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const fn: allow use of trait impls from bounds

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This commit is contained in:
Jonas Schievink 2020-11-22 04:19:46 +01:00
parent 71d350e33a
commit e69fcea609
6 changed files with 129 additions and 4 deletions
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40
compiler/rustc_mir/src/transform/check_consts/validation.rs
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@ -4,6 +4,7 @@ use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorReported};
use rustc_hir::def_id::DefId;
use rustc_hir::{self as hir, HirId, LangItem};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::{ImplSource, Obligation, ObligationCause};
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::cast::CastTy;
@ -11,9 +12,10 @@ use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::{
self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt, TypeAndMut,
};
use rustc_middle::ty::{Binder, TraitPredicate, TraitRef};
use rustc_span::{sym, Span, Symbol};
use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
use rustc_trait_selection::traits::{self, TraitEngine};
use rustc_trait_selection::traits::{self, SelectionContext, TraitEngine};
use std::mem;
use std::ops::Deref;
@ -765,9 +767,39 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
}
};
// Resolve a trait method call to its concrete implementation, which may be in a
// `const` trait impl.
if self.tcx.features().const_trait_impl {
// Attempting to call a trait method?
if let Some(trait_id) = tcx.trait_of_item(callee) {
if !self.tcx.features().const_trait_impl {
self.check_op(ops::FnCallNonConst(callee));
return;
}
let trait_ref = TraitRef::from_method(tcx, trait_id, substs);
let obligation = Obligation::new(
ObligationCause::dummy(),
param_env,
Binder::bind(TraitPredicate {
trait_ref: TraitRef::from_method(tcx, trait_id, substs),
}),
);
let implsrc = tcx.infer_ctxt().enter(|infcx| {
let mut selcx = SelectionContext::new(&infcx);
selcx.select(&obligation).unwrap()
});
// If the method is provided via a where-clause that does not use the `?const`
// opt-out, the call is allowed.
if let Some(ImplSource::Param(_, hir::Constness::Const)) = implsrc {
debug!(
"const_trait_impl: provided {:?} via where-clause in {:?}",
trait_ref, param_env
);
return;
}
// Resolve a trait method call to its concrete implementation, which may be in a
// `const` trait impl.
let instance = Instance::resolve(tcx, param_env, callee, substs);
debug!("Resolving ({:?}) -> {:?}", callee, instance);
if let Ok(Some(func)) = instance {