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, 6 insertions, 0 deletions

diff --git a/compiler/GHC/Hs/Extension.hs b/compiler/GHC/Hs/Extension.hs
index 0a43cb8aa6..99b0bbc1ab 100644
--- a/compiler/GHC/Hs/Extension.hs
+++ b/compiler/GHC/Hs/Extension.hs
@@ -32,6 +32,8 @@ import GHC.Types.SrcLoc (GenLocated(..), unLoc)
 import GHC.Utils.Panic
 import GHC.Parser.Annotation
 
+import Data.Void
+
 {-
 Note [IsPass]
 ~~~~~~~~~~~~~
@@ -217,6 +219,10 @@ type OutputableBndrId pass =
   , IsPass pass
   )
 
+-- | See Note [Constructor cannot occur]
+dataConCantHappen :: Void -> a
+dataConCantHappen = absurd
+
 -- useful helper functions:
 pprIfPs :: forall p. IsPass p => (p ~ 'Parsed => SDoc) -> SDoc
 pprIfPs pp = case ghcPass @p of GhcPs -> pp