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Do not adjust rank of lambda sets under alias arguments

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Ayaz Hafiz 2023-03-25 15:21:40 -05:00
parent f7455deb06
commit f37ede036a
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1 changed files with 17 additions and 1 deletions
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18
crates/compiler/solve/src/solve.rs
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@ -3918,7 +3918,23 @@ fn adjust_rank_content(
Alias(_, args, real_var, _) => {
let mut rank = Rank::toplevel();
for var_index in args.all_variables() {
// Avoid visiting lambda set variables stored in the type variables of the alias
// independently.
//
// Why? Lambda set variables on the alias are not truly type arguments to the alias,
// and instead are links to the lambda sets that appear in functions under the real
// type of the alias. If their ranks are adjusted independently, we end up looking at
// function types "inside-out" - when the whole point of rank-adjustment is to look
// from the outside-in to determine at what rank a type lies!
//
// So, just wait to adjust their ranks until we visit the function types that contain
// them. If they should be generalized (or pulled to a lower rank) that will happen
// then; otherwise, we risk generalizing a lambda set too early, when its enclosing
// function type should not be.
let adjustable_variables =
(args.type_variables().into_iter()).chain(args.infer_ext_in_output_variables());
for var_index in adjustable_variables {
let var = subs[var_index];
rank = rank.max(adjust_rank(subs, young_mark, visit_mark, group_rank, var));
}