• Ryan Scott's avatar
    Merge types and kinds in DsMeta · b3b564fb
    Ryan Scott authored
    Summary:
    Types and kinds are now the same in GHC... well, except in the code
    that involves Template Haskell, where types and kinds are given separate
    treatment. This aims to unify that treatment in the `DsMeta` module.
    
    The gist of this patch is replacing all uses of `repLKind` with `repLTy`.
    This is isn't quite as simple as one might imagine, since `repLTy` returns a
    `Core (Q Type)` (a monadic expression), whereas `repLKind` returns a
    `Core Kind` (a pure expression). This causes many awkward impedance mismatches.
    
    One option would be to change every combinator in `Language.Haskell.TH.Lib` to
    take `KindQ` as an argument instead of `Kind`. But this would be a breaking
    change of colossal proportions.
    
    Instead, this patch takes a somewhat different approach. This migrates the
    existing `Language.Haskell.TH.Lib` module to
    `Language.Haskell.TH.Lib.Internal`, and changes all `Kind`-related combinators
    in `Language.Haskell.TH.Lib.Internal` to live in `Q`. The new
    `Language.Haskell.TH.Lib` module then re-exports most of
    `Language.Haskell.TH.Lib.Internal` with the exception of the `Kind`-related
    combinators, for which it redefines them to be their current definitions (which
    don't live in `Q`). This allows us to retain backwards compatibility with
    previous `template-haskell` releases, but more importantly, it allows GHC to
    make as many changes to the `Internal` code as it wants for its purposes
    without fear of disrupting the public API.
    
    This solves half of #11785 (the other half being `TcSplice`).
    
    Test Plan: ./validate
    
    Reviewers: goldfire, austin, bgamari
    
    Reviewed By: goldfire
    
    Subscribers: rwbarton, thomie
    
    GHC Trac Issues: #11785
    
    Differential Revision: https://phabricator.haskell.org/D3751
    b3b564fb
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