stack+ghcjs with two different resolvers breaks.

[benclifford]

We have two ghcjs projects which use different resolver versions. Either project will build for a user from an empty home directory, but if a user tries to build both projects, one of them fails with the inability to find some libraries. Superficially it looks like whichever project happened to bootstrap ghcjs is the project that works.

I have attempted to assemble a minimal reproduction of the problem here:
https://github.com/BeautifulDestinations/issue-365-reproduction

This is with:

$ stack --version
Version 1.1.2, Git revision cebe10e845fed4420b6224d97dcabf20477bbd4b (3646 commits) x86_64 hpack-0.14.0

[mgsloan]

Interesting! I haven't yet looked at the repro, but my guess is that it has to do with the shared .ghcjs dir.

One possibility is that there are two different ghcjs tarballs, but they both think they are the same version (0.2.0). I think in this case they will use the same global package DB despite being different. Can you please check if this is the case?

[benclifford]

The two stack.yaml files refer to the same URL:
https://github.com/nrolland/ghcjs/releases/download/v.0.2.0.20151230.3/ghcjs-0.2.0.20151230.3.tar.gz

Curiouser and curiouser, if I run in a clean environment:

cd project-b; stack setup; stack build
cd project-a;
rm -rfv .stack-work; stack setup; stack build  #A
rm -rfv .stack-work; stack setup; stack build  #B 

then #A fails but #B succeeds.

[tolysz]

I been playing with multiple ghcjs version and resolvers eg.: https://github.com/tolysz/spock-ghcjs-sample

So I realised that ghcjs and boot might be exactly the same between different ltss or different nightlys (as I try to build them as soon as I see them) builds as long as the boot packages are not changed, there is like (a dozen of them). But then if the compiler version is the same ghcjs will try to use the same cache (per compiler) to save all builds.

My guess will be to make ghcjs stack aware and make it use some "custom" build prefix which stack could set, or make it guess the resolver.

[mgsloan]

Yes, my guess that this is caused by many different ghcjs tarballs all claiming to be 0.2.0. So, if that guess is correct, this will be fixed once ghcjs has a proper release cycle.

[tolysz]

I used different ghcjs versions per resolver, but they had the same cabal versions and still building in the same folder causes cache not updating.

[mgsloan]

Yes, that will cause problems, unfortunately. Not sure if there's much I can do about it :/