+ operator on a depset is forbidden

[cushon]

Fixes:

ERROR: test/proto/BUILD:36:1: in scala_proto_srcjar rule //test/proto:test_proto_java_conversions_srcjar:
Traceback (most recent call last):
	File "test/proto/BUILD", line 36
		scala_proto_srcjar(name = 'test_proto_java_conversions_srcjar')
	File "scala_proto/scala_proto.bzl", line 332, in _gen_proto_srcjar_impl
		transitive_proto_paths += target.proto.transitive_proto_path
`+` operator on a depset is forbidden. See https://docs.bazel.build/versions/master/skylark/depsets.html for recommendations. Use --incompatible_depset_union=false to temporarily disable this check.

See also #480

[johnynek]

lgtm

confused why our test with --all_incompatible_changes didn't catch this.

[cushon]

confused why our test with --all_incompatible_changes didn't catch this.

That's how I noticed it, but I was testing with 0.12. Are you still using 0.11 because of the change to strict deps in 0.12?

[johnynek]

we are still using 0.11 because the PR to bump to 0.12 failed CI: #481 and no one has diagnosed/repaired it AFAIK.

[cushon]

Makes sense. This is the only issue I saw with 0.12 related to --all_incompatible_changes, so I think it's worth fixing even though it isn't sufficient to get 0.12 working.

[johnynek]

thanks!