Added initial configuration to measure K2 performance

Author: Tapchicoma

.gitignore

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+.idea/
+.gradle/
+build/
+.kotlin/
+local.properties
+/reports

README.md

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+# Description
+
+This projects allows you to run performance tests on your Gradle project to compare 
+performance difference between [Kotlin K1 and K2 compilers](https://blog.jetbrains.com/kotlin/2023/02/k2-kotlin-2-0/). 
+
+Performance tests will build your project with kotlin `2.0.0-RC1` and kotlin `1.9.23` releases by running `assmeble` task.
+The `assemble` task is used by default to build your project.
+Benchmarks will be run three scenarios: "clean build",
+"incremental build with non-ABI changes" and "incremental build with ABI changes".
+After benchmark will finish open [benchmarkResult.ipynb](benchmarkResult.ipynb) Kotlin notebook to compare Gradle
+and Kotlin time in the produced result.
+
+## Getting Started
+
+## Project requirements
+
+Project should allow changing the Kotlin version via `kotlin_version` Gradle property.
+
+If a project is using version catalog,
+you can update `settings.gradle.kts` files in it to override the kotlin version:
+```kotlin
+versionCatalogs {
+    create("libs") {
+        val kotlinVersion = System.getenv("kotlin_version")
+        if (kotlinVersion != null) {
+            version("kotlin", kotlinVersion)
+        }
+    }
+}
+
+```
+
+## Tested project
+
+There are two options to configure your project for performance tests:
+- set the path to your project via `project.path` in [gradle.properties](gradle.properties).
+- set `project.git.url` and `project.git.commit.sha` in [gradle.properties](gradle.properties) to clone a project from git repository. 
+
+In addition, you can specify directory where the project will be stored with `project.git.directory` property, 
+otherwise Git project name will be used.
+
+## Update build scenarios for your project  
+
+Additional scenarios configuration is required to run performance tests on your project. 
+Please set in [gradle.properties](gradle.properties) the following properties:
+- set list of files split by comma for incremental build with non-ABI changes in `scenario.non.abi.changes` property
+- set a single file path for incremental build with ABI change in `scenario.abi.changes` property
+- set the default task to build your project in `scenario.task` property, otherwise `assemble` task will be used.
+
+## Custom build scenarios
+
+If you are interested in running performance build on custom scenarios, you can configure them via 
+`PerformanceTask.scenarios` task input,
+or set [Gradle profiler](https://github.com/gradle/gradle-profiler) scenario file via `PerformanceTask.scenarioFile` task input.
+
+For example, you can do follow update in [build.gradle.kts](build.gradle.kts) file to use custom scenarios:
+
+```kotlin
+
+import org.jetbrains.kotlin.k2.blogpost.PerformanceTask
+
+val customScenarios = listOf(Scenario(
+    name = "new scenario",
+    cleanTasks = listOf("clean_task_if_need"),
+    kotlinVersion = kotlinVersion,
+    tasks = listOf("task_to_execute"),
+    projectDir = project.projectDir,
+    nonAbiChanges = listOf("path_to_file"),
+    warmUpRounds = 5,
+    executionRounds = 5,
+))
+
+val benchmark_2_0 = PerformanceTask.registerPerformanceTask(project, "benchmark_2_0", "2.0.0-RC1") {
+    scenarios.set(customScenarios)
+}
+
+val benchmark_1_9 = PerformanceTask.registerPerformanceTask(project, "benchmark_1_9", "1.9.23") {
+    scenarios.set(customScenarios)
+}
+
+tasks.register("runBenchmarks") {
+    dependsOn(benchmark_2_0, benchmark_1_9)
+}
+
+```
+
+## Run performance test
+Please set up `JAVA_HOME` and `ANDROID_HOME`(if need) variables before run tests
+
+Execute 
+```bash
+./gradlew runBenchmarks
+```
+
+## Visualise results
+
+To analyse benchmark results,
+you need to have installed [Kotlin notebook](https://blog.jetbrains.com/kotlin/2023/07/introducing-kotlin-notebook/) 
+plugin in IntelliJ IDEA.
+
+Please open [benchmarkResult.ipynb](benchmarkResult.ipynb) and run it with `Run All` action to compare produced results. 
+
+## Troubleshooting
+
+It is possible that a new warning appears in the build with kotlin `2.0.0`. 
+Please either fix them or disable `allWarningsAsErrors` compiler option if you use it.
+
+If  [dependencies verification](https://docs.gradle.org/8.2.1/userguide/dependency_verification.html#sub:enabling-verification) is enabled,
+please check that both kotlin `1.9` and kotlin `2.0` dependencies are included.
+
+The `JSON` build report output type is available since kotlin `2.0.0-RC1` and kotlin `1.9.23`. 
+If a `kotlinDsl` plugin is applied in the `buildSrc` subproject,
+we recommend to also apply `kotlin(“jvm”)` plugin to avoid any issues with unknown output type.