bjoernager/rust
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Rollup merge of #81351 - lcnr:big-money-big-prices, r=oli-obk

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combine: stop eagerly evaluating consts

`super_relate_consts` eagerly evaluates constants which doesn't seem too great.

I now also finally understand why all of the unused substs test passed. The reason being
that we just evaluated the constants in `super_relate_consts` 😆

While this change isn't strictly necessary as evaluating consts here doesn't hurt, it still feels a lot cleaner to do it this way

r? `@oli-obk` `@nikomatsakis`
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Dylan DPC 2021-03-27 20:37:04 +01:00 • committed by GitHub
commit 520c9a25df
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14 changed files with 109 additions and 30 deletions
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17
compiler/rustc_middle/src/ty/relate.rs
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@ -33,15 +33,6 @@ pub trait TypeRelation<'tcx>: Sized {
/// relation. Just affects error messages.
fn a_is_expected(&self) -> bool;
/// Whether we should look into the substs of unevaluated constants
/// even if `feature(const_evaluatable_checked)` is active.
///
/// This is needed in `combine` to prevent accidentially creating
/// infinite types as we abuse `TypeRelation` to walk a type there.
fn visit_ct_substs(&self) -> bool {
false
}
fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R
where
F: FnOnce(&mut Self) -> R,
@ -432,9 +423,9 @@ pub fn super_relate_tys<R: TypeRelation<'tcx>>(
let sz_a = sz_a.try_eval_usize(tcx, relation.param_env());
let sz_b = sz_b.try_eval_usize(tcx, relation.param_env());
match (sz_a, sz_b) {
(Some(sz_a_val), Some(sz_b_val)) => Err(TypeError::FixedArraySize(
expected_found(relation, sz_a_val, sz_b_val),
)),
(Some(sz_a_val), Some(sz_b_val)) if sz_a_val != sz_b_val => Err(
TypeError::FixedArraySize(expected_found(relation, sz_a_val, sz_b_val)),
),
_ => Err(err),
}
}
@ -532,7 +523,7 @@ pub fn super_relate_consts<R: TypeRelation<'tcx>>(
}
(ty::ConstKind::Unevaluated(au), ty::ConstKind::Unevaluated(bu))
if tcx.features().const_evaluatable_checked && !relation.visit_ct_substs() =>
if tcx.features().const_evaluatable_checked =>
{
tcx.try_unify_abstract_consts(((au.def, au.substs), (bu.def, bu.substs)))
}