Linker failure: multiple definition of

Linker fails on a normal project built with cabal (-O1), both on my home machine (GNU gold (GNU Binutils for Ubuntu 2.22) 1.11) and on travis with GHC 8.0.1:

https://travis-ci.org/LambdaHack/LambdaHack/jobs/159457149#L589

and with head:

https://travis-ci.org/LambdaHack/LambdaHack/jobs/159457156#L602

It compiles fine with -O0 (but if fails with -O2):

https://travis-ci.org/LambdaHack/LambdaHack/jobs/159457144

with older GHCs:

https://travis-ci.org/LambdaHack/LambdaHack/jobs/159457155

and after the symbol the linker complains about is removed:

https://travis-ci.org/LambdaHack/LambdaHack/jobs/159506870

As seen on travis, the way to reproduce it is just cabal install of

https://github.com/LambdaHack/LambdaHack/commit/0d2bbd6eadca7a10292ab67ab1fa708b4c20aaf6

which also shows the offending line.

I took the liberty of adding it to 8.0.2 milestone, because if it affects all x86_64 machines, it's pretty serious. Please feel free to downgrade.

If the bug is confirmed, I can attempt creating a small reproducing case, but it would require gtk, so it would compile forever anyway.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed milestone to %8.0.2

changed weight to 7

added Tbug Trac import labels

Hmm, oddly enough I encounter a completely unrelated segfault(!) while building functor-infix when trying to reproduce this. GHC appears to crash right after linking. It seems your project is cursed.

I managed to reproduce this. It has something to do with BangPatterns apparently. Here is a reproducer with just two modules:

-- U.hs
module U where
u :: Int
u = 1

-- Main.hs
{-# LANGUAGE BangPatterns #-}
import U
main = print $ let !x = u in x

ghc-8.0.1 -O Main fails with the same sort of linker error.

Great test case thank you Reid. It's something to do with desugaring of bang patterns. Stay tuned. I'm on a plane tomorrow...

Trac metadata

Trac field	Value
CC	- → mikolaj.konarski@funktory.com

mentioned in commit 2fbfbca2

Thanks for such a nice small test case!

Ben: worth merging this if it's trouble-free

Trac metadata

Trac field	Value
Test case	- → deSugar/should_run/T12595

added 1 deleted label

closed

#12595 (closed) merged to ghc-8.0 as d2695b84.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

mentioned in issue #13043 (closed)

added Phigh label