The concept of runtime issues

[DevAndArtist (Adrian Meister)]

Hi community, during SE-0196 I said that it would be really cool if we would eventually extend the language to emit runtime issues triggered by some compiler diagnostic directives.

SE-0196 — Compiler Diagnostic Directives

I'm in favor of these directives, but I would go the #directive(...) route from the beginning. Here is why I think we should use the approach from the alternatives rather than the proposed one: At least for #warning directive I think it doesn't have to be a compile time only warning. Similar to how thread sanitizer in Xcode emits warnings at runtime, I think we should also be able to emit runtime warnings in our projects if at runtime something unexpected happened. Ideally this is a better wa…

This idea intrigued a few of the community members and even the core team mentioned it in the rationale:

@tkremenek

The review discussion also covered a variety of possible extensions or variants to this proposal, including support for using #warning as an expression instead of a line directive and support for runtime issues.

Now I had the chance to watch the following WWDC session 'Debugging with Xcode 11'. I noticed that SwiftUI provides custom 'runtime issues' similar to the idea mentioned above.

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• Is this a hidden compiler feature or SwiftUI internal hook for Xcode?

• In case of the former, can we expose it to the rest of the community?

cc @John_McCall @Joe_Groff @dabrahams @Douglas_Gregor

[DevAndArtist (Adrian Meister)]

Let's bump this thread. Is there a chance we could possibly get this feature rolling? Maybe it's now the right time as we are currently discussing the concrete implementation for these directives as macros. (cc @Douglas_Gregor again)

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Today I think this feature should be standalone and not tied to the directives. It should be something lightweight and on par with assert but without a failure. Maybe some kind of global emit function with parameters similar to print?

[gwendal.roue (Gwendal Roué)]

You may get some inspiration from Unobtrusive runtime warnings for libraries by Point-Free.

Sample code: swift-composable-architecture/RuntimeWarnings.swift at main · pointfreeco/swift-composable-architecture · GitHub

[technogen (Gor Gyolchanyan)]

I'd love to see this feature being made official. It would be hugely helpful for writing robust, invariant-checking code!

[Alejandro_Martinez]

It's one of the things I was expecting them to release a separate package. It's so useful!

[filip-sakel]

@DevAndArtist

• Is this a hidden compiler feature or SwiftUI internal hook for Xcode?
• In case of the former, can we expose it to the rest of the community?

As the resources shared by @gwendal.roue indicate, runtime warnings occur by a call to the logging framework. However, instead of using your app's DSO handle, you use one of the Apple-internal frameworks, such as SwiftUI or Foundation.

[DevAndArtist (Adrian Meister)]

Well I've seen that post, my original questions were three years old though.