Type mismatching cased by duplicate associated type resolution #59326
Labels
A-diagnostics
Area: Messages for errors, warnings, and lints
A-typesystem
Area: The type system
C-bug
Category: This is a bug.
D-incorrect
Diagnostics: A diagnostic that is giving misleading or incorrect information.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
Comments
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Can you please post the full output from your compiler related to this error? Also, if you could use the flag |
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Here you go: |
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Okay, I'm able to create a small example demonstrating this problem: use std::marker::PhantomData;
use bytes::Bytes; // 0.4.11;
trait Service {
type Request;
type Response;
}
trait Framing {
type Request;
type Response;
}
trait HttpService<B>: Service<Request = B::Request, Response = B::Response>
where
B: Framing + Send + 'static,
{
type Handler;
}
pub struct Http2Transport;
impl Framing for Http2Transport {
type Request = Bytes;
type Response = Bytes;
}
type BoxService<H> = Box<
HttpService<Http2Transport, Handler = H, Request = Bytes, Response = Bytes> + Send + 'static,
>;
fn build_server<F, SVC, H>(factory: F)
where
F: FnOnce() -> SVC + Send + Sync + Clone + 'static,
SVC: Fn(i32) -> Result<BoxService<H>, std::io::Error>,
H: 'static,
{
}
pub trait MyAwesomeService: Send + Sync + 'static {}
struct MyServiceImpl;
impl MyAwesomeService for MyServiceImpl {}
trait ProtocolFactory {
type Frame: Framing;
}
pub struct Http2ProtocolFactory<F> {
_phantom: PhantomData<F>,
}
impl<F> ProtocolFactory for Http2ProtocolFactory<F>
where
F: Framing,
{
type Frame = F;
}
pub struct ServiceProcessor<PF, H> {
service: H,
_phantom: PhantomData<(PF, H)>,
}
impl<PF, H> ServiceProcessor<PF, H>
where
PF: ProtocolFactory + 'static,
H: MyAwesomeService,
{
pub fn new(service: H) -> Self {
Self {
service,
_phantom: PhantomData,
}
}
}
impl<PF, H> Service for ServiceProcessor<PF, H>
where
PF: ProtocolFactory + 'static,
PF::Frame: Send + 'static,
H: MyAwesomeService,
{
type Request = <<PF as ProtocolFactory>::Frame as Framing>::Request;
type Response = <<PF as ProtocolFactory>::Frame as Framing>::Response;
}
impl<PF, H> HttpService<PF::Frame> for ServiceProcessor<PF, H>
where
PF: ProtocolFactory + 'static,
PF::Frame: Send + 'static,
H: MyAwesomeService,
{
type Handler = H;
}
fn make_server<F, H>(
proto: i32,
handler: H,
) -> Result<
Box<
HttpService<
F,
Handler = H,
Request = <F as Framing>::Request,
Response = <F as Framing>::Response,
> + Send
+ 'static,
>,
std::io::Error,
>
where
F: Framing + Send + 'static,
H: MyAwesomeService,
{
Ok(Box::new(
ServiceProcessor::<Http2ProtocolFactory<F>, H>::new(handler),
))
}
fn main() {
build_server(|| |i: i32| make_server(i, MyServiceImpl {}))
}This code compiles in 1.32.0 but not in 1.33.0. Tested locally: |
estebank
added
T-compiler
spastorino
added
I-prioritize
|
Would be nice to find an mcve and to bisect to find the culprit ... @rustbot ping cleanup |
rustbot
added
the
ICEBreaker-Cleanup-Crew
|
Hey Cleanup Crew ICE-breakers! This bug has been identified as a good cc @AminArria @camelid @chrissimpkins @contrun @DutchGhost @elshize @ethanboxx @h-michael @HallerPatrick @hdhoang @hellow554 @imtsuki @kanru @KarlK90 @LeSeulArtichaut @MAdrianMattocks @matheus-consoli @mental32 @nmccarty @Noah-Kennedy @pard68 @PeytonT @pierreN @Redblueflame @RobbieClarken @RobertoSnap @robjtede @SarthakSingh31 @senden9 @shekohex @sinato @spastorino @turboladen @woshilapin @yerke |
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Tagging this one as |
spastorino
added
P-high
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Seems the regression is in nightly-2019-01-06. |
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Not sure, if it is the smallest possible code, but it's pretty darn good trait Service {
type S;
}
trait Framing {
type F;
}
impl Framing for () {
type F = ();
}
trait HttpService<F: Framing>: Service<S = F::F> {}
type BoxService = Box<dyn HttpService<(), S = ()>>;
fn build_server<F: FnOnce() -> BoxService>(_: F) {}
fn make_server<F: Framing>() -> Box<dyn HttpService<F, S = F::F>> {
unimplemented!()
}
fn main() {
build_server(|| make_server())
} |
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Out of those rolled-up PRs, #56837 seems like the strongest candidate for the cause of the regression. |
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@hellow554 thanks! that's a great reduction. ❤️ |
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I'm pretty sure this is caused because of a duplicated rust/src/librustc_middle/ty/relate.rs Lines 260 to 277 in e55d3f9 It seems we could perform a sort&dedup on Edit: ah! We were indeed doing that before #56837. https://github.com/rust-lang/rust/pull/56837/files#diff-af1c8bc6ae3623b749b5aebeaa1e0bffL609-L631 Created #73485 to do a perf run on the naïve approach. If it doesn't cause a massive regression we can merge it and fix this. |
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#73485 would solve this and incur no perf regression, but I noticed that with the following code trait Service {
type S;
}
trait Framing {
type F;
}
impl Framing for () {
type F = ();
}
impl Framing for u32 {
type F = u32;
}
trait HttpService<F: Framing>: Service<S = F::F> {}
type BoxService = Box<dyn HttpService<u32, S = ()>>;
fn build_server<F: FnOnce() -> BoxService>(_: F) {}
fn make_server<F: Framing>() -> Box<dyn HttpService<F, S = F::F>> {
unimplemented!()
}
fn main() {
build_server(|| make_server())
}we don't get any specialized error, we would still be getting what we get now but we should still handle the case of multiple predicates having conflicting obligations with a clearer error. This is a tangentially related problem to the raised case of multiple predicates with the same obligation causing the return of |
lcnr
removed
the
E-needs-mcve
Manishearth
added a commit
to Manishearth/rust
that referenced
this issue
Jun 26, 2020
Perform obligation deduplication to avoid buggy `ExistentialMismatch` Address rust-lang#59326.
estebank
added
A-diagnostics
|
The regression is fixed, but reopening as a diagnostics bug for the case outlined in my previous comment where the obligations diverge. |
|
Triage: no change |
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Apologize that I could not give any code example right now. I'm working on creating one but it seems tricky.
The compiler is complaining about
[E0308]: mismatched typeswhere it said it's expecting for a traitSomeTrait<Apple=SomeApple, Apple=SomeApple, Banana=SomeBanana, Banana=SomeBanana>but gotSomeTrait<Apple=SomeAPple, Banana=SomeBanana>. Only some of the associated types in that trait are repeated once and there are few others are not repeated.The example I gave in #59324 is an intermediate result of my attempt to create a minimal reproducible code to this issue. The type mismatch happened at the
with_factorymethod when resolving concrete type forThriftService.The error happened when I'm doing the update from 1.32.0 to 1.33.0 so it's clearly a regression.
Also, please let me know if you have any suggestion on bypassing this problem or tips on re-creating the problematic code.
Thanks.
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