build.cabal.sh breaks badly if hadrian's dependencies do not successfully install.

[duog]

running build.cabal.sh with Cabal <2.1 triggers this code path:

    if ! ( "$CABAL" sandbox hc-pkg list > /dev/null 2>&1); then
        "$CABAL" sandbox init
        "$CABAL" sandbox add-source ../libraries/Cabal/Cabal
        "$CABAL" install                \
            --dependencies-only         \
            --disable-library-profiling \
            --disable-shared
    fi

If dependencies do not cleanly install one must manually delete the sandbox to proceed.

[snowleopard]

Thanks @duog! I suppose the right solution is to detect the failure and delete the sandbox?

I'm not familiar with Cabal sandboxes so it will take me some time to dig out the right commands to run. Presumably this is an easy fix, so a PR is very welcome.

[chitrak7]

@snowleopard @izgzhen deleting .sandbox file and then rerunning build works whenever I get this error. I believe this should be a good fix here. We can simply add command $CABAL sandbox delete method with a check. if [-e cabal.sandbox.config] then cabal sandbox delete

[izgzhen]

related to #524