When coding Groovy, @CompileStatic can help to spot errors and improve performance of production code. Unfortunately, @CompileStatic is optional and hence easy to forget, but thankfully Groovy has documented a way to make @CompileStatic for all production code: http://docs.groovy-lang.org/latest/html/documentation/#_static_compilation_by_default
(Test code is not affected, because it is nice with flexibility when testing.)
However, with Grails you really want to use @GrailsCompileStatic instead of @CompileStatic, because it saves you from adding @CompileDynamic all the places that dynamic Grails functionality is used while still ensuring that your own code is @CompileStatic. Unfortunately, the above solution cannot be used for applying @GrailsCompileStatic to all production code. This is due to @GrailsCompileStatic is not available at the Compile Configuration and trying to @Grab it from grails-core only yields new dependency problems.
Eventually, I realised that @GrailsCompileStatic is just @CompileStatic with some extensions – those can be included in the Compile Configuration manually and then it works as expected.
This is my src/groovyCompile/groovyConfig.groovy:
// Extensions are copied from @GrailsCompileStatic due to that @GrailsCompileStatic is not available in the Compile Configuration
ASTTransformationCustomizer grailsCompileStatic = new ASTTransformationCustomizer([extensions: extensions], CompileStatic)
At build.gradle, I also added the following:
compileGroovy.groovyOptions.configurationScript = file('src/groovyCompile/groovycConfig.groovy')
Let me know if this works for you – feedback is the best motivator!