Template Haskell: unboxedTupleTypeName doesn't handle unboxed 0- and 1-tuples

GHC has a notion of unboxed 0-tuples and 1-tuples:

λ> :set -XUnboxedTuples
λ> :k (##)
(##) :: TYPE 'GHC.Types.VoidRep
λ> :k (# Int #)
(# Int #) :: TYPE 'GHC.Types.UnboxedTupleRep

But it is impossible to acquire the Names of these type constructors using unboxedTupleTypeName from template-haskell:

λ> :set -XTemplateHaskell
λ> :m + Language.Haskell.TH Language.Haskell.TH.Syntax 
λ> :k $(conT (unboxedTupleTypeName 0))

<interactive>:1:1: error:
    • Exception when trying to run compile-time code:
        unboxedTupleTypeName 0
CallStack (from HasCallStack):
  error, called at libraries/template-haskell/Language/Haskell/TH/Syntax.hs:1179:26 in template-haskell:Language.Haskell.TH.Syntax
      Code: conT (unboxedTupleTypeName 0)
    • In the untyped splice: $(conT (unboxedTupleTypeName 0))
λ> :k $(conT (unboxedTupleTypeName 1))

<interactive>:1:1: error:
    • Exception when trying to run compile-time code:
        unboxedTupleTypeName 1
CallStack (from HasCallStack):
  error, called at libraries/template-haskell/Language/Haskell/TH/Syntax.hs:1180:26 in template-haskell:Language.Haskell.TH.Syntax
      Code: conT (unboxedTupleTypeName 1)
    • In the untyped splice: $(conT (unboxedTupleTypeName 1))

And similarly for unboxedTupleDataName.

This is because of silly restrictions put in place on the definitions of unboxedTupleTypeName and unboxedTupleDataName within template-haskell:

-- Unboxed tuple data and type constructors
-- | Unboxed tuple data constructor
unboxedTupleDataName :: Int -> Name
-- | Unboxed tuple type constructor
unboxedTupleTypeName :: Int -> Name

unboxedTupleDataName 0 = error "unboxedTupleDataName 0"
unboxedTupleDataName 1 = error "unboxedTupleDataName 1"
unboxedTupleDataName n = mk_unboxed_tup_name (n-1) DataName

unboxedTupleTypeName 0 = error "unboxedTupleTypeName 0"
unboxedTupleTypeName 1 = error "unboxedTupleTypeName 1"
unboxedTupleTypeName n = mk_unboxed_tup_name (n-1) TcClsName

It should be possible to lift this restriction. I'll work on this.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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