The previous behaviour would work fine as long as `symlink` is a link to
a file. If is a link to a directory though, the new `ln` wouldn't
overwrite it but would create a new link *in that directory* (with the
name of the link source).
Instead, we can precompute the target location, then first remove the
symlink and write the new one in its place.
Bazel computes the default value of output_user_root before parsing the
flag[0]. The computation of the default value involves getting the $USER
from the environment. I don't have that variable when building with
sandbox enabled.
[0]: 9323c57607/src/main/cpp/startup_options.cc (L123-L124)
A separate function for building Bazel-bazed packages. Internally it splits the
build into two phases, fetching and building.
Users are expected to provide `fetchArgs.sha256` -- checksum of fetched
dependencies. Local dependencies should be removed in `fetchArgs.preInstall`.
Overall `fetchArgs` and `buildArgs` can be used to add specific steps to fetch
and build.
