[Build] Failure to build with "expected identifier before ‘alignas’`"

[veblush]

What version of protobuf and what language are you using?

Protobuf commit 9f40411

What operating system (Linux, Windows, ...) and version?

Linux Debian 11 using Docker

What runtime / compiler are you using (e.g., python version or gcc version)

gcc 10 / cmake build with -DBUILD_SHARED_LIBS=ON

What did you do?

Build protobuf with cmake -DBUILD_SHARED_LIBS=ON option

What did you expect to see

Successful build

What did you see instead?

Build failure with log

[ 36%] Building CXX object third_party/protobuf/CMakeFiles/libprotobuf.dir/src/google/protobuf/any.cc.o
In file included from /var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/any.pb.h:21,
                 from /var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/any.pb.cc:6:
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:145:23: error: expected identifier before ‘alignas’
  145 | class PROTOBUF_EXPORT alignas(8) Arena final {
      |                       ^~~~~~~
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:145:40: error: expected initializer before ‘final’
  145 | class PROTOBUF_EXPORT alignas(8) Arena final {
      |                                        ^~~~~
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:659:61: error: invalid use of incomplete type ‘class google::protobuf::Arena’
  659 | PROTOBUF_NOINLINE void* Arena::DefaultConstruct(Arena* arena) {
      |                                                             ^
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:51:7: note: forward declaration of ‘class google::protobuf::Arena’
   51 | class Arena;    // defined below
      |       ^~~~~
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:667:76: error: invalid use of incomplete type ‘class google::protobuf::Arena’
  667 | PROTOBUF_NOINLINE void* Arena::CopyConstruct(Arena* arena, const void* from) {
      |                                                                            ^
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:51:7: note: forward declaration of ‘class google::protobuf::Arena’
   51 | class Arena;    // defined below
      |       ^~~~~
/var/local/jenkins/grpc/third_party/protobuf/src/google/protobuf/arena.h:675:37: error: expected initializer before ‘<’ token
  675 | inline void* Arena::AllocateInternal() {

Anything else we should know about your project / environment

• You can check the PR catching this issue; [Deps] Protobuf at head grpc/grpc#36626
• This test is running under this docker image; us-docker.pkg.dev/grpc-testing/testing-images-public/cxx_debian11_x64:a9c5d062364adc836b4068cad93a3e448b25c37c@sha256:9f9285da21c1053ac715027e0cee66c20c70ebf016053328a4cee61ffd37e59b

[zhangskz]

@sbenzaquen Looks like this was introduced in ec126a5, which undoes previous fix for this 32caf511c8. Can you take a look?

[veblush]

Verified and thanks for the quick fix. This issue can be closed if there is nothing to follow up with.

[zhangskz]

Thanks for confirming -- closing.

This was fixed via rollback: baeab50