cgibbard authored Feb 22, 2021 and Marge Bot committed Mar 04, 2021

Commit 2a942285

 dramatically simplified the implementation and improved
the performance of COMPLETE sets while making them applicable in more
scenarios at the same time.
But it turned out that there was a change in semantics that (to me
unexpectedly) broke users' expectations (see #14422): They relied on the
"type signature" of a COMPLETE pragma to restrict the scrutinee types of
a pattern match for which they are applicable.

This patch brings back that filtering, so the semantics is the same as
it was in GHC 9.0.
See the updated Note [Implementation of COMPLETE pragmas].

There are a few testsuite output changes (`completesig13`, `T14422`)
which assert this change.

Co-authored-by: Sebastian Graf <sebastian.graf@kit.edu>