GHC panic depending on what a Haskell module is named
I'm trying to make bindings for the imgui C++ library and have encountered an apparent bug. I'm unable to produce a minimal example so I've packed up the whole project in a zip file. It only works on Windows for now but I assume this problem is platform dependant anyways.
There's a module
UI.Imgui that imports two things. A
FunPtr wrapping function and an actual function defined in a .cpp file. Another module Main imports this module.
If the project is run in a repl (in my case I'm doing
stack repl) and then the
test function is evaluated it results in a GHC panic
ghc.exe: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-mingw32): loadObj "C:\\Users\\Luka\\AppData\\Local\\Temp\\ghc5900_0\\ghc_5.o": failed Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Now here's the fun part. If you rename the module, file and it's import to something like Imgui2 it works. If you rename it to UI2.Imgui (with appropriate folder renaming) it also works!
I'm sure a huge portion of the code is irrelevant. I couldn't reproduce this with simple .cpp files.
Here's a link to the file (3MB) https://dl.dropboxusercontent.com/u/35032740/ShareX/2016/05/imgui.zip
Update: Ok so it seems that the "reason" why renaming the file works is because I forgot to change the entry in the cabal file so the next time I run the repl it fails to recompile the project but it launches the repl using the previous build. Why it doesn't panic in that case I have no idea.
Also, here's another thing that fixes is: Run the repl -> try test -> GHC panic -> save the Imgui file (without changing anything, just so you can :r it) -> do :r in GHCi -> try test -> works