Multiple tests fail on Mac with "Error: DEVELOPER_DIR not set"

[agrue]

First I should mention that I needed to upgrade my rules_haskell version for the project to build at all. My WORKSPACE looks like:

git_repository(
    name = "rules_haskell",
    remote = "https://github.com/tweag/rules_haskell",
    commit = "7abaefdde3d0a29bfe15e02be4ad2a0bd4484600",
    shallow_since = "1626246473 +0000",
)

When building on my Mac I ran into this issue, which I fixed with export BAZEL_USE_CPP_ONLY_TOOLCHAIN=1 in my shell. But when I ran the tests under //hrepl/tests (via run_tests.sh) I noticed that many of them (but not all) failed with the same error in the logs. (Sorry, I don't have the complete list handy, but atomic_primops_test was one of them.)

It seems that the BAZEL_USE_CPP_ONLY_TOOLCHAIN environment variable doesn't make its way into the builds that hrepl itself is doing (which makes sense, since it should try to be hermetic). Unfortunately the only workaround I could find was to edit ReplTestLib.hs and manually add it to the constructed environment. This clearly isn't a good permanent solution since it's Mac-specific.