Deprecate the default_backend_packages option.

Review Request #4017 — Created June 22, 2016 and submitted

stuhood, zundel

We don't need it now that we can append and filter list options.
Repos can modify the backend_packages option directly, removing
any default backends they don't need and appending their custom

Verified that we get the deprecation option under the right conditions.

CI passes here:

  2. It occurs to me that this is going to be a common misconfiguration after we remove --default-backend-packages too. A possible mitigation is to add a hint to do this if both pants.backend.jvm and pants.backend.python are missing.

    1. Interesting. Although the only repos affected will be those explicitly setting backend_packages today, and they will presumably see these deprecation warnings in plenty of time, no? But it's a good idea to reach out to the affected repos and confirm that they've handled this before removing --default-backend-packages, as an extra courtesy.

    2. The misconfiguration I'm thinking of is:

      backend_packages: [

      Which will add the module, but drop all of the built-in modules necessary to run pants.

    3. Right, and this change will give you a deprecation warning for this case.

    4. I'm saying way in the future, in pants 2.0 this could happen. This is the only config item (so far) in the entire system that you configure with the new syntax and it seems like a very easy mistake to make.

Review request changed

Status: Closed (submitted)

Change Summary: