Summary:
Parsing

    {-# LANGUAGE TupleSections #-}

    baz = (1, "hello", 6.5,,) 'a' (Just ())

Results in the following AST fragment

    (L tests/examples/Tuple.hs:3:7-25
       (ExplicitTuple
          [ L tests/examples/Tuple.hs:3:8
              (Present
                 (L tests/examples/Tuple.hs:3:8
                    (HsOverLit
                       (OverLit
                          (HsIntegral [ '1' ] 1)
                          PlaceHolder
                          (HsLit
                             (HsString
                                []
                                {abstract:FastString}))
                          PlaceHolder))))
          , L tests/examples/Tuple.hs:3:11-17
              (Present
                 (L tests/examples/Tuple.hs:3:11-17
                    (HsLit
                       (HsString
                          [ '"'
                          , 'h'
                          , 'e'
                          , 'l'
                          , 'l'
                          , 'o'
                          , '"'
                          ]
                          {abstract:FastString}))))
          , L tests/examples/Tuple.hs:3:20-22
              (Present
                 (L tests/examples/Tuple.hs:3:20-22
                    (HsOverLit
                       (OverLit
                          (HsFractional
                             (FL
                                [ '6' , '.' , '5' ]
                                (:% 13 2)))
                          PlaceHolder
                          (HsLit
                             (HsString
                                []
                                {abstract:FastString}))
                          PlaceHolder))))
          , L tests/examples/Tuple.hs:3:24
              (Missing PlaceHolder)
          , L tests/examples/Tuple.hs:3:24
              (Missing PlaceHolder)
          ]

The final `Missing PlaceHolder` has a duplicated `SrcSpan`

Test Plan: ./validate

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: thomie, bgamari, mpickering

Differential Revision: https://phabricator.haskell.org/D995

GHC Trac Issues: #10537