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Ryan Scott authored
Summary: The validity check which rejected things like: ```lang=haskell type family B x where A x = x ``` Used to live in the typechecker. But it turns out that this validity check was //only// being run on closed type families without CUSKs! This meant that GHC would silently accept something like this: ```lang=haskell type family B (x :: *) :: * where A x = x ``` This patch fixes the issue by moving this validity check to the renamer, where we can be sure that the check will //always// be run. Test Plan: make test TEST=T16002 Reviewers: simonpj, bgamari Reviewed By: simonpj Subscribers: goldfire, rwbarton, carter GHC Trac Issues: #16002 Differential Revision: https://phabricator.haskell.org/D5420
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