SubclassOptInRequired: add extra test about inheritance and superseding

compiler/testData/diagnostics/testsWithStdLib/experimental/subclassOptInInheritance.kt

@@ -0,0 +1,64 @@
+// FIR_IDENTICAL
+@RequiresOptIn
+annotation class Marker
+
+@Marker
+interface I1
+
+@SubclassOptInRequired(Marker::class)
+interface I2
+
+// Should not be enough, and should not depend on the order of I1, I2
+@SubclassOptInRequired(Marker::class)
+interface Impl1 : <!OPT_IN_USAGE_ERROR!>I1<!>, I2
+
+@SubclassOptInRequired(Marker::class)
+interface Impl2 : I2, <!OPT_IN_USAGE_ERROR!>I1<!>
+
+@Marker
+class C
+
+open class D {
+    @Marker
+    open fun bar() {}
+
+    @Marker
+    open fun baz() {}
+}
+
+@SubclassOptInRequired(Marker::class)
+open class E : D() {
+    init {
+        val c = <!OPT_IN_USAGE_ERROR!>C<!>()
+        D().<!OPT_IN_USAGE_ERROR!>bar<!>()
+    }
+
+    fun foo() {
+        val c = <!OPT_IN_USAGE_ERROR!>C<!>()
+        bar() // Error is not needed here (already reported on 'fun bar' declaration)
+        <!OPT_IN_USAGE_ERROR!>baz<!>()
+    }
+
+    override fun <!OPT_IN_OVERRIDE_ERROR!>bar<!>() {
+
+    }
+
+    @Marker
+    override fun baz() {
+
+    }
+}
+
+@SubclassOptInRequired(Marker::class)
+interface Foo {
+    fun foo() = Unit
+}
+
+<!NOTHING_TO_INLINE!>inline<!> fun inlineFoo() {
+    object : <!OPT_IN_USAGE_ERROR!>Foo<!> { }
+}
+
+fun test() {
+    // call site
+    inlineFoo()
+}