Description of the problem

I believe custom build flags don't play well with proper @namespace//...-like references.

Bugs: what's the simplest, easiest way to reproduce this bug?

I set up a repository with a repro -- check out the README. It follows closely the running example of drinks and flavors in the documentation. Except that it actually sets up a named workspace.

In the master branch of the repo, everything is fine: I'm able to pass the flag in the command line. In the bug branch I add the workspace prefix when referencing the flag target from the attribute of my rule. This breaks the setup: I pass the flag in the command-line as before but it has no effect. If I try to add the workspace prefix when referencing the flag from the command-line, I get "Unrecognized option".

What operating system are you running Bazel on?

Ubuntu 18.04

What's the output of bazel info release?

release 0.28.0- (@non-git)

If bazel info release returns "development version" or "(@Non-Git)", tell us how you built Bazel.

This is the version of Bazel imported by Nixpkgs version referenced in the current rules_haskell (master branch).

Have you found anything relevant by searching the web?

No. I only looked up the Issues here.