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Ryan Scott authored
Summary: Two places in GHC effectively attempt to //guess// whether a data type was declared using GADT syntax: 1. When reifying a data type in Template Haskell 2. When pretty-printing a data type (e.g., via `:info` in GHCi) But there's no need for heuristics here, since we have a 100% accurate way to determine whether a data type was declared using GADT syntax: the `isGadtSyntaxTyCon` function! By simply using that as the metric, we obtain far more accurate TH reification and pretty-printing results. This is technically a breaking change, since Template Haskell reification will now reify some data type constructors as `(Rec)GadtC` that it didn't before, and some data type constructors that were previously reified as `(Rec)GadtC` will no longer be reified as such. But it's a very understandable breaking change, since the previous behavior was simply incorrect. Test Plan: ./validate Reviewers: simonpj, goldfire, austin, bgamari Reviewed By: simonpj Subscribers: rwbarton, thomie GHC Trac Issues: #14167 Differential Revision: https://phabricator.haskell.org/D3901
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