Automatically detect Android Java 1.8 source+target (KT-21030)

When Android Java 8 desugaring is set as follows (or above):

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

set the Kotlin JVM target to 1.8

Issue #KT-21030 Fixed

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

@@ -673,4 +673,30 @@ fun getSomething() = 10
             assertFileExists("libAndroid/build/tmp/kotlin-classes/debugUnitTest/foo/PlatformTest.class")
         }
     }
+
+    @Test
+    fun testDetectAndroidJava8() = with(Project("AndroidProject")) {
+        setupWorkingDir()
+
+        val kotlinJvmTarget18Regex = Regex("Kotlin compiler args: .* -jvm-target 1.8")
+
+        build(":Lib:assemble") {
+            assertSuccessful()
+            assertNotContains(kotlinJvmTarget18Regex)
+        }
+
+        gradleBuildScript("Lib").appendText(
+            "\n" + """
+            android.compileOptions {
+                sourceCompatibility JavaVersion.VERSION_1_8
+                targetCompatibility JavaVersion.VERSION_1_8
+            }
+            """.trimIndent()
+        )
+
+        build(":Lib:assemble") {
+            assertSuccessful()
+            assertContainsRegex(kotlinJvmTarget18Regex)
+        }
+    }
 }

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

@@ -734,6 +734,10 @@ abstract class AbstractAndroidProjectHandler<V>(private val kotlinConfigurationT
         }
 
         val kotlinOptions = KotlinJvmOptionsImpl()
+        project.whenEvaluated {
+            applyAndroidJavaVersion(project.extensions.getByType(BaseExtension::class.java), kotlinOptions)
+        }
+
         kotlinOptions.noJdk = true
         ext.addExtension(KOTLIN_OPTIONS_DSL_NAME, kotlinOptions)
 
@@ -778,6 +782,13 @@ abstract class AbstractAndroidProjectHandler<V>(private val kotlinConfigurationT
         }
     }
 
+    private fun applyAndroidJavaVersion(baseExtension: BaseExtension, kotlinOptions: KotlinJvmOptions) {
+        val javaVersion =
+            listOf(baseExtension.compileOptions.sourceCompatibility, baseExtension.compileOptions.targetCompatibility).min()!!
+        if (javaVersion >= JavaVersion.VERSION_1_8)
+            kotlinOptions.jvmTarget = "1.8"
+    }
+
     private fun processVariant(
         variantData: V,
         compilation: KotlinJvmAndroidCompilation,