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Rollup merge of #81309 - lcnr:lazy-norm-err-msgh, r=nikomatsakis

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always eagerly eval consts in Relate

r? ```@nikomatsakis``` cc ```@varkor```
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Dylan DPC 2021-03-10 17:55:37 +01:00 • committed by GitHub
commit 49bf48a33d
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4 changed files with 11 additions and 7 deletions
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8
compiler/rustc_middle/src/ty/relate.rs
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@ -421,12 +421,14 @@ pub fn super_relate_tys<R: TypeRelation<'tcx>>(
let t = relation.relate(a_t, b_t)?;
match relation.relate(sz_a, sz_b) {
Ok(sz) => Ok(tcx.mk_ty(ty::Array(t, sz))),
// FIXME(#72219) Implement improved diagnostics for mismatched array
// length?
Err(err) if relation.tcx().lazy_normalization() => Err(err),
Err(err) => {
// Check whether the lengths are both concrete/known values,
// but are unequal, for better diagnostics.
//
// It might seem dubious to eagerly evaluate these constants here,
// we however cannot end up with errors in `Relate` during both
// `type_of` and `predicates_of`. This means that evaluating the
// constants should not cause cycle errors here.
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) {