toConfiguredComponent: unix (Windows)

[alexbiehl]

Trying new-build with cabal-install from HEAD on a project of mine:

$ cabal new-build hunt-searchengine

Results in:

$ Resolving dependencies...
$ toConfiguredComponent: unix
$ CallStack (from HasCallStack):
$ error, called at .\Distribution\Backpack\ConfiguredComponent.hs:131:20 in
$ Cabal-1.25.0.0-2vbl2DGycuL3ehQ9RJKv1s:Distribution.Backpack.ConfiguredComponent

I would cabal expect to fail on building unix (since I am on Windows) instead of some internal error.

[23Skidoo]

@ezyang, can you please look into this?

[ezyang]

@alexbiehl Any chance I can get some -v logs? (Or better yet, -v3)

[alexbiehl]

Yes of course, I will hand them in tomorrow.

Edward Z. Yang [email protected] schrieb am Do., 13. Okt. 2016,
19:50:

@alexbiehl https://github.com/alexbiehl Any chance I can get some -v
logs?

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[alexbiehl]

cabal new-build hunt-searchengine -v3 with dist-newstyle deleted first:
https://gist.github.com/alexbiehl/b303b584dcf636b54d2b84392088c20d

And here the same command as a subsequent run (with a dist-newstyle present). Not sure if needed though.
https://gist.github.com/alexbiehl/47c2b561de69cf4b0085eb55cbfdc4ba

I have one question to add:

Somewhere in the logs it says targets: html-hunter, hunt-client, hunt-crawler, hunt-searchengine, hunt-server, hunt-server-cli. But I only requested to build hunt-searchengine which does not depend on any of the other targets. Is this something weird or is it just listing all available targets?

[ezyang]

new-build will solve for ALL local packages in your project, so that when you decide to build some of the other ones, it doesn't have to resolve.

[ezyang]

If you can, apply this patch and then give me the non-verbose log?

diff --git a/Cabal/Distribution/Backpack/ConfiguredComponent.hs b/Cabal/Distribution/Backpack/ConfiguredComponent.hs
index 184b8bb..86cb899 100644
--- a/Cabal/Distribution/Backpack/ConfiguredComponent.hs
+++ b/Cabal/Distribution/Backpack/ConfiguredComponent.hs
@@ -128,7 +128,8 @@ toConfiguredComponent pkg_descr this_cid
     bi = componentBuildInfo component
     find_it :: PackageName -> VersionRange -> (ComponentId, PackageId)
     find_it name reqVer =
-        fromMaybe (error ("toConfiguredComponent: " ++ display name)) $
+        fromMaybe (error ("toConfiguredComponent: " ++ display (packageName pkg_descr) ++
+                            " " ++ display name)) $
             lookup_name lib_map <|>
             lookup_name external_lib_map
       where

[alexbiehl]

$ cabal new-build hunt-searchengine
Resolving dependencies...
toConfiguredComponent: hxt-cache unix
CallStack (from HasCallStack):
error, called at .\Distribution\Backpack\ConfiguredComponent.hs:131:20 in
Cabal-1.25.0.0-2vbl2DGycuL3ehQ9RJKv1s:Distribution.Backpack.ConfiguredComponent

[ezyang]

So, I guess this is not a direct dependency of hunt-searchengine, but one of the other packages that are local?

[alexbiehl]

Yes, right. hxt-cache is the offender here.

[ezyang]

I guess I have some guesses how I might reproduce this locally. I guess this is not urgent, since you can just remove the unbuildable packages from your project?

[alexbiehl]

No not urgent. I already filled a pull-request for hxt-cache and use a modifed copy.

[ezyang]

OK, the bug seems to be somehow related to buildable. Min repro:

name: p
version: 0.1
build-type: Simple
cabal-version: >= 1.25

library
    buildable: False

Stick this in a package with a building package (say q), and then run cabal new-build q.

[ezyang]

OK, so here's the problem: when the library of a pckage is marked as non-buildable, new-build does NOT eagerly fail. In 1.24, the error would only happen if you tried to build it, or anything that depended on it:

cabal: Unknown build target 'lib:p'.
There is no library component 'p' or component 'lib'.

or

cabal: No executables, libraries, tests, or benchmarks found. Nothing to do.

I suppose that's reasonable behavior; it lets you build some part of your project even when other parts are non-buildable.

But when I refactored this code for Backpack, I assumed that I would only ever get plans with packages that depended upon buildable things. Thus the assert failure! The library doesn't exist and never was configured.

I guess one way we could fix this is to have the solver reject a package if the library is marked as non-buildable (as opposed to executables/tests/etc. May god have mercy on your soul if you have a non-buildable library with a buildable executable.) But maybe this is not so good for you because it means that you can't develop a project if any of the local deps transitively depends on a non-buildable thing. But maybe you didn't care so much about this case?

By the way, unix also has build-depends: buildable < 0, so you might wonder why the solver didn't fail? Well, that's because when buildable: False we ignore the build-depends. This is desirable for executables but not for libraries.

[dcoutts]

@ezyang fyi, I've seen the same error toConfiguredComponent: blah, but I don't think it was the same problem as unix here. Can we add any more detail to this internal error so we can get better info if we hit it again in future.

[ezyang]

@dcoutts Do you have a repro?

[phadej]

I get this error when

% cabal new-build -w ghc-7.8.4 --enable-tests all
Resolving dependencies...
Error:
    Dependency on unbuildable library from http-client
    In the stanza 'library'
    In the package 'http-client-tls-0.3.5.3'

with servant 0c66b9c0559721ea682cd0d1fa35f403ec075cda

[phadej]

Now I see the problem: http://hdiff.luite.com/cgit/http-client/diff?id=0.5.12.1&id2=0.5.12

clicksaver

+  -- See build failure at https://travis-ci.org/snoyberg/http-client/jobs/359573631
+  if impl(ghc < 7.10)
+    buildable: False

[grayjay]

I opened an issue for the new type of failure: #5325