FIR: add test for KT-50969

compiler/fir/analysis-tests/testData/resolveWithStdlib/problems/immutableName.kt

@@ -0,0 +1,36 @@
+// SCOPE_DUMP: ImplDerived:foo, DerivedImpl:foo
+// FILE: Base.java
+
+import org.jetbrains.annotations.NotNull;
+
+public interface Base {
+    Base foo(@NotNull String name);
+}
+
+// FILE: Derived.java
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public interface Derived extends Base {
+    @Override
+    @NotNull Derived foo(@Nullable String name);
+}
+
+// FILE: Impl.kt
+
+abstract class Impl : Base {
+    override fun foo(name: String): Base {
+        return this
+    }
+}
+
+// FILE: test.kt
+
+abstract <!RETURN_TYPE_MISMATCH_ON_INHERITANCE!>class ImplDerived<!> : Impl(), Derived {
+    abstract <!NOTHING_TO_OVERRIDE!>override<!> fun foo(name: String?): Derived
+}
+
+abstract class DerivedImpl : Derived, Impl() {
+    abstract override fun foo(name: String?): Derived
+}