Refactor type family instance abstract syntax declarations

This implements @simonpj's suggested refactoring of the abstract syntax
for type/data family instances (from
https://ghc.haskell.org/trac/ghc/ticket/14131#comment:9). This combines
the previously separate `TyFamEqn` and `DataFamInstDecl` types into a
single `FamEqn` datatype. This also factors the `HsImplicitBndrs` out of
`HsTyPats` in favor of putting them just outside of `FamEqn` (as opposed
to before, where all of the implicit binders were embedded inside of
`TyFamEqn`/`DataFamInstDecl`). Finally, along the way I noticed that
`dfid_fvs` and `tfid_fvs` were completely unused, so I removed them.

Aside from some changes in parser test output, there is no change in
behavior.

Requires a Haddock submodule commit from my fork (at
https://github.com/RyanGlScott/haddock/commit/815d2deb9c0222c916becccf84
64b740c26255fd)

Test Plan: ./validate

Reviewers: simonpj, austin, goldfire, bgamari, alanz

Reviewed By: bgamari

Subscribers: mpickering, goldfire, rwbarton, thomie, simonpj

GHC Trac Issues: #14131

Differential Revision: https://phabricator.haskell.org/D3881

1 files changed, 20 insertions, 20 deletions

diff --git a/compiler/parser/RdrHsSyn.hs b/compiler/parser/RdrHsSyn.hs
index ecfae760a8..41d8a4a339 100644
--- a/compiler/parser/RdrHsSyn.hs
+++ b/compiler/parser/RdrHsSyn.hs
@@ -159,14 +159,14 @@ mkATDefault :: LTyFamInstDecl GhcPs
 --
 -- We use the Either monad because this also called
 -- from Convert.hs
-mkATDefault (L loc (TyFamInstDecl { tfid_eqn = L _ e }))
-      | TyFamEqn { tfe_tycon = tc, tfe_pats = pats, tfe_fixity = fixity
-                 , tfe_rhs = rhs } <- e
-      = do { tvs <- checkTyVars (text "default") equalsDots tc (hsib_body pats)
-           ; return (L loc (TyFamEqn { tfe_tycon = tc
-                                     , tfe_pats = tvs
-                                     , tfe_fixity = fixity
-                                     , tfe_rhs = rhs })) }
+mkATDefault (L loc (TyFamInstDecl { tfid_eqn = HsIB { hsib_body = e }}))
+      | FamEqn { feqn_tycon = tc, feqn_pats = pats, feqn_fixity = fixity
+               , feqn_rhs = rhs } <- e
+      = do { tvs <- checkTyVars (text "default") equalsDots tc pats
+           ; return (L loc (FamEqn { feqn_tycon  = tc
+                                   , feqn_pats   = tvs
+                                   , feqn_fixity = fixity
+                                   , feqn_rhs    = rhs })) }
 
 mkTyData :: SrcSpan
          -> NewOrData
@@ -221,10 +221,11 @@ mkTyFamInstEqn :: LHsType GhcPs
                -> P (TyFamInstEqn GhcPs,[AddAnn])
 mkTyFamInstEqn lhs rhs
   = do { (tc, tparams, fixity, ann) <- checkTyClHdr False lhs
-       ; return (TyFamEqn { tfe_tycon = tc
-                          , tfe_pats  = mkHsImplicitBndrs tparams
-                          , tfe_fixity = fixity
-                          , tfe_rhs   = rhs },
+       ; return (mkHsImplicitBndrs
+                  (FamEqn { feqn_tycon  = tc
+                          , feqn_pats   = tparams
+                          , feqn_fixity = fixity
+                          , feqn_rhs    = rhs }),
                  ann) }
 
 mkDataFamInst :: SrcSpan
@@ -239,18 +240,17 @@ mkDataFamInst loc new_or_data cType (L _ (mcxt, tycl_hdr)) ksig data_cons maybe_
   = do { (tc, tparams, fixity, ann) <- checkTyClHdr False tycl_hdr
        ; mapM_ (\a -> a loc) ann -- Add any API Annotations to the top SrcSpan
        ; defn <- mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
-       ; return (L loc (DataFamInstD (
-                  DataFamInstDecl { dfid_tycon = tc
-                                  , dfid_pats = mkHsImplicitBndrs tparams
-                                  , dfid_fixity = fixity
-                                  , dfid_defn = defn, dfid_fvs = placeHolderNames }))) }
+       ; return (L loc (DataFamInstD (DataFamInstDecl (mkHsImplicitBndrs
+                  (FamEqn { feqn_tycon = tc
+                          , feqn_pats = tparams
+                          , feqn_fixity = fixity
+                          , feqn_rhs = defn }))))) }
 
 mkTyFamInst :: SrcSpan
-            -> LTyFamInstEqn GhcPs
+            -> TyFamInstEqn GhcPs
             -> P (LInstDecl GhcPs)
 mkTyFamInst loc eqn
-  = return (L loc (TyFamInstD (TyFamInstDecl { tfid_eqn  = eqn
-                                             , tfid_fvs  = placeHolderNames })))
+  = return (L loc (TyFamInstD (TyFamInstDecl eqn)))
 
 mkFamDecl :: SrcSpan
           -> FamilyInfo GhcPs