Introduce Concrete# for representation polymorphism checks

PHASE 1: we never rewrite Concrete# evidence.

This patch migrates all the representation polymorphism checks to
the typechecker, using a new constraint form

  Concrete# :: forall k. k -> TupleRep '[]

Whenever a type `ty` must be representation-polymorphic
(e.g. it is the type of an argument to a function), we emit a new
`Concrete# ty` Wanted constraint. If this constraint goes
unsolved, we report a representation-polymorphism error to the user.
The 'FRROrigin' datatype keeps track of the context of the
representation-polymorphism check, for more informative error messages.

This paves the way for further improvements, such as
allowing type families in RuntimeReps and improving the soundness
of typed Template Haskell. This is left as future work (PHASE 2).

fixes #17907 #20277 #20330 #20423 #20426

updates haddock submodule

-------------------------
Metric Decrease:
    T5642
-------------------------

1 files changed, 4 insertions, 1 deletions

diff --git a/compiler/GHC/HsToCore.hs b/compiler/GHC/HsToCore.hs
index 2824b1fafe..bc87d42a75 100644
--- a/compiler/GHC/HsToCore.hs
+++ b/compiler/GHC/HsToCore.hs
@@ -648,7 +648,7 @@ or (Core)
             (x |> (GRefl :: a ~# (a |> TYPE co1)) ; co2)
 
 It looks like we can write this in Haskell directly, but we can't:
-the reprsentation polymorphism checks defeat us. Note that `x` is a
+the representation polymorphism checks defeat us. Note that `x` is a
 representation-polymorphic variable. So we must wire it in with a
 compulsory unfolding, like other representation-polymorphic primops.
 
@@ -755,10 +755,13 @@ mkUnsafeCoercePrimPair _old_id old_expr
 
              info = noCafIdInfo `setInlinePragInfo` alwaysInlinePragma
                                 `setUnfoldingInfo` mkCompulsoryUnfolding' rhs
+                                `setArityInfo`     arity
 
              ty = mkSpecForAllTys [ runtimeRep1TyVar, runtimeRep2TyVar
                                   , openAlphaTyVar, openBetaTyVar ] $
                   mkVisFunTyMany openAlphaTy openBetaTy
 
+             arity = 1
+
              id   = mkExportedVanillaId unsafeCoercePrimName ty `setIdInfo` info
        ; return (id, old_expr) }