gradlegroovydslgradle-pluginbuild-script

What kind of code element is the 'apply from' part in the gradle DSL closure passed to 'buildscript'?

I'm trying to figure out what kind of code element the apply from is:

buildscript {
    apply from: rootProject.file("gradle/versions.gradle")
    repositories {
        google()
        ...
    }
    dependencies {
        classpath plugin.android_gradle_plugin
        ...
    }
}

From this post i understand that the buildscript gradle function is called with a closure, so we can add the omitted brackets:

buildscript ({
    apply from: rootProject.file("gradle/versions.gradle")
    repositories ({
        google()
        ...
    })
    dependencies ({
        classpath plugin.android_gradle_plugin
        ...
    })
})

I first thougt the apply from is a label but then when could that label actually be used? Not to mention that groovy doesn't mention that labels are allowed to have spaces.

Then i thought it could be a property initialization (new Coordinates(latitude: 43.23, longitude: 3.67)), but apply from is in a closure.

At last i read about "curry", like this:

def nCopies = { int n, String str -> str*n }    
def twice = nCopies.curry(2)                    
assert twice('bla') == 'blabla'

So the apply from part could be evaluated first when using the closure, but even then i am still unaware if the apply from is a label or some kind of assignment and what purpose it serves.

So, what kind of code element is the apply from part?

Solution

  • TL;DR: It's a function call with a map as argument

    apply from: rootProject.file("gradle/versions.gradle")

    Is short for:

    apply(from: rootProject.file("gradle/versions.gradle"))

    ("Parens are optional, if unambiguous")

    Is short for:

    apply([from: rootProject.file("gradle/versions.gradle"]))

    (If maps are passed, you can leave out the [] around the map literal)