Kotlin 2.1.0 cross compilation support

Closes #291

Author: fzhinkin

src/functionalTest/kotlin/kotlinx/validation/test/KlibVerificationTests.kt

@@ -850,4 +850,25 @@ internal class KlibVerificationTests : BaseKotlinGradleTest() {
                 .contains("+// Targets: [linuxArm64]")
         }
     }
+
+    @Test
+    fun `check cross compilation support`() {
+        Assume.assumeFalse(HostManager().isEnabled(KonanTarget.MACOS_ARM64))
+
+        val runner = test {
+            settingsGradleKts {
+                resolve("/examples/gradle/settings/settings-name-testproject.gradle.kts")
+            }
+            buildGradleKts {
+                resolve("/examples/gradle/base/withNativePluginAndCrossCompilation.gradle.kts")
+            }
+            additionalBuildConfig("/examples/gradle/configuration/appleTargets/targets.gradle.kts")
+            addToSrcSet("/examples/classes/TopLevelDeclarations.kt")
+            runner {
+                arguments.addAll(listOf(":apiDump", "-Pkotlin.native.enableKlibsCrossCompilation=true"))
+            }
+        }
+
+        checkKlibDump(runner.build(), "/examples/classes/TopLevelDeclarations.klib.all.dump")
+    }
 }

src/functionalTest/resources/examples/gradle/base/withNativePluginAndCrossCompilation.gradle.kts

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2016-2025 JetBrains s.r.o.
+ * Use of this source code is governed by the Apache 2.0 License that can be found in the LICENSE.txt file.
+ */
+
+plugins {
+    kotlin("multiplatform") version "2.1.0"
+    id("org.jetbrains.kotlinx.binary-compatibility-validator")
+}
+
+repositories {
+    mavenCentral()
+}
+
+kotlin {
+    linuxX64()
+    linuxArm64()
+    mingwX64()
+    androidNativeArm32()
+    androidNativeArm64()
+    androidNativeX64()
+    androidNativeX86()
+
+    sourceSets {
+        val commonMain by getting
+        val commonTest by getting {
+            dependencies {
+                implementation(kotlin("stdlib"))
+                implementation(kotlin("test-common"))
+                implementation(kotlin("test-annotations-common"))
+            }
+        }
+    }
+}
+
+apiValidation {
+    klib.enabled = true
+}

src/main/kotlin/BinaryCompatibilityValidatorPlugin.kt

@@ -17,7 +17,6 @@ import org.jetbrains.kotlin.gradle.plugin.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinNativeTarget
 import org.jetbrains.kotlin.konan.target.HostManager
 import org.jetbrains.kotlin.library.abi.ExperimentalLibraryAbiReader
-import org.jetbrains.kotlin.library.abi.LibraryAbiReader
 import java.io.*
 import java.util.*
 
@@ -320,6 +319,7 @@ private inline fun <reified T : Task> Project.task(
 private const val BANNED_TARGETS_PROPERTY_NAME = "binary.compatibility.validator.klib.targets.disabled.for.testing"
 private const val KLIB_DUMPS_DIRECTORY = "klib"
 private const val KLIB_INFERRED_DUMPS_DIRECTORY = "klib-all"
+private const val ENABLE_CROSS_COMPILATION_PROPERTY_NAME = "kotlin.native.enableKlibsCrossCompilation"
 
 /**
  * KLib ABI dump validation and dump extraction consists of multiple steps that extracts and transforms dumps for klibs.
@@ -544,10 +544,14 @@ private class KlibValidationPipelineBuilder(
 
     private fun Project.targetIsSupported(target: KotlinTarget): Boolean {
         if (bannedTargets().contains(target.targetName)) return false
-        return when (target) {
-            is KotlinNativeTarget -> HostManager().isEnabled(target.konanTarget)
-            else -> true
+        if (target !is KotlinNativeTarget || HostManager().isEnabled(target.konanTarget)) {
+            return true
         }
+
+        // Starting from Kotlin 2.1.0, cross compilation could be enabled via property
+        if (!isKgpVersionAtLeast2_1(getKotlinPluginVersion())) return false
+
+        return (project.properties[ENABLE_CROSS_COMPILATION_PROPERTY_NAME] as String?).toBoolean()
     }
 
     // Compilable targets not supported by the host compiler
@@ -770,3 +774,11 @@ private var Configuration.isCanBeDeclaredCompat: Boolean
             isCanBeDeclared = value
         }
     }
+
+private fun isKgpVersionAtLeast2_1(kgpVersion: String): Boolean {
+    val parts= kgpVersion.split('.')
+    if (parts.size < 2) return false
+    val major = parts[0].toIntOrNull() ?: return false
+    val minor = parts[1].toIntOrNull() ?: return false
+    return major > 2 || (major == 2 && minor >= 1)
+}