Panicking typechecker plugins

If I use a typechecker plugin that fails then ghc panics and I'm asked to report a bug with GHC;

ghc: panic! (the 'impossible' happened)
      (GHC version 8.2.2 for x86_64-apple-darwin):
    	Prelude.undefined
    CallStack (from HasCallStack):
      error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
      undefined, called at plugin/Undefined/Solve/Plugin.hs:14:39 in
      undefined-solve-plugin-1.0.0.0-56evBabJYBHHTUlrE3HO5m:Undefined.Solve.Plugin

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

Could we please say that it is the typechecker plugin that is panicking and ask for a bug report for the faulty typechecker, giving the issues URL for the plugin if we know it?

The following undefined plugins fail for init, solve and stop functions.

module Undefined.Init.Plugin (plugin) where

import Plugins (Plugin(..), tcPlugin, defaultPlugin)
import TcRnTypes (TcPluginM, TcPluginResult(..), Ct, TcPlugin(..))
import GHC.TcPluginM.Extra (tracePlugin)

plugin :: Plugin
plugin = defaultPlugin { tcPlugin = const $ Just undefinedPlugin }

undefinedPlugin :: TcPlugin
undefinedPlugin = tracePlugin "undefined-init-plugin" $
    TcPlugin
        { tcPluginInit  = undefined
        , tcPluginSolve = \_ _ _ _ -> return $ TcPluginOk [] []
        , tcPluginStop  = const $ return ()
        }

module Undefined.Solve.Plugin (plugin) where

import Plugins (Plugin(..), tcPlugin, defaultPlugin)
import TcRnTypes (TcPluginM, TcPluginResult, Ct, TcPlugin(..))
import GHC.TcPluginM.Extra (tracePlugin)

plugin :: Plugin
plugin = defaultPlugin { tcPlugin = const $ Just undefinedPlugin }

undefinedPlugin :: TcPlugin
undefinedPlugin = tracePlugin "undefined-solve-plugin" $
    TcPlugin
        { tcPluginInit  = return ()
        , tcPluginSolve = \_ _ _ _ -> undefined
        , tcPluginStop  = const $ return ()
        }

module Undefined.Stop.Plugin (plugin) where

import Plugins (Plugin(..), tcPlugin, defaultPlugin)
import TcRnTypes (TcPluginM, TcPluginResult(..), Ct, TcPlugin(..))
import GHC.TcPluginM.Extra (tracePlugin)

plugin :: Plugin
plugin = defaultPlugin { tcPlugin = const $ Just undefinedPlugin }

undefinedPlugin :: TcPlugin
undefinedPlugin = tracePlugin "undefined-stop-plugin" $
    TcPlugin
        { tcPluginInit  = return ()
        , tcPluginSolve = \_ _ _ _ -> return $ TcPluginOk [] []
        , tcPluginStop  = const $ undefined
        }

Trac metadata

Trac field	Value
Version	8.2.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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