id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
5971	"Referencing a newName in a VarE without definition triggers ""the impossible happened"""	josh		"Test case:

{{{
{-# LANGUAGE TemplateHaskell #-}
import Language.Haskell.TH

_ = $(newName ""x"" >>= varE)
}}}

Result:

{{{
$ runghc test.hs 
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
	nameModule x_aSd{v}

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

Similar results from ghci:

{{{
$ ghci
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :set -XTemplateHaskell
Prelude> import Language.Haskell.TH
Prelude Language.Haskell.TH> $(newName ""x"" >>= varE)
Loading package array-0.4.0.0 ... linking ... done.
Loading package deepseq-1.3.0.0 ... linking ... done.
Loading package containers-0.4.2.1 ... linking ... done.
Loading package pretty-1.1.1.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
	nameModule x_aSm{v}

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

Note that referencing an undefined name via mkName generates a reasonable error message rather than ""the impossible happened"":

{{{
Prelude Language.Haskell.TH> $(varE $ mkName ""x"")

<interactive>:6:3:
    Not in scope: `x'
    In the result of the splice:
      $(varE $ mkName ""x"")
    To see what the splice expanded to, use -ddump-splices
    In the expression: $(varE $ mkName ""x"")
    In an equation for `it': it = $(varE $ mkName ""x"")
}}}"	bug	closed	normal		Compiler	7.4.1	fixed			Unknown/Multiple	Unknown/Multiple	Compile-time crash	Unknown	th/T5971