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Mark tag unions to recursive when they become so during unification

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See the comment on line 811 of unify.rs in this commit for motivation
and justification.

Closes #2217
This commit is contained in:
ayazhafiz 2021-12-22 17:51:07 -06:00
parent 78a247e6f2
commit 88888b0854
4 changed files with 101 additions and 36 deletions
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37
compiler/solve/src/solve.rs
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@ -1227,44 +1227,11 @@ fn check_for_infinite_type(
while let Err((recursive, _chain)) = subs.occurs(var) {
let description = subs.get(recursive);
let content = description.content;
// try to make a tag union recursive, see if that helps
match content {
match description.content {
Content::Structure(FlatType::TagUnion(tags, ext_var)) => {
let rec_var = subs.fresh_unnamed_flex_var();
subs.set_rank(rec_var, description.rank);
subs.set_content(
rec_var,
Content::RecursionVar {
opt_name: None,
structure: recursive,
},
);
let new_variable_slices = SubsSlice::reserve_variable_slices(subs, tags.len());
let it = new_variable_slices.indices().zip(tags.iter_all());
for (variable_slice_index, (_, slice_index)) in it {
let slice = subs[slice_index];
let new_variables = VariableSubsSlice::reserve_into_subs(subs, slice.len());
for (target_index, var_index) in new_variables.indices().zip(slice) {
let var = subs[var_index];
subs.variables[target_index] =
subs.explicit_substitute(recursive, rec_var, var);
}
subs.variable_slices[variable_slice_index] = new_variables;
}
let new_ext_var = subs.explicit_substitute(recursive, rec_var, ext_var);
let new_tags = UnionTags::from_slices(tags.tag_names(), new_variable_slices);
let flat_type = FlatType::RecursiveTagUnion(rec_var, new_tags, new_ext_var);
subs.set_content(recursive, Content::Structure(flat_type));
subs.mark_tag_union_recursive(recursive, tags, ext_var);
}
_other => circular_error(subs, problems, symbol, &loc_var),