Improve the user experience around sandboxes with multiple source packages

[tibbe]

• Allow the cabal binary itself to be used as a Setup.hs file, removing errors related to not having the right version of Cabal installed/available (e.g. when doing parallel builds.) (Allow using cabal program itself as the external setup method #2633)
• Track down and fix issue (probably timestamp related) with unnecessary rebuilds in source packages that haven't changed.
• Allow build targets that include package names/directories, not just components in the current directory.
• Implicit "add-source" for packages in subdirectories.
• Allow dist/ to live inside the sandbox directory, rather than in the package directory.
• Search upwards for sandbox directory.
• Cabal configure should produce and save an install plan. Cabal build should install the plan (by invoking cabal install --only-dep).
• Come up with catchy title for issue.

/cc @dcoutts

[BardurArantsson]

Is there any of this that a noob such as myself could help with? (And which would have value on as a feature of its own.)

[dcoutts]

@BardurArantsson you could have a look at the one "Search upwards for sandbox directory". It shouldn't be hard to implement, and then you'd want to play around with it a bit and see if there's any unexpected issues with that approach.

[BardurArantsson]

Thanks, I'll have a look at that tomorrow (or the day after). Hopefully, it's pretty independent of the rest of all the others?

(I think I can already theoretically foresee a few issues wrt. backward compatibility, but we'll see, I guess...)

[dcoutts]

@BardurArantsson yeah, should be independent.

[BardurArantsson]

EDIT: Removed comment because it was just noise

[BardurArantsson]

Ok, so I've added a new issue #2810 for the "Search upwards..." sub-task. Could someone please edit it into the first post on this issue?

I'll do a pull req for #2810 shortly just for initial review.

[phadej]

sandbox functionality is removed.