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Auto merge of #86700 - lqd:matthews-nll-hrtb-errors, r=nikomatsakis

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Matthew's work on improving NLL's "higher-ranked subtype error"s

This PR rebases `@matthewjasper's` [branch](https://github.com/matthewjasper/rust/tree/nll-hrtb-errors) which has great work to fix the obscure higher-ranked subtype errors that are tracked in #57374.

These are a blocker to turning full NLLs on, and doing some internal cleanups to remove some of the old region code.

The goal is so `@nikomatsakis` can take a look at this early, and I'll then do my best to help do the changes and followup work to land this work, and move closer to turning off the migration mode.

I've only updated the branch and made it compile, removed a warning or two.

r? `@nikomatsakis`

(Here's the [zulip topic to discuss this](https://rust-lang.zulipchat.com/#narrow/stream/122657-t-compiler.2Fwg-nll/topic/.2357374.3A.20improving.20higher-ranked.20subtype.20errors.20via.20.2386700) that Niko wanted)
This commit is contained in:
bors 2021-08-18 15:54:59 +00:00
commit 3d0774d0dc
63 changed files with 1043 additions and 345 deletions
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2
compiler/rustc_traits/src/lib.rs
View file

@ -19,6 +19,8 @@ mod normalize_erasing_regions;
mod normalize_projection_ty;
mod type_op;
pub use type_op::type_op_prove_predicate_with_span;
use rustc_middle::ty::query::Providers;
pub fn provide(p: &mut Providers) {

26
compiler/rustc_traits/src/type_op.rs
View file

@ -8,7 +8,7 @@ use rustc_middle::ty::query::Providers;
use rustc_middle::ty::subst::{GenericArg, Subst, UserSelfTy, UserSubsts};
use rustc_middle::ty::{self, FnSig, Lift, PolyFnSig, Ty, TyCtxt, TypeFoldable, Variance};
use rustc_middle::ty::{ParamEnv, ParamEnvAnd, Predicate, ToPredicate};
use rustc_span::DUMMY_SP;
use rustc_span::{Span, DUMMY_SP};
use rustc_trait_selection::infer::InferCtxtBuilderExt;
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::query::normalize::AtExt;
@ -236,11 +236,25 @@ fn type_op_prove_predicate<'tcx>(
canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, ProvePredicate<'tcx>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |infcx, fulfill_cx, key| {
let (param_env, ProvePredicate { predicate }) = key.into_parts();
fulfill_cx.register_predicate_obligation(
infcx,
Obligation::new(ObligationCause::dummy(), param_env, predicate),
);
type_op_prove_predicate_with_span(infcx, fulfill_cx, key, None);
Ok(())
})
}
/// The core of the `type_op_prove_predicate` query: for diagnostics purposes in NLL HRTB errors,
/// this query can be re-run to better track the span of the obligation cause, and improve the error
/// message. Do not call directly unless you're in that very specific context.
pub fn type_op_prove_predicate_with_span<'a, 'tcx: 'a>(
infcx: &'a InferCtxt<'a, 'tcx>,
fulfill_cx: &'a mut dyn TraitEngine<'tcx>,
key: ParamEnvAnd<'tcx, ProvePredicate<'tcx>>,
span: Option<Span>,
) {
let cause = if let Some(span) = span {
ObligationCause::dummy_with_span(span)
} else {
ObligationCause::dummy()
};
let (param_env, ProvePredicate { predicate }) = key.into_parts();
fulfill_cx.register_predicate_obligation(infcx, Obligation::new(cause, param_env, predicate));
}