ClosureParams: how to specify generic types for closure parameter in groovy

Question

I have the following method in Java:

public void myMethod(
        @ClosureParams(
                value = SimpleType.class,
                options = {
                        "java.util.Map"
                }
        ) Closure closure
) {
    ...
}

which has @ClosureParams to specify closure's parameter types for static type checker and type inference in IDEA.

In the Groovy script, I call this method as follows:

myMethod { Map doc ->
    ...
}

and it works fine. But when I try to specify generic types for java.util.Map of closure in my java method:

public void myMethod(
        @ClosureParams(
                value = SimpleType.class,
                options = {
                        "java.util.Map" // <-- added here
                }
        ) Closure closure
) {
    ...
}

groovy's static type checker fails with error:

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
C:\myproject\script.groovy: 1: Expected parameter of type java.util.Map but got java.util.Map 
 @ line 1, column 8.
myMethod { Map doc ->

although IDEA infers the type of doc without any Map or Map<...> using @ClosureParams hint.

When I look into the source of groovy.transform.stc.SimpleType class, I see that this class does not give the ability to specify generic types as it uses plain Class.forName:

public class SimpleType extends SingleSignatureClosureHint {
    @Override
    public ClassNode[] getParameterTypes(final MethodNode node, final String[] options, final SourceUnit sourceUnit, final CompilationUnit unit, final ASTNode usage) {
        ClassNode[] result = new ClassNode[options.length];
        for (int i = 0; i < result.length; i++) {
            result[i] = findClassNode(sourceUnit, unit, options[i]);
        }
        return result;
    }
 }

    // findClassNode method:
    protected ClassNode findClassNode(final SourceUnit sourceUnit, final CompilationUnit compilationUnit, final String className) {
        if (className.endsWith("[]")) {
            return findClassNode(sourceUnit, compilationUnit, className.substring(0, className.length() - 2)).makeArray();
        }
        ClassNode cn = compilationUnit.getClassNode(className);
        if (cn == null) {
            try {
                cn = ClassHelper.make(Class.forName(className, false, sourceUnit.getClassLoader()));
            } catch (ClassNotFoundException e) {
                cn = ClassHelper.make(className);
            }
        }
        return cn;
    }

My question: how to specify closure parameter type with generics in groovy? Preferably with support in IDEA.

user_2194470 · Answer

You can use groovy.transform.stc.FromString signature hint to get the generic types working. Consider the following example:

JavaClass.java

import groovy.lang.Closure;
import groovy.transform.stc.ClosureParams;
import groovy.transform.stc.FromString;

import java.util.HashMap;

public class JavaClass {

    public static void processRendered(@ClosureParams(
            value = FromString.class,
            options = {"java.util.Map"}) Closure closure) {

        closure.call(new HashMap());
    }
}

script.groovy

import groovy.transform.CompileStatic
import static JavaClass.processRendered

@CompileStatic
def test() {
  processRendered { Map map ->
    map.put("test", 1)
  }

  processRendered {
    it.put("test", 2)
  }
}

test()

It compiles and gives you signature hint, also for the implicit it variable.

The following example uses Groovy 2.5.7.

ClosureParams: how to specify generic types for closure parameter in groovy

1 Answers