Use of typechecker plugin erroneously triggers "unbound implicit parameter" error

To document this bug, we're going to need a typechecker plugin to test it with. I've built a dummy plugin for this purpose, so we can be sure it is not interference from a particular plugin.

dummy-plugin/dummy-plugin.cabal

name:                dummy-plugin
version:             0.1.0.0
category:            Development
build-type:          Simple
cabal-version:       >=1.10

library
  hs-source-dirs:      .
  exposed-modules:     DummyPlugin
  build-depends:       base, ghc
  default-language:    Haskell2010
  GHC-options:         -Wall -O2

dummy-plugin/DummyPlugin.hs

module DummyPlugin(plugin) where

import TcRnMonad ( TcPlugin(..), TcPluginResult(..) )
import Plugins ( defaultPlugin, Plugin(..), CommandLineOption )

plugin :: Plugin
plugin = defaultPlugin { tcPlugin = Just . thePlugin }

thePlugin :: [CommandLineOption] -> TcPlugin
thePlugin opts = TcPlugin
  { tcPluginInit  = return ()
  , tcPluginSolve = \_ _ _ _ -> return $ TcPluginOk [] []
  , tcPluginStop  = \_ -> return ()
  }

Bug.hs

{-# OPTIONS_GHC -fplugin=DummyPlugin #-}

module Bug where

impossible :: a
impossible = undefined

First, compile the dummy plugin. From its directory, run cabal install to install the plugin.

Then, from the main directory, run ghc Bug.hs.

Expected result: the file compiles. Actual result:

Bug.hs:6:14: error:
    • Unbound implicit parameter ?callStack::GHC.Stack.Types.CallStack
        arising from a use of implicit parameter ‘?callStack’
    • In the expression: undefined
      In an equation for ‘impossible’: impossible = undefined

Further, observe that commenting out the line which invokes the type-checker plugin (the pragma on line 1) causes the file to compile correctly.

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler (Type checker)
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