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use rustc version of fulfill_obligation now that we can #314

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Aug 26, 2017
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use rustc version of fulfill_obligation now that we can #314

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86 changes: 3 additions & 83 deletions src/librustc_mir/interpret/eval_context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,10 +10,9 @@ use rustc::traits::Reveal;
use rustc::ty::layout::{self, Layout, Size, Align, HasDataLayout};
use rustc::ty::subst::{Subst, Substs, Kind};
use rustc::ty::{self, Ty, TyCtxt, TypeFoldable, Binder};
use rustc::traits;
use rustc_data_structures::indexed_vec::Idx;
use syntax::codemap::{self, DUMMY_SP, Span};
use syntax::ast::{self, Mutability};
use syntax::codemap::{self, DUMMY_SP};
use syntax::ast::Mutability;
use syntax::abi::Abi;

use super::{EvalError, EvalResult, EvalErrorKind, GlobalId, Lvalue, LvalueExtra, Memory,
Expand Down Expand Up @@ -2312,7 +2311,7 @@ fn resolve_associated_item<'a, 'tcx>(
);

let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
let vtbl = fulfill_obligation(tcx, DUMMY_SP, ty::Binder(trait_ref));
let vtbl = tcx.trans_fulfill_obligation(DUMMY_SP, ty::Binder(trait_ref));

// Now that we know which impl is being used, we can dispatch to
// the actual function:
Expand Down Expand Up @@ -2419,85 +2418,6 @@ fn type_is_sized<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, ty: Ty<'tcx>) -> bool {
ty.is_sized(tcx, ty::ParamEnv::empty(Reveal::All), DUMMY_SP)
}

/// Attempts to resolve an obligation. The result is a shallow vtable resolution -- meaning that we
/// do not (necessarily) resolve all nested obligations on the impl. Note that type check should
/// guarantee to us that all nested obligations *could be* resolved if we wanted to.
fn fulfill_obligation<'a, 'tcx>(
tcx: TyCtxt<'a, 'tcx, 'tcx>,
span: Span,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> traits::Vtable<'tcx, ()> {
// Remove any references to regions; this helps improve caching.
let trait_ref = tcx.erase_regions(&trait_ref);

debug!(
"trans::fulfill_obligation(trait_ref={:?}, def_id={:?})",
trait_ref,
trait_ref.def_id()
);

// Do the initial selection for the obligation. This yields the
// shallow result we are looking for -- that is, what specific impl.
tcx.infer_ctxt().enter(|infcx| {
let mut selcx = traits::SelectionContext::new(&infcx);

let obligation_cause = traits::ObligationCause::misc(span, ast::DUMMY_NODE_ID);
let obligation = traits::Obligation::new(
obligation_cause,
ty::ParamEnv::empty(Reveal::All),
trait_ref.to_poly_trait_predicate(),
);

let selection = match selcx.select(&obligation) {
Ok(Some(selection)) => selection,
Ok(None) => {
// Ambiguity can happen when monomorphizing during trans
// expands to some humongo type that never occurred
// statically -- this humongo type can then overflow,
// leading to an ambiguous result. So report this as an
// overflow bug, since I believe this is the only case
// where ambiguity can result.
debug!(
"Encountered ambiguity selecting `{:?}` during trans, \
presuming due to overflow",
trait_ref
);
tcx.sess.span_fatal(
span,
"reached the recursion limit during monomorphization \
(selection ambiguity)",
);
}
Err(e) => {
span_bug!(
span,
"Encountered error `{:?}` selecting `{:?}` during trans",
e,
trait_ref
)
}
};

debug!("fulfill_obligation: selection={:?}", selection);

// Currently, we use a fulfillment context to completely resolve
// all nested obligations. This is because they can inform the
// inference of the impl's type parameters.
let mut fulfill_cx = traits::FulfillmentContext::new();
let vtable = selection.map(|predicate| {
debug!(
"fulfill_obligation: register_predicate_obligation {:?}",
predicate
);
fulfill_cx.register_predicate_obligation(&infcx, predicate);
});
let vtable = infcx.drain_fulfillment_cx_or_panic(span, &mut fulfill_cx, &vtable);

debug!("Cache miss: {:?} => {:?}", trait_ref, vtable);
vtable
})
}

pub fn resolve_drop_in_place<'a, 'tcx>(
tcx: TyCtxt<'a, 'tcx, 'tcx>,
ty: Ty<'tcx>,
Expand Down