state the application has been at any point in time. In other words, we can time travel.

comet-time_travel.mp4

comet-time_travel-02.mp4

comet-time_travel-03.mp4

Pretty cool, huh? Time traveling can be enabled with the new time-travel feature. Activating it will force a Clone bound on your Message type.

It goes without saying but... the feature is very experimental! It will only work well if your update logic is pure; meaning it does not rely on external state (e.g. calling Instant::now).

Use it carefully, it may eat your laundry!

[Tahinli]

This update is more than awesome. Thanks a lot!