Create FileSystem.SYSTEM property in shared source set

okio/api/okio.api

@@ -755,6 +755,10 @@ public abstract interface class okio/Source : java/io/Closeable {
 	public abstract fun timeout ()Lokio/Timeout;
 }
 
+public final class okio/SystemFileSystem {
+	public static final synthetic fun getSYSTEM (Lokio/FileSystem$Companion;)Lokio/FileSystem;
+}
+
 public final class okio/Throttler {
 	public fun <init> ()V
 	public final fun bytesPerSecond (J)V

okio/build.gradle.kts

@@ -47,6 +47,8 @@ plugins {
  *
  * The `hashFunctions` source set builds on all platforms. It ships as a main source set on non-JVM
  * platforms and as a test source set on the JVM platform.
+ *
+ * The `systemFileSystem` source set is used on jvm and native targets, and provides the FileSystem.SYSTEM property.
  */
 kotlin {
   configureOrCreateOkioPlatforms()
@@ -87,6 +89,10 @@ kotlin {
       dependsOn(commonMain)
     }
 
+    val systemFileSystemMain by creating {
+      dependsOn(commonMain)
+    }
+
     val nonJvmTest by creating {
       dependsOn(commonTest)
     }
@@ -104,6 +110,7 @@ kotlin {
 
     val jvmMain by getting {
       dependsOn(zlibMain)
+      dependsOn(systemFileSystemMain)
     }
     val jvmTest by getting {
       kotlin.srcDir("src/jvmTest/hashFunctions")
@@ -131,6 +138,7 @@ kotlin {
       createSourceSet("nativeMain", parent = nonJvmMain)
         .also { nativeMain ->
           nativeMain.dependsOn(zlibMain)
+          nativeMain.dependsOn(systemFileSystemMain)
           createSourceSet("mingwMain", parent = nativeMain, children = mingwTargets).also { mingwMain ->
             mingwMain.dependsOn(nonAppleMain)
           }

okio/src/jvmMain/kotlin/okio/FileSystem.System.kt

@@ -0,0 +1,13 @@
+@file:JvmName("SystemFileSystem")
+
+package okio
+
+/*
+ * JVM and native platforms do offer a [SYSTEM] [FileSystem], however we cannot refine an 'expect' companion object.
+ * Therefore an extension property is provided, which on respective platforms (here JVM) will be shadowed by the
+ * original implementation.
+ */
+@Suppress("EXTENSION_SHADOWED_BY_MEMBER")
+actual inline val FileSystem.Companion.SYSTEM: FileSystem
+  @JvmSynthetic
+  get() = SYSTEM

okio/src/nativeMain/kotlin/okio/FileSystem.kt

@@ -112,3 +112,12 @@ actual abstract class FileSystem {
     actual val SYSTEM_TEMPORARY_DIRECTORY: Path = PLATFORM_TEMPORARY_DIRECTORY
   }
 }
+
+/*
+ * JVM and native platforms do offer a [SYSTEM] [FileSystem], however we cannot refine an 'expect' companion object.
+ * Therefore an extension property is provided, which on respective platforms (here JVM) will be shadowed by the
+ * original implementation.
+ */
+@Suppress("EXTENSION_SHADOWED_BY_MEMBER")
+actual inline val FileSystem.Companion.SYSTEM: FileSystem
+  get() = SYSTEM

okio/src/systemFileSystemMain/kotlin/okio/FileSystem.System.kt

@@ -0,0 +1,7 @@
+package okio
+
+/*
+ * The current process's host file system. Use this instance directly, or dependency inject a
+ * [FileSystem] to make code testable.
+ */
+expect val FileSystem.Companion.SYSTEM: FileSystem

samples/build.gradle.kts

@@ -11,12 +11,23 @@ kotlin {
   jvm {
     withJava()
   }
+
+  linuxX64()
+  linuxArm64()
+  macosArm64()
+  macosX64()
+
   sourceSets {
     commonMain {
       dependencies {
         implementation(projects.okio)
       }
     }
+    commonTest {
+      dependencies {
+        implementation(libs.kotlin.test)
+      }
+    }
     val jvmTest by getting {
       dependencies {
         implementation(libs.test.junit)

samples/src/commonMain/kotlin/okio/samples/MultiplatformFileSystem.kt

@@ -0,0 +1,17 @@
+package okio.samples
+
+import okio.FileSystem
+import okio.Path.Companion.toPath
+import okio.SYSTEM
+
+class MultiplatformFileSystem {
+  fun run() {
+    val currentWorkingDirectory = FileSystem.SYSTEM.canonicalize("".toPath())
+    val children = FileSystem.SYSTEM.listOrNull(currentWorkingDirectory)
+    println("The current working directory is: $currentWorkingDirectory, containing: ${children?.joinToString()}")
+  }
+}
+
+fun main() {
+  MultiplatformFileSystem().run()
+}

samples/src/commonTest/kotlin/okio/samples/MultiplatformFileSystemTest.kt

@@ -0,0 +1,10 @@
+package okio.samples
+
+import kotlin.test.Test
+
+class MultiplatformFileSystemTest {
+  @Test
+  fun testSystemFileSystem() {
+    MultiplatformFileSystem().run()
+  }
+}