$location expansion in Bazel

I want to add $(location) expansion to rules_scala for jvm_flags attribute where I set the dependency in the data attribute but that fails with:
label '//src/java/com/google/devtools/build/lib:worker' in $(location) expression is not a declared prerequisite of this rule.
I define a dependency in my target on that label in the data attribute like this:

scala_specs2_junit_test(
    ...
    data = ["//src/java/com/google/devtools/build/lib:worker"],
    jvm_flags = ["-XX:HeapDumpPath=/some/custom/path", "-Dlocation.expanded=$(location //src/java/com/google/devtools/build/lib:worker)"],
)

I saw that when I add ctx.attr.data to the expand_location call expansion works but I wasn't really sure why this is not a hack. Is data indeed a special case?

    location_expanded_jvm_flags = []
    for jvm_flag in jvm_flags:
        location_expanded_jvm_flags.append(ctx.expand_location(jvm_flag, ctx.attr.data))

Also tried looking in the java_* rules sources to see how this works (since $(location) expansion there supports the data attribute) but couldn't find the relevant place.

Full target:

scala_specs2_junit_test(
    name = "Specs2Tests",
    srcs = ["src/main/scala/scala/test/junit/specs2/Specs2Tests.scala"],
    deps = [":JUnitCompileTimeDep"],
    size = "small",
    suffixes = ["Test"],
    data = ["//src/java/com/google/devtools/build/lib:worker"],
    jvm_flags = ["-XX:HeapDumpPath=/some/custom/path", "-Dlocation.expanded=$(location //src/java/com/google/devtools/build/lib:worker)"],
)