Write Build Summary to Local Build Directory

[julmb]

Describe the feature request
I would like to configure Cabal in such a way that cabal build only writes to the project directory.

Additional context
I want to run cabal build as part of coding tools (openai codex, claude code, crush, etc.). For safety, these tools run all commands in a sandbox that prevents writes outside of the project directory. Currently, cabal build fails to run in this environment since it tries to write to ~/.cache/cabal/logs/build.log, which is outside of the project directory.

The documentation mentions the build-summary configuration directive and says that it is not implemented. This seems to be outdated, as the directive does have an effect. Unfortunately, it only adds another path where it tries to write the build summary to, but also still tries to write to the default location. I also tried using the logs-dir directive, but could not observe any effect.

I am running Cabal 3.14.2.0.

[ulysses4ever]

Will it help if you set the CABAL_DIR environment variable to a path under the project directory? In that case, the invariant you seek should be upheld.

[julmb]

I was about to reply that this does not seem like a great way to do it, since it would move the config, store, and package cache into the project directory, which could be tens of gigabytes in size for each project, instead of being shared by all projects. But then I realized that that is precisely what would be needed to have truly project-local builds, so your suggestion is appropriate.

However, I do not think that I would want to go that far. Most builds will not touch the package cache or cabal store, since at least the more common packages will already exist in the correct configuration. I think would be happy if there was a way to move just the logs. I do not quite understand why those logs do not live inside of dist-newstyle to begin with, but maybe there is a good reason.

[ulysses4ever]

I think would be happy if there was a way to move just the logs.

that's fair. My suggestion was merely a workaround.

Now that you have a more precise goal, we should probably update the title of the issue to say precisely what we want...

Putting logs in the local build folder instead of the cabal dir does make sense. It will require some investigation to figure out how to achieve this. Our best shot would be you doing this investigation, if you're interested. Otherwise, this will probably have to wait for a volunteer indefinitely.