rust-analyzer: New weekly build crashs reproducily

Small guide to minimizing the reproducer for such a crash, in case someone is interested:

• we know the function that crashes RA already, and indeed rust-analyzer analysis-stats -o internal_into_boxed . causes the crash; otherwise I’d see where the progress bar says we are and hope that’s the right function
• I removed the other impls of internal_into_boxed so they don’t interfere, and checked that it still crashes
• then, since I suspected the dyn type, I commented out the where clause involving the dyn, and indeed then the crash is gone
• then I just commented out various groups of lines to see whether it still crashes - we can remove all the other where clauses, actually, and only need the self.order.into(); call (keep in mind that we don’t need the result to type-check, just to crash in the same way…)
• then I replaced some names by non-existing ones to see whether it’s necessary that they resolve, and removed the Options and Boxes
• then I copied the definitions of the remaining types next to the impl, and simplified them a bit as well
• and I kept removing things to simplify.

In the end I ended up with:

trait BoxedDsl<DB> {
    type Output;
    fn internal_into_boxed(self) -> Self::Output;
}

struct SelectStatement<From, Select, Distinct, Where, Order, LimitOffset, GroupBy, Locking> {
    order: Order,
}

trait QueryFragment<DB: Backend> {}

trait Into<T> { fn into(self) -> T; }

impl<F, S, D, W, O, LOf, DB> BoxedDsl<DB>
    for SelectStatement<F, S, D, W, O, LOf, G>
where
    O: Into<dyn QueryFragment<DB>>,
{
    type Output = XXX;

    fn internal_into_boxed(self) -> Self::Output {
        self.order.into();
    }
}

and copied that to a test, where it indeed still crashed. With that, finding and fixing the bug was just a matter of some print debugging 😉

That’s where @edwin0cheng’s page gets its test cases from, IIRC 😄

Actually, diesel would be a good example. I’ll add it to CI, once we stop crashing on it.

Hm, actually, why re-invent the wheel? We should just re-use https://github.com/rust-lang/rustc-perf/tree/master/collector/benchmarks

Yeah, either cargo build --release from source (you really need the release build), or download a nightly build from our releases.

if !nightly {

Ah, so that wasn’t a Deja vu 😃

but I can’t find that in the workflows.

That’s in dist.rs

What would you say about enabling debug info for nightly builds?

Yes 😃