Refactor tuple constraints

Make tuple constraints be handled by a perfectly ordinary
type class, with the component constraints being the
superclasses:
    class (c1, c2) => (c2, c2)

This change was provoked by

  #10359  inability to re-use a given tuple
          constraint as a whole

  #9858   confusion between term tuples
          and constraint tuples

but it's generally a very nice simplification. We get rid of
 -  In Type, the TuplePred constructor of PredTree,
    and all the code that dealt with TuplePreds
 -  In TcEvidence, the constructors EvTupleMk, EvTupleSel

See Note [How tuples work] in TysWiredIn.

Of course, nothing is ever entirely simple. This one
proved quite fiddly.

- I did quite a bit of renaming, which makes this patch
  touch a lot of modules. In partiuclar tupleCon -> tupleDataCon.

- I made constraint tuples known-key rather than wired-in.
  This is different to boxed/unboxed tuples, but it proved
  awkward to have all the superclass selectors wired-in.
  Easier just to use the standard mechanims.

- While I was fiddling with known-key names, I split the TH Name
  definitions out of DsMeta into a new module THNames.  That meant
  that the known-key names can all be gathered in PrelInfo, without
  causing module loops.

- I found that the parser was parsing an import item like
      T( .. )
  as a *data constructor* T, and then using setRdrNameSpace to
  fix it.  Stupid!  So I changed the parser to parse a *type
  constructor* T, which means less use of setRdrNameSpace.

  I also improved setRdrNameSpace to behave better on Exact Names.
  Largely on priciple; I don't think it matters a lot.

- When compiling a data type declaration for a wired-in thing like
  tuples (,), or lists, we don't really need to look at the
  declaration.  We have the wired-in thing!  And not doing so avoids
  having to line up the uniques for data constructor workers etc.
  See Note [Declarations for wired-in things]

- I found that FunDeps.oclose wasn't taking superclasses into
  account; easily fixed.

- Some error message refactoring for invalid constraints in TcValidity

- Haddock needs to absorb the change too; so there is a submodule update

1 files changed, 17 insertions, 18 deletions

diff --git a/compiler/hsSyn/HsPat.hs b/compiler/hsSyn/HsPat.hs
index 6cde90854d..5d74edf2e0 100644
--- a/compiler/hsSyn/HsPat.hs
+++ b/compiler/hsSyn/HsPat.hs
@@ -302,17 +302,24 @@ pprParendPat p | hsPatNeedsParens p = parens (pprPat p)
                | otherwise          = pprPat p
 
 pprPat :: (OutputableBndr name) => Pat name -> SDoc
-pprPat (VarPat var)       = pprPatBndr var
-pprPat (WildPat _)        = char '_'
-pprPat (LazyPat pat)      = char '~' <> pprParendLPat pat
-pprPat (BangPat pat)      = char '!' <> pprParendLPat pat
-pprPat (AsPat name pat)   = hcat [pprPrefixOcc (unLoc name), char '@', pprParendLPat pat]
-pprPat (ViewPat expr pat _) = hcat [pprLExpr expr, text " -> ", ppr pat]
-pprPat (ParPat pat)         = parens (ppr pat)
+pprPat (VarPat var)           = pprPatBndr var
+pprPat (WildPat _)            = char '_'
+pprPat (LazyPat pat)          = char '~' <> pprParendLPat pat
+pprPat (BangPat pat)          = char '!' <> pprParendLPat pat
+pprPat (AsPat name pat)       = hcat [pprPrefixOcc (unLoc name), char '@', pprParendLPat pat]
+pprPat (ViewPat expr pat _)   = hcat [pprLExpr expr, text " -> ", ppr pat]
+pprPat (ParPat pat)           = parens (ppr pat)
+pprPat (LitPat s)             = ppr s
+pprPat (NPat l Nothing  _)    = ppr l
+pprPat (NPat l (Just _) _)    = char '-' <> ppr l
+pprPat (NPlusKPat n k _ _)    = hcat [ppr n, char '+', ppr k]
+pprPat (SplicePat splice)     = pprSplice splice
+pprPat (CoPat co pat _)       = pprHsWrapper (ppr pat) co
+pprPat (SigPatIn pat ty)      = ppr pat <+> dcolon <+> ppr ty
+pprPat (SigPatOut pat ty)     = ppr pat <+> dcolon <+> ppr ty
 pprPat (ListPat pats _ _)     = brackets (interpp'SP pats)
-pprPat (PArrPat pats _)     = paBrackets (interpp'SP pats)
-pprPat (TuplePat pats bx _) = tupleParens (boxityNormalTupleSort bx) (interpp'SP pats)
-
+pprPat (PArrPat pats _)       = paBrackets (interpp'SP pats)
+pprPat (TuplePat pats bx _)   = tupleParens (boxityTupleSort bx) (pprWithCommas ppr pats)
 pprPat (ConPatIn con details) = pprUserCon (unLoc con) details
 pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
                     pat_binds = binds, pat_args = details })
@@ -325,14 +332,6 @@ pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts,
           <+> pprConArgs details
     else pprUserCon (unLoc con) details
 
-pprPat (LitPat s)           = ppr s
-pprPat (NPat l Nothing  _)  = ppr l
-pprPat (NPat l (Just _) _)  = char '-' <> ppr l
-pprPat (NPlusKPat n k _ _)  = hcat [ppr n, char '+', ppr k]
-pprPat (SplicePat splice)   = pprSplice splice
-pprPat (CoPat co pat _)     = pprHsWrapper (ppr pat) co
-pprPat (SigPatIn pat ty)    = ppr pat <+> dcolon <+> ppr ty
-pprPat (SigPatOut pat ty)   = ppr pat <+> dcolon <+> ppr ty
 
 pprUserCon :: (OutputableBndr con, OutputableBndr id) => con -> HsConPatDetails id -> SDoc
 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> pprInfixOcc c <+> ppr p2