vscode-java reports "cannot be resolved" errors in Gradle plugin project with mix of Groovy and Java

In Gradle plugins implemented with a mix of Java and Groovy, vscode-java reports "cannot be resolved" errors in .java files that reference classes defined in .groovy files. Gradle can compile and build the plugin successfully.

Environment

• Operating System: macOS 10.15.4
• JDK version:

  openjdk version "13.0.2" 2020-01-14
  OpenJDK Runtime Environment (build 13.0.2+8)
  OpenJDK 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)
  

• Visual Studio Code version:

  Version: 1.45.0-insider
  Commit: abb4a35cfc26102f93fd00df7b59ce1a19c2017a
  Date: 2020-04-28T05:34:21.109Z (20 hrs ago)
  

• Java extension version: 0.60.0

Steps To Reproduce

1. Clone https://github.com/a01fe/gradle-groovy-java-plugin
2. cd gradle-groovy-java-plugin/test; ./gradlew javaTask
   This builds the plugin and runs a task in the plugin to verify it compiles and builds successfully
3. Open the project in vscode and open src/main/groovy/foo/task/JavaTask.java, vscode-java reports errors on all the references to JavaTaskSpec.

まず cd gradle-groovy-java-plugin/test; ./gradlew javaTask で問題を再現し、次に VS Code で src/main/groovy/foo/task/JavaTask.java を開いて、JavaTaskSpec への参照に表示される診断を確認します。language server の動作を成功する Gradle ビルドと比較し、これらの誤った "cannot be resolved" エラーが表示されなくなれば完了です。