protobuf-kotlin 3.20 duplicate classes with protobuf-java

[maikelvdh]

What version of protobuf and what language are you using?
Version: 3.20.0
Language: Kotlin

What operating system (Linux, Windows, ...) and version?
macOS 12.2.1

What runtime / compiler are you using (e.g., python version or gcc version)
Protoc 3.20.0
Gradle 7.4.2

What did you do?
Steps to reproduce the behavior:

1. Create a new Android studio project
2. Add dependency on com.google.protobuf:protobuf-kotlin:3.20.0
3. Build project
4. See error

What did you expect to see
Project builds successfully

What did you see instead?
Gradle outputs the following set of errors (reduced the size):

Duplicate class com.google.protobuf.Any found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.Any$1 found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.Any$Builder found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.AnyOrBuilder found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.AnyProto found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.Api found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.Api$1 found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.Api$Builder found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.ApiOrBuilder found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.ApiProto found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.BoolValue found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)
Duplicate class com.google.protobuf.BoolValue$1 found in modules protobuf-java-3.20.0 (com.google.protobuf:protobuf-java:3.20.0) and protobuf-kotlin-3.20.0 (com.google.protobuf:protobuf-kotlin:3.20.0)

As the error suggests, this is caused because both protobuf-kotlin and protobuf-java include the same generated sources from proto files. This seems to be introduced with following change: a32a2a3

[deannagarcia]

Thanks for this report! Working on a PR to fix it now.

[deannagarcia]

Should be fixed by #9909, let me know if you still see this problem.