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improve tag union errors

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This commit is contained in:
Folkert 2020-04-06 21:40:28 +02:00
parent 3f4346f573
commit 67f8f2e943
4 changed files with 222 additions and 24 deletions
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20
compiler/unify/src/unify.rs
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@ -457,16 +457,36 @@ fn unify_tag_union(
let sub1 = fresh(subs, pool, ctx, Structure(flat_type1));
let sub2 = fresh(subs, pool, ctx, Structure(flat_type2));
// NOTE: for clearer error messages, we rollback unification of the ext vars when either fails
//
// This is inspired by
//
//
// f : [ Red, Green ] -> Bool
// f = \_ -> True
//
// f Blue
//
// In this case, we want the mismatch to be between `[ Blue ]a` and `[ Red, Green ]`, but
// without rolling back, the mismatch is between `[ Blue, Red, Green ]a` and `[ Red, Green ]`.
// TODO is this also required for the other cases?
let snapshot = subs.snapshot();
let ext1_problems = unify_pool(subs, pool, rec1.ext, sub2);
if !ext1_problems.is_empty() {
subs.rollback_to(snapshot);
return ext1_problems;
}
let ext2_problems = unify_pool(subs, pool, sub1, rec2.ext);
if !ext2_problems.is_empty() {
subs.rollback_to(snapshot);
return ext2_problems;
}
subs.commit_snapshot(snapshot);
let mut tag_problems =
unify_shared_tags(subs, pool, ctx, shared_tags, other_tags, ext, recursion_var);