Check for large tuples more thoroughlywip/T18723

This fixes #18723 by:

* Moving the existing `GHC.Tc.Gen.HsType.bigConstraintTuple` validity
  check to `GHC.Rename.Utils.checkCTupSize` for consistency with
  `GHC.Rename.Utils.checkTupSize`, and
* Using `check(C)TupSize` when checking tuple _types_, in addition
  to checking names, expressions, and patterns.

Note that I put as many of these checks as possible in the typechecker so
that GHC can properly distinguish between boxed and constraint tuples. The
exception to this rule is checking names, which I perform in the renamer
(in `GHC.Rename.Env`) so that we can rule out `(,, ... ,,)` and
`''(,, ... ,,)` alike in one fell swoop.

While I was in town, I also removed the `HsConstraintTuple` and
`HsBoxedTuple` constructors of `HsTupleSort`, which are functionally
unused. This requires a `haddock` submodule bump.

1 files changed, 5 insertions, 8 deletions

diff --git a/compiler/GHC/Hs/Type.hs b/compiler/GHC/Hs/Type.hs
index a193eefa12..ed3b20a0ec 100644
--- a/compiler/GHC/Hs/Type.hs
+++ b/compiler/GHC/Hs/Type.hs
@@ -1060,20 +1060,19 @@ namely HsTupleTy, but keep track of the tuple kind (in the first argument to
 HsTupleTy, a HsTupleSort). We can tell if a tuple is unboxed while parsing,
 because of the #. However, with -XConstraintKinds we can only distinguish
 between constraint and boxed tuples during type checking, in general. Hence the
-four constructors of HsTupleSort:
+two constructors of HsTupleSort:
 
         HsUnboxedTuple                  -> Produced by the parser
-        HsBoxedTuple                    -> Certainly a boxed tuple
-        HsConstraintTuple               -> Certainly a constraint tuple
         HsBoxedOrConstraintTuple        -> Could be a boxed or a constraint
                                         tuple. Produced by the parser only,
                                         disappears after type checking
+
+After typechecking, we use TupleSort (which clearly distinguishes between
+constraint tuples and boxed tuples) rather than HsTupleSort.
 -}
 
 -- | Haskell Tuple Sort
 data HsTupleSort = HsUnboxedTuple
-                 | HsBoxedTuple
-                 | HsConstraintTuple
                  | HsBoxedOrConstraintTuple
                  deriving Data
 
@@ -1988,11 +1987,9 @@ hsTypeNeedsParens p = go_hs_ty
     -- Special-case unary boxed tuple applications so that they are
     -- parenthesized as `Identity (Solo x)`, not `Identity Solo x` (#18612)
     -- See Note [One-tuples] in GHC.Builtin.Types
-    go_hs_ty (HsTupleTy _ con [L _ ty])
+    go_hs_ty (HsTupleTy _ con [_])
       = case con of
-          HsBoxedTuple               -> p >= appPrec
           HsBoxedOrConstraintTuple   -> p >= appPrec
-          HsConstraintTuple          -> go_hs_ty ty
           HsUnboxedTuple             -> False
     go_hs_ty (HsTupleTy{})            = False
     go_hs_ty (HsSumTy{})              = False