Add a system for client-side tests (#1219)

- Add a new ClientJavaExec Gradle task, which is used for client-side
   tests. This:

   - Copies the exec spec from another JavaExec task.
   - Sets some additional system properties to configure on gametest framework.
   - Runs Java inside an X framebuffer (when available), meaning we
     don't need to spin up a new window.

   We also configure this task so that only one instance can run at
   once, meaning we don't spawn multiple MC windows at once!

 - Port our 1.16 client test framework to 1.19. This is mostly the same
   as before, but screenshots no longer do a golden test: they /just/
   write to a folder. Screenshots are compared manually afterwards.

   This is still pretty brittle, and there's a lot of sleeps scattered
   around in the code. It's not clear how well this will play on CI.

 - Roll our own game test loader, rather than relying on the mod loader
   to do it for us. This ensures that loading is consistent between
   platforms (we already had to do some hacks for Forge) and makes it
   easier to provide custom logic for loading client-only tests.

 - Run several client tests (namely those involving monitor rendering)
   against Sodium and Iris too. There's some nastiness here to set up
   new Loom run configurations and automatically configure Iris to use
   Complementary Shaders, but it's not too bad. These tests /don't/ run
   on CI, so it doesn't need to be as reliable.

buildSrc/src/main/kotlin/cc/tweaked/gradle/MinecraftExec.kt

@@ -0,0 +1,202 @@
+package cc.tweaked.gradle
+
+import org.gradle.api.GradleException
+import org.gradle.api.file.FileSystemOperations
+import org.gradle.api.invocation.Gradle
+import org.gradle.api.provider.Provider
+import org.gradle.api.services.BuildService
+import org.gradle.api.services.BuildServiceParameters
+import org.gradle.api.tasks.*
+import org.gradle.kotlin.dsl.getByName
+import org.gradle.language.base.plugins.LifecycleBasePlugin
+import java.io.File
+import java.nio.file.Files
+import java.util.concurrent.TimeUnit
+import java.util.function.Supplier
+import javax.inject.Inject
+import kotlin.random.Random
+
+/**
+ * A [JavaExec] task for client-tests. This sets some common setup, and uses [MinecraftRunnerService] to ensure only one
+ * test runs at once.
+ */
+abstract class ClientJavaExec : JavaExec() {
+    private val clientRunner: Provider<MinecraftRunnerService> = MinecraftRunnerService.get(project.gradle)
+
+    init {
+        group = LifecycleBasePlugin.VERIFICATION_GROUP
+        usesService(clientRunner)
+    }
+
+    /**
+     * When [false], tests will not be run automatically, allowing the user to debug rendering.
+     */
+    @get:Input
+    val clientDebug get() = project.hasProperty("clientDebug")
+
+    /**
+     * When [false], tests will not run under a framebuffer.
+     */
+    @get:Input
+    val useFramebuffer get() = !clientDebug && !project.hasProperty("clientNoFramebuffer")
+
+    /**
+     * The folder screenshots are written to.
+     */
+    @get:OutputDirectory
+    val screenshots = project.layout.buildDirectory.dir("testScreenshots")
+
+    /**
+     * The path test results are written to.
+     */
+    @get:OutputFile
+    val testResults = project.layout.buildDirectory.file("test-results/$name.xml")
+
+    /**
+     * Copy configuration from a task with the given name.
+     */
+    fun copyFrom(path: String) = copyFrom(project.tasks.getByName(path, JavaExec::class))
+
+    /**
+     * Copy configuration from an existing [JavaExec] task.
+     */
+    fun copyFrom(task: JavaExec) {
+        for (dep in task.dependsOn) dependsOn(dep)
+        task.copyToFull(this)
+
+        if (!clientDebug) systemProperty("cctest.client", "")
+        systemProperty("cctest.gametest-report", testResults.get().asFile.absoluteFile)
+        workingDir(project.buildDir.resolve("gametest").resolve(name))
+    }
+
+    /**
+     * Only run tests with the given tags.
+     */
+    fun tags(vararg tags: String) {
+        systemProperty("cctest.tags", tags.joinToString(","))
+    }
+
+    /**
+     * Write a file with the given contents before starting Minecraft. This may be useful for writing config files.
+     */
+    fun withFileContents(path: Any, contents: Supplier<String>) {
+        val file = project.file(path).toPath()
