[BUG][Protobuf-Generator] generating arbitray protocol buffers - commit c96d3088c506f6af09b095e7b25828fce17985dc breaks existing protobuf users

Bug Report Checklist

• What's the actual output vs expected output? In a protobuf file: fileName vs file_name

Description

in https://github.com/OpenAPITools/openapi-generator/commit/c96d3088c506f6af09b095e7b25828fce17985dc the protobuf generator switches the variable names inside the proto from camelCase to snake_case. While this is the correct way to deal with protobufs, it breaks existing projects.

It would be delightful if you provided an option to keep the old behavior to not break systems that already use the protobuf-generator.

openapi-generator version

7.13.0, it is a regression for existing projects that have been using < 7.13.0

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Watch the diff of a proto file generated from 7.12 and 7.13 - the content has been changed.

Related issues/PRs

Suggest a fix

In modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ProtobufSchemaCodegen.java, I think around line 518 I think we would need to check with an if statement if someone provided a command line switch to use the old behavior.

Start in modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ProtobufSchemaCodegen.java around line 518, and compare the generated proto output from versions 7.12 and 7.13. Determine how a command-line switch should select the previous naming behavior, then verify that enabled and default generation produce the expected variable names.