Gradle share properties in multi-project - gradle

Question

I'm quite new to Gradle, trying to make multi-project. In root project declares all common libs (also their versions as properties) and apply plugins.
For example, root and child common projects.
In root's settings.gradle type:
rootProject.name = 'root'
include 'common'
In root's build.gradle type:
buildscript {
ext.kotlin_version = '1.3.11'
repositories {
mavenCentral()
}
dependencies {
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
}
}
subprojects {
buildscript {
repositories {
mavenCentral()
}
}
apply plugin: 'kotlin'
repositories {
mavenCentral()
}
dependencies {
compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
}
}
And now I'd like to use another library only in specific child project. Do this in common's build.gradle:
buildscript {
dependencies {
classpath "org.jetbrains.kotlin:kotlin-allopen:$kotlin_version"
}
}
It's work fine when running gradle commands from root's folder, but failed with message Could not get unknown property 'kotlin_version' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler when running from common's folder.
What I'm doing wrong? Or is there any way around? And what are best practices for sharing libs and properties in multi-project?
For me, it looks like common know nothing about it's "parent" project, all relations defined in root's settings.

Answer 1

The reason why Gradle cannot resolve the property is because the project in folder common is named commons. This is caused by a spelling mistake in common's settings.gradle. This is fortunately easy to fix (common/settings.gradle) :
rootProject.name = 'common'
Alternatively, just delete the common/settings.gradle, it's fully optional in this case.
Consider reading the official Gradle documentation for authoring multi-project builds and the guide create multi-project builds for more information and best practices around multi-project builds.