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Make sure to apply "is-open" constraints at the very end of pattern constraining

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Closes #3298
This commit is contained in:
Ayaz Hafiz 2022-07-21 15:47:44 -04:00
parent 613606a67d
commit 13b0ce7ca0
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5 changed files with 85 additions and 62 deletions
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21
crates/compiler/unify/src/unify.rs
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@ -838,26 +838,7 @@ fn unify_structure<M: MetaCollector>(
match other {
FlexVar(_) => {
// If the other is flex, Structure wins!
let outcome = merge(subs, ctx, Structure(*flat_type));
// And if we see a flex variable on the right hand side of a presence
// constraint, we know we need to open up the structure we're trying to unify with.
match (ctx.mode.is_present(), flat_type) {
(true, FlatType::TagUnion(tags, _ext)) => {
let new_ext = subs.fresh_unnamed_flex_var();
let mut new_desc = ctx.first_desc;
new_desc.content = Structure(FlatType::TagUnion(*tags, new_ext));
subs.set(ctx.first, new_desc);
}
(true, FlatType::FunctionOrTagUnion(tn, sym, _ext)) => {
let new_ext = subs.fresh_unnamed_flex_var();
let mut new_desc = ctx.first_desc;
new_desc.content = Structure(FlatType::FunctionOrTagUnion(*tn, *sym, new_ext));
subs.set(ctx.first, new_desc);
}
_ => {}
}
outcome
merge(subs, ctx, Structure(*flat_type))
}
FlexAbleVar(_, ability) => {
// Structure wins