Fix Uncovered set of literal patterns

Issues #16289 and #15713 are proof that the pattern match checker did
an unsound job of estimating the value set abstraction corresponding to
the uncovered set.

The reason is that the fix from #11303 introducing `NLit` was
incomplete: The `LitCon` case desugared to `Var` rather than `LitVar`,
which would have done the necessary case splitting analogous to the
`ConVar` case.

This patch rectifies that by introducing the fresh unification variable
in `LitCon` in value abstraction position rather than pattern postition,
recording a constraint equating it to the constructor expression rather
than the literal. Fixes #16289 and #15713.

0 files changed, 0 insertions, 0 deletions