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

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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
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GPG key ID: 4AEE18F83AFDEB23
6 changed files with 96 additions and 44 deletions
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88
compiler/rustc_trait_selection/src/traits/coherence.rs
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@ -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>,
@ -360,42 +362,66 @@ 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 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;
}
let Some(o) = o.flip_polarity(tcx) else {
return false;
};
let mut outlives_env = OutlivesEnvironment::new(param_env);
// FIXME -- add "assumed to be well formed" types into the `outlives_env`
let mut fulfillment_cx = FulfillmentContext::new();
fulfillment_cx.register_predicate_obligation(infcx, o);
// "Save" the accumulated implied bounds into the outlives environment
// (due to the FIXME above, there aren't any, but this step is still needed).
// The "body id" is given as `CRATE_HIR_ID`, which is the same body-id used
// by the "dummy" causes elsewhere (body-id is only relevant when checking
// function bodies with closures).
outlives_env.save_implied_bounds(CRATE_HIR_ID);
let errors = fulfillment_cx.select_all_or_error(infcx);
infcx.process_registered_region_obligations(
outlives_env.region_bound_pairs_map(),
Some(tcx.lifetimes.re_root_empty),
param_env,
);
if !errors.is_empty() {
return false;
}
let errors =
infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
if !errors.is_empty() {
return false;
}
let mut outlives_env = OutlivesEnvironment::new(param_env);
// FIXME -- add "assumed to be well formed" types into the `outlives_env`
true
})
.unwrap_or(false)
// "Save" the accumulated implied bounds into the outlives environment
// (due to the FIXME above, there aren't any, but this step is still needed).
// The "body id" is given as `CRATE_HIR_ID`, which is the same body-id used
// by the "dummy" causes elsewhere (body-id is only relevant when checking
// function bodies with closures).
outlives_env.save_implied_bounds(CRATE_HIR_ID);
infcx.process_registered_region_obligations(
outlives_env.region_bound_pairs_map(),
Some(tcx.lifetimes.re_root_empty),
param_env,
);
let errors = infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
if !errors.is_empty() {
return false;
}
true
}
pub fn trait_ref_is_knowable<'tcx>(