--offline does not stop Cabal from attempting to access the network

[9999years]

Describe the bug

Cabal attempts to access the network, even if --offline is given.

To Reproduce

$ rm -rf dist-newstyle/ ~/.cabal/packages && cabal exec -v --offline -- ghc --print-libdir
...
Trying to locate mirrors via DNS for initial bootstrap of secure repository
'http://hackage.haskell.org/' ...
located 2 mirrors for http://hackage.haskell.org/ :
- http://hackage.fpcomplete.com/
- http://objects-us-east-1.dream.io/hackage-mirror/
Selected mirror http://hackage.haskell.org/
Downloading root
Including the following directories in PATH:
- /Users/wiggles/.cabal/bin
Running: /nix/store/c8zjxnirrs9w62rh5mnzd54rx9w31zai-curl-8.9.0-bin/bin/curl 'http://hackage.haskell.org/root.json' --output /tmp/nix-shell.HDXhum/transportAdapterGet36559-3 --location --write-out '%{http_code}' --user-agent 'cabal-install/3.12.1.0 (osx; aarch64)' --silent --show-error --dump-header /tmp/nix-shell.HDXhum/curl-headers36559-4.txt
...

Expected behavior

If --offline is set, Cabal should not attempt to access the network.

System information

Operating system: macOS Sonoma 14.6.1 (23G93)

$ cabal --version
cabal-install version 3.12.1.0
compiled using version 3.12.1.0 of the Cabal library
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.6.3

[ulysses4ever]

Prior issue: #8752. I believe it was fixed by #8676 for the build command but exec was never looked at perhaps.

[9999years]

@ulysses4ever No, cabal build -v2 --offline shows the exact same curl invocation.

[ulysses4ever]

Oh, good catch! Then it's a new revelation, and we need to fix it!

I can't reproduce your issue neither with exec nor with build though. What context are you calling cabal from? Any project files involved? Here's what I see with a clean package:

❯ cabal init -nm --lib
...
❯ rm -rf dist-newstyle/ ~/.cabal/packages && cabal-3.12.1.0 exec -v --offline -- ghc --print-libdir
Project settings changed, reconfiguring...
creating /home/artem/Dev/tmp/dist-newstyle
creating /home/artem/Dev/tmp/dist-newstyle/cache
Compiler settings changed, reconfiguring...
Running: /run/current-system/sw/bin/ghc --numeric-version
looking for tool ghc-pkg near compiler in /run/current-system/sw/bin
found ghc-pkg in
/nix/store/j7pf2p2dpyi7psvmgm6aqyqm7iqwbfz8-ghc-9.6.5/bin/ghc-pkg-9.6.5
Running: /nix/store/j7pf2p2dpyi7psvmgm6aqyqm7iqwbfz8-ghc-9.6.5/bin/ghc-pkg-9.6.5 --version
Running: /run/current-system/sw/bin/ghc --supported-languages
Running: /run/current-system/sw/bin/ghc --info
Running: /run/current-system/sw/bin/ghc --print-global-package-db
Reading available packages of hackage.haskell.org...
Using most recent state specified from most recent cabal update
index-state(hackage.haskell.org) = 2024-08-27T15:07:51Z
Failed to query pkg-config, Cabal will continue without solving for pkg-config
constraints: Cannot find pkg-config program
Resolving dependencies...
Component graph for tmp-0.1.0.0: component lib
component tmp-0.1.0.0-inplace include base-4.18.2.1
unit tmp-0.1.0.0-inplace
    include base-4.18.2.1
    MyLib=tmp-0.1.0.0-inplace:MyLib
creating /home/artem/Dev/tmp/dist-newstyle/tmp
Running: /run/current-system/sw/bin/ghc --print-libdir
/nix/store/j7pf2p2dpyi7psvmgm6aqyqm7iqwbfz8-ghc-9.6.5/lib/ghc-9.6.5/lib

Without any package available, it just errors citing no package (which may be not the best idea but that's another issue):

❯ rm -rf dist-newstyle/ ~/.cabal/packages && cabal-3.12.1.0 exec -v --offline -- ghc --print-libdir
Project settings changed, reconfiguring...
No cabal.project file or cabal file matching the default glob './*.cabal' was found.
Please create a package description file <pkgname>.cabal or a cabal.project file referencing the packages you want to build.

[9999years]

Where is your cabal reading this index from? Maybe it's not ~/.cabal/packages on your machine.

Using most recent state specified from most recent cabal update
index-state(hackage.haskell.org) = 2024-08-27T15:07:51Z

On both my Linux and macOS machines those commands error in the cabal init -nm --lib, so I'm not sure.

[ulysses4ever]

Ah, sorry about that: it's the XDG stuff. https://cabal.readthedocs.io/en/stable/config.html#directories