Cabal new-build sometimes requires Internet access?

[jwiegley]

I built a certain work project several times while at home today. Then I went to a café where I didn't have Internet access, and wanted to continue working on the project. I was greeted with this:

$ cabal new-build
dieVerbatim: user error (cabal: '/usr/bin/curl' exited with an error:
curl: (6) Could not resolve host: objects-us-west-1.dream.io
)

Given that every necessary dependency was on my machine, it seems most unfortunate that I couldn't use new-build because the Internet was temporarily unavailable.

[gbaz]

cf #5363 and #4821

[hvr]

@jwiegley here's a workaround I believe should work that you could try:

edit your ~/.cabal/config temporarily to comment out the two lines

repository hackage.haskell.org
  url: http://hackage.haskell.org/
  -- ...

into

-- repository hackage.haskell.org
--    url: http://hackage.haskell.org/
  -- ...

this will effectively disable the package index and might help if all your library dependencies are pre-provisioned by Nix in your package-db -- it might however cause problems for build-tools, as we don't have a build-tool registry yet (i.e. the equivalent of the global pkg-db for libraries for build-tools).

[23Skidoo]

v1-install had an --offline flag IIRC, should be possible to implement it for v2-build too.

[m-renaud]

Do you have steps to reproduce? When using cabal from head and trying to build various projects after disabling network it succeeded without error. Is there a specific configuration you need to get yourself into to trigger this? If I can reproduce locally I'd be happy to take a stab at adding the --offline flag.

[arrowd]

I get this problem too when trying to use cabal-install as a packaging tool for FreeBSD ports, however I managed to workaround it.

When issuing cabal new-build --offline for the package, Cabal's home dir was empty. This caused cabal-install to create it and also create default config file with Hackage repo. So, now I just run touch $HOME/.cabal/config before running cabal new-build and it works perfectly.

[schmittlauch]

cabal-install 3.4 includes a documented fix/ workaround: #4821 (comment)

[AleXoundOS]

Also, it would be useful to configure cabal with a legal option for offline usage on a permanent basis for a user (a workaround with empty/commented ~/.cabal/config exists). Without a need to pass --offline or edit cabal.project for every project (am I right?). Maybe the undocumented offline option in ~/.cabal/config is initially suited for this?

[gbaz]

Can we close this as resolved?

[schmittlauch]

As long as nothing has changed since my previous comment, I'm not entirely sure about closing:

Being able to configure the project itself via a cabal.project is already a good start. But maybe adding an --offline flag to cabal-build or defaulting to the repo fetching only being a warning as long as all required packages are already present on the machine might still be a good change.

I still deem cabal run always triggering a hard-failing network request to be a bad default behaviour.

[gbaz]

Oh I agree we should add the --offline flag, but that's tracked by #5346 . If that covers the request, we'll resolve in favor of that.