[Gradle] Test that nullability is correctly inferred in metadata compilation

^KT-56380

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/HierarchicalMppIT.kt

@@ -1183,6 +1183,14 @@ open class HierarchicalMppIT : KGPBaseTest() {
         }
     }
 
+    @GradleTest
+    @DisplayName("KT-56380: correct nullability inference in metadata compilations")
+    fun `test correct nullability inference in metadata compilation`(gradleVersion: GradleVersion) {
+        project("kt-56380_correct_nullability_inference", gradleVersion) {
+            build(":b:compileCommonMainKotlinMetadata")
+        }
+    }
+
 
     private fun TestProject.testDependencyTransformations(
         subproject: String? = null,

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/a/build.gradle.kts

@@ -0,0 +1,8 @@
+plugins {
+    kotlin("multiplatform")
+}
+
+kotlin {
+    jvm()
+    linuxX64()
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/a/src/commonMain/kotlin/a/A.kt

@@ -0,0 +1,5 @@
+package a
+
+class A(
+    val data: Any?
+)

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/b/build.gradle.kts

@@ -0,0 +1,24 @@
+import org.jetbrains.kotlin.gradle.dsl.KotlinCompile
+
+plugins {
+    kotlin("multiplatform")
+}
+
+kotlin {
+    jvm()
+    linuxX64()
+
+    sourceSets {
+        commonMain {
+            dependencies {
+                api(project(":a"))
+            }
+        }
+    }
+}
+
+tasks.withType(KotlinCompile::class.java).configureEach {
+    kotlinOptions {
+        allWarningsAsErrors = true
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/b/src/commonMain/kotlin/a/A.kt

@@ -0,0 +1,13 @@
+package b
+
+import a.A
+
+fun foo(response: A) {
+    if (response.data != null) {
+        doSomethingWithNonNullable(response.data!!)
+    }
+}
+
+fun doSomethingWithNonNullable(data: Any) {
+    print(data)
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/build.gradle.kts

@@ -0,0 +1,10 @@
+plugins {
+    kotlin("multiplatform") apply false
+}
+
+allprojects {
+    repositories {
+        mavenLocal()
+        mavenCentral()
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/gradle.properties

@@ -0,0 +1 @@
+kotlin.mpp.enableCompatibilityMetadataVariant=true

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-56380_correct_nullability_inference/settings.gradle.kts

@@ -0,0 +1,2 @@
+include(":a")
+include(":b")