Add a proto_library rule for well-known types and update the proto_lang_toolchain rules

[cgrushko]

Bazel now has built-in rules for building Java and C++ protos (proto_libarry, java_proto_library, java_lite_proto_library and cc_proto_library).

For users to import well-known types (e.g., descriptor.proto) from their .proto files, they must depend on a proto_library that srcs the former.

This FR is about adding such a proto_library.

#2598 is a blocker.

[kamalmarhubi]

@xfxyjwf do you know if you'll get to this in the near term?

[cgrushko]

bazelbuild/bazel#2265 is a blocker.

[kamalmarhubi]

@cgrushko ah, I kept running into that error and didn't realize it was a bug in bazel.

[buchgr]

bazelbuild/bazel#2265 has been fixed and should be part of the next bazel release.

[thaidn]

So is this issue fixed? If so, can I build bazel from HEAD and depend on well-known protos in my proto_library rules?

[buchgr]

hey @thaidn

bazelbuild/bazel#2265 has been fixed and reverted again, because it caused trouble inside of google's programming environment. See the bug for details.

It's really embarrassing and I apologize for the trouble's this causes.

Inside bazel we also need well known types and thus made a simple hack that copies the well known types from src/com/google/protobuf to com/google/protobuf and then it works. Here is the patch that does that: https://bazel-review.googlesource.com/c/10690/

[xfxyjwf]

@buchgr Is a proper fix of this issue depending on b/37798101 (making both internal and external protoc accepts the same file path)?

[cgrushko]

Yes, it does. Adding proto_library requires compiling generated files (because the request to move the well known types one level up the tree was rejected). In order to compile generated files we need to pass bazel-bin/ paths, which require b/37798101. We can workaround this in a number of ways, not all of which are easy.

…

On Fri, May 5, 2017 at 2:10 PM Feng Xiao ***@***.***> wrote: @buchgr <https://github.com/buchgr> Is a proper fix of this issue depending on b/37798101 (making both internal and external protoc accepts the same file path)? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#2763 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AB5_YVPtz5J4hQryMjsUQwg9valaZFyiks5r22X9gaJpZM4MMPuw> .

[junghoahnsc]

Is there any workaround to import well-known protos for now?

[buchgr]

@junghoahnsc
You can do what I described in my previous comment that bazel does.

[junghoahnsc]

@buchgr you mean using a patch https://bazel-review.googlesource.com/c/10690 ?

Would it be a workaround to have all well-known protos in local repo with BUILD?

[buchgr]

@junghoahnsc yes to both :-).

[kamalmarhubi]

I have an example repo defining an extra com_google_protobuf_well_known_protos repository: https://github.com/kamalmarhubi/bazel-well-known-protos-example

[buchgr]

@kamalmarhubi smart to use strip-prefix :-).

Anyways, the fix is in bazel upstream again and will be part of the 0.5.4 release.

[perezd]

So, once 0.5.4 is available, what should we do to make use of this? Will it start to just work automatically?

[buchgr]

Someone needs to add proto_library rules to protobuf's BUILD file :-). I can do that next week.

[aj-michael]

Now that bazel 0.5.4 is released, can someone please fix this 😄

[buchgr]

I am working on a change.

[buchgr]

Thanks @xfxyjwf !