Groovy: compiler mismatch after installation

You can also add an extension from the Spring Dashboard and keep using the "same" workspace.

On the sidebar of Dashboard click on "IDE EXTENSIONS".
Choose the groovy compiler that you need and click install.

After that you can customize each project to compile with a version of your choice.

Click on a project and then Project>Properties>Groovy Compiler and choose the version from the dropdown menu.

For example the latest version of Grails(2.4.0) is "buggy" under GGTS(3.5.1) until you install Groovy 2.3 Compiler extension and change your Projects properties accordingly.

Grails 2.4 doc whatsNew

UPDATE for Grails 3.0

For Grails 3.0.x you should install and use Groovy 2.4 Compiler

Grails 3.0 doc whatsNew

I got same error but following option resolved it for me Right Click on Project , Go to Groovy -> Fix Compiler Mismatch Problems. Click on it , it asks for selecting the correct version of compiler select it , clean-build your application and restart it , it should work fine.