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Don't unify real vars when there are no type variables, or nothing changed

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Ayaz Hafiz 2022-04-05 17:51:30 -04:00
parent 163c6b39d6
commit 886e5a0c8f
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3 changed files with 53 additions and 48 deletions
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15
compiler/unify/src/unify.rs
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@ -322,6 +322,8 @@ fn unify_alias(
.into_iter()
.zip(other_args.all_variables().into_iter());
let args_unification_snapshot = subs.snapshot();
for (l, r) in it {
let l_var = subs[l];
let r_var = subs[r];
@ -332,13 +334,12 @@ fn unify_alias(
problems.extend(merge(subs, ctx, *other_content));
}
// NOTE: we need to do this unification because unification of type variables
// may have made them larger, which then needs to be reflected in the `real_var`.
//
// We can skip this if we know type variable unification didn't require
// modification of any variables, but we don't have that kind of information
// yet.
if problems.is_empty() {
let args_unification_had_changes = !subs.vars_since_snapshot(&args_unification_snapshot).is_empty();
subs.commit_snapshot(args_unification_snapshot);
if !args.is_empty() && args_unification_had_changes && problems.is_empty() {
// We need to unify the real vars because unification of type variables
// may have made them larger, which then needs to be reflected in the `real_var`.
problems.extend(unify_pool(subs, pool, real_var, *other_real_var, ctx.mode));
}