Introduce `hsExprType :: HsExpr GhcTc -> Type` in the new modulewip/hsExprType

`GHC.Hs.Syn.Type`

The existing `hsPatType`, `hsLPatType` and `hsLitType` functions have also been
moved to this module

This is a less ambitious take on the same problem that !2182 and !3866
attempt to solve. Rather than have the `hsExprType` function attempt to
efficiently compute the `Type` of every subexpression in an `HsExpr`, this
simply computes the overall `Type` of a single `HsExpr`.

- Explicitly forbids the `SplicePat` `HsIPVar`, `HsBracket`, `HsRnBracketOut`
  and `HsTcBracketOut` constructors during the typechecking phase by using
  `Void` as the TTG extension field
- Also introduces `dataConCantHappen` as a domain specific alternative to `absurd`
  to handle cases where the TTG extension points forbid a constructor.
- Turns HIE file generation into a pure function that doesn't need access to the
  `DsM` monad to compute types, but uses `hsExprType` instead.
- Computes a few more types during HIE file generation
- Makes GHCi's `:set +c` command also use `hsExprType` instead of going through
  the desugarer to compute types.

Updates haddock submodule

Co-authored-by: Zubin Duggal <zubin.duggal@gmail.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/docs/users_guide/9.4.1-notes.rst b/docs/users_guide/9.4.1-notes.rst
index 73901ad8be..68417b0a6b 100644
--- a/docs/users_guide/9.4.1-notes.rst
+++ b/docs/users_guide/9.4.1-notes.rst
@@ -40,3 +40,11 @@ Version 9.4.1
 - The ``GHC.Exts.RuntimeRep`` parameter to ``GHC.Exts.raise#`` is now inferred: ::
 
         raise# :: forall (a :: Type) {r :: RuntimeRep} (b :: TYPE r). a -> b
+
+``ghc`` library
+~~~~~~~~~~~~~~~
+
+- A new ``GHC.Hs.Syn.Type`` module has been introduced which defines functions
+  for computing the ``Type`` of an ``HsExpr GhcTc`` in a pure fashion.
+  The ``hsLitType`` and ``hsPatType`` functions that previously lived in
+  ``GHC.Tc.Utils.Zonk`` have been moved to this module.