Explicit Specificity

Implementation for Ticket #16393.
Explicit specificity allows users to manually create inferred type variables,
by marking them with braces.
This way, the user determines which variables can be instantiated through
visible type application.

The additional syntax is included in the parser, allowing users to write
braces in type variable binders (type signatures, data constructors etc).
This information is passed along through the renamer and verified in the
type checker.
The AST for type variable binders, data constructors, pattern synonyms,
partial signatures and Template Haskell has been updated to include the
specificity of type variables.

Minor notes:
- Bumps haddock submodule
- Disables pattern match checking in GHC.Iface.Type with GHC 8.8

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/GHC/Tc/Solver.hs b/compiler/GHC/Tc/Solver.hs
index 134b230c06..b1017de024 100644
--- a/compiler/GHC/Tc/Solver.hs
+++ b/compiler/GHC/Tc/Solver.hs
@@ -745,7 +745,7 @@ simplifyInfer rhs_tclvl infer_mode sigs name_taus wanteds
    = do { -- When quantifying, we want to preserve any order of variables as they
           -- appear in partial signatures. cf. decideQuantifiedTyVars
           let psig_tv_tys = [ mkTyVarTy tv | sig <- partial_sigs
-                                          , (_,tv) <- sig_inst_skols sig ]
+                                          , (_,Bndr tv _) <- sig_inst_skols sig ]
               psig_theta  = [ pred | sig <- partial_sigs
                                    , pred <- sig_inst_theta sig ]
 
@@ -1056,7 +1056,7 @@ decideMonoTyVars infer_mode name_taus psigs candidates
 
        -- If possible, we quantify over partial-sig qtvs, so they are
        -- not mono. Need to zonk them because they are meta-tyvar TyVarTvs
-       ; psig_qtvs <- mapM zonkTcTyVarToTyVar $
+       ; psig_qtvs <- mapM zonkTcTyVarToTyVar $ binderVars $
                       concatMap (map snd . sig_inst_skols) psigs
 
        ; psig_theta <- mapM TcM.zonkTcType $
@@ -1222,7 +1222,7 @@ decideQuantifiedTyVars name_taus psigs candidates
              -- See Note [Quantification and partial signatures]
              --     Wrinkles 2 and 3
        ; psig_tv_tys <- mapM TcM.zonkTcTyVar [ tv | sig <- psigs
-                                                  , (_,tv) <- sig_inst_skols sig ]
+                                                  , (_,Bndr tv _) <- sig_inst_skols sig ]
        ; psig_theta <- mapM TcM.zonkTcType [ pred | sig <- psigs
                                                   , pred <- sig_inst_theta sig ]
        ; tau_tys  <- mapM (TcM.zonkTcType . snd) name_taus