id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
7423	panic on typo in deriving clause	guest		"Consider the following:

data T = T deriving (eq)

Note the misspelled lower-case capital - Eq was intended instead. Rather than reporting a syntax error, GHC panics:

mnykanen@localhost$ ghc -v -dcore-lint extest.hs
Glasgow Haskell Compiler, Version 7.4.1, stage 2 booted by GHC version 7.0.2
Using binary package database: /home/mnykanen/bin/ghc-7.4.1/lib/ghc-7.4.1/package.conf.d/package.cache
Using binary package database: /home/mnykanen/.ghc/x86_64-linux-7.4.1/package.conf.d/package.cache
wired-in package ghc-prim mapped to ghc-prim-0.2.0.0-c2ff696e5b8ec4d4b2bc2e42085fe471
wired-in package integer-gmp mapped to integer-gmp-0.4.0.0-3cccac07aef8e27023f605c1f45bdf74
wired-in package base mapped to base-4.5.0.0-6db966b4cf8c1a91188e66d354ba065e
wired-in package rts mapped to builtin_rts
wired-in package template-haskell mapped to template-haskell-2.7.0.0-133c0fdb189e05de22bd926d39f99fe3
wired-in package dph-seq not found.
wired-in package dph-par not found.
Hsc static flags: -static
*** Chasing dependencies:
Chasing modules from: *extest.hs
Stable obj: []
Stable BCO: []
Ready for upsweep
  [NONREC
      ModSummary {
         ms_hs_date = Sat Nov 17 10:05:25 EET 2012
         ms_mod = main:Main,
         ms_textual_imps = [import (implicit) Prelude]
         ms_srcimps = []
      }]
*** Deleting temp files:
Deleting: 
compile: input file extest.hs
Created temporary directory: /tmp/ghc2802_0
*** Checking old interface for main:Main:
[1 of 1] Compiling Main             ( extest.hs, extest.o )
*** Parser:
*** Renamer/typechecker:
*** Deleting temp files:
Deleting: /tmp/ghc2802_0/ghc2802_0.s
Warning: deleting non-existent /tmp/ghc2802_0/ghc2802_0.s
*** Deleting temp dirs:
Deleting: /tmp/ghc2802_0
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
	nameModule eq{tv a9I}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug"	bug	closed	normal		Compiler	7.4.1	duplicate			Linux	Other	None/Unknown