How to import a helper class in buildSrc/build.gradle.kts, settings.gradle.kts, and build.gradle.kts?

Question

I'd like to create a class to help me loading different types of properties (local.properties, gradle.properties, $GRADLE_HOME/gradle.properties, environment variables, system properties, and custom properties files (maybe in other formats like yml, xml, etc.).

Also, I'd like to use this in my buildSrc/build.gradle.kts, settings.gradle.kts, and build.gradle.kts.

Please consider that we are using Gradle 6.+.

A simple implementation of this class would be (the full implementation would be a lot of more powerful):

plugins/properties/build.gradle.kts:

package com.example

object Properties {
    val environmentVariables = System.getenv()
}

How can we successfully import this Properties class in all of those files (buildSrc/build.gradle.kts, settings.gradle.kts, build.gradle.kts) and use it from there? Something like:

println(com.example.Properties.environmentVariables["my.property"])

Can we do that creating this class inside of a plugin and applying it from there? Without pre-compiling and releasing the plugin? Maybe something like:

apply("plugins/properties/build.gradle.kts")

How would it be a minimal implementation for this?

I tried different approaches but I'm not being able to find a way that work with those 3 files altogether.

Abbreviation

Answer 1

I'm not completely satisfied with this approach but maybe it can help others. I wasn't able to reuse a class but a function in all places, like this:

settings.gradle.kts

    apply("plugin/properties/build.gradle.kts")
    @Suppress("unchecked_cast", "nothing_to_inline")
    inline fun <T> uncheckedCast(target: Any?): T = target as T
    val getProperty = uncheckedCast<(key: String) -> String>(extra["getProperty"])
    println(getProperty("group"))

buildSrc/build.gradle.kts

    apply("../plugin/properties/build.gradle.kts")
    @Suppress("unchecked_cast", "nothing_to_inline")
    inline fun <T> uncheckedCast(target: Any?): T = target as T
    val getProperty = uncheckedCast<(key: String) -> String>(extra["getProperty"])
    println(getProperty("group"))

build.gradle.kts

    // Can be used inside of the file
    apply("plugin/properties/build.gradle.kts")
    @Suppress("unchecked_cast", "nothing_to_inline")
    inline fun <T> uncheckedCast(target: Any?): T = target as T
    val getProperty = uncheckedCast<(key: String) -> String>(extra["getProperty"])
    println(getProperty("group"))

    buildScript {
        // Since the other getProperty is not visible here we need to do this again.
        apply("plugin/properties/build.gradle.kts")
        @Suppress("unchecked_cast", "nothing_to_inline")
        inline fun <T> uncheckedCast(target: Any?): T = target as T
        val getProperty = uncheckedCast<(key: String) -> String>(extra["getProperty"])
        println(getProperty("group"))
    }

plugin/properties/build.gradle.kts

    import java.io.File
    import java.nio.file.Path
    import java.nio.file.Paths
    import java.util.Properties as JavaProperties
    import org.gradle.api.initialization.ProjectDescriptor
    
    object Properties {
    
        lateinit var rootProjectAbsolutePath : String
    
        val local: JavaProperties by lazy {
            loadProperties(JavaProperties(), Paths.get(rootProjectAbsolutePath, "local.properties").toFile())
        }
    
        val environment by lazy {
            System.getenv()
        }
    
        val system: JavaProperties = JavaProperties()
    
        val gradle: JavaProperties by lazy {
            loadProperties(JavaProperties(), Paths.get(rootProjectAbsolutePath, "gradle.properties").toFile())
        }
    
        val globalGradle: JavaProperties by lazy {
            loadProperties(JavaProperties(), Paths.get(System.getProperty("user.home"), ".gradle", "gradle.properties").toFile())
        }
    
        fun containsKey(vararg keys: String): Boolean {
            if (keys.isNullOrEmpty()) return false
    
            keys.forEach {
                when {
                    local.containsKey(it) -> return true
                    environment.containsKey(it) -> return true
                    system.containsKey(it) -> return true
                    gradle.containsKey(it) -> return true
                    globalGradle.containsKey(it) -> return true
                }
            }
    
            return false
        }
    
        fun get(vararg keys: String): String {
            return this.getAndCast<String>(*keys) ?: throw IllegalArgumentException("Property key(s) ${keys} not found.")
        }
    
        fun getOrNull(vararg keys: String): String? {
            return getAndCast<String>(*keys)
        }
    
        inline fun <reified R> getOrDefault(vararg keys: String, default: R?): R? {
            return getAndCast<R>(*keys) ?: default
        }
    
        inline fun <reified R> getAndCast(vararg keys: String): R? {
            if (keys.isNullOrEmpty()) return null
    
            keys.forEach {
                val value = when {
                    local.containsKey(it) -> local[it]
                    environment.containsKey(it) -> environment[it]
                    system.containsKey(it) -> system[it]
                    gradle.containsKey(it) -> gradle[it]
                    globalGradle.containsKey(it) -> globalGradle[it]
                    else -> null
                }
    
                // TODO Improve the casting using Jackson
                if (value != null) return value as R
            }
    
            return null
        }
    
        private fun loadProperties(target: JavaProperties, file: File): JavaProperties {
            if (file.canRead()) {
                file.inputStream().use { target.load(it) }
            }
    
            return target
        }
    }
    
    if (rootProject.name == "buildSrc") {
        Properties.rootProjectAbsolutePath = rootDir.parent
    } else {
        Properties.rootProjectAbsolutePath = rootDir.absolutePath
    }
    
    extra["getProperty"] = {key: String -> Properties.get(key)}

Abbreviation