hpc ignores files containing LINES pragmas that refer to .hsc files

[dons]

ghc -hpc generates no ticks for files containing LINE pragmas that point back to .hsc files. Removing the LINE pragmas, and ticks are generated.

An example. This simple .hsc file:

main = print "hello, world"

Generates this A.hs file:

{-# LINE 1 "A.hsc" #-}
main = print "hello, world"
{-# LINE 2 "A.hsc" #-}

Compiling this with -fhpc, we see no ticks produced:

{ AbsBinds [] [] [Main.main <= [] main_aif]

    Main.main :: GHC.IOBase.IO ()
    []
    { print_aie = System.IO.print @ [GHC.Base.Char] $dShow_ail
      main_aif = print_aie "hello, world" }
  :Main.main = GHC.TopHandler.runMainIO @ () Main.main
  $dShow_ail = GHC.Show.$f21 @ GHC.Base.Char $dShow_aiW
  $dShow_aiW = GHC.Show.$f18 }

Run this, and get the hpc report:

$ ./a.out 
"hello, world"

$ hpc report a.out.tix 
100% expressions used (0/0)
100% boolean coverage (0/0)

0/0 declarations.

However, an identical file, without LINE pragmas, goes through just fine:

$ ghc -fhpc B.hs -ddump-hpc 
{ AbsBinds [] [] [Main.main <= [] main_aif]
    Main.main :: GHC.IOBase.IO ()
    []
    { print_aie = System.IO.print @ [GHC.Base.Char] $dShow_ail
      -- tick id = (2, [])
      main_aif = tick<1>(print_aie (tick<0>("got you"))) }
  :Main.main = GHC.TopHandler.runMainIO @ () Main.main
  $dShow_ail = GHC.Show.$f21 @ GHC.Base.Char $dShow_aiW
  $dShow_aiW = GHC.Show.$f18 }

And the result has valid hpc .tix

$ hpc report a.out.tix 
100% expressions used (2/2)
100% boolean coverage (0/0)

[igloo]

This sounds like it should be trivial to fix, so let's aim to do so for 6.8.3.

[AndyGill]

It is not quite that easy, because the Span info has been messed up. Typically this just effects the error messages, but here the info *has* to be correct for hpc to work.

[igloo]

Hmm; you can generate the ticks and report percentages at least, I'd have thought? While this isn't ideal, it's better than nothing.