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I'm proposing this not as a specific feature but as a general strategy: everything the compiler can conceivably recover from in a way that allows the rest of th

I'm proposing this not as a specific feature but as a general strategy: everything the compiler can conceivably recover from in a way that allows the rest of the application to run, should. Think borrow checking, for example. If it could be changed automatically to Arc<Mutex<T>> from &T, when running the test you could say not only the borrow checker error, but also point at the specific runtime case that the borrow checker protected you from if any test exercises it. Adding `return todo!()` works well enough for some cases, but not all, because it can't confirm against impl Trait return types. And these strategies are things that people need to be taught about, individually. I'm not saying that the current state is terrible, just that there might be things we can do to make them better.

JoshTriplett 1y ago
> I'm proposing this not as a specific feature but as a general strategy: everything the compiler can conceivably recover from in a way that allows the rest of the application to run, should. I do think that'd be useful in a variety of cases, especially for testsuites. I don't think I'd want to go as far as trying to guess how to substitute `Arc`/`Mutex`/`RwLock` for a failed borrow, but there are a few different strategies that do seem reasonably safe. In addition to the automatic todo!() approach, there's the approach of compile-time tainting of branches of the item tree that failed to compile. If something doesn't compile, turn it into an item that when referenced makes the item referencing it also fail to compile. That would then allow any items that do compile to get tested in the testsuite. > Adding `return todo!()` works well enough for some cases, but not all, because it can't confirm against impl Trait return types. Not in the fully general case, but ! does implement Display, so it would work in the case you posted.

JoshTriplett 1y ago

> I'm proposing this not as a specific feature but as a general strategy: everything the compiler can conceivably recover from in a way that allows the rest of the application to run, should. I do think that'd be useful in a variety of cases, especially for testsuites. I don't think I'd want to go as far as trying to guess how to substitute `Arc`/`Mutex`/`RwLock` for a failed borrow, but there are a few different strategies that do seem reasonably safe. In addition to the automatic todo!() approach, there's the approach of compile-time tainting of branches of the item tree that failed to compile. If something doesn't compile, turn it into an item that when referenced makes the item referencing it also fail to compile. That would then allow any items that do compile to get tested in the testsuite. > Adding `return todo!()` works well enough for some cases, but not all, because it can't confirm against impl Trait return types. Not in the fully general case, but ! does implement Display, so it would work in the case you posted.