[GHC] #16093: mkPluginUsage: file not found

[GHC]

#16093: mkPluginUsage: file not found
-------------------------------------+-------------------------------------
        Reporter:  lerkok            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by lerkok):

 Some further bad news; this impacts `haddock` as well:

 {{{
 $ haddock --optghc="-package ghc" Test.hs
 Haddock coverage:
 Warning: Package name is not available.
    0% (  0 /  2) in 'TestPlugin'
   Missing documentation for:
     Module header
     plugin (./TestPlugin.hs:5)
 haddock: ^^ Could not load '_TestPlugin_plugin_closure', dependency
 unresolved. See top entry above.
 }}}

 There's a related cabal issue:
 https://github.com/haskell/cabal/issues/888, which suggests adding `{-#
 LANGUAGE TemplateHaskell #-}` to the `Test.hs` program though it should
 not be necessary. But doing so doesn't help either. With this `Test.hs`
 file:

 {{{#!hs
 {-# OPTIONS_GHC -fplugin TestPlugin #-}

 {-# LANGUAGE TemplateHaskell #-}  -- shouldn't be needed, but let's try

 main :: IO ()
 main = return ()
 }}}

 `cabal` now says:

 {{{
 [istanbul]~/qq>haddock --optghc="-package ghc" Test.hs
 Haddock coverage:
 Warning: Package name is not available.
    0% (  0 /  2) in 'TestPlugin'
   Missing documentation for:
     Module header
     plugin (./TestPlugin.hs:5)
 haddock: panic! (the 'impossible' happened)
   (GHC version 8.6.3 for x86_64-apple-darwin):
         mkPluginUsage: file not found

 TestPlugin
 /var/folders/ty/r22vmk1j7kxc60j8f5l3wgzc0000gn/T/.haddock-85267/TestPlugin.o
 Call stack:
     CallStack (from HasCallStack):
       callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
       pprPanic, called at compiler/deSugar/DsUsage.hs:234:15 in
 ghc:DsUsage

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 So, we're back to square one here. Unfortunately, the workaround of "first
 create a .o" file doesn't really work in this context as I don't think
 that's something I can instruct `haddock` to do; much less if it's coming
 from `cabal haddock`.

 Really stumped on how to proceed here.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16093#comment:5>
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