Caret diagnostics for GADT constructor error message don't span the whole constructor

Inspecting the caret diagnostics in the error message for this program:

{-# LANGUAGE GADTs #-}
module Bug where

data Foo1 where
  MkFoo1 :: Bool

newtype Foo2 where
  MkFoo2 :: Foo2

$ /opt/ghc/8.2.2/bin/ghc Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

Bug.hs:5:3: error:
    • Data constructor ‘MkFoo1’ returns type ‘Bool’
        instead of an instance of its parent type ‘Foo1’
    • In the definition of data constructor ‘MkFoo1’
      In the data type declaration for ‘Foo1’
  |
5 |   MkFoo1 :: Bool
  |   ^

Bug.hs:8:3: error:
    • The constructor of a newtype must have exactly one field
        but ‘MkFoo2’ has none
    • In the definition of data constructor ‘MkFoo2’
      In the newtype declaration for ‘Foo2’
  |
8 |   MkFoo2 :: Foo2
  |   ^

We notice something fishy: the carets don't span the entirey of the constructor! Contrast this with the carets for the error message in this program:

{-# LANGUAGE GADTs #-}
module Bug where

data Foo where
  MkFoo, MkFoo :: Foo

$ /opt/ghc/8.2.2/bin/ghc Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

Bug.hs:5:3: error:
    Multiple declarations of ‘MkFoo’
    Declared at: Bug.hs:5:3
                 Bug.hs:5:3
  |
5 |   MkFoo, MkFoo :: Foo
  |   ^^^^^^^^^^^^^^^^^^^

Where the carets span everything that is relevant.

I know what is causing this: patch incoming.

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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