[Build, IGS] Deserialize setup json using kotlinx-serialization-json

#KTI-1223 In Progress

repo/gradle-settings-conventions/internal-gradle-setup/build.gradle.kts

@@ -1,6 +1,7 @@
 plugins {
     `kotlin-dsl`
-    id("org.jetbrains.kotlin.jvm")
+    kotlin("jvm")
+    kotlin("plugin.serialization")
 }
 
 repositories {
@@ -8,8 +9,19 @@ repositories {
     gradlePluginPortal()
 }
 
+dependencies {
+    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.5.0")
+    implementation(kotlin("test-junit5"))
+}
+
 kotlin.jvmToolchain(8)
 
+tasks {
+    test {
+        useJUnitPlatform()
+    }
+}
+
 gradlePlugin {
     plugins {
         create("internal-gradle-setup") {

repo/gradle-settings-conventions/internal-gradle-setup/src/main/kotlin/SetupFile.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.build
+
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.decodeFromString
+import kotlinx.serialization.json.Json
+import java.io.BufferedReader
+import java.io.InputStream
+import java.io.InputStreamReader
+import kotlin.streams.asSequence
+
+@Serializable
+internal data class SetupFile(
+    val properties: Map<String, String>,
+)
+
+// can't use decodeFromStream: https://github.com/Kotlin/kotlinx.serialization/issues/2218
+internal fun parseSetupFile(inputStream: InputStream): SetupFile =
+    Json.decodeFromString(BufferedReader(InputStreamReader(inputStream)).lines().asSequence().joinToString("\n"))

repo/gradle-settings-conventions/internal-gradle-setup/src/test/kotlin/SetupFileParseTest.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.build
+
+import kotlin.test.*
+
+class SetupFileParseTest {
+    private fun openPropertiesJsonStream() =
+        SetupFileParseTest::class.java.classLoader.getResourceAsStream("properties.json")
+            ?: error("No properties.json file found in test resources")
+
+    @Test
+    fun testSimpleParsing() {
+        val setupFile = openPropertiesJsonStream().use {
+            parseSetupFile(it)
+        }
+        assertEquals(
+            mapOf(
+                "newProperty1" to "someValue",
+                "newProperty2" to "someOtherValue",
+                "alreadySetProperty" to "newValue",
+            ),
+            setupFile.properties
+        )
+    }
+}

repo/gradle-settings-conventions/internal-gradle-setup/src/test/resources/properties.json

@@ -0,0 +1,7 @@
+{
+  "properties": {
+    "newProperty1": "someValue",
+    "newProperty2": "someOtherValue",
+    "alreadySetProperty": "newValue"
+  }
+}