protobuf build for i686-unknown-linux-gnu fails in devcontainer

[mzabaluev]

While the protobuf crate is built successfully with the default toolchain in the devcontainer on x86_64 Linux, trying to build it for the i686 architecture results in C++ compiler failures.

Steps to reproduce

1. Enter the devcontainer shell in e.g. Visual Studio Code.
2. Run rustup target install i686-unknown-linux-gnu ¹.
3. Run sudo apt-get install gcc-multilib g++-multilib ¹.
4. Run cargo test --target i686-unknown-linux-gnu -p tests.

Error output

Lots of C++ compiler errors, including:

   /workspaces/prost/third_party/protobuf/src/google/protobuf/test_messages_proto2.pb.cc:10781:24: error: ‘::PROTOBUF_NAMESPACE_ID’ has not been declared
  10781 |     uint8_t* target, ::PROTOBUF_NAMESPACE_ID::io::EpsCopyOutputStream* stream) const {
        |                        ^~~~~~~~~~~~~~~~~~~~~
  /workspaces/prost/third_party/protobuf/src/google/protobuf/test_messages_proto2.pb.cc:10781:70: error: expected ‘,’ or ‘...’ before ‘*’ token
  10781 |     uint8_t* target, ::PROTOBUF_NAMESPACE_ID::io::EpsCopyOutputStream* stream) const {
        |                                                                      ^

Other observations

Building with the x86_64 target has google::protobuf generated instead of PROTOBUF_NAMESPACE_ID in the *.pb.cc files.

Footnotes

1. It would be nice to have these installed in the x86_64 devcontainer out of the box. ↩ ↩²