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Deal with destructuring tag unions behind opaques correctly

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Closes #2702
This commit is contained in:
ayazhafiz 2022-03-13 17:40:16 -05:00
parent ceb69ace4d
commit 5670fe06cd
3 changed files with 79 additions and 8 deletions
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22
compiler/constrain/src/pattern.rs
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@ -504,12 +504,22 @@ pub fn constrain_pattern(
);
// Link the entire wrapped opaque type (with the now-constrained argument) to the type
// variables of the opaque type
// TODO: better expectation here
let link_type_variables_con = constraints.equal_types(
(**specialized_def_type).clone(),
Expected::NoExpectation(arg_pattern_type),
Category::OpaqueWrap(*opaque),
// variables of the opaque type.
//
// For example, suppose we have `O k := [ A k, B k ]`, and the pattern `@O (A s) -> s == ""`.
// Previous constraints will have solved `typeof s ~ Str`, and we have the
// `specialized_def_type` being `[ A k1, B k1 ]`, specializing `k` as `k1` for this opaque
// usage.
// We now want to link `typeof s ~ k1`, so to capture this relationship, we link
// the type of `A s` (the arg type) to `[ A k1, B k1 ]` (the specialized opaque type).
//
// This must **always** be a presence constraint, that is enforcing
// `[ A k1, B k1 ] += typeof (A s)`, because we are in a destructure position and not
// all constructors are covered in this branch!
let link_type_variables_con = constraints.pattern_presence(
arg_pattern_type,
PExpected::NoExpectation((**specialized_def_type).clone()),
PatternCategory::Opaque(*opaque),
loc_arg_pattern.region,
);