src/librustc_traits/normalize_projection_ty.rs

use rustc::infer::canonical::{Canonical, QueryResponse};
use rustc::traits::query::{normalize::NormalizationResult, CanonicalProjectionGoal, NoSolution};
use rustc::traits::{self, ObligationCause, SelectionContext, TraitEngineExt};
use rustc::ty::query::Providers;
use rustc::ty::{ParamEnvAnd, TyCtxt};
use rustc_hir as hir;
use rustc_span::DUMMY_SP;
use std::sync::atomic::Ordering;

crate fn provide(p: &mut Providers<'_>) {
    *p = Providers { normalize_projection_ty, ..*p };
}

fn normalize_projection_ty<'tcx>(
    tcx: TyCtxt<'tcx>,
    goal: CanonicalProjectionGoal<'tcx>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, NormalizationResult<'tcx>>>, NoSolution> {
    debug!("normalize_provider(goal={:#?})", goal);

    tcx.sess.perf_stats.normalize_projection_ty.fetch_add(1, Ordering::Relaxed);
    tcx.infer_ctxt().enter_canonical_trait_query(
        &goal,
        |infcx, fulfill_cx, ParamEnvAnd { param_env, value: goal }| {
            let selcx = &mut SelectionContext::new(infcx);
            let cause = ObligationCause::misc(DUMMY_SP, hir::DUMMY_HIR_ID);
            let mut obligations = vec![];
            let answer = traits::normalize_projection_type(
                selcx,
                param_env,
                goal,
                cause,
                0,
                &mut obligations,
            );
            fulfill_cx.register_predicate_obligations(infcx, obligations);
            Ok(NormalizationResult { normalized_ty: answer })
        },
    )
}