libprotoc version is not correct in docker build

[bonito-skipjack]

What type of bug is this?

Other

What subsystems are affected?

Other

What happened?

The README.md file clearly states if I built from source, that protoc version needs greater or equal to 3.15. But in Dockerfile, after docker builds, the version is 3.12.4.

What operating system did you use?

Ubuntu 22.04

Relevant log output and stack trace

# protoc --version
libprotoc 3.12.4

How can we reproduce the bug?

Run docker build

[waynexia]

Thanks for your report!

I search into protoc's changelog and find out that

• optional support is added in 3.12.0 as an experimental feature, need experimental_allow_proto3_optional flag to enable it
• it goes stable in 3.15.0, and doesn't require extra flags since then.

2020-05-12 version 3.12.0 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)

  Protocol Compiler
  * [experimental] Singular, non-message typed fields in proto3 now support
    presence tracking. This is enabled by adding the "optional" field label and
    passing the --experimental_allow_proto3_optional flag to protoc.
    * For usage info, see docs/field_presence.md.
    * During this experimental phase, code generators s

2021-02-05 version 3.15.0 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)

  Protocol Compiler
  * Optional fields for proto3 are enabled by default, and no longer require
    the --experimental_allow_proto3_optional flag.

And tonic-build also mentions this: https://github.com/hyperium/tonic/blob/933f5607350af983e479219a2ef3688484976968/tonic-build/src/prost.rs#L354-L360

But now the codebase doesn't contain optional protocol as we are in progress of refactoring our gRPC protocol. I guess that's why 3.12.4 could compile.