src/librustc_traits/normalize_erasing_regions.rs

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use rustc::traits::{Normalized, ObligationCause};
use rustc::traits::query::NoSolution;
use rustc::ty::query::Providers;
use rustc::ty::{self, ParamEnvAnd, Ty, TyCtxt};
use std::sync::atomic::Ordering;

crate fn provide(p: &mut Providers) {
    *p = Providers {
        normalize_ty_after_erasing_regions,
        ..*p
    };
}

fn normalize_ty_after_erasing_regions<'tcx>(
    tcx: TyCtxt<'_, 'tcx, 'tcx>,
    goal: ParamEnvAnd<'tcx, Ty<'tcx>>,
) -> Ty<'tcx> {
    debug!("normalize_ty_after_erasing_regions(goal={:#?})", goal);

    let ParamEnvAnd { param_env, value } = goal;
    tcx.sess.perf_stats.normalize_ty_after_erasing_regions.fetch_add(1, Ordering::Relaxed);
    tcx.infer_ctxt().enter(|infcx| {
        let cause = ObligationCause::dummy();
        match infcx.at(&cause, param_env).normalize(&value) {
            Ok(Normalized {
                value: normalized_value,
                obligations: normalized_obligations,
            }) => {
                // We don't care about the `obligations`; they are
                // always only region relations, and we are about to
                // erase those anyway:
                debug_assert_eq!(
                    normalized_obligations
                        .iter()
                        .find(|p| not_outlives_predicate(&p.predicate)),
                    None,
                );

                let normalized_value = infcx.resolve_type_vars_if_possible(&normalized_value);
                let normalized_value = infcx.tcx.erase_regions(&normalized_value);
                tcx.lift_to_global(&normalized_value).unwrap()
            }
            Err(NoSolution) => bug!("could not fully normalize `{:?}`", value),
        }
    })
}

fn not_outlives_predicate(p: &ty::Predicate<'_>) -> bool {
    match p {
        ty::Predicate::RegionOutlives(..) | ty::Predicate::TypeOutlives(..) => false,
        ty::Predicate::Trait(..)
        | ty::Predicate::Projection(..)
        | ty::Predicate::WellFormed(..)
        | ty::Predicate::ObjectSafe(..)
        | ty::Predicate::ClosureKind(..)
        | ty::Predicate::Subtype(..)
        | ty::Predicate::ConstEvaluatable(..) => true,
    }
}