Groovy closure without preceding equal sign prop = {} vs prop {} - groovy

Question

I'm trying to create a config file for my java app that can have lazy evaluation, for instance, contain an e-mail template with current date time. I use ConfigSlurper to parse the config file.
For some reason I can't find at https://groovy-lang.org/closures.html the description of the commonly used form (see build.gradle): prop1 { ... } prop2 { ... }. Am I looking at the wrong place?
My tests show that such closures are evaluated immediately and the example above can be rewritten as: prop1 = { ... }() prop2 = { ... }() (notice the parentheses, without them the evaluation is lazy).
I also don't understand why using dots in property without the equal sign cause MissingMethodException: No signature of method: groovy.util.ConfigObject.URL() if I use: server.URL { System.out.println('ccc'); 'asd' } in the example below.
It's disappointing that the choice is completely transparent for Groovy, but you have to check that a value is instance of Closure or GString when using java.
I used this article as the starting point https://blog.mrhaki.com/2009/08/grassroots-groovy-configuration-with.html
// We can group settings.
// The following settings are created:
// app.version, app.setting1, app.setting2, app.setting3, app.date, app.active
app {
System.out.println('aaa')
version = "1.0"
// We can write code to set up settings.
[1, 2, 3].each {
this."setting${it}" = it * 10
}
// We can use Java objects
date = new Date()
active = true
}
server.URL = "http://default"
// Environment specific settings override settings with the
// same name.
environments {
development {
server = { System.out.println('ccc'); 'asd' }
// server.URL = "${-> System.out.println('bbb');new Date()}http://localhost"
}
test {
server.URL = 'http://test:9080'
}
integrationtest {
server.URL = 'http://integrationtest/url'
}
production {
server.URL = 'http://prod/url'
}
}

Answer 1

My tests show that such closures are evaluated immediately and the
example above can be rewritten as: prop1 = { ... }()
Closures are not evaluated immediately. The parens above are causing the closure to be evaluated.
For some reason I can't find at https://groovy-lang.org/closures.html
the description of the commonly used form (see build.gradle): prop1 {
... } prop2 { ... }.
prop1 {} is invoking a method named prop1 and passing a closure as a parameter That code is equivalent to this:
def myClosure = {}
prop1(myClosure)
I also don't understand why using dots in property without the equal
sign cause MissingMethodException: No signature of method:
groovy.util.ConfigObject.URL()
Something like server.URL = 'http://test:9080' is assigning a value (http://test:9080) to a property (server.URL). If you remove the equal sign you are changing the expression fundamentally and then would be invoking a method named URL on an object named server and passing http://test:9080 as a parameter.