GH-38: Import .proto files from maven dependencies

[ascopes]

New features to add the ability to "import" protobuf sources from other locations, including other JARs and other directories, without including them for compilation.

This allows referencing dependencies in a similar way to how Java manages this, and provides the ability to recursively pull in these imports. This has been done because, as an example, depending on com.google.api.grpc:proto-google-common-protos requires protoc to be able to see the protobuf stubs in com.google.protobuf:protobuf-java as well.

Example configuration and output

<plugin>
  <groupId>${plugin-group-id}</groupId>
  <artifactId>${plugin-artifact-id}</artifactId>
  <version>${plugin-version}</version>

  <configuration>
    <additionalImports>
      <additionalImport>mvn:com.google.api.grpc:proto-google-common-protos:2.29.0</additionalImport>
    </additionalImport>
    <protocVersion>${protobuf.version}</protocVersion>
  </configuration>

  <executions>
    <execution>
      <phase>generate-sources</phase>
      <goals>
        <goal>generate</goal>
      </goals>
    </execution>
  </executions>
</plugin>

[INFO] --- protobuf:0.0.2-SNAPSHOT:generate (default) @ example ---
[INFO] Resolving mvn:com.google.protobuf:protoc:3.25.0:exe:linux-x86_64 from Maven repositories
[INFO] Resolved mvn:com.google.protobuf:protoc:3.25.0:exe:linux-x86_64 to local path '/.../protoc-3.25.0-linux-x86_64.exe'
[INFO] Resolving mvn:com.google.api.grpc:proto-google-common-protos:2.29.0:jar from Maven repositories
[INFO] Resolving dependencies of mvn:com.google.api.grpc:proto-google-common-protos:2.29.0:jar from Maven repositories
[INFO] Extracting contents of '/.../protobuf-java-3.25.1.jar' to /.../target/protobuf-extracted/protobuf-java-3.25.1
[INFO] Extracting contents of '/.../proto-google-common-protos-2.29.0.jar' to /.../target/protobuf-extracted/proto-google-common-protos-2.29.0
[INFO] Discovering protobuf sources in /.../src/main/protobuf
[INFO] Discovered a total of 1 protobuf source(s) to compile
[INFO] Invoking [/.../protoc-3.25.0-linux-x86_64.exe, --version]
[INFO] >>> libprotoc 25.0
[INFO] Protoc completed after 7ms with exit code 0
[INFO] Invoking [/.../protoc-3.25.0-linux-x86_64.exe, --proto_path=/.../target/protobuf-extracted/protobuf-java-3.25.1, --proto_path=/.../target/protobuf-extracted/proto-google-common-protos-2.29.0, --proto_path=/.../src/main/protobuf, --java_out=/.../target/generated-sources/protobuf, /.../src/main/protobuf/car.proto]
[INFO] Protoc completed after 3ms with exit code 0

This implementation is a work in progress and may not yet be fully functional for certain cases.

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (cd3147d) 85.82% compared to head (9d57d4f) 86.98%.

Files	Patch %	Lines
...avenplugin/dependencies/MavenArtifactResolver.java	84.00%	4 Missing ⚠️
.../protobufmavenplugin/generate/SourceGenerator.java	88.57%	3 Missing and 1 partial ⚠️
...obufmavenplugin/dependencies/ArchiveExtractor.java	93.54%	1 Missing and 1 partial ⚠️
...tobufmavenplugin/dependencies/MavenCoordinate.java	94.28%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
+ Coverage   85.82%   86.98%   +1.15%     
==========================================
  Files          15       18       +3     
  Lines         395      507     +112     
  Branches       27       35       +8     
==========================================
+ Hits          339      441     +102     
- Misses         45       52       +7     
- Partials       11       14       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.