[KMP] Implement ACTUAL_TYPE_ALIAS_TO_NOTHING/TO_NULLABLE_TYPE errors

^KT-60650 Done

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -807,6 +807,8 @@ public interface Errors {
             ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
     DiagnosticFactory0<KtTypeAlias> ACTUAL_TYPE_ALIAS_WITH_USE_SITE_VARIANCE = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
     DiagnosticFactory0<KtTypeAlias> ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
+    DiagnosticFactory0<KtTypeAlias> ACTUAL_TYPE_ALIAS_TO_NULLABLE_TYPE = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
+    DiagnosticFactory0<KtTypeAlias> ACTUAL_TYPE_ALIAS_TO_NOTHING = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
     DiagnosticFactory0<PsiElement> ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory2<KtNamedDeclaration, ClassDescriptor, Collection<FunctionDescriptor>> DEFAULT_ARGUMENTS_IN_EXPECT_WITH_ACTUAL_TYPEALIAS = DiagnosticFactory2.create(ERROR);
     DiagnosticFactory1<PsiElement, ValueParameterDescriptor> ACTUAL_ANNOTATION_CONFLICTING_DEFAULT_ARGUMENT_VALUE =

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -361,6 +361,8 @@ public class DefaultErrorMessages {
         MAP.put(ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE, "Aliased class should not have type parameters with declaration-site variance");
         MAP.put(ACTUAL_TYPE_ALIAS_WITH_USE_SITE_VARIANCE, "Right-hand side of actual type alias cannot contain use-site variance or star projections");
         MAP.put(ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION, "Type arguments in the right-hand side of actual type alias should be its type parameters in the same order, e.g. 'actual typealias Foo<A, B> = Bar<A, B>'");
+        MAP.put(ACTUAL_TYPE_ALIAS_TO_NULLABLE_TYPE, "Right-hand side of actual type alias cannot be a nullable type");
+        MAP.put(ACTUAL_TYPE_ALIAS_TO_NOTHING, "Right-hand side of actual type alias cannot be of type kotlin.Nothing");
         MAP.put(ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS, "Actual function cannot have default argument values, they should be declared in the expected function");
         MAP.put(ACTUAL_ANNOTATION_CONFLICTING_DEFAULT_ARGUMENT_VALUE, "Parameter ''{0}'' has conflicting values in the expected and actual annotation", NAME);
         MAP.put(DEFAULT_ARGUMENTS_IN_EXPECT_WITH_ACTUAL_TYPEALIAS,

compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt

@@ -191,6 +191,16 @@ class DeclarationsChecker(
             trace.report(ACTUAL_TYPE_ALIAS_WITH_COMPLEX_SUBSTITUTION.on(declaration))
             return
         }
+
+        if (rhs.isNothing()) {
+            trace.report(ACTUAL_TYPE_ALIAS_TO_NOTHING.on(declaration))
+            return
+        }
+
+        if (rhs.isMarkedNullable) {
+            trace.report(ACTUAL_TYPE_ALIAS_TO_NULLABLE_TYPE.on(declaration))
+            return
+        }
     }
 
     private fun getUsedTypeAliasParameters(type: KotlinType, typeAlias: TypeAliasDescriptor): Set<TypeParameterDescriptor> =