copy command fails when building only some components

[snoyberg]

Actions:

1. Create a project with both a library and executable
2. cabal clean
3. cabal configure
4. cabal build lib:packagename
5. cabal copy

Expected: command succeeds, copying over the library only, and not the test suite

Actual: errors out since the executable does not exist, e.g.:

Installing library in
/home/vagrant/.cabal/lib/x86_64-linux-ghc-7.10.2/tmp-0.1.0.0-JdaAODhQa7p5WhxMngbYYt
Installing executable(s) in /home/vagrant/.cabal/bin
Setup.hs: dist/build/tmp-exe/tmp-exe: does not exist

This problem could be mitigated by allowing copy to take a list of components like build does.

[lukehoersten]

+1

[mgsloan]

Recently ran into this one... +1

[mgsloan]

@ezyang Ahh, I didn't realize that exe-name was a valid cabal build target. Thanks!

You seem to be assuming that there is a way to configure a set of packages to install in 1.24! Did you mean to copy whatever what was last built? I suppose that is possible, but this would imply ./Setup build somehow saves the set of arguments it was called with, which copy then takes. Isn't just specifying it explicitly better?

Sorry, maybe I am massively misunderstanding the question.

True, I meant the build step. Yeah, explicit is probably better for the Cabal layer.

Backporting this to 1.24 looks non-trivial, so I'm inclined to leave it be.

Would you be inclined to merge if I implemented a new fix atop 1.24? The alternative is going to be to move more and more Cabal functionality into stack / Setup.hs hacks.

[ezyang]

Surely it can't be that hard to backport. The main thing is I refactored Install to operate on a per-CLBI basis prior to this patch; you'd have to also bring in those changes as well.

[23Skidoo]

Looking at #3022 (which is the version that got merged), I see that the patch in question (f88f502 ) is number 25 in a series that includes 2040c1c among other things. This makes me somewhat uncomfortable with the amount of changes required in the supposedly stable branch.

@mgsloan

Would you be inclined to merge if I implemented a new fix atop 1.24?

Sure, if you or @ezyang are willing to do the actual work, I'll reconsider.

[23Skidoo]

@mgsloan

So people are asking for a new 1.24 release, should I wait for your patch or remilestone this ticket for Cabal 1.24.0.2?

[mgsloan]

Feel free to make the release. I'll take a look and may have a patch ready soon

[23Skidoo]

@mgsloan Thanks!

[ezyang]

@mgsloan GHC 8.0.2 is coming soon, so this is your last chance to get a 1.24 patch in!

[23Skidoo]

@mgsloan @ezyang Guys, is this still broken or is the ticket only open because the fix is not in 1.24? If it's the latter, I think we should close it.

[snoyberg]

The problem still exists with Cabal 2.0:

$ stack --resolver ghc-8.2.1 exec --no-ghc-package-path -- runghc Setup.hs configure --user
Configuring foo-0.1.0.0...
$ stack --resolver ghc-8.2.1 exec --no-ghc-package-path -- runghc Setup.hs build lib:foo
Preprocessing library for foo-0.1.0.0..
Building library for foo-0.1.0.0..
[1 of 1] Compiling Lib              ( src/Lib.hs, dist/build/Lib.o )
$ stack --resolver ghc-8.2.1 exec --no-ghc-package-path -- runghc Setup.hs copy
Installing library in /Users/michael/.cabal/lib/x86_64-osx-ghc-8.2.1/foo-0.1.0.0-wI4nsLkf3p3YT1pJBa9gp
Installing executable foo-exe in /Users/michael/.cabal/bin
Warning: The directory /Users/michael/.cabal/bin is not in the system search
path.
dist/build/foo-exe/foo-exe: copyFile: does not exist (No such file or directory)

I understand that Cabal 2.0 has introduced per-component configuration, which is intended as a workaround. I've discussed with @ezyang, and the ultimate plan is to add support for this to Stack (which will be necessary for Backpack anyway). In the meanwhile, we have a workaround in Stack that forces the executable component to be built the first time.

So my take: I still consider this a bug that is unfixed in Cabal 2.0, but we're effectively working around it in Stack.

[23Skidoo]

@snoyberg Thanks!

[ezyang]

Sorry I missed the conversation here. Let me clarify a few points:

• Per-component build will solve the problem, as @snoyberg says
• ./Setup build someexe && ./Setup copy indeed does not work in Cabal HEAD (and it will never work, for reasons explicated earlier in this ticket; specifically, Cabal would need to start tracking state of "what the most recent set of executables that were built" where, and this just doesn't seem like a good answer when there's a better solution below)
• ./Setup build someexe && ./Setup copy someexe (@snoyberg suggested alleviation at the very beginning of this ticket) works in Cabal 2.0, and it may be worth adding the little bit of logic to support it