Question about: store-dir, package-dbs, and simulate sandbox

[chansey97]

What is your question?

Even though the sandbox functionality has been removed, I still wish a way to simulate its functionality.

I tried the --store-dir=DIR option on, it works well on Windows.

For example,

cabal --store-dir "./store-dir" build

It will build all the packages in the current project directory.

## My project folder now generate a new subfolder `store-dir`
\---store-dir
    \---ghc-9.8.1
        +---incoming
        +---package.db
        +---linear-1.22-bd032fa56680dc724a9bbbfee960b52b4c4a70c6
        +---OpenGL-3.0.3.0-2ae721ae6ad7822f734a3392b576ce1d14f6aabd
        +---kan-extensions-5.2.5-4b3c60b0ae89aab3067951ef9c1cac496a515b
        +...

However, --store-dir=DIR can only be set via command line at the moment.

The 1st question is that is it possible to set --store-dir=DIR in cabal.project in the future version?

The 2nd question is that, in this context, what role does the option package-dbs: play?

P.s. In the above command, i.e. cabal --store-dir "./store-dir" build, I did not set package-dbs in cabal.project at all, but it works. Why we have both --store-dir and --package-db (or package-dbs:) at the same time?

If I config cabal.project as the follows

-- cabal.project
packages: ./*.cabal
package-dbs: in-place

and type cabal build on command line.

It complains

ghc-9.8.1.exe: can't find a package database at in-place

I also tried

-- cabal.project
packages: ./*.cabal
package-dbs: ./in-place/ghc-9.8.1/package.db

and on command line cabal --store-dir "./input" build.

It doesn't work as well.

ghc-9.8.1.exe: can't find a package database at ./in-place/ghc-9.8.1/package.db

System information

• Operating system: Windows + MSYS64 MINGW
• ghc-9.8.1, cabal-install version 3.10.2.1

[mpickering]

See #9678 for a discussion about the semantics of --package-db flag. In short, you probably don't want to use it for this use case.

You could set store-dir in a cabal.config file instead of a cabal.project file but that is supposed to be for system-wide configuration. I don't think you are really supposed to set --store-dir per project which is why you can't set it in a cabal.project file.

[chansey97]

@mpickering Thanks for clarification.

And sorry for slightly off topic, do you know any practical use case for utilizing the --package-db?

[mpickering]

@chansey97 If you/a distro want to augment the global package database with some more packages which are always available then you can build the package database yourself (probably not with cabal-install) and then make it available for cabal-install to use.

In the cabal testsuite we do this in order to provide up-to-date Cabal library versions for cabal-install to use.

[chansey97]

@mpickering I see, thanks! Close this issue.