protoc extensions supported.

[noel-yap]

Custom protoc options (https://developers.google.com/protocol-buffers/docs/proto3#custom_options) are implemented via extensions (https://developers.google.com/protocol-buffers/docs/reference/java-generated#extension). If a custom option is to be processed by a protoc plugin, the plugin code must register the extension. For example (from the docs):

ExtensionRegistry registry = ExtensionRegistry.newInstance();
registry.add(Baz.fooExt);
Foo foo = Foo.parseFrom(input, registry);

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @noel-yap to sign the Salesforce Contributor License Agreement.

[codecov]

Codecov Report

Merging #27 into master will decrease coverage by 1.03%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master      #27      +/-   ##
============================================
- Coverage     58.14%   57.11%   -1.04%     
  Complexity       97       97              
============================================
  Files            19       19              
  Lines           442      450       +8     
  Branches         33       34       +1     
============================================
  Hits            257      257              
- Misses          177      185       +8     
  Partials          8        8

Impacted Files	Coverage Δ	Complexity Δ
...main/java/com/salesforce/jprotoc/ProtocPlugin.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...ava/com/salesforce/jprotoc/jdk8/Jdk8Generator.java	0% <0%> (ø)	0% <0%> (ø)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2dd1eb8...75afb39. Read the comment docs.

[rmichela]

Thanks for the PR! Could you elaborate on what this does?

[rmichela]

Looking good! Can you also add a section to the JProtoc README.md with an example of how to author an generator that uses extensions?

[rmichela]

Needs JavaDoc.

[noel-yap]

Done.

[rmichela]

Please add a comment explaining what the extensionRegistry does.

[noel-yap]

Done.

[rmichela]

Do I have to run the protobuf generator as part of the build process for my protobuf plugin? Do I need to add this to my plugin project's POM?

[noel-yap]

I'm not familiar with Maven but I don't see any reason anything in the build would have to change. All the processing is done at protoc run-time when protoc calls the protoc plugin.

[rmichela]

Maybe I'm not understanding correctly. Where does the type com.example.proto.options.ServerOptionsProto.server come from in the example below? Perhaps you could add an elaborated example in jprotoc-test?

[noel-yap]

Oh, that's generated by protoc. Those not creating custom options don't need to run protoc to generate the related Java code for the option. I'm assuming those creating custom options would know how to run protoc to do that. I can add a blurb about running protoc if you want.

[rmichela]

I see...My JProtoc Protobuf generator project would itself contain Protobuf generated code (it's proto all the way down!). A line to say "Run the Protoc generator on the Extension proto" should suffice.

[noel-yap]

Done.

[noel-yap]

I'm not understanding the output of the code coverage report. Some lines (eg ProtocPlugin.java:44) are marked red but I don't see how that could be since the entrypoint should have been covered by some previous test. Were the reports added later and there's actually no test covering ProtocPlugin.generate()? I'm not finding any test code that calls it.

[rmichela]

Ignore the CodeCov report. I'm still trying to get it working right. 😉