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, 9 insertions, 2 deletions

diff --git a/compiler/GHC/Tc/Gen/Bind.hs b/compiler/GHC/Tc/Gen/Bind.hs
index e540e3db91..93fa9a7e2c 100644
--- a/compiler/GHC/Tc/Gen/Bind.hs
+++ b/compiler/GHC/Tc/Gen/Bind.hs
@@ -34,6 +34,7 @@ import GHC.Data.FastString
 import GHC.Hs
 import GHC.Tc.Errors.Types
 import GHC.Tc.Gen.Sig
+import GHC.Tc.Utils.Concrete ( hasFixedRuntimeRep )
 import GHC.Tc.Utils.Monad
 import GHC.Tc.Types.Origin
 import GHC.Tc.Utils.Env
@@ -519,6 +520,11 @@ tcPolyBinds sig_fn prag_fn rec_group rec_tc closed bind_list
          InferGen mn        -> tcPolyInfer rec_tc prag_fn sig_fn mn bind_list
          CheckGen lbind sig -> tcPolyCheck prag_fn sig lbind
 
+    ; _concrete_evs <-
+        mapM (\ poly_id ->
+          hasFixedRuntimeRep (FRRBinder $ idName poly_id) (idType poly_id))
+          poly_ids
+
     ; traceTc "} End of bindings for" (vcat [ ppr binder_names, ppr rec_group
                                             , vcat [ppr id <+> ppr (idType id) | id <- poly_ids]
                                           ])
@@ -1181,7 +1187,7 @@ tcMonoBinds :: RecFlag  -- Whether the binding is recursive for typechecking pur
             -> [LHsBind GhcRn]
             -> TcM (LHsBinds GhcTc, [MonoBindInfo])
 
--- SPECIAL CASE 1: see Note [Inference for non-recursive function bindings]
+-- SPECIAL CASE 1: see Note [Special case for non-recursive function bindings]
 tcMonoBinds is_rec sig_fn no_gen
            [ L b_loc (FunBind { fun_id = L nm_loc name
                               , fun_matches = matches })]
@@ -1210,7 +1216,7 @@ tcMonoBinds is_rec sig_fn no_gen
                        , mbi_sig       = Nothing
                        , mbi_mono_id   = mono_id }]) }
 
--- SPECIAL CASE 2: see Note [Inference for non-recursive pattern bindings]
+-- SPECIAL CASE 2: see Note [Special case for non-recursive pattern bindings]
 tcMonoBinds is_rec sig_fn no_gen
            [L b_loc (PatBind { pat_lhs = pat, pat_rhs = grhss })]
   | NonRecursive <- is_rec   -- ...binder isn't mentioned in RHS
@@ -1470,6 +1476,7 @@ tcRhs (TcPatBind infos pat' grhss pat_ty)
     do  { traceTc "tcRhs: pat bind" (ppr pat' $$ ppr pat_ty)
         ; grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
                     tcGRHSsPat grhss (mkCheckExpType pat_ty)
+
         ; return ( PatBind { pat_lhs = pat', pat_rhs = grhss'
                            , pat_ext = pat_ty
                            , pat_ticks = ([],[]) } )}