Why does “cabal init” break “ghc-mod check”?

Question

ghc-mod works in a directory with just a haskell source file but if I run "cabal init" in that directory (/tmp/test), I get the following error:

(p1)dave@peach:/tmp/test$ !ghc
ghc-mod check Main.hs 
ghc-mod: /tmp/test/dist/setup-config: hGetContents: invalid argument (invalid byte sequence)

What's going wrong here?

I'm running ghc-mod 5.2.11, and cabal 1.21.1.0, on a 64 bit ubuntu 14.04 computer. the LANG environment variable is set to en_US.UTF-8 ( I saw responses to some other questions that suggest that the LANG setting may be important here ). I tried running cabal version 1.16.0 but it didn't make any difference.

Here's a transcript that shows more detail:

(p1)dave@peach:/tmp/test$ ls -la
total 80
drwxrwxr-x  2 dave dave  4096 Dec  4 07:07 .
drwxrwxrwt 35 root root 69632 Dec  4 07:06 ..
-rw-rw-r--  1 dave dave   143 Dec  4 07:04 Main.hs

(p1)dave@peach:/tmp/test$ set | grep LANG
GDM_LANG=en_US
LANG=en_US.UTF-8
LANGUAGE=en_US

(p1)dave@peach:/tmp/test$ ghc-mod version
ghc-mod version 5.2.1.1 compiled by GHC 7.6.3

(p1)dave@peach:/tmp/test$ cabal -V
cabal-install version 1.21.1.0
using version 1.21.1.0 of the Cabal library 

(p1)dave@peach:/tmp/test$ ghc-mod check Main.hs 
Main.hs:7:1:Warning: Top-level binding with no type signature:  haqify :: [Char] -> [Char]

(p1)dave@peach:/tmp/test$ cabal init
Package name? [default: test] 
Package version? [default: 0.1.0.0] 
Please choose a license:
 * 1) (none)
   2) GPL-2
   3) GPL-3
   4) LGPL-2.1
   5) LGPL-3
   6) AGPL-3
   7) BSD2
   8) BSD3
   9) MIT
  10) ISC
  11) MPL-2.0
  12) Apache-2.0
  13) PublicDomain
  14) AllRightsReserved
  15) Other (specify)
Your choice? [default: (none)] 2
Author name? [default: XXXXXXXXXXXX] 
Maintainer email? [default: XXXXXXXXXXXXXXXXXXXXXX] 
Project homepage URL? 
Project synopsis? 
Project category:
 * 1) (none)
   2) Codec
   3) Concurrency
   4) Control
   5) Data
   6) Database
   7) Development
   8) Distribution
   9) Game
  10) Graphics
  11) Language
  12) Math
  13) Network
  14) Sound
  15) System
  16) Testing
  17) Text
  18) Web
  19) Other (specify)
Your choice? [default: (none)] 
What does the package build:
   1) Library
   2) Executable
Your choice? 2
What is the main module of the executable:
 * 1) Main.hs
   2) Other (specify)
Your choice? [default: Main.hs] 
What base language is the package written in:
 * 1) Haskell2010
   2) Haskell98
   3) Other (specify)
Your choice? [default: Haskell2010] 
Include documentation on what each field means (y/n)? [default: n] 
Source directory:
 * 1) (none)
   2) src
   3) Other (specify)
Your choice? [default: (none)] 

Guessing dependencies...

Generating LICENSE...
Generating Setup.hs...
Generating test.cabal...

Warning: no synopsis given. You should edit the .cabal file and add one.
You may want to edit the .cabal file and add a Description field.

(p1)dave@peach:/tmp/test$ !ghc
ghc-mod check Main.hs 
ghc-mod: /tmp/test/dist/setup-config: hGetContents: invalid argument (invalid byte sequence)
(p1)dave@peach:/tmp/test$

ghc-mod runs cabal configure, so I would capture the output of that command and see if you see anything suspicious. — ErikR
Also, what happens if you run cabal configure before running ghc-mod check ... ? — ErikR
Also check the file dist/setup-config. That's the file ghc-mod reads after running cabal configure — ErikR
cabal configure runs without any problems. dist/setup-config exists and appears to be a binary format - beyond that I don't know how to what to look for in dist/setup-config — Dave Compton
running "cabal configure" didn't affect the original problem. — Dave Compton

Tonn Tonn · Accepted Answer · 2015-01-20T15:26:45

ghc-mod doesn't work with GHC < 7.10 and Cabal-1.22.

If you are still on GHC 7.8.3 or 7.8.4, you may want to hold off on updating cabal or cabal-install.

Why does “cabal init” break “ghc-mod check”?

2 Answers