Please follow these instructions to get and compile the source code:

1. Download Eclipse "for RCP and RAP Developers"
2. Get the latest version of Xtext and EMF SDK
3. Get protobuf-dt source from the Git repo
4. Create the folder "src-gen" in both projects com.google.eclipse.protobuf and com.google.eclipse.protobuf.ui
5. Go to project com.google.eclipse.protobuf and navigate to the file GenerateProtobuf.mwe2 (in the package com.google.eclipse.protobuf, in the src folder)
6. Right-click GenerateProtobuf.mwe2 and select "Run As" > "MWE2 Workflow"

That will generate the Xtext-based infrastructure needed. Now the source code is complete, simply run the project com.google.eclipse.protobuf as an "Eclipse Application."

Enjoy!