Add a link to docs in MPP stability warning; add a flag that hides it

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinProperties.kt

@@ -9,6 +9,7 @@ import org.gradle.api.Project
 import org.jetbrains.kotlin.gradle.dsl.Coroutines
 import org.jetbrains.kotlin.gradle.dsl.NativeCacheKind
 import org.jetbrains.kotlin.gradle.plugin.KotlinJsCompilerType.Companion.jsCompilerProperty
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinMultiplatformPlugin
 import org.jetbrains.kotlin.gradle.targets.native.DisabledNativeTargetsReporter
 import org.jetbrains.kotlin.gradle.tasks.AbstractKotlinCompile
 import org.jetbrains.kotlin.gradle.tasks.CacheBuilder
@@ -92,6 +93,9 @@ internal class PropertiesProvider private constructor(private val project: Proje
     val enableCompatibilityMetadataVariant: Boolean
         get() = booleanProperty("kotlin.mpp.enableCompatibilityMetadataVariant") ?: true
 
+    val mppStabilityNoWarn: Boolean?
+        get() = booleanProperty(KotlinMultiplatformPlugin.STABILITY_NOWARN_FLAG)
+
     val ignoreDisabledNativeTargets: Boolean?
         get() = booleanProperty(DisabledNativeTargetsReporter.DISABLE_WARNING_PROPERTY_NAME)
 

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/KotlinMultiplatformPlugin.kt

@@ -66,7 +66,15 @@ class KotlinMultiplatformPlugin(
         checkGradleCompatibility("the Kotlin Multiplatform plugin", GradleVersion.version("6.0"))
 
         project.plugins.apply(JavaBasePlugin::class.java)
-        SingleWarningPerBuild.show(project, "Kotlin Multiplatform Projects are an Alpha feature.")
+
+        if (PropertiesProvider(project).mppStabilityNoWarn != true) {
+            SingleWarningPerBuild.show(
+                project,
+                "Kotlin Multiplatform Projects are an Alpha feature. " +
+                        "See: https://kotlinlang.org/docs/reference/evolution/components-stability.html. " +
+                        "To hide this message, add '$STABILITY_NOWARN_FLAG=true' to the Gradle properties.\n"
+            )
+        }
 
         val targetsContainer = project.container(KotlinTarget::class.java)
         val kotlinMultiplatformExtension = project.extensions.getByType(KotlinMultiplatformExtension::class.java)
@@ -294,6 +302,8 @@ class KotlinMultiplatformPlugin(
 
         internal fun sourceSetFreeCompilerArgsPropertyName(sourceSetName: String) =
             "kotlin.mpp.freeCompilerArgsForSourceSet.$sourceSetName"
+
+        internal const val STABILITY_NOWARN_FLAG = "kotlin.mpp.stability.nowarn"
     }
 }