1
Fork 0

Rollup merge of #95039 - spastorino:overlap-super-predicates, r=nikomatsakis

Make negative coherence work when there's impl negative on super predicates

r? `@nikomatsakis`
This commit is contained in:
Matthias Krüger 2022-03-18 05:21:55 +01:00 committed by GitHub
commit 588d389dc5
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
6 changed files with 96 additions and 44 deletions

View file

@ -748,6 +748,13 @@ pub struct TraitPredicate<'tcx> {
pub constness: BoundConstness,
/// If polarity is Positive: we are proving that the trait is implemented.
///
/// If polarity is Negative: we are proving that a negative impl of this trait
/// exists. (Note that coherence also checks whether negative impls of supertraits
/// exist via a series of predicates.)
///
/// If polarity is Reserved: that's a bug.
pub polarity: ImplPolarity,
}

View file

@ -17,8 +17,8 @@ use crate::traits::{
use rustc_errors::Diagnostic;
use rustc_hir::def_id::{DefId, LOCAL_CRATE};
use rustc_hir::CRATE_HIR_ID;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::TraitEngine;
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::{util, TraitEngine};
use rustc_middle::traits::specialization_graph::OverlapMode;
use rustc_middle::ty::fast_reject::{self, TreatParams};
use rustc_middle::ty::fold::TypeFoldable;
@ -353,6 +353,8 @@ fn negative_impl<'cx, 'tcx>(
})
}
/// Try to prove that a negative impl exist for the given obligation and their super predicates.
#[instrument(level = "debug", skip(selcx))]
fn negative_impl_exists<'cx, 'tcx>(
selcx: &SelectionContext<'cx, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
@ -360,13 +362,39 @@ fn negative_impl_exists<'cx, 'tcx>(
o: &PredicateObligation<'tcx>,
) -> bool {
let infcx = &selcx.infcx().fork();
if resolve_negative_obligation(infcx, param_env, region_context, o) {
return true;
}
// Try to prove a negative obligation exist for super predicates
for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
if resolve_negative_obligation(infcx, param_env, region_context, &o) {
return true;
}
}
false
}
#[instrument(level = "debug", skip(infcx))]
fn resolve_negative_obligation<'cx, 'tcx>(
infcx: &InferCtxt<'cx, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
region_context: DefId,
o: &PredicateObligation<'tcx>,
) -> bool {
let tcx = infcx.tcx;
o.flip_polarity(tcx)
.map(|o| {
let Some(o) = o.flip_polarity(tcx) else {
return false;
};
let mut fulfillment_cx = FulfillmentContext::new();
fulfillment_cx.register_predicate_obligation(infcx, o);
let errors = fulfillment_cx.select_all_or_error(infcx);
if !errors.is_empty() {
return false;
}
@ -387,15 +415,13 @@ fn negative_impl_exists<'cx, 'tcx>(
param_env,
);
let errors =
infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
let errors = infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
if !errors.is_empty() {
return false;
}
true
})
.unwrap_or(false)
}
pub fn trait_ref_is_knowable<'tcx>(

View file

@ -0,0 +1,12 @@
// check-pass
#![feature(negative_impls)]
#![feature(with_negative_coherence)]
trait A {}
trait B: A {}
impl !A for u32 {}
impl !B for u32 {}
fn main() {}

View file

@ -1,3 +1,5 @@
// check-pass
#![feature(negative_impls)]
#![feature(rustc_attrs)]
#![feature(trait_alias)]
@ -13,7 +15,5 @@ impl !A for u32 {}
trait C {}
impl<T: AB> C for T {}
impl C for u32 {}
//~^ ERROR: conflicting implementations of trait `C` for type `u32` [E0119]
// FIXME this should work, we should implement an `assemble_neg_candidates` fn
fn main() {}

View file

@ -1,11 +0,0 @@
error[E0119]: conflicting implementations of trait `C` for type `u32`
--> $DIR/coherence-overlap-negate-alias-strict.rs:15:1
|
LL | impl<T: AB> C for T {}
| ------------------- first implementation here
LL | impl C for u32 {}
| ^^^^^^^^^^^^^^ conflicting implementation for `u32`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0119`.

View file

@ -0,0 +1,18 @@
// check-pass
#![feature(negative_impls)]
#![feature(rustc_attrs)]
#![feature(with_negative_coherence)]
trait Trait1: Trait2 {}
trait Trait2 {}
struct MyType {}
impl !Trait2 for MyType {}
#[rustc_strict_coherence]
trait Foo {}
impl<T: Trait1> Foo for T {}
impl Foo for MyType {}
fn main() {}