[GHC] #11329: Visible type applications: failing tests with WAY=hpc

[GHC]

#11329: Visible type applications: failing tests with WAY=hpc
-------------------------------------+-------------------------------------
        Reporter:  thomie            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
                                     |  TypeApplications
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  parser/should_compile/VtaParse
                                     |  typecheck/should_compile/Vta1
                                     |  typecheck/should_compile/Vta2
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 So in an expression like `print @Double 3` the type argument is getting a
 tick, so that the ticked expression looks like `tick print (tick @Double)
 (tick 3)`. Then `dsExpr`'s `HsApp` case no longer recognizes the
 construction `tick print (tick @Double)` as a type application, due to the
 second `tick`, and later tries and fails to desugar the argument
 `@Double`.

 One solution would be to look through ticks in `isLHsTypeExpr`, so that
 `dsExpr`'s `HsApp` case would still recognize a type application even if
 there are ticks in it. That would be simple and the type argument is then
 thrown away at that point anyways. But maybe it's better not to introduce
 a tick around a type argument in the first place, since that makes no
 sense.

 `Coverage.addTickHsExpr` has a case
 {{{
 addTickHsExpr e@(HsTypeOut _) = return e
 }}}
 but it doesn't work as intended because `addTickHsExpr` only controls what
 ticks are added to the body of an expression. Whether to add a tick around
 the whole expression is controlled by `addTickLHsExpr` and a number of
 similar functions.

 I'm building a fix that recognizes type applications in `addTickHsExpr`
 and will post it on Phab when ready.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11329#comment:4>
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