Why did json views syntax change between Grails 4 and Grails 5?

Question

While upgrading a Grails 4 application to Grails 5, I encountered a failure in one of the json views (.gson file) when specifying a field having an empty map. In Grails 4, this worked fine, but in Grails 5 I have to put parentheses around the empty map literal, or the render call fails saying that there is no property of the view class with that name.

I wrote the following unit test to reproduce the behavior:

import grails.plugin.json.view.test.JsonRenderResult
import grails.plugin.json.view.test.JsonViewTest
import spock.lang.Specification

class GrailsViewsCollectionsSpec extends Specification implements JsonViewTest {

    void "test value rendering in json views"() {
        when: "A gson view is rendered"
        JsonRenderResult result = render("""json {
            foo null
            bar false
            baz 0
            cheese "is good"
            hello([])
            world([:])
        }""")

        then:
        result.json.toString() == "{foo=null, bar=false, baz=0, cheese=is good, hello=[], world={}}"
    }
}

In Grails 4, I can get away with world [:], but in Grails 5, it needs to be world([:]).

What changed that causes this syntax to become less groovy?

Answer 1

Part of Grails 5 was upgrading to Apache Groovy 3.

Alpha versions of Groovy 3 incorrectly let you leave off the brackets when printing empty maps, but they are now required, e.g println([:]).

Refs:
Grails Blog -> Grails Framework Exciting Updates -> Announcing Grails 5!.

Release notes for Groovy 3.0 -> Other breaking changes