[tests] Add new (and refactor existing) tests for @SubclassOptInRequired

KT-54617

compiler/testData/diagnostics/testsWithStdLib/annotations/subclassOptInRequired/WithOpenClasses.kt

@@ -0,0 +1,34 @@
+// FIR_IDENTICAL
+
+@RequiresOptIn
+annotation class ApiMarker
+
+@SubclassOptInRequired(ApiMarker::class)
+open class OpenKlassOptInApi
+
+// no opt-in: diagnostic reported
+open class OpenKlassOptInApiInheritorA: <!OPT_IN_USAGE_ERROR!>OpenKlassOptInApi<!>()
+
+// opt-in present: no diagnostic, opt-in isn't propagated
+@OptIn(ApiMarker::class)
+open class OpenKlassOptInApiInheritorB: OpenKlassOptInApi()
+
+// inheritance opt-in required: no diagnostic, opt-in is propagated
+@SubclassOptInRequired(ApiMarker::class)
+open class OpenKlassOptInApiInheritorC: OpenKlassOptInApi()
+
+// full opt-in required: no diagnostic, stricter opt-in is propagated
+@ApiMarker
+open class OpenKlassOptInApiInheritorD: OpenKlassOptInApi()
+
+open class OpenKlassOptInApiInheritorE: OpenKlassOptInApiInheritorB() // inheritance opt-in isn't propagated
+open class OpenKlassOptInApiInheritorF: <!OPT_IN_USAGE_ERROR!>OpenKlassOptInApiInheritorC<!>() // inheritance opt-in is propagated
+open class OpenKlassOptInApiInheritorG: <!OPT_IN_USAGE_ERROR!>OpenKlassOptInApiInheritorD<!>() // inheritance opt-in is propagated
+
+fun useSiteTestOpenClasses() {
+    OpenKlassOptInApi()           // usage opt-in isn't required
+    OpenKlassOptInApiInheritorB() // usage opt-in isn't required
+    OpenKlassOptInApiInheritorC() // usage opt-in isn't required
+    <!OPT_IN_USAGE_ERROR!>OpenKlassOptInApiInheritorD<!>() // usage opt-in is required
+    OpenKlassOptInApiInheritorE() // usage opt-in isn't required
+}