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Warn on the presence of unnecessary wildcards in output positions

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Ayaz Hafiz 2022-10-26 10:49:19 -05:00
parent d55dbbf0ae
commit cfe7c8e5ef
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17 changed files with 151 additions and 106 deletions
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13
crates/compiler/can/src/annotation.rs
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@ -334,7 +334,7 @@ pub(crate) fn canonicalize_annotation(
}
}
#[derive(Clone, Copy)]
#[derive(Clone, Copy, PartialEq, Eq)]
enum CanPolarity {
/// Polarity should be disregarded for now; relevant in aliaes + opaques.
Disregard,
@ -1081,6 +1081,17 @@ fn can_extension_type<'a>(
references,
);
if valid_extension_type(shallow_dealias_with_scope(scope, &ext_type)) {
if matches!(loc_ann.extract_spaces().item, TypeAnnotation::Wildcard)
&& matches!(ext_problem_kind, ExtensionTypeKind::TagUnion)
&& pol == CanPolarity::Pos
{
// Wildcards are redundant in positive positions, since they will always be
// inferred as necessary there!
env.problem(roc_problem::can::Problem::UnnecessaryOutputWildcard {
region: loc_ann.region,
})
}
ext_type
} else {
// Report an error but mark the extension variable to be inferred