Allow actuals with more permissive visibility

Allow non-virtual expects to have actuals with more permissive
visibility.

^KT-19664 Fixed

compiler/resolution/src/org/jetbrains/kotlin/resolve/multiplatform/ExpectedActualResolver.kt

@@ -262,7 +262,7 @@ object ExpectedActualResolver {
         if (!equalsBy(aTypeParams, bTypeParams, TypeParameterDescriptor::getName)) return Incompatible.TypeParameterNames
 
         if (!areCompatibleModalities(a.modality, b.modality)) return Incompatible.Modality
-        if (a.visibility != b.visibility) return Incompatible.Visibility
+        if (!areDeclarationsWithCompatibleVisibilities(a, b)) return Incompatible.Visibility
 
         areCompatibleTypeParameters(aTypeParams, bTypeParams, platformModule, substitutor).let { if (it != Compatible) return it }
 
@@ -427,6 +427,20 @@ object ExpectedActualResolver {
                 a == b
     }
 
+    private fun areDeclarationsWithCompatibleVisibilities(
+        a: CallableMemberDescriptor,
+        b: CallableMemberDescriptor
+    ): Boolean {
+        val compare = Visibilities.compare(a.visibility, b.visibility)
+        return if (a.isOverridable) {
+            // For overridable declarations visibility should match precisely, see KT-19664
+            compare == 0
+        } else {
+            // For non-overridable declarations actuals are allowed to have more permissive visibility
+            compare != null && compare <= 0
+        }
+    }
+
 
     private fun areCompatibleClassScopes(
         a: ClassDescriptor,

compiler/testData/diagnostics/tests/multiplatform/headerClass/morePermissiveVisibilityOnActual.kt

@@ -15,6 +15,7 @@ expect open class Container {
     protected fun protectedFun3()
 
     open internal fun openInternalFun()
+    open fun openPublicFun()
 }
 
 // MODULE: m2-jvm(m1-common)
@@ -24,14 +25,15 @@ expect open class Container {
 actual open class Container {
     actual fun publicFun() {}               // OK: public -> public
 
-    actual fun <!ACTUAL_WITHOUT_EXPECT!>internalFun1<!>() {}            // OK: internal -> public
+    actual fun internalFun1() {}            // OK: internal -> public
     actual internal fun internalFun2() {}   // OK: internal -> internal
 
-    actual fun <!ACTUAL_WITHOUT_EXPECT!>protectedFun1<!>() {}           // OK: protected -> public
+    actual fun protectedFun1() {}           // OK: protected -> public
     actual protected fun protectedFun2() {} // OK: protected -> protected
 
     actual <!ACTUAL_WITHOUT_EXPECT!>internal<!> fun protectedFun3() {}  // BAD: protected -> internal
     actual <!ACTUAL_WITHOUT_EXPECT!>protected<!> fun internalFun3() {}  // BAD: internal -> protected
 
     actual open fun <!ACTUAL_WITHOUT_EXPECT!>openInternalFun<!>() {}    // BAD: internal+open -> public
+    actual internal fun <!ACTUAL_WITHOUT_EXPECT!>openPublicFun<!>() {}  // BAD: open+public -> internal
 }

compiler/testData/diagnostics/tests/multiplatform/headerClass/morePermissiveVisibilityOnActual.txt

@@ -8,6 +8,7 @@ public open expect class Container {
     internal final expect fun internalFun2(): kotlin.Unit
     internal final expect fun internalFun3(): kotlin.Unit
     internal open expect fun openInternalFun(): kotlin.Unit
+    public open expect fun openPublicFun(): kotlin.Unit
     protected final expect fun protectedFun1(): kotlin.Unit
     protected final expect fun protectedFun2(): kotlin.Unit
     protected final expect fun protectedFun3(): kotlin.Unit
@@ -27,6 +28,7 @@ public open actual class Container {
     internal final actual fun internalFun2(): kotlin.Unit
     protected final actual fun internalFun3(): kotlin.Unit
     public open actual fun openInternalFun(): kotlin.Unit
+    internal final actual fun openPublicFun(): kotlin.Unit
     public final actual fun protectedFun1(): kotlin.Unit
     protected final actual fun protectedFun2(): kotlin.Unit
     internal final actual fun protectedFun3(): kotlin.Unit

compiler/testData/diagnostics/tests/multiplatform/headerClass/morePermissiveVisibilityOnActualViaTypeAlias.kt

@@ -19,4 +19,4 @@ public class Foo {
 
 // FILE: jvm.kt
 
-actual typealias <!NO_ACTUAL_CLASS_MEMBER_FOR_EXPECTED_CLASS!>Container<!> = foo.Foo
+actual typealias Container = foo.Foo

compiler/testData/multiplatform/incompatibleCallables/output.txt

@@ -125,12 +125,6 @@ The following declaration is incompatible because number of type parameters is d
 
 actual fun <K, V> f7() {}
            ^
-compiler/testData/multiplatform/incompatibleCallables/jvm.kt:16:1: error: actual function 'f8' has no corresponding expected declaration
-The following declaration is incompatible because visibility is different:
-    internal expect fun f8(): Unit
-
-public actual fun f8() {}
-^
 compiler/testData/multiplatform/incompatibleCallables/jvm.kt:17:1: error: actual function 'f10' has no corresponding expected declaration
 The following declaration is incompatible because visibility is different:
     public expect fun f10(): Unit