Fix #13363wip/T13363

The pattern match checker doesn't handle pattern synonyms (yet); it
just regards them as additional data constructors. But that's wrong
from the perspective of redudancy checking: A match on a pattern synonym
will always lead to an overlap warning, because the mismatch case in
`ConCon` will always return `NotCovered`, which is unsound.

The proper conservative approximation is to return `Covered` whenever we
mismatched against a pattern synonym.

0 files changed, 0 insertions, 0 deletions