+        doFirst {
+            Files.createDirectories(file.parent)
+            Files.writeString(file, contents.get())
+        }
+    }
+
+    /**
+     * Copy a file to the provided path before starting Minecraft. This copy only occurs if the file does not already
+     * exist.
+     */
+    fun withFileFrom(path: Any, source: Supplier<File>) {
+        val file = project.file(path).toPath()
+        doFirst {
+            Files.createDirectories(file.parent)
+            if (!Files.exists(file)) Files.copy(source.get().toPath(), file)
+        }
+    }
+
+    @TaskAction
+    override fun exec() {
+        Files.createDirectories(workingDir.toPath())
+        fsOperations.delete { delete(workingDir.resolve("screenshots")) }
+
+        if (useFramebuffer) {
+            clientRunner.get().wrapClient(this) { super.exec() }
+        } else {
+            super.exec()
+        }
+
+        fsOperations.copy {
+            from(workingDir.resolve("screenshots"))
+            into(screenshots)
+        }
+    }
+
+    @get:Inject
+    protected abstract val fsOperations: FileSystemOperations
+}
+
+/**
+ * A service for [JavaExec] tasks which start Minecraft.
+ *
+ * Tasks may run `usesService(MinecraftRunnerService.get(gradle))` to ensure that only one Minecraft-related task runs
+ * at once.
+ */
+abstract class MinecraftRunnerService : BuildService<BuildServiceParameters.None> {
+    private val hasXvfb = lazy {
+        System.getProperty("os.name", "").equals("linux", ignoreCase = true) && ProcessHelpers.onPath("xvfb-run")
+    }
+
+    internal fun wrapClient(exec: JavaExec, run: () -> Unit) = when {
+        hasXvfb.value -> runXvfb(exec, run)
+        else -> run()
+    }
+
+    /**
+     * Run a program under Xvfb, preventing it spawning a window.
+     */
+    private fun runXvfb(exec: JavaExec, run: () -> Unit) {
+        fun ProcessBuilder.startVerbose(): Process {
+            exec.logger.info("Running ${this.command()}")
+            return start()
+        }
+
+        CloseScope().use { scope ->
+            val dir = Files.createTempDirectory("cctweaked").toAbsolutePath()
+            scope.add { fsOperations.delete { delete(dir) } }
+
+            val authFile = Files.createTempFile(dir, "Xauthority", "").toAbsolutePath()
+
+            val cookie = StringBuilder().also {
+                for (i in 0..31) it.append("0123456789abcdef"[Random.nextInt(16)])
+            }.toString()
+
+            val xvfb =
+                ProcessBuilder("Xvfb", "-displayfd", "1", "-screen", "0", "640x480x24", "-nolisten", "tcp").also {
+                    it.inheritIO()
+                    it.environment()["XAUTHORITY"] = authFile.toString()
+                    it.redirectOutput(ProcessBuilder.Redirect.PIPE)
+                }.startVerbose()
+            scope.add { xvfb.destroyForcibly().waitFor() }
+
+            val server = xvfb.inputReader().use { it.readLine().trim() }
+            exec.logger.info("Running at :$server (XAUTHORITY=$authFile.toA")
+
+            ProcessBuilder("xauth", "add", ":$server", ".", cookie).also {
+                it.inheritIO()
+                it.environment()["XAUTHORITY"] = authFile.toString()
+            }.startVerbose().waitForOrThrow("Failed to setup XAuthority file")
+
+            scope.add {
+                ProcessBuilder("xauth", "remove", ":$server").also {
+                    it.inheritIO()
+                    it.environment()["XAUTHORITY"] = authFile.toString()
+                }.startVerbose().waitFor()
+            }
+
+            // Wait a few seconds for Xvfb to start. Ugly, but identical to xvfb-run.
+            if (xvfb.waitFor(3, TimeUnit.SECONDS)) {
+                throw GradleException("Xvfb unexpectedly exited (with status code ${xvfb.exitValue()})")
+            }
+
+            exec.environment("XAUTHORITY", authFile.toString())
+            exec.environment("DISPLAY", ":$server")
+
+            run()
+        }
+    }
+
+    @get:Inject
+    protected abstract val fsOperations: FileSystemOperations
+
+    companion object {
+        fun get(gradle: Gradle): Provider<MinecraftRunnerService> =
+            gradle.sharedServices.registerIfAbsent("cc.tweaked.gradle.ClientJavaExec", MinecraftRunnerService::class.java) {
+                maxParallelUsages.set(1)
+            }
+    }
+}