Eclipse Mars was recently released and I felt like trying it out. It listed tighter integration with Gradle as one of its features via Buildship.
With Luna I was usi
Currently there is no "Convert to Gradle project" implemented in Buildship. However, if you remove the project and reimport it using the Gradle import wizard you should see the same exact project with the proper nature and the classpath container.
On top of that, if you have a Gradle project in your workspace and update the dependencies in the build script, you can refresh the classpath container by right-clicking on the project and select Gradle > Refresh projects
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A similar problem you were facing was discussed in the Gradle forums: discuss.gradle.org/t/adding-dependencies-to-projects/10415.
We also have a bug dedicated for this feature request: bugs.eclipse.org/bugs/show_bug.cgi?id=465355. Please vote for it and share your thoughts there too.
Regarding to the documentation: It's true that we haven't provided an official documentation for the central Eclipse help system, but there are some resources explaining the current functionality